HomeMy WebLinkAboutPROSPECT 7-ELEVEN STORE NO. 35506 - PDP - PDP120002 - SUBMITTAL DOCUMENTS - ROUND 1 - CORRESPONDENCEREPORT OF GEOTECHNICAL
ENGINEERING EVALUATION
PROPOSED 7-ELEVEN
3045 WEST PROSPECT ROAD
FORT COLLINS, COLORADO
PSI PROJECT NUMBER 0532395
Prepared for
Ripsaw Development, LLC
c/o Verdad Real Estate
1121 Grant Street
Suite 2-A
Denver, Colorado
Attn: Ms. Jen Volin
Prepared by
Professional Service Industries, Inc. ELECTRONIC COPY
1070 West 124th Avenue, Suite 800
Westminster, Colorado 80241 Matthew R. Satterfield, P.E.
(303) 424-5578 Project Engineer
ELECTRONIC COPY
Chris P. Willden, E.I.
Staff Engineer
Reviewed By:
Kevin C. Miller, P.E.
December 9, 2011 Principal Consultant
TABLE OF CONTENTS
1.0 INTRODUCTION.........................................................................................................1
2.0 PROJECT INFORMATION.........................................................................................1
3.0 SUBSURFACE INFORMATION.................................................................................2
3.1 SITE GEOLOGY AND GEOLOGIC HAZARDS...................................................................2
3.2 SUBSURFACE CONDITIONS.........................................................................................2
3.2.1 Subsurface Profile .............................................................................................2
3.2.2 Groundwater Conditions....................................................................................3
3.2.3 Laboratory Testing.............................................................................................3
4.0 GEOTECHNICAL EVALUATION...............................................................................4
5.0 SITE GRADING RECOMMENDATIONS....................................................................4
5.1 ENGINEERED FILL ......................................................................................................4
5.1.1 Imported Structural Fill ......................................................................................5
5.2 GENERAL FILL PLACEMENT AND TESTING ...................................................................5
5.3 BACKFILL OF EXISTING UNDERGROUND STORAGE TANKS ...........................................6
6.0 GEOTECHNICAL RECOMMENDATIONS.................................................................6
6.1 FOUNDATIONS ...........................................................................................................6
6.2 SLABS ON GRADE ......................................................................................................8
6.4 SEISMIC PARAMETERS .............................................................................................10
6.5 PAVEMENT DESIGN RECOMMENDATIONS ..................................................................10
6.5.1 Subgrade Preparation Recommendations ......................................................10
6.5.2 Pavement Thickness Recommendations ........................................................11
6.5.3 Flexible Pavement ...........................................................................................12
6.4.4 Aggregate Base Course ..................................................................................12
6.5.5 Rigid Pavement ...............................................................................................12
7.0 LIMITATIONS ...........................................................................................................13
ATTACHMENTS
Site Location Map (Figure 1)
Boring Location Map (Figure 2)
Boring Logs (Figures 3 through 6)
Key to Symbols (Figure 7)
Appendix A – Laboratory Test Results
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3045 West Prospect Road PSI Project No. 0532395
Fort Collins, Colorado Page 1 of 13
1.0 INTRODUCTION
Professional Service Industries, Inc. (PSI) has conducted a geotechnical engineering
exploration of the site for the proposed 7-Eleven to be located at 3045 West Prospect
Road in Fort Collins, Colorado. The purpose of our study was to characterize the
subsurface strata at the subject site and to develop recommendations for site
preparation and foundation design for the proposed 7-Eleven structure. Our services on
this project were in accordance with the PSI Proposal No. 57484, which was authorized
by TK Keen with Ripsaw Development on November 15, 2011.
PSI’s scope of services for the geotechnical study did not include an assessment of
environmental conditions in the soil, bedrock, surface water, groundwater, or air, on or
below, or around this site. Any statements in this report or on the boring logs regarding
odors, colors, and unusual or suspicious items or conditions are strictly for informational
purposes.
