HomeMy WebLinkAboutReports - Soils - 02/18/2025
Report Cover Page
Prepared for:
LCS Building Corporation
1725 Sharp Point Drive
Fort Collins, Colorado 80525
Liberty School Addition
Geotechnical Engineering Report
Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
CDN#3493A-032
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
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 ............................................................................. 5
Seismic Site Class ............................................................................................ 5
Corrosivity ...................................................................................................... 6
Geotechnical Overview .................................................................................... 6
Existing, Undocumented Fill ........................................................................ 6
Expansive Soils and Bedrock ....................................................................... 7
Shallow Groundwater ................................................................................ 7
Foundation and Floor System Recommendations ............................................ 7
Earthwork ....................................................................................................... 8
Demolition ............................................................................................... 8
Site Preparation ........................................................................................ 9
Excavation ............................................................................................... 9
Subgrade Preparation ............................................................................... 10
Subgrade Stabilization .............................................................................. 11
Fill Material Types .................................................................................... 12
Fill Placement and Compaction Requirements ............................................... 13
Utility Trench Backfill ............................................................................... 14
Grading and Drainage ............................................................................... 14
Exterior Slab Design and Construction ......................................................... 15
Earthwork Construction Considerations ....................................................... 15
Construction Observation and Testing ......................................................... 16
Shallow Foundations ..................................................................................... 16
Spread Footings – Design Recommendations ................................................ 17
Shallow Foundation Construction Considerations ........................................... 18
Construction Adjacent to Existing Buildings .................................................. 19
Floor Slabs .................................................................................................... 19
Floor Slabs - Design Recommendations ....................................................... 20
Floor Slab Construction Considerations ........................................................ 20
Lateral Earth Pressures ................................................................................. 21
Design Parameters ................................................................................... 21
General Comments ........................................................................................ 23
Figures
GeoModel
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials ii
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
which direct the reader to that section and clicking on the logo will bring you
back to this page. For more interactive features, please view your project online at
client.terracon.com .
Refer to each individual Attachment for a listing of contents.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials i
Report Summary
Topic 1 Overview Statement 2
Project
Description
A geotechnical exploration has been performed for the proposed
Liberty School Addition to be constructed between the two
existing single-story buildings located at 1825 and 1901 Sharp
Point Drive in Fort Collins, Colorado. Five borings were performed
to depths of approximately 10 to 29.4 feet below existing grades.
Geotechnical
Characterization
Subsurface conditions encountered in our exploratory borings
generally consisted of poorly graded sand with gravel and variable
amounts of silt and cobbles overlying claystone bedrock.
Claystone bedrock was encountered at depths of approximately 16
to 21 feet below existing site grades. Existing fill consisting
primarily of sandy lean clay and sandy silt was encountered in
most of the borings at depths of approximately 2 to 7 feet below
existing grades. Groundwater was encountered at depths of
approximately 6 to 13.3 feet below existing grades.
Earthwork
On-site soils typically appear suitable for use as engineered fill
and backfill for the project 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.
Remove existing fill from within the planned building addition
area. Geotechnical engineer to further evaluate areas where
existing fill is present after site stripping.
Shallow
Foundations
We believe the proposed building addition can be constructed on a
shallow, spread footing foundation system provided all existing fill
within the building addition area is removed full depth a nd the
soils are over -excavated to a depth of at least 2 feet below the
bottom of footings and replaced with moisture conditioned,
properly compacted engineered fill. On -site soils are suitable for
use as engineered fill below foundations. Design recommendations
for foundations for the proposed structure and related st ructural
elements are presented in the Shallow Foundations section of
this report.
Allowable bearing pressure = 3,000 psf
Expected settlements: about 1 inch total
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials ii
Topic 1 Overview Statement 2
Floor Slabs
A slab-on-grade Floor Slab can be used for the proposed building
provided all existing fill within the building addition area is
removed full depth and the soils are over -excavated to a depth of
at least 2 feet below the bottom of the proposed floor slab , if the
existing fill thickness does not already extend to this depth below
the floor slab, and replaced with moisture conditioned, properly
compacted engineered fill. On -site soils are suitable as engineered
fill below floor slabs .
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.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 1
Introduction
This report presents the results of our subsurface exploration and Geotechnical
Engineering services performed for the proposed school addition to be located at 1825
and 1901 Sharp Point Drive in Fort Collins, Colorado . The purpose of these services was
to provide information and geotechnical engineering recommendations relative to:
■ Sub surface soil and rock conditions
■ Groundwater conditions
■ Seismic site classification per IBC
■ Site preparation and earthwork
■ Dewatering considerations
■ Foundation design and construction
■ Floor s ystem design and construction
■ Lateral earth pressure s
The geotechnical engineering Scope of Services for this project included the
advancement of 5 test borings, laboratory testing, engineering analysis, and preparation
of this report.
