HomeMy WebLinkAboutAPEX - HAVEN APARTMENTS - FDP210012 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT
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TABLE OF CONTENTS
SUMMARY .................................................................................................................................... 1
PURPOSE AND SCOPE OF WORK ............................................................................................ 2
PROPOSED CONSTRUCTION .................................................................................................... 2
SITE CONDITIONS ...................................................................................................................... 3
SUBSURFACE CONDITIONS ...................................................................................................... 3
LABORATORY TESTING ............................................................................................................. 4
WATER-SOLUBLE SULFATES .................................................................................................... 5
GEOTECHNICAL ENGINEERING CONSIDERATIONS .............................................................. 5
FOUNDATION RECOMMENDATIONS ........................................................................................ 6
FLOOR SLABS ............................................................................................................................. 7
SITE SEISMIC CRITERIA ............................................................................................................ 9
SURFACE DRAINAGE ................................................................................................................. 9
SITE GRADING .......................................................................................................................... 10
PAVEMENT THICKNESS DESIGN ............................................................................................ 14
DESIGN AND CONSTRUCTION SUPPORT SERVICES .......................................................... 17
LIMITATIONS ............................................................................................................................. 17
FIG. 1 – LOCATION OF EXPLORATORY BORINGS
FIG. 2 – LOGS OF EXPLORATORY BORINGS
FIG. 3 – LEGEND AND NOTES
FIGS. 4 through 7 – SWELL-CONSOLIDATION TEST RESULTS
FIG. 8 – GRADATION TEST RESULTS
FIG. 9 – MOISTURE-DENSITY (PROCTOR) RELATIONSHIPS
TABLE I – SUMMARY OF LABORATORY TEST RESULTS
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SUMMARY
1. Eight (8) exploratory borings were drilled for this study. The borings generally
encountered a thin layer of topsoil overlying nil to approximately 5 feet of man-placed fill
consisting of sandy lean clay to clayey sand to silty sand which was underlain by natural
clayey and granular soils. The natural overburden soils were underlain by claystone
bedrock in Borings 1, 3, 6 and 7 that continued to the explored depths of about 40 to 45
feet below the ground surface. The natural soils continued to the explored depths of about
5 to 20 feet in Borings 2, 4, 5, and P-1. Borings 1, 2 and P-1 encountered about 3 to 6
inches of gravel surfacing overlying the man-placed fill and natural soils.
Groundwater was encountered in the borings at depths of about 21 to 22 feet at the time
of drilling and at depths of about 20 to 21.5 feet when subsequently checked 16 days after
drilling.
2. Shallow spread footings are feasible for the structures constructed on the site. Spread
footings should be placed on natural soils or structural fill extending to natural soils.
Spread footings should be designed for a net allowable bearing pressure of 3,000 psf.
3. Slab-on-grade construction is also feasible at the site. Slab on grade floors should be
underlain by at least 4 feet of properly compacted fill material. Additional design
considerations and recommendations are presented herein.
4. For proper performance of the building foundation and floor slab, the existing fill should be
removed and replaced at the moisture and density requirements provided herein.
5. Flexible pavements should consist of a minimum of 5.5 inches of full-depth asphalt in the
automobile parking areas and 6 inches in the drive and fire lanes. In lieu of the full-depth
asphalt section, an acceptable alternate consisting of 4 inches of asphalt and 6 inches of
base course may be used in the parking areas and 4 inches of asphalt overlying 8 inches
of aggregate base coarse may be used in the drive and fire lanes.
A 6.0-inch Portland cement concrete pavement section may also be used in parking areas
subject to automobile and light-truck traffic only. Areas subjected to combined traffic and
where truck turning movements are concentrated should be paved with 7 inches of
Portland cement concrete. Concrete pavement should contain sawed or formed joints to
¼ of the depth of the slab at a maximum distance of 12 to 14 feet on center.
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PURPOSE AND SCOPE OF WORK
This report presents the results of a geotechnical engineering study and pavement thickness
design for the proposed Haven Apartments to be located north of 720 West Prospect Road in Fort
Collins, Colorado. The project site is shown on Fig. 1. This study was performed in general
accordance with our Proposal No. P3-19-285 to Maxiiimo Develop Group dated October 11, 2019.