The report, which follows, presents a brief review of our understanding of the project, a
discussion of the site and subsurface conditions, and our recommendations.
2.0 PROJECT INFORMATION
PSI understands that Ripshaw Development is planning the construction of a new 7-
Eleven convenience store to be located at the southeast corner of West Prospect Road
and South Overland Trail in Fort Collins, Colorado (See Figures 1 and 2). PSI’s project
understanding is based on information provided by Ms. Volin via email on November 14,
2011, along with information provided for our Environmental Phase I proposal. This
information included a “Concept Layout – Alt 0” dated November 10, 2011, and a site
survey dated October 25, 2011
The site currently has a gas station occupying the the lot. The existing gas station has
underground storage tanks for their fueling services. PSI has included recommendations
in this report for backfilling excavations if the tanks are removed. The latitude and
longitude of the subject site is approximately 40º 34’ 04” North and 105º 08’ West. The
site is bounded by South Overland Trail to west, West Prospect Road to the north, and
commercial developments to the south and east. The site is relatively flat with grade
changes on the order of approximately two feet.
Based on the information provided to PSI, we understand that the proposed 7-Eleven
development will include the construction of a 3,008 square foot, single story-building. A
slab-on-grade floor system is preferred for the 7-Eleven Structure. Foundation loads
were not provided to PSI at the time of this study. However, this report is based on the
project loads having typical ranges as follows: column loads from 75 to 120 kips and wall
loads of 1 to 1.5 kips per linear foot. Grading plans were provided to PSI, we expect cuts
and fills on the site will be on the magnitude two feet.
Descriptions of the site are based upon observations made during our field exploration
program. The geotechnical recommendations presented in this report are based upon
the available project information and the subsurface materials described in this report. If
any of the noted information is incorrect, please inform us so that we may amend the
recommendations presented in this report, if needed.
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3.0 SUBSURFACE INFORMATION
The following sections provide information relating to subsurface conditions in the area
of the proposed addition. The geology section is based upon the “Geologic Map of
Colorado” by Ogden Tweto, dated 1979 and information relating to subsurface
conditions within the property gathered from our current field study.
3.1 Site Geology and Geologic Hazards
The site is located on the high plains approximately 1 mile east of the foothills of the
Rocky Mountains. Based on the United States Geological Survey (USGS) “Geologic
Map of Colorado” by Ogden Tweto, 1979, the majority of the site is mapped as being
underlain by Colorado Group (Kc) deposits which includes either Benton shale or Carlile,
Greenhorn, and Graneros formations.
3.2 Subsurface Conditions
As part of PSI’s evaluation of this site, 4 exploratory borings were drilled at the subject site
as indicated on Figure 2, the Boring Location Map. Borings B1 and B2 were drilled within
the footprint of the proposed 7-Eleven and extended to depths of approximately 20 feet
below the existing grade. Borings B3 and B4 were drilled within the proposed new
pavement area and extended to depths of approximately 5 feet below grade. The borings
were advanced using a CME-55 truck mounted drill rig equipped with 4-inch diameter,
solid-stem, continuous-flight auger. Soil samples were recovered at selected depths during
drilling with the truck-mounted drill rig using a Modified California Barrel Sampler (inside
diameter- 2.0 inches and outside diameter- 2.4 inches) or a Standard Split Spoon Sampler
(inside diameter- 1.375 inches and outside diameter- 2 inches) driven by a 140-lb. weight
free falling 30 inches. The number of blows required to drive the sampler 12 inches is
designated as the penetration resistance (N-value, blows per foot) and provides an
indication of the consistency of cohesive soils and the relative density of granular materials.
While the procedure is similar to that employed in the Standard Penetration Test (ASTM
D1586), the penetration resistance obtained using the California barrel sampler is generally
higher than that obtained using the standard split spoon sampler.