Drawings showing the site and boring locations are shown in the Site Location and
Exploration Plan section of this report . The results of the laboratory testing performed
on soil and bedrock 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:
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 2
Item Description
Information
Provided
The project information described below is based on the
following:
■ Request for Proposal – Liberty School dated October 10,
2024
■ 2024 1002 – Liberty Common Junior High – proposed
geotech boring locations.pdf
■ Email and phone communication with the project design
team
Project
Description
We understand the project will consist of the construction of a
new building addition to connect the two existing single -story
buildings with addresses of 1825 and 1901 Sharp Point Drive.
The two existing buildings along with the new addition will form
a new junior high school for Liberty School. We anticipate
Riverbend Court will be closed permanently to accommodate the
proposal addition.
The new addition will be a single -story structure which will add
about 20,000 square feet of space to the two existing
structures. The addition will include space for a cafeteria and
gymnasium. Building construction for the addition is anticipated
to consist of precast walls with a shallow, spread footing
foundation system and a slab-on-grade floor system.
Finished Floor
Elevation
Finished floor elevation for the addition is planned to be at
4,897 feet AMSL. This elevation is anticipated to be close to the
finished floor of the existing building at 1825 Sharp Point Drive.
The building at 1901 Sharp Point Drive has a slightly lower
finished floor elevation than the existing building at 1825 Sharp
Point Drive.
Maximum Loads
(provided by
project design
team)
■ Columns: up to 60 kips
■ Walls: up to 7 kips per linear foot (klf)
■ Slabs: 100 to 200 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 3 feet
or less will be required to achieve proposed grades. We also
anticipate deeper cuts and fills could be required for utility
construction.
Below-Grade
Structures We understand no below-grade areas are planned for this site.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 3
Item Description
Free-Standing
Retaining Walls
Retaining walls are not expected to be constructed as part of
site development to achieve final grades.
Pavements
The existing pavements will stay in place. LCS Building
Corporation (LCS) does not plan to reconstruct the pavement s
at this time. We have not performed a pavement condition
assessment, and we are unsure of the age of the existing
pavements. Therefore, we cannot provide an opinion on the
quality of the existing pavements.
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 and topographic
maps.
Item Description
Parcel
Information
The site of the new addition is planned on the existing alignment
of Riverbend Court between the two existing buildings with
addresses of 1825 and 1901 Sharp Point Drive in Fort Collins,
Colorado.
Latitude/Longitude (approximate): 40.56237° N, 105.02839° W
See Site Location
Existing
Improvements
The site of the proposed addition is an existing asphalt -paved
roadway with concrete curb and gutter and sidewalks.
Current Ground
Cover The existing roadway is paved with asphalt.
Existing
Topography
Based on publicly available USGS topographic maps, ground
surface elevations at the location of the proposed addition are
relatively level along the existing street. Ground surface
elevations on the site with an address of 1901 Sharp Point Drive
site are somewhat lower than those of the site with an address
of 1825 Sharp Point Drive.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
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 of
our geotechnical calculations and evaluation of the site. Conditions observed at each
exploration point are indicated on the individual logs. The individual l ogs 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 .
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 clay and sand soils to have low expansive potential or to be non -
expansive. The claystone bedrock is anticipated to have low to moderate expansive
p otential.
Model
Layer Layer Name General Description
Existing
Pavement
Section
About 4 to 8 inches of asphalt. About 20 inches of
aggregate base course was e ncountered below the
asphalt in Boring No. B-1 only.
1 Existing Fill
Existing fill consisting primarily of sandy lean clay and
sandy silt; dark brown . Encountered in all borings
except Boring No. B-1.
2 Sand
Poorly graded sand with gravel with var iable amounts
of silt and cobbles; loose to very dense, brown, gray,
pink, red, tan
3 Bedrock Claystone bedrock; very hard, light gray to dark gray
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 5
Groundwater Conditions
The boreholes were observed while drilling and shortly after completion 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:
Boring
Number
Depth to
Groundwater While
Drilling, ft.
Depth to
Groundwater After
Drilling, ft.
Elevation of
Groundwater After
Drilling, ft.1
B-1 7 9 +/- 4,888
B-2 6 7 +/- 4,890
B-3 13 7.7 +/- 4,890
B-4 Not encountered Backfilled after drilling
B-5 Not encountered Backfilled after drilling
1. Elevation of groundwater is based on the ground surface elevations, interpolated from a
publicly available USGS topographic map (https://apps.nationalmap.gov/viewer/).
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 borings were performed. Therefore, groundwater levels during
con struction or at other times in the life of the structure may be higher or lower than the
levels indicated on the boring logs. The possibility of groundwater level fluctuations
should be considered when developing the design and construction plans for the p roject.
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 and bedrock
properties observed at the site as described on the exploration logs and laboratory test
results, our professional opinion is a Seismic Site Classification of C be considered for
the project. Subsurface explorations at this site were extended to a maximum depth of
29.4 feet. The site properties below the boring depth to 100 feet were estimated based
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 6
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 below
the current boring depth.
Corrosivity
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 can be specified for all project concrete on and below grade .
