HomeMy WebLinkAboutTHE ELLIE AT OLD TOWN NORTH - FDP240015 - SUBMITTAL DOCUMENTS - ROUND 1 - Geotechnical (Soils) Report
Geotechnical Evalua tion
The Ellie at Old Town North
East Suniga Road & Blondel Street
Fort Collins, Colorado
Ellie OTN, LLC
c/o Van Horn Development Management
14143 Denver West Parkway #100 | Golden, Colorado 80401
May 23, 2024 | Project No. 502957001
Geophysics | Engineering Geology | Laboratory Testing | Industrial Hygiene | Occupational Safety | Air Quality | GIS
9707 East Easter Lane | Centennial, Colorado 80112 | p. 303.629.6000 | www.ninyoandmoore.com
May 23, 2024
Project No. 502957001
Mr. Ryan Van Horn
Ellie OTN, LLC
c/o Van Horn Development Management
14143 Denver West Parkway #100
Golden, Colorado 80401
Subject: Geotechnical Evaluation
The Ellie at Old Town North
East Suniga Road & Blondel Street
Fort Collins, Colorado
Dear Mr. Van Horn:
In accordance with your request and authorization, we have performed a geotechnical evaluation for
the proposed The Ellie at Old Town North in Fort Collins, Colorado. This report presents our
geotechnical findings, conclusions, and recommendations regarding the proposed project.
We appreciate the opportunity to be of service on this project.
Sincerely,
NINYO & MOORE
Nathaniel Boehler, EI
Project Engineer
Brian F. Gisi, PE
Principal Engineer
NJB/BFG/mht
05/23/2024
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CONTENTS
1.INTRODUCTION 1
2.SCOPE OF SERVICES 1
3.SITE DESCRIPTION AND BACKGROUND REVIEW 1
4.PROPOSED CONSTRUCTION 2
5.FIELD EXPLORATION AND LABORATORY TESTING 3
6.GEOLOGIC AND SUBSURFACE CONDITIONS 4
6.1.Geologic Setting 4
6.2.Subsurface Conditions 4
6.2.1. Fill Materials 4
6.2.2. Alluvium 5
6.2.3. Pierre Shale Formation 5
6.3.Groundwater 6
7.GEOLOGIC AND OTHER HAZARDS 6
7.1. Seismicity 6
7.2.Expansive Soils 7
7.3.Compressible and Collapsible Soils 8
8.CONCLUSIONS 9
9.RECOMMENDATIONS 11
9.1. Earthwork 11
9.1.1. Excavations 11
9.1.2. Temporary Excavation Slopes 12
9.1.3. Site and Remedial Grading 12
9.1.4. Re-Use of Site Soils 14
9.1.5. Fill Placement and Compaction 14
9.1.6. Imported Soil 15
9.1.7. Controlled Low Strength Material 15
9.1.8. Utility Installation 16
9.2.Spread Footing Foundations 17
9.3. Post -T ensioned Slab -On-Grade Foundations 18
9.4. Slab-On-Grade Floors 20
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9.5.Lateral Earth Pressures 21
9.6.Pavement Design 22
9.6.1. Pavement Subgrade Characterization 23
9.6.2. Traffic Loading 23
9.6.3. Pavement Thickness 23
9.6.4. Pavement Materials 24
9.6.5. Pavement Subgrade Preparation 24
9.6.6. Pavement Maintenance 25
9.7.Concrete Flatwork 25
9.8.Corrosion Considerations 26
9.8.1. Concrete 26
9.8.2. Buried Metal Pipes 27
9.9. Scaling 27
9.10.Frost Heave 28
9.11.Construction in Cold or Wet Weather 28
9.12.Site Drainage 29
9.13.Construction Observation and T esting 30
9.14.Plan Review 30
9.15. Pre-Construction Meeting 31
10.LIMITATIONS 31
11.REFERENCES 33
TABLES
1 – Boring Coordinates 3
2 – Top of Bedrock Depth and Elevation 5
3 – Approximate Groundwater Elevation 6
4 – 2021 International Building Code Seismic Design Criteria 7
5 – Pavement Performance Risk Categories 8
6 – Slab Performance Risk Categories 8
7 – PTI Parameters 19
8 – PTI Post Equilibrium Parameters 19
9 – PTI Post Construction Parameters 19
10 – Recommended Lateral Earth Pressures 22
11 – Corrosion Potential to Steel 27
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FIGURES
1 – Site Location
2 – Boring Locations
APPENDICES
A – Boring Logs
B – Laboratory Testing
C – Site Photographs and Descriptions
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 1
1.INTRODUCTION
In accordance with your request and authorization, and our proposal dated August 22, 2023, we
have performed a geotechnical evaluation for The Ellie at Old Town North project located southwest
from the intersection of East Suniga Road and Blondel Street in Fort Collins, Colorado. The
approximate location of the site is depicted on Figure 1.
The purpose of our study was to evaluate the subsurface conditions and to provide design and
construction recommendations regarding geotechnical aspects of the proposed project. This report
presents the findings of our subsurface exploration, results of our laboratory testing, conclusions
regarding the subsurface conditions at the site, and geotechnical recommendations for the design
and construction of this project.
2.SCOPE OF SERVICES
The scope of our services for the project generally included:
•Review of referenced background information, including aerial photographs, published geologic
and soil maps, in-house geotechnical data, and available topographical information pertaining to
the project site and vicinity.
•Site reconnaissance to document site conditions and establish boring locations, and arrange for
the mark-out of publicly owned underground utilities through Utility Notification Center of
Colorado of the boring locations prior to drilling. Site photographs and descriptions are presented
in Appendix C.
•Drilling, logging, and sampling of four small-diameter exploratory borings in general accordance
with ASTM D-1586 within the project site. Borings were advanced to depths ranging from
approximately 19.3 to 24 feet below ground surface (bgs). The boring logs are presented in
Appendix A. Approximate boring locations are presented on Figure 2.
•Performing laboratory tests on selected samples obtained from the borings to evaluate
engineering properties including in-situ moisture content and dry density, Atterberg limits, percent
materials passing the No. 200 sieve and grain size analysis including hydrometer,
swell/consolidation potential, direct shear, and soil corrosivity characteristics (including pH,
resistivity, water soluble sulfates and chlorides). The results of the laboratory testing are
presented on the boring logs and in Appendix B.
•Compilation and analysis of the data obtained.
•Preparation of this report presenting our findings, conclusions, and geotechnical
recommendations regarding design and construction of the project.
3.SITE DESCRIPTION AND BACKGROUND REVIEW
The project site is located southwest of the intersection of East Suniga Road and Blondel Street in
Fort Collins, Colorado (site). The property is bounded by East Suniga Road to the north, by Blondel
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Street to the east, and by an alley and multifamily developments to the south and west. The
approximate location of the site is depicted on Figure 1. Site photographs and descriptions are
presented in Appendix C.
An initial site visit was performed on April 18, 2024, in order to assess the current site conditions and
mark our boring locations. Based on our observations, the site had experienced some extent of
grading operations in the past due to adjacent developments and improvements. Publicly available
historical aerial photography revealed that the multifamily development to the south of the project
site begun around 2006. Publicly available photographs also indicated that Blondel Street was
completed between 2015 and 2016, and East Suniga Road was completed between 2019 and 2020.
Based on review of existing topographical information presented on the Overall Grading Plan (TJC
Limited, 2024), elevations between 4,968 to 4,970 feet occur at the site’s perimeter and generally
decrease towards the center of the site to an elevation of approximately 4,966 feet.
4. PROPOSED CONSTRUCTION
The project will consist of the design and construction of two buildings with 26 townhomes as
depicted in Exhibit 1. Exhibit 1 presents the grading plan for the development (TJC Limited, 2024).
The townhomes will be two- to three-stories tall with tuck-under garages and will not have below-
grade levels. The overall site development will encompass the design and construction of
pavements, utility improvements, rain garden, and landscaping enhancements.
Exhibit 1 – Overall Grading Plan (TJC Limited, 2024)
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Finished floor elevations of the townhomes range from 4,970.66 to 4,972 feet, while the townhome
garage finished floor elevations range from 4,969.7 to 4,971.4 feet (TJC Limited, 2024). Based on
the grading information and existing topography, grade-raise fill up to approximately 6 feet will be
needed to achieve the proposed finished floor elevations. An approximately 1.5 to 2-foot deep rain
garden is proposed adjacent to the furthest east townhomes. The rain garden will outlet to existing
storm drain system.
5.FIELD EXPLORATION AND LABORATORY TESTING
On April 30, 2024, Ninyo & Moore conducted subsurface exploration services at the project site to
evaluate the existing subsurface conditions and to collect soil and bedrock samples for visual
observation and laboratory testing. The evaluation consisted of the drilling, logging, and sampling of
four exploratory borings using a truck-mounted drill rig equipped with 4-inch diameter, continuous-
flight, solid-stem augers. The borings were advanced within the project site to depths ranging
between approximately 19.3 and 24 feet bgs. Relatively undisturbed and disturbed soil and bedrock
samples were collected at selected intervals. The locations of the borings are presented on Figure
2. The borings logs are presented in Appendix A. Boring coordinates and ground elevations were
measured in the field using a Trimble Model DA2-BT survey unit with a global navigation satellite
system (GNSS) output of NAD83 (2011) and referencing Geoid model GEOID18. The boring
coordinates and elevations are presented in the table below:
Table 1 – Boring Coordinates
Boring No. Elevation (feet) Latitude (Decimal Degrees) Longitude (Decimal Degrees)
B-1 4,968.03 40.59966504 -105.07294949
B-3 4,968.12 40.59966279 -105.07237914
B-4 4,967.13 40.5994994 -105.07214287
Note: Coordinates and elevations collected with Trimble DA2-BT survey unit with GNSS output of NAD83 (2011) and GEOID 18. Vertical
precision of +/-2 inches and horizontal precision of +/- 1-inch using the above GNSS output and geoid model at this site.
Soil and bedrock samples collected during the subsurface exploration were transported to the Ninyo
& Moore laboratory for geotechnical laboratory analyses. Selected samples were analyzed to
evaluate engineering properties including in-situ moisture content and dry density, Atterberg limits,
percent materials passing the No. 200 sieve and grain size analysis including hydrometer,
swell/consolidation potential, direct shear, and soil corrosivity characteristics (including pH,
resistivity, water soluble sulfates and chlorides). The results of the in-situ moisture content and dry
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density tests are presented on the boring logs in Appendix A. Descriptions of the laboratory test
methods and the remainder of the test results are presented in Appendix B.
6. GEOLOGIC AND SUBSURFACE CONDITIONS
6.1. Geologic Setting
The site is located in Fort Collins, Colorado, approximately 6 miles east of the Rocky Mountains,
within the Colorado Piedmont section of the Great Plains Physiographic Province. Seas prograded
and retrograded several times over eastern Colorado within the early Cretaceous Period depositing
sandstone and shale of the Pierre Shale Formation within the project site area. The Laramide
Orogeny then uplifted the Rocky Mountains during the late Cretaceous and early Tertiary Periods.
Subsequent erosion deposited sediments east of the Rocky Mountains. As a result of regional uplift
approximately 5 to 10 million years ago, streams down-cut and excavated into the Great Plains
forming the Colorado Piedmont section (Trimble, 1980). A series of alpine glaciations occurred within
Colorado and the southern Rockies, concurrently as the Colorado Piedmont was being carved.
These glaciations were offset by a warm interglacial period, and as the glaciers ablated, meltwater
and wind helped deposit clay, silt, sand, gravel, cobbles, and boulders in the form of loess (wind
deposited) and alluvium (stream) throughout the Colorado Front Range (Chronic and Williams,
2014).