A PSI engineer from our office observed the drilling and prepared borings and logs of the
conditions encountered. Individual logs of the borings are presented on Figures 3 through
6. It should be noted that the subsurface conditions presented on the boring logs are
representative of the conditions at the specific locations drilled. Variations may occur and
should be expected across the site. The stratification represents the approximate boundary
between subsurface materials and the transitions may be gradual and indistinct. Water
level information, if encountered, obtained during our field operations is also shown on the
boring logs.
3.2.1 Subsurface Profile
In general, PSI encountered fill material to approximately 2 feet below grade. Beneath
the fill material, native overburden soils were encountered to the termination of the
borings, approximately 20 feet below grade. PSI encountered approximately 3 inches of
asphalt pavement in the borings. The fill material was generally dark gray to dark brown,
gravelly in parts and fine to coarse grained sand. Underlying the fill material, the native
overburden material generally consisted of clayey sand and sandy clay. In general the
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Fort Collins, Colorado Page 3 of 13
native overburden material was reddish brown, fine to medium grained sand, moist and
soft to stiff. Sedimentary bedrock was not encountered during our field activities.
The table below provides general engineering properties for the native overburden
materials encountered.
Material / Property
Dry Density
(pcf)
Moisture
Content (%)
Liquid Limit (%)
Plastic Limit (%)
N Value
(blows/ft)
Swell (%)
CLAYEY SAND/ Range 110-128 8-19 24-30 13-16 10-30 0.3-1.2
SANDY CLAY
(SC-CL) Average 116 11 28 15 17 0.6
* Swell percentage when wetted under a 250 psf surcharge pressure
As can be seen above, PSI performed Denver Swell Testing on selected samples of the
overburden material collected during our field investigation. The test results indicated
swell percentages ranging from 0.3% in building area to 1.2% in the pavement area,
when tested under a 250 psf surcharge pressure. PSI classifies the soil conditions
encountered in our investigation as having low swell potential. PSI does not recommend
swell mitigation be performed for the proposed construction.
The Boring Logs illustrated in Figures 3 through 6 should be reviewed for specific
information at individual boring locations. These records include soil descriptions,
stratifications, penetration resistances, locations of the samples and laboratory test data.
3.2.2 Groundwater Conditions
Groundwater was not encountered during our drilling operations. However, the in-situ
moisture contents of samples collected in the field indicate that the native soils may be
saturated. PSI believes that the actual groundwater elevation may be as high as 5 feet
below grade. It should be noted that it is possible for the groundwater table to fluctuate
during the year depending upon climatic and rainfall conditions and changes to surface
topography and drainage patterns. Discontinuous zones of perched water may also
exist, or develop, within the overburden materials subsequent to the construction. The
groundwater levels presented in this report are the levels that were measured at the time
of our field activities.
3.2.3 Laboratory Testing
The soil samples obtained during the field exploration were transported to the laboratory
and selected soil samples were tested in the laboratory to determine material properties
for our evaluation. Laboratory testing was accomplished in general accordance with
ASTM and other applicable procedures. Laboratory testing was performed on selected
samples to evaluate the classification, swell and other engineering characteristics of the
subsurface materials. Laboratory test data along with detailed descriptions of the soils
can be found on the logs of borings and in Appendix A. The samples that were not
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altered by laboratory testing will be retained for 30 days from the date of this report and
then will be discarded without further notice.
4.0 GEOTECHNICAL EVALUATION
The following geotechnical related recommendations have been developed on the basis
of the subsurface conditions encountered and PSI’s understanding of the proposed
development. Should changes in the project criteria occur, a review must be made by
PSI to determine if modifications to our recommendations will be required.
There are 2 primary geotechnical concerns at the site, which will affect the performance
of the foundations for this structure. The following summarizes those concerns.
1. The shear strength and compressibility of the upper soils will control the behavior
of the proposed structure.
2. Existing undocumented fill material was encountered within the proposed
development area.