Foundation concrete can be designed for low sulfate exposure in accordance with th e
provisions of the ACI 318 .
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 to modera tely expansive soils and bedrock. We have identified several
geotechnical conditions that could impact design, construction and performance of the
proposed structure and other site improvements. These included existing, undocumented
fill , expansive soils and bedrock, and shallow groundwater . 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 7 feet in all borings
drilled at the site except Boring No. B-1. 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. Therefore, the fill is
considered undocumented. Undocumented fill can present a greater than normal risk of
post -construction movement of site improvements supported on or above these
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 7
materials. A low risk alternative is complete removal of existing fill below foundations,
slabs, and other site improvements and replacement with newly compacted engineered
fill .
Expansive Soils and Bedrock
Expansive soils and bedrock are present on this site; however, our experience in the
area and laboratory swell test results indicate the site soils are generally low swelling.
The claystone bedrock is generally considered low to moderate swelling; however, the
bedrock was encountered at depths not likely to impact new construction. 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 t he
addition 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 soils and bedrock. Eliminatin g 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.
Shallow Groundwater
As previously stated, groundwater was measured at depths ranging from about 6 to 13.3
feet below existing site grades. We understand a building addition is planned at this site.
Terracon recommends maintaining a separation of at least 3 feet between the bottom of
proposed below -grade foundations and measured groundwater levels. It is also possible
and likely that groundwater levels below this site may rise as water levels in the Cache
la Poudre River and the surrounding ponds rise. Final site grading shoul d be planned and
designed to avoid cuts where shallow groundwater is known to exist, and also in areas
where such grading would create shallow groundwater conditions. If deeper cuts are
unavoidable, temporary construction dewatering and/or installation of a subsurface
drainage system may be needed.
Foundation and Floor System Recommendations
We believe the proposed building addition can be constructed on a shallow, spread
footing foundation system provided all existing fill within the building addition area is
removed full depth and the soils are over-excavated to a depth of at least 2 feet below
the bottom of footings and replaced with moisture conditioned, properly compacted
engineered fill. On -site soils are suitable for use as engineered fill below foundations.
Design recommendations for foundations for the proposed structure and related
structural elements are presented in the Shallow Foundations section of this report.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 8
We believe a concrete slab -on -grade floor system can be used for the proposed building
addition provided all existing fill within the building addition area is removed full depth
and the soils are over-excavated to a depth of at least 2 feet below the proposed floor slab, if
the existing fill thickness does not already extend to this depth below the floor slab, and
replaced with moisture conditioned, properly compacted engineered fill. On-site soils are
suitable as over-excavation backfill below floor slabs. Design recommendations for floor
systems for the proposed structure and related structural elements are presented in the
Floor Slabs 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.
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
site in the state considered in our geotechnical engineering evaluation for foundations
and floor slabs .
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.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 9
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 (if any). As previously stated, we also recommend complete
removal of existing, undocumented fill within proposed building areas. Existing fill was
encountered in our borings extending to depths of about 2 to 7 feet below existing site
grades. Stripped organic materials should be wasted from the site or used to re-vegetate
landscaped areas or exposed slopes 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 the proposed addition , 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 root ball and all
associated dry and desiccated soils should be removed. The soil materia ls 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 (Horizontal:Vertical), 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. T his 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.
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.
Excavation
We anticipate excavations for the proposed construction can be accomplished with
conventional earthmoving equipment. Excavations into the on-site soils could encounter
weak/loose 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 excavation extending below the bottom of foundation elevation should extend
laterally beyond all edges of the foundations at least 8 inches per foot of excavation
depth below the foundation base elevation. The excavation should be backfilled to the
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 10
foundation base elevation in accordance with the recommendations presented in this
report.
Any existing building foundations exposed during the excavation of the existing fill or for
the new foundation excavations should be examined and evaluated by Terracon to
determine the need for any shoring or underpinning. Excavations should not extend int o
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):1(V) (Horizontal:Vertical ) slope from the bottom edge of the existing found ation.
Excavations within the influence zone of existing foundations can result in loss of
support and can create settlement or failure of the existing foundations. While 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 preparati on, complete removal of existin g fill within the building addit ion area,
and completion of any required undercuts or the recommended over -excavation s, the
top 10 inches of the exposed ground surface should be scarified, moisture conditioned,
and compacted to at least 95 percent of the maximum dry unit weight as determined by
ASTM D698 before any new fill , foundations, slabs 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 -
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 11
loaded tandem-axle dump truck. Proof rolling should be performed 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.
After the bottom of the excavation has been prepared as recommended above ,
engineered fill can be placed to bring the building pad to the desired grade. Engineered
fill should be placed in accordance with the recommendations 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 subgra de stability. Typical undercut depths would be
expected to range from about 6 to 24 inches below finished subgrade elevation.
Crushed stone and/or concrete can be tracked or “crowded” into the unstable
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 12
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.
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 suitable 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 compaction .
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 froz en subgrade.