The surficial geology of the site vicinity is mapped by Hershey and Schneider (1972) as middle to
late Pleistocene and Holocene alluvial flood-plain and terrace deposits consisting of sand, silt, and
clay along with gravel and sand with cobble to boulder size material, respectively. The Pierre Shale
Formation is mapped underlying the project area at depth consisting of interbedded sandstone and
shale.
6.2. Subsurface Conditions
Our understanding of the subsurface conditions at the project site is based on our field exploration
and laboratory testing, review of published geologic maps, historic aerial photographs, and our
experience with the general geology of the area. The following sections provide a generalized
description of the subsurface materials encountered. More detailed descriptions are presented on
the boring logs in Appendix A.
6.2.1. Fill Materials
Fill was encountered at the surface in each boring. Fill extended to depths ranging from
approximately 3 to 4 feet bgs, but may be present with varying thickness in locations that were
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not explored. Based on site observations, fill was primarily observed near the perimeter of the
site, due to adjacent improvements, and decreased toward the center of the site. The extent of
fill material near the center of the site could be further evaluated through test pit excavation.
The fill material encountered within our borings generally consisted of moist, lean clay with sand
and varying amount of gravel. Information regarding ground preparation, remedial excavation,
and the degree of compaction during placement, is unknown to this firm. As a result, the fill
material is considered undocumented.
6.2.2. Alluvium
Alluvium was encountered below fill in each boring. The alluvial deposits extended to depths
ranging from approximately 19 to 21 feet bgs.
The alluvium generally consisted of moist, stiff to hard, silty to lean clay with various amounts
of sand overlying relatively clean alluvial deposits of sand and gravel. Cobbles should be
anticipated within the sand and gravel deposits.
6.2.3. Pierre Shale Formation
Bedrock mapped as the Pierre Shale Formation was encountered underlying fill and alluvial
deposits at depths of approximately 19 to 21 feet bgs and extended to the borings’ termination
depths of approximately 19.3 to 24 feet bgs. Ground elevations were measured in the field using
a Trimble Model DA2-BT survey unit with a GNSS output of NAD83 (2011) and referencing
Geoid model GEOID18. Bedrock elevations are presented in the table below and were
estimated using the measured ground elevations.
Table 2 – Top of Bedrock Depth and Elevation
B-1 19.0 4,949.0
B-2 21.0 4,945.3
B-3 19.0 4,949.1
The Pierre Shale Formation generally consisted of moderately soft to very hard, sandy shale.
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6.3. Groundwater
Groundwater was encountered in each boring during drilling at depths of approximately 8 to 13 feet
bgs. Approximate groundwater elevations at the time of drilling are presented in the table below.
Table 3 – Approximate Groundwater Elevation
Boring No. Depth to Groundwater (feet)Groundwater Elevation
B-1 9.0 4,959.0
B-2 13.0 4,953.3
B-4 8.0 4,959.7
Groundwater levels will fluctuate due to seasonal variations in the amount of rainfall, runoff, water
level within nearby streams and rivers, groundwater withdrawal from adjacent sites, and other
factors.
Grade-raise fill will be placed at this site in order to achieve the proposed site grades and finished
floor elevations. Finished floor elevations range from 4,970.66 to 4,972 feet, while the townhome
garage finished floor elevations range from 4,969.7 to 4,971.4 feet (TJC Limited, 2024). Proposed
pavement grades also range from approximately 4,969 feet to a high point of 4,971.17 feet (TJC
Limited, 2024). Groundwater was generally encountered during drilling approximately 9.3 to 15.7
feet below the lowest proposed site grade of 4,969 feet.
As a result, groundwater is not anticipated to be a constraint to the construction of the townhomes
or pavements, but may be encountered during construction of deep utilities which may require
temporary dewatering activity. Local and state requirements for temporary dewatering should be
followed.
7.GEOLOGIC AND OTHER HAZARDS
The following sections describe potential geologic hazards at the site including seismicity, expansive
soils, and compressible and collapsible soils.
7.1. Seismicity
Historically, several minor earthquakes have been recorded along the Front Range. Based on our
field observations and our review of readily available published geological maps and literature, there
are no known active faults underlying or adjacent to the subject site.
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Design of the proposed improvements should be performed in accordance with the requirements of
the governing jurisdictions and applicable building codes. Table 4 presents the seismic design
parameters for the site in accordance with the 2021 International Building Code (IBC) and ASCE 7-
16 guidelines and adjusted maximum considered earthquake spectral response acceleration
parameters evaluated using a web-based ground motion calculator (OSHPD, 2023). It was assumed
buildings are Risk Category II structures based on building use and occupancy as detailed in Table
1604.5 of the 2021 IBC.
Table 4 – 2021 International Building Code Seismic Design Criteria
Site Class D
Risk Category II
Site Coefficient, Fa 1.6
Site Coefficient, Fv 2.4
Mapped Spectral Acceleration at 0.2-second Period, Ss 0.195 g
Mapped Spectral Acceleration at 1.0-second Period, S1 0.056 g
Spectral Acceleration at 0.2-second Period Adjusted for Site Class, SMS 0.311 g
Spectral Acceleration at 1.0-second Period Adjusted for Site Class, SM1 0.134 g
DS
D1
7.2. Expansive Soils
One of the more significant geologic hazards in the Front Range area is the presence of swelling
clays in bedrock or surficial deposits. Wetting and drying of bedrock or surficial deposits containing
swelling clays can result in expansion and collapse of those units, which can cause major damage
to structures. A review of a Colorado Geological Survey map delineating areas based on their relative
potential for swelling in the Front Range by Hart (1973-1974) indicates that the soil and bedrock
materials in the site vicinity are typically sandy to gravelly alluvium, which typically exhibits low swell
potential, underlain by shale, which can contribute low to high swell potential.
A select sample was tested for swell percent against a surcharge pressure of 200 pounds per square-
foot (psf) in order to evaluate swell risk to proposed pavement areas. The selected sample tested
exhibited a swell potential of approximately 1.2 percent. On-site soils expected to be encountered
during project development would have a pavement performance risk category of “LOW” to
“MODERATE” based on the criteria presented in Table 5.
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Table 5 – Pavement Performance Risk Categories
NONE 0
LOW 0 to <1
MODERATE 1 to <5
HIGH 5 to 20
VERY HIGH > 20
The information provided in this table is based on Colorado Department of Transportation (CDOT) Pavement Design Manual
(2021), Chapter 4.
In order to evaluate slab-on-grade performance, a select sample was tested for swell/consolidation
at a representative field surcharge pressure of 500 psf. Based on the results of our laboratory testing,
the selected sample tested against a surcharge pressure of 500 psf exhibited a swell potential of
approximately 0.4 percent. The soils expected to be encountered during project development would
have a slab performance risk category of “LOW” based on the criteria presented in Table 6.
Table 6 – Slab Performance Risk Categories
Slab Performance Risk
Category
Representative
Percent Swell
Representative
Percent Swell
LOW 0 to <3 0 to <2
MODERATE 3 to <5 2 to <4
HIGH 5 to <8 4 to <6
Note: The information provided in this table is based on Colorado Association of Geotechnical Engineers (CAGE), Guidelines for Slab
Performance Risk Evaluation and Residential Basement Floor System Recommendations (Denver Metropolitan Area, 1996).
7.3. Compressible and Collapsible Soils
Compressible soils are generally comprised of soils that undergo settlement when exposed to new
loadings, such as fill or foundation loads. Soil collapse (or hydrocollapse) is a phenomenon where
soils undergo a significant decrease in volume upon an increase in moisture content, with or without
an increase in external loads. Buildings, structures, and other improvements may be subject to
excessive settlement-related distress when compressible soils or collapsible soils are present.
Based on the results of our subsurface exploration, the alluvial deposits and fill expected to be
encountered during project development are expected to have a low collapse potential.
However, compression of existing undocumented fill at this site could occur due to the new building
loads and other improvements. Ninyo & Moore has not been provided records of testing during the
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fill placement. As a result, removal and recompaction of the existing fill material as newly placed
engineered fill will be needed below the building foundation and slab-on-grade floor systems.
Complete removal and replacement of the existing fill material below pavement areas may be cost
prohibitive to the project. As a result, pavement and exterior flatwork recommendations are provided
in this report to reduce the impacts of the existing fill material assuming the owner is willing to accept
some risk of poor performance as a result of post-construction movement associated with
compression of existing fill material below new pavements.
8. CONCLUSIONS
Based on our geotechnical evaluation, it is our opinion that construction of the proposed townhomes
at the subject site is feasible from a geotechnical standpoint, provided the following
recommendations are incorporated into the design and construction of the project.
• Fill was encountered at the surface in each boring.
o Fill extended to depths ranging from approximately 3 to 4 feet bgs, but may be present with
varying thickness in locations that were not explored.
o The fill material encountered within our borings generally consisted of moist, lean clay with
sand and varying amount of gravel.
o The extent of fill material near the center of the site could be further evaluated through test
pit excavation.
o Fill is considered undocumented.
• Alluvium was encountered below fill in each boring and extended to depths ranging from
approximately 19 to 21 feet bgs.
o The alluvium generally consisted of moist, stiff to hard, silty to lean clay with various amounts
of sand overlying relatively clean alluvial deposits of sand and gravel. Cobbles should be
anticipated within the sand and gravel deposits.
• Bedrock mapped as the Pierre Shale Formation was encountered underlying fill and alluvial
deposits at depths of approximately 19 to 21 feet bgs and extended to the borings’ termination
depths of approximately 19.3 to 24 feet bgs.
o The Pierre Shale Formation generally consisted of moderately soft to very hard, sandy shale.
o Table 2 presents top of bedrock depth and approximate elevations.
• Groundwater was encountered in each boring during drilling at depths of approximately 8 to 13
feet bgs.
o Approximate groundwater elevations are presented in Table 3.
o Groundwater was generally encountered during drilling approximately 9.3 to 15.7 feet below
the lowest proposed site grade of 4,969 feet.
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o Groundwater is not anticipated to be a constraint to the construction of the townhomes or
pavements, but may be encountered during construction of deep utilities which may require
temporary dewatering activity.
• One of the more significant geologic hazards in the Front Range area is the presence of swelling
clays in bedrock or surficial deposits. A review of a Colorado Geological Survey map delineating
areas based on their relative potential for swelling in the Front Range by Hart (1973-1974)
indicates the soil and bedrock materials in the site vicinity can exhibit up to very high swell
potential.
o Expansion potential is not considered a geologic hazard within the native alluvium granular
soils.
o On-site soils expected to be encountered during project development would have a
pavement performance risk category of “LOW” to “MODERATE” based on the criteria
presented in Table 5.
o The soils and bedrock expected to be encountered during project development would have
a slab performance risk category of “LOW” based on the criteria presented in Table 6.
• Site soils generated from on-site excavation activities that are free of deleterious materials, and
do not contain particles larger than 3 inches in diameter, can generally be used as engineered
fill during site grading. Environmental factors that may restrict the re-use of site soils was not
studied in this report.
o The on-site soils should generally be excavated with medium- to heavy-duty earthmoving or
excavation equipment in good operating condition. Cobbles may be encountered within the
alluvial deposits which could complicate excavation activities.
o In our opinion, the site soils should generally be considered a Type C soil when applying
Occupational Safety and Health Administration (OSHA) regulations. For these soil
conditions, OSHA recommends a temporary slope inclination of 1.5H (Horizontal):1V
(Vertical) or flatter for excavations 20 feet or less in depth.
• Following remedial grading as described in Section 9.1.3, the townhomes may be supported on
conventional spreading footings provided with slab-on-grade floor systems, or post-tensioned
slab-on-grade foundation systems.
• The sulfate content of the tested soils presents a low risk of sulfate attack to concrete.
