HomeMy WebLinkAboutBALFOUR SENIOR LIVING - PDP220001 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT
800 Stockton Avenue, #4
Fort Collins, CO 80524
phone: (970) 416-9045
fax: (970) 416-9040
email: kaftcollins@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
GEOTECHNICAL ENGINEERING STUDY
AND PAVEMENT THICKNESS DESIGN
BALFOUR SENIOR LIVING FACILTY
NEAR THE SOUTHEAST CORNER OF CINQUEFOIL LANE
AND EAST HARMONY ROAD
FORT COLLINS, COLORADO
DRAFT SUBMITTAL
Prepared By: Reviewed By:
Jacob A. Hanson, P.E.
Joshua L. Barker, P.E.
Prepared For:
Balfour Senior Living
183 S. Taylor Ave., Ste 155
Louisville, CO 80027
Attn: Mr. Chris Smith
Project No. 21-3-154 June 29, 2021
Kumar & Associates, Inc.®
TABLE OF CONTENTS
SUMMARY ................................................................................................................................ 1
PURPOSE AND SCOPE OF STUDY ......................................................................................... 2
PROPOSED DEVELOPMENT ................................................................................................... 2
SITE CONDITIONS ................................................................................................................... 3
SUBSURFACE CONDITIONS ................................................................................................... 3
LABORATORY TESTING .......................................................................................................... 4
WATER SOLUBLE SULFATES ................................................................................................. 5
FOUNDATION RECOMMENDATIONS...................................................................................... 5
FLOOR SLABS .......................................................................................................................... 7
SEISMIC DESIGN CRITERIA .................................................................................................... 9
SURFACE DRAINAGE .............................................................................................................. 9
SITE GRADING ........................................................................................................................11
UNDERDRAIN SYSTEM ..........................................................................................................13
PAVEMENT DESIGN ................................................................................................................14
DESIGN AND CONSTRUCTION SUPPORT SERVICES .........................................................16
LIMITATIONS ...........................................................................................................................17
FIG. 1 – LOCATION OF EXPLORATORY BORINGS
FIG. 2 – LOGS OF EXPLORATORY BORINGS
FIG. 3 – LEGEND AND NOTES
FIGS. 4 through 6 – SWELL-CONSOLIDATION TEST RESULTS
FIG. 7 – GRADATION TEST RESULTS
TABLE I – SUMMARY OF LABORATORY TEST RESULTS
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SUMMARY
1. A total of ten (10) exploratory borings were drilled for this study at the approximate
locations shown on Fig. 1. The borings generally encountered a thin layer of topsoil
overlying layers of natural granular and fine-grained soils that extended to the explored
depths of about 20 feet below the ground surface in Borings 1, 2, 5, 8, and 9. Borings 3,
4, 6, 7 and 10 encountered claystone bedrock underlying the natural soils that extended
to the explored depths of about 20 to 40 feet below the ground surface. The natural
granular soils consisted of well to poorly graded sand to poorly graded sand with silt and
clayey sand to silty sand. The natural fine-grained soils consisted of silt with varying sand
and gravel content to sandy lean clay. Boring 1 encountered a layer of gravel overlying
the natural overburden soils.
Groundwater was encountered in the borings at depths ranging from about 9 to 28 feet
below the ground surface at the time of drilling and was encountered in the borings at
depths of about 9 to 25 feet when subsequently checked 6 to 7 days after drilling.
Groundwater levels are expected to fluctuate with time and may fluctuate upward after wet
weather.
2. Shallow spread footing foundations should be feasible provided they are underlain by a
minimum of 2 feet properly compacted structural fill extending to undisturbed natural soils.
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 a minimum of 2 feet of properly compacted fill material extending to
undisturbed natural soils. Additional design considerations and recommendations are
presented herein.
4. For proper performance of the building foundation and floor slab, the existing fill underlying
building areas should be completely removed and replaced at the moisture and density
requirements provided herein.
5. The following table presents the minimum pavement thickness recommendations for this
development.