1. Shear Strength and Compressibility of Soil
Due to the sandy nature of the soils found during our investigation, the calculated
settlements will control the foundation size of the structures. Even though the clayey
sand material yields a relatively high allowable bearing capacity, limiting the loads
applied to the strata can limit the potential settlement of the structures. PSI provides
allowable bearing capacities along with the calculated settlements that could be
anticipated.
2. Existing Undocumented Fill
Based on PSI’s field investigation, the site is underlain by 1 ½ to 2 feet of fill material. Due
to the consistency of the fill material encountered, PSI does not recommend that the fill
material be overexcavated and replaced. However, if loose material is encountered during
excavations, PSI recommends that the loose soils be overexcavated and replaced as
structural fill material.
5.0 SITE GRADING RECOMMENDATIONS
Prior to excavation for foundation construction, the site should be stripped of asphalt
pavement, vegetation, topsoil, loose uncompacted fill, soil stockpiles, and debris. The
stripped vegetation/topsoil may be re-placed as topsoil in designated landscape areas.
The loose soils or stockpiled soils may be incorporated and placed as structural fill.
Trash and debris should be disposed of in accordance with local and state regulations.
5.1 Engineered Fill
Based on PSI’s field and laboratory data it is our opinion that on-site overburden soils will
be suitable for re-use as backfill soils and for use as structural fill, provided the material is
properly moisture conditioned and compacted. If unanticipated material such as
construction debris, trash, or other undesirable material is encountered during construction,
they should be removed off site.
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5.1.1 Imported Structural Fill
Imported structural fill, if required, should be free of organic or other deleterious
materials, have a liquid limit less than 30, a plasticity index less than 10, and meet the
following gradation outlined below. This structural fill criteria is intended as a general
guideline. Imported structural fill materials should have a swell potential of less than 1
percent when compacted to 95 percent of maximum dry unit weight (MDUW) and at 2
percent below optimum moisture content (OMC) and tested under a swell test surcharge
of 500 psf. The MDUW and OMC should be determined by ASTM D698 (Standard
Proctor).
Screen Size Percent Passing
2 Inch 100
#4 50 – 100
#200 < 30
Imported fill material proposed for use on this site that does not meet these criteria
should be submitted to the project geotechnical engineer for evaluation and approval.
The geotechnical engineer should evaluate the proposed import fill prior to purchase and
delivery. Fine-grained soils used for fill require close moisture content control and
careful placement by the contractor to achieve the recommended degree of compaction
and to control swell potential and settlement.
5.2 General Fill Placement and Testing
Unless otherwise specified, fill material should be compacted to at least 95 percent of
the maximum dry unit weight as determined by the Standard Proctor Test (ASTM D
698). Each lift of compacted fill should be tested for density by a representative of the
geotechnical engineer prior to placement of subsequent lifts. Sand fill soils should be
moisture conditioned to between two percent below and two percent above optimum
moisture content and clay fill soils should be moisture conditioned to a range from
optimum moisture content to four percent above optimum moisture content. Fill material
should be placed in maximum eight inch loose lifts.
A sample(s) of the proposed backfill soil(s) should be obtained for moisture density
relationship (proctor test) three to four days prior to backfilling operations to expedite
compaction and moisture content testing by the materials testing service provider.
Weather conditions in the site area are typically dry in the summer and early fall.
Precipitation in the form of snowfall is common from October through March. While
grading can be inhibited for short periods during and following times of precipitation,
grading can generally be conducted year round. The major factor that must be
considered during the winter months is ground freezing. During extended periods of
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sub-freezing weather, it can be difficult to properly moisture condition and compact soils.
Grading must be conducted during the warmer parts of the day in freezing weather.
5.3 Backfill of Existing Underground Storage Tanks
If the existing underground storage tanks at the site are removed, PSI recommends
backfilling the excavations with CDOT Class 2 material to approximately 3 feet below the
final grade. The CDOT Class 2 material should be placed in loose 8’’ lifts and each lift
should be compacted in accordance with section 5.2 of this report. When the CDOT
Class 2 material is within 3 feet below final grade, a geo-fabric should be placed over the
material and structural fill should be used to backfill the top 3 feet of the excavations.
