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Prepared for:
Bank of America C/o Cushman & Wakefield
225 West Wacker Drive
Chicago, Illinois 60606
BofA S. College and Drake
– CO1-136
Geotechnical Engineering Report
Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials i
Table of Contents
Report Summary .............................................................................................. i
Introduction .................................................................................................... 1
Project Description .......................................................................................... 1
Site Conditions ................................................................................................ 3
Geotechnical Characterization ......................................................................... 4
Subsurface Profile ..................................................................................... 4
Groundwater Conditions ............................................................................. 4
Seismic Site Class ............................................................................................ 5
Corrosivity ...................................................................................................... 6
Geotechnical Overview .................................................................................... 6
Existing, Undocumented Fill ........................................................................ 7
Expansive/Collapsible Soils ......................................................................... 7
Low Strength Soils .................................................................................... 7
Foundation and Floor System Recommendations ............................................ 8
Earthwork ....................................................................................................... 9
Demolition .............................................................................................. 10
Site Preparation ....................................................................................... 10
Existing Fill ............................................................................................. 11
Excavation .............................................................................................. 11
Subgrade Preparation ............................................................................... 12
Subgrade Stabilization .............................................................................. 13
Fill Material Types .................................................................................... 14
Fill Placement and Compaction Requirements ............................................... 15
Utility Trench Backfill ............................................................................... 16
Grading and Drainage ............................................................................... 17
Exterior Slab Design and Construction ......................................................... 17
Earthwork Construction Considerations ....................................................... 18
Construction Observation and Testing ......................................................... 18
Shallow Foundations ..................................................................................... 19
Spread Footings – Design Recommendations ................................................ 19
Shallow Foundation Construction Considerations ........................................... 21
Ground Improvement .................................................................................... 21
Compaction Grouting or Foam Injection ....................................................... 21
Aggregate Piers ....................................................................................... 22
Deep Foundations .......................................................................................... 22
Helical Pile Lateral Loading ........................................................................ 22
Helical Pile Foundations ............................................................................ 23
Lateral Earth Pressures ................................................................................. 24
Design Parameters ................................................................................... 24
Floor Slabs .................................................................................................... 25
Floor Slabs - Design Recommendations ....................................................... 26
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials ii
Floor Slab Construction Considerations ........................................................ 26
Pavements .................................................................................................... 27
General Pavement Comments .................................................................... 27
Pavements – Subgrade Preparation ............................................................ 27
Pavements – Design Recommendations ....................................................... 28
Pavements – Construction Considerations .................................................... 30
Pavements – Maintenance ......................................................................... 31
General Comments ........................................................................................ 31
Figures
GeoModel
Attachments
Exploration and Testing Procedures
Site Location and Exploration Plans
Exploration and Laboratory Test Results
Supporting Information
Note: This report was originally delivered in a web -based format. Blue Bold text in the
report indicates a referenced section heading. The PDF version also includes hyperlinks
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Refer to each individual Attachment for a listing of contents.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials i
Report Summary
Topic 1 Overview Statement 2
Project
Description
A geotechnical exploration has been performed for the proposed
Bank of America to be constructed at 2413 South College Avenue
in Fort Collins, Colorado. Four borings were performed to depths
of approximately 10 to 30.5 feet below existing site grades.
Geotechnical
Characterization
Subsurface conditions encountered in our exploratory borings
generally consisted of about 7 to 9 feet of existing fill consisting of
lean clay, sandy lean clay with variable amounts of gravel and
clayey sand with variable amounts of gravel, over about 15 feet of
sand with variable amounts of clay, over lean clay with sand.
Groundwater was encountered at depths of about 15 to 19½ feet
below existing site grades.
Earthwork
On-site soils typically appear suitable for use as general
engineered fill and backfill on the site provided they are placed
and compacted as described in this report. Import materials (if
needed) should be evaluated and approved by Terracon prior to
delivery to the site.
Shallow
Foundations
Existing fill was encountered at anticipated shallow foundation and
conven tional floor slab bearing depths. We recommend
constructing the proposed building on a shallow, spread footing
foundation system with ground improvement including compaction
grouting, foam injection or aggregate piers.
Allowable bearing pressure with compaction grouting or foam
injection = 2,500 to 3,000 psf
Allowable bearing pressure with aggregate piers = 3,000 to 5,000
psf with the potential for 6,000 psf.
Expected settlements: 1 -inch total, ½ to ¾ inch differential
Deep
Foundations
Deep foundations with a structurally supported floor can also be
used for the site. Helical piles are a common foundation type in
this region and can be used to support the structure loads .
Pavements
Recommended pavement thicknesses for this project include 4
inches of asphalt over 6 inches of aggregate base course in
parking areas and 6 inches of asphalt over 6 inches of aggregate
base course in drive lanes and loading areas.
Prior to pavement construction and after the pavement areas have
been stripped, and any required undercuts and the recommended
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials ii
Topic 1 Overview Statement 2
2 feet of over-excavation due to the presence of existing fill
materials have been completed within the planned pavement
areas, the top 10 inches of the exposed ground surface should be
scarified, moisture conditioned, and compacted as described in
this report before any new fill is placed or constructed. After the
subgrade has been scarified and compacted and before placement
of new fill and pavement, we recommend the subgrade be proof
rolled. Additional pavement discussion is presented in the report.
General
Comments
This section contains important information about the limitations
of this geotechnical engineering report.
1. If the reader is reviewing this report as a pdf, the topics above can be used to
access the appropriate section of the report by simply clicking on the topic
itself.
2. This summary is for convenience only. It should be used in conjunction with the
entire report for design purposes.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 1
Introduction
This report presents the results of our subsurface exploration and Geotechnical
Engineering services performed for the proposed bank to be located at 2413 South
College Avenue in Fort Collins, Colorado . The purpose of these services was to provide
information and geotechnical engineering recommendations relative to:
■ Sub surface soil conditions
■ Groundwater conditions
■ Seismic site classification per IBC
■ Site preparation and earthwork
■ Demolition considerations
■ Foundation design and construction
■ Floor s ystem design and construction
■ Lateral earth pressure s
■ Pavement design and construction
The geotechnical engineering Scope of Services for this project included the
advancement of test borings, laboratory testing, engineering analysis, and preparation
of this report.
Drawings showing the site and boring locations are presented in the Site Location and
Exploration Plan section of this report . The results of the laboratory testing performed
on soil samples obtained from the site during our field exploration are included on the
boring logs and as separate graphs in the Exploration Results section.
Project Description
Our initial understanding of the project was provided in our proposal and was discussed
during project planning. A period of collaboration has transpired since the project was
initiated, and our final understanding of the project conditions is as follows:
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 2
Item Description
Information
Provided
The project information described below is based on the
following:
■ Email request from Mr. Greg Malmgren
■ Coordination with Lyle Healy
■ PDF of project plans entitled “2024.07.12_CO1 -136_S
College and Drake_DD_COE”
■ PDF of project plans entitled “2024.10.15_CO1 -136_S
College and Drake_DD_90”
■ ALTA/NSPS Land Title Survey dated September 24, 2024
Project
Description
We understand the proposed project will consist of the
construction of a new single -story, approximately 4,250 square -
foot building with adjacent parking areas and drive lanes. We
anticipate no below -grade areas are planned below the building.
A canopy over the drive -thru area i s indicated on the provided
plans. An existing restaurant building located at the project site
is planned to be demolished prior to new construction .
Finished Floor
Elevation
Plans were not provided at the time of this report. We anticipate
the finished floor elevation for the proposed building will be near
or slightly above site grades at the time of our geotechnical
study.
Maximum Loads
(assumed)
■ Columns: 50 to 100 kips
■ Walls: 1 to 3 kips per linear foot (klf)
■ Slabs: 150 pounds per square foot (psf)
Grading/Slopes
Grading plans were not provided to Terracon at the time of this
report. We anticipate minor cuts and fills on the order of 5 feet
or less will be required to achieve proposed grades. We also
anticipate deeper cuts and fills will be required for demolition of
existing site features, new utility construction and/or removal
and replacement/recompaction of existing, undocumented fill.
Below-Grade
Structures We understand no below -grade areas are planned for this site.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 3
Item Description
Pavements
New pavements are planned as part of this project and will
likely consist of flexible asphalt and rigid concrete pavement.
Traffic loads were not available at the time of this report. We
will assume traffic loads consistent with that of similar use.
Unless information is provided prior to the report, we assume
the traffic classification will consist of:
■ Automobile Parking: Parking stalls for passenger vehicles
and pickup trucks
■ Main Traffic Corridors: Traffic consisting of passenger
vehicles, single -unit delivery trucks and garbage trucks
■ The pavement design period is 20 years.
Building Code 2021 International Building Code (IBC)
Terracon should be notified if any of the above information is inconsistent with the
planned construction, especially the grading limits, as modifications to our
recommendations may be necessary.
Site Conditions
The following description of site conditions is derived from our site visit in association
with the field exploration and our review of publicly available geologic maps.
Item Description
Parcel
Information
The project site is located at 2413 South College Avenue in Fort
Collins, Colorado.
Latitude/Longitude (approximate): 40.55524°N, 105.07754°W
See Site Location .
Existing
Improvements
An existing restaurant building is on the western portion of the
site. The remaining parts of the site are parking areas and drive
lanes and sidewalks. A few mature trees are also on the site.
Current Ground
Cover The site is currently paved with asphalt.
Existing
Topography
Based on publicly available USGS topographic maps and street
view images, ground surface elevations at the project site
appears relatively level. Elevations measured in the field using
an engineer’s level and grade show a slight slope from the south
down towards the north with a total change in elevation of about
2 feet across the site.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 4
Geotechnical Characterization
We have developed a general characterization of the subsurface conditions based upon
our review of the subsurface exploration, laboratory data, geologic setting and our
understanding of the project. This characterization, termed GeoModel, forms the basis o f
our geotechnical calculations and evaluation of the site. Conditions observed at each
exploration point are indicated on the individual logs. The individual logs can be found in
the Exploration Results and the GeoModel can be found in the Figures attachment of
this report.
Subsurface Profile
As part of our analyses, we identified the following model layers within the subsurface
profile. For a more detailed view of the model layer depths at each boring location, refer
to the GeoModel .
Model
Layer Layer Name General Description
1 Existing Fill
Existing fill consisting of lean clay, sandy lean clay with
variable amounts of gravel and clayey sand with
variable amounts of gravel; brown, red brown, tan
2 Sand Sand with variable amounts of clay; very loose to
medium dense, red brown
3 Clay Lean clay with sand; soft to stiff, red brown
Stratification boundaries on the boring logs represent approximate locations of changes
in material types; in situ, the transition between materials may be gradual. Further
details of the borings can be found on the boring logs in Exploration Results.
Based on the results of the laboratory testing and our experience with similar materials,
we anticipate the site soils to have low expansive potential or to be non -expansive.
Groundwater Conditions
The boreholes were observed while drilling and shortly after completion of drilling for the
presence and level of groundwater. The water levels observed in the boreholes are noted
on the attached boring logs, and are summarized below:
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 5
Boring
Number
Depth to
Groundwater While
Drilling, ft.
Depth to
Groundwater After
Drilling, ft.
Elevation of
Groundwater After
Drilling, ft.1
B-1 Not encountered Backfilled after drilling
B-2 17 19.5 179.9
B-3 15 15.4 184.2
B-4 Not encountered Backfilled after drilling
1. Elevation of groundwater is based on the ground surface elevation, obtained by Terracon using
an engineer’s level, referencing an on-site benchmark.