Paved Area
Full Depth
Asphalt
(inches)
Composite Section
Asphalt/ABC
(inches)
PCCP
(inches)
Light Duty 5.5 3.5 / 7.0 5.0
Heavy Duty 6.5 4.5 / 7.0 6.0
ABC – Aggregate Base Course
PCCP – Portland Cement Concrete Pavement
All pavements should be placed on a minimum of 2 feet of moisture-density conditioned
on-site overburden soils.
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DRAFT
Kumar & Associates, Inc.®
PURPOSE AND SCOPE OF STUDY
This report presents the results of a geotechnical engineering study and pavement thickness
design for the proposed Balfour Senior Living Facility and associated development to be
constructed at the southeast corner of Cinquefoil Lane and East Harmony Road in Fort Collins,
Colorado. The study was conducted for the purpose of developing building foundation, floor slab
and site paving recommendations. This study was performed in general accordance with our
Proposal No. P3-21-175 to Balfour Senior Living dated March 26, 2021 and revised on May 20,
2021.
A field exploration program consisting of exploratory borings was conducted to obtain information
on subsurface conditions. Samples of the soils and bedrock obtained during the field exploration
program were tested in the laboratory to determine their classification and engineering
characteristics. The results of the field exploration program and laboratory testing were analyzed
to develop geotechnical engineering recommendations for use in site earthwork and in design
and construction of the proposed development.
This report has been prepared to summarize the data obtained during this study and to present
our conclusions and recommendations based on the proposed construction and the subsurface
conditions encountered. Design parameters and a discussion of geotechnical engineering
considerations related to construction of the proposed development are included in the report.
PROPOSED DEVELOPMENT
Preliminary site plans provided to us indicate that the structures on the site will consist of an
assisted living facility with a finished floor slab elevation near the existing ground surface. We
anticipate that the buildings will be constructed with wood-framing that will have relatively light
foundation loads, typical of this type of construction. Areas outside of the building footprint will be
provided with pavement for drive lanes and parking areas. We anticipate the overall structures
will have 2 to 4 above grade levels with a slab-on-grade first floor level.
If the proposed development varies significantly from that generally described above or depicted
throughout this report, we should be notified to reevaluate the recommendations provided herein.
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SITE CONDITIONS
At the time of our exploration, the site contained two (2) abandoned residential structures, a barn
structure, a shed, and a shade structure for livestock. The site contained thick weeds and grasses
and was gently to steeply sloping down to the east. The was bounded to the north by East
Harmony Road, to west by Cinquefoil Lane, to the south by a vacant field and to the east by a
canal.
SUBSURFACE CONDITIONS
A total of ten (10) exploratory borings were drilled for this study 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 is presented on Fig. 3.
The borings generally encountered a thin layer of topsoil overlying layers of natural granular and
fine-grained soils that extended to the explored depths of about 20 feet below the ground surface
in Borings 1, 2, 5, 8, and 9. Borings 3, 4, 6, 7 and 10 encountered claystone bedrock underlying
the natural soils that extended to the explored depths of about 20 to 40 feet below the ground
surface. The natural granular soils consisted of well to poorly graded sand to poorly graded sand
with silt and clayey sand to silty sand. The natural fine-grained soils consisted of silt with varying
sand and gravel content to sandy lean clay. Boring 1 encountered a layer of gravel overlying the
natural overburden soils.
The natural granular overburden soils were fine to coarse grained with gravel, slightly moist to
wet below groundwater and brown to orange. The natural fine-grained overburden soils contained
a fine to coarse grained sand fraction and were slightly moist to moist and brown to light brown.
The claystone bedrock was fine to medium grained, moist and brown. Based on sampler
penetration resistance, the natural granular soils had consistencies ranging from medium dense
to very dense, the natural fine-grained soils were stiff to very stiff and the claystone bedrock was
very hard.
Groundwater was encountered in the borings at depths ranging from about 9 to 28 feet below the
ground surface at the time of drilling and was encountered in the borings at depths of about 9 to
25 feet when subsequently checked 6 to 7 days after drilling. Groundwater levels are expected
to fluctuate with time and may fluctuate upward after wet weather.