The structural fill should meet the criteria mentioned in this report and be placed and
compacted in accordance with section 5.2 of this report.
6.0 GEOTECHNICAL RECOMMENDATIONS
The proposed structure may be founded on continuous or individual column footings
bearing in competent native clayey sand and sandy clay materials and may also employ
slab-on-grade floors, provided the site is prepared as previously outlined. The
geotechnical engineer should verify that the soils encountered in our investigation are
consistent with the conditions encountered during foundations excavations.
6.1 Foundations
PSI recommends that the proposed structure be supported on continuous or individual
column footings and should be designed for an allowable soil bearing pressure as shown
in the following tables:
Allowable Bearing Column Pad Size (inches)
Capacity of Individual
Column Pad 48 X 48 60 X 60 66 X 66 72 X 72
1 ½ feet N/A N/A N/A 3,700 psf
3 feet N/A 4,950 psf 5,125 psf 5,275 psf
4 feet N/A 6,100 psf 6,250 psf 6,400 psf
Bearing
Depth of
Foundation
below
existing
grade 5 feet N/A 7,325 psf 7,450 psf 7,575 psf
N/A= Allowable bearing capacities do not meet the required bearing loads based on the
120 kips column load used in the calculations.
Allowable Bearing Capacity of
Continuous Footing Allowable Bearing Capacity
1 ½ feet 1,650 psf
3 feet 3,350 psf
Bearing Depth of
Foundation Below
Existing Grade
4 feet 4,675 psf
Proposed 7-Eleven December 9, 2011
3045 West Prospect Road PSI Project No. 0532395
Fort Collins, Colorado Page 7 of 13
The allowable bearing capacities provided in the tables above are based on a factor of
safety of 3 and that the existing grade is at or near the proposed final grade elevation.
The above bearing capacities were calculated using 120 kip column loads and a 1.5 kips
per linear foot continuous footing loads.
PSI has calculated the expected settlement using 120 kip column loads and 1.5 kips per
linear foot continuous footing loads. The expected settlement results are displayed in the
following tables.
Column Pad Size (inches)
Expected Settlement
48 X 48 60 X 60 66 X 66 72 X 72
1 ½ feet N/A N/A N/A 1-1/8 in.
3 feet N/A 1-3/8 in. 1-1/4 in. 1 in.
4 feet N/A 1-3/8 in. 1-1/8 in. 1 in.
Bearing
Depth of
Foundation
below
existing
grade 5 feet N/A 1-1/4 in. 1-1/8 in. 1 in.
N/A= Not calculated because the bearing capacities do not meet the required bearing
loads based on the 120 kip column load used in the calculations.
Expected Settlement
(inches) Continuous Footing – 16 Inches Wide
1 ½ feet ¼ inch
3 feet ¼ inch
Bearing
Depth of
Foundation
below
existing
grade 4 feet ¼ inch
Continuous footings supporting bearing walls should incorporate a minimum lateral
dimension of 16 inches. Exterior footings should bear at a minimum of 36 inches below
final grade for frost protection. Interior footings should bear at 18 inches below final
grade. However, if the footing excavations expose the onsite fill material at the elevation
of the bottom of the footing, PSI recommends extending the bottom of the footing depths
to native soil.
The uplift capacity of shallow foundations should be limited to the weight of the
foundation concrete plus the weight of the soil immediately above the footing. A
concrete unit weight of 145 pcf and a soil unit weight of 110 pcf should be used for
design purposes.
Lateral loads applied to the foundations will be resisted by a combination of passive
pressure against the sides and friction along the base. For design purposes, PSI
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recommends using an equivalent fluid pressure of 50 pcf for the “active” case and 70 pcf
for the “at-rest” case. A passive pressure of 250 pcf to a depth of 15 feet along with a
coefficient of friction of 0.3 is recommended.