Gradation Percent Finer by Weight (ASTM C136)
3 ” 100
1 ” 70-100
No. 4 Sieve 30-100
No. 200 Sieve 15-50
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 13
Soil Properties Values
Liquid Limit 35 (max.)
Plasticity Index 15 (max.)
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 or 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.
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.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 14
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(H):1(V) projection from existing foundations without engineering review of shoring
requirements a nd 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.
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 areas.
Grading and Drainage
All grades must provide effective drainage away from the existing buildings and
proposed addition during and after construction and should be maintained throughout
the life of the structure s. Water retained next to the building s 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 ont o 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 s for at least 10 feet beyond the perimeter of the building s. 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 document effective drainage has been achieved. Grades around the structure s
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 15
should also be periodically inspected and adjusted, as necessary, as part of the
structures’ 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 -
constru ction movement of flatwork, particularly if such movement would be critical.
Where paving or flatwork abuts the structures, care should be taken that joints are
properly sealed and maintained to prevent the infiltration of surface water.
Planters located adjacent to structures (if any) 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 s.
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
10 inches, moisture conditioned, and compacted prior to placement/construction of new
engineered fill, aggregate base course, o r 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. 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 mater ials should be scarified, moisture 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
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 16
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 g round
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
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 recommendations and requirements
noted in Geotechnical Overview and Earthwork, the following design parameters are
applicable for shallow foundations for the proposed addition .
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 17
Spread Footings – Design Recommendations
Item Description
Maximum Net Allowable Bearing
Pressure 1 3,000 psf
Required Bearing Stratum 2
At least 2 feet of moisture conditioned ,
properly compacted engineered fill and all
existing fill has been completely removed
below foundations
Minimum Foundation Dimensions Columns: 30 inches
Continuous: 18 inches
Lateral Earth Pressure Coefficients 3
On-site granular soils and engineered fill:
Active, Ka = 0.33
Passive, Kp = 3.00
At-rest, Ko = 0.50
Sliding Resistance On-site granular soils and engineered fill:
μ = 0.46 (ultimate)
Moist Soil Unit Weight γ = 120 pcf
Minimum Embedment Below
Finished Grade 4
Exterior footings in unheated areas: 30
inches
Interior footings and column pads in heated
areas: 12 inches
Estimated Total Movement 5 About 1 inch
Estimated Differential Movement 5 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 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. 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.
5. The estimated movements presented above assume the maximum footing dimension is
8 feet for column footings and maximum footing width is 3½ feet for continuous
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 18
Item Description
footings. Larger foundation footprints will likely require reduced net allowable soil
bearing pressures to reduce risk for potential settlement.
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
Drain age section of the Earthwork section of this report will nullify the movement
estimates provided above.
Any excavation extending below the bottom of foundation elevation should extend
laterally beyond all edges of the foundations at least 8 inches per foot of excavation
depth below the foundation base elevation. The excavation should be backfilled to the
foundation base elevation i n accordance with the recommendations presented in this
report.
Shallow Foundation Construction Considerations
F oundation 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/reconditi oned before foundation concrete is placed.
Spread footing construction should only be considered if the estimated foundation
movement can be tolerated. Subgrade soils beneath footings should be moisture
conditioned and compacted as described in Earthwork. The moisture content and
compaction of subgrade soils should be maintained until foundation construction.
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 the Geotechnical Engineer to assess the subgrade and provide suitable alternatives
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 19
for stabilization. Typical methods of stabilization/improvement are presented in the
Subgrade Stabilization section of Earthwork .
Construction Adjacent to Existing Building s
Differential settlement between the additions and the existing building s is expected to
approach the magnitude of the total settlement of the addition. Expansion joints should
be provided between the existing building s and the proposed addition to accommodate
differential movements between the two structures. Underground piping between the
addition and existing structures should be designed with flexible couplings and utility
knockouts in foundation walls should be oversized so minor deflections in alignmen t do
not result in breakage or distress. Care should be taken during excavation adjacent to
existing foundations to avoid disturbing existing foundation bearing soils.
New footings should bear at or near the bearing elevation of immediately adjacent
existing foundations. Depending upon their locations and current loads on the existing
footings, footings for the new addition could cause settlement of adjacent walls. To
reduce this concern and risk, clear distances at least equal to the new footing widths
should be maintained between the addition’s footings and footings supporting the
existing building s.
Additional loads (if any) from the new addition placed on the existing foundations could
cause other building settlements to occur. The structural capacity of existing foundations
should be evaluated by a licensed structural engineer, where increases in loading are
planned.
Floor Slabs
A slab-on-grade floor system can be used for the proposed building addition provided all
existing fill within the building addition area is removed full depth and the soils are over -
excavated to a depth of at least 2 feet below the bottom of the proposed floor slab , if
the existing fill thickness does not already extend to this depth below the floor slab, and
replaced with moisture conditioned, properly compacted engineered fill. On -site soils are
suitable as engineered fill below floor slabs.
If the estimated movement cannot be tolerated, a structurally -supported floor system,
supported independent of the subgrade materials, is recommended.
Subgrade soils beneath interior and exterior slabs and at the base of the recommended
over-excavation should be scarified to a depth of at least 10 inches, moisture
conditioned, and compacted. The moisture content and compaction of subgrade soils
should be maintained until slab construction.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 20
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 over -excavated and 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.
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 refer 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
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.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 21
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.
Lateral Earth Pressures
Design Parameters
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).
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 22
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) Granular - 0.33 (0.33)S (40)H (85)H
At-Rest (Ko) Granular -0.50 (0.50)S (60)H (95)H
Passive (Kp) Granular -3.00 --- --- ---
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 120 pcf.
3. Uniform surcharge, where S is surcharge pressure.
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 and 60 degrees from vertical
for the active and passive cases, respectively.
To control hydrostatic pressure behind walls, we typically recommend a drain be
installed at the base of walls with a collection pipe leading to a reliable discharge.
However, if no below -grade drainage system is planned for the proposed building
addition, the below-grade walls of the new building addition should be designed to resist
combined hydrostatic and lateral earth pressures. The hydrostatic and lateral earth
pressures should be calculated for granular backfill using the submerged earth pressures
provided in the above table. These pressures do not include the influence of surcharge,
equipment, or floor loading, which should be added. Heavy equipment should not
operate within a distance closer than the exposed height of retaining walls to prevent
lateral pressures more than those provided.
Foundations , floor slabs or other loads bearing on backfill behind walls may have a
significant influence on the lateral earth pressure. Placing fo undations within wall backfill
and in the zone of active soil influence on the wall should be avoided unless structural
analyses indicate 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
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 23
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 su ch wall systems upon request.
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
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 a nd is not
intended for third parties. Any use or reliance of the provided information by third
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 support 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
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials 24
water flow during 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 no t be considered valid unless we review the changes and either
verify or modify our conclusions in writing.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
Figures
Contents:
GeoModel
CDN#3493A-032
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
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
B-5
Legend
This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.
GeoModel
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
Liberty School Addition
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
Poorly-graded Sand
with Gravel
Sandy Lean Clay Poorly-graded Sand
with Silt and Gravel
Sandy Silt
Model Layer Layer Name General Description
1 Existing fill consisting primarily of sandy lean clay and
sandy silt; dark brown
3 Claystone bedrock; very hard, light gray to dark gray
2
Poorly graded sand with gravel with variable amounts of silt
and cobbles; loose to very dense, brown, gray, pink, red,
tan
Existing Fill
Bedrock
Sand
2
3
9
7
16
29.4
1
2
3
7
6
4
21
29.3
1
2
3
7.7
13
4
20
29.4
1
2
7
10
1
2
2
10
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
Attachments
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
Exploration and Testing Procedures
Field Exploration
Number of Borings Approximate Boring
Depth (feet) Location
3
(Boring Nos. B -1 through
B-3)
29.3 to 29.4
Near and within the
proposed building addition
area
2
(Boring Nos. B-4 and B-5) 10 Parking areas
Boring Layout and Elevations: 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
estimated using a publicly available USGS topographic map . If surface elevations and 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 and hollow -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 automatic 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 resistan ce 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
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
on the field boring logs. These field logs included visual classifications of the 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 Geotec hnical 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 cementitious flowable backfill after completion of drilling.
Pavements were patched with hot -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.
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
■ Unconfined Compressi ve Strength
■ Water-soluble Sulfates
The laboratory testing program 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. Rock classification
was conducted using locally accepted practices for engineering purposes.
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 .
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
Site Location and Exploration Plans
Contents:
Site Location Plan
Exploration Plan
Note: All attachments are one page unless noted above.
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
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
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
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
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
Exploration and Laboratory Results
Contents:
Boring Logs (B-1 through B-5)
Atterberg Limits
Grain Size Distribution
Consolidation/Swell (3 pages)
Unconfined Compressive Strength
Water-Soluble Sulfates
Note: All attachments are one page unless noted above.
CDN#3493A-032
4896.7
4895
4881
4867.6
ASPHALT, about 4 inches thick
AGGREGATE BASE COURSE, about 20 inches
thick
POORLY GRADED SAND WITH GRAVEL, with
cobbles, brown with gray, pink and red,
medium dense to very dense
CLAYSTONE BEDROCK, light gray to dark
gray, very hard
Boring Terminated at 29.4 Feet
Boring Log No. B-1
De
p
t
h
(
F
t
.
)
5
10
15
20
25
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
Facilities | Environmental |Geotechnical | Materials
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
1.1
0.9
6.7
13.0
9.6
18.1
14.8
22.4
127
112
0.3
2.0
16.0
29.4
12-23
35/12"
15-23-31
N=54
50/6"
9-6-10
N=16
11-11
22/12"
50/5"
50/4"
50/5"
Abandonment Method
Borings were backfilled with cementitous flowable fill and
patched with asphalt
Advancement Method
4.25-inch inside diameter, continuous-flight, hollow-stem
augers
Liberty School Addition
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
Water Level Observations
7 feet while drilling
9 feet at completion of drilling
Fort Collins, CO
1901 Sharp Point Dr Ste C
Notes
See Exploration and Testing Procedures for a description of field and laboratory
procedures used and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were interpolated from a publicly available USGS
topographic map
Drill Rig
CME 55
Boring Started
01-30-2025
Boring Completed
01-30-2025
Logged by
PA
Hammer Type
Automatic, Hammer
Efficiency = 68%
Driller
Terracon Consultants
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Un
c
o
n
f
i
n
e
d
Co
m
p
r
e
s
s
i
v
e
St
r
e
n
g
t
h
(
p
s
f
)
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Approximate Elevation: 4897 (Ft.)
LL-PL-PI
Atterberg
LimitsSeeExploration Plan
Latitude: 40.5624° Longitude: -105.0281°
Location:
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
2
3
CDN#3493A-032
4896.3
4893
4876
4867.7
ASPHALT, about 8 inches thick
FILL - SANDY LEAN CLAY (CL), dark brown
POORLY GRADED SAND WITH GRAVEL, with
cobbles, brown with gray, pink and red,
medium dense to very dense
loose at about 14 feet
CLAYSTONE BEDROCK, light gray to dark
gray, very hard
Boring Terminated at 29.3 Feet
Boring Log No. B-2
De
p
t
h
(
F
t
.
)
5
10
15
20
25
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
Facilities | Environmental |Geotechnical | Materials
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
66.519.2
2.1
2.0
5.8
14.1
18.6
18.1
20.7
108
97
107
100
41-16-25
0.7
4.0
21.0
29.3
+0.3/2005-7
12/12"
3-8-11
N=19
34-46
80/12"
18-24-25
N=49
4-11
15/12"
44-50/4"
50/5"
50/3"
Abandonment Method
Borings were backfilled with cementitous flowable fill and
patched with asphalt
Advancement Method
4.25-inch inside diameter, continuous-flight, hollow-stem
augers
Liberty School Addition
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
Water Level Observations
6 feet while drilling
7 feet at completion of drilling
Fort Collins, CO
1901 Sharp Point Dr Ste C
Notes
See Exploration and Testing Procedures for a description of field and laboratory
procedures used and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were interpolated from a publicly available USGS
topographic map
Drill Rig
CME 75
Boring Started
01-21-2025
Boring Completed
01-21-2025
Logged by
PA
Hammer Type
Automatic, Hammer
Efficiency = 95%
Driller
Terracon Consultants
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Un
c
o
n
f
i
n
e
d
Co
m
p
r
e
s
s
i
v
e
St
r
e
n
g
t
h
(
p
s
f
)
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Approximate Elevation: 4897 (Ft.)
LL-PL-PI
Atterberg
LimitsSeeExploration Plan
Latitude: 40.5624° Longitude: -105.0283°
Location:
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
1
2
3
CDN#3493A-032
4897.3
4894
4878
4868.6
ASPHALT, about 8 inches thick
FILL - SANDY LEAN CLAY, dark brown
POORLY GRADED SAND WITH SILT AND
GRAVEL (SP-SM), with cobbles, tan to brown
with gray, red and pink, dense to very dense
CLAYSTONE BEDROCK,
dark gray, very hard
Boring Terminated at 29.4 Feet
Boring Log No. B-3
De
p
t
h
(
F
t
.
)
5
10
15
20
25
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
Facilities | Environmental |Geotechnical | Materials
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
8.4
974010
21.1
1.8
0.9
4.4
5.6
19.4
17.7
18.6
100
132
110
NP
51-20-31
0.7
4.0
20.0
29.4
+0.5/2006-10
16/12"
16-20-25
N=45
29-34
63/12"
18-26-25
N=51
11-50/5"
13-14-24
N=38
50/5"
50/5"
Abandonment Method
Borings were backfilled with cementitous flowable fill and
patched with asphalt
Advancement Method
4.25-inch inside diameter, continuous-flight, hollow-stem
augers
Liberty School Addition
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
Water Level Observations
13 feet while drilling
7.7 feet at completion of drilling
Fort Collins, CO
1901 Sharp Point Dr Ste C
Notes
See Exploration and Testing Procedures for a description of field and laboratory
procedures used and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were interpolated from a publicly available USGS
topographic map
Drill Rig
CME 75
Boring Started
01-21-2025
Boring Completed
01-21-2025
Logged by
PA
Hammer Type
Automatic, Hammer
Efficiency = 95%
Driller
Terracon Consultants
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Un
c
o
n
f
i
n
e
d
Co
m
p
r
e
s
s
i
v
e
St
r
e
n
g
t
h
(
p
s
f
)
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Approximate Elevation: 4898 (Ft.)
LL-PL-PI
Atterberg
LimitsSeeExploration Plan
Latitude: 40.5623° Longitude: -105.0286°
Location:
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
1
2
3
CDN#3493A-032
4895.7
4889
4886
ASPHALT, about 4 inches thick
FILL - SANDY SILT (ML), dark brown
POORLY GRADED SAND WITH GRAVEL,
brown with gray, pink and red, medium dense
to dense
Boring Terminated at 10 Feet
Boring Log No. B-4
De
p
t
h
(
F
t
.
)
5
10
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
Facilities | Environmental |Geotechnical | Materials
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
51.8
20.4
20.8
6.5
13.5
107
103 NP
0.3
7.0
10.0
<-0.1/500
6-8
14/12"
3-4
7/12"
18-20-21
N=41
17-27
44/12"
Abandonment Method
Borings were backfilled with cementitous flowable fill and
patched with asphalt
Advancement Method
4-inch outside diameter, continuous-flight, solid-stem
augers
Liberty School Addition
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
No free water observed
Water Level Observations
Fort Collins, CO
1901 Sharp Point Dr Ste C
Notes
See Exploration and Testing Procedures for a description of field and laboratory
procedures used and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were interpolated from a publicly available USGS
topographic map
Drill Rig
CME 75
Boring Started
01-21-2025
Boring Completed
01-21-2025
Logged by
PA
Hammer Type
Automatic, Hammer
Efficiency = 95%
Driller
Terracon Consultants
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Un
c
o
n
f
i
n
e
d
Co
m
p
r
e
s
s
i
v
e
St
r
e
n
g
t
h
(
p
s
f
)
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Approximate Elevation: 4896 (Ft.)
LL-PL-PI
Atterberg
LimitsSeeExploration Plan
Latitude: 40.5625° Longitude: -105.0290°
Location:
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
1
2
CDN#3493A-032
4894.7
4893
4885
ASPHALT, about 4 inches thick
FILL - SANDY LEAN CLAY, dark brown
POORLY GRADED SAND WITH GRAVEL, tan to
brown with gray, red and pink, medium dense
to very dense
Boring Terminated at 10 Feet
Boring Log No. B-5
De
p
t
h
(
F
t
.
)
5
10
Wa
t
e
r
L
e
v
e
l
Ob
s
e
r
v
a
t
i
o
n
s
Facilities | Environmental |Geotechnical | Materials
Gr
a
p
h
i
c
L
o
g
Mo
d
e
l
L
a
y
e
r
1.3
1.3
2.8
6.3
123
118
0.3
2.0
10.0
6-27
33/12"
17-32
49/12"
8-50/6"
32-47
79/12"
Abandonment Method
Borings were backfilled with cementitous flowable fill and
patched with asphalt
Advancement Method
4-inch outside diameter, continuous-flight, solid-stem
augers
Liberty School Addition
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
No free water observed
Water Level Observations
Fort Collins, CO
1901 Sharp Point Dr Ste C
Notes
See Exploration and Testing Procedures for a description of field and laboratory
procedures used and additional data (If any).
See Supporting Information for explanation of symbols and abbreviations.
Elevation Reference: Elevations were interpolated from a publicly available USGS
topographic map
Drill Rig
CME 75
Boring Started
01-21-2025
Boring Completed
01-21-2025
Logged by
PA
Hammer Type
Automatic, Hammer
Efficiency = 95%
Driller
Terracon Consultants
Sa
m
p
l
e
T
y
p
e
Pe
r
c
e
n
t
Fi
n
e
s
Un
c
o
n
f
i
n
e
d
Co
m
p
r
e
s
s
i
v
e
St
r
e
n
g
t
h
(
p
s
f
)
Wa
t
e
r
Co
n
t
e
n
t
(
%
)
Dr
y
U
n
i
t
We
i
g
h
t
(
p
c
f
)
Approximate Elevation: 4895 (Ft.)
LL-PL-PI
Atterberg
LimitsSeeExploration Plan
Latitude: 40.5618° Longitude: -105.0282°
Location:
Depth (Ft.)
Sw
e
l
l
-
C
o
n
s
o
l
/
Lo
a
d
(
%
/
p
s
f
)
Fi
e
l
d
T
e
s
t
Re
s
u
l
t
s
1
2
CDN#3493A-032
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
25
NP
31
NP
66.5
8.4
97.0
51.8
CL
SP-SM
CH
ML
16
NP
20
NP
25
NP
31
NP
66.5
8.4
97.0
51.8
CL
SP-SM
CH
ML
16
NP
20
NP
41
NP
51
NP
SANDY LEAN CLAY
POORLY GRADED SAND with SILT and GRAVEL
K
SANDY SILT
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
4 - 5.5
24 - 24.4
4 - 5
B-2
B-3
B-3
B-4
Boring ID Depth (Ft)
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245058
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Liberty School Addition
CDN#3493A-032
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 (14)
A-1-a (0)
A-7-6 (33)
A-4 (0)
CL
SP-SM
CH
ML
SANDY LEAN CLAY
POORLY GRADED SAND with SILT and
GRAVEL
K
SANDY SILT
Facilities | Environmental |Geotechnical | Materials
41
NP
51
NP
0.66
25
NP
31
NP
16
NP
20
NP
%CobblesD60
5.952
0.12
D100
40.08
%Clay%Sand%Gravel
0.2
44.2
0.0
2.3
33.2
47.5
3.0
45.9
66.5
8.4
97.0
51.8
LL PL PI Cc Cu
0.0
0.0
0.0
0.0
D10
0.149
D30
0.763
9.5
37.5
4.75
12.5
%Fines %Silt
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245058
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Liberty School Addition
Boring ID
2 - 3
4 - 5.5
24 - 24.4
4 - 5
B-2
B-3
B-3
B-4
2 - 3
4 - 5.5
24 - 24.4
4 - 5
Depth (Ft)Boring ID
B-2
B-3
B-3
B-4
Depth (Ft)
CDN#3493A-032
-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 0.3 percent swell upon wetting under an applied pressure of 200 psf.