• The subgrade soils at the site present a severe potential for corrosivity to ferrous metals. Special
consideration should be given to the use of heavy gauge, corrosion-protected, underground steel
pipe or culverts, if any are planned. As an alternative, plastic pipe or reinforced concrete pipe
could be considered. A corrosion specialist should be consulted for further recommendations.
• Positive drainage should be established and maintained away from the proposed buildings.
Positive drainage may be established by providing a surface gradient for paved areas of 2 to 5
percent or more for a distance of 10 feet or more away from structures. Where concrete flatwork
is placed adjacent to structures and other considerations are required by law, such as ADA
requirements, slopes of 1 percent or more are considered acceptable. For unpaved areas,
positive drainage may be established by a slope of 5 to 10 percent for 10 feet or more away from
structures, where possible. Additional site drainage recommendations are presented in Section
9.12 and should be reviewed by the Civil Engineer and Landscaper.
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•Rain gardens are depicted adjacent to the townhome structures (TJC Limited, 2024).
o Rain gardens in close proximity to structures can adversely affect building performance and
may result in water intrusion issues of below-grade levels. The proposed rain garden should
be lined or constructed with a closed bottom to reduce infiltration.
9.RECOMMENDATIONS
Based on our understanding of the project, the following sections present our geotechnical
recommendations for design and construction of the proposed site improvements. These
recommendations were prepared based on the results of our subsurface exploration and our
experience with similar projects.
It is important that Ninyo & Moore be notified and given an opportunity to review the project progress
drawings and reevaluate our recommendations as the project design progresses.
9.1. Earthwork
The following sections provide our earthwork recommendations for this project. In general, the City
of Fort Collins and/or project specific earthwork specifications are expected to apply, unless noted.
9.1.1. Excavations
Our evaluation of the excavation characteristics of the on-site materials is based on the results
of our subsurface exploration, our site observations, and our experience with similar materials.
The on-site surface and near surface soils (fill and alluvium) may generally be excavated with
medium- to heavy-duty earthmoving or excavation equipment in good operating condition. Fill
materials and alluvium contain various amounts of gravel and cobble size material may be
encountered, which could complicate excavations and increase wear and tear on equipment.
Groundwater was encountered at depths ranging from approximately 8 to 13 feet bgs and
temporary excavations for utility construction may extend below the groundwater table.
Implementation of various dewatering and groundwater cut-off techniques and associated
permitting may be needed.
Equipment and procedures that do not cause significant disturbance to the excavation bottoms
should be used. Excavators and backhoes with buckets having large claws to loosen the
subgrade material should be avoided when excavating the bottom 6 to 12 inches of excavations
as such equipment may disturb the excavation bases.
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9.1.2. Temporary Excavation Slopes
Temporary excavations will be needed for this project to construct foundations and utilities.
Based on the subsurface information obtained from our exploratory excavations and our
experience with similar projects, we anticipate that the soil conditions and stability of the
excavation sidewalls may vary with depth. Soils with higher fines content may stand vertically
for a short time (less than 12 hours) with little sloughing. However, as the soil dries after
excavation or as the excavations are exposed to rainfall, sloughing may occur. Soils with low
cohesion (e.g., predominately sandy or gravelly material), may slough or cave during
excavation, especially if wet or saturated.
The contractor should provide safely sloped excavations or an adequately constructed and
braced shoring system, in compliance with (OSHA, 2005), for employees working in excavations
that may expose them to the danger of moving ground. Reducing the inclination of the sidewalls
of the excavations, where feasible, may increase the stability of the excavations. If construction
or earth material is stored, or equipment is operated near an excavation, flatter slope geometry
or shoring should be used during construction. Appropriate slope inclinations should be
evaluated in the field by an OSHA-qualified “Competent Person” based on the conditions
encountered.
In our opinion, the overburden site soils should generally be considered a Type C soil when
applying OSHA regulations. For these soil conditions, OSHA recommends a temporary slope
inclination of 1.5H:1V or flatter for excavations 20 feet or less in depth. Steeper cut slopes may
be utilized for excavations that are less than 4 feet deep depending on the strength, moisture
content, and homogeneity of the soils as observed in the field.
Appropriate slope inclinations should be evaluated in the field by an OSHA-qualified “Competent
Person” based on the conditions encountered.
9.1.3. Site and Remedial Grading
Prior to grading, the ground surface in proposed structure and improvement areas should be
cleared of any surface obstructions, debris, topsoil, organics (including vegetation) and other
deleterious material. Materials generated from clearing operations should be removed from the
project site for disposal (e.g. at a legal landfill site). Obstructions that extend below finish grade,
if present, should be removed and resulting voids filled with compacted, engineered fill or
Controlled Low Strength Material (CLSM).
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Approximately 3 to 4 feet of undocumented fill was encountered in the borings during the
subsurface exploration. Prior to the performance of overlot grading, including the placement of
grade raise fill, remedial grading should consist of removal of the existing fill material below
existing ground surface until firm native deposits are encountered, and recompaction as
engineered fill. This remedial grading should extend laterally 1 or more feet laterally beyond the
buildings for each foot below the finish floor elevation. The project budget should account for
the need for additional removal and recompaction of existing fill material within the townhome
footprints.
Following the removal and recompaction of existing fill material as engineered fill, the
townhomes may be supported on shallow foundation systems consisting of spread-footings or
post-tensioned slab-on-grade foundation systems bearing on 12 or more inches of moisture-
conditioned, and compacted engineered fill.
If conventional spread-footings are elected, the townhomes may be provided with slab-on-grade
floors bearing on 12 or more inches of moisture-conditioned and compacted engineered fill.
Where fill thicknesses equal to or above the outlined remedial grading are planned, no additional
remedial grading is recommended.
There are risks associated with supporting pavements and exterior flatwork over existing fill
material without providing complete removal and replacement with moisture-conditioned and
compacted engineered fill. Generally, the costs associated with remediating pavement subgrade
for undocumented fill materials are cost prohibitive. Therefore, the following recommendation
for pavement subgrade and exterior flatwork support are provided assuming the owner is willing
to accept some risk of poor pavement performance as a result of post-construction movements
associated with the fill materials that remain in areas outside the proposed building footprints.
Asphalt and concrete pavements and flatwork (curb and gutter, sidewalk) may be placed on 12
or more inches of moisture conditioned and compacted engineered fill.
The exposed subgrade materials should be firm and unyielding prior to grade-raise fill
placement. The extent of and depths of removal should be evaluated by a representative of
Ninyo and Moore during the excavation work based on observation of the exposed soils.
Additional recommendations specific to the site conditions encountered may be provided at the
time of construction. The project budget should include additional cost associated with the
removal and replacement of fill material.
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Care should be taken to maintain the subgrade moisture content after fill placement but prior to
construction of grade supported slabs and pavements. The site should be graded to prevent
ponding of surface water on the prepared subgrades or in excavations. If the subgrade should
become desiccated, saturated, frozen, or disturbed, the affected material should be removed or
these materials should be scarified, moisture conditioned, and compacted prior to slab and
pavement construction.
The geotechnical consultant should be retained to observe the remedial excavations, and the
elevations of the excavation bottoms should be surveyed by the Project Civil Engineer.
9.1.4. Re-Use of Site Soils
Soils generated from on-site excavation activities in the fill material and alluvium that are free of
deleterious materials and organic matter, and do not contain particles larger than 3 inches in
diameter, can generally be used as engineered fill as evaluated by the geotechnical consultant,
provided they are compacted and moisture conditioned as recommended in this report.
Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) larger than
3 inches in diameter may be incorporated into the project fills in non-structural areas and below
the anticipated utility installation depths. A Geotechnical Engineer should be consulted
regarding appropriate recommendations for usage of such materials on a case-by-case basis
when such materials have been observed during earthwork. Care should be taken to avoid
nesting of oversized materials during placement.
An evaluation of the potential for contamination by hazardous materials was beyond the scope
of this study.
9.1.5. Fill Placement and Compaction
Granular soils (on-site soils that classify as SC, SW-SC, GP-GC or import soils) used as
engineered fill should be moisture-conditioned to moisture contents within 2 percent of optimum
moisture content. Fine-grained soils (on-site soils that classify as CL, CL-ML) used as
engineered fill should be moisture-conditioned to moisture contents between 1 percent below
and 3 percent over optimum moisture content. Engineered fill should be compacted to a relative
compaction of 95 percent or more as evaluated by ASTM D698. The contractor should be
prepared either to dry or moisten fill material, as needed, prior to compaction.
The engineered fill should be compacted by appropriate mechanical methods. Lift thickness for
fill will be dependent upon the type of compaction equipment utilized. Backfill should be placed
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in lifts not exceeding 8 inches in loose thickness in areas compacted by other-than hand
operated machines. Backfill should be placed in lifts not exceeding 6 inches in loose thickness
in areas compacted by hand operated machines.
Fill materials should not be placed, worked, rolled while they are frozen, thawing, or during
poor/inclement weather conditions.
Compaction areas should be kept separate, and no lift should be covered by another until
relative compaction and moisture content within the recommended ranges are obtained.
9.1.6. Imported Soil
Imported soil will be needed for proposed site grading. Imported soil for use as engineered fill
should have less than 50 percent passing the No. 200 sieve, a very low swell potential
(approximately 1 percent or less when wetted against a surcharge pressure of 500 psf), and a
low plasticity index (less than 15). Imported soil should not contain organic matter, clay lumps,
bedrock (claystone, sandstone, etc.) fragments, debris, other deleterious matter, or rocks or
hard chunks larger than approximately 3 inches’ nominal diameter.
Imported soil for use as engineered fill should exhibit low corrosion potential. Imported soil
placed in contact with ferrous materials should have a saturated soil resistivity of 2,000 ohm-cm
or more and a chloride content of 25 parts per million or less. Soils in contact with concrete
should exhibit a soluble sulfate content less than 0.1 percent.
We further recommend that proposed import material be evaluated by the project’s geotechnical
consultant at the borrow source for its suitability prior to importation to the project site.
9.1.7. Controlled Low Strength Material
Use of CLSM should be considered in lieu of compacted fill for areas with low tolerances for
surface settlements, for excavations that extend below the groundwater table and in areas with
difficult access for compaction equipment. CLSM consists of a fluid, workable mixture of
aggregate, Portland cement, and water. CLSM should be placed in lifts of 5 feet or less with a
24-hour or more curing period between each lift.
The use of CLSM has several advantages:
• A narrower excavation can be used where shoring is present, thereby minimizing the
quantity of soil to be excavated and possibly reducing disturbance to the near-by traffic;
• Compaction requirements do not apply;
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• There is less risk of damage to improvements, since little compaction is needed to place
CLSM;
• CLSM can be batched to flow into irregularities in excavation bottoms and walls; and
• The number of workers needed inside the trench excavation is reduced.
The CLSM mix design should be submitted for review prior to placement. The 28-day strength
of the material should be no less than 50 pounds per square inch (psi) and no more than 150
psi. CLSM should be observed and tested by the geotechnical consultant.
9.1.8. Utility Installation
The contractor should take care to achieve and maintain adequate compaction of the backfill
soils around manholes, valve risers and other vertical pipeline elements where settlements
commonly are observed. Use of CLSM should be considered in lieu of compacted soil backfill
for areas with low tolerances for surface settlements. This would also reduce the permeability
of the utility trenches.
Pipe bedding materials, placement and compaction should meet the specifications of the pipe
manufacturer and applicable municipal standards. Materials proposed for use as pipe bedding
should be tested for suitability prior to use.
Special care should be exercised to avoid damaging the pipe or other structures during the
compaction of the backfill. In addition, the underside (or haunches) of the buried pipe should be
supported on bedding material that is compacted as described above. This may need to be
performed with placement by hand or small-scale compaction equipment.