The foundation excavations should be observed by a representative of PSI prior to
reinforcing steel or concrete placement to assess that the foundation bearing materials
are capable of supporting the design loads and are consistent with the materials
discussed in this report. Soft or loose zones encountered at the bottom of the footing
should be removed and replaced with properly compacted fill as directed by the
geotechnical engineer.
After the foundation bearing materials have been approved, steel reinforcement and
concrete should be placed as quickly as possible to avoid exposure of the footing
bottoms to wetting and drying. Surface run-off water should be drained away from the
excavations and not be allowed to pond. If possible, the foundation concrete should be
placed during the same day the excavation is made. If it is required that the excavation
be left open for more than one day, they should be protected to reduce evaporation or
entry of moisture.
6.2 Slabs on Grade
A slab-on-grade interior floor slab system may be utilized for the proposed addition. PSI
anticipates that slabs-on-grade placed on soil prepared as stated in this could
experience total movement on the order of 1 inch with differential movements on the
order of ½ inch over a 50 foot span. This settlement is based on the slabs not exceeding
150 psf loading. PSI recommends proofrolling the subgrade for the slabs to identify
areas of loose soils prior to placement of concrete. The proofroll should be conducted
with a loaded tandem-axle dump truck or similar pneumatic-tired equipment with a
minimum weight of 15 tons and a maximum weight of 25 tons. If soft spots are
discovered in the subgrade, they should be overexcavated and replaced with
reconditioned and compacted structural fill in accordance with this report.
If the slab is placed on structural fill material PSI recommends a subgrade support
modulus (k-value) of 125-pci (based on a 1 foot square plate load test) be used for slab
design. However, depending on how the slab load is applied, the value will have to be
geometrically modified. The value should be adjusted for larger areas using the following
expression for cohesive and cohesionless soil:
Modulus of Subgrade Reaction, ks = (
B
k ) for cohesive soil and
ks = k (
B
B
2
1
)2 for cohesionless soil
where: ks = coefficient of vertical subgrade reaction for loaded area,
k = coefficient of vertical subgrade reaction for 1x1 square foot area,
and
B = width of area loaded, in feet
Where concrete slabs will be covered with tile or other moisture sensitive covering, we
recommend the use of a vapor retarder beneath the slabs on grade to reduce vapor
transmission through the slab.
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The precautions listed below are considered good construction practice. Due to the non-
expansive soils encountered on-site, these recommendations are not required, but can
be followed to prevent moisture content variation.
Cracking of slabs-on-grade can occur as a result of heaving or compression of the
supporting soil, but also as a result of concrete curing stresses. The occurrence of
concrete shrinkage cracks, and problems associated with concrete curing may be
reduced and/or controlled by limiting the slump of the concrete, proper concrete
placement, finishing, and curing, and by the placement of crack control joints at
frequent intervals, particularly, where re-entrant slab corners occur. The American
Concrete Institute (ACI) recommends a maximum panel size (in feet) equal to
approximately three times the thickness of the slab (in inches) in both directions. For
example, joints are recommended at a maximum spacing of 12 feet assuming a four-
inch thick slab. We also recommend that control joints be scored three feet in from and
parallel to all foundation walls. Using fiber reinforcement in the concrete can also
control shrinkage cracking.
A minimum 1-inch void space is recommended above, or below partitions that are
placed on the slab. In finished areas, all furring strips, drywall and paneling should stop
at least 1 inch from the top of the slab. The void space can be covered with a molding
strip. Doorways should also be designed for this movement. NOTE: These void
spaces are not intended to anticipate total potential slab movement. They are intended
to prevent immediate damage to the superstructure and serve as an indicator of slab
movement. They must be monitored and maintained by the owner for the life of the
structure.