A field exploration program consisting of exploratory borings was conducted to obtain site specific
information on subsurface conditions. Samples of 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 and laboratory testing programs were analyzed
to develop geotechnical engineering recommendations for use 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 project are included in the report.
PROPOSED CONSTRUCTION
Based on the information provided, a four-story apartment building will be constructed on the
north side of the site and will have an approximate footprint of 14,000 square feet. Trees and
other landscaping will be provided around the proposed structure. We anticipate that the finished
floor elevations for the structure will be near the existing ground surface. A primary access drive
to the development will be provided from Prospect Road on the southern site boundary. A
secondary access point will also be created on the west side of the project site and will access
Lake Street to the north.
We also understand two buildings currently exist on the site and renovations to each of the
buildings are planned for this project.
If the proposed construction varies significantly from that described above or depicted in this
report, we should be notified to reevaluate the recommendations provided herein.
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SITE CONDITIONS
The site is bounded on the west and north by apartment buildings and associated developments,
to the east by single-family residences, and to the south by West Prospect Road. This site
contains two residential structures with gravel surfaced drives. At the time of our exploration,
trees and other vegetation were noted on the site. The site was relatively flat with a slight slope
down to the south.
SUBSURFACE CONDITIONS
The subsurface conditions at the site were explored by drilling two exploratory borings to depths
of about 5 to 45 feet at the approximate locations shown on Fig. 1. Graphic logs of the borings
are presented on Fig. 2, and a legend and notes describing the soils encountered are presented
on Fig. 3.
The borings generally encountered a thin layer of topsoil overlying nil to approximately 5 feet of
man-placed fill consisting of sandy lean clay to clayey sand to silty sand which was underlain by
natural clayey and granular soils. The natural overburden soils were underlain by claystone
bedrock in Borings 1, 3, 6 and 7 that continued to the explored depths of about 40 to 45 feet below
the ground surface. The natural soils continued to the explored depths of about 5 to 20 feet in
Borings 2, 4, 5, and P-1. Boring 1, 2 and P-1 encountered about 3 to 6 inches of gravel surfacing
overlying the man-placed fill and natural soils.
The man-placed fill material was fine to coarse grained with occasional gravel, slightly moist to
moist, and red to brown to black. The natural clayey soils were fine to coarse grained with
occasional gravel, slightly moist to moist, and red to brown. The natural granular soils were fine
to coarse grained with gravel, slightly moist to wet, and brown. The claystone bedrock was fine
to medium grained, moist, and brown. Based on sampler penetration resistance, the natural
clayey soils were generally stiff to very stiff, the natural granular soils were generally loose to
dense, and the claystone bedrock was hard to very hard in consistency.
Groundwater was encountered in the borings at depths of about 21 to 22 feet at the time of drilling
and at depths of about 20 to 21.5 feet when subsequently checked 16 days after drilling.
Groundwater levels are expected to fluctuate with time, and may fluctuate upward after wet
weather or subsequent to landscape irrigation.
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LABORATORY TESTING
Laboratory testing was performed on selected samples obtained from the borings to determine
in-situ moisture content and dry density, Atterberg limits, gradation, swell-consolidation
characteristics, and water-soluble sulfates. The results of the laboratory tests are shown next to
the boring logs on Fig. 2, graphically plotted on Figs. 4 through 9, and summarized in the attached
Table I. The testing was conducted in general accordance with recognized test procedures,
primarily those of the ASTM International and the Colorado Department of Transportation
(CDOT).
Swell-Consolidation: Swell-consolidation tests were conducted on selected samples of the man-
placed fill and natural overburden material in order to evaluate the compressibility and swell
characteristics under loading and when submerged in water. The samples were 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. 4 through 7. Based on the
results of the laboratory swell-consolidation testing, a sample of man-placed fill exhibited low swell
potential (1.1%) upon wetting under a 200-psf surcharge pressure and samples of the natural
overburden soils exhibited low consolidation potential (0.2% to 2.6%) upon wetting under a 1,000-
psf surcharge pressure. A sample of claystone bedrock exhibited low swell potential (1.6%) upon
wetting under a 1,000-psf surcharge pressure. The consolidation potential exhibited by the
samples of natural overburden soils was likely due to the sample disturbance.
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. The results of a gradation test are presented on Fig. 8.
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Moisture-Density Relationship: A composite sample of the existing fill was tested for moisture-
density relationship (Proctor) in order to determine the characteristics of the existing fill with
respect to adequacy of the compacted fill. The test resulted in a maximum dry density of 118.9
pcf at an optimum moisture content of 12.2%. The test results are shown on Fig. 9.
WATER-SOLUBLE SULFATES
The concentration of water-soluble sulfates measured in a sample of the overburden soils
obtained from the exploratory borings was 0.00%. This concentration of water-soluble sulfates
represents a Class S0 severity exposure of 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 test results, we believe special sulfate resistant cement will generally not
be required for concrete exposed to the natural on-site soils and/or bedrock.
GEOTECHNICAL ENGINEERING CONSIDERATIONS
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 considered to have erratic moisture contents but generally below the optimum
moisture content, which in turn indicates a potential for settlement of structures or slabs placed
on the existing fills.
Criteria for shallow spread footing foundations are presented below; however, it is very important
to the long-term performance of the building that all of the existing fill materials be removed from
below foundation elements and floor slabs and to a distance beyond the building area equal to
the depth of the removed fill. In our opinion, the removed fill, excluding deleterious materials, is
suitable to be moisture conditioned and recompacted as structural fill below foundation elements,
floor slabs and exterior flatwork.
Depending on the depths of fill encountered during site grading, complete fill removal and
replacement could be costly. We have no way to accurately predict the total magnitude of
potential settlements if the existing fill is left in place; however, movements on the order of 1 to 2
inches (or more) are possible. As discussed above, to reduce settlement potential, all existing
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fills beneath planned foundations and slabs-on-grade should be removed and replaced with
structural fill.
PT-slab foundations or other shallow foundations would also be considered acceptable
alternatives for construction on the site. Additional recommendations for alternative foundations
such as PT-slab foundations may be provided if requested.
FOUNDATION RECOMMENDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the proposed building and other incidental structures
be founded on spread footings placed on natural soils or properly compacted structural fill material
extending to natural soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system. The construction details should be considered when preparing project
documents.
1. Footings placed on natural soils or properly compacted structural fill extending to natural
soils should be designed for a net allowable bearing pressure of 3,000 psf. Structural fill
should meet the material and placement requirements provided in the “Site Grading”
section of this report.
2. Based on experience, we estimate total settlement for footings designed and constructed
as discussed in this section will be less than 1 inch. Differential settlements between
individual foundations are estimated to be approximately ½ to ¾ of the total settlement.
Due to the presence of near-surface granular soils, settlements should occur during or
shortly after construction.
3. Spread footings should have a minimum footing width of 16 inches for continuous footings
and of 24 inches for isolated pads.
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4. Exterior footings and footings beneath unheated areas should be provided with adequate
soil cover above their bearing elevation for frost protection. Placement of foundations at
least 30 inches below the exterior grade is typically used in this area.
5. The lateral resistance of a spread footing supported as recommended herein will be a
combination of the sliding resistance of the footing on the foundation materials and passive
earth pressure against the side of the footing. Resistance to sliding at the bottoms of the
footings can be calculated based on a coefficient of friction of 0.35. Passive pressure
against the sides of the footings can be calculated using an equivalent fluid unit weight of
195 pcf. The above values are working values. Structural fill placed against the sides of
footings to resist lateral loads should meet the material and placement requirements
provided in the “Site Grading” section of this report.
6. Continuous foundation walls should be reinforced top and bottom to span an unsupported
length of at least 10 feet.
7. Areas of existing fill, loose and/or soft material, or deleterious substances encountered
within footing excavations should be removed and replaced with structural fill. New fill
should extend down from the edges of the footings at a 1 horizontal to 1 vertical projection.
8. Care should be taken when excavating the foundations to avoid disturbing the supporting
materials.
9. A representative of the geotechnical engineer should observe all footing excavations prior
to concrete placement.
FLOOR SLABS
To reduce settlement potential, we recommend that all existing fills beneath planned slabs-on-
grade and settlement-sensitive exterior flatwork be removed and replaced with properly
compacted structural fill. As previously discussed, complete fill removal and replacement could
be costly. Alternatively, and if the owner is willing to accept the risk of potential settlements in
excess of normal tolerances, the existing fill within 4 feet of the floor slab subgrade elevation may
be removed and replaced with structural fill. It is also very important to provide the recommended
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isolation between the structure and the slab-on-grade floors to reduce damage in the event that
slab movement occurs. The following measures should be taken to reduce damage which could
result from movement should the underslab materials be subjected to moisture changes.
1. Floor slabs should be separated from all bearing walls and columns with expansion joints
that allow unrestrained vertical movement.
2. 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 1½ 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 spread footings 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.
3. 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). The requirements for slab
reinforcement should be established by the designer based on experience and the
intended slab use.
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4. 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.
5. 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.
It should be noted that reducing the depths of fill removal will not eliminate the risk of movement
due to post-construction settlement of existing fill left in place; however, the total magnitude of
potential movement will be reduced.
SITE SEISMIC CRITERIA
The soil profile consists of clay and sand overburden soils underlain by bedrock expected to
extend to depths greater than 100 feet. The overburden soils classify as IBC Site Class D and
the bedrock should classify as Site Class C. Based on our experience on sites with similar
profiles, IBC Site Class C should be used for design. Based on the subsurface profile and site
seismicity, liquefaction is not a design consideration.
SURFACE DRAINAGE
Proper surface drainage is very important for acceptable performance of the facility during
construction and after construction has been completed. Drainage recommendations provided
by local, state and national entities should be followed based on the intended use of the facility.
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 foundation and slab subgrades should be avoided during
construction.
2. The ground surface surrounding the exterior of the buildings and exterior flatwork and
paved areas should be sloped to drain away in all directions. We recommend a minimum
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slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in
the first 10 feet in impervious flatwork and paved areas. Site drainage beyond the 10-foot
zone should be designed to promote runoff and reduce infiltration. These slopes may be
changed as required for handicap access points in accordance with the Americans with
Disabilities Act.
3. To promote runoff, the upper 1 to 2 feet of the backfill adjacent to buildings should be a
relatively impervious on-site soil or be covered by flatwork or a pavement structure.
4. Exterior backfill should be adjusted to near optimum moisture content (generally optimum
to +3% of optimum unless indicated otherwise in this report) and compacted to at least
95% of the standard Proctor (ASTM D698) maximum dry density.
5. Ponding of water should not be allowed in backfill material or in a zone within 10 feet of
the building foundations, whichever is greater.
6. Roof downspouts and drains should discharge well beyond the limits of all backfill.
SITE GRADING
Site Preparation: Based on our understanding of the proposed construction and observed site
topography, site grading within the building footprint is expected to consist of minimal permanent
cuts and fills. Material types encountered during site grading will generally consist of man-placed
fill to natural clayey and granular materials. These materials can be excavated during site grading
operations with moderate to heavy-duty earth moving equipment.
Existing fills, where present, are considered non-engineered and unsuitable in their current
condition for support of foundations, floor slabs, settlement-sensitive exterior flatwork, and
pavements unless properly prepared. Proper preparation should include complete removal of
existing fill from beneath foundations, floor slabs, settlement sensitive flatwork, and rigid
pavements.
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The on-site overburden soils, including the existing fills, should be suitable for use as general site
fill and as structural fill beneath foundations and slabs, provided they do not contain organic or
other deleterious materials.
Temporary Excavations and Dewatering: Temporary excavations should be constructed in
accordance with OSHA requirements, as well as state, local and other applicable requirements.
Site excavations will generally encounter fills and granular soils classifying as OSHA Type C soils
and natural clay soils classifying as Type B soils. Excavations encountering loose granular soils,
or groundwater, will require much shallower side slopes than those allowed by OSHA and/or
temporary shoring.
Excavated slopes in existing fill and granular soils may loosen due to construction traffic and
erode from surface runoff. Measures to keep surface runoff from excavation slopes, including
diversion berms, should be considered.
Cut and Fill Slopes: Permanent unretained cuts in the overburden soils and fill slopes up to 10
feet high should be constructed at a 2H:1V (horizontal to vertical) or flatter inclination for stability
purposes and at a 3H:1V or flatter inclination for limiting the potential for erosion. If groundwater
seepage is encountered during or prior to cut slope excavation, a stability evaluation should be
conducted to determine if the seepage would adversely affect the cut.
Material Specifications: Unless specifically modified in the preceding sections of this report, the
following recommended material and compaction requirements are presented for compacted fills
on the project site. A geotechnical engineer should evaluate the suitability of all proposed fill
materials for the project prior to placement.
1. Structural Fill beneath Footings, Slab-on-Grade Floors, and Settlement-Sensitive Exterior
Flatwork: Structural fill should consist of moisture conditioned on-site soils or, if
necessary, imported non-expansive soils containing 20% to 60% passing the No. 200
sieve, a maximum liquid limit of 30, and a maximum plasticity index of 12. Fill source
materials, including on-site soils, not meeting one or more of these criteria may be
acceptable if they meet the swell criteria presented in Item 6 below.
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2. Site Grading Fill Beneath Pavements and Movement-Tolerant Exterior Flatwork:
Compacted fill should consist of moisture-conditioned on-site materials or non-expansive
imported soil materials.
3. Pipe Bedding Material: Pipe bedding material should be a free draining, coarse-grained
sand and/or fine gravel. The near-surface on-site soils generally consist of clay soils and
sands within relatively high silt and/or clay content and are not considered suitable for pipe
bedding.
4. Utility Trench Backfill: Materials excavated from the utility trenches may be used for trench
backfill above the pipe zone fill provided they do not contain unsuitable material or
particles larger than 4 inches and can be placed and compacted as recommended herein.
5. Base Course: Base course placed in conjunction with pavements should consist of
material meeting the requirements of CDOT Class 6 aggregate base course.
6. Material Suitability: Unless otherwise defined herein, all fill material should be a non-
expansive soil free of vegetation, brush, sod, trash and debris, and other deleterious
substances, and should not contain rocks or lumps having a diameter of more than 4
inches. A fill material should be considered non-expansive if the swell potential of the
material, when remolded to 95% of the standard Proctor (ASTM D698) maximum dry
density at optimum moisture content, does not exceed 0.5% when wetted under a 200 psf
surcharge pressure. If grading is performed during times of freezing weather, the fill
should not contain frozen materials, and, if the subgrade is allowed to freeze, all frozen
material should be removed prior to additional fill placement or footing, slab or pavement
construction.
Based on the data from the borings and results of the laboratory testing, the on-site soils
should be suitable for reuse as compacted site grading fill and as structural fill.
Evaluation of potential structural fill sources, particularly those not meeting the above
liquid limit and plasticity index criteria for imported fill materials, should include
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determination of laboratory moisture-density relationships and swell-consolidation tests
on remolded samples prior to acceptance.
Compaction Requirements: We recommend the following compaction criteria be used on the
project:
1. Moisture Content: Fill materials should be compacted at moisture contents within 2
percentage points of the optimum moisture content for predominantly granular materials
and between 0 and +3 percentage points of optimum for predominantly cohesive
materials, if used. The contractor should be aware that clay materials, including on-site
and imported materials, may become somewhat unstable and deform under wheel loads
if placed near the upper end of the moisture range.
2. Placement and Degree of Compaction: Unless otherwise defined herein, compacted fill
should be placed in maximum 8-inch-thick loose lifts. The following compaction criteria
should be followed during construction:
Percentage of Maximum
Standard Proctor Density
Fill Location ...................................................................................... (ASTM D-698)
Beneath Spread Footing Foundations ........................................................... 100%
Adjacent to Foundations .................................................................................. 95%
Beneath Floor Slabs, Settlement-Sensitive Flatwork Areas and Pavements1
Fill less than 8 Feet below the final ground surface .................................. 95%
Fill more than 8 Feet below the final ground surface .............................. 100%
Utility Trenches
Interior ........................................................................................................ 95%
Exterior Less Than 15 Feet below the final ground surface ...................... 95%
Exterior More Than 15 Feet below the final ground surface ................... 100%
Landscape and Other Areas ............................................................................ 90%
1 Aggregate base course should be compacted to a minimum of 95
percent of the modified Proctor (ASTM D 1557) maximum dry density
at moisture contents within 2 percentage points of optimum.
3. Subgrade Preparation: Areas receiving new fill should be prepared as recommended in
specific sections of this report to provide a uniform base for fill placement. All other areas
to receive new fill not specifically addressed herein should be scarified to a depth of at
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least 8 inches and recompacted to at least 95% of the standard Proctor (ASTM D698)
maximum dry density at the moisture contents recommended above.
Subgrade preparation should include proofrolling with a heavily loaded pneumatic-tired
vehicle or a heavy, smooth-drum roller compactor. Areas that deform excessively during
proofrolling should be removed and replaced to achieve a reasonably stable subgrade
prior to placement of compacted fill or slabs, flatwork or pavements.
PAVEMENT THICKNESS 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. Soils are represented for pavement design purposes by
means of a resilient modulus value (MR) for flexible pavements and a modulus of subgrade
reaction (k) for rigid pavements.
Subgrade Materials: Based on the results of the field and laboratory studies, the majority of the
subgrade materials at the site classify as A-1-b to A-6 with group indices between 0 and 5 in
accordance with the American Association of State Highway and Transportation Officials
(AASHTO) soil classification system. For design purposes, a subgrade resilient modulus of 4,000
psi for flexible pavements and a modulus of subgrade reaction of 40 psi was selected for rigid
pavements.
Design Traffic: Actual traffic conditions for this project were unavailable at the time of report
preparation. Therefore, we have estimated traffic loading conditions based on experience with
similar facilities. We have assumed that the traffic loading conditions for automobile parking areas
will be represented by an Equivalent Daily Load Application (EDLA) of 5. Given the site will be
accessed occasionally to frequently by medium to heavy duty vehicles, an EDLA of 10 was
selected for the access drives and fire lanes. The EDLA assumptions included a 20-year design
life with minimal growth in traffic volumes over the design life. If traffic loading conditions are
different from those described, we should be notified to re-evaluate the recommendations
presented herein.
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Flexible Pavement Sections: The pavement thicknesses were determined in accordance with the
1993 AASHTO pavement design procedures. For design purposes, a reliability of 80% was
assumed for all pavement areas. A minimum section consisting of 5.5 inches of full-depth asphalt
is recommended in the automobile parking areas and 6 inches in the drive and fire lanes. In lieu
of the full-depth asphalt section, composite pavement sections may be considered. A composite
section consisting of 4 inches of asphalt and 6 inches of base course may be used in the parking
areas, and a composite section consisting of 4 inches of asphalt overlying 8 inches of aggregate
base coarse may be used in the drive and fire lanes. Aggregate base course materials should
meet the material and placement requirements provided in the “Site Grading” section of this
report. Asphalt pavement should be placed in accordance with current CDOT standards.
Asphalt cement selected for the proposed pavements should meet the criteria for performance
graded binders PG 58-28 or PG 64-22 that conform to requirements outlined in the CDOT
Pavement Design Manual. The binder recommendations are based on the design 20-year, 18-
kip equivalent single axle load (ESAL20) application values calculated from the assumed EDLA
values. The ESAL20 values also indicate an NDESIGN value of 75 for the gyratory method of
compaction and design.
Rigid Pavements: Unreinforced concrete drive lanes and slabs used in delivery or trash collection
areas should be 7 inches in thickness. A 6-inch thick concrete pavement section is also an
acceptable alternative to the flexible pavement sections listed above for parking areas.
Portland cement concrete pavement (PCCP) should be based on a mix design established by a
qualified engineer. Concrete used for drive lanes should meet the requirements established by
CDOT for Class P concrete.
Subgrade Preparation: Prior to placing the pavement sections, the entire subgrade should be
scarified to a depth of 12 inches, adjusted to a moisture content near optimum and compacted as
indicated in the following table:
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Subgrade Compaction Requirements
Soil Type
Minimum Percent Compaction
of the Standard Proctor
Maximum Dry Density
(ASTM D698)
Moisture Content Range from
the Optimum Moisture
Content
A-6, A-7-6 95%0% to +3%
A-4 100%-3% to +1%
A-1, A-2, A-3 100%-2% to +2%
The pavement subgrade should be proofrolled with a heavily loaded pneumatic-tired vehicle such
as a loaded water truck or paving truck. Pavement design procedures assume a stable subgrade.
Areas that deform under wheel loads are not stable and should be removed and replaced to
achieve a stable subgrade prior to paving.
