HomeMy WebLinkAboutTHE LANDING AT LEMAY MULTIFAMILY AND MIXED-USE - FDP230020 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT
800 Stockton Avenue, #4
Fort Collins, CO 80524
phone: (970) 416-9045
fax: (970) 416-9040
email: kaftcollins@kumarusa.com
www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
GEOTECHNICAL ENGINEERING STUDY
AND PAVEMENT THICKNESS DESIGN
PROPOSED WATERMARK APARTMENTS AT LEMAY
NEAR THE NORTHEAST CORNER OF NORTH LEMAY AVENUE
AND DUFF DRIVE
FORT COLLINS, COLORADO
DRAFT SUBMITTAL
Prepared By: Reviewed By:
Jacob A. Hanson, P.E.
Joshua L. Barker, P.E.
Prepared For:
Thompson Thrift Residential
111 Monument Circle, Suite 1500
Indianapolis, IN 46204
Attn: Mr. Tim Govert
Project No. 22-3-168 July 29, 2022
Kumar & Associates, Inc.®
TABLE OF CONTENTS
SUMMARY ................................................................................................................................ 1
PURPOSE AND SCOPE OF STUDY ......................................................................................... 2
PROPOSED DEVELOPMENT ................................................................................................... 2
SITE CONDITIONS ................................................................................................................... 3
SUBSURFACE CONDITIONS ................................................................................................... 3
LABORATORY TESTING .......................................................................................................... 4
WATER SOLUBLE SULFATES ................................................................................................. 5
GEOTECHNICAL ENGINEERING CONSIDERATIONS ............................................................ 5
FOUNDATION RECOMMENDATIONS...................................................................................... 6
FLOOR SLABS .......................................................................................................................... 8
SWIMMING POOL ....................................................................................................................10
SURFACE DRAINAGE .............................................................................................................13
UNDERDRAIN SYSTEM ..........................................................................................................14
SITE GRADING ........................................................................................................................15
PAVEMENT DESIGN ................................................................................................................17
DESIGN AND CONSTRUCTION SUPPORT SERVICES .........................................................20
LIMITATIONS ...........................................................................................................................20
FIG. 1 – LOCATION OF EXPLORATORY BORINGS
FIGS. 2 through 5 – LOGS OF EXPLORATORY BORINGS, LEGEND AND NOTES
FIG. 6 – LEGEND AND NOTES
FIGS. 7 through 10 – SWELL-CONSOLIDATION TEST RESULTS
FIGS. 11 through 14 – GRADATION TEST RESULTS
FIG. 15 – MOISTURE-DENSITY RELATIONSHIPS
TABLE I – SUMMARY OF LABORATORY TEST RESULTS
APPENDIX A – TEST PIT PHOTOGRAPHS
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SUMMARY
1. Twenty-seven (27) exploratory borings were drilled and six (6) exploratory test pits were
excavated for this study at the approximate locations shown on Fig. 1. The borings and
test pits generally encountered a thin layer of topsoil overlying nil to approximately 5 feet
of man-placed fill consisting of lean clay with sand to clayey sand to sandy silt. The man-
placed fill was underlain by layers of naturally deposited (natural) clayey to granular soils
that extended to the explored depths of about 5 to 20 ft below the ground surface. Borings
2 through 8, 13, 15, and 19 through 22 encountered claystone bedrock underlying the
natural soils that extended to the explored depths of about 20 feet below the ground
surface.
The natural clayey soils consisted of lean clay to sandy lean clay with occasional layers
of clayey sand. The natural granular soils consisted of well to poorly graded sand and
well to poorly graded gravel with silt and sand and well to poorly graded sand with silt and
gravel. Cobbles up to 9 inches of diameter were noted in the granular soils within borings
and test pits.
Groundwater was encountered in the borings and test pits at the time of excavation at
depths about 6 to 9 feet below the ground surface and was encountered in Borings 2, 5,
7 and 8 at depths ranging from about 7 to 7.5 feet below the ground surface when
subsequently checked 7 to 17 days after drilling. Caving was noted in the majority of the
borings when subsequently checked at depths of about 3.5 to 8.5 feet below the ground
surface. Groundwater levels are expected to fluctuate with time and may fluctuate upward
after wet weather.
2 We understand that post-tensioned slab foundations are desired for the proposed
apartment buildings. PT-slabs supported on a minimum of 3-feet of properly moisture-
conditioned compacted structural fill should be designed for a maximum allowable bearing
pressure of 2,500 psf.
3. The following table presents the minimum pavement thickness recommendations for this
development.
Paved Area
Full Depth
Asphalt
(inches)
Composite Section
Asphalt/ABC
(inches)
PCCP
(inches)
Light Duty 5.5 4.0 / 7.0 6.0
Heavy Duty 6.5 4.5 / 8.0 7.0
ABC – Aggregate Base Course
PCCP – Portland Cement Concrete Pavement
All pavements should be placed on a minimum of 2 feet of moisture-density conditioned
on-site overburden soils. Additional pavement design alternatives are provided in the
body of this report.
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a geotechnical engineering study and pavement thickness
design for the proposed Watermark Apartments at Lemay Development to be located near the
northeast corner of North Lemay Avenue and Duff Drive in Fort Collins, Colorado. The study was
conducted for the purpose of developing building foundation, floor slab and site paving
recommendations. This study was performed in general accordance with our Proposal No. P3-
22-196 to Thompson Thrift Residential dated May 6, 2022
A field exploration program consisting of exploratory borings was conducted to obtain information
on subsurface conditions. Samples of the soils and bedrock obtained during the field exploration
program were tested in the laboratory to determine their classification and engineering
characteristics. The results of the field exploration program and laboratory testing were analyzed
to develop geotechnical engineering recommendations for use in site earthwork and in design
and construction of the proposed development.
This report has been prepared to summarize the data obtained during this study and to present
our conclusions and recommendations based on the proposed construction and the subsurface
conditions encountered. Design parameters and a discussion of geotechnical engineering
considerations related to construction of the proposed development are included in the report.
PROPOSED DEVELOPMENT
Based on the site plan provided, we understand the site will be developed by construction of
eleven (11) for-rent, multi-story, multi-family apartment buildings, and a clubhouse with a pool.
Drive lanes and automobile parking will surround the buildings.
We assume apartment buildings will be three-story structures and the clubhouse will be a single-
story structure. Other than the swimming pool, we assume there will be no below ground
structures or basements as part of the construction.
If the proposed development varies significantly from that generally described above or depicted
throughout this report, we should be notified to reevaluate the recommendations provided herein.
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SITE CONDITIONS
At the time of drilling, the site was vacant of structures and contained sparse weeds and grasses
at the surface. The site also contained trees near the middle of the site and a dry ditch running
north and south near the middle of the site. The site was generally flat with a slight slope down
towards the south and east. The site is bounded to the north by a vacant field follow by East Vine
Drive, to the east by commercial properties, to the south by Duff Drive followed by a multi-family
residential property and to the west by North Lemay Avenue.
SUBSURFACE CONDITIONS
Information on the subsurface conditions was obtained by excavating twenty-seven (27)
exploratory borings and six (6) exploratory test pits at the locations shown on Fig. 1. Graphic logs
of the borings/test pits are presented on Figs. 2 through 5 and a legend and notes describing the
soils encountered is presented on Fig. 6.
The borings and test pits generally encountered a thin layer of topsoil overlying nil to
approximately 5 feet of man-placed fill consisting of lean clay with sand to clayey sand to sandy
silt. The man-placed fill was underlain by layers of naturally deposited (natural) clayey to granular
soils that extended to the explored depths of about 5 to 20 ft below the ground surface. Borings
2 through 8, 13, 15, and 19 through 22 encountered claystone bedrock underlying the natural
soils that extended to the explored depths of about 20 feet below the ground surface.
The natural clayey soils consisted of lean clay to sandy lean clay with occasional layers of clayey
sand. The natural granular soils consisted of well to poorly graded sand and well to poorly graded
gravel with silt and sand and well to poorly graded sand with silt and gravel. Cobbles up to 9
inches of diameter were noted in the granular soils within borings and test pits.
The man-placed fill material contained a fine to coarse grained sand fraction and was moist and
brown. The natural clayey overburden soils contained a fine to coarse grained sand fraction and
were moist and brown. The natural granular soils were fine to coarse grained with gravel and
cobbles, moist to wet below groundwater and brown. The claystone bedrock was fine to medium
grained, moist and gray. Based on sampler penetration resistance, the natural clayey soils were
medium stiff to very stiff, the natural granular soils were loose to very dense and the bedrock was
hard to very hard.
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Groundwater was encountered in the borings and test pits at the time of excavation at depths
about 6 to 9 feet below the ground surface and was encountered in Borings 2, 5, 7 and 8 at depths
ranging from about 7 to 7.5 feet below the ground surface when subsequently checked 7 to 17
days after drilling. Caving was noted in the majority of the borings when subsequently checked
at depths of about 3.5 to 8.5 feet below the ground surface. Groundwater levels are expected to
fluctuate with time and may fluctuate upward after wet weather.
LABORATORY TESTING
Laboratory testing was performed on selected samples obtained from the borings to determine
in-situ moisture content and dry density, Atterberg limits, swell-consolidation characteristics, and
water soluble sulfates. The results of the laboratory tests are shown next to the boring logs on
Figs. 2 through 5, graphically plotted on Figs. 7 through 15, and summarized in the attached Table
I. The testing was conducted in general accordance with recognized test procedures, primarily
those of ASTM and the Colorado Department of Transportation (CDOT).
Index Properties: Samples were classified into categories of similar engineering properties in
general accordance with the Unified Soil Classification System. This system is based on index
properties, including liquid limit and plasticity index and gradation characteristics. Values for
moisture content and dry density, liquid limit and plasticity index, and the percent of soil passing
the U.S. No. 4 and No. 200 sieves are presented in Table I and adjacent to the corresponding
sample on the boring logs.
Swell-Consolidation: Swell-consolidation tests were conducted on samples of the man-placed fill,
natural lean clay and the claystone bedrock. The swell-consolidation tests were performed in
order to determine the compressibility and swell characteristics of the samples under loading and
when submerged in water. Each sample was prepared and placed in a confining ring between
porous discs, subjected to a surcharge pressure of 200- or 1,000-psf, and allowed to consolidate
before being submerged. The sample height was monitored until deformation practically ceased
under each load increment.
Results of the swell-consolidation tests are plotted as a curve of the final strain at each increment
of pressure against the log of the pressure and are presented on Figs. 7 through 10. Based on
the results of the laboratory swell-consolidation testing, samples of man-placed fill exhibited low
to high swell potential (2.4% to 7.7%) upon wetting under a 200-psf surcharge pressure. Samples
of natural clayey soils exhibited low to moderate to high swell potential (3.8% to 7.5%) upon
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wetting under a 200-psf surcharge pressure and moderate swell potential (3.5%) upon wetting
under a 1,000-psf surcharge pressure. A sample of claystone bedrock exhibited low swell
potential (0.1%) upon wetting under a 1,000-psf surcharge pressure.
Results of moisture-density relationships from a composite sample of overburden soils, as
determined by standard Proctor (ASTM D698), are presented on Fig. 15. The maximum dry
density of the composite sample from the borings was 108.1 pcf at an optimum moisture content
of 16.9 percent.
WATER SOLUBLE SULFATES
The concentration of water soluble sulfates measured in samples of the overburden material
obtained from the exploratory borings ranged from 0.02% to 0.78%. These concentrations of
water soluble sulfates represents a Class S0 to Class S02 severity exposure to sulfate attack on
concrete exposed to these materials. These degrees of attack are based on a range of Class S0,
Class S1, Class S2, and Class S3 severity exposure as presented in ACI 201.2R-16.
Based on the laboratory testing, we recommend all concrete exposed to the on-site materials
meet the cement requirements for Class S2 exposure as presented in ACI 201. Alternatively, the
concrete could meet the Colorado Department of Transportation’s (CDOT) cement requirements
for Class S2 exposure as presented in Section 601.04 of the CDOT Standard Specifications for
Road and Bridge Construction.
GEOTECHNICAL ENGINEERING CONSIDERATIONS
Existing Fill: Without documentation of placement conditions, including many (minimum 1 test per
1,000 ft3 every foot of depth) density tests, documenting the degree of compaction, the existing
fill materials are considered non-engineered and generally not suitable for support of foundations
or floor slabs. Based upon the results of the laboratory testing, the existing fill materials are
estimated to have moisture contents well above the assumed optimum moisture content, which
in turn indicates a potential for movement of structures or slabs constructed on the undocumented
fills upon structural loading.
Supporting the apartment buildings on post-tensioned (PT) slab foundations should be acceptable
provided proper subgrade preparation is performed. PT slab foundations should provide a better
mitigation of differential foundation and floor slab movements over a shallow spread footing and
slab on grade combination.
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We recommend that PT-slab foundations be supported on a minimum of 3-feet of properly
moisture-conditioned compacted structural fill. The minimum 3-foot depth should be measured
from the bottom of the slab.
Movements of floor slabs (non-PT) and exterior flatwork are often more tolerable to owners than
movements of the foundation system. As such, we believe that the floor slabs and exterior
flatwork within 5 feet of the building walls may be constructed as slabs-on-grade provided that a
minimum depth of 6 feet of properly moisture conditioned and compacted on-site soils are
provided below the slabs. Providing this thickness of properly compacted material below the
slabs will not eliminate the potential for movement; however, we believe that the risk of slab
movements will be mitigated sufficiently that observed movements will likely not exceed 1½
inches. If the owner is not willing to accept the risk of floor movement, then all floors within the
building footprint should be constructed as structurally supported slabs.
Exterior flatwork adjacent to structures that are relatively sensitive to movement, such as entry
areas, should be supported on the PT-slab foundation to mitigate differential movement that may
lead to difficult door operation. Less sensitive areas of flatwork, such as sidewalks away from
doorways and flatwork away from buildings, may be prepared the same as pavement subgrade
areas as recommended below.
Natural onsite soils, man-placed fill and bedrock (excluding claystone) should be suitable for use
as site grading fill and may be suitable for use as structural fill beneath buildings and other
structures, provided they can be properly moisture conditioned and compacted.
FOUNDATION RECOMMENDATIONS
Post-Tensioned (PT) Slab Foundations: We assume that PT-slab foundation design will be
conducted in accordance with the Post- Tensioning Institute’s (PTI) design approach. PTI’s
current design approach is outlined in their publication "Design of Post-Tensioned Slabs-On-
Ground (Third Edition, 2004)" and subsequent addenda, which revised the approach that was
outlined in their publication "Design and Construction of Post-Tensioned Slabs-On-Ground
(Second Edition, 1996)". It is the opinion of K+A and many other geotechnical engineers practicing
in this area that the guidelines provided in both the Second and Third Editions are empirical
methods developed for application in other parts of the country, and may not be strictly applicable
for local conditions due to the method not taking into account direct measurements of a soil’s
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swell-consolidation characteristics, which are routinely used for foundation design in the Colorado
Front Range area.
Based on the properties of the existing on-site soils, we recommend that the proposed apartment
building PT slabs should be constructed as BRAB Type III.
The International Building Code (IBC) permits designing PT-slabs in accordance with the methods
outlined in either the Second or Third Editions. The values presented for design are based on
guidelines in the PTI’s Third Edition.
The design and construction criteria presented below should be observed for a PT-slab
foundation. The construction details should be considered when preparing project documents.
1. We recommend that PT-slab foundations be supported on a minimum of 3 feet of properly
moisture-conditioned compacted structural fill. The minimum 3-foot depth should be
measured from the bottom of the slab (not the tendon trenches). The over-excavation for
the compacted fill zone should extend beyond the limits of the PT-slab foundation to a
minimum distance equal to the depth of over-excavation. Loose or soft material
encountered within the foundation excavation should be removed and replaced with
compacted structural fill.
2. Structural fill may consist of properly compacted, moisture conditioned, on-site materials
in accordance with the criteria presented in the Site Grading section of this report. Prior to
placing the structural fill, the exposed subgrade surface at the base of the sub- excavation
should be scarified, adjusted to a moisture content within 2 percentage points of optimum,
and re-compacted to at least 95% of the standard Proctor (ASTM D 698) maximum dry
density provide a firm, uniform base for subsequent fill placement.
3. PT-slab foundations bearing on compacted fill material placed as recommended herein
should be designed for a maximum allowable bearing pressure of 2,500 psf.
4. Based on the methodology in PTI’s Third Edition, the slabs should be designed using the
following criteria:
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Criteria Center Lift Edge Lift
Moisture variation (em) (ft.) 9.0 4.6
Differential swell (ym) (in) 0.2 0.5
The parameters used to calculate these values include a soil suction (pF) of 3.9, and a
depth to constant soil suction of 7 feet in accordance with the PTI Manual 3rd Edition.
These parameters were selected from the PTI Design Manual based on soil index
parameters and our opinion regarding the site's swell and compressibility potential; they
are not actual measurements or estimates of soil suction and soil moisture distributions
across the site.
5. The exterior perimeter slab beams should have sufficient embedment for frost protection.
The down-turned edges should have a minimum of 30 inches of soil cover.
6. Once the building pad area has been prepared as described above, it should be protected
from excessive wetting or drying until after the foundation has been completed.
7. We recommend an experienced PT-slab contractor construct the slabs. Representatives
of the geotechnical and structural engineer should check the foundation excavations and
tendon positions prior to placement of concrete, respectively. Fill placement and
subgrade preparation should be observed and tested by a representative of the
geotechnical engineer.
FLOOR SLABS
Floor slabs (not PT) present a very difficult problem where expansive soils are present near floor
slab elevation because sufficient dead load cannot be imposed on them to resist the uplift
pressure generated when the materials are wetted and expand.
The following measures should be taken to reduce damage that could result from movement
should the underslab materials be subjected to moisture changes.
1. Floor slabs should be placed on a minimum of 6 feet of properly compacted structural fill
extending to undisturbed natural soil. Structural fill below floor slabs should meet the
material and placement criteria in the “Site Grading” section of this report.
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2. Floor slabs should be separated from all bearing walls and columns with expansion joints
that allow unrestrained vertical movement.
3. Interior nonbearing partitions resting on floor slabs should be provided with slip joints so
that, if the slabs move, the movement cannot be transmitted to the upper structure. This
detail is also important for wallboards, stairways and door frames. Slip joints which will
allow at least 2 inches of vertical movement are recommended.
If wood or metal stud partition walls are used, the slip joints should preferably be placed
at the bottoms of the walls so differential slab movement won’t damage the partition wall.
If slab bearing masonry block partitions are constructed, the slip joints will have to be
placed at the tops of the walls. If slip joints are provided at the tops of walls and the floors
move, it is likely the partition walls will show signs of distress, such as cracking. An
alternative, if masonry block walls or other walls without slip joints at the bottoms are
required, is to found them on grade beams and piers and to construct the slabs
independently of the foundation. If slab bearing partition walls are required, distress may
be reduced by connecting the partition walls to the exterior walls using slip channels. Floor
slabs should not extend beneath exterior doors or over foundation grade beams, unless
saw cut at the beam after construction.
4. Floor slab control joints should be used to reduce damage due to shrinkage cracking.
Joint spacing is dependent on slab thickness, concrete aggregate size, and slump, and
should be consistent with recognized guidelines such as those of the Portland Cement
Association (PCA) or American Concrete Institute (ACI). We suggest joints be provided
on the order of 12 to 15 feet apart in both directions. The requirements for slab
reinforcement should be established by the designer based on experience and the
intended slab use.
5. If moisture-sensitive floor coverings will be used, mitigation of moisture penetration into
the slabs, such as by use of a vapor barrier, may be required. If an impervious vapor
barrier membrane is used, special precautions will be required to prevent differential
curing problems which could cause the slabs to warp. This topic is addressed by ACI
302.1R.
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6. All plumbing lines should be tested before operation. Where plumbing lines enter through
the floor, a positive bond break should be provided. Flexible connections should be
provided for slab-bearing mechanical equipment.
The precautions and recommendations itemized above will not prevent the movement of floor
slabs if the underlying expansive materials are subjected to moisture increases. However, the
precautions should reduce the damage if such movement occurs.
Exterior Flatwork: It is extremely important that exterior slabs-on-grade and pavements be
isolated from the building foundations. Many expansive soil related problems are related to
ineffective isolation between pavements/floor slabs and foundation-supported components of
structures. Careful design detailing is necessary at locations such as exterior stairway landings
and entry points.
Exterior flatwork adjacent to structures that is relatively sensitive to movement, such as entry
areas, should be supported on the PT-slab foundation to mitigate differential movement that may
lead to difficult door operation. Less sensitive areas of flatwork, such as sidewalks away from
doorways and flatwork away from buildings, may be prepared the same as pavement subgrade
areas as recommended below.
SWIMMING POOL
Proper design and construction of below-ground pool structures is critical to their satisfactory
performance. All swimming pools have a tendency to leak. A small amount of leakage can cause
the subsoils to swell and/or settle, and result in pool or slab movement, which widens existing
cracks and introduces more water into the subsoils, thereby compounding the problem.
Based on these considerations and the subsurface conditions, we suggest the following
precautions be taken in the design and construction of the proposed pool.
1. The pool should be designed and constructed to withstand some differential movement
without serious cracking. Pools constructed of flexible materials frequently perform better
than rigid pools.
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2. The subgrade below the pool should be removed to a depth of 2 feet and replaced with a
non- to low expansive structural fill material satisfying requirements indicated in the “Site
Grading” section of the report.
3. A minimum 4-inch thick layer of CDOT Class C filter material or ASTM C33 fine concrete
aggregate should be placed immediately below the pool, with a sump constructed at the
low point of the excavation where the water can be removed by pumping or gravity
drainage. Depending upon the size and depth of the swimming pool, individual drain lines
may be required for adequate subsurface drainage.
The drain lines should consist of a minimum 4-inch diameter slotted Schedule 40 or SDR
35 PVC pipe surrounded by a minimum of 12 inches of free-draining granular aggregate
material. The drain slot width should be sized to be filter-compatible with the aggregate,
and the aggregate should satisfy filter-compatibility requirements with the drainage layer
material. We can assess the filter-compatibility of the materials, and provide
recommendations based on that assessment if requested.
4. A water-tight joint should be provided between the pool and deck so water splashed from
the pool will not infiltrate into the pool backfill soils. The deck should be properly
maintained, including sealing of cracks which develop on the deck while the pool is in
service, to mitigate water infiltration.
The above measures will not eliminate the risk of damage to the pool and deck due to movement
of expansive/consolidation materials, but should reduce the amount of subsurface materials
becoming wetted, which should help limit potential movement due to wetting of the subgrade
materials.
LATERAL EARTH PRESSURES
Retaining structures should be designed for the lateral earth pressure generated by the backfill
materials, which is a function of the degree of rigidity of the retaining structure and the type of
backfill material used. Retaining structures that are laterally supported and can be expected to
undergo only a moderate amount of deflection, such as basement or vault walls, should be
designed for a lateral earth pressure based on the following equivalent at-rest fluid pressures:
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CDOT Class 1 (<20% passing No. 200 Sieve) ............................................ 55 pcf
Imported, non-expansive, silty or clayey sand ............................................ 65 pcf
On-site or imported, moisture-conditioned granular backfill ........................ 65 pcf
On-site, moisture-conditioned fine-grained backfill* .................................... 70 pcf
* Swell potential less than 2%
Cantilevered retaining structures that can be expected to deflect sufficiently to mobilize the full
active earth pressure condition should be designed for the following equivalent fluid pressures:
CDOT Class 1 (<20% passing No. 200 Sieve) ............................................ 40 pcf
Imported, non-expansive, silty or clayey sand ............................................ 45 pcf
On-site or imported, moisture-conditioned granular backfill ........................ 45 pcf
On-site, moisture-conditioned fine-grained backfill* .................................... 55 pcf
* Swell potential less than 2%
The equivalent fluid pressures recommended above assume drained conditions behind retaining
structures and a horizontal backfill surface. The buildup of water behind a retaining structure or
an upward sloping backfill surface will increase the lateral pressure imposed on the retaining
structure. All retaining structures should also be designed for appropriate surcharge pressures
such as traffic, construction materials and equipment.
The zone of backfill placed behind retaining structures to within 2 feet of the ground surface should
be sloped upward from the base of the structure at an angle no steeper than 45 degrees measured
from horizontal. To reduce surface water infiltration into the backfill, the upper 2 feet of the backfill
should consist of a relatively impervious imported soil containing at least 30% passing the No.
200 sieve, or the backfill zone should be covered by a slab or pavement structure.
Backfill should be compacted to at least 95% of the standard Proctor (ASTM D698) maximum dry
density at moisture contents within 2 percentage points of optimum for granular materials and
between 0 and +3 percentage points of optimum for clay materials. Care should be taken not to
over compact the backfill since this could cause excessive lateral pressure on the wall. Hand
compaction procedures, if necessary, should be used to prevent lateral pressures from exceeding
the design values.
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SITE SEISMIC CRITERIA
The soil profile generally consists of approximately 15 to 19.5 feet of overburden soils overlying
hard to very hard claystone. According to the International Building Code (IBC) and Chapter 20
of ASCE 7, the overburden soils encountered at the site generally classify as IBC Site Class D,
and the bedrock encountered classifies as Site Class C. Based on the soil and bedrock profile
encountered in our borings and the standard penetration testing from the field exploration, the
estimated weighted average of shear wave velocity in the upper 100 feet indicates that IBC Site
Class D should be used in the design. Based on the subsurface profile, site seismicity, and the
anticipated ground water conditions, liquefaction is not a design consideration.
SURFACE DRAINAGE
Proper surface drainage is very important for acceptable performance of the buildings during
construction and after the construction has been completed. Drainage recommendations
provided by local, state and national entities should be followed based on the intended use of the
structures. The following recommendations should be used as guidelines and changes should
be made only after consultation with the geotechnical engineer.
1. Excessive wetting or drying of the foundation and slab subgrades should be avoided
during construction.
2. Exterior backfill should be adjusted to near optimum moisture content (generally between
optimum and +3% of optimum unless indicated otherwise in the report) and compacted to
at least 95% of the ASTM D 698 (standard Proctor) maximum dry density. Backfill material
should meet the requirements stated in the “Site Grading” section of the report.
3. Care should be taken when compacting around the foundation walls and underground
structures to avoid damage to the structure. Hand compaction procedures, if necessary,
should be used to prevent lateral pressures from exceeding the design values.
4. The ground surface surrounding the exterior of the building should be sloped to drain away
from the foundation in all directions. We recommend a minimum slope of 12 inches in the
first 10 feet in unpaved areas. Site drainage beyond the 10-foot zone should be designed
to promote runoff and reduce infiltration. A minimum slope of 3 inches in the first 10 feet
is recommended in the paved areas. These slopes may be changed as required for
handicap access points in accordance with the Americans with Disabilities Act.
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5. The upper 1 to 2 feet of the backfill should be relatively impervious material compacted as
recommended above to limit infiltration of surface runoff.
6. Ponding of water should not be allowed in backfill material of in a zone within 10 feet of
the foundation walls, whichever is greater.
7. Roof downspouts and drains should discharge well beyond the limits of all backfill.
8. Landscaping which requires relatively heavy irrigation and lawn sprinkler heads should be
located at least 10 feet from foundation walls. Irrigation schemes are available which allow
placement of lightly irrigated landscape near foundation walls in moisture sensitive soil
areas. Drip irrigation heads with main lines located at least 10 feet from the foundation
walls are acceptable provided irrigation quantities are limited.
9. Plastic membranes should not be used to cover the ground surface adjacent to foundation
walls.
Surface Drainage Considerations: Proper surface drainage during and after construction is very
important to mitigate wetting of the subgrade soils. We recommend that landscape areas
adjacent to the building be provided with the maximum slope possible to promote good surface
drainage. A means of allowing water to readily leave the landscape areas, such as drain pans or
chases through a sidewalk, are recommended. All efforts possible should be made to ensure that
surface water on the site is allowed to sheet-flow to an off-site location via a storm sewer inlet or
water quality pond located as far from the buildings as possible.
UNDERDRAIN SYSTEM
We recommend that the foundations be protected by underdrain systems. Although groundwater
was not encountered in our explorations at depths near the proposed foundation elevation, it has
been our experience that local perched groundwater may develop during times of heavy
precipitation, snow melt, or seasonal irrigation. If an underdrain system is not constructed, below
grade walls (if any) should be designed for the full hydrostatic pressure conditions. We also
recommend a standby pump be available to discharge water that may develop in the below
ground areas.
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The drain system should consist of rigid drainpipe placed in the bottom of a trench or the exterior
side of the foundation and surrounded above the invert level with free-draining granular material.
Free-draining granular material used in the drain system should contain less than 5% passing the
No. 200 sieve, less than 35% passing the No. 4 sieve and have a maximum size of 2 inches. The
free-draining backfill should be hydraulically connected to the drainage zone on the exterior face
of the walls discussed above. The perimeter drains should be at least 4 inches in diameter. The
drain lines should be placed at least 1 foot below the floor level and graded to sumps at a minimum
slope of 1/2%. The granular underdrain system should be sloped to a sump or multiple sumps
where water can be removed by pumping or gravity drainage.
Standby pump capacity should be provided in the event of pump failure. We also believe an
overdesigned pump capacity is desirable in the event groundwater conditions change.
SITE GRADING
Temporary Excavations: For temporary excavations that occur during site grading, the natural
overburden soils classify as OSHA Type C soil. All excavations should be constructed in
accordance with the applicable OSHA regulations. If groundwater is encountered, the
geotechnical engineer should be notified so that additional recommendations can be provided, if
necessary.
Material Specifications: The following recommendations for material specifications are presented
for new fills on the project site. A geotechnical engineer should evaluate the suitability of all
proposed import fill material, if required, for the project prior to placement.
1. Structural Fill Beneath Buildings and Settlement-Sensitive Exterior Flatwork: Onsite
overburden soils, excluding bedrock, should be acceptable for use as structural fill.
Imported non-expansive structural fill, where required, should contain 30 to 80 percent
passing the No. 200 sieve, have a maximum liquid limit of 35 and a maximum plasticity
index of 12. Also, the swell potential of non-expansive fill materials when remolded to
95% of the standard Proctor (ASTM D 698) maximum dry density at the optimum moisture
content should be less than 1% when wetted under a 200 psf surcharge pressure.
2. Pavement Subgrade: The upper 2 feet of pavement subgrade fill should consist of the
moisture conditioned on-site overburden soils.
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If chemical stabilization is provided, we recommend the upper 2 feet of pavement
subgrade fill be a combination of moisture conditioned and compacted on-site overburden
soil and chemically stabilized soil. More specifically, the lower 12 inches of material
(between 12 inches and 24 inches below the subgrade elevation) should be properly
moisture conditioned and compacted on-site soils. The upper 12 inches (between the
subgrade elevation and 12 inches below subgrade elevation) should be chemically
conditioned and compacted.
3. Pipe Bedding Material: Pipe bedding material should be a free draining, coarse grained
sand and/or fine gravel.
4. Utility Trench Backfill: Material excavated from the utility trenches may be used for backfill
provided it does not contain unsuitable material or particles larger than 4 inches.
5. Material Suitability: It is the intent of the recommendations provided herein to use the on-
site soils as part of the structural fill material required on the site.
All fill material should be free of vegetation, brush, sod and other deleterious substances
and should not contain rocks, debris or lumps having a diameter of more than 4 inches.
Rocks, debris or lumps should be dispersed throughout the fill and "nesting" of these
materials should be avoided. The geotechnical engineer should evaluate the suitability of
proposed import fill materials prior to placement.
Fill Placement Specifications: We recommend the following compaction criteria be used on the
project:
1. Moisture Content: Fill materials should be compacted as outlined below with moisture
contents of +/- 2 percent for granular soils and between 1 and 5 percentage points above
optimum moisture for clayey soils. The on-site clay soils may become somewhat unstable
and deform under wheel loads if placed near the upper end of the recommended moisture
range.
2. Degree of Compaction: The following compaction criteria should be followed during
construction:
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AREA
MINIMUM PERCENTAGE OF
STANDARD PROCTOR MAXIMUM
DRY DENSITY (ASTM D 698)
Below PT Slab Foundations 98%
Fills Beneath Pavements and Interior/Exterior
Flatwork 95%
Utility Trenches 95%
Foundation Wall Backfill 95%
3. A representative of the geotechnical engineer should observe fill placement on a full time basis.
PAVEMENT DESIGN
A pavement section is a layered system designed to distribute concentrated traffic loads to the
subgrade. Performance of the pavement structure is directly related to the physical properties of
the subgrade soils and traffic loadings. Pavement design procedures are based on strength
properties of the subgrade and pavement materials assuming stable, uniform conditions. Soils
are represented for pavement design purposes by means of a soil support value for flexible
pavements and a modulus of subgrade reaction for rigid pavements. Both values are empirically
related to strength.
Subgrade Materials: Based on the results of the field and laboratory studies, the near surface
subgrade materials at the site classify as between A-1-a and A-7-6 soils with group indices
between 20 and 25 in accordance with the American Association of State Highway and
Transportation Officials (AASHTO) classification system. Soils classifying as A-1-a and A-1-b are
generally considered to provide good subgrade support, soils classifying as A-2-4 and A-4 are
generally considered to provide fair subgrade support and soils classifying as A-6 and A-7-6 are
generally considered to provide poor subgrade support A soil support value of 4,025 psi was
selected for flexible pavements. A modulus of subgrade reaction of 60 pci was selected for rigid
pavements
Design Traffic: Since anticipated traffic loading information was not available at the time of report
preparation, an equivalent 18-kip daily load application (EDLA) of 5 was assumed for automobile
and light truck traffic areas and an EDLA of 15 was assumed for areas that will be accessed by
multi-unit trucks as well as fire lanes elsewhere on the site.
Pavement Design: The following table presents the minimum pavement thickness
recommendations for this development.
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Paved Area
Full Depth
Asphalt
(inches)
Composite Section
Asphalt/ABC
(inches)
PCCP
(inches)
Light Duty 5.5 4.0 / 7.0 6.0
Heavy Duty 6.5 4.5 / 8.0 7.0
ABC – Aggregate Base Course
PCCP – Portland Cement Concrete Pavement
An alternative pavement section to the above sections would be to incorporate a chemically
stabilized subgrade into the pavement section. If a minimum of 12 inches of chemically stabilized
subgrade is provided below the pavement section, a full depth asphalt thickness of 3.5 inches
would be required in parking areas and 4 inches of asphalt would be required in the in the heavy
duty/fire lanes. Chemical stabilization should consist of blending the clayey subgrade materials
with cement or flyash such that the final product provides a minimum compressive strength of 160
psi at 5 days under moist curing conditions. The total pavement section would still consist of 2-
feet of processed subgrade materials. Specifically, the lower 12 inches of material (between 12
inches and 24 inches below the subgrade elevation) should be moisture conditioned and
compacted. The upper 12 inches (between the subgrade elevation and 12 inches below
subgrade elevation) would be chemically conditioned and compacted. There is no requirement
for base course material between the chemically stabilized subgrade and the asphalt; however,
providing a thin layer of base material would result in a bond breaking condition that would mitigate
cracks in the subgrade from propagating through the asphalt surface.