Slabs should be separated from exterior walls, column posts, interior bearing members
and utility lines to allow independent vertical movement of the slab. If project structural
and architectural details require the slab on grade to be structurally tied to the exterior
wall/foundation system, then control joints should be placed in the slab within
approximately 3 feet of the wall. The owner must understand and accept the risk of
cracking at or near the control joints if the slab on grade is tied to the foundation
system.
Some increase in moisture content is inevitable as a result of development and
associated landscaping. However, extreme moisture content increases can be
largely controlled by proper and responsible site drainage, building maintenance
and irrigation practices.
Utility backfill in areas supporting slabs should be moisture conditioned or dried by
scarification, and compacted. Backfill in all interior and exterior water and sewer line
trenches should be uniformly compacted.
Exterior slabs should be isolated from the building. These slabs should be reinforced to
function as independent units. Movement of these slabs should not be transmitted to the
building foundation or superstructure.
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Fort Collins, Colorado Page 10 of 13
6.4 Seismic Parameters
The project site is located within a municipality that employs the International Building
Code, 2006 edition. As part of this code, the design of structures must consider dynamic
forces resulting from seismic events. These forces are dependent upon the magnitude of
the earthquake event as well as the properties of the soils that underlie the site. As part of
the procedure to evaluate seismic forces, the code requires the evaluation of the Seismic
Site Class, which categorizes the site based upon the characteristics of the subsurface
profile within the upper 100 feet of the ground surface. To define the Site Class for this
project, we have interpreted the expected results of soil test borings drilled with the project
site and estimated appropriate soil properties below grade to a depth of 100 feet, as
permitted by Section 1615.1.1 of the code. The estimated soil properties were based upon
data available in published geologic reports as well as our experience with subsurface
conditions in the general site area.
Based upon our evaluation, it is our opinion that the subsurface conditions within the site
are consistent with the characteristics of Site Class D as defined in Table 1615.1.1 of the
building code.
The USGS-NEHRP interpolated probabilistic ground motion values near 40º 34’ 04”
North and 105º 08’ West obtained from the USGS geohazards web page are as follows:
Period
2% Probability
of Event in 50
years
Site
Coefficient
Site
Coefficient
(seconds) (% g) Fa Fv
0.2 (Ss) 18.9 1.6 NA
1.0 (S1) 5.9 NA 2.4
The Site Coefficients, Fa and Fv presented in the above table were interpolated from
IBC Tables 1615.1.2(1) and 1615.1.2(2) as a function of the site classification and
mapped spectral response acceleration at the short (Ss) and 1 second (S1) periods.
6.5 Pavement Design Recommendations
The following analysis and pavement thickness recommendations are in general
accordance with AASHTO and the Colorado Department of Transportation Pavement
Design Manual.
6.5.1 Subgrade Preparation Recommendations
Due the fill material encountered during PSI’s field investigation, PSI recommends that
the subsurface material be overexcavated to a depth of 1 foot below final subgrade
elevation and replaced as moisture conditioned and compacted structural fill. This will
provide a more uniform subgrade for support of the proposed pavement sections.
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PSI recommends that the subgrade soils to support the proposed pavements be
overexcavated to a depth of 1 feet below final subgrade elevation and replaced as
moisture conditioned compacted structural fill in accordance with Section 5.1.
Once the areas below the parking area have been overexcavated, the existing site soils
should be proofrolled to identify areas of loose soils prior to placement of moisture
conditioned, compacted soils (either on-site or imported). The proofroll should be
conducted with a loaded tandem-axle dump truck or similar pneumatic-tired equipment
with a minimum weight of 15 tons and a maximum weight of 25 tons.
6.5.2 Pavement Thickness Recommendations
Based on the sandy clay material encountered during our subsurface investigation, PSI has
based this report on an R-value of 7 to support the proposed pavement sections.