Surface drainage should direct water away from utility trench alignments. Where topography,
site constraints or other factors limit or preclude adequate surface drainage, the granular
bedding materials should be surrounded by non-woven filter fabric (e.g., TenCate Mirafi® 140N
or the equivalent) to reduce migration of fines into the bedding which can result in severe,
isolated settlements.
Due to relatively shallow groundwater, development of site grading plans should consider the
subsurface transfer of water in utility trenches and the pipe bedding. Pipe bedding materials can
function as efficient conduits for re-distribution of natural and applied waters in the subsurface.
Cut-off walls in utility trenches or other water-stopping measures should be implemented to
reduce the rates and volumes of water transmitted along utility alignments and toward buildings,
pavements and other structures where excessive wetting of the underlying soils will be
damaging. Incorporation of water cut-offs and/or outlet mechanisms for saturated bedding
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materials into development plans will be beneficial to the project. These measures also will
reduce the risk of loss of fine-grained backfill soils into the bedding material with resultant
surface settlement. Cut-off walls could be constructed using 2 or more feet thick clay earth
material or 1 or more feet thick CLSM extending 12 or more inches into undisturbed soil on each
side and bottom of the trench, and extending 2 or feet above the utility pipe. The placement
locations for such cut off walls should be decided by the Project Civil Engineer based on
susceptibility of the utility bedding to groundwater intrusion and at a minimum include the
placement of cut-off walls within 5 feet of the building exterior to discourage water transmittal
along utility alignments toward the building.
9.2. Spread Footing Foundations
The proposed townhomes may be supported on conventional spread footing foundations. Perimeter
footings should extend to 36 inches or more below the lowest exterior finished grade (for frost
protection). Continuous wall footings should have a width of 18 inches or more and column footings
should have a width of 24 inches or more. Footings should be reinforced in accordance with the
recommendations of the Structural Engineer. Footings should be bear on prepared subgrade soils
as described in Section 9.1.3.
Footings may be designed using a net allowable soil bearing pressure of 3,000 psf for static
conditions. The bearing capacity may be increased by one-third when considering loads of short
duration such as wind or seismic forces. The foundations should preferably be proportioned such
that the resultant force from design loads, including lateral loads, falls within the kern (i.e., middle
on-third of the footing base).
Uplift resistance can be developed from the weight of the footings, the effective weight of any
overlying soil, and the weight of the supported structure itself. The effective unit weight of the soil
can be assumed to be 120 pounds per cubit foot (pcf) above the groundwater level. Soil uplift
resistance may be calculated as the weight of the soil prism defined by a diagonal line extending
from the perimeter of the foundation to the ground surface at an angle θ of up to 20 degrees from
the vertical. Under large moment and/or shear loading, the effective size of the uplift soil prism may
be reduced. An appropriate safety factor should be applied.
Lateral earth pressures and the ultimate coefficient of friction between soil and concrete described
in Section 9.5 may be used for resistance to sliding.
The base of foundation excavations should be free of water and loose soil prior to placing concrete.
Should the soils at bearing level become excessively dry, disturbed, or saturated, the affected soil
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should be stabilized, moisture conditioned and recompacted. Concrete should be placed soon after
subgrade compaction to reduce bearing soil disturbance. It is recommended that Ninyo & Moore be
retained to observe, test, and evaluate the soil foundation bearing materials.
Based on the results of our subsurface exploration and laboratory testing, we estimate total post-
construction movements and differential movements of up to about 1-inch and ½-inch may occur,
respectively. Distortions of about 1/2-inch (vertical) over 50 feet (horizontal) are possible. Differential
movement potential will decrease depending on the homogeneity of the fill prism below the
foundations.
9.3. Post-Tensioned Slab-On-Grade Foundations
As an alternative to spread footing foundations, the townhomes may be supported using a post-
tensioned slab-on-grade foundation system. Post-tensioned slab-on-grade foundations should be
designed by the project’s Structural Engineer in accordance with the 2021 IBC and the Post-
Tensioning Institute (PTI) (PTI, 2008), 3rd Edition of the Design of Post-Tensioned Slabs-on-Ground.
Remedial grading, as outlined in Section 9.1.3, will need to be performed prior to construction of
post-tensioned foundations.
PTI design parameters were estimated based on the stratigraphic information described in our boring
logs and laboratory testing, proposed site grading, and using the procedures outlined in the
referenced PTI manual (PTI, 2008). The subsurface materials encountered included fill and alluvium
consisting of lean to silty clay with various amounts of sand overlying granular alluvial deposits of
sand and gravel. Existing fill and alluvium clay soils extended up to a depth of approximately 8 feet
bgs. Ninyo & Moore opines that the depth of wetting at this site is dependent on the depth of the clay
soils, and is also controlled by the shallow groundwater table. As a result, a depth of wetting of 8 feet
was assumed for the site to estimate PTI design parameters. Additionally, conservative design
parameters were utilized for the existing site soils and import soils needed to achieve the proposed
finished floor elevations.
Differential vertical swell was estimated for center lift and edge lift conditions for use in designing
foundation slabs based on the lithology encountered in our borings and our understanding of the
proposed site grading. These values were calculated using a computer program titled VOLFLO Win
1.5 and the parameters are presented on the following table:
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Table 7 – PTI Parameters
Allowable Net Bearing Capacity 3,000 psf
Approximate Thornthwaite Moisture Index -20
Constant Soil Suction (estimated) 3.9 pF
(estimated) About 8 feet
Soil Fabric Factor 1.0
Frost Depth 3 feet
Note: PTI design parameters were estimated using conservative input values for two layer soil, Layer 1 consisting of engineered fill and
Layer 2 consisting of clay alluvium; *Input used for Layer 1, **Input used for Layer 2
The Estimated Edge Moisture Variation Distance (em) due to shrinking soils (center lift condition) is
approximately 8.5 feet, while the Estimated Edge Moisture Variation Distance due to swelling soils
(edge lift condition) is approximately 4.3 feet. These values were calculated based on the guidelines
PTI provided in the referenced PTI manual (PTI, 2008). The Estimated Differential Soil Movement
(ym) as calculated based on the Post Equilibrium Case guidelines provided in the referenced PTI
manual (PTI, 2008), where pF varies from 2.5 to 4.5, are presented on Table 8.
Table 8 – PTI Post Equilibrium Parameters
Condition ym (in)
Center Lift (Shrinking) -0.99 Wet to Constant
Edge Lift (Swelling) 0.48 Dry to Constant
The ym was calculated based on the Post Construction Case guidelines provided in the PTI Manual,
where pF varies from 2.9 to 4.5 are presented on Table 9.
Table 9 – PTI Post Construction Parameters
Condition ym (in)
Center Lift (Shrinking) -1.52 Wet to Dry
Edge Lift (Swelling) 2.37 Dry to Wet
The parameters provided above include estimated differential soil movement for two cases: post-
equilibrium and post-construction. The post-construction case tends to be conservative as wetting
around the foundations is taken into account in the calculations and therefore, recommended for use
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to the design the post-tensioned slab-on-grade foundations at this site. However, the Structural
Engineer should select which case is appropriate for the design. Exterior slab edges should be
placed 3 or more feet below the lowest exterior finished grade (for frost protection). Interior partitions
and bearing walls resting on the post-tensioned slabs should be designed to account for slab flexure
as evaluated by the Structural Engineer. Utility lines entering the slab should be provided with
positive bond breaks that allow 1 or more inch of differential movement.
The estimated moisture variation distance around the differential soil movements presented above
do not consider the effects of non-climatic factors (e.g. tree location, landscaping, etc. depth of
exterior grade beams or other moisture retardant, etc.). The final PTI design should take into account
such features, which may exist, or be anticipated.
Lateral earth pressures and the ultimate coefficient of friction between soil and concrete described
in Section 9.5 may be used for resistance to sliding.
The need for a moisture-retarding system should be considered by the Structural Engineer or
Architect, based on the moisture sensitivity of the anticipated flooring. The placement of a vapor
retarder is recommended in areas where moisture-sensitive floor coverings are anticipated.
9.4. Slab-On-Grade Floors
If conventional spread footings are utilized, the buildings may be designed with a slab-on-grade floor.
The design of the floor slab (including jointing and reinforcement) is the responsibility of the Structural
Engineer. Joints should be constructed at intervals designed by the Structural Engineer to help
reduce random cracking of the slab. Recommendations based on structural considerations for slab
thickness, jointing, and steel reinforcement should be developed by the Structural Engineer in
accordance with American Concrete Institute (ACI) recommendations. Soils underlying the slabs
should be prepared, moisture conditioned, and compacted in accordance with the recommendations
presented in Section 9.1.3 of this report.
For slab design, a design modulus of subgrade reaction (K) of 150 pounds per square inch per inch
of deflection (psi/inch) may be used for the subgrade soils in evaluating such deflections. This value
is based on a unit square foot area and can be adjusted for large slabs. Adjusted values of the
modulus of subgrade reaction, Kv, can be obtained from the following equation for slabs of various
widths:
Kv = K[(B+1)/2B]2 (psi/inch)
B in the above equation represents the width of the slab in feet between line loads/point loads.
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The slab should be constructed so that it “floats” independent of the foundations. The need for a
moisture-retarding system should be designed by the Structural Engineer or Architect based on the
moisture sensitivity of the anticipated flooring. The placement of a vapor retarder is recommended
in areas where moisture-sensitive floor coverings or storage of moisture-sensitive materials directly
on the slab are anticipated.
Floor slabs should be separated from bearing walls and columns with expansion joints, which allow
unrestrained vertical movement. Joints should be observed periodically, particularly during the first
several years after construction. Slab movement can cause previously free-slipping joints to bind.
Measures should be taken so that slab isolation is maintained in order to reduce the likelihood of
damage to walls and other interior improvements.
Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other
construction objectives, our experience indicates that any differential movement between the walls
and slabs will probably be observed in adjacent slab expansion joints or floor slab cracks that occur
beyond the length of the structural dowels. The Structural Engineer should account for this potential
differential settlement through use of sufficient control joints, appropriate reinforcing or other means.
9.5. Lateral Earth Pressures
Earth pressures are used to compute the lateral forces acting on below-grade walls. These pressures
can be classified as at-rest, active, and passive. The direction and magnitude of the soil/wall
movement just before failure affects the resulting pressure condition. At-rest conditions exist when
there is no movement, such as for a restrained wall. Active stresses are exerted when the wall moves
out and the soil moves toward the wall away from the soil mass, thereby mobilizing the shear strength
of the soil. Passive stresses exist when the wall moves toward the soil mass.
The lateral outward movement required to develop the active pressure for cohesive site soils is
approximately 1 to 2 percent of the wall height (1.2 to 2.4 inches for a 10-foot [retained height] wall)
or when backfilled with stiff cohesive soils and for granular soil (CDOT Class I structural fill) is about
0.1 to 0.2 percent of the wall height (0.1 to 0.3 inches for a 10-foot wall backfilled with granular soils).
Where granular soils are used for backfilling the walls, the granular soils should extend at least ½ or
more of the wall height behind the wall.
The recommended equivalent fluid pressures in Table 10 assumes an angle of internal friction (φ) of
24 degrees and a unit weight of 120 pcf for near surface site soils consisting of lean clay with sand
and silty clay with sand. An angle of internal friction (φ) of 34 degrees, a unit weight of 125 pcf was
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assumed for CDOT Class I structural fill. The values listed below are for static conditions and
horizontal backfill.
Table 10 – Recommended Lateral Earth Pressures
Soil Condition Active Pressure
(pcf)
At-rest Pressure
(pcf) (pcf)
Cohesive Site Soils 51 70 285
The maximum passive pressure for site soils should be limited to 2,850 psf for horizontal backfill.