Truck loading dock areas and other areas where truck turning movements are concentrated
should be paved with 7.0 inches of Portland cement concrete. The concrete pavement should
contain sawed or formed joints to ¼ of the depth of the slab at a maximum distance of 12 to 15
feet on center.
The above PCCP thicknesses are presented as un-reinforced slabs. If heavy vehicular loading
will occur in certain areas, we recommend that dowels be provided at transverse and longitudinal
joints within the slabs located in the travel lanes of heavily loaded vehicles, loading docks and
areas where truck turning movements are likely to be concentrated. Additionally, curbs and/or
pans should be tied to the slabs. The dowels and tie bars will help minimize the risk for differential
movements between slabs to assist in more uniformly transferring axle loads to the
subgrade. The current CDOT “Standard Specifications for Road and Bridge Construction”
provides some guidance on dowel and tie bar placement, as well as in the Standard Plans: M&S
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Standards. The proper sealing and maintenance of joints to minimize the infiltration of surface
water is critical to the performance of PCCP, especially if dowels and tie bars are not installed.
Pavement Materials: The following are recommended material and placement requirements for
pavement construction for this project site. We recommend that properties and mix designs for all
materials proposed to be used for pavements be submitted for review to the geotechnical
engineer prior to placement.
1. Aggregate Base Course: Aggregate base course (ABC) used beneath hot mixed asphalt
(HMA) pavements should meet the material specifications for Class 6 ABC stated in the
current Colorado Department of Transportation (CDOT) “Standard Specifications for Road
and Bridge Construction”. The ABC should be placed and compacted as outlined in the
Site Grading section of this report.
2. Hot Mix Asphalt: Hot mix asphalt (HMA) materials and mix designs should meet the
applicable requirements indicated in the current CDOT “Standard Specifications for Road
and Bridge Construction”. We recommend that the HMA used for this project is designed
in accordance with the Super Pave gyratory mix design method. The mix should generally
meet Grading S or SX specifications with a Super Pave gyratory design revolution
(NDESIGN) of 75. The mix design for the HMA should use a performance grade PG 58-28
asphalt binder. Placement and compaction of HMA should follow current CDOT standards
and specifications.
3. Portland Cement Concrete: Portland cement concrete pavement (PCCP) should meet
Class P specifications and requirements in the current CDOT “Standard Specifications for
Road and Bridge Construction”. Rigid PCCP is more sensitive to distress due to
movement resulting from settlement or heave of the underlying base layer and/or
subgrade than flexible asphalt pavements.
Subgrade Preparation: The pavement subgrade within 2 feet of the subgrade elevation should
be removed and replaced with properly moisture conditioned and compacted fill as outlined in the
“Site Grading” section of this report. Prior to placing the pavement section, the entire subgrade
area should be thoroughly plowed and well mixed to a minimum depth of 12 inches, adjusted to
a moisture content within 2 percentage points of optimum and compacted to 95% of the standard
Proctor maximum dry density.
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Pavement design procedures assume a stable subgrade. The pavement subgrade should be
proof-rolled with a heavily loaded pneumatic-tired vehicle with a tire pressure of at least 100 psi
capable of applying a minimum load of 18-kips per axle. Areas which deform excessively under
heavy wheel loads are not stable and should be removed and replaced to achieve a stable
subgrade prior to paving. Areas of existing fill may also require deeper removal and replacement
if they are unstable.
Drainage: The collection and diversion of surface drainage away from paved areas is extremely
important to the satisfactory performance of pavement. Drainage design should provide for the
removal of water from paved areas and prevent the wetting of the subgrade soils.
It is critical to the performance of the structure and surrounding pavement that the pavement
surfaces be properly maintained. Proper maintenance includes sealing of cracks that appear in
the pavement surface. More aggressive cleaning and sealing techniques may be required if
larger cracks develop.
DESIGN AND CONSTRUCTION SUPPORT SERVICES
Kumar & Associates, Inc. should be retained to review the project plans and specifications for
conformance with the recommendations provided in our report. We are also available to assist
the design team in preparing specifications for geotechnical aspects of the project, and performing
additional studies if necessary to accommodate possible changes in the proposed construction.
We recommend that Kumar & Associates, Inc. be retained to provide construction observation
and testing services to document that the intent of this report and the requirements of the plans
and specifications are being followed during construction. This will allow us to identify possible
variations in subsurface conditions from those encountered during this study and to allow us to
re-evaluate our recommendations, if needed. We will not be responsible for implementation of
the recommendations presented in this report by others, if we are not retained to provide
construction observation and testing services.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
practices in this area for exclusive use by the client for design purposes. The conclusions and
recommendations submitted in this report are based upon the data obtained from the exploratory
borings at the locations indicated on Fig. 1, and the proposed type of construction. This report
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may not reflect subsurface variations that occur between the exploratory borings, and the nature
and extent of variations across the site may not become evident until “Site Grading” and
excavations are performed. If during construction, fill, soil, rock or water conditions appear to be
different from those described herein, Kumar & Associates, Inc. should be advised at once so that
a re-evaluation of the recommendations presented in this report can be made. Kumar &
Associates, Inc. is not responsible for liability associated with interpretation of subsurface data by
others.