PSI has identified two pavement categories based on anticipated traffic use and traffic
loads. We have assigned estimated traffic loads to each category expressed in EDLA’s,
where the EDLA is the equivalent daily load applications of vehicles relative to an 18-kip
single axle load. We have also based the pavement thickness design on the following
design criteria; a 20-yr design life, a Pavement Serviceability Index (PSI) of 2.0 and a
Reliability of 85%.
PSI has assigned an estimated EDLA of 2 for the general parking stall (Light Duty
Traffic) area. Anticipated traffic in this area includes private passenger vehicles or
similar vehicles.
The drive lanes within the site have been assigned an estimated EDLA of 5 (Heavy
Duty Traffic - Drive Lanes), PSI anticipates that traffic in this area will be mixed use
consist of delivery vehicles of varying size and weight and passenger vehicles.
Pavement section options are provided for full depth asphalt, asphalt over aggregate
base course, and rigid (Portland Cement Concrete) pavement. However, it is PSI’s
experience that pavements with properly placed base aggregate on a properly drained
grade outperforms full depth pavement sections. Based on this information for the
subject pavement, the following pavement sections were determined, as presented
below.
Pavement Area Composite Section
(inches)
Full-Depth Asphalt
(inches)
Full-Depth
Portland Cement
Concrete (inches)
Light Duty Traffic
Parking Stalls
(EDLA = 2)
3 ½ inches Asphalt
over
7 inches Aggregate
Base Course
6 inches 6 inches
Heavy Duty Traffic
Drive Lanes
(EDLA = 5)
4 inches Asphalt
over
8 inches Aggregate
Base Course
6 ½ inches 6 inches
Proposed 7-Eleven December 9, 2011
3045 West Prospect Road PSI Project No. 0532395
Fort Collins, Colorado Page 12 of 13
Concrete pavement at least seven inches thick is recommended for the trash
dumpster run-up due to the heavy wheel and impact loads that this area receives. The
run-up should extend far enough away to support all wheels of the sanitation truck while
stopped and in the loading position. Concrete pavement is also recommended in areas,
which receive continuous repetitive traffic such as product unloading areas and parking
lot entrances.
6.5.3 Flexible Pavement
Structural sections for parking lot and drive lane pavements may be full depth asphalt, a
composite section of asphalt pavement over aggregate base course or Portland Cement
concrete pavement.
Flexible pavement is not recommended for Dumpster Pad/ Sanitation Truck Run-up
areas. For Dumpster Pad/Sanitation Truck Run-up areas we recommend rigid
pavement as discussed in the following Rigid Pavement Section. Allowances for proper
drainage and proper material selection of base materials are most important for
performance of asphaltic pavements. Ruts and birdbaths in asphalt pavement allow for
quick deterioration of the pavement primarily due to saturation of the underlying base
and subgrade.
Hot bituminous pavement should meet the requirements as detailed for SuperPave
Mixtures in Colorado Department of Transportation Standard Specifications for Road and
Bridge Construction. Material meeting the Colorado Department of Transportation
requirements for Grading S (¾ inch nominal) or Grading SG (1 ½ inch nominal) is
recommended. In addition, the following are presented as general guidelines for properties
of asphaltic concrete.
Parking Lot
Asphalt Cement PG 64-22
Asphalt Content As per mix design
Percent Air Voids 3½-5
Asphalt material should be obtained from an approved mix design stating the SuperPave
Mixture properties, including optimum asphalt content, job mix formula, and recommended
mixing and placing temperatures. Materials and construction methods should be in
accordance with the CDOT Standard Specifications for Road and Bridge Construction
Section 403.
6.4.4 Aggregate Base Course
If aggregate base course is used as part of the pavement section, the materials should
conform to CDOT requirements for Class 5 or 6 aggregate base course per Table 703-2
and construction methods should conform to Section 304 of the Colorado Department of
Transportation Standard Specifications for Road and Bridge Construction.
6.5.5 Rigid Pavement
The use of concrete for on-site pavements may be considered by the owner. Should
concrete pavement be utilized, