HomeMy WebLinkAboutSUN COMMUNITIES - THE FOOTHILLS - PDP210001 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT400 North Link Lane | Fort Collins, Colorado 80524
Telephone: 970-206-9455 Fax: 970-206-9441
GEOLOGIC AND PRELIMINARY
GEOTECHNICAL INVESTIGATION
THE FOOTHILLS
FORT COLLINS, COLORADO
Prepared For:
SUN ACQ LLC
2777 Franklin Road
Southfield, MI 48034
Attention: Chris Sveum
Project No. FC09654-115
January 4, 2021
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TABLE OF CONTENTS
SCOPE ....................................................................................................................... 1
SUMMARY OF CONCLUSIONS ............................................................................... 1
SITE DESCRIPTION ................................................................................................. 2
PROPOSED DEVELOPMENT .................................................................................. 2
SITE GEOLOGY ........................................................................................................ 3
GEOLOGIC HAZARDS ............................................................................................. 3
Expansive Soils and Bedrock ................................................................................ 4
Hard Bedrock and Difficult Excavation .................................................................. 4
Groundwater ........................................................................................................... 4
Frost Heave ............................................................................................................ 5
Seismicity ............................................................................................................... 5
Radioactivity ........................................................................................................... 6
FIELD AND LABORATORY INVESTIGATIONS ...................................................... 7
SUBSURFACE CONDITIONS .................................................................................. 7
Natural Sandy Clay ................................................................................................ 8
Bedrock .................................................................................................................. 8
Groundwater ........................................................................................................... 9
DEVELOPMENT RECOMMENDATIONS ................................................................. 9
Over-Excavation ..................................................................................................... 9
Site Grading ......................................................................................................... 10
Permanent Cut and Fill Slopes ............................................................................ 11
Utility Construction ............................................................................................... 11
Underdrain System .............................................................................................. 12
PRELIMINARY PAVEMENT RECOMMENDATIONS ............................................ 13
Subgrade Preparation .......................................................................................... 13
Preliminary Pavement Thickness Design ............................................................ 13
PRELIMINARY RECOMMENDATIONS FOR STRUCTURES ............................... 14
Foundations .......................................................................................................... 15
Slabs-on-Grade and Basement Floor Construction ............................................ 15
Below-Grade Construction ................................................................................... 16
Surface Drainage ................................................................................................. 16
General Design Considerations ........................................................................... 17
WATER-SOLUBLE SULFATES .............................................................................. 17
RECOMMENDED FUTURE INVESTIGATIONS .................................................... 19
LIMITATIONS .......................................................................................................... 19
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TABLE OF CONTENTS cont’d
FIGURE 1 – LOCATIONS OF EXPLORATORY BORINGS
FIGURE 2 – DEPTH TO BEDROCK AT BORING LOCATIONS
FIGURES 3 & 4 – SUMMARY LOGS OF EXPLORATORY BORINGS
APPENDIX A – LABORATORY TEST RESULTS
APPENDIX B – GUIDELINE SITE GRADING SPECIFICATIONS
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SCOPE
This report presents the results of our Geologic and Preliminary Geotechnical
Investigation. The purpose of our investigation was to identify geologic hazards that
may exist at the site and to evaluate the subsurface conditions to assist in planning
and budgeting for the proposed development. The report includes descriptions of
site geology, our analysis of the impact of geologic conditions on site development,
a description of subsoil, bedrock and groundwater conditions found in our
exploratory borings, and discussions of site development as influenced by
geotechnical considerations. The scope was described in our Service Agreement
(CTL Proposal No. DN-19-0439R) revised October 28, 2020.
This report was prepared based upon our understanding of the development
plans. The recommendations are considered preliminary and can be used as
guidelines for further planning of development and design of grading. We should
review final development and grading plans to determine if additional investigation is
merited, or if we need to revise our recommendations. Additional investigations will
be required to design building foundations and pavements. A summary of our
findings and recommendations is presented below. More detailed discussions of the
data, analysis and recommendations are presented in the report.
SUMMARY OF CONCLUSIONS
1. The site contains geologic hazards that should be mitigated during
planning and development. No geologic or geotechnical conditions
were identified which would preclude development of this site.
Shallow groundwater, expansive soils and bedrock, as well as
regional issues of seismicity and radioactivity are the primary geologic
concerns pertaining to the development of the site.
2. The subsurface conditions encountered in our borings were variable
across the site. In general, the soils and bedrock encountered in our
borings consisted of 1 to 14 feet of sandy clay over weathered and
competent interbedded claystone and sandstone bedrock to the
maximum depths explored. Groundwater was encountered at depths
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ranging from ½-foot to 21 feet below the existing ground surface.
Groundwater levels will likely affect planned development in portions
of this site.
3. Soils exhibited low to moderate swell potential throughout the site.
The weathered and competent bedrock was generally more expansive
than overburden soils encountered at this site. The bedrock is judged
predominately to be moderately to highly expansive. We anticipate
footings can be used over approximately 30 percent of the site. The
remainder of the site will likely require drilled piers or footings on an
over-excavation.
4. Pavement subgrade mitigation for swell is likely over the majority of
the site. Mitigation may consist of moisture and/or chemical treatment
of the subgrade soils. A minimum of 12 inches of chemical treatment
(fly ash or lime) should be expected. Asphaltic pavement sections on
the order of 4 inches of hot-mix asphalt (HMA) over 6 inches of
aggregate base course (ABC) for streets, parking areas, access
drives are anticipated for preliminary planning purposes. Higher
volume pavement will likely require thicker HMA sections, on the order
of 5 to 6½ inches.
SITE DESCRIPTION
The site is located south of Trilby Road and East of US-287 (College
Avenue), on the south side of Fort Collins, Colorado. The site is generally in a
plains area and is primarily vegetated with grasses and weeds. At the time of our
exploration the site was undeveloped. The 52+/- acre parcel contains a drainage
flowing west to east from north of boring TH-1 to south of TH-4. The majority of the
site north of the drainage slopes gently to the south, and the majority of the site
south of the drainage slopes gently to the north. A lake was observed approximately
1,000 feet southwest of the subject site at the nearest point. An existing residence
and associated outbuildings were observed on the property, between boring TH-6
and College Avenue. Several existing subdivisions surround the site.
PROPOSED DEVELOPMENT
We understand the parcel is planned for development of a manufactured
housing development. We assume the residences will be 1 to 2-story, wood frame
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structures, with basements or crawl spaces.
SITE GEOLOGY
The geology of the site was investigated through review of mapping by R.B.
Colton (Geologic Map of the Boulder-Fort Collins-Greeley Area, Colorado, 1978).
Geology was further evaluated through review of conditions found in exploratory
borings, and our experience in the area.
According to the referenced mapping, the site is underlain predominately by
the upper unit of the Pierre Shale, which consists primarily of silty and sandy shales.
The materials encountered in our borings were in general agreeance with the
referenced mapping. Overburden soils at the site are of eolian origin, alluvial origin,
or some combination of the two.
GEOLOGIC HAZARDS
Our investigation identified several geologic hazards that must be considered
during the planning and development phases of this project. None of the geologic
hazards identified will preclude development of the property. Development plans
are preliminary. No economically valuable extractable minerals are known to occur
in the immediate area of the site. Therefore, the risk of ground subsidence due to
past mining appears nil.
Planning should consider the geologic hazards discussed below. The
hazards require mitigation which could include avoidance, non-conflicting use or
engineered design and construction during site development. Geologic hazards at
the site that need to be addressed include expansive soils and bedrock, difficult
bedrock excavation, shallow groundwater, frost heave and regional issues of
seismicity and radioactivity. The following sections discuss each of these geologic
hazards and associated development concerns. Mitigation concepts are discussed
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below and in the DEVELOPMENT RECOMMENDATIONS section of the report.
Expansive Soils and Bedrock
The soils and bedrock at this site include moderately to very highly expansive
weathered and competent bedrock. Approximately 70 percent of the site is judged
to be moderate or greater swell risk. Problems associated with the existence of
expansive materials are typically mitigated through currently utilized foundation and
floor slab techniques. Individual soils and foundation investigations conducted for
specific sites should address procedures for mitigating problems associated with
expansive soils and bedrock.
Hard Bedrock and Difficult Excavation
The competent bedrock is hard and may contain very hard, cemented lenses
and/or beds. These materials were not encountered in our borings but may be
present within the bedrock at the site and encountered during construction.
Depending on the depth to bedrock beneath the site, it may be encountered during
grading or utility trenching. The hard bedrock is likely to be encountered in
excavations that extend through the surficial soils at the site. The hardness of the
bedrock may make pre-ripping of overlot borrow areas appropriate to expedite
excavation. During utility installation, heavy-duty trackhoes with rock buckets and
rock teeth may be needed. Depending upon the excavation procedures, some
oversize material, not suitable for reuse in trench backfill, may be generated.
Groundwater
Groundwater was encountered in four borings during drilling at depths of 10
to 24 feet. When checked several days later, groundwater was encountered at
depths of ½-foot to 21 feet in six borings. During secondary groundwater
measurements, borings TH-5 and TH-9 did not contain water to the maximum drilled
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depth, whereas borings TH-4 and TH-6 could not be located or measured.
Groundwater may rise due to site development. Perched water conditions may
develop where residential construction and irrigation occur in shallow bedrock areas.
The depth to groundwater should be evaluated during Geotechnical
Investigations at the site. In general, grading should be designed to raise the
elevations in areas of shallow groundwater. Construction of underdrain systems with
the sanitary sewer trenches is a commonly employed method to mitigate the
accumulation of shallow groundwater after construction. A minimum separation of 5
feet is desirable between the groundwater elevations and the lowest elevation of any
below-grade structure.
Frost Heave
Our borings indicate fairly shallow groundwater is present and the overburden
soils at the site consist of materials that are susceptible to frost heave. Based on
our experience and local construction practice in the area, the minimum depth of
cover for frost protection is 30 inches. We recommend foundations have a minimum
cover of 30 inches. If the foundations are constructed with the appropriate frost
protection, we do not believe frost heave will affect the proposed structures. Slabs-
on-grade may experience some movement due to frost heave. If the buildings are
insulated or heated, the potential for slab movement due to frost heave is minimal.
If the buildings are not insulated or heated, slabs-on-grade should be constructed
with frost protection.
Seismicity
This area, like most of central Colorado, is subject to a low degree of seismic
risk. No indications of recent movements of any of the faults in the Larimer County
area have been reported in the available geologic literature. As in most areas of
recognized low seismicity, the record of the past earthquake activity in Colorado is
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somewhat incomplete.
Based on the subsurface conditions encountered in our borings and our
understanding of the geology, the site classifies as a Seismic Site Class C or D
(2018 International Building Code). Only minor damage to relatively new, properly
designed and built buildings would be expected. Wind loads, not seismic
considerations, typically govern dynamic structural design in this area. If it is
determined that seismic site class is critical to the design, CTL|Thompson can
provide a proposal for services to determine the site class based on a geophysical
study.
Radioactivity
It is normal in the Front Range of Colorado and nearby eastern plains to
measure radon gas in poorly ventilated spaces in contact with soil or bedrock.
Radon 222 gas is considered a health hazard and is one of several radioactive
products in the chain of the natural decay of uranium into stable lead. Radioactive
nuclides are common in the soils and sedimentary rocks underlying the subject site.
Because these sources exist on most sites, there is potential for radon gas
accumulation in poorly ventilated spaces. The amount of soil gas that can
accumulate is a function of many factors, including the radio-nuclide activity of the
soil and bedrock, construction methods and materials, pathways for soil gas and
existence of poorly-ventilated accumulation areas. It is difficult to predict the
concentration of radon gas in finished construction.
During our investigation, we did not detect any radiation levels above normal
background levels for the area. We recommend testing to evaluate radon levels
after construction is completed. If required, typical mitigation methods for residential
construction may consist of sealing soil gas entry areas and periodic ventilation of
below-grade spaces and perimeter drain systems. It is relatively economical to
provide for ventilation of perimeter drain systems or underslab gravel layers at the
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time of construction, compared to retrofitting a structure after construction. Radon
rarely accumulates to significant levels in above-grade, heated and ventilated
spaces.
FIELD AND LABORATORY INVESTIGATIONS
Subsurface conditions were investigated by drilling ten exploratory borings at
the approximate locations shown on Figure 1. The borings were drilled using a
truck-mounted drill rig and with 4-inch diameter, continuous-flight auger. Our field
representative observed drilling, logged the soils and bedrock encountered in the
borings and obtained samples. Summary logs of the soils and bedrock found in the
borings and field penetration resistance values are presented on Figure 2.
Samples of soil and bedrock were obtained during drilling by driving a
modified California-type sampler (2.5 inch O.D.) into the subsoils and bedrock using
a 140-pound hammer falling 30 inches. Samples recovered from the test holes
were returned to our laboratory and visually classified by the geotechnical engineer.
Laboratory testing included determination of moisture content and dry density,
swell-consolidation characteristics, Atterberg limits, particle-size analysis and water-
soluble sulfate content. Laboratory test results are presented in Appendix A.
SUBSURFACE CONDITIONS
Subsurface conditions encountered in the borings included approximately 1
to 14 feet of sandy clay, underlain by weathered and/or competent interbedded
claystone and sandstone bedrock to the depths explored. Table 1 provides a
summary of the swell-consolidation testing. A more detailed description of the
subsurface conditions is presented below and in our boring logs and laboratory
testing. A measured depth to bedrock map is presented on Figure 2.
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TABLE 1: Summary of Swell-Consolidation Testing by Soil Type
Soil Type Compression Range of Measured Swell (%)*
0 to <2 2 to <4 4 to <6 >6
Number of Samples and Percent
Sandy Clay 1 3 1 0 0
20% 60% 20% 0% 0%
Weathered Bedrock 1 3 2 1 2
11% 33% 22% 11% 22%
Bedrock 0 5 6 2 0
0% 38% 46% 15% 0%
Overall Sample
Number 2 11 9 3 2
Overall Sample
Percent 7% 41% 33% 11% 7%
Natural Sandy Clay
The soils encountered on this site included sandy clay. The thickness of soil
was variable across the site, ranging from about 1 to 14 feet. Field penetration
resistance tests indicated the sandy clay was medium stiff to very stiff. Particle size
analysis from two samples tested indicated 81 to 87 percent silt and/or clay content.
One Atterberg test on the material resulted in a liquid limit of 53 and a plasticity
index of 31, which classifies as a highly plastic clay (CH) in accordance with United
Soil Classification System (USCS).
Bedrock
Bedrock was encountered in all the borings. Bedrock was encountered 1 to
14 feet below the existing ground surface, and is generally deepest near borings
TH-1, TH-3, and TH-4. The bedrock encountered was predominately interbedded
claystone and sandstone. The weathered bedrock was firm to medium hard. The
competent bedrock was hard to very hard. One sample of the bedrock indicated a
liquid limit of 44, a plasticity index of 25 percent and 78 percent silt and clay fines
(passing the No. 200 Sieve).
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Groundwater
Groundwater was encountered in four borings during drilling at depths of 10
to 24 feet. When checked several days later, groundwater was encountered at
depths of ½-foot to 21 feet in six borings. During secondary groundwater
measurements, borings TH-5 and TH-9 did not contain water to the maximum drilled
depth, whereas borings TH-4 and TH-6 could not be located or measured.
Groundwater may rise due to site development. Perched water conditions may
develop where residential construction and irrigation occur in shallow bedrock areas.
Groundwater levels will likely affect planned development at this site.
DEVELOPMENT RECOMMENDATIONS
Over-Excavation
Over-excavation can be considered at this site to potentially allow for a
shallow foundation and slab-on-grade basement floors in areas of moderate to high
swelling soils. Over-excavation consists of removal of expansive soils/bedrock and
reworking the material as fill compacted in a controlled manner. This will reduce
the potential heave of improvements. Excavation observations and density testing
are commonly recommended for sites such as this in addition to a design level
geotechnical investigation.
When plans are available, we are available to consult with your
design/construction team as they develop a sub-excavation grading plan. A detailed
plan is recommended to incorporate details of building locations and elevations, and
also allow documentation by surveyors and be as explicit and efficient as possible
for the contractor.
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Site Grading
At the time of this investigation, site grading plans were not available for
review in conjunction with this subsurface exploration program. It is important that
deep fills (if planned) be constructed as far in advance of surface construction as
possible. It is our experience that fill compacted in accordance with the compaction
recommendations in this report may settle about 1 percent of its height under its
own weight. Most of this settlement usually occurs during and soon after
construction. Some additional settlement is possible after development and
landscape irrigation increases soil moisture. We recommend delaying the
construction of buildings underlain by deep fills as long as possible to allow for this
settlement to occur. Delaying construction of structures up to one year where
located on deep fills is recommended.
The existing on-site soils are suitable for re-use as fill material provided
debris or deleterious organic materials are removed. Prior to fill placement, all trash
and debris should be removed from fill areas and properly disposed. Import fill
should generally have similar or better engineering properties as the onsite
materials and should be approved by CTL. The ground surface in areas to be filled
should be stripped of vegetation, topsoil and other deleterious materials, scarified to
a depth of at least 8 inches, moisture conditioned and compacted as recommended
below. The depth of any topsoil is not anticipated to be more than 2 to 3 inches in
most areas.
Site grading fill should be placed in thin, loose lifts, moisture conditioned and
compacted. In areas of deep fill, we recommend higher compaction criteria to help
reduce settlement of the fill. Compaction and moisture requirements are presented
in Appendix B. The placement and compaction of fill should be observed and
density tested during construction. Guideline site grading specifications are
presented in Appendix B.
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Permanent Cut and Fill Slopes
We recommend permanent cut and fill slopes be designed with a maximum
inclination of 3:1 (horizontal to vertical). Where fills will be placed on slopes
exceeding 20 percent (5:1) the slope should be benched. Structures should be
setback from the top or bottom of cut and fill slopes. If site constraints (property
boundaries and streets) do not permit construction with recommended slopes, we
should be contacted to evaluate the subsurface soils and steeper slopes.
Utility Construction
We believe excavations for utility installation in the overburden soils can be
performed with conventional heavy-duty trenchers or large backhoes. The
excavation contractor should anticipate difficult bedrock excavation techniques may
be merited depending on the conditions exposed at the site. Groundwater will likely
be encountered in excavations over portions of the site. If groundwater is
encountered during construction, dewatering may be accomplished by sloping
excavations to occasional sumps where water can be removed by pumping.
Utility trenches should be sloped or shored to meet local, State and federal
safety regulations. Based on our investigation, we believe the clay and weathered
bedrock classify as Type B and the competent bedrock classifies as Type A soil
based on OSHA standards. Excavation slopes specified by OSHA are dependent
upon soil types and groundwater conditions encountered. Seepage and
groundwater conditions in trenches may downgrade the soil type. Contractors
should identify the soils encountered in the excavation and refer to OSHA standards
to determine appropriate slopes. Excavations deeper than 20 feet should be
designed by a professional engineer.
The width of the top of an excavation may be limited in some areas. Bracing
or “trench box” construction may be necessary. Bracing systems include sheet
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piling, braced sheeting and others. Lateral loads on bracing depend on the depth of
excavation, slope of excavation above the bracing, surface loads, hydrostatic
pressures, and allowable movement. For trench boxes and bracing allowed to move
enough to mobilize the strength of the soils, with associated cracking of the ground
surface, the “active” earth pressure conditions are appropriate for design. If
movement is not tolerable, the “at rest” earth pressures are appropriate. We
suggest an equivalent fluid density of 40 pcf for the “active” earth pressure condition
and 55 pcf for the “at rest” earth pressure condition, assuming level backfill. These
pressures do not include allowances for surcharge loading or for hydrostatic
conditions. We are available to assist further with bracing design if desired.
Water and sewer lines are usually constructed beneath paved roads.
Compaction of trench backfill can have significant effect on the life and serviceability
of pavements. We believe trench backfill should be placed in thin, loose lifts, and
moisture conditioned to between optimum and 3 percent above optimum content for
clay soils and within 2 percent of optimum moisture content for sand. Trench backfill
should be compacted to at least 95 percent of maximum dry density (ASTM D 698).
The placement and compaction of fill and backfill should be observed and tested by
our firm during construction. If deep excavations are necessary for planned utilities,
the compaction requirements provided in Appendix B should be considered.
Underdrain System
The use of underdrain systems below sewer mains and services is a common
method to control groundwater in response to development. We recommend an
underdrain system be incorporated into sanitary sewer and sewer collection systems
where shallow groundwater exists. Underdrains should also be installed below
sewer service lines to each residence planned in this area with connection to
residence foundation drains.
The underdrain should consist of free-draining gravel surrounding a rigid PVC
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pipe. The pipe should be sized for anticipated flow. Guidelines for underdrain sizing
are shown in Table A. The line should consist of smooth, perforated or slotted rigid
PVC pipe laid at a grade of at least 0.5 percent. A gravel cross-section of at least 2
square feet should be placed around the pipe. A positive cutoff collar (concrete)
should be constructed around the sewer pipe and underdrain pipe immediately
downstream of the point the underdrain pipe leaves the sewer trench. Solid pipe
should be used down gradient of this collar to the daylight point. Clean-outs should
be provided along the system. The entity responsible for maintenance should be
identified and guidelines developed for maintenance. The underdrain should be
designed to discharge to a gravity outfall provided with a permanent concrete
headwall and trash rack, or to a storm sewer with a check valve to control water
backing up into the underdrain system. The underdrain system should be designed
by a professional engineer that is licensed in the State of Colorado.
PRELIMINARY PAVEMENT RECOMMENDATIONS
Subgrade Preparation
Based on the borings, the near surface soils on this site will consist of sandy
clay or weathered bedrock. These materials will range from moderately to highly
plastic and will provide relatively poor subgrade support below the pavements. Lime
or fly ash stabilization of these soils will improve their subgrade support
characteristics, in addition to enhancing the workability of the clays and reducing
water infiltration into the underlying subgrade and the potential movements under
the pavements.
Preliminary Pavement Thickness Design
Preliminary guidelines for pavement systems for this site are provided. Final
pavement sections should be determined based a design level geotechnical
investigation and anticipated frequency of load applications on the pavement during
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the desired design life. Flexible hot mix asphalt (HMA) over aggregate base course
(ABC) or rigid Portland cement concrete (PCC) pavements can be used at this site
for automobile and light truck traffic use. Rigid pavements are recommended in any
areas subject to heavy truck traffic. We defer to the 2016 Larimer County Urban
Street Standards for minimum pavement requirements. Minimum pavement section
thicknesses are provided in Table 2.
Table 2: Minimum Pavement Thickness
Roadway
Designation
Hot Mix Asphalt
(HMA) +
Aggregate Base
Course (ABC)
Full Depth
Asphalt
Portland Cement
Concrete (PCC)
Local 4.0” HMA +
6.0” ABC 6.0” 6”
Residential
Cul-de-sac
5.4” HMA +
6.0” ABC 6.5” 6”
Collector Minor 5.5” HMA +
7.0” ABC Not Allowed 6”
Collector Major 6.5” HMA +
9.0” ABC Not Allowed 6”
Portland cement concrete (PCC) pavement is recommended in areas subject
to any heavy truck traffic such as garbage pickup and/or dumpster trucks and any
heavy delivery trucks. Any areas subject to frequent heavy trucks should be
designed based on frequency and wheel loads. PCC pavements in this area are
typically reinforced due to the underlying active clays. Properly designed control
joints and other joints systems are required to control cracking and allow pavement
movement.
PRELIMINARY RECOMMENDATIONS FOR STRUCTURES
The property is currently planned for residential construction. Our field and
laboratory data indicate the soil and bedrock conditions vary across the site. The
following discussions are preliminary and are not intended for design or
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construction. After grading is completed, a detailed soils and foundation
investigation should be performed.
Due to the preliminary nature of this project, subdivision organization or site
grading plans have not been prepared, and therefore not available for review in
conjunction with this subsurface exploration program. Recommendations provided
here are general and for planning purposes only.
Foundations
Soils exhibited low to moderate swell potential throughout the site. The
weathered and competent bedrock was generally more expansive than overburden
soils encountered at this site. The bedrock is judged predominately to be moderately
to highly expansive. We anticipate footings can be used over approximately 30
percent of the site. The remainder of the site will likely require drilled piers or
footings placed on an over-excavation.
Slabs-on-Grade and Basement Floor Construction
The use of slab-on-grade floors for unfinished basements should be limited to
areas where soils within the depth likely to influence floor performance are
consolidating to low swelling granular soils or clay. We believe approximately 70
percent of the site will be rated with moderate to high risk of poor slab performance
and would required a structural floor for the basement and the remainder will allow
for slab-on-grade basement floors. Over-excavation can be considered to allow for
slab-on-grade basement floors in area with moderate to high risk. Structurally
supported floor systems should be planned in all non-basement finished living
areas. Slab performance risk should be more thoroughly defined during the design
level soils and foundation investigation.
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Below-Grade Construction
Groundwater was encountered during this investigation. With long-term
development and associated landscaping, a “perched” water table may develop on
the bedrock surface or on relatively impermeable soils and bedrock layers. To
reduce the risk of hydrostatic pressure developing on foundation walls, foundation
drains will be necessary around all below-grade areas. We suggest foundation
drains be tied to the sewer underdrain system. They may also discharge to sumps
where water can be removed by pumping. In our opinion, underdrain systems offer
more comprehensive control of groundwater and better mitigate impacts of
groundwater and swelling soils on foundations, slabs and pavements. Foundation
walls and grade beams should be designed to withstand lateral earth pressures.
The design pressure should be established during design-level soils investigations.
Surface Drainage
The performance of foundations will be influenced by surface drainage. The
ground surface around proposed residences should be shaped to provide runoff of
surface water away from the structure and off of pavements. We generally
recommend slopes of at least 12 inches in the first 10 feet where practical in the
landscaping areas surrounding residences. There are practical limitations on
achieving these slopes. Irrigation should be minimized to control wetting. Roof
downspouts should discharge beyond the limits of backfill. Water should not be
allowed to pond on or adjacent to pavements. Proper control of surface runoff is
also important to limit the erosion of surface soils. Sheet flow should not be directed
over unprotected slopes. Water should not be allowed to pond at the crest of
slopes. Permanent slopes should be re-vegetated to reduce erosion.
Water can follow poorly compacted fill behind curb and gutter and in utility
trenches. This water can soften fill and undermine the performance of the roadways,
flatwork and foundations. We recommend compactive effort be used in placement
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of all fill.
General Design Considerations
Exterior sidewalks and pavements supported above the on site clays are
subject to post construction movement. Flat grades should be avoided to prevent
possible ponding, particularly next to the building due to soil movement. Positive
grades away from the buildings should be used for sidewalks and flatwork around
the perimeter of the buildings in order to reduce the possibility of lifting of this
flatwork, resulting in ponding next to the structures. Where movement of the
flatwork is objectionable, procedures recommended for on-grade floor slabs should
be considered.
Joints next to buildings should be thoroughly sealed to prevent the infiltration
of surface water. Where concrete pavement is used, joints should also be sealed to
reduce the infiltration of water. Since some post construction movement of
pavement and flatwork may occur, joints around the buildings should be periodically
observed and resealed where necessary.
Roof drains should be discharged well away from the structures, preferably
by closed pipe systems. Where roof drains are allowed to discharge on concrete
flatwork or pavement areas next to the structures, care should be taken to insure the
area is as water tight as practical to eliminate the infiltration of this water next to the
buildings.
WATER-SOLUBLE SULFATES
Concrete that comes into contact with soils can be subject to sulfate attack.
We measured water-soluble sulfate concentrations in six samples from this site.
Concentrations were measured from below measurable limits to 0.39 percent, with
two samples having sulfate concentrations greater than 0.2 percent and four
SUN ACQ LLC 18
THE FOOTHILLS
CTL | T PROJECT NO. FC09654-115
samples with concentrations less than 0.2 percent. Water-soluble sulfate
concentrations between 0.2 and 2 percent indicate Class 2 sulfate exposure,
according to the American Concrete Institute (ACI). For sites with Class 2 sulfate
exposure, ACI recommends using a cement meeting the requirements for Type V
(sulfate resistant) cement or the equivalent, with a maximum water-to-cementitious
material ratio of 0.45 and air entrainment of 5 to 7 percent. As alternative, ACI
allows the use of cement that conforms to ASTM C 150 Type II requirements, if it
meets the Type V performance requirements (ASTM C 1012) of ACI 201, or ACI
allows a blend of any type of Portland cement and fly ash that meets the
performance requirements (ASTM C 1012) of ACI 201. In Colorado, Type II cement
with 20 percent Class F fly ash usually meets these performance requirements. The
fly ash content can be reduced to 15 percent for placement in cold weather months,
provided a water-to-cementitious material ratio of 0.45 or less is maintained. ACI
also indicates concrete with Class 2 sulfate exposure should have a minimum
compressive strength of 4500 psi.
Sulfate attack problems are comparatively rare in this area when quality
concrete is used. Considering the range of test results, we believe risk of sulfate
attack is lower than indicated by the few laboratory tests performed. The risk is also
lowered to some extent by damp-proofing the surfaces of concrete walls in contact
with the soil. ACI indicates sulfate resistance for Class 1 exposure can be achieved
by using Type II cement, a maximum water-to-cementitious material ratio of 0.50,
and a minimum compressive strength of 4000 psi. We believe this approach should
be used as a minimum at this project. The more stringent measures outlined in the
previous paragraph will better control risk of sulfate attack and are more in
alignment with written industry standards.
The use of sulfate resistant concrete is most appropriate for foundation
elements. Surface flatwork (such as sidewalks, driveways and patios) is usually
constructed with a mix that exhibits moderate resistance to sulfate attack. We have
rarely seen instances of sulfate attack on surface flatwork.
SUN ACQ LLC 19
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RECOMMENDED FUTURE INVESTIGATIONS
Based on the results of this investigation and the proposed development, we
recommend the following investigations be performed:
1. Review of final site grading plans by our firm;
2. Design and sizing of the underdrain systems;
3. Construction testing and observation for site development;
4. Subgrade investigation and pavement design after site grading is
complete;
5. Design-level soils and foundation investigations after grading;
6. Construction testing and observation for residential building
construction and paving.
LIMITATIONS
Our exploratory borings were located to obtain preliminary subsoil data
indicative of conditions on this site. Although our borings were spaced to obtain a
reasonably accurate picture of subsurface conditions, variations in the subsoils not
indicated in our borings are always possible. We believe this investigation was
conducted in a manner consistent with that level of skill and care ordinarily used by
members of the profession currently practicing under similar conditions in the
locality of this project. No warranty, express or implied, is made.
This report was prepared from data developed during our field exploration,
laboratory testing, engineering analysis and experience with similar conditions. The
recommendations contained in this report were based upon our understanding of
the planned construction. If plans change or differ from the assumptions presented
herein, we should be contacted to review our recommendations.
SUN ACQ LLC 20
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CTL | T PROJECT NO. FC09654-115
If we can be of further service in discussing the contents of this report or in
the analysis of the building and pavement from the geotechnical point of view,
please call.
Very truly yours,
CTL | THOMPSON, INC.
Taylor H. Ray, EIT Spencer A. Schram, PE
Staff Geotechnical Engineer Project Manager
TH-6
TH-1 TH-2 TH-3
TH-4
TH-5
TH-10TH-9
TH-8
TH-7Highway 287 / College AvenueTrilby Road
LEGEND:
INDICATES APPROXIMATE
LOCATION OF EXPLORATORY
BORING
TH-1
S COLLEGE AVE.S LEMAY AVE.CARPENTER RD.
TRILBY RD.
SITE
SUN ACQ LLC
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CTL I T PROJECT NO. FC09654-115 FIGURE 1
Locations of
Exploratory
Borings
500'250'
APPROXIMATE
SCALE: 1" = 500'
0'
VICINITY MAP
FORT COLLINS AREA
NOT TO SCALE
TH-6
TH-1 TH-2 TH-3
TH-4
TH-5
TH-10TH-9
TH-8
TH-7Highway 287 / College AvenueTrilby Road
(14)(1)
(14)
(14)
(5)(1)
(4)
(6)
(2)
(2)
LEGEND:
INDICATES APPROXIMATE
LOCATION OF EXPLORATORY
BORING
INDICATES ESTIMATED DEPTH TO
BEDROCK SURFACE (FEET)
TH-1
(5)
SUN ACQ LLC
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CTL I T PROJECT NO. FC09654-115 FIGURE 2
Estimated
Depth to
Bedrock
500'250'
APPROXIMATE
SCALE: 1" = 500'
0'
0
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
7/12
6/12
13/12
8/12
42/12
WC=24.3DD=102SW=0.6SS=0.380
WC=22.6DD=102SW=-0.1
WC=26.0DD=97SW=0.9
WC=26.5DD=100SW=-0.1
WC=16.7DD=112SW=1.7
WC=24.3DD=102SW=0.6SS=0.380
WC=22.6DD=102SW=-0.1
WC=26.0DD=97SW=0.9
WC=26.5DD=100SW=-0.1
WC=16.7DD=112SW=1.7
TH-1
43/12
50/10
50/6
50/5
50/6
WC=13.9DD=116SW=2.8
WC=13.3DD=122SW=1.5
WC=13.9DD=116SW=2.8
WC=13.3DD=122SW=1.5
TH-2
9/12
5/12
50/10
50/7
50/5
50/3
WC=20.8DD=104SW=0.8SS=0.390
WC=16.5DD=116SW=1.7
WC=12.6DD=116LL=41 PI=25-200=77
WC=20.8DD=104SW=0.8SS=0.390
WC=16.5DD=116SW=1.7
WC=12.6DD=116LL=41 PI=25-200=77
TH-3
12/12
10/12
13/12
9/12
50/5
50/5
WC=23.7DD=103SW=0.8
WC=22.4DD=99LL=44 PI=25-200=78
WC=25.9DD=99SW=0.0
WC=23.7DD=103SW=0.8
WC=22.4DD=99LL=44 PI=25-200=78
WC=25.9DD=99SW=0.0
TH-4
46/12
50/7
50/5
50/6
50/4
WC=9.1DD=124SW=14.7SS=<0.01
WC=12.5DD=129SW=2.7
WC=9.1DD=124SW=14.7SS=<0.01
WC=12.5DD=129SW=2.7
TH-5
Summary Logs of
Exploratory Borings
FIGURE 3 DEPTH - FEETDEPTH - FEETSUN ACQ LLC
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CTL | T PROJECT NO. FC09654-120
0
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
25/12
34/12
50/11
50/10
50/9
50/9
WC=8.6DD=121SW=5.8SS=<0.01
WC=17.2DD=113SW=3.3
WC=17.7DD=113SW=2.8
WC=18.4DD=112SW=3.2
WC=17.9DD=116SW=2.6
WC=8.6DD=121SW=5.8SS=<0.01
WC=17.2DD=113SW=3.3
WC=17.7DD=113SW=2.8
WC=18.4DD=112SW=3.2
WC=17.9DD=116SW=2.6
TH-6
15/12
50/12
50/8
50/8
50/7
WC=10.3DD=128-200=81
WC=15.5DD=120SW=4.2
WC=16.0DD=116LL=44 PI=26-200=83
WC=10.3DD=128-200=81
WC=15.5DD=120SW=4.2
WC=16.0DD=116LL=44 PI=26-200=83
TH-7
17/12
50/10
50/9
50/6
50/6
50/6
WC=10.1DD=108SW=3.6SS=0.010
WC=14.4DD=120SW=5.2
WC=9.9DD=120SW=1.7
WC=10.1DD=108SW=3.6SS=0.010
WC=14.4DD=120SW=5.2
WC=9.9DD=120SW=1.7
TH-8
27/12
50/9
50/6
50/6
WC=10.4DD=127SW=13.0SS=0.010
WC=14.1DD=123SW=3.1
WC=10.4DD=127SW=13.0SS=0.010
WC=14.1DD=123SW=3.1
TH-9
7/12
44/12
50/8
50/10
50/8
WC=26.8DD=85LL=53 PI=31-200=87
WC=16.1DD=116SW=3.6
WC=15.5DD=111SW=0.4
WC=16.1DD=116SW=0.9
WC=26.8DD=85LL=53 PI=31-200=87
WC=16.1DD=116SW=3.6
WC=15.5DD=111SW=0.4
WC=16.1DD=116SW=0.9
TH-10
DEPTH - FEETDRIVE SAMPLE. THE SYMBOL 25/12 INDICATES 25 BLOWS OF A 140-POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE A 2.5-INCH O.D. SAMPLER 12 INCHES.
CLAY, SANDY, MOIST, MEDIUM STIFF TO VERY STIFF, LIGHT BROWN TO DARK BROWN (CL,
CH)
1.
NOTES:
THESE LOGS ARE SUBJECT TO THE EXPLANATIONS, LIMITATIONS AND CONCLUSIONS IN
THIS REPORT.
WATER LEVEL MEASURED SEVERAL DAYS AFTER DRILLING.
WEATHERED INTERBEDDED SANDSTONE AND CLAYSTONE BEDROCK, MOIST, FIRM TO
MEDIUM HARD, GRAY, BROWN
3.
LEGEND:
INTERBEDDED SANDSTONE AND CLAYSTONE BEDROCK, MOIST, HARD TO VERY HARD,
GREY, BROWN, BLACK
DEPTH - FEETWATER LEVEL MEASURED AT TIME OF DRILLING.
Summary Logs of
Exploratory Borings
THE BORINGS WERE DRILLED NOVEMBER, 2020 USING 4-INCH DIAMETER
CONTINUOUS-FLIGHT AUGERS AND A TRUCK-MOUNTED DRILL RIG.
FIGURE 4
WC
DD
SW
-200
LL
PI
UC
SS
-
-
-
-
-
-
-
-
INDICATES MOISTURE CONTENT (%).
INDICATES DRY DENSITY (PCF).
INDICATES SWELL WHEN WETTED UNDER OVERBURDEN PRESSURE (%).
INDICATES PASSING NO. 200 SIEVE (%).
INDICATES LIQUID LIMIT.
INDICATES PLASTICITY INDEX.
INDICATES UNCONFINED COMPRESSIVE STRENGTH (PSF).
INDICATES SOLUBLE SULFATE CONTENT (%).
2.
SUN ACQ LLC
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CTL | T PROJECT NO. FC09654-120
FIGURE 5
Sewer
Underdrain
DetailSUN ACQ LLC
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CTL\T Project No. FC09654-115
FIGURE 6
Underdrain
Cutoff Wall
DetailSUN ACQ LLC
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CTL\T Project No. FC09654-115
FIGURE 7
Conceptual
Underdrain
Service
Profile
SUN ACQ LLC
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CTL\T Project No. FC09654-115
APPENDIX A
LABORATORY TEST RESULTS
TABLE A-1: SUMMARY OF LABORATORY TEST RESULTS
TABLE A-2: ESTIMATED POTENTIAL HEAVE
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=102 PCF
From TH - 1 AT 4 FEET MOISTURE CONTENT=24.3 %
SUN ACQ LLC
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CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-1
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=102 PCF
From TH - 1 AT 9 FEET MOISTURE CONTENT=22.6 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-2
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
ADDITIONAL COMPRESSION UNDER
CONSTANT PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=97 PCF
From TH - 1 AT 14 FEET MOISTURE CONTENT=26.0 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-3
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=100 PCF
From TH - 1 AT 19 FEET MOISTURE CONTENT=26.5 %
SUN ACQ LLC
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CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-4
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
ADDITIONAL COMPRESSION UNDER
CONSTANT PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=112 PCF
From TH - 1 AT 24 FEET MOISTURE CONTENT=16.7 %
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=116 PCF
From TH - 2 AT 9 FEET MOISTURE CONTENT=13.9 %
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APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
FIGURE A-5COMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=122 PCF
From TH - 2 AT 19 FEET MOISTURE CONTENT=13.3 %
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=104 PCF
From TH - 3 AT 4 FEET MOISTURE CONTENT=20.8 %
SUN ACQ LLC
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APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
FIGURE A-6COMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=116 PCF
From TH - 3 AT 14 FEET MOISTURE CONTENT=16.5 %
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=103 PCF
From TH - 4 AT 9 FEET MOISTURE CONTENT=23.7 %
SUN ACQ LLC
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APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
FIGURE A-7COMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=99 PCF
From TH - 4 AT 19 FEET MOISTURE CONTENT=25.9 %
SUN ACQ LLC
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CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-8
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
NO MOVEMENT DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=124 PCF
From TH - 5 AT 2 FEET MOISTURE CONTENT=9.1 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-9
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=129 PCF
From TH - 5 AT 14 FEET MOISTURE CONTENT=12.5 %
SUN ACQ LLC
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CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-10
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=121 PCF
From TH - 6 AT 4 FEET MOISTURE CONTENT=8.6 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-11
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=113 PCF
From TH - 6 AT 9 FEET MOISTURE CONTENT=17.2 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-12
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=113 PCF
From TH - 6 AT 14 FEET MOISTURE CONTENT=17.7 %
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=112 PCF
From TH - 6 AT 19 FEET MOISTURE CONTENT=18.4 %
SUN ACQ LLC
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APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
FIGURE A-13COMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-3
-2
-1
0
1
2
3
4
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=116 PCF
From TH - 6 AT 24 FEET MOISTURE CONTENT=17.9 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-14
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=120 PCF
From TH - 7 AT 14 FEET MOISTURE CONTENT=15.5 %
SUN ACQ LLC
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CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-15
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=108 PCF
From TH - 8 AT 4 FEET MOISTURE CONTENT=10.1 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-16
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=120 PCF
From TH - 8 AT 9 FEET MOISTURE CONTENT=14.4 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-17
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=120 PCF
From TH - 8 AT 19 FEET MOISTURE CONTENT=9.9 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-18
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=127 PCF
From TH - 9 AT 2 FEET MOISTURE CONTENT=10.4 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-19
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=123 PCF
From TH - 9 AT 14 FEET MOISTURE CONTENT=14.1 %
SUN ACQ LLC
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APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-20
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED DRY UNIT WEIGHT=116 PCF
From TH - 10 AT 9 FEET MOISTURE CONTENT=16.1 %
SUN ACQ LLC
THE FOOTHILLS
CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
Test Results FIGURE A-21
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=111 PCF
From TH - 10 AT 19 FEET MOISTURE CONTENT=15.5 %
Sample of INTERBEDDED CLAYSTONE AND SANDSTONE DRY UNIT WEIGHT=116 PCF
From TH - 10 AT 24 FEET MOISTURE CONTENT=16.1 %
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THE FOOTHILLS
CTL | T PROJECT NO. FC09654-115
APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONSwell Consolidation
FIGURE A-22COMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
PASSING WATER-
MOISTURE DRY LIQUID PLASTICITY APPLIED SWELL NO. 200 SOLUBLE
DEPTH CONTENT DENSITY LIMIT INDEX SWELL*PRESSURE PRESSURE SIEVE SULFATES
BORING (FEET)(%)(PCF)(%)(PSF)(PSF)(%)(%)DESCRIPTION
TH-1 4 24.3 102 0.6 500 1,100 0.38 CLAY, SANDY (CL)
TH-1 9 22.6 102 -0.1 1,100 CLAY, SANDY (CL)
TH-1 14 26.0 97 0.9 1,800 3,800 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-1 19 26.5 100 -0.1 2,400 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-1 24 16.7 112 1.7 3,000 8,800 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-2 9 13.9 116 2.8 1,100 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-2 19 13.3 122 1.5 2,400 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-3 4 20.8 104 0.8 500 0.39 CLAY, SANDY (CL)
TH-3 14 16.5 116 1.7 1,800 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-3 19 12.6 116 41 25 77 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-4 9 23.7 103 0.8 1,100 CLAY, SANDY (CL)
TH-4 14 22.4 99 44 25 78 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-4 19 25.9 99 0.0 2,400 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-5 2 9.1 124 14.7 500 <0.01 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-5 14 12.5 129 2.7 1,800 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-6 4 8.6 121 5.8 500 7,100 <0.01 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-6 9 17.2 113 3.3 1,100 9,100 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-6 14 17.7 113 2.8 1,800 9,800 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-6 19 18.4 112 3.2 2,400 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-6 24 17.9 116 2.6 3,000 15,000 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-7 2 10.3 128 81 CLAY, SANDY (CL)
TH-7 14 15.5 120 4.2 1,800 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-7 19 16.0 116 44 26 83 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-8 4 10.1 108 3.6 500 0.01 CLAY, SANDY (CL)
TH-8 9 14.4 120 5.2 1,100 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-8 19 9.9 120 1.7 2,400 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-9 2 10.4 127 13.0 500 0.01 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-9 14 14.1 123 3.1 1,800 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-10 2 26.8 85 53 31 87 CLAY, SANDY (CL)
TH-10 9 16.1 116 3.6 1,100 INTERBEDDED CLAYSTONE AND SANDSTONE, WEATHERED
TH-10 19 15.5 111 0.4 2,400 INTERBEDDED CLAYSTONE AND SANDSTONE
TH-10 24 16.1 116 0.9 3,000 INTERBEDDED CLAYSTONE AND SANDSTONE
SWELL TEST RESULTS*
TABLE A-I
SUMMARY OF LABORATORY TESTING
ATTERBERG LIMITS
Page 1 of 1
* NEGATIVE VALUE INDICATES COMPRESSION.
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THE FOOTHILLS
CTL|T PROJECT NO. FC09654-115
TABLE A-2: Estimated Potential Heave
Location
Basement
Slab
Performance
Risk
Estimated Heave (inches)
24-foot Depth of Wetting
Ground Basement
TH-1 Low 1.1 0.8
TH-2 Moderate 7.9 3.2
TH-3 Low 1.8 1.3
TH-4 Low 1.7 1.3
TH-5 Moderate 10.4 3.6
TH-6 High 7.8 4.4
TH-7 High 7.8 5.6
TH-8 High 7.4 5.3
TH-9 High 9.5 4.3
APPENDIX B
GUIDELINE SITE GRADING SPECIFICATIONS
SUN ACQ LLC
THE FOOTHILLS
CTLT PROJECT NO. FC09654-115
Appendix B-1
GUIDELINE SITE GRADING SPECIFICATIONS
1. DESCRIPTION
This item shall consist of the excavation, transportation, placement and
compaction of materials from locations indicated on the plans, or staked by the
Engineer, as necessary to achieve preliminary street and overlot elevations.
These specifications shall also apply to compaction of excess cut materials
that may be placed outside of the development boundaries.
2. GENERAL
The Soils Engineer shall be the Owner's representative. The Soils Engineer
shall approve fill materials, method of placement, moisture contents and
percent compaction, and shall give written approval of the completed fill.
3. CLEARING JOB SITE
The Contractor shall remove all vegetation and debris before excavation or fill
placement is begun. The Contractor shall dispose of the cleared material to
provide the Owner with a clean, neat appearing job site. Cleared material
shall not be placed in areas to receive fill or where the material will support
structures of any kind.
4. SCARIFYING AREA TO BE FILLED
All topsoil and vegetable matter shall be removed from the ground surface
upon which fill is to be placed. The surface shall then be plowed or scarified
until the surface is free from ruts, hummocks or other uneven features, which
would prevent uniform compaction.
5. COMPACTING AREA TO BE FILLED
After the foundation for the fill has been cleared and scarified, it shall be
disked or bladed until it is free from large clods, brought to the proper moisture
content (0 to 3 percent above optimum moisture content for clays and within 2
percent of optimum moisture content for sands) and compacted to not less
than 95 percent of maximum dry density as determined in accordance with
ASTM D698.
6. FILL MATERIALS
Fill soils shall be free from organics, debris or other deleterious substances,
and shall not contain rocks or lumps having a diameter greater than six (6)
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Appendix B-2
inches. Fill materials shall be obtained from cut areas shown on the plans or
staked in the field by the Engineer.
On-site materials classifying as CL, CH, SC, SM, SW, SP, GP, GC and GM
are acceptable. Concrete, asphalt, organic matter and other deleterious
materials or debris shall not be used as fill.
7. MOISTURE CONTENT AND DENSITY
Fill material shall be moisture conditioned and compacted to the criteria in the
table, below. Maximum density and optimum moisture content shall be
determined from the appropriate Proctor compaction tests. Sufficient
laboratory compaction tests shall be made to determine the optimum moisture
content for the various soils encountered in borrow areas.
FILL COMPACTION AND MOISTURE REQUIREMENTS
Soil
Type
Depth from
Overlot Grade
(feet)
Moisture Requirement
(% from optimum)
Density Requirement
Clay
0 to 20 feet
+1 to +4 95% of ASTM D 698
Sand -2 to +2 95% of ASTM D 698
Clay Greater than 20
feet
-2 to +1 98% of ASTM D 698
Sand -2 to +1 95% of ASTM D 1557
The Contractor may be required to add moisture to the excavation materials in
the borrow area if, in the opinion of the Soils Engineer, it is not possible to
obtain uniform moisture content by adding water on the fill surface. The
Contractor may be required to rake or disc the fill soils to provide uniform
moisture content through the soils.
The application of water to embankment materials shall be made with any type
of watering equipment approved by the Soils Engineer, which will give the
desired results. Water jets from the spreader shall not be directed at the
embankment with such force that fill materials are washed out.
Should too much water be added to any part of the fill, such that the material is
too wet to permit the desired compaction from being obtained, rolling and all
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Appendix B-3
work on that section of the fill shall be delayed until the material has been
allowed to dry to the required moisture content. The Contractor will be
permitted to rework wet material in an approved manner to hasten its drying.
8. COMPACTION OF FILL AREAS
Selected fill material shall be placed and mixed in evenly spread layers. After
each fill layer has been placed, it shall be uniformly compacted to not less than
the specified percentage of maximum density. Fill shall be compacted to the
criteria above. At the option of the Soils Engineer, soils classifying as SW,
GP, GC, or GM may be compacted to 95 percent of maximum density as
determined in accordance with ASTM D 1557 or 70 percent relative density for
cohesionless sand soils. Fill materials shall be placed such that the thickness
of loose materials does not exceed 12 inches and the compacted lift thickness
does not exceed 6 inches.
Compaction as specified above, shall be obtained by the use of sheepsfoot
rollers, multiple-wheel pneumatic-tired rollers, or other equipment approved by
the Engineer for soils classifying as CL, CH, or SC. Granular fill shall be
compacted using vibratory equipment or other equipment approved by the
Soils Engineer. Compaction shall be accomplished while the fill material is at
the specified moisture content. Compaction of each layer shall be continuous
over the entire area. Compaction equipment shall make sufficient trips to
ensure that the required density is obtained.
9. COMPACTION OF SLOPES
Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable
equipment. Compaction operations shall be continued until slopes are stable,
but not too dense for planting, and there is not appreciable amount of loose
soils on the slopes. Compaction of slopes may be done progressively in
increments of three to five feet (3' to 5') in height or after the fill is brought to its
total height. Permanent fill slopes shall not exceed 3:1 (horizontal to vertical).
10. PLACEMENT OF FILL ON NATURAL SLOPES
Where natural slopes are steeper than 20 percent in grade and the placement
of fill is required, benches shall be cut at the rate of one bench for each 5 feet
in height (minimum of two benches). Benches shall be at least 10 feet in
width. Larger bench widths may be required by the Engineer. Fill shall be
placed on completed benches as outlined within this specification.
11. DENSITY TESTS
Field density tests shall be made by the Soils Engineer at locations and depths
of his choosing. Where sheepsfoot rollers are used, the soil may be disturbed
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Appendix B-4
to a depth of several inches. Density tests shall be taken in compacted
material below the disturbed surface. When density tests indicate that the
density or moisture content of any layer of fill or portion thereof is not within
specification, the particular layer or portion shall be reworked until the required
density or moisture content has been achieved.
12. SEASONAL LIMITS
No fill material shall be placed, spread or rolled while it is frozen, thawing, or
during unfavorable weather conditions. When work is interrupted by heavy
precipitation, fill operations shall not be resumed until the Soils Engineer
indicates that the moisture content and density of previously placed materials
are as specified.
13. NOTICE REGARDING START OF GRADING
The Contractor shall submit notification to the Soils Engineer and Owner
advising them of the start of grading operations at least three (3) days in
advance of the starting date. Notification shall also be submitted at least 3
days in advance of any resumption dates when grading operations have been
stopped for any reason other than adverse weather conditions.
14. REPORTING OF FIELD DENSITY TESTS
Density tests made by the Soils Engineer, as specified under "Density Tests"
above, shall be submitted progressively to the Owner. Dry density, moisture
content, and percentage compaction shall be reported for each test taken.
15. DECLARATION REGARDING COMPLETED FILL
The Soils Engineer shall provide a written declaration stating that the site was
filled with acceptable materials, and was placed in general accordance with
the specifications.