This is assuming the ground is horizontal for a distance of 10 feet or three times the height generating
the passive pressure. The use of heavy compaction equipment adjacent to below-grade walls could
result in lateral earth pressures well in excess of those predicted in Table 10. We recommend that
the upper 24 inches of soil that is not protected by pavement or a concrete slab, be neglected when
calculating passive resistance. This zone, where applicable, should be backfilled with cohesive soils
to minimize infiltration of surface water into the backfill. For frictional resistance to lateral loads, we
recommend that an ultimate coefficient of friction of 0.35 be used between site soils and concrete.
An ultimate coefficient of friction of 0.44 may be used between CDOT Class 1 structural fill and
concrete.
Measures should be taken so that moisture does not build up behind the below-grade walls. Below-
grade walls should be dampproofed or waterproofed in accordance with the recommendations of the
project Architect and Structural Engineer.
To reduce the potential for water- and sulfate/salt-related damage to the foundation walls and
efflorescent development, particular care should be taken in selection of the appropriate type of
waterproofing material to be utilized and in the application of this material.
9.6. Pavement Design
We assume the project pavements will be privately maintained and will include only Portland cement
concrete pavements. Pavement section alternatives for the paved surfaces were developed in
general accordance with the guidelines and procedures of the American Association of State
Highway and Transportation Officials (AASHTO), CDOT, and Larimer County Urban Area Street
Standards (2021).
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9.6.1. Pavement Subgrade Characterization
The subgrade soils encountered during the subsurface exploration typically consisted of lean to
silty clay with varying amounts of sand, which classify as A-7-6 to A-4 soils in accordance with
the AASHTO soil classification system. It is assumed soils imported to the site would classify as
A-4 soils or better.
A mean R-value of 10 was assumed for subgrade support for pavement design. If, during
construction, the subgrade is found to vary from the expected soil conditions, we should be
contacted so we may re-evaluate our recommended resilient modulus value.
9.6.2. Traffic Loading
An Equivalent Single Axle Loads of 73,000 was assumed for site pavements for a 20-year
design life. Pavement section alternatives for the paved surfaces were developed in general
accordance with the guidelines and procedures of the AASHTO, CDOT, and Larimer County
Urban Area Street Standards (2021).
The design of rigid pavements was based on the following input parameters:
6
9.6.3. Pavement Thickness
Based on the above-mentioned design traffic and input parameters, and following the AASHTO
method of pavement design, the structural section should consist of 5 or more inches of Portland
cement concrete.
We recommend PCCP be utilized in dumpster pads, loading areas, or other areas where
extensive wheel maneuvering are expected. PCCP in dumpster area should be increased to 6
or more inches and be large enough to support the wheels of the truck which will bear the load
of the dumpster. Although the use of ABC is not integral for structural support in PCCP
pavements, the placement of 4 or more inches of ABC below PCCP will develop a more stable
subgrade for concrete truck traffic associated with the pavement construction and help reduce
potential slab curl, shrinkage cracking, and subgrade “pumping” through joints. Adequate joint
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spacing is recommended to prevent loss of load transfer across control joints. Joints should be
sealed to reduce water infiltration.
Adequate surface drainage should be provided to reduce ponding and infiltration of water into
the pavement and subgrade materials. We suggest that the paved areas have a surface gradient
of 2 percent or more. In addition, surface runoff from surrounding areas should be intercepted,
collected, and not permitted to flow onto the pavement or infiltrate the subgrade. We recommend
that perimeter swales, edge drains, curbs and gutters, or combination of these drainage devices,
be constructed to reduce the adverse effects of surface water runoff.
9.6.4. Pavement Materials
PCCP should consist of a plant mix composed of a mixture of high-quality aggregate, Portland
cement and appropriate admixtures meeting the requirements of the City of Fort Collins and
Larimer County Urban Area Street Standards (2021). Concrete should have a modulus of
rupture of third point loading of 600 psi or more. The concrete should be air-entrained with
approximately 6 percent air and should have a cement content of six or more sacks per cubic
yard. Allowable slump should be approximately 4 inches.
PCCP should be provided with longitudinal and transverse joints that meet the City of Fort
Collins and Larimer County Urban Area Street Standards (2021) design criteria and construction
specifications.
The ABC material placed beneath pavements should meet the criteria of CDOT Class 6
aggregate base. Requirements for CDOT Class 6 aggregate base can be found in Section 703
of the current CDOT Standards and Specifications for Road and Bridge Construction (2022).
9.6.5. Pavement Subgrade Preparation
Pavement sections should be supported on moisture-conditioned and compacted engineered
fill as described in Section 9.1.3 of this report.
The contractor should be prepared either to dry the subgrade materials or moisten them, as
needed, prior to compaction. Some site soils may pump or deflect during compaction if moisture
levels are not carefully monitored and as the site finished grades approach the groundwater
table. The contractor should be prepared to process and compact such soils to establish a stable
platform for paving, including the use of chemical stabilization or geotextiles, where needed.
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The prepared subgrade should be protected from the elements prior to pavement placement.
Subgrades that are exposed to the elements may need additional moisture conditioning and
compaction, prior to pavement placements.
Immediately prior to paving, the subgrade should be proof rolled with a heavily loaded,
pneumatic tired vehicle and checked for moisture. Areas that show excessive deflection during
proof rolling should be excavated and replaced and/or stabilized. Areas allowed to pond prior to
paving may need to be re-worked prior to proof rolling.
9.6.6. Pavement Maintenance
The collection and diversion of surface drainage away from paved areas is vital to satisfactory
performance of the pavements. The subsurface and surface drainage systems should be
carefully designed to facilitate removal of the water from paved areas and subgrade soils.
Allowing surface waters to pond on pavements will cause premature pavement deterioration.
Where topography, site constraints or other factors limit or preclude adequate surface drainage,
pavements should be provided with edge drains to reduce loss of subgrade support. The long-
term performance of the pavement also can be improved greatly by backfilling and compaction
behind curbs, gutters, and sidewalks so that ponding is not permitted and water infiltration is
reduced.
The standard care of practice in pavement design describes the recommended flexible
pavement section as a “20-year” design pavement; however, many pavements will not remain
in satisfactory condition without routine, preventive maintenance and rehabilitation procedures
performed during the life of the pavement. Preventive pavement treatments are surface
rehabilitation and operations applied to improve or extend the functional life of a pavement.
These treatments preserve, rather than improve, the structural capacity of the pavement
structure. In the event the existing pavement is not structurally sound, the preventive
maintenance will have no long-lasting effect. Therefore, a routine maintenance program to seal
joints and cracks, and repair distressed areas is recommended.
9.7. Concrete Flatwork
Exterior walkways and flatwork should be 4 or more inches thick. The slab edges should be
deepened by two or more inches where exterior slabs-on-grade are placed adjacent to landscaping
areas and taper to the recommended thickness 12 inches inward from the edge.
Concrete flatwork should be supported on 12 or more inches of moisture-conditioned and compacted
engineered fill as described in Section 9.1.3 of this report.
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Ground-supported flatwork, such as walkways, will be subject to soil-related movements resulting
from heave/settlement, frost, etc. Thus, where these types of elements abut rigid building
foundations or isolated/suspended structures, differential movements should be anticipated. We
recommend that flexible joints be provided where such elements abut the main structure to allow for
differential movement at these locations. Positive drainage should be established and maintained
adjacent to flatwork. Water should not be allowed to pond on flatwork.
To reduce the potential manifestation of distress to exterior concrete flatwork due to movement of
the underlying soil, we recommend that such flatwork be installed with crack-control joints at
appropriate spacing as designed by the Structural Engineer.
In no case should exterior flatwork extend under any portion of the buildings where there is less than
2 inches of clearance between the flatwork and any element of the building. Exterior flatwork in
contact with brick, rock facades, or any other element of the building can cause damage to the
structure if the flatwork experiences movements.
9.8. Corrosion Considerations
The corrosion potential of on-site soils to concrete and buried metal was evaluated in the laboratory
using selected samples obtained from the exploratory borings. Laboratory testing was performed to
assess the effects of sulfate on concrete and the effects of soil resistivity on buried metal. Results of
these tests are presented in Appendix B. Recommendations regarding concrete to be utilized in
construction of proposed improvements and for buried metal pipes are provided in the following
sections.
9.8.1. Concrete
The test for water-soluble sulfate content of the soils was performed using CDOT Test Method
CP-L 2103 Method B. The laboratory test results indicated 0.034 percent sulfates in soil by mass
for the selected bulk sample. Based on Table 601-2 of the CDOT 2022 Standard Specifications
for Road and Bridge Construction, the on-site soils represent a Class 0 severity of sulfate
exposure to concrete on a scale that ranges between Class 0 and Class 3. Therefore, we
recommend that the cement used for this project should meet one of the below outlined
requirements.
•ASTM C150 Type I, II, III or V
•ASTM C595 Type IL, IP, IP(MS), IP(HS) or IT
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 27
The Structural Engineer should ultimately select the concrete design strength based on the
project specific loading conditions. However, higher strength concrete may be selected for
increased durability, resistance to slab curling and shrinkage cracking. We recommend the use
of concrete with a design 28-day compressive strength of 4,000 psi or more, for concrete slabs
at this site. Concrete exposed to the elements should be air-entrained.
9.8.2. Buried Metal Pipes
The corrosion potential of the on-site materials was analyzed to evaluate its potential effects on
buried metals. Corrosion potential was evaluated using the results of laboratory testing of
samples obtained during the subsurface evaluation that were considered representative of soils
at the subject site.
Minimum resistivity was measured to be approximately 800 ohm-cm within the selected sample.
The results of the laboratory testing indicate the on-site materials have low resistivity and could
have severe corrosivity potential to ferrous metals based on the criteria in Table 11. Therefore,
special consideration should be given to the use of heavy gauge, corrosion protected,
underground steel pipe or culverts, if any are planned. As an alternative, plastic pipe or
reinforced concrete pipe could be considered. A corrosion specialist should be consulted for
further recommendations.
Table 11 – Corrosion Potential to Steel
0 - 500 Very Severe
500 – 2,000 Severe
2,000 – 10,000 Moderate
10,000 – 30,000 Mild
>30,000 Low
9.9. Scaling
Climatic conditions in the project area including relatively low humidity, large temperature changes
and repeated freeze-thaw cycles, may cause surficial scaling and spalling of exterior concrete.
Occurrence of surficial scaling and spalling can be aggravated by poor workmanship during
construction, such as “over-finishing” concrete surfaces and the use of de-icing salts on exterior
concrete flatwork, particularly during the first winter after construction. The use of de-icing salts on
nearby roadways, which can be transferred by vehicle traffic onto newly placed concrete, can be
sufficient to induce scaling.
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 28
The measures below can be beneficial for reducing the concrete scaling. However, because of the
other factors involved, including workmanship, surface damage to concrete can develop even though
the measures provided below were followed. The mix design criteria should be coordinated with
other project requirements including the criteria for soluble sulfate resistance presented in Section
9.8.1.
• Curing concrete in accordance with applicable codes and guidelines.
• Maintaining a water/cement ratio of 0.45 by weight for exterior concrete mixes.
• Including Type F fly ash in exterior concrete mixes as 20 percent of the cementitious material.
• Specifying a 28-day, compressive strength of 4,500 or more psi for exterior concrete that may be
exposed to de-icing salts.
• Avoiding the use of de-icing salts through the first winter after construction.
• If colored concrete is being proposed for use at this site, Ninyo & Moore should be consulted for
additional recommendations.
9.10. Frost Heave
Site soils are susceptible to frost heave if allowed to become saturated and exposed to freezing
temperatures and repeated freeze/thaw cycling. The formation of ice in the underlying soils can result
in two or more inches of heave of pavements, flatwork and other hardscaping in sustained cold
weather. A portion of this movement may be recovered when the soils thaw, but due to loss of soil
density some degree of displacement will remain. Frost heave of hardscaping could also result in
areas where the subgrade soils were placed on engineered fill.
In areas where hardscape movements are a design concern (i.e. exterior flatwork located adjacent
to the building within the doorway swing zone), replacement of the subgrade soils with 2.5 or more
feet of clean, coarse sand or gravel, or supporting the element on foundations similar to the building,
or spanning over a void should be considered. Detailed recommendations in this regard can be
provided upon request.
9.11. Construction in Cold or Wet Weather
During construction, the site should be graded such that surface water can drain readily away from
the building areas. Given the soil conditions, it is important to avoid ponding of water in or near
excavations. Water that accumulates in excavations should be promptly pumped out or otherwise
removed and these areas should be allowed to dry out before resuming construction. Berms, ditches,
and similar means should be used to decrease stormwater entering the work area and to efficiently
convey it off site.
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 29
Earthwork activities undertaken during the cold weather season may be difficult and should be done
by an experienced contractor. Fill should not be placed on top of frozen soils. The frozen soils should
be removed prior to the placement of fill or other construction material. Frozen soil should not be
used as engineered fill or backfill. The frozen soil may be reused (provided it meets the selection
criteria) once it has thawed completely. In addition, compaction of the soils may be more difficult due
to the viscosity change in water at lower temperatures.
If construction proceeds during cold weather, foundations, slabs, or other concrete elements should
not be placed on frozen subgrade soil. Frozen soil should either be removed from beneath concrete
elements, or thawed and recompacted. To limit the potential for soil freezing, the time passing
between excavation and construction should be minimized. Blankets, straw, soil cover, or heating
may be used to discourage the soil from freezing.
9.12. Site Drainage
Infiltration of water into subsurface soils can lead to soil movement and associated distress, and
chemically and physically related deterioration of concrete and masonry structures. To reduce the
potential for infiltration of moisture into subsurface soils at the site, we recommend the following:
• Positive drainage should be established and maintained away from the proposed townhome
foundations. Positive drainage may be established by providing a surface gradient for paved
areas of 2 to 5 percent or more for a distance of 10 feet or more away from structures. Where
concrete flatwork is placed adjacent to structures and other considerations are required by law,
such as ADA requirements, slopes of 1 percent or more are considered acceptable. For unpaved
areas, positive drainage may be established by a slope of 5 to 10 percent for 10 feet or more
away from structures, where possible.
• Adequate surface drainage should be provided to channel surface water away from on-site
structures and off paved surfaces to a suitable outlet such as a storm drain. Adequate surface
drainage may be enhanced by utilization of graded swales, area drains, and other drainage
devices. Surface run-off should not be allowed to pond near structures.
• Building roof drains should have downspouts tightlined to an appropriate outlet, such as a storm
drain or the street, away from structures, pavements, and flatwork. If tightlining of the downspouts
is not practicable, they should discharge 5 feet or more away from structures and onto surfaces
that slope away from the structure. Downspouts should not be allowed to discharge onto the
ground surface adjacent to building foundations or on exterior walkways.
• The possibility of moisture infiltration beneath a structure, in the event of plumbing leaks, should
be considered in the design and construction of underground water and sewer conduits.
Permitting increases in moisture to the building supporting soils may result in a decrease in
bearing capacity and an increase in settlement, heave, and/or differential movement.
• Incorporating a perimeter drainage system around the building foundations that will aid in
reduction of the moisture infiltration of subsurface soils may be considered. Due to the proposed
construction (i.e. no below grade construction) and anticipated utilities within the structure, not
placing the perimeter drainage would be considered a low risk to the owner.
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 30
• Detention ponds, retention ponds, and rain gardens in close proximity to structures can adversely
affect building performance due to moisture infiltration beneath building foundations leading to
increase potential for differential and total settlement. The proposed rain garden should be lined
or constructed with a closed bottom to reduce infiltration.
• Irrigated landscaping, consisting of sprinklers to water plants with high demands for water, should
not be placed within 10 feet of the townhomes. Drip irrigation is considered acceptable between
5 and 10 feet of the building exteriors. If drip irrigated plants are needed within 5 feet of the
building exterior, drip irrigation system should be provided with sensors that limit over irrigation.
• Utility trenches should be backfilled with compacted, low permeability fill (i.e. permeability of 5-
10 cm/s or less) within 5 feet of the building.
9.13. Construction Observation and Testing
A qualified geotechnical consultant should perform appropriate observation and testing services
during grading and construction operations. These services should include observation of any soft,
loose, or otherwise unsuitable soils, evaluation of subgrade conditions where soil removals are
performed, evaluation of the suitability of proposed borrow materials for use as fill, evaluation of the
stability of open temporary excavations, evaluation of the results of any subgrade stabilization or
dewatering activities, and performance of observation and testing services during placement and
compaction of engineered fill and backfill soils.
The geotechnical consultant should also perform observation and testing services during placement
of concrete, mortar, grout, asphalt concrete, and steel reinforcement. If another geotechnical
consultant is selected to perform observation and testing services for the project, we request that
the selected consultant provide a letter to the owner, with a copy to Ninyo & Moore, indicating that
they fully understand our recommendations and they are in full agreement with the recommendations
contained in this report. Qualified subcontractors utilizing appropriate techniques and construction
materials should perform construction of the proposed improvements.
9.14. Plan Review
The recommendations presented in this report are based on the Overall Grading Plan (TJC Limited,
2024) and on the findings of our geotechnical evaluation. When finished, project plans and
specifications should be reviewed by the geotechnical consultant prior to submitting the plans and
specifications for bid. Additional field exploration and laboratory testing may be needed upon review
of the project design plans.
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 31
9.15. Pre-Construction Meeting
We recommend a pre-construction meeting be held. The owner or the owner’s representative, the
architect, the contractor, and the geotechnical consultant should be in attendance to discuss the
plans and the project.
10. LIMITATIONS
The field evaluation, laboratory testing, and geotechnical analyses presented in this geotechnical
report have been conducted in general accordance with current practice and the standard of care
exercised by geotechnical consultants performing similar tasks in the project area. No warranty,
expressed or implied, is made regarding the conclusions, recommendations, and opinions presented
in this report. There is no evaluation detailed enough to reveal every subsurface condition. Variations
may exist and conditions not observed or described in this report may be encountered during
construction. Uncertainties relative to subsurface conditions can be reduced through additional
subsurface exploration. Additional subsurface evaluation will be performed upon request.
This document is intended to be used only in its entirety. No portion of the document, by itself, is
designed to completely represent any aspect of the project described herein. Ninyo & Moore should
be contacted if the reader requires additional information or has questions regarding the content,
interpretations presented, or completeness of this document.
This report is intended for design purposes only. It does not provide sufficient data to prepare an
accurate bid by contractors. It is suggested that the bidders and their geotechnical consultant
perform an independent evaluation of the subsurface conditions in the project areas. The
independent evaluations may include, but not be limited to, review of other geotechnical reports
prepared for the adjacent areas, site reconnaissance, and additional exploration and laboratory
testing.
Our conclusions, recommendations, and opinions are based on an analysis of the observed site
conditions. If geotechnical conditions different from those described in this report are encountered,
our office should be notified, and additional recommendations, if warranted, will be provided upon
request. It should be understood that the conditions of a site could change with time as a result of
natural processes or the activities of man at the subject site or nearby sites. In addition, changes to
the applicable laws, regulations, codes, and standards of practice may occur due to government
action or the broadening of knowledge. The findings of this report may, therefore, be invalidated over
time, in part or in whole, by changes over which Ninyo & Moore has no control.
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 32
This report is intended exclusively for use by the client. Any use or reuse of the findings, conclusions,
and/or recommendations of this report by parties other than the client is undertaken at said parties’
sole risk.
Ninyo & Moore | The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024 33
11. REFERENCES
American Association of State Highway and Transportation Officials (AASHTO), 1993, AASHTO
Guide for Design of Pavement Structures.
American Association of State Highway and Transportation Officials (AASHTO), 2011, Standard
Specifications for Transportation Materials and Methods of Sampling and Testing, 31st
Edition, and Provisional Standards.
American Concrete Institute (ACI), 2019, Building Code Requirements for Structural Concrete (ACI
318-08) and Commentary.
American Concrete Institute (ACI), 2010, Guide to Design of Slabs-on-Ground (ACI 360 10).
American Society for Testing and Materials (ASTM), 2019 Annual Book of ASTM Standards.
Chronic, Halka, Williams, Felicie, 2014, Roadside Geology of Colorado, Third Edition.
Colorado Association of Geotechnical Engineers (CAGE), 1996, Guideline for Slab Performance
Risk Evaluation and Residential Basement Floor System Recommendations (Denver
Metropolitan Area), dated December.
Colorado Association of Geotechnical Engineers (CAGE), 2007, Geotechnical Study Guidelines for
Light Commercial and Residential Buildings in Colorado, dated September.
Colorado Department of Transportation (CDOT), 2021 Pavement Design Manual.
Google Earth, September 1993, January 2017, June 2021.
Hart, Stephen S., 1973-4, Potentially Swelling Soil and Rock in the Front Range Urban Corridor,
Colorado: Colorado Geological Survey.
Hershey, L.A. and Schneider, P.A., 1972, Geologic map of the lower Cache La Poudre River basin,
north-central Colorado, U.S. Geological Survey, Miscellaneous Geologic Investigations Map
I-687, 1:62,500.
International Code Council, 2021, International Building Code.
Larimer County, 2021, Larimer County Urban Area Street Standards, dated August 1.
Ninyo & Moore, In-house proprietary information.
Occupational Safety and Health Administration (OSHA), 2005, OSHA Standards for the Construction
Industry, 29 CFR Part 1926, dated June.
OSHPD, 2024, Seismic Design Maps, http://seismicmaps.org/
Post-Tensioning Institute (PTI), 2008, 3rd Edition of the Design of Post-Tensioned Slabs-on-Ground.
Trimble, Donald E. and Machette, Michael M., 1979, Geologic Map of the Greater Denver Area, Front
Range Urban Corridor, Colorado: United States Geological Survey.
TJC Limited, 2024, Overall Grading Plan, dated April 24.
Trimble, Donald E., 1980, The Geologic Story of the Great Plains, Geological Survey Bulletin 1493.
United States Geological Survey and Colorado Geological Survey (USGS & CGS), 2020, Quaternary
fault and fold database for the United States, from USGS web site:
http://earthquakes.usgs.gov/regional/qfaults/.
Ninyo & Moore The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024
FIGURES
SITE
Geotechnical & Environmental Sciences Consultants
50
2
9
5
7
0
0
1
_
S
L
.
d
w
g
5
/
2
4
B
S
M
SITE LOCATION
FIGURE 1
NOTE: DIMENSIONS, DIRECTIONS AND LOCATIONS ARE APPROXIMATE. I REFERENCE: USGS, 2018.0
FEET
2,000 4,000
THE ELLIE AT OLD TOWN NORTH
EAST SUNIGA ROAD & BLONEL STREET
FORT COLLINS, COLORADO
502957001 I 5/24
N
SUNIGA ROAD
B-1 B-3
B-2
B-4
BL
O
N
D
E
L
S
T
R
E
E
T
Geotechnical & Environmental Sciences Consultants
BORING LOCATIONS
0
FEET
50
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9
5
7
0
0
1
_
S
P
.
d
w
g
5
/
2
4
B
S
M
50 1000
LEGEND
THE ELLIE AT OLD TOWN NORTH
EAST SUNIGA ROAD & BLONEL STREET
FORT COLLINS, COLORADO
502957001 I 5/24
FIGURE 2
N
NOTE: DIMENSIONS, DIRECTIONS AND LOCATIONS ARE APPROXIMATE. I REFERENCE: GOOGLE EARTH 2022.