Swelling soils occur on this site. Such soils are stable at their natural moisture content but will
undergo high volume changes with changes in moisture content. The recommendations
presented in this report are based on current theories and experience of our engineers on the
behavior of swelling soil in this area. The owner should be aware that there is a risk in constructing
a building in an expansive soil area. Following the recommendations given by a geotechnical
engineer, careful construction practice and prudent maintenance by the owner can, however,
decrease the risk of foundation movement due to expansive soils.
JAH/mr
Rev. by: JLB
cc: File
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Project No.:22-3-168
Project Name: Watermark Apartments at Lemay
Date Sampled: June 6, 16, 21, 23, and 30, 2022
Date Received: June 6, 16, 21, 23, and 30, 2022
Boring/Test Pit Depth (Feet)
Gravel
(%)Sand (%)
Liquid
Limit (%)
Plasticity
Limit (%)
1 9 6/7/22 6.0 59 36 5 NV NP A-1-a (1)Poorly Graded Gravel with Silt and Sand (GP-GM)
2 1 6/8/22 16.0 101.2 0 22 78 41 15 0.02 A-7-6 (12)Fill: Lean Clay with Sand (CL)
3 4 6/7/22 9.7 123.1 27 27 46 30 15 A-6 (3)Clayey Sand with Gravel (SC)
3 19 6/8/22 14.1 111.6 5 26 69 36 14 Claystone Bedrock
4 1 6/7/22 8.0 112.7 14 40 46 32 18 A-6 (4)Fill: Clayey Sand (SC)
5 4 6/21/22 8.7 113.1 6 79 15 NV NP A-1-a (0)Silty Sand (SM)
6 4 6/7/22 2.0 53 39 8 NV NP A-1-a (1)Poorly Graded Gravel with Silt and Sand (GP-GM)
7 4 6/21/22 22.5 99.3 5 18 77 39 20 A-6 (14)Lean Clay with Sand (CL)
8 4 6/22/22 16.4 109.6 82 41 21 A-7-6 (17)Lean Clay with Sand (CL)
9 1-3 7/1/22 18.8 0 36 64 31 13 A-6 (6)Sandy Lean Clay (CL)
10 1-3 7/1/22 11.8 8 48 44 24 9 A-4 (1)Clayey Sand (SC)
11 1-3 7/1/22 19.3 87 35 16 A-6 (13)Lean Clay with Sand (CL)
12 1 6/27/22 16.3 106.9 78 38 19 A-6 (14)Lean Clay with Sand (CL)
13 9-14 6/7/22 3.4 68 25 7 NV NP A-1-a (1)Poorly Graded Gravel with Silt and Sand (GP-GM)
14 1 7/1/22 15.6 89 41 18 A-7-6 (17)Lean Clay (CL)
15 4 7/1/22 1.9 54 42 4 NV NP A-1-a (1)Poorly Graded Gravel with Sand (GP)
16 1 6/27/22 9.2 110.8 6 52 42 25 8 0.78 A-4 (0)Clayey Sand (SC)
17 9 6/27/22 9.3 129.2 34 55 11 NV NP A-1-a (0)Poorly Graded Sand with Silt and Gravel (SP-SM)
18 1 6/27/22 1.8 47 40 13 NV NP A-1-a (0)Silty Gravel with Sand (GM)
19 4 6/27/22 5.2 96.0 1 88 11 NV NP A-1-a (0)Poorly Graded Sand with Silt (SP-SM)
20 1 6/27/22 6.8 105.3 12 33 55 26 7 A-4 (1)Fill: Sandy Silty Clay (CL-ML)
21 14 6/27/22 8.5 124.0 25 72 3 NV NP A-1-a (1)Poorly Graded Sand with Gravel (SP)
22 4 6/27/22 10.0 5 76 19 NV NP A-1-b (0)Silty Sand (SM)
P-1 1 7/1/22 13.1 25 34 17 A-2-6 (0)Clayey Sand (SC)
P-2 1 6/27/22 8.4 108.0 17 22 51 27 10 A-4 (2)Sandy Lean Clay (CL)
P-3 1 6/8/22 6.8 116.6 1 22 77 40 16 A-6 (12)Fill: Lean Clay with Sand (CL)
P-4 1 6/27/22 9.8 108.7 1 47 52 NV NP A-4 (0)Fill: Sandy Silt (ML)
P-5 4 6/27/22 22.3 101.5 68 30 14 A-6 (7)Fill: Sandy Lean Clay (CL)
P-6 1 6/27/22 9.5 111.1 16 28 56 33 17 A-6 (6)Sandy Lean Clay with Gravel (CL)
P-7 1 7/1/22 14.3 73 37 18 A-6 (12)Lean Clay with Sand (CL)
P-8 4 6/27/22 7.4 89.9 3 88 9 NV NP A-1-a (1)Poorly Graded Sand with Silt (SP-SM)
P-9 14 6/27/22 16.0 111.6 7 NV NP A-1-a (1)Poorly Graded Sand with Silt (SP-SM)
D-1 1 6/27/22 7.2 109.1 19 48 33 NV NP A-2-4 (0)Silty Sand with Gravel (SM)
D-2 1 6/27/22 8.0 101.1 61 26 11 A-6 (4)Sandy Lean Clay (CL)
1-4 1-5 6/7/22 16.9*108.1*8 28 64 35 17 A-6 (9)Sandy Lean Clay (CL)
Table I
Sample Location Gradation Atterberg Limits
Date
Tested
Natural
Moisture
Content
(%)
Natural
Dry
Density
(pcf)
Percent
Passing
No. 200
Sieve
* - Optimum moisture content and maximum dry density as determined by standard Proctor (ASTM D 698)
Water
Soluble
Sulfates
(%)
AASHTO
Classification
(Group Index)Soil or Bedrock Type
Summary of Laboratory Test Results
APPENDIX A
TEST PIT PHOTOGRAPHS
Test Pit-B-9
Test Pit-B-10
Test Pit-B-11
Test Pit-B-14
Test Pit-P-7