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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, 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 7, 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).
Index Properties: Samples were classified into categories of similar engineering properties in
general accordance with the Unified Soil Classification System. This system is based on index
properties, including liquid limit and plasticity index and gradation characteristics. Values for
moisture content and dry density, liquid limit and plasticity index, and the percent of soil passing
the U.S. No. 4 and No. 200 sieves are presented in Table I and adjacent to the corresponding
sample on the boring logs.
Swell-Consolidation: Swell-consolidation tests were conducted on samples of the overburden
soils and bedrock in order to determine their compressibility and swell characteristics under
loading and when submerged in water. Each sample was prepared and placed in a confining ring
between porous discs, subjected to a surcharge pressure of 200 or 1,000 psf, and allowed to
consolidate before being submerged in water. The samples were then inundated with water, and
the change in sample height was measured with a dial gauge. The sample heights were
monitored until deformation practically ceased under each load increment.
Results of the swell-consolidation tests are presented on Figs. 4 through 6 as plots of the curve
of the final strain at each increment of pressure against the log of the pressure. Based on the
results of the laboratory swell-consolidation testing, samples of the natural silty soils exhibited low
consolidation potential (0.4% to 1.1%) upon wetting under a surcharge pressure of 1,000 psf. A
sample of the natural clayey soils exhibited low swell potential (1.2%) upon wetting under a
surcharge pressure of 200 psf. The claystone bedrock exhibited low swell potential (1.4%) upon
wetting under a surcharge pressure of 1,000 psf. Based on our experience, the consolidation
potential exhibited by the natural silty soils was likely due to sample disturbance.
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WATER SOLUBLE SULFATES
The concentration of water soluble sulfates measured in a sample of the natural overburden soil
obtained from the exploratory borings was 0.01%. These concentrations of water soluble sulfates
represents a Class S0 severity exposure to sulfate attack on concrete exposed to these materials.
These degrees of attack are based on a range of Class S0, Class S1, Class S2, and Class S3
severity exposure as presented in ACI 201.2R-16.
Based on the laboratory test results, we believe special sulfate resistant cement will generally not
be required for concrete exposed to the on-site soils.
GEOTECHNICAL ENGINEERING CONSIDERATIONS
Removal of Existing Structures: Projects, such as this one, that may require demolition of existing
structures can be problematic unless the contractor is careful during structure removal and
backfill. The contractor should anticipate the need to completely remove the existing structure
foundations during demolition. The voids left by the foundation removal process should be
properly backfilled according the requirements outlined in the “Site Grading” section of this report.
Failure to properly moisture condition and compact the materials may result in unacceptable
movements of the proposed structure foundation elements and floor slabs.
We understand that structures on the site may contain below grade elements (i.e. basements).
For below grade elements, we recommend an underdrain system be constructed at the base of
the footing subgrade elevation as described in the “Underdrain System” section of this report.
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 2 feet of 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.
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1. Footings placed on a minimum of 2 feet of properly compacted structural fill extending to
natural soils should be designed for an allowable soil bearing pressure of 3,000 psf. The
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 foundation settlements
across the building are estimated to be approximately ½ to ¾ of the total settlement.
3. Spread footings should have a minimum footing width of 16 inches for continuous footings
and of 24 inches for isolated pads.
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 36 inches below the exterior grade is typically used in this area.
5. The lateral resistance of a spread footing placed on properly compacted structural fill 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 200 pcf. The above values are working values with a factor of safety applied.
6. Compacted fill placed against the sides of the footings to resist lateral loads should be a
non-expansive material. Fill should be placed and compacted to at least 95% of the
standard Proctor (ASTM D698) maximum dry density at a moisture content near optimum.
7. The results of our field exploration program indicate existing fill may be encountered in
foundation excavations below the proposed foundation bearing elevations. The existing
fill material should be removed to adequate natural bearing material. Areas of loose or
soft material and/or deleterious substances encountered within the foundation excavation
should also be removed and the zone of sub-excavation extended to adequate bearing
material. Removed materials should be replaced per the recommendations listed in the
“Site Grading” section of this report. New compacted structural fill should extend down
and out from the edges of the footings at a 1 horizontal to 1 vertical projection.
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8. Continuous foundation walls should be reinforced top and bottom to span an unsupported
length of at least 10 feet.
9. Areas of existing fill, loose and/or soft material, or deleterious substances encountered
within footing excavations should be removed and replaced with structural fill.
10. Care should be taken when excavating the foundations to avoid disturbing the supporting
materials.
11. A representative of the geotechnical engineer should observe all footing excavations prior
to concrete placement.
FLOOR SLABS
We recommend that slabs on grade be placed on a minimum of 2 feet of properly compacted
structural fill extending to undisturbed natural soils to mitigate the potential for settlement due to
compression of existing fills remaining beneath the floor slabs. The owner should be made aware
that there is an increased risk of floor slab movements if existing fills are left in place below floor
slabs.
To reduce the effects of some differential movement, floor slabs should be separated from all
bearing walls and columns with expansion joints which allow unrestrained vertical movement.
Interior non-bearing 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.
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)
and American Concrete Institute (ACI). The joint spacing and slab reinforcement should be
established by the designer based on experience and the intended slab use. We suggest joints
be provided on the order of about 12 to 15 feet apart in both directions. The requirements for slab
reinforcement should be established by the designer based on experience and the intended slab
use.
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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. A minimum 2-inch sand layer between the concrete and the vapor barrier
is sometimes used for this purpose.
LATERAL EARTH PRESSURES
Retaining structures should be designed for the lateral earth pressure generated by the backfill
materials, which is a function of the degree of rigidity of the retaining structure and the type of
backfill material used. Retaining structures that are laterally supported and can be expected to
undergo only a moderate amount of deflection, such as basement or vault walls, should be
designed for a lateral earth pressure based on the following equivalent at-rest fluid pressures:
CDOT Class 1 (<20% passing No. 200 Sieve) ............................................ 55 pcf
Imported, non-expansive, silty or clayey sand ............................................ 65 pcf
On-site or imported, moisture-conditioned granular backfill ........................ 65 pcf
On-site, moisture-conditioned fine-grained backfill* .................................... 70 pcf
* Swell potential less than 2%
Cantilevered retaining structures that can be expected to deflect sufficiently to mobilize the full
active earth pressure condition should be designed for the following equivalent fluid pressures:
CDOT Class 1 (<20% passing No. 200 Sieve) ............................................ 40 pcf
Imported, non-expansive, silty or clayey sand ............................................ 45 pcf
On-site or imported, moisture-conditioned granular backfill ........................ 45 pcf
On-site, moisture-conditioned fine-grained backfill* .................................... 55 pcf
* Swell potential less than 2%
The equivalent fluid pressures recommended above assume drained conditions behind retaining
structures and a horizontal backfill surface. The buildup of water behind a retaining structure or
an upward sloping backfill surface will increase the lateral pressure imposed on the retaining
structure. All retaining structures should also be designed for appropriate surcharge pressures
such as traffic, construction materials and equipment.
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The zone of backfill placed behind retaining structures to within 2 feet of the ground surface should
be sloped upward from the base of the structure at an angle no steeper than 45 degrees measured
from horizontal. To reduce surface water infiltration into the backfill, the upper 2 feet of the backfill
should consist of a relatively impervious imported soil containing at least 30% passing the No.
200 sieve, or the backfill zone should be covered by a slab or pavement structure.
Backfill should be compacted to at least 95% of the standard Proctor (ASTM D698) maximum dry
density at moisture contents within 2 percentage points of optimum for granular materials and
between 0 and +3 percentage points of optimum for clay materials. Care should be taken not to
over compact the backfill since this could cause excessive lateral pressure on the wall. Hand
compaction procedures, if necessary, should be used to prevent lateral pressures from exceeding
the design values.
SEISMIC DESIGN CRITERIA
The Colorado Front Range is located in a low seismic activity area. The soil profile will generally
consist of relatively dense overburden soils overlying claystone bedrock. It is assumed that the
bedrock materials extend to depths greater than 100 feet. The overburden soils classify as Site
Class D in accordance with International Building Code (IBC) 2012, which references ASCE 7 –
2010 for Seismic Site Class determination. The natural clayey soils and bedrock at the site will
generally classify as Site Class C. Based on our experience with similar profiles (including shear
wave velocities measured for similar subsurface profiles), and the weighted average of estimated
shear wave velocities calculated for the upper 100 feet of the site, we recommend a design soil
profile of IBC Site Class D. Based on site seismicity, the subsurface profile, and the depth to
groundwater, liquefaction is not a design consideration.
SURFACE DRAINAGE
Proper surface drainage is very important for acceptable performance of the building during
construction and after the construction has been completed. Drainage recommendations
provided by local, state and national entities should be followed based on the intended use of the
structures. The following recommendations should be used as guidelines and changes should
be made only after consultation with the geotechnical engineer.
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1. Excessive wetting or drying of the foundation and slab subgrades should be avoided
during construction.
2. Exterior backfill should be adjusted to near optimum moisture content (generally between
optimum and +3% of optimum unless indicated otherwise in the report) and compacted to
at least 95% of the ASTM D 698 (standard Proctor) maximum dry density. Backfill material
should meet the requirements stated in the “Site Grading” section of the report.
3. Care should be taken when compacting around the foundation walls and underground
structures to avoid damage to the structure. Hand compaction procedures, if necessary,
should be used to prevent lateral pressures from exceeding the design values.
4. The ground surface surrounding the exterior of the building should be sloped to drain away
from the foundation in all directions. We recommend a minimum slope of 6 inches in the
first 10 feet in unpaved areas. Site drainage beyond the 10-foot zone should be designed
to promote runoff and reduce infiltration. A minimum slope of 3 inches in the first 10 feet
is recommended in the paved areas. These slopes may be changed as required for
handicap access points in accordance with the Americans with Disabilities Act.
5. The upper 1 to 2 feet of the backfill should be relatively impervious material compacted as
recommended above to limit infiltration of surface runoff.
6. Ponding of water should not be allowed in backfill material of in a zone within 10 feet of
the foundation walls, whichever is greater.
7. Roof downspouts and drains should discharge well beyond the limits of all backfill.
8. Landscaping which requires relatively heavy irrigation and lawn sprinkler heads should be
located at least 10 feet from foundation walls. Irrigation schemes are available which allow
placement of lightly irrigated landscape near foundation walls in moisture sensitive soil
areas. Drip irrigation heads with main lines located at least 10 feet from the foundation
walls are acceptable provided irrigation quantities are limited.
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9. Plastic membranes should not be used to cover the ground surface adjacent to foundation
walls.
Surface Drainage Considerations: Proper surface drainage during and after construction is very
important to mitigate wetting of the subgrade soils. We recommend that landscape areas
adjacent to the building be provided with the maximum slope possible to promote good surface
drainage. A means of allowing water to readily leave the landscape areas, such as drain pans or
chases through a sidewalk, are recommended. All efforts possible should be made to ensure that
surface water on the site is allowed to sheet-flow to an off-site location such as a storm sewer
inlet or water quality pond located as far from the building as possible.
SITE GRADING
Temporary Excavations: For temporary excavations that occur during site grading, the man-
placed fill and natural overburden soils generally classify as OSHA Type C soil. All excavations
should be constructed in accordance with the applicable OSHA regulations. If groundwater is
encountered, the geotechnical engineer should be notified so that additional recommendations
can be provided, if necessary.
Material Specifications: The following recommendations for material specifications are presented
for new fills on the project site. A geotechnical engineer should evaluate the suitability of all
proposed import fill material, if required, for the project prior to placement.
1. Structural Fill beneath Foundations, 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 with a maximum of 50% 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 5 below.
2. Pavement Subgrade: The upper 2 feet of pavement subgrade fill should consist of the
moisture conditioned on-site overburden soils.
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3. Pipe Bedding Material: Pipe bedding material should be a free draining, coarse grained
sand and/or fine gravel.
4. Utility Trench Backfill: Material excavated from the utility trenches may be used for backfill
provided it does not contain unsuitable material or particles larger than 4 inches.
5. Material Suitability: 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 mat erials, should include
determination of laboratory moisture-density relationships and swell-consolidation tests
on remolded samples prior to acceptance.
Fill Placement Specifications: We recommend the following compaction criteria be used on the
project:
1. Moisture Content: Fill materials should be compacted as outlined below with moisture
contents of +/- 2 percent for granular soils and between optimum and 3 percentage points
above optimum moisture for clayey soils. The on-site clay soils may become somewhat
unstable and deform under wheel loads if placed near the upper end of the recommended
moisture range.
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2. Degree of Compaction: The following compaction criteria should be followed during
construction:
AREA
MINIMUM PERCENTAGE OF
STANDARD PROCTOR MAXIMUM
DRY DENSITY (ASTM D 698)
Beneath Foundations and Underslab Fill More
than 4 Feet Below Slab Subgrade Elevation 100%
Underslab Fill less than 4 Feet Beneath
Building Floor Slabs 95%
Fills Beneath Pavements and Exterior
Flatwork 95%
Utility Trenches 95%
Foundation Wall Backfill 95%
3. A representative of the geotechnical engineer should observe fill placement on a full time
basis.
UNDERDRAIN SYSTEM
The criteria presented below should be followed for construction of the subsurface (underdrain)
system.
We recommend that the foundations be protected by a perimeter drain system. Although
groundwater was not encountered in our explorations at depths near the proposed foundation/
slab elevations, it has been our experience that local perched groundwater may develop during
times of heavy precipitation, snow melt, or seasonal irrigation.
The drain system should consist of rigid drainpipe placed in the bottom of a trench or the exterior
side of the foundation and surrounded above the invert level with free-draining granular material.
Free-draining granular material used in the drain system should contain less than 5% passing the
No. 200 sieve, less than 35% passing the No. 4 sieve and have a maximum size of 2 inches. The
perimeter drain should be at least 4 inches in diameter. The drain lines should be placed at the
bottom of the structural fill layer beneath the footings and graded to sumps at a minimum slope
of 1/2%. The granular underdrain system should be sloped to a sump or multiple sumps where
water can be removed by pumping or gravity drainage.
Standby pump capacity should be provided in the event of pump failure. We also believe an
overdesigned pump capacity is desirable in the event groundwater conditions change.
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PAVEMENT DESIGN
A pavement section is a layered system designed to distribute concentrated traffic loads to the
subgrade. Performance of the pavement structure is directly related to the physical properties of
the subgrade soils and traffic loadings. Pavement design procedures are based on strength
properties of the subgrade and pavement materials assuming stable, uniform conditions. Soils
are represented for pavement design purposes by means of a soil support value for flexible
pavements and a modulus of subgrade reaction for rigid pavements. Both values are empirically
related to strength.
Subgrade Materials: Based on the results of the field and laboratory studies, the near surface
subgrade materials at the site generally classify as A-1-a to A-6 soils with group indices of 0 and
12 in accordance with the American Association of State Highway and Transportation Officials
(AASHTO) classification system. Soils classifying as A-1-a are generally considered to provide
good subgrade support, soils classifying as A-4 are generally considered to provide fair subgrade
support and soils classifying as A-6 are generally considered to provide poor subgrade support.
For design purposes, a soil support value of 4,000 psi was selected for flexible pavements.
Design Traffic: Since anticipated traffic loading information was not available at the time of report
preparation, an equivalent 18-kip daily load application (EDLA) of 5 was assumed for automobile
and light truck traffic areas and an EDLA of 15 was assumed for areas that will be accessed by
multi-unit trucks as well as fire lanes elsewhere on the site.
Pavement Design: The following table presents the minimum pavement thickness
recommendations for this development.
Paved Area
Full Depth
Asphalt
(inches)
Composite Section
Asphalt/ABC
(inches)
PCCP
(inches)
Light Duty 5.5 3.5 / 7.0 5.0
Heavy Duty 6.5 4.5 / 7.0 6.0
ABC – Aggregate Base Course
PCCP – Portland Cement Concrete Pavement
Truck loading dock areas and other areas where truck turning movements are concentrated
should be paved with 6.0 inches of Portland cement concrete. The concrete pavement should
contain sawed or formed joints to ¼ of the depth of the slab at a maximum distance of 12 to 15
feet on center.
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The above PCCP thicknesses are presented as un-reinforced slabs. If heavy vehicular loading
will occur in certain areas, we recommend that dowels be provided at transverse and longitudinal
joints within the slabs located in the travel lanes of heavily loaded vehicles, loading docks and
areas where truck turning movements are likely to be concentrated. Additionally, curbs and/or
pans should be tied to the slabs. The dowels and tie bars will help minimize the risk for differential
movements between slabs to assist in more uniformly transferring axle loads to the
subgrade. The current CDOT “Standard Specifications for Road and Bridge Construction”
provides some guidance on dowel and tie bar placement, as well as in the Standard Plans: M&S
Standards. The proper sealing and maintenance of joints to minimize the infiltration of surface
water is critical to the performance of PCCP, especially if dowels and tie bars are not installed.
Pavement Materials: The following are recommended material and placement requirements for
pavement construction for this project site. We recommend that properties and mix designs for all
materials proposed to be used for pavements be submitted for review to the geotechnical
engineer prior to placement.
1. Aggregate Base Course: Aggregate base course (ABC) used beneath hot mixed asphalt
(HMA) pavements should meet the material specifications for Class 6 ABC stated in the
current Colorado Department of Transportation (CDOT) “Standard Specifications for Road
and Bridge Construction”. The ABC should be placed and compacted as outlined in the
Site Grading section of this report.
2. Hot Mix Asphalt: Hot mix asphalt (HMA) materials and mix designs should meet the
applicable requirements indicated in the current CDOT “Standard Specifications for Road
and Bridge Construction”. We recommend that the HMA used for this project is designed
in accordance with the Super Pave gyratory mix design method. The mix should generally
meet Grading S or SX specifications with a Super Pave gyratory design revolution
(NDESIGN) of 75. The mix design for the HMA should use a performance grade PG 58-28
asphalt binder. Placement and compaction of HMA should follow current CDOT standards
and specifications.
3. Portland Cement Concrete: Portland cement concrete pavement (PCCP) should meet
Class P specifications and requirements in the current CDOT “Standard Specifications for
Road and Bridge Construction”. Rigid PCCP is more sensitive to distress due to
movement resulting from settlement or heave of the underlying base layer and/or
subgrade than flexible asphalt pavements.
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Subgrade Preparation: The pavement subgrade within 2 feet of the subgrade elevation should
be removed and replaced with properly moisture conditioned and compacted fill as outlined in the
“Site Grading” section of this report. Prior to placing the pavement section, the entire subgrade
area should be thoroughly plowed and well mixed to a minimum depth of 12 inches, adjusted to
a moisture content within 2 percentage points of optimum and compacted to 95% of the standard
Proctor maximum dry density.
Pavement design procedures assume a stable subgrade. The pavement subgrade should be
proof-rolled with a heavily loaded pneumatic-tired vehicle with a tire pressure of at least 100 psi
capable of applying a minimum load of 18-kips per axle. Areas which deform excessively under
heavy wheel loads are not stable and should be removed and replaced to achieve a stable
subgrade prior to paving. Areas of existing fill may also require deeper removal and replacement
if they are unstable.
Drainage: The collection and diversion of surface drainage away from paved areas is extremely
important to the satisfactory performance of pavement. Drainage design should provide for the
removal of water from paved areas and prevent the wetting of the subgrade soils.
It is critical to the performance of the structure and surrounding pavement that the pavement
surfaces be properly maintained. Proper maintenance includes sealing of cracks that appear in
the pavement surface. More aggressive cleaning and sealing techniques may be required if
larger cracks develop.
DESIGN AND CONSTRUCTION SUPPORT SERVICES
Kumar & Associates, Inc. should be retained to review the project plans and specifications for
conformance with the recommendations provided in this report. We are also available to assist
the design team in preparing specifications for geotechnical aspects of the project and, if
necessary, perform additional studies to accommodate any changes in the proposed construction.
We recommend that Kumar & Associates, Inc. be retained to provide construction observation
and testing services to document that the intent of this report and the requirements of the plans
and specifications are being followed during construction. This will allow us to identify possible
variations in subsurface conditions from those encountered during this study and to allow us to
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Kumar & Associates, Inc.®
re-evaluate our recommendations, if needed. We will not be responsible for implementation of the
recommendations presented in this report by others, if we are not retained to provide construction
observation and testing services.
LIMITATIONS
This study has been conducted for exclusive use by the client for geotechnical related design and
construction criteria for the project. The conclusions and recommendations submitted in this
report are based upon the data obtained from the exploratory borings at the locations indicated
on Fig. 1 or as described in the report, and the proposed type of construction. This report may
not reflect subsurface variations that occur between the exploratory borings, and the nature and
extent of variations across the site may not become evident until site grading and excavations are
performed. If during construction, fill, soil, rock or water conditions appear to be different from
those described herein, Kumar & Associates, Inc. should be advised at once so that a re-
evaluation of the recommendations presented in this report can be made. Kumar & Associates,
Inc. is not responsible for liability associated with interpretation of subsurface data by others.
Swelling soils occur on this site. Such soils are stable at their natural moisture content but 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.
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/ma
Rev. by: JLB
cc: book, file
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
Project No.:21-3-164
Project Name: Balfour-Fort Collins
Date Sampled: June 2, 2021 and June 3, 2021
Date Received:
Boring Depth (Feet)
Gravel
(%)Sand (%)
Liquid
Limit (%)
Plasticity
(%)
1 4 6/11/21 4.7 95.8 83 NV NP 0.01 A-4 (0)Silt with Sand (ML)
2 1 6/11/21 18.4 103.1 14 11 75 NV NP A-4 (0)Silt with Gravel (ML)
3 4 6/11/21 17.7 106.7 69 30 12 A-6 (6)Sandy Lean Clay (CL)
3 9 6/11/21 9.1 104.0 5 89 6 NV NP A-1-a (1)Poorly Graded Sand with Silt (SP-SM)
4 1 6/11/21 5.8 110.0 23 65 12 NV NP A-1-a (0)Poorly Graded Sand with Silt (SP-SM)
4 14 6/11/21 17.8 107.2 Claystone Bedrock
5 4 6/11/21 5.3 91.7 87 NV NP A-4 (0)Silt (ML)
6 1 6/11/21 21.1 102.8 1 23 76 36 18 A-6 (12)Sandy Lean Clay (CL)
7 4 6/11/21 6.3 95.4 82 NV NP A-4 (0)Silt with Sand (ML)
8 1 6/11/21 10.9 10 40 50 30 13 A-6 (3)Sandy Lean Clay (CL)
9 4 6/11/21 5.0 11 50 39 28 13 A-6 (1)Clayey Sand (SC)
9 9 6/11/21 2.7 21 79 0 NV NP A-1-a (2)Well Graded Sand with Gravel (SW)
10 1 6/11/21 15.0 111.2 12 39 49 33 13 A-6 (3)Clayey Sand (SC)
Table I
Sample Location Gradation Atterberg Limits
Date
Tested
Natural
Moisture
Content
(%)
Natural
Dry
Density
(pcf)
Percent
Passing
No. 200
Sieve
June 4, 2021
Water
Soluble
Sulfates
(%)
AASHTO
Classification
(Group Index)Soil or Bedrock Type
Summary of Laboratory Test Results