BORINGB-4
Ninyo & Moore The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024
APPENDIX A
Boring Logs
Ninyo & Moore The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024
Description
APPENDIX A
BORING LOGS
Field Procedure for the Collection of Disturbed Samples
Disturbed soil samples were obtained in the field using the following method.
Bulk Samples
Bulk samples of representative earth materials were obtained from the exploratory borings. The
samples were bagged and transported to the laboratory for testing.
The Standard Penetration Test (SPT) Sampler
Disturbed drive samples of earth materials were obtained by means of a Standard Penetration
Test sampler. The sampler is composed of a split barrel with an external diameter of 2 inches
and an unlined internal diameter of 1-3/8 inches. The sampler was driven into the ground 12 to
18 inches with a 140-pound hammer falling freely from a height of 30 inches in general
accordance with ASTM D 1586. The blow counts were recorded for every 6 inches of
penetration; the blow counts reported on the logs are those for the last 12 inches of penetration.
Soil samples were observed and removed from the sampler, bagged, sealed and transported to
the laboratory for testing.
Field Procedure for the Collection of Relatively Undisturbed Samples
Relatively undisturbed soil samples were obtained in the field using the following method.
The California Drive Sampler
The sampler, with an external diameter of 2.4 inches, was lined with four 4-inch long, thin brass
rings with inside diameters of approximately 1.9 inches. The sample barrel was driven into the
ground with the weight of a hammer in general accordance with ASTM D 3550. The driving
weight was permitted to fall freely. The approximate length of the fall, the weight of the hammer,
and the number of blows per foot of driving are presented on the boring logs as an index to the
relative resistance of the materials sampled. The samples were removed from the sample barrel
in the brass liners, sealed, and transported to the laboratory for testing.
0
5
10
15
SM
CL
Bulk sample.
Modified split-barrel drive sampler.
2-inch inner diameter split-barrel drive sampler.
No recovery with modified split-barrel drive sampler or 2-inch inner diameter split-barrel
drive sampler.
Sample retained by others.
Standard penetration test (SPT).
No recovery with SPT.
Shelby tube sample. Distance pushed in inches/length of sample recovered in inches.
No recovery with Shelby tube sampler.
Continuous push sample.
Seepage.
Groundwater encountered during drilling.
Groundwater measured after drilling.
MAJOR MATERIAL TYPE (SOIL):Solid line denotes unit change.
Dashed line denotes material change.
Attitudes: Strike/Dip
b: Bedding
c: Contact
j: Joint
f: Fracture
F: Fault
cs: Clay Seam
s: Shear
bss: Basal Slide Surface
sf: Shear Fracture
sz: Shear Zone
sbs: Shear Bedding Surface
The total depth line is a solid line that is drawn at the bottom of the boring.
BORING LOG FIGURE
Explanation of Boring Log Symbols
DE
P
T
H
(
f
e
e
t
)
Bu
l
k
SA
M
P
L
E
S
Dr
i
v
e
n
B
L
O
W
S
/
F
O
O
T
MO
I
S
T
U
R
E
(
%
)
DR
Y
D
E
N
S
I
T
Y
(
P
C
F
)
SY
M
B
O
L
CL
A
S
S
I
F
I
C
A
T
I
O
N
U.
S
.
C
.
S
.
BORING LOGS
FIGURE 1
BORING LOG EXPLANATION SHEET
0
5
10
15
SM
CL
Bulk sample.
Modified split-barrel drive sampler.
2-inch inner diameter split-barrel drive sampler.
No recovery with modified split-barrel drive sampler or 2-inch inner diameter split-barrel
drive sampler.
Sample retained by others.
Standard penetration test (SPT).
No recovery with SPT.
Shelby tube sample. Distance pushed in inches/length of sample recovered in inches.
No recovery with Shelby tube sampler.
Continuous push sample.
Seepage.
Groundwater encountered during drilling.
Groundwater measured after drilling.
MAJOR MATERIAL TYPE (SOIL):Solid line denotes unit change.
Dashed line denotes material change.
Attitudes: Strike/Dip
b: Bedding
c: Contact
j: Joint
f: Fracture
F: Fault
cs: Clay Seam
s: Shear
bss: Basal Slide Surface
sf: Shear Fracture
sz: Shear Zone
sbs: Shear Bedding Surface
The total depth line is a solid line that is drawn at the bottom of the boring.
BORING LOG FIGURE
Explanation of Boring Log Symbols
DE
P
T
H
(
f
e
e
t
)
Bu
l
k
SA
M
P
L
E
S
Dr
i
v
e
n
B
L
O
W
S
/
F
O
O
T
MO
I
S
T
U
R
E
(
%
)
DR
Y
D
E
N
S
I
T
Y
(
P
C
F
)
SY
M
B
O
L
CL
A
S
S
I
F
I
C
A
T
I
O
N
U.
S
.
C
.
S
.
20
Soil Classification Chart Per ASTM D 2488
Primary Divisions Secondary Divisions
Group Symbol Group Name
COARSE-
GRAINED
SOILS
more than
50% retained
on No. 200
sieve
GRAVEL
more than
50% of
coarse
fraction
retained on
No. 4 sieve
CLEAN GRAVEL
less than 5% fines
GW well-graded GRAVEL
GP poorly graded GRAVEL
GRAVEL with
DUAL
CLASSIFICATIONS
5% to 12% fines
GW-GM well-graded GRAVEL with silt
GP-GM poorly graded GRAVEL with silt
GW-GC well-graded GRAVEL with clay
GP-GC poorly graded GRAVEL with clay
GRAVEL with
FINES
more than
12% fines
GM silty GRAVEL
GC clayey GRAVEL
GC-GM silty, clayey GRAVEL
SAND
50% or more
of coarse
fraction
passes
No. 4 sieve
CLEAN SAND
less than 5% fines
SW well-graded SAND
SP poorly graded SAND
SAND with
DUAL
CLASSIFICATIONS
5% to 12% fines
SW-SM well-graded SAND with silt
SP-SM poorly graded SAND with silt
SW-SC well-graded SAND with clay
SP-SC poorly graded SAND with clay
SAND with FINES
more than
12% fines
SM silty SAND
SC clayey SAND
SC-SM silty, clayey SAND
FINE-
GRAINED
SOILS
50% or
more passes
No. 200 sieve
SILT and
CLAY
liquid limit
less than 50%
INORGANIC
CL lean CLAY
ML SILT
CL-ML silty CLAY
ORGANIC
OL (PI > 4)organic CLAY
OL (PI < 4)organic SILT
SILT and
CLAY
liquid limit
50% or more
INORGANIC
CH fat CLAY
MH elastic SILT
ORGANIC
OH (plots on or
above “A”-line)organic CLAY
OH (plots
below “A”-line)organic SILT
Highly Organic Soils PT Peat
USCS METHOD OF SOIL CLASSIFICATION
Geotechnical & Environmental Sciences Consultant
Apparent Density - Coarse-Grained Soil
Apparent
Density
Spooling Cable or Cathead Automatic Trip Hammer
SPT (blows/foot)
Modified Split Barrel (blows/foot)
SPT (blows/foot)
Modified Split Barrel (blows/foot)
Very Loose < 4 < 8 < 3 < 5
Loose 5 - 10 9 - 21 4 - 7 6 - 14
Medium
Dense 11 - 30 22 - 63 8 - 20 15 - 42
Dense 31 - 50 64 - 105 21 - 33 43 - 70
Very Dense > 50 > 105 > 33 > 70
Consistency - Fine-Grained Soil
Consis-tency
Spooling Cable or Cathead Automatic Trip Hammer
SPT (blows/foot)
Modified Split Barrel
(blows/foot)
SPT (blows/foot)
Modified Split Barrel (blows/foot)
Very Soft < 2 < 3 < 1 < 2
Soft 2 - 4 3 - 5 1 - 3 2 - 3
Firm 5 - 8 6 - 10 4 - 5 4 - 6
Stiff 9 - 15 11 - 20 6 - 10 7 - 13
Very Stiff 16 - 30 21 - 39 11 - 20 14 - 26
Hard > 30 > 39 > 20 > 26
LIQUID LIMIT (LL), %
P
L
A
S
T
I
C
I
T
Y
I
N
D
E
X
(
P
I
)
,
%
0 10
107
4
20
30
40
50
60
70
0 20 30 40 50 60 70 80 90 100
MH or OH
ML or OLCL - ML
Plasticity Chart
Grain Size
Description Sieve
Size Grain Size Approximate
Size
Boulders > 12”> 12”Larger than
basketball-sized
Cobbles 3 - 12”3 - 12”Fist-sized to
basketball-sized
Gravel
Coarse 3/4 - 3”3/4 - 3”Thumb-sized to
fist-sized
Fine #4 - 3/4”0.19 - 0.75”Pea-sized to
thumb-sized
Sand
Coarse #10 - #4 0.079 - 0.19”Rock-salt-sized to
pea-sized
Medium #40 - #10 0.017 - 0.079”Sugar-sized to
rock-salt-sized
Fine #200 - #40 0.0029 -
0.017”
Flour-sized to
sugar-sized
Fines Passing
#200 < 0.0029”Flour-sized and
smaller
CH or OH
CL or OL
De
p
t
h
(
f
t
)
5
10
15
20
25
30
35
Bu
l
k
Dr
i
v
e
n
Bl
o
w
s
/
F
o
o
t
14
16
14
50
50/3"
Mo
i
s
t
u
r
e
C
o
n
t
e
n
t
(
%
)
22.3
10.2
1.4
Dr
y
D
e
n
s
i
t
y
(
P
C
F
)
97.5
122.4
130.7
US
C
S
SW-SC
GP-GC
Total Depth: 19.3 feet.
Groundwater was encountered during drilling at approximately 9 feet.
Backfilled with on-site soil after drilling on 4/30/2024.
Notes:
Groundwater may rise to a level higher than that measured in borehole due to seasonal variations
in precipitation and several other factors as discussed in the report.
FILL: Dark brown, moist, very stiff, lean CLAY with sand; trace gravel.
ALLUVIUM: Brown, moist, medium dense, fine to coarse SAND with clay and gravel.
Dry; loose.
@9': Groundwater encountered during drilling.
Dark brown, wet, dense, GRAVEL with clay and sand.
PIERRE SHALE FORMATION: Brown, dry to moist, very hard, sandy SHALE.
FIGURE A-1
THE ELLIE AT OLD TOWN NORTH
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
502957001 | 05/24
De
p
t
h
(
f
t
)
5
10
15
20
25
30
35
Bu
l
k
Dr
i
v
e
n
Bl
o
w
s
/
F
o
o
t
23
7
50/11"
50/3"
16
Mo
i
s
t
u
r
e
C
o
n
t
e
n
t
(
%
)
17.0
19.8
5.5
Dr
y
D
e
n
s
i
t
y
(
P
C
F
)
99.2
93.0
125.4
US
C
S
CL-ML
SW-SC
GP-GC
Total Depth: 24 feet.
Groundwater was encountered during drilling at approximately 13 feet.
Borehole left open for delayed groundwater reading.
Notes:
Groundwater may rise to a level higher than that measured in borehole due to seasonal variations
in precipitation and several other factors as discussed in the report.
FILL: Dark brown, dry, very stiff, lean CLAY with sand.
ALLUVIUM: Brown, moist, stiff, silty CLAY with sand.
Brownish black and orange, moist to wet, dense, SAND with clay and gravel.
Grayish brown, moist to wet, very dense, GRAVEL with clay and sand.
@13': Groundwater encountered during drilling.
PIERRE SHALE FORMATION: Gray, sandy SHALE.
FIGURE A-2
THE ELLIE AT OLD TOWN NORTH
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
502957001 | 05/24
De
p
t
h
(
f
t
)
5
10
15
20
25
30
35
Bu
l
k
Dr
i
v
e
n
Bl
o
w
s
/
F
o
o
t
19
33
50/10"
8
34
Mo
i
s
t
u
r
e
C
o
n
t
e
n
t
(
%
)
16.3
1.4
Dr
y
D
e
n
s
i
t
y
(
P
C
F
)
98.9
131.9
US
C
S
CL-ML
SW-SC
Total Depth: 24 feet.
Groundwater was encountered during drilling at approximately 12 feet.
Borehole left open for delayed groundwater reading.
Notes:
Groundwater may rise to a level higher than that measured in borehole due to seasonal variations
in precipitation and several other factors as discussed in the report.
FILL: Dark brown, dry, stiff, lean CLAY with sand; trace gravel.
ALLUVIUM: Brown, dry, hard, silty CLAY with sand.
Brown, dry, dense, fine to coarse SAND with clay and gravel.
Wet; loose.
@12': Groundwater encountered during drilling.
PIERRE SHALE FORMATION: Brown, moist, moderately soft, sandy SHALE.
FIGURE A-3
THE ELLIE AT OLD TOWN NORTH
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
502957001 | 05/24
De
p
t
h
(
f
t
)
5
10
15
20
25
30
35
Bu
l
k
Dr
i
v
e
n
Bl
o
w
s
/
F
o
o
t
23
21
50/10"
39
56
Mo
i
s
t
u
r
e
C
o
n
t
e
n
t
(
%
)
11.0
12.7
2.1
Dr
y
D
e
n
s
i
t
y
(
P
C
F
)
118.1
117.9
136.8
US
C
S
CL
SW-SC
GP-GC
Total Depth: 20.5 feet.
Groundwater was encountered during drilling at approximately 8 feet.
Backfilled with on-site soil after drilling on 4/30/2024.
Notes:
Groundwater may rise to a level higher than that measured in borehole due to seasonal variations
in precipitation and several other factors as discussed in the report.
FILL: Dark brown, dry to moist, very stiff, sandy lean CLAY with gravel.
ALLUVIUM: Brown, dry to moist, very stiff, sandy lean CLAY; trace gravel.
Gray and brown, dry, dense, SAND with clay and gravel.
@8': Groundwater encountered during drilling.
Brown, wet, very dense, GRAVEL with clay and sand.
PIERRE SHALE FORMATION: Brown, dry to moist, moderately soft, sandy SHALE.
FIGURE A-4
THE ELLIE AT OLD TOWN NORTH
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
502957001 | 05/24
Ninyo & Moore The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024
APPENDIX B
Laboratory Testing
Ninyo & Moore The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024
APPENDIX B
LABORATORY TESTING
Classification
Soils were visually and texturally classified in accordance with the Unified Soil Classification System (USCS)
in general accordance with ASTM D 2488-00. Soil classifications are indicated on the logs of the exploratory
borings in Appendix B.
In-Place Moisture and Density Tests
The moisture content and dry density of relatively undisturbed samples obtained from the exploratory borings
were evaluated in general accordance with ASTM D 2937-04. The test results are presented on the logs of
the exploratory borings in Appendix B.
Atterberg Limits
Tests were performed on selected representative fine-grained soil samples to evaluate the liquid limit, plastic
limit, and plasticity index in general accordance with ASTM D 4318. These test results were utilized to evaluate
the soil classification in accordance with the Unified Soil Classification System. The test results and
classifications are shown on Figure B-1.
No. 200 Sieve Analysis
An evaluation of the percentage of particles finer than the No. 200 sieve in selected soil samples was
performed in general accordance with ASTM D 1140. The results of the tests are presented on Figure B-2.
Gradation Analysis
Gradation analysis tests were performed on a selected representative soil sample in general accordance with
ASTM D 6913. The grain-size distribution curves are shown on Figure B-3. These test results were utilized in
evaluating the soil classifications in accordance with the USCS.
Gradation and Hydrometer Analysis
Gradation analysis and hydrometer analysis tests were performed on a select soil sample in general
accordance with ASTM D422. The test results were utilized in evaluating the soil classifications in accordance
with the Unified Soil Classification System. The grain-size distribution curves are shown on Figure B-4.
Swell/Consolidation Tests
The consolidation and/or swell potential of selected materials were evaluated in general accordance with
ASTM D 4546. Specimens were loaded with a specified surcharge before inundation with water. Readings of
volumetric consolidation/swell were recorded until completion of primary consolidation/swell. After the
completion of primary swell, surcharge loads were increased incrementally to evaluate swell pressure. The
results of the consolidation/swell tests are presented on Figures B-5 and B-6.
Direct Shear Tests
Direct shear tests were performed on relatively undisturbed samples in general accordance with ASTM D 3080
to evaluate the shear strength characteristics of selected materials. The samples were inundated during
shearing to represent adverse field conditions. The results are shown on Figure B-7.
Soil Corrosivity Tests
A soil pH test was performed on a representative sample in general accordance with ASTM Test Method D
4972. A soil minimum resistivity test was performed on a representative sample in general accordance with
AASHTO T288. The sulfate content of a selected sample was evaluated in general accordance with CDOT
Test Method CP-L 2103 Method B. The chloride content of a selected sample was evaluated in general
accordance with CDOT Test Method CP-L 2104. The test results are presented on Figure B-8.
NP - INDICATES NON-PLASTIC
PERFORMED IN GENERAL ACCORDANCE WITH ASTM D 4318
4.0-5.0 21
7
CL-ML
181.0-2.0 2947 CL
CL-ML
CL
EQUIVALENT
USCS
No. 40 Sieve)
SYMBOL LOCATION DEPTH (ft)LIQUID
LIMIT (Fraction Finer ThanINDEX
PLASTIC
LIMIT
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
THE ELLIE AT OLD TOWN NORTH
502957001 5/24
CH or OH
CL or OL
MH or OH
ML or OLCL -ML
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100 110 120
PL
A
S
T
I
C
I
T
Y
I
N
D
E
X
,
P
I
LIQUID LIMIT, LL
5/24
SAMPLE
LOCATION
SAMPLE
(ft)
PERCENT
NO. 200
PERCENT
NO. 4
DESCRIPTION
98 85
EQUIVALENT
USCS
B-1
B-2 90 55
CL1.0-2.0
21.0-22.5 Grayish Brown Sandy SHALE; PIERRE SHALE
FORMATION
NO. 200 SIEVE ANALYSIS TEST RESULTS
FIGURE B-2
Coarse Fine Coarse Medium SILT CLAY
3" 2"1-1/2" 1" 3/4" 3/8" 4 10 30 50
PERFORMED IN GENERAL ACCORDANCE WITH ASTM D 6913
----
GRAVEL SAND FINES
Symbol Plasticity
Index
Plastic
Limit
Liquid
Limit
Depth
(ft)D30
Sample
Location
100
D10
16 200
D60 Cu
Equivalent
USCS
SW-SC5.00 41.7 1.2 8.7
Passing
No. 200
(percent)
Cc
--0.12 0.85B-2 9.0-9.9
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0.00010.0010.010.1110100
GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE NUMBERS HYDROMETER
GRADATION TEST RESULTS
FIGURE B-3
Coarse Fine Coarse Medium SILT CLAY
3" 2" 1-1/2" 1" 3/4" 3/8"4 10 30 50 200
PERFORMED IN GENERAL ACCORDANCE WITH ASTM D 7928
Passing
No. 200
(%)
GRAVEL SAND FINES
Symbol Plasticity
Index
Plastic
Limit
Fine
Sample
Location CcCu
100
Depth
(ft)D30D10
16
USCS
B-3 4.0-5.0 28 21 7 --------
D60
Liquid
Limit
--75 CL-ML
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0.00010.0010.010.1110100
GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE NUMBERS HYDROMETER
GRADATION TEST RESULTS
FIGURE B-4
Sample Location:B-1
Depth:1.0-2.0
Soil Type:CL(Fill)
PERFORMED IN GENERAL ACCORDANCE WITH ASTM D 4546
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
502957001 5/24
-4.0
-2.0
0.0
2.0
4.0
0.1 1.0 10.0 100.0
ST
R
A
I
N
(
%
)
STRESS (KSF)
Seating Cycle
Load Prior to Inundation
Load After Inundation
Swell Pressure
CONSOLIDATION TEST RESULTS
FIGURE B-5
Sample Location:B-2
Depth:4.0-5.0
Soil Type:CL-ML
PERFORMED IN GENERAL ACCORDANCE WITH ASTM D 4546
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
502957001 5/24
-4.0
-2.0
0.0
2.0
4.0
0.1 1.0 10.0 100.0
ST
R
A
I
N
(
%
)
STRESS (KSF)
Seating Cycle
Load Prior to Inundation
Load After Inundation
Swell Pressure
CONSOLIDATION TEST RESULTS
FIGURE B-6
Sand B-2 Peak
Sand
4.0-5.0
Cohesion
(psf)
Friction Angle
(degrees)
Equivalent
USCS
CL-ML24
28
264
CL-ML
Description Symbol Sample
Location
245
Depth
(ft)
Shear
Strength
X Ultimate4.0-5.0B-2
EAST SUNIGA ROAD & BLONDEL STREET, FORT COLLINS, COLORADO
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 500 1000 1500 2000 2500 3000 3500 4000 4500
SH
E
A
R
S
T
R
E
S
S
(
P
S
F
)
NORMAL STRESS (PSF)
FIGURE B-7
DIRECT SHEAR TEST RESULTS
1 PERFORMED IN GENERAL ACCORDANCE WITH ASTM D 4972
2 PERFORMED IN GENERAL ACCORDANCE WITH AASHTO T288
3 PERFORMED IN GENERAL ACCORDANCE WITH CDOT TEST METHOD CP-L 2103 METHOD B
4 PERFORMED IN GENERAL ACCORDANCE WITH CDOT TEST METHOD CP-L 2104
5/24
pH 1SAMPLE
DEPTH (ft)LOCATION
RESISTIVITY 2
(ohm-cm)IN SOIL
(ppm) (%)
7.1 408003400.034B-1, B-2, B-3, B-4 0.0-5.0
502957001
CHLORIDE
CONTENT 4
(ppm)
FIGURE B-8
Ninyo & Moore The Ellie at Old Town North, Fort Collins, Colorado | 502957001 R | May 23, 2024
APPENDIX C
Site Photographs and Descriptions
PHOTOGRAPHS
12/2023 1
Project No.502957001
Photo No.1 Location:Southeast Corner of Project Site Date:Various
Overview of Boring B-4, looking west.
Project Name:The Ellie at Old Town North
Gas utility crosses the southeast corner of the site.
PHOTOGRAPHS
12/2023 2
Project No.502957001Project Name:The Ellie at Old Town North
Photo No.3 Location:Northeast Corner of Project Site Date:Various
Concrete culverts exist under Blondel Street.
Overview of Boring B-2, looking east. The surrounding improvements generally sit 3 to 4 feet
about the sites low topographic point.
PHOTOGRAPHS
12/2023 3
Project No.502957001Project Name:The Ellie at Old Town North
Photo No.5 Location:Boring B-1 Date:Various
Drilling was completed with a truck mounted drill rig equipped with solid stem augers.
Overview of Boring B-1, looking southeast. Fill material was apparent near the outter edges
of the site.
9707 E. Easter Lane | Centennial, Colorado 80112 | p. 303.629.6000
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