Existing fill materials as well as relatively loose natural soils may be encountered at subgrade in
some areas of proposed pavement. In general, any existing fill material left in place should
conform to the requirements for new fill material. However, in areas of deeper existing fill and in
areas where interference with buried utilities precludes removal of existing fill, removal of all
existing fill may not be practical.
In general, evaluation and removal of any materials more than 3 feet below pavement subgrade
elevation should not be necessary, provided that preparation as recommended herein results in
a stable subgrade.
In areas where existing fill is present at subgrade elevation, the fill should be evaluated by proof
rolling the surface, and by obtaining in-place density tests both at and 1 foot below the subgrade
elevation at a grid spacing of no more than 200 feet. If subgrade stability is adequate based on
proof rolling and the density tests indicate compaction meets specifications, the fill may be left in
place. If the condition of the existing fill materials is determined to be acceptable, the upper 2 feet
of the exposed subgrade soils should be removed, the remaining surface scarified to a depth of
12 inches and adjusted to a moisture content near optimum, and recompacted to provide a stable
subgrade for placement of backfill. The upper 2 feet should then be placed according to
requirements provided in the “Site Grading” section of this report.
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Kumar & Associates, Inc. ®
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.
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 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, and to identify possible variations in
subsurface conditions from those encountered in this study so that we can re-evaluate our
recommendations, if needed.
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 data obtained from the exploratory
borings at the locations indicated on Fig. 1, and the proposed construction. This report may not
reflect subsurface variations that occur between the explorations, 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 groundwater 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 can
undergo high volume changes with changes in moisture content. The extent and amount of
perched water beneath the building site as a result of area irrigation and inadequate surface
drainage is difficult, if not impossible, to foresee.
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Kumar & Associates, Inc. ®
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 risk of movement and possible damage to foundations, interior slab-on-grade floors, and
exterior slabs and pavements on sites where expansive soils and/or bedrock occur. Following the
recommendations given by a geotechnical engineer, careful construction practice and prudent
maintenance by the owner can, however, decrease this risk.
JAH/js
Rev. by: JLB
cc: book, file
Project No.: 19-3-221Project Name: Haven ApartmentsDate Sampled: October 23, 2019Date Received: October 27, 2019Boring Depth (Feet)Gravel (%) Sand (%)Liquid Limit (%)Plasticity (%)1 1 10/30/19 8.0 131.4 4 49 47 27 14 A-6 (3) Clayey Sand (SC)2 4 10/30/19 3.9 121.9 8 41 31 26 14 A-2-6 (0) Silty Sand (SM)2 19 10/30/19 18.0 108.2 0 58 42 NV NP A-4 (0) Silty Sand (SM)3 4 10/30/19 3.4 123.0 8 60 32 NV NP 0.00 A-2-4 (0) Silty Sand (SM)3 34 10/30/19 13.9 122.0Claystone Bedrock4 1 10/30/19 8.1 110.8 4 51 45 28 13 A-6 (2) Fill: Clayey Sand (SC)4 9 10/30/19 5.6 125.0 2 61 37 NV NP A-4 (0) Fill: Silty Sand (SM)4 19 10/30/19 0.3 134.1 2 64 34 NV NP A-2-4 (0) Silty Sand (SM)5 9 10/30/19 11.9 119.1 0 37 63 28 12 A-6 (5) Sandy Lean Clay (CL)6 1 10/30/19 4.7 97.5 27 39 34 31 17 A-2-6 (1) Clayey Sand with Gravel (SC)6 39 10/30/19 12.8 121.9Claystone Bedrock7 4 10/30/19 2.5 113.4 5 76 19 NV NP A-1-b (0) Silty Sand (SM)7 9 10/30/19 3.6 131.6 0 57 43 25 12 A-6 (2) Clayey Sand (SC)P-1 1 10/30/19 11.9 118.0 10 45 45 35 21 A-6 (5) Fill: Clayey Sand (SC)1-7 1-4 10/30/19 12.2* 118.9* 17 49 34 NV NP A-2-4 (0) Silty Sand with Gravel (SM) * - 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 TypeSummary of Laboratory Test ResultsTable ISample Location Gradation Atterberg LimitsDate TestedNatural Moisture Content (%)Natural Dry Density (pcf)Percent Passing No. 200 Sieve