These observations represent relatively short -term groundwater conditions at the time of
and after completion of the field exploration and may not be indicative of other times or
at other locations. Long -term groundwater monitoring was outside the scope of services
for this project.
Groundwater level fluctuations occur due to seasonal variations in the water levels
present in nearby water features, amount of rainfall, runoff, and other factors not
evident at the time the boring was performed. Therefore, groundwater levels during
const ruction or at other times in the life of the structure may be higher or lower than the
levels indicated on the boring log s. The possibility of groundwater level fluctuations
should be considered when developing the design and construction plans for the pro ject.
However, we do not anticipate groundwater conditions with significantly impact the
proposed construction .
Seismic Site Class
The seismic design requirements for buildings and other structures are based on Seismic
Design Category. Site Classification is required to determine the Seismic Design
Category for a structure. The Site Classification is based on the upper 100 feet of the
site profile defined by a weighted average value of either shear wave velocity, standard
penetration resistance, or undrained shear strength in accordance with Section 20.4 of
ASCE 7 and the International Building Code (IBC). Based on the soil properties observed
at the site as described on the exploration logs and laboratory test results, our
professional opinion is a Seismic Site Classification of D be considered for the project.
Subsurface explorations at this site were extended to a maximum depth of 30½ feet.
The site properties below the boring depth to 100 feet were estimated based on our
experience and knowledge of geologic conditions of the general area. Additional deeper
borings or geophysical testing may be performed to confirm the conditions belo w the
current boring depth.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 6
Corrosivity
The table below lists the results of laboratory soluble sulfate, soluble chloride , sulfides,
electrical resistivity, Redox, and pH testing. The values may be used to estimate
potential corrosive characteristics of the on -site soils with respect to contact with the
various underground materials which will be used for project construction.
Corrosivity Test Results Summary
Boring
(Sample
Depth)
Soluble
Sulfate
(%)
Soluble
Chloride
(%)
Sulfides
Total
Salts
(mg/
kg)
Electrical
Resistivity
(Ω-cm)1
Redox
(mV) pH
B-2 at 0.6
to 4.8 feet 0.0451 0.199 Nil 675 1,300 252 8.3
1. Laboratory electrical resistivity testing was performed on a saturated sample.
Results of water-soluble sulfate testing indicate Exposure Class S0 according to ACI
(American Concrete Institute) 318. ASTM Type I or II portland cement , or Type IL
portland-limestone cement should be specified for all project concrete on and below
grade. Foundation concrete should be designed for low sulfate exposure in accordance
with the provisions of the ACI Design Manual, Section 318, Chapter 4.
Numerous sources are available to characterize corrosion potential to buried metals
using the parameters above. ANSI/AWWA is commonly used for ductile iron, while
threshold values for evaluating the effect on steel can be specific to the buried feature
(e.g., piling, culverts, welded wire reinforcement, etc.) or agency for which the work is
performed. Imported fill materials may have significantly different properties than the
site materials noted above and should be evaluated if expected to be in contact w ith
metals used for construction. Consultation with a NACE certified corrosion professional is
recommended for buried metals on the site.
Geotechnical Overview
Based on subsurface conditions encountered in the borings, the site appears suitable for
the proposed construction from a geotechnical point of view provided certain precautions
and design and construction recommendations described in this report are followed and
the owner understands the inherent risks associated with construction on sites underlain
by low expansive /collapsible soils. We have identified several geotechnical conditions
that could impact design, construction and performance of the proposed s tructures,
pavements, and other site improvements. These included existing, undocumented fill,
expansive/collapsible soils, and potentially loose, low relative density sand and soft, low
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 7
strength clay soils. These conditions will require particular attention in project planning,
design and during construction and are discussed in greater detail in the following
sections.
Existing, Undocumented Fill
Existing, undocumented fill was encountered to depths up to about 9 feet in the borings
drilled at the site. Existing fill could exist at other locations on the site and extend to
greater depths. We do not possess any information regarding whether the fill was placed
under the observation of a geotechnical engineer. Undocumented fill can present a
greater than normal risk of post -construction movement of site improvements supported
on or above these materials. Low risk alternative s are using ground improvem ent and/or
complete removal of existing fill below foundations, slabs, pavements and other site
improvements and replacement with newly compacted engineered fill. Discussion
regarding alternatives to complete removal of existing fill are presented in the Existing
Fill section of Earthwork.
Expansive /Collapsible Soils
Expansive soils are present on this site ; however, laboratory swell test results indicate
the site soils are generally low swelling to slightly compressible . This report provides
recommendations to help mitigate the effects of soil shrinkage and expansion. However,
even if these procedures are followed, some movement and cracking in the structures,
pavements, and flatwork is possible. The severity of cracking and other damage such as
uneven floor slabs and flatwork will probably increase if modification of the site results in
excessive wetting or drying of the expansive clays. Eliminating the risk of movement and
cosmetic distress is generally not feasible . It is imperative the recommendations
described in section Grading and Drainage section of the Earthwork section of this
report be followed to reduce potential movement.
Low Strength Soils
Comparatively loose, low relative density sand soils were encountered in Boring Nos. B-2
and B -3 at approximate depths of about 7 to 14 feet, and 19 to 24 feet below existing
site grades . Soft lean clay soils were encountered in Boring No. B-2 at an approximate
depth of 4 to 7 feet below existing site grades and in Boring No. B -3 at an approximate
depth of 24 to 29 feet below existing site grades. These materials present a risk for
potential settlement of shallow foundations, floor slabs, pavements and othe r surficial
improvements. These materials can also be susceptible to disturbance and loss of
strength under repeated construction traffic loads and unstable conditions could develop.
Stabilization of soft soils may be required at some locations to provide adequate support
for construction equipment and proposed structures. Terracon should be contacted if
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 8
these conditions are encountered to observe the conditions exposed and to provide
guidance regarding stabilization (if needed).
Foundation and Floor System Recommendations
Existing fill was encountered at anticipated shallow foundation and conventional floor
slab bearing depths. We recommend construct ing the proposed building on shallow,
spread footing foundation system with ground improvement including compaction
grouting, foam injection or aggregate piers. As an alternative, we believe the proposed
building can be constructed on a deep foundation system.
Design recommendations for foundations for the proposed structures and related
structural elements are presented in the Deep Foundations / Shallow Foundations
section of this report.
If a deep foundation option is selected to construct the building, we believe a
structurally supported floor system can be used for the proposed building . If a shallow
foundation option is selected to construct the building, w e believe a concrete slab -on-
grade floor system can be used for the proposed building provided ground improvement
with compaction grouting, foam injection or aggregate piers are installed. On-site soils are
suitable as over-excavation backfill below floor slabs. Design recommendations for floor
systems for the proposed structures and related structural elements are presented in the
Floor S ystems section of this report.
The recommendations contained in this report are based upon the results of field and
laboratory testing (presented in the Exploration Results ), engineering analyses, and
our current understanding of the proposed project. The General Comments section
provides an understanding of the report limitations. A brief summary of some of the
potential advantages and disadvantages associated with several options for foundations
and ground improvement is presented in the table below.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 9
Foundation Options
Advantages Disadvantages
Compaction Grouting with
Spread Footings
■ Improves in-situ soil
subgrade strength
■ Quick construction
schedule
■ Significantly reduces risk
for potential foundation
and floor slab movements
■ Eliminates need for
removal of existing fill and
replacement with
engineered fill
■ Higher cost s for ground
improvement
Spread Footings with
Aggregate Piers
■ Low cost foundation and
floor slab
■ Significantly reduces risk
for potential foundation
and floor slab movements
■ Eliminates need for
removal of existing fill and
replacement with
engineered fill
■ Higher costs for ground
improvement
Helical Piles
■ Low risk of movement
■ Casing isn’t needed to
install
■ Little amount of earthwork
■ Quick installation
■ Removal of existing fill is
not required
■ Higher cost
■ Longer pile lengths are
likely needed
Drilled Piers ■ Existing fill can stay in
place
■ Comparatively long
construction time
■ Casing will be needed to
install
■ Lower parameters for pier
capacity
Earthwork
Earthwork is anticipated to include demolition, site preparation, excavations, subgrade
preparation, soil stabilization (if needed), and engineered fill placement. The following
sections provide recommendations for use in the preparation of specifications for the
project. Recommendations include critical quality criteria, as necessary, to render the
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 10
site in the state considered in our geotechnical engineering evaluation for foundations,
floor slabs, and pavements.
Demolition
Demolition of any portions of the existing development at the project site should include
complete removal of all above -grade structures/improvements, foundation systems,
below -grade structural elements, retaining walls, landscaping, pavements, and exterio r
flatwork within the proposed construction area. This should include removal of any
utilities to be abandoned along with any loose utility trench backfill or loose backfill
found adjacent to existing foundations. All materials derived from the demolition of
existing structures and pavements should be removed from the site.
Consideration could be given to re -using the asphalt and concrete produced from the
demolition of any existing improvements or pavements provided the materials are
processed and uniformly blended with the on -site soils. Asphalt and/or concrete
materials sh ould be processed to a maximum size of 2 inches and blended at a ratio of
30 percent asphalt/concrete to 70 percent of on -site soils.
Site Preparation
Prior to placing fill, existing vegetation, topsoil, and root mats should be removed.
Complete stripping of the topsoil should be performed in the proposed building and
parking/driveway areas. Existing fill was encountered in our borings extending to depths of
about 7 to 9 feet below existing site grades. Ground improvement techniques are
recommended for this site. Stripped organic materials should be wasted from the site or used
to re-vegetate landscaped areas after completion of grading operations. Prior to the
placement of fills, the site should be graded to create a relatively level surface to receive fill,
and to provide for a relatively uniform thickness of fill beneath proposed structures.
Mature trees are located within or near the footprint of some of the proposed buildings,
which will require removal at the onset of construction. Tree root systems can remove
substantial moisture from surrounding soils. Where trees are removed, the full ro ot ball
and all associated dry and desiccated soils should be removed. The soil materials which
contain less than 5 percent organics can be reused as engineered fill provided the
material is moisture conditioned and properly compacted.
Where fill is placed on existing slopes steeper than 5H:1V, benches should be cut into
the existing slopes prior to fill placement. The benches should have a minimum vertical
face height of 1 foot and a maximum vertical face height of 3 feet and should be cut
wide enough to accommodate the compaction equipment. This benching will help provide
a positive bond between the fill and natural soils and reduce the possibility of failure
along the fill/natural soil interface.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 11
Although no evidence of underground facilities (such as septic tanks, cesspools and
basements) was observed during the exploration and site reconnaissance, such features
could be encountered during construction. If unexpected underground facilities are
encountered, such features should be removed, and the excavation thoroughly cleaned
prior to backfill placement and/or construction.
Existing Fill
As noted in Geotechnical Characterization , borings encountered existing fill to depths
ranging from about 7 to 9 feet below the ground surface at the time of our field
subsurface exploration . Existing fill could exist at other locations on the site and extend
to greater depths. We do not possess any information regarding whether the fill was
placed under the observation of a geotechnical engineer. Undocumented fill can present
a greater than normal risk of post -construction movement of site improvements
supported on or above these materials. Low risk alternative s include in-place ground
improvement or complete removal of existing fill below foundations, slabs, pavements
and other site improvements and replacement with newly compacted engineered fill. The
disadvantages of removal of existing fill are significant for this project site. It will be
difficult to avoid undermining adjacent utilities and flatwork and shoring will likely be
needed.
Excavation
We anticipate excavations for the proposed construction can be accomplished with
conventional earthmoving equipment. Excavations into the on-site soils will encounter
weak and/or saturated soil conditions with possible caving conditions. The bottom of
excavations should be thoroughly cleaned of loose/disturbed materials prior to backfill
placement and/or construction.
Any over-excavation that extends below the bottom of foundation elevation should
extend laterally beyond all edges of the foundations at least 8 inches per foot of over -
excavation depth below the foundation base elevation. The over -excavation should be
backfilled to the foundation base elevation in accordance with the recommendations
presented in this report.
Any existing building foundations exposed during excavation should be examined and
evaluated by Terracon to determine the need for any shoring or underpinning.
Excavations should not extend into the stress influence zone of the existing foundations
without prior evaluation by Terracon. The stress influence zone is defined as the area
below a line projected down at a 1(h) to 1(v) slope from the bottom edge of the existing
foundation. Excavations within the influence zone of existing foundations can result in
loss of support, and can create settlement or failure of th e existing foundations. While
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 12
the evaluation of existing foundations and the design of a shoring system are beyond the
scope of this study, we can perform these tasks as a separate study.
Depending upon depth of excavation and seasonal conditions, surface water infiltration
and/or groundwater may be encountered in excavations on the site. We anticipate
pumping from sumps may be utilized to control water within excavations . Well points
may be required for significant groundwater flow, or where excavations penetrate
groundwater to a significant depth.
The subgrade soil conditions should be evaluated during the excavation process and the
stability of the soils determined at that time by the contractors’ Competent Person as
defined by OSHA . Slope inclinations flatter than the OSHA maximum values may have to
be used. The individual contractor(s) should be made responsible for designing and
constructing stable, temporary excavations as required to maintain stability of both the
excavation sides and bottom. All excavations should be sloped or shored in the in terest
of safety following local, and federal regulations, including current OSHA excavation and
trench safety standards.
As a safety measure, we recommend all vehicles and soil piles be kept a minimum
lateral distance from the crest of the slope equal to the slope height. The exposed slope
face should be protected against the elements.
Subgrade Preparation
After site preparation and ground improvement , the top 10 inches of the exposed ground
surface should be scarified, moisture conditioned, and compac ted to at least 95 percent
of the maximum dry unit weight as determined by ASTM D698 before any new fill,
foundations, slabs, pavements , and other site improvements are placed or constructed.
Large areas of prepared subgrade should be proof rolled prior to new construction. Proof
rolling is not required in areas which are inaccessible to proof rolling equipment.
Subgrades should be proof rolled with an adequately loaded vehicle such as a fully -
loaded tandem-axle dump truck. Proof rolling should be p erformed under the
observation of the Geotechnical Engineer or representative. Areas excessively deflecting
under the proof roll should be delineated and subsequently addressed by the
Geotechnical Engineer . Excessively wet or dry material should either be removed or
moisture conditioned and compacted.
Our experience indicates the subgrade materials below existing pavements and other
flatwork after demolition will likely have relatively high moisture content and will tend to
deflect and deform (pump) under construction traffic wheel loads. After removal of
existing pavements and flatwork , the contractor should expect unstable subgrade
materials will need to be stabilized prior to fill placement and/or construction.
Consequently, Terracon recommends a contingency be provided in the construction
budget to stabilize and correct weak/unstable subgrade.
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After the bottom of the excavation has been prepared as recommended above ,
engineered fill can be placed to bring the building pad and pavement subgrade to the
desired grade. Engineered fill should be placed in accordance with the recommen dations
presented in subsequent sections of this report.
Subgrade Stabilization
Methods of subgrade stabilization/improvement, as described below, could include
scarification, moisture conditioning and compaction, removal of unstable materials and
replacement with granular fill (with or without geosynthetics), and chemical treatment.
The appropriate method of improvement, if required, would be dependent on factors
such as schedule, weather, the size of area to be stabilized, and the nature of the
instability. More detailed recommendations can be provided during construction as the
need for subgrade stabilization occurs . Performing site grading operations during warm
seasons and dry periods would help reduce the amount of subgrade stabilization
required.
If the exposed subgrade is unstable during proof rolling operations, it could be stabilized
using one of the methods described below.
■ Scarification and Compaction - It may be feasible to scarify, dry, and compact
the exposed soils. The success of this procedure would depend primarily upon
favorable weather and sufficient time to dry the soils. Stable subgrades likely
would not be achievable if the thickness of the unstable soil is greater than about
1 foot, if the unstable soil is at or near groundwater levels, or if construction is
performed during a period of wet or cool weather when drying is difficult.
■ Crushed Stone - The use of crushed stone or crushed concrete is a common
procedure to improve subgrade stability. Typical undercut depths would be
expected to range from about 6 to 18 inches below finished subgrade elevation.
Crushed stone and/or concrete can be tracked or “crowded” into the unstable
subgrade until a stable working surface is attained. The use of high modulus
geosynthetics (i.e., geotextile or geogrid) could also be considered after
underground work such as utility construction is completed . Prior to placing the
geosynthetic, we recommend all below -grade construction, such as utility line
installation, be completed to avoid damaging the geosynthetic. Equipment should
not be operated above the geosynthetic until one full lift of crushed stone fill is
placed above it.
■ Chemical Treatment - Improvement of subgrades with portland cement , lime or
fly ash could be considered for improving unstable soils. Chemical treatment
should be performed by a pre -qualified contractor having experience with
successfully treating subgrades in the project area on similar sized projects with
similar soil conditions. Results of chemical analysis of the chemical treatment
materials should be provided to the Geotechnical Engineer for review prior to use.
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The hazards of chemicals blowing across the site or onto adjacent propert ies
should also be considered. Additional testing would be needed to develop specific
recommendations to improve subgrade stability by blending chemicals with the
site soils. Additional testing could include, but not be limited to, determining the
most suitab le chemical treating agent, the optimum amounts required, the
presence of sulfates in the soil, and freeze -thaw durability of the subgrade.
Further evaluation of the need and recommendations for subgrade stabilization can be
provided during construction as the geotechnical conditions are exposed.
Fill Material Types
Fill for this project should consist of engineered fill. Engineered fill is fill that meets the
criteria presented in this report and has been properly documented. On-site soils free of
deleterious materials or approved granular and low plasticity cohesive imported
materials may be used as fill material. The earthwork contractor should expect
significant mechanical processing and moisture conditioning of the site soils will be
needed to achieve proper compact ion .
As recommended below floor slabs, CDOT Class 1 structure backfill should meet the
following material property requirements:
Gradation Percent Finer by Weight (ASTM C136)
2” 100
No. 4 Sieve 30-100
No. 50 Sieve 10-60
No. 200 Sieve 5-20
Soil Properties Values
Liquid Limit 35 (max.)
Plasticity Index 6 (max.)
Imported fill materials (if required) should meet the following material property
requirements. Regardless of its source, compacted fill should consist of approved
materials that are free of organic matter and debris. Frozen material should not be used,
and fill should not be placed on a frozen subgrade.
Gradation Percent Finer by Weight (ASTM C136)
3 ” 100
1 ” 70-100
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Gradation Percent Finer by Weight (ASTM C136)
No. 4 Sieve 30-100
No. 200 Sieve 15-50
Soil Properties Values
Liquid Limit 35 (max.)
Plasticity Index 15 (max.)
Aggregate base course used below new pavements should meet CDOT requirements for
Class 5 or 6 aggregate base course materials.
Other import fill material types may be suitable for use on the site depending upon
proposed application and location on the site and could be tested and approved for use
on a case-by-case basis.
Fill Placement and Compaction Requirements
Engineered fill should be placed and compacted in horizontal lifts, using equipment and
procedures that will produce recommended moisture contents and densities throughout
the lift.
Item Description
Maximum Lift
Thickness
9 inches or less in loose thickness when heavy, self -propelled
compaction equipment is used
4 to 6 inches in loose thickness when hand -guided equipment
(i.e., jumping jack or plate compactor) is used
Minimum
Compaction
Requirements 1
Engineered Fill : At least 95% of the maximum dry unit weight
as determined by ASTM D698.
Engineered Fill 8 Feet of Greater : At least 98% of the maximum
dry unit weight as determined by ASTM D698 for the entire
depth of fill in areas receiving 8 feet of fill or greater.
Aggregate Base Course: At least 95% of maximum dry unit
weight as determined by ASTM D1557 (or AASHTO T180) in
pavement areas.
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Item Description
Water Content
Range 2 ,3
Cohesive (clay): -1% to +3% of optimum moisture content
Granular (sand): -3% to +3% of optimum moisture content
1. We recommend engineered fill be tested for moisture content and compaction during
placement. If the results of the in -place density tests indicate the specified moisture or
compaction limits have not been met, the area represented by the test should be
reworked and retested as required until the specified moisture and compaction
requirements are achieved.
2. Moisture conditioned clay materials should not be allowed to dry out. A loss of moisture
within these materials could result in an increase in the material’s expansive potential.
Subsequent wetting of these materials could result in undesirable movement.
3. Specifically, moisture levels should be maintained low enough to allow for satisfactory
compaction to be achieved without the fill material pumping when proof rolled.
Utility Trench Backfill
Any loose, soft, or unsuitable materials encountered at the bottom of utility trench
excavations should be removed and replaced with engineered fill or bedding material in
accordance with public works specifications for the utility to be supported. This
recommendation is particularly applicable to utility work where settlement control of the
utility is critical. Utility t rench excavation should not be conducted below a downward
1:1 projection from existing foundations without engineering review of shoring
requirements and geotechnical observation during construction.
On -site materials are considered suitable for backfill of utility and pipe trenches provided
the material is free of organic matter and deleterious substances.
Utility trench backfill should be placed and compacted as discussed earlier in this report.
Compaction of initial lifts should be accomplished with hand -operated tampers or other
lightweight compactors. Flooding or jetting for placement and compaction of backfill i s
not recommended. If utility trenches are backfilled with relatively clean granular material,
they should be capped with at least 18 inches of cohesive fill in non-pavement areas to reduce
the infiltration and conveyance of surface water through the trench backfill.
For low permeability subgrades , utility trenches are a common source of water
infiltration and migration. Utility trenches penetrating beneath the building should be
effectively sealed to restrict water intrusion and flow through the trenches, which could
migrate below the building. The trench should provide an effective trench plug that
extends at least 5 feet from the face of the building exterior. The plug material should
consist of cementitious flowable fill or low permeability clay. The trench plug material
should be placed to surr ound the utility line. If used, the trench plug material should be
placed and compacted to comply with the water content and compaction
recommendations for engineered fill stated previously in this report.
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All underground piping within or near the proposed structure should be designed with
flexible couplings, so minor deviations in alignment do not result in breakage or distress.
Utility knockouts in foundation walls should be oversized to accommodate differ ential
movements.
We recommend a representative of the Geotechnical Engineer provide full-time
observation and compaction testing of trench backfill within building and pavement
areas.
Grading and Drainage
All grades must provide effective drainage away from the building during and after
construction and should be maintained throughout the life of the structure. Water
retained next to the building can result in soil movements greater than those discussed
in this report. Greater movements can result in unacceptable differential floor slab
and/or foundation movements, cracked slabs and walls, and roof leaks . The roof should
have gutters/drains with downspouts that discharge onto splash blocks at a distance of
at least 10 feet from the building s.
Exposed ground should be sloped and maintained at a minimum 5% away from the
building for at least 10 feet beyond the perimeter of the building. Locally, flatter grades
may be necessary to transition ADA access requirements for flatwork. After building
construction and landscaping have been completed, final grades should be verified to
docu ment effective drainage has been achieved. Grades around the structure should also
be periodically inspected and adjusted, as necessary, as part of the structure’s
maintenance program.
Flatwork and pavements will be subject to post -construction movement. Maximum
grades practical should be used for paving and flatwork to prevent areas where water
can pond. In addition, allowances in final grades should take into consideration post -
construction movement of flatwork, particularly if such movement would be critical.
Where paving or flatwork abuts the structure, care should be taken that joints are
properly sealed and maintained to prevent the infiltration of surface water.
Planters located adjacent to structure should preferably be self -contained. Sprinkler
mains and spray heads should be located a minimum of 5 feet away from the building
line(s). Low-volume, drip style landscaped irrigation should be used sparingly near the
building.
Exterior Slab Design and Construction
Exterior slabs -on-grade, exterior architectural features, and utilities founded on, or in
backfill or the site soils will likely experience some movement due to the volume change
of the material. Subgrade soils below new fill should be scarified to a depth of at least
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10 inches, moisture conditioned, and compacted prior to placement/construction of new
engineered fill, aggregate base course, or pavement/flatwork materials. Potential
movement could be reduced by:
■ Minimizing moisture increases in subgrade soils and new fill;
■ Controlling moisture -density during subgrade preparation and new fill placement;
■ Using designs which allow vertical movement between the exterior features and
adjoining structural elements; and
■ Placing control joints on relatively close centers.
Earthwork Construction Considerations
Upon completion of filling and grading, care should be taken to maintain the subgrade
water content prior to construction of grade -supported improvements such as floor slabs
and pavements. Construction traffic over the completed subgrades should be avoided.
The site should also be graded to prevent ponding of surface water on the prepared
subgrades or in excavations. Water collecting over or adjacent to construction areas
should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the
affected material should be removed, or the materials should be scarified, moistur e
conditioned, and recompacted prior to floor slab construction.
Construction site safety is the sole responsibility of the contractor who controls the
means, methods, and sequencing of construction operations. Under no circumstances
shall the information provided herein be interpreted to mean Terracon is assuming
responsibility for construction site safety or the contractor's activities; such
responsibility shall neither be implied nor inferred.
Excavations or other activities resulting in ground disturbance have the potential to
affect adjoining properties and structures. Our scope of services does not include review
of available final grading information or consider potential temporary grading performed
by the contractor for potential effe cts such as ground movement beyond the project
limits. A preconstruction/ precondition survey should be conducted to document nearby
property/infrastructure prior to any site development activity. Ex cavation or ground
disturbance activit i es adjacent or near property lines should be monitored or
instrumented for potential ground movements that could negatively af fect adjoining
property and/or structures.
Construction Observation and Testing
The earthwork efforts should be observed by the Geotechnical Engineer (or others under
their direction). Observation should include documentation of adequate removal of
surficial materials (vegetation, topsoil, and existing pavements), evaluation and
remediation of existing fill materials, subgrade stabilization, as well as proof rolling and
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mitigation of unsuitable areas delineated by the proof roll. Each lift of compacted fill
should be tested, evaluated, and reworked, as necessary, as recommended by the
Geotechnical Engineer prior to placement of additional lifts.
In areas of foundation excavations, the bearing subgrade and exposed conditions at the
base of the recommended over -excavation should be evaluated by the Geotechnical
Engineer. If unanticipated conditions are observed, the Geotechnical Engineer should
prescribe mitigation options.
In addition to the documentation of the essential parameters necessary for construction,
the continuation of the Geotechnical Engineer into the construction phase of the project
provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface
conditions, including assessing variations and associated design changes.
Shallow Foundations
If the site has been prepared in accordance with the requirements noted in Earthwork,
the following design parameters are applicable for shallow foundations.
Spread Footings – Design Recommendations
Item Description
Maximum Net Allowable Bearing
Pressure 1
2,500 to 3,000 psf with compaction
grouting/foam injection
OR
3,000 to 5,000 psf with the potential for
6,000 psf with aggregate piers .
(determined by ground improvement
contractor)
Required Bearing Stratum 2
Modified with ground improvement or all
existing fill has been completely removed
below foundations and replaced with
moisture conditioned, properly compacted
engineered fill
Minimum Foundation Dimensions Columns: 30 inches
Continuous: 18 inches
Lateral Earth Pressure Coefficients 3
On-site soil:
Active, Ka = 0.36
Passive, Kp = 2.77
At-rest, K o = 0.53
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Item Description
Sliding Resistance 4 On-site soil:
μ = 0.43
Moist Soil Unit Weight On-site soil:
γ = 1 10 pcf
Minimum Embedment Below
Finished Grade 5
Exterior footings in unheated areas: 30
inches
Interior footings and column pads in heated
areas: 12 inches
Estimated Total Movement 6 About 1 inch or less
Estimated Differential Movement 6 About ½ to ¾ of total movement
1. The maximum net allowable bearing pressure is the pressure in excess of the minimum
surrounding overburden pressure at the footing base elevation. Values assume exterior
grades are no steeper than 20% within 10 feet of structure. The design bearing
pressure applies to a dead load plus design live load condition. The design bearing
pressure may be increased by one -third when considering total loads that include wind
or seismic conditions.
2. Unsuitable or soft /loose soils should be over-excavated and replaced with engineered fill
per the recommendations presented in Earthwork.
3. Use of lateral earth pressures require the sides of the excavation for the spread footing
foundation to be nearly vertical and the concrete placed neat against these vertical
faces or the footing forms be removed and compacted engineered fill be placed against
the vertical footing face. Assumes no hydrostatic pressure. The lateral earth pressure
coefficients are ultimate values and do not include a factor of safety. The foundation
designer should include the appropriate factors of safety.
4. For fine-grained materials, lateral resistance using cohesion should not exceed ½ the
dead load.
5. Embedment necessary to minimize the effects of frost and/or seasonal water content
variations. For sloping ground, maintain depth below the lowest adjacent exterior grade
within 5 horizontal feet of the structure.
6. The estimated movements presented above assume the maximum footing dimension is
6 feet for column footings and maximum footing width is 3 feet for continuous footings.
Larger foundation footprints will likely require reduced net allowable soil bearing
pressures to reduce risk for potential settlement. These maximum foundation sizes will
likely vary if ground improvement if performed.
Footings should be proportioned to reduce differential foundation movement. As
discussed, total movement resulting from the assumed structural loads is estimated to
be on the order of about 1 inch. Additional foundation movements could occur if water
from any source infiltrates the foundation soils; therefore, proper drainage should be
provided in the final design and during construction and throughout the life of the
structure. Failure to maintain the proper drainage as recommended in the Grading and
Drainage section of the Earthwork section of this report will nullify the movement
estimates provided above.
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Any over-excavation that extends below the bottom of foundation elevation should
extend laterally beyond all edges of the foundations at least 8 inches per foot of over -
excavation depth below the foundation base elevation. The over -excavation should be
backfilled to the foundation base elevation in accordance with the recommendations
presented in this report.
Shallow Foundation Construction Considerations
As noted in Earthwork, foundation excavations should be evaluated under the
observation of the Geotechnical Engineer. The base of all foundation excavations should
be free of water and loose soil, prior to placing concrete. Concrete should be placed soon
after excavating to reduce bearing soil disturbance. Care should be taken to prevent
wetting or drying of the bearing materials during construction. Excessively wet or dry
material or any loose/disturbed material in the bottom of foundation excavations should
be removed/reconditioned before foundation concrete is placed.
To reduce the potential of “pumping” and softening of the foundation soils at the
foundation bearing level and the requirement for corrective work, we suggest the
foundation excavation for the building be completed remotely with a track -hoe operating
outside of the excavation limits.
Foundation elements should be reinforced as necessary to reduce the potential for
distress caused by differential foundation movement.
Unstable subgrade conditions encountered in foundation excavations should be observed
by Terracon to assess the subgrade and provide suitable alternatives for stabilization.
Typical methods of stabilization/improvement are presented in the Subgrade
Stabilization section of Earthwork.
Ground Improvement
Compaction Grouting or Foam Injection
In the area of the new building foundation, compaction grouting or foam injection could
be used to increase the density of the subgrade soils. This method would reduce risk for
settlement for the proposed foundation and floor slab that could be caused by
constructing on existing fill. Compaction grouting /foam injection involves injecting low -
slump grout or foam in individual boreholes at various depths, which results in a bulb of
grout or foam densifying soils.
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Aggregate Piers
A possible ground improvement alternative that may allow more efficient shallow
foundation support (i.e. higher allowable bearing pressures and/or lower estimated
settlement) includes the installation of aggregate piers. An aggregate pier consists of a
stone-filled column constructed by excavating a cylindrical hole and backfilling it with
crushed stone placed in lifts and applying a high degree of compactive effort resulting in
stone filled piers. The aggregate pier construction process not only results in a rigid
stone-filled column that lends support to structures, it also helps to densify the soils
surrounding the pier. Aggregate pier foundations are a proprietary product and, if
considered, should be designed and installed by a specialty contractor. Due to the
specialty of this soil improvement procedure, we recommend a performance specification
be used for this system.
If ground improvement with aggregate piers is selected for this project, we understand
the aggregate pier design firm will be the geotechnical engineer of record for these
ground improvement elements . As such, the design firm would provide the necessary
geotechnical design parameters for the planned foundation system including, but not
limited to, allowable soil bearing pressure, settlement estimates and foundation -specific
earthwork recommendations.
Deep Foundations
Helical Pile Lateral Loading
The following table lists input values for use in LPILE analyses. Modern versions of LPILE
provide estimated default values of k h and E 50 based on strength and are recommended
for the project. Since deflection or a service limit criterion will most likely control lateral
capacity design, no safety/resistance factor is included with the parameters.
Stratigraphy 1 LPILE Soil
Model
Su
(psf)2
(deg)2
’
(pcf)2 ε50
K (pci)
Depth
(feet)
Soil
Layer Static Cyclic
0 to 9 Existing
Fill
Stiff Clay w/o
Free Water 2,000 --- 125 Use Default Value
9 to 15 Sand Sand (Reese) --- 35° 125 Use Default Value
15 to 24 Sand Sand (Reese) --- 30° 50 Use Default Value
24 to 30.5
Lean
Clay with
Sand
Stiff Clay w/o
Free Water 1,000 --- 60 Use Default Value
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Stratigraphy 1 LPILE Soil
Model
Su
(psf)2
(deg)2
’
(pcf)2 ε50
K (pci)
Depth
(feet)
Soil
Layer Static Cyclic
1. See Subsurface Profile in Geotechnical Characterization for more details on
Stratigraphy.
2. Definition of Terms:
S u: Undrained shear strength
: Internal friction angle
’: Effective unit weight
Helical Pile Foundations
We believe helical piles with a structurally supported floor system can be used to
support of the proposed bank building. We do not recommend using vertically installed
helical piles to resist lateral loads without approved lateral load test data, as these types
of foundations are typically designed to resist axial loads. Only the horizontal component
of the allowable axial l oad should be considered to resist the lateral loading and only in
the direction of the batter. Terracon should be retained to observe helical pile
installation to verify that pro per bearing materials have been encountered during
installation.
In accordance with local building code requirements, a load test should be performed by
the helical pile installer to validate achieving the allowable design load. Load tests
should be performed using helical piles consistent in size and materials with tho se piles
planned for use during construction. Similarly, the same installation techniques and
equipment planned for use during installation of production piles should be used when
installing piles for load testing.
If a helical pile foundation system is selected by the project team, we recommend the helical
pile designer follow the recommendations presented in Chapter 18 of the applicable
International Building Code (IBC). Deeper soil borings may be needed if helical piles are
selected to explore subsurface conditions for a comparatively stiffer or denser layer of soils
and/or bedrock that would provide higher capacities. The helical pile designer should select
the size and number of helical bearing plates for each helical pile based on planned loads and
bearing materials described in our exploratory boring logs. Torque measurements during
installation of helical piles should be used to verify the axial capacity of the helical piles.
Terracon should be provided with the torque to capacity relationships for each type of pile
used on the project for our review and comment prior to mobilization to the site. We
recommend the helical pile installation contractor provide confirmation that the installation
equipment has been calibrated within one year of installation at this project. The helical
foundations should be installed by a qualified specialty contractor per the manufacturer’s
recommendations.
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Lateral Earth Pressures
Design Parameters
Although no below-grade areas are planned for the proposed bank building, we have
elected to provide geotechnical recommendations and design criteria for lateral loads on
b uried walls. Structures with unbalanced backfill levels on opposite sides should be
designed for earth pressures at least equal to values indicated in the following table.
Earth pressures will be influenced by structural design of the walls, conditions of wall
restraint, methods of construction, and/or compaction and the strength of the materials
being restrained. Two wall restraint conditions are shown in the diagram below. Active
earth pressure is commonly used for design of free -standing cantilever retaining walls
and assumes wall movement. The “at -rest” condition assumes no wall movement and is
commonly used for basement walls, loading dock walls, or other walls restrained at the
top. The recommended design lateral earth pressures do not include a factor of safety
and do not provide for possible hydrostatic pressure on the walls (unless stated).
Lateral Earth Pressure Design Parameters
Earth
Pressure
Condition 1
Coefficient for
Backfill Type 2
Surcharge
Pressure 3
p1 (psf)
Equivalent Fluid Pressures
(psf) 2,4
Unsaturated 5 Submerged 5
Active (Ka) 0.36 (0.36)S (35)H (75)H
At-Rest (Ko) 0.53 (0.53)S (55)H (80)H
Passive (Kp) 2.77 --- --- ---
1. For active earth pressure, wall must rotate about base, with top lateral
movements 0.002 H to 0.004 H, where H is wall height. For passive earth
pressure, wall must move horizontally to mobilize resistance. Fat clay or other
expansive soils should not be used as backfill behind the wall.
2. Uniform, horizontal backfill, with a maximum unit weight of 100 pcf.
3. Uniform surcharge, where S is surcharge pressure.
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Lateral Earth Pressure Design Parameters
Earth
Pressure
Condition 1
Coefficient for
Backfill Type 2
Surcharge
Pressure 3
p1 (psf)
Equivalent Fluid Pressures
(psf) 2,4
Unsaturated 5 Submerged 5
4. Loading from heavy compaction equipment is not included.
5. To achieve “Unsaturated” conditions, follow guidelines in Subsurface Drainage
for Below-Grade Walls below. “Submerged” conditions are recommended
when drainage behind walls is not incorporated into the design.
Backfill placed against structures should consist of granular soils or low plasticity
cohesive soils. For the granular values to be valid, the granular backfill must extend out
and up from the base of the wall at an angle of at least 45 degrees from vertic al for the
active case.
Footings, floor slabs or other loads bearing on backfill behind walls may have a
significant influence on the lateral earth pressure. Placing footings within wall backfill
and in the zone of active soil influence on the wall should be avoided unless structural
analyses indicat e the wall can safely withstand the increased pressure.
The lateral earth pressure recommendations given in this section are applicable to the
design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity
type concrete walls. These recommendations are not applicable to the design of modular
block - geogrid reinforced backfill walls (also termed MSE walls). Recommendations
covering these types of wall systems are beyond the scope of services for this
assignment. However, we would be pleased to develop a proposal for evaluation and
design of such wall systems upon request.
Floor Slabs
If a deep foundation option is selected to construct the building, we believe a
structurally supported floor system can be used for the proposed building . If a shallow
foundation option is selected to construct the building, w e believe a concrete slab -on-
grade floor system can be used for the proposed building provided ground improvement
including compaction grouting, foam injection or aggregate piers are installed. Another option
is to remove the existing fill is removed below the proposed floor slab and replaced with
moisture conditioned, properly compacted engineered fill. On-site soils are suitable as over-
excavation backfill below floor slabs.
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Floor Slab s - Design Recommendations
Even when bearing on properly prepared soils, movement of the slab -on-grade floor
system is possible should the subgrade soils undergo an increase in moisture content.
We estimate movement of about 1 inch is possible. If the owner cannot accept the risk
of slab movement, a structural floor should be used. If conventional slab -on-grade is
utilized, the subgrade soils should be prepared as recommended above and in the
Earthwork section of this report.
For structural design of concrete slabs -on -grade subjected to point loadings, a modulus
of subgrade reaction of 150 pounds per cubic inch (pci) may be used for floors. As an
alternative, a modulus of subgrade reaction value of 200 pci can be used for floors if the
upper 6 inches of the recommended over -excavation zone consists of CDOT class 1
structure backfill and the floors are supported on the CDOT class 1 structure backfill.
The use of a vapor retarder should be considered beneath concrete slabs on grade
covered with wood, tile, carpet, or other moisture sensitive or impervious coverings,
when the project includes humidity -controlled areas, or when the slab will support
equipment sensitive to moisture. When conditions warrant the use of a vapor retarder,
the slab designer should r efer to ACI 302 and/or ACI 360 for procedures and cautions
regarding the use and placement of a vapor retarder.
Additional floor slab design and construction recommendations are as follows:
■ Positive separations and/or isolation joints should be provided between slabs and
all foundations, columns, or utility lines to allow independent movement.
■ Control joints should be saw -cut in slabs in accordance with ACI Design Manual,
Section 302.1R -37 8.3.12 (tooled control joints are not recommended) to control
the location and extent of cracking.
■ Interior utility trench backfill placed beneath slabs should be compacted in
accordance with the recommendations presented in the Earthwork section of this
report.
■ Floor slabs should not be constructed on frozen subgrade.
■ Other design and construction considerations, as outlined in the ACI Design
Manual, Section 302.1R are recommended.
Floor Slab Construction Considerations
Movements of slabs -on-grade using the recommendations discussed in previous sections
of this report will likely be reduced and tend to be more uniform. The estimates
discussed above assume that the other recommendations in this report are followed.
Additional movement could occur should the subsurface soils become wetted to
significant depths, which could result in potential excessive movement causing uneven
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 27
floor slabs and severe cracking. This could be due to over watering of landscaping, poor
drainage, improperly functioning drain systems, and/or broken utility lines. Therefore, it
is imperative that the recommendations presented in this report be followed.
Finished subgrade, within and for at least 10 feet beyond the floor slab, should be
protected from traffic, rutting, or other disturbance and maintained in a relatively moist
condition until floor slabs are constructed. If the subgrade should become damage d or
desiccated prior to construction of floor slabs, the affected material should be removed,
and engineered fill should be added to replace the resulting excavation. Final
conditioning of the finished subgrade should be performed immediately prior to
placement of the floor slab support course.
The Geotechnical Engineer should observe the condition of the floor slab subgrades
immediately prior to placement of the floor slab support course, reinforcing steel, and
concrete. Attention should be paid to high traffic areas that were rutted and disturb ed
earlier, and to areas where backfilled trenches are located.
Pavements
General Pavement Comments
Pavement designs are provided for the traffic conditions and pavement life conditions as
noted in Project Description and in the following sections of this report. A critical
aspect of pavement performance is site preparation. Pavement designs noted in this
section must be applied to the site which has been prepared as recommended in the
Earthwork section.
Pavements – Subgrade Preparation
On most project sites, the site grading is accomplished relatively early in the
construction phase. Fills are typically placed and compacted in a uniform manner.
However, as construction proceeds, the subgrade may be disturbed due to utility
excavations, c onstruction traffic, desiccation, or rainfall/snow melt. As a result, the
pavement subgrade may not be suitable for pavement construction and corrective action
will be required. The subgrade should be carefully evaluated at the time of pavement
constructio n for signs of disturbance or instability. We recommend the pavement
subgrade be thoroughly proof rolled with a loaded tandem -axle dump truck prior to final
grading and paving. All pavement areas should be moisture conditioned and properly
compacted to the recommendations in this report immediately prior to paving.
Prior to pavement construction and after the pavement areas have been stripped, and
any required undercuts and the recommended 2 feet of over-excavation due to the
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 28
presence of existing fill materials have been completed within the planned pavement
areas, the top 10 inches of the exposed ground surface should be scarified, moisture
conditioned, and compacted as described in this report before any new fill is placed or
constructed. After the subgrade has been scarified and compacted and before placement
of new fill and pavement, we recommend the subgrade be proof rolled as described
above.
Pavements – Design Recommendations
Design of new privately -maintained pavements for the project has been based on the
procedures described by the National Asphalt Pavement Associations (NAPA) and the
American Concrete Institute (ACI).
We assumed the following design parameters for NAPA flexible pavement thickness
design:
■ Automobile Parking Areas
o Class I - Parking stalls and parking lots for cars and pick -up trucks, with
Equivalent Single Axle Load (ESAL) up to 7,000 over 20 years
■ Main Traffic Corridors
o Class II – Parking lots with a maximum of 10 trucks per day with
Equivalent Single Axle Load (ESAL) up to 27,000 over 20 years (including
trash trucks)
■ Subgrade Soil Characteristics
o USCS Classification – CL, classified by NAPA as poor
We assumed the following design parameters for ACI rigid pavement thickness design
based upon the average daily truck traffic (ADTT):
■ Automobile Parking Areas
o ACI Category A: Automobile parking with an ADTT of 1 over 20 years
■ Main Traffic Corridors
o ACI Category A: Automobile parking area and service lanes with an ADTT
of up to 10 over 20 years
■ Subgrade Soil Characteristics
o USCS Classifica tion – CL
■ Concrete modulus of rupture value of 600 psi
We should be contacted to confirm and/or modify the recommendations contained herein
if actual traffic volumes differ from the assumed values shown above.
Recommended alternatives for flexible and rigid pavements are summarized for each
traffic areas as shown in the following table.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 29
Traffic Area Alternative
Recommended Pavement Thicknesses (Inches)
Asphaltic
Concrete
Surface
Portland
Cement
Concrete
Aggregate
Base
Course
Total
Automobile
Parking
(NAPA Class I
and ACI
Category A)
A 4 -- 6 10
B -- 5 4 1 9
Main Traffic
Corridors
(NAPA Class II
and ACI
Category A)
A 6 -- 6 12
B -- 6 4 1 10
1. Although not required for structural support, a minimum 4-inch thick aggregate base course
layer is suggested for the portland cement concrete (PCC) pavements to help reduce the
potential for slab curl, shrinkage cracking, and subgrade “pumping” through joints.
Aggregate base course should consist of a blend of sand and gravel which meets strict
specifications for quality and gradation. Use of materials meeting Colorado Department
of Transportation (CDOT) Class 5 or 6 specifications is recommended for aggregate b ase
course. Aggregate base course should be placed in lifts not exceeding 6 inches and
compacted to a minimum of 95 percent of the maximum dry unit weight as determined
by ASTM D1557 (or AASHTO T180).
Asphaltic concrete should be composed of a mixture of aggregate, filler and additives (if
required) and approved bituminous material. The asphalt concrete should conform to
approved mix designs stating the Superpave properties, optimum asphalt content, job
mix formula and recommended mixing and placing temperatures. Aggregate used in
asphalt concrete should meet particular gradations. Material meeting CDOT Grading S or
SX specifications or equivalent is recommended for asphalt concrete. Mix designs should
b e submitted prior to construction to verify their adequacy. Asphalt material should be
placed in maximum 3 -inch lifts and compacted within a range of 92 to 96 percent of the
theoretical maximum (Rice) density (ASTM D2041).
Where rigid pavements are used, the concrete should be produced from an approved mix
design with the following minimum properties:
Properties Value
Compressive strength 4,500 psi
Cement type Type I or II portland cement, or Type IL
portland-limestone cement
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 30
Properties Value
Entrained air content (%) 5 to 8
Concrete aggregate ASTM C33 and CDOT section 703
Concrete should be deposited by truck mixers or agitators and placed a maximum of 90
minutes from the time the water is added to the mix. Longitudinal and transverse joints
should be provided as needed in concrete pavements for expansion/contraction and
isolation per ACI 330 and ACI 325. The location and extent of joints should be based
upon the final pavement geometry.
Proper joint spacing will also be required for PCC pavements to prevent excessive slab
curling and shrinkage cracking. All joints should be sealed to prevent entry of foreign
material and dowelled where necessary for load transfer.
For areas subject to concentrated and repetitive loading conditions (if any) such as
dumpster pads, truck delivery docks and ingress/egress aprons, we recommend using a
portland cement concrete pavement with a thickness of at least 7 inches underlain by at
least 4 inches of granular base. Prior to placement of the granular base, the subgrade
soils should be prepared as previously discussed. For dumpster pads, the concrete
pavement area should be large enough to support the container and tipping axle of the
refuse truck.
Pavement performance is affected by its surroundings. In addition to providing
preventive maintenance, the civil engineer should consider the following
recommendations in the design and layout of pavements:
■ Site grades should slope a minimum of 2 percent away from the pavements;
■ The subgrade and the pavement surface have a minimum 2 percent slope to
promote proper surface drainage;
■ Consider appropriate edge drainage and pavement under drain systems;
■ Install pavement drainage surrounding areas anticipated for frequent wetting;
■ Install joint sealant and seal cracks immediately;
■ Seal all landscaped areas in, or adjacent to pavements to reduce moisture
migration to subgrade soils; and
■ Placing compacted, low permeability backfill against the exterior side of curb and
gutter.
Pavements – Construction Considerations
Openings in pavement, such as landscape islands, are sources for water infiltration into
surrounding pavements. Water collects in the islands and migrates into the surrounding
subgrade soils thereby degrading support of the pavement. This is especially app licable
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 31
for islands with raised concrete curbs, irrigated foliage, and low permeability near -
surface soils. The civil design for pavements with these conditions should include
features to restrict or to collect and discharge excess water from the islands. Examples
of features are edge drains connected to the storm water collection system or other
suitable outlet and impermeable barriers preventing lateral migration of water such as a
cutoff wall installed to a depth below the pavement structure.
Pavements – Maintenance
The pavement sections represent minimum recommended thicknesses and, as such,
periodic upkeep should be anticipated. Preventive maintenance should be planned and
provided for through an on -going pavement management program. Maintenance
activities are inten ded to slow the rate of pavement deterioration and to preserve the
pavement investment. Pavement care consists of both localized (e.g., crack and joint
sealing and patching) and global maintenance (e.g., surface sealing). Additional
engineering consultation is recommended to determine the type and extent of a cost -
effective program. Even with periodic maintenance, some movements and related
cracking may still occur, and repairs may be required.
General Comments
Our analysis and opinions are based upon our understanding of the project, the
geotechnical conditions in the area, and the data obtained from our site exploration.
Variations will occur between exploration point locations or due to the modifying effects
of construction or weather. The nature and extent of such variations may not become
evident until during or after construction. Terracon should be retained as the
Geotechnical Engineer, where noted in this report, to provide observation and testing
services during pertinent construction phases. If variations appear, we can provide
further evaluation and supplemental recommendations. If variations are noted in the
absence of our observation and testing services on -site, we should be immediately
notified so th at we can provide evaluation and supplemental recommendations.
Our Scope of Services does not include either specifically or by implication any
environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or
identification or prevention of pollutants, hazardous materials or conditions. If the owner
is concerned about the potential for such contamination or pollution, other studies
should be undertaken.
Our services and any correspondence are intended for the sole benefit and exclusive use
of our client for specific application to the project discussed and are accomplished in
accordance with generally accepted geotechnical engineering practices with no th ird-
party beneficiaries intended. Any third -party access to services or correspondence is
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials 32
solely for information purposes to support the services provided by Terracon to our
client. Reliance upon the services and any work product is limited to our client and is not
intended for third parties. Any use or reliance of the provided information by t hird
parties is done solely at their own risk. No warranties, either express or implied, are
intended or made.
Site characteristics as provided are for design purposes and not to estimate excavation
cost. Any use of our report in that regard is done at the sole risk of the excavating cost
estimator as there may be variations on the site that are not apparent in the data that
could significantly effect excavation cost. Any parties charged with estimating excavation
costs should seek their own site characterization for specific purposes to obtain the
specific level of detail necessary for costing. Site safety and cost estimating including
excavation supp ort and dewatering requirements/design are the responsibility of others.
Construction and site development have the potential to affect adjacent prop erties. Such
impacts can include damages due to vibration, modification of groundwater/surface
water flow d uring construction, foundation movement due to undermining or subsidence
from excavation , as well as noise or air quality concerns. Evaluation of these items on
nearby properties are commonly associated with contractor means and methods and are
not addressed in this report. The owner and contractor should consider a
preconstruction/precondition survey of surrounding development. If changes in the
nature, design, or location of the project are planned, our conclusions and
recommendations shall not be conside red valid unless we review the changes and either
verify or modify our conclusions in writing.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Figures
Contents:
GeoModel
165
170
175
180
185
190
195
200
205
EL
E
V
A
T
I
O
N
(
M
S
L
)
(
f
e
e
t
)
Layering shown on this figure has been developed by the geotechnical
engineer for purposes of modeling the subsurface conditions as
required for the subsequent geotechnical engineering for this project.
Numbers adjacent to soil column indicate depth below ground surface.
NOTES:
B-1
B-2 B-3 B-4
Legend
This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.
GeoModel
2413 South College Avenue | Fort Collins, CO
Terracon Project No. 20245044
BofA S. College and Drake - C01-136
1901 Sharp Point Dr Ste C
Fort Collins, CO
Second Water Observation
First Water Observation
Groundwater levels are temporal. The levels shown are representative of
the date and time of our exploration. Significant changes are possible
over time.
Water levels shown are as measured during and/or after drilling. In
some cases, boring advancement methods mask the presence/absence
of groundwater. See individual logs for details.
Asphalt Aggregate Base
Course
Lean Clay Sandy Lean Clay
Clayey Sand Poorly-graded Sand
Lean Clay with Sand
Model Layer Layer Name General Description
1
Existing fill consisting of lean clay, sandy lean clay with
variable amounts of gravel and clayey sand with variable
amounts of gravel; brown, red brown, tan
3 Lean clay with sand; soft to stiff, red brown
2 Sand with variable amounts of clay; very loose to medium
dense, red brown
Existing Fill
Clay
Sand
1
2 9
10
1
2
3
19.5
17
9
24
30.5
1
2
3
15.415
9
24
30
1
3
2
7
9
10.5
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Attachments
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Exploration and Testing Procedures
Field Exploration
Number of Borings Approximate Boring
Depth (feet) Location
2
(Boring Nos. B-2 and B-3) 30 to 30.5 Building area
2
(Boring Nos. B-1 and B-4) 10 to 10.5 Parking/driveway areas
Boring Layout and Elevati ons: Terracon personnel provided the boring layout using
handheld GPS equipment (estimated horizontal accuracy of about ±1 5 feet) and
referencing existing site features. Approximate ground surface elevations were obtained
were obtained using a level and grade rod referenced to a temporary benchmark . If a
more precise boring layout are desired, we recommend the borings be surveyed.
Subsurface Exploration Procedures: We advanced the borings with a truck -mounted,
drill rig using solid-stem, continuous-flight augers . Sampling was performed using
standard split -barrel and modified California barrel sampling procedures . Bulk samples of
auger cuttings from the upper approximately 5 feet of each borehole were also collected
for laboratory testing . In the split-barrel sampling procedure, a standard 2 -inch outer
diameter split -barrel sampling spoon was driven into the ground by a 140 -pound
aut omatic hammer falling a distance of 30 inches. The number of blows required to
advance the sampling spoon the last 12 inches of a normal 18 -inch penetration is
recorded as the Standard Penetration Test (SPT) resistance value. The SPT resistance
values, also referred to as N -values, are indicated on the boring logs at the test depths.
In the modified California barrel sampling procedure, a 2½-inch outer diameter split-
barrel sampling spoon is used for sampling. Modified California barrel sampling
procedures are similar to standard split spoon sampling procedure; however, blow
counts are typically recorded for 6 -inch intervals for a total of 12 inches of penetration.
Modified California barrel sampler blow counts are not considered N -values. The samples
were placed in appropriate containers and taken to our soil laboratory for testing and
classification by a Geotechnical Engineer.
We also observed the boreholes while drilling and at the completion of drilling for the
presence of groundwater. The groundwater levels are shown on the attached boring
logs.
Our exploration team prepared field boring logs as part of the drilling operations. The
sampling depths, penetration distances, and other sampling information were recorded
on the field boring logs. These field logs included visual classifications of the materials
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
observed during drilling and our interpretation of the subsurface conditions between
samples. Final boring logs were prepared from the field logs. The final boring logs
represent the Geotechnical Engineer's interpretation of the subsurface conditions at the
boring locations based on field data, observation of samples, and laboratory test results.
We backfilled the borings with auger cuttings after completion of drilling. Pavements
were patched with cold -mix asphalt. Our services did not include repair of the site
beyond backfilling the boreholes and patching existing pavements. Excess auger cuttings
were removed from the site. Because backfill material often settles below the surface
after a period, we recommend checking boreholes periodically and backfilling, if
necessary.
Laboratory Testing
The project engineer reviewed the field data and assigned laboratory tests. The
laboratory testing program included the following types of tests:
■ Moisture Content
■ Dry Unit Weight
■ Atterberg Limits
■ Grain-size Analysis
■ One-dimensional Swell
■ Corrosive Properties
The laboratory testing program often included examination of soil samples by an
engineer and/or geologist . Based on the results of our field and laboratory programs, we
described and classified the soil samples in accordance with the Unified Soil
Classification System. A brief description of this classification system as well as the
General Notes can be found in the Supporting Information section.
Laboratory test results are indicated on the boring logs and are presented in depth in
the Exploration Results section. Laboratory tests are performed in general accordance
with applicable local standards or other acceptable standards. In some cases, variations
to methods are applied as a result of local practice or professional judgement.
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Site Location and Exploration Plans
Contents:
Site Location Plan
Exploration Plan
Note: All attachments are one page unless noted above.
Geotechnical Engineering Report
BofA S. College and Drake – CO1 -136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Note to Preparer: This is a large table with outside borders. Just click inside the table
above this text box, then paste your GIS Toolbox image.
When paragraph markers are turned on you may notice a line of hidden text above
and outside the table – please leave that alone. Limit editing to inside the table.
The line at the bottom about the general location is a separate table line. You can edit
it as desired, but try to keep to a single line of text to avoid reformatting the page.
Site Location
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS
Geotechnical Engineering Report
BofA S. College and Drake – CO1 -136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Note to Preparer: This is a large table with outside borders. Just click inside the table
above this text box, then paste your GIS Toolbox image.
When paragraph markers are turned on you may notice a line of hidden text above
and outside the table – please leave that alone. Limit editing to inside the table.
The line at the bottom about the general location is a separate table line. You can edit
it as desired, but try to keep to a single line of text to avoid reformatting the page.
Exploration Plan
tempDIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Exploration and Laboratory Results
Contents:
Boring Logs (B-1 through B-4)
Atterberg Limits
Grain Size Distribution
Consolidation/Swell (4 pages)
Corrosivity
Note: All attachments are one page unless noted above.
197.46
197.16
193.66
190.66
188.66
187.66
ASPHALT, about 2.5 inches thick
AGGREGATE BASE COURSE, about 4 inches thick
FILL - LEAN CLAY (CL), brown
FILL - SANDY LEAN CLAY, brown
FILL - SANDY LEAN CLAY TO CLAYEY SAND, red
brown, with some gravel
POORLY GRADED SAND, fine to coarse grained, red
brown, medium dense
Boring Terminated at 10 Feet
Boring Log No. B-1
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
De
p
t
h
(
F
t
.
)
5
10
Facilities | Environmental |Geotechnical | Materials
Elevation: 197.66 (Ft.)
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
15.5
17.5
7.9
3.7
107
121
4-5-5
N=10
3-4
7/12"
3-5-5
N=10
9-13
22/12"
0.2
0.5
4.0
7.0
9.0
10.0
Advancement Method
4-inch diameter, continuous-flight, solid-stem auger
Notes
Water Level Observations
No free water observed
See Exploration and Testing Procedures for a description of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were measured in the field using an engineer's level and graderod. A temporary benchmark was used at the northeast corner of the pavement in front of theexisting building with an assumed elevation of 200 feet.
BofA S. College and Drake - C01-136
Hammer Type
Automatic;
Hammer Efficiency
= 95%
2413 South College Avenue | Fort Collins, CO
Terracon Project No. 20245044 Fort Collins, CO
1901 Sharp Point Dr Ste C
Drill Rig
CME 75
Driller
Terracon Fort Collins
Logged by
P. Agudelo
Boring Started
02-28-2025
Boring Completed
02-28-2025
Abandonment Method
Boring backfilled with auger cuttings upon
completion and patched with asphalt
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
Atterberg
Limits
LL-PL-PI
See Exploration PlanLocation:
Latitude: 40.555550° Longitude: -105.077550°
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
1
2
199.05
198.75
192.35
190.35
185.35
180.35
175.35
168.85
ASPHALT, about 3 inches thick
AGGREGATE BASE COURSE, about 4 inches thick
FILL - SANDY LEAN CLAY, brown
FILL - CLAYEY SAND (SC), brown, tan, red brown,
with trace gravel
CLAYEY SAND, red brown, loose
POORLY GRADED SAND, fine to coarse grained, red
brown, medium dense
CLAYEY SAND, red brown, loose
LEAN CLAY WITH SAND, red brown, medium stiff
Boring Terminated at 30.5 Feet
Boring Log No. B-2
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
De
p
t
h
(
F
t
.
)
5
10
15
20
25
30
Facilities | Environmental |Geotechnical | Materials
Elevation: 199.35 (Ft.)
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
92.4
49.3
18.3
17.2
15.4
8.3
6.3
20.1
24.4
26.5
108
101
112
103
6-8
14/12"
2-2-2
N=4
4-7
11/12"
3-2-2
N=4
19-22
41/12"
5-4-3
N=7
2-3
5/12"
2-3-5
N=8
43-17-26
32-17-15
0.3
0.6
7.0
9.0
14.0
19.0
24.0
30.5
+1.4/200
-0.2/1000
Advancement Method
4-inch diameter, continuous-flight, solid-stem auger
Notes
Water Level Observations
19.5 feet at completion of drilling
17 feet while drilling
See Exploration and Testing Procedures for a description of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were measured in the field using an engineer's level and graderod. A temporary benchmark was used at the northeast corner of the pavement in front of theexisting building with an assumed elevation of 200 feet.
BofA S. College and Drake - C01-136
Hammer Type
Automatic;
Hammer Efficiency
= 95%
2413 South College Avenue | Fort Collins, CO
Terracon Project No. 20245044 Fort Collins, CO
1901 Sharp Point Dr Ste C
Drill Rig
CME 75
Driller
Terracon Fort Collins
Logged by
P. Agudelo
Boring Started
02-28-2025
Boring Completed
02-28-2025
Abandonment Method
Boring backfilled with auger cuttings upon
completion and patched with asphalt
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
Atterberg
Limits
LL-PL-PI
See Exploration PlanLocation:
Latitude: 40.555260° Longitude: -105.077350°
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
1
2
3
199.26
198.96
192.56
190.56
175.56
169.56
ASPHALT, about 3.5 inches thick
AGGREGATE BASE COURSE, about 4 inches thick
FILL - SANDY LEAN CLAY (CL), brown, with trace
gravel
FILL - SANDY LEAN CLAY TO CLAYEY SAND, red
brown
POORLY GRADED SAND, fine to coarse grained, red
brown, loose to medium dense
LEAN CLAY WITH SAND, red brown, soft to medium
stiff
Boring Terminated at 30 Feet
Boring Log No. B-3
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
De
p
t
h
(
F
t
.
)
5
10
15
20
25
30
Facilities | Environmental |Geotechnical | Materials
Elevation: 199.56 (Ft.)
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
61.211.5
10.7
12.7
1.6
11.1
13.0
25.9
27.2
110
108
122
99
4-3-3
N=6
2-4
6/12"
3-3-4
N=7
6-7
13/12"
9-9-8
N=17
7-7
14/12"
3-2-2
N=4
3-3
6/12"
38-16-22
0.3
0.6
7.0
9.0
24.0
30.0
+0.3/500
Advancement Method
4-inch diameter, continuous-flight, solid-stem auger
Notes
Water Level Observations
15.4 at completion of drilling
15 feet while drilling
See Exploration and Testing Procedures for a description of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were measured in the field using an engineer's level and graderod. A temporary benchmark was used at the northeast corner of the pavement in front of theexisting building with an assumed elevation of 200 feet.
BofA S. College and Drake - C01-136
Hammer Type
Automatic;
Hammer Efficiency
= 95%
2413 South College Avenue | Fort Collins, CO
Terracon Project No. 20245044 Fort Collins, CO
1901 Sharp Point Dr Ste C
Drill Rig
CME 75
Driller
Terracon Fort Collins
Logged by
P. Agudelo
Boring Started
02-28-2025
Boring Completed
02-28-2025
Abandonment Method
Boring backfilled with auger cuttings upon
completion and patched with asphalt
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
Atterberg
Limits
LL-PL-PI
See Exploration PlanLocation:
Latitude: 40.555140° Longitude: -105.077450°
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
1
2
3
199.77
199.47
192.97
190.97
189.47
ASPHALT, about 2.5 inches thick
AGGREGATE BASE COURSE, about 4 inches thick
FILL - SANDY LEAN CLAY (CL), brown, with trace
gravel
LEAN CLAY WITH SAND, red brown, stiff
POORLY GRADED SAND, fine to coarse grained, red
brown, medium dense
Boring Terminated at 10.5 Feet
Boring Log No. B-4
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
De
p
t
h
(
F
t
.
)
5
10
Facilities | Environmental |Geotechnical | Materials
Elevation: 199.97 (Ft.)
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
61.8
15.6
14.0
20.3
2.5
104
96
4-6
10/12"
3-2-3
N=5
5-7
12/12"
4-5-6
N=11
35-16-19
0.2
0.5
7.0
9.0
10.5
+0.6/200
Advancement Method
4-inch diameter, continuous-flight, solid-stem auger
Notes
Water Level Observations
No free water observed
See Exploration and Testing Procedures for a description of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were measured in the field using an engineer's level and graderod. A temporary benchmark was used at the northeast corner of the pavement in front of theexisting building with an assumed elevation of 200 feet.
BofA S. College and Drake - C01-136
Hammer Type
Automatic;
Hammer Efficiency
= 95%
2413 South College Avenue | Fort Collins, CO
Terracon Project No. 20245044 Fort Collins, CO
1901 Sharp Point Dr Ste C
Drill Rig
CME 75
Driller
Terracon Fort Collins
Logged by
P. Agudelo
Boring Started
02-28-2025
Boring Completed
02-28-2025
Abandonment Method
Boring backfilled with auger cuttings upon
completion and patched with asphalt
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
Atterberg
Limits
LL-PL-PI
See Exploration PlanLocation:
Latitude: 40.555030° Longitude: -105.077740°
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
1
3
2
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100 110
"A" Line
ASTM D4318
CH or OH
CL or OL
ML or OL
MH or OH
26
15
22
19
92.4
49.3
61.2
61.8
CL
SC
CL
CL
17
17
16
16
26
15
22
19
92.4
49.3
61.2
61.8
CL
SC
CL
CL
17
17
16
16
43
32
38
35
Atterberg Limit Results
"U" Line
Liquid Limit
LL PL PI Fines USCS DescriptionFines
Pl
a
s
t
i
c
i
t
y
I
n
d
e
x
CL - ML
16
4
7
Facilities | Environmental |Geotechnical | Materials
2 - 3
7 - 8
2 - 3.5
4 - 5.5
B-2
B-2
B-3
B-4
Boring ID Depth (Ft)
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245044
2413 South College Avenue | Fort Collins, CO
BofA S. College and Drake - C01-136
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
140
HydrometerU.S. Sieve Opening in Inches
Grain Size Distribution
ASTM D422 / ASTM C136
SandGravel
2 10 14 506 2001.5 83/4 1/23/8 30 403 601
U.S. Sieve Numbers
16 2044 10063
Grain Size (mm)
coarse fine coarse finemedium Silt or ClayCobbles
Pe
r
c
e
n
t
C
o
a
r
s
e
r
b
y
W
e
i
g
h
t
Pe
r
c
e
n
t
F
i
n
e
r
b
y
W
e
i
g
h
t
100
90
80
70
60
50
40
30
20
10
0
AASHTOUSCSUSCS Classification
A-7-6 (25)
A-6 (4)
A-6 (10)
A-6 (9)
CL
SC
CL
CL
FILL - LEAN CLAY
FILL - CLAYEY SAND
FILL - SANDY LEAN CLAY
FILL - SANDY LEAN CLAY
Facilities | Environmental |Geotechnical | Materials
43
32
38
35
26
15
22
19
17
17
16
16
%CobblesD60
0.154
D100 %Clay%Sand%Gravel
0.0
3.5
3.0
11.0
7.6
47.2
35.7
27.2
92.4
49.3
61.2
61.8
LL PL PI Cc Cu
0.0
0.0
0.0
0.0
D10D30
4.75
19
19
25
%Fines %Silt
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245044
2413 South College Avenue | Fort Collins, CO
BofA S. College and Drake - C01-136
Boring ID
2 - 3
7 - 8
2 - 3.5
4 - 5.5
B-2
B-2
B-3
B-4
2 - 3
7 - 8
2 - 3.5
4 - 5.5
Depth (Ft)Boring ID
B-2
B-2
B-3
B-4
Depth (Ft)
-4
-3
-2
-1
0
1
2
3
4
100 1,000 10,000
Ax
i
a
l
S
t
r
a
i
n
(
%
)
Pressure (psf)
ASTM D4546
One-Dimensional Swell or Collapse
Facilities | Environmental |Geotechnical | Materials
(pcf) WC (%)Description USCS
CLFILL - LEAN CLAY (CL)
Boring ID Depth (Ft)
2 - 3B-2
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245044
2413 South College Avenue | Fort Collins, CO
BofA S. College and Drake - C01-136
-4
-3
-2
-1
0
1
2
3
4
100 1,000 10,000
Ax
i
a
l
S
t
r
a
i
n
(
%
)
Pressure (psf)
ASTM D4546
One-Dimensional Swell or Collapse
Facilities | Environmental |Geotechnical | Materials
Notes: Sample exhibited 0.2% compression when inundated at an applied pressure of 1,000 psf.
(pcf) WC (%)Description USCS
SCFILL - CLAYEY SAND (SC)
Boring ID Depth (Ft)
7 - 8B-2
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245044
2413 South College Avenue | Fort Collins, CO
BofA S. College and Drake - C01-136
-4
-3
-2
-1
0
1
2
3
4
100 1,000 10,000
Ax
i
a
l
S
t
r
a
i
n
(
%
)
Pressure (psf)
ASTM D4546
One-Dimensional Swell or Collapse
Facilities | Environmental |Geotechnical | Materials
(pcf) WC (%)Description USCS
FILL - SANDY LEAN CLAY
Boring ID Depth (Ft)
4 - 5B-3
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245044
2413 South College Avenue | Fort Collins, CO
BofA S. College and Drake - C01-136
-4
-3
-2
-1
0
1
2
3
4
100 1,000 10,000
Ax
i
a
l
S
t
r
a
i
n
(
%
)
Pressure (psf)
ASTM D4546
One-Dimensional Swell or Collapse
Facilities | Environmental |Geotechnical | Materials
(pcf) WC (%)Description USCS
FILL - SANDY LEAN CLAY
Boring ID Depth (Ft)
2 - 3B-4
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245044
2413 South College Avenue | Fort Collins, CO
BofA S. College and Drake - C01-136
Client
B-2
0.6-4.8'
AASHTO T289 8.33
ASTM C1580 451
AWWA 4500-S,D Nil
ASTM D512 199
ASTM G200 252
AWWA 2520 B 675
ASTM G57 1300
These tests were performed in general accordance with the applicable AASHTO, ASTM, and AWWA test methods. This report is exclusively for
the use of the client indicated above and shall not be reproduced without the full written consent of Terracon Consultants Inc.. Test results
transmitted herein are only applicable to the actual samples tested at the location(s) referenced and are not necessarily indicative of the properties
of other apparently similar materials.
Myles Warner
3/24/2025
Verified By:
Corrosivity Suite -Results
Sample Location
Sample Depth (ft.)
Acidity (pH)
Water Soluble Sulfate Ion
Content (mg/Kg)
Water Soluble Sulfide Content
(mg/Kg)
Oxidation-Reduction Potential
(RmV)
Total Dissolved Salts (mg/Kg)
Electrical Resistivity (Ω·cm)
Water Soluble Chloride Ion
Content (mg/Kg)
Project
Cushman & Wakefield US Inc.BofA S. College and Drake - C01-136
Chicago, IL 20245044
Date Received:3/18/2025
Geotechnical Engineering Report
BofA S. College and Drake – CO1-136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Supporting Information
Contents:
General Notes
Unified Soil Classification System
Note: All attachments are one page unless noted above.
Auger
Cuttings
Modified
California
Ring
Sampler
Standard
Penetration
Test
Facilities | Environmental |Geotechnical | Materials
less than 500
1,000 to 2,000
2,000 to 4,000
> 8,000
500 to 1,000
4,000 to 8,000
Unconfined
Compressive
Strength Qu (psf)
BofA S. College and Drake - C01-136
2413 South College Avenue | Fort Collins, CO
Terracon Project No. 20245044
1901 Sharp Point Dr Ste C
Fort Collins, CO
N
(HP)
(T)
(DCP)
UC
(PID)
(OVA)
Standard Penetration Test
Resistance (Blows/Ft.)
Hand Penetrometer
Torvane
Dynamic Cone Penetrometer
Unconfined Compressive
Strength
Photo-Ionization Detector
Organic Vapor Analyzer
Water Level After a
Specified Period of Time
Water Level After
a Specified Period of Time
Cave In
Encountered
Water Level Field Tests
Water Initially
Encountered
Sampling
Water levels indicated on the soil boring logs are the
levels measured in the borehole at the times indicated.
Groundwater level variations will occur over time. In
low permeability soils, accurate determination of
groundwater levels is not possible with short term
water level observations.
General Notes
Location And Elevation Notes
Exploration point locations as shown on the Exploration Plan and as noted on the soil boring logs in the form of Latitude and Longitude are
approximate. See Exploration and Testing Procedures in the report for the methods used to locate the exploration points for this project. Surface
elevation data annotated with +/- indicates that no actual topographical survey was conducted to confirm the surface elevation. Instead, the surface
elevation was approximately determined from topographic maps of the area.
Soil classification as noted on the soil boring logs is based Unified Soil Classification System. Where sufficient laboratory data exist to classify the soils
consistent with ASTM D2487 "Classification of Soils for Engineering Purposes" this procedure is used. ASTM D2488 "Description and Identification of
Soils (Visual-Manual Procedure)" is also used to classify the soils, particularly where insufficient laboratory data exist to classify the soils in accordance
with ASTM D2487. In addition to USCS classification, coarse grained soils are classified on the basis of their in-place relative density, and fine-grained
soils are classified on the basis of their consistency. See "Strength Terms" table below for details. The ASTM standards noted above are for reference
to methodology in general. In some cases, variations to methods are applied as a result of local practice or professional judgment.
Exploration/field results and/or laboratory test data contained within this document are intended for application to the project as described in this
document. Use of such exploration/field results and/or laboratory test data should not be used independently of this document.
Relevance of Exploration and Laboratory Test Results
Descriptive Soil Classification
Strength Terms
4 - 8
0 - 1
> 30
4 - 9
30 - 50
> 50
15 - 46
47 - 79
> 80 Very Stiff
Hard
< 3
3 - 5
11 - 18
19 - 36
2 - 4
8 - 15
15 - 30
(50% or more passing the No. 200 sieve.)
Consistency determined by laboratory shear strength testing, field visual-manual
procedures or standard penetration resistance
Relative Density of Coarse-Grained Soils
Very Loose
Loose
Medium Dense
Dense
Very Dense
10 - 29
0 - 3 0 - 5
6 - 14
Very Soft
Soft
Medium Stiff
Stiff
6 - 10
Consistency of Fine-Grained Soils
(More than 50% retained on No. 200 sieve.)
Density determined by Standard Penetration Resistance
Ring Sampler
(Blows/Ft.)Relative Density Consistency
Standard Penetration
or N-Value
(Blows/Ft.)
Standard Penetration
or N-Value
(Blows/Ft.)
Ring
Sampler
(Blows/Ft.)
> 37
_
Geotechnical Engineering Report
BofA S. College and Drake – CO1 -136 | Fort Collins, Colorado
June 9, 2025 | Terracon Project No. 20245044
Facilities | Environmental | Geotechnical | Materials
Unified Soil Classification System
Criteria for Assigning Group Symbols and Group Names Using
Laboratory Tests A
Soil Classification
Group
Symbol Group Name B
Coarse-Grained Soils:
More than 50% retained
on No. 200 sieve
Gravels:
More than 50% of
coarse fraction
retained on No. 4
sieve
Clean Gravels:
Less than 5% fines C
Cu≥4 and 1≤Cc≤3 E GW Well-graded gravel F
Cu<4 and/or [Cc<1 or Cc>3.0] E GP Poorly graded gravel F
Gravels with Fines:
More than 12% fines C
Fines classify as ML or MH GM Silty gravel F, G, H
Fines classify as CL or CH GC Clayey gravel F, G, H
Sands:
50% or more of
coarse fraction
passes No. 4 sieve
Clean Sands:
Less than 5% fines D
Cu≥6 and 1≤Cc≤3 E SW Well-graded sand I
Cu<6 and/or [Cc<1 or Cc>3.0] E SP Poorly graded sand I
Sands with Fines:
More than 12% fines D
Fines classify as ML or MH SM Silty sand G, H, I
Fines classify as CL or CH SC Clayey sand G, H, I
Fine-Grained Soils:
50% or more passes the
No. 200 sieve
Silts and Clays:
Liquid limit less than
50
Inorganic: PI > 7 and plots above “A” line J CL Lean clay K, L, M
PI < 4 or plots below “A” line J ML Silt K, L, M
Organic: 𝐿𝐿 𝑜𝑣𝑒𝑛 𝑑𝑟𝑖𝑒𝑑
𝐿𝐿 𝑛𝑜𝑡 𝑑𝑟𝑖𝑒𝑑<0.75 OL Organic clay K, L, M, N
Organic silt K, L, M, O
Silts and Clays:
Liquid limit 50 or
more
Inorganic: PI plots on or above “A” line CH Fat clay K, L, M
PI plots below “A” line MH Elastic silt K, L, M
Organic: 𝐿𝐿 𝑜𝑣𝑒𝑛 𝑑𝑟𝑖𝑒𝑑
𝐿𝐿 𝑛𝑜𝑡 𝑑𝑟𝑖𝑒𝑑<0.75 OH Organic clay K, L, M, P
Organic silt K, L, M, Q
Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3 -inch (75-mm) sieve.
B If field sample contained cobbles or boulders, or both, add “with
cobbles or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW -GM well-
graded gravel with silt, GW -GC well-graded gravel with clay, GP -GM
poorly graded gravel with silt, GP -GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW -SM well-
graded sand with silt, SW -SC well -graded sand with clay, SP -SM
poorly graded sand with silt, SP -SC poorly graded sand with clay.
E Cu = D 60/D 10 Cc =
F If soil contains ≥ 15% sand, add “with sand” to group name.
G If fines classify as CL -ML, use dual symbol GC -GM, or SC -SM.
H If fines are organic, add “with organic fines” to group name.
I If soil contains ≥ 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL -ML, silty clay.
K If soil contains 15 to 29% plus No. 200, add “with sand” or
“with gravel,” whichever is predominant.
L If soil contains ≥ 30% plus No. 200 predominantly sand, add
“sandy” to group name.
M If soil contains ≥ 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.
N PI ≥ 4 and plots on or above “A” line.
O PI < 4 or plots below “A” line.
P PI plots on or above “A” line.
Q PI plots below “A” line.
6010
2
30
DxD
)(D