19.2108
(pcf) WC (%)Description USCS
CLSANDY LEAN CLAY (CL)
Boring ID Depth (Ft)
2 - 3B-2
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245058
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Liberty School Addition
CDN#3493A-032
-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 0.5 percent swell upon wetting under an applied pressure of 200 psf.
21.189
(pcf) WC (%)Description USCS
SANDY LEAN CLAY
Boring ID Depth (Ft)
2 - 3B-3
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245058
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Liberty School Addition
CDN#3493A-032
-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 less than 0.1 percent compression upon wetting under an applied pressure of 500 psf.
20.8105
(pcf) WC (%)Description USCS
MLSANDY SILT (ML)
Boring ID Depth (Ft)
4 - 5B-4
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245058
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Liberty School Addition
CDN#3493A-032
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Facilities | Environmental |Geotechnical | Materials
Depth (Ft)
24 - 24.4
ASTM D2166
Unconfined Compression Test
Specimen Test DataSpecimen Failure Mode
Sample type LL PL PI
Strain Rate (in/min):
Boring ID Description
CLAYSTONE BEDROCK
Unconfined Compressive Strength (psf):
B-3 97.0
Fines (%)
1901 Sharp Point Dr Ste C
Fort Collins, COTerracon Project No. 20245058
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Liberty School Addition
0.08
CDN#3493A-032
Client
B-1 B-5
2'-5'0.3'-5'
5 129 5 140 5
5
Laboratory Manager
LCS Building Corporation Liberty School Addition
Fort Collins, CO
Sample Location
Sample Depth (ft.)
The tests were performed in general accordance with applicable ASTM and AWWA test methods. This report is exclusively for the use of the client
indicated above and shall not be reproduced except in full without the written consent of our company. 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 or identical materials.
2/7/2025Date Received:
Results from Corrosion Testing
Water Soluble Sulfate, ASTM C1580, (mg/kg)
20245058
Project
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
Facilities | Environmental | Geotechnical | Materials
Supporting Information
Contents:
General Notes
Unified Soil Classification System
Note: All attachments are one page unless noted above.
CDN#3493A-032
Auger
Cuttings
Modified
California
Ring
Sampler
Standard
Penetration
Test
Facilities | Environmental |Geotechnical | Materials
Unconfined
Compressive
Strength
Qu (tsf)
less than 0.25
0.25 to 0.50
0.50 to 1.00
1.00 to 2.00
2.00 to 4.00
> 4.00
Liberty School Addition
1825 and 1901 Sharp Point Drive | Fort Collins, CO
Terracon Project No. 20245058
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
> 30
15 - 30
8 - 15
4 - 8
2 - 4
0 - 1
Very Stiff
Consistency of Fine-Grained Soils Bedrock
(More than 50% retained on No. 200 sieve.)
Density determined by Standard Penetration
Resistance
Relative Density of Coarse-Grained Soils
< 3
Consistency
Stiff
Medium Stiff
Soft
Very Soft
(50% or more passing the No. 200 sieve.)
Consistency determined by laboratory shear strength testing, field
visual-manual procedures or standard penetration resistance
Strength Terms
6- 10
11 - 18
19 - 36
> 36
Standard
Penetration
or N-Value
(Blows/Ft.)
Ring
Sampler
(Blows/Ft.)
Relative Density
Very Loose
Loose
Standard
Penetration
or N-Value
(Blows/Ft.)
> 50
30 - 50
10 - 29
4 - 9
Ring
Sampler
(Blows/Ft.)
Hard
Medium Dense
Dense
Very Dense
15 - 46
0 - 3
3 - 5
Consistency
Standard
Penetration or
N-Value
(Blows/Ft.)
< 20
20 - 29
30 - 49
50 - 79
> 96
0 - 5
6 - 14
> 80
Firm
_
47 - 79
Medium Hard
Hard
Very Hard
Ring
Sampler
(Blows/Ft.)
< 24
24 - 35
36 - 60
61 - 96
>79
CDN#3493A-032
Geotechnical Engineering Report
Liberty School Addition | Fort Collins, Colorado
February 18, 2025 | Terracon Project No. P20245058
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
CDN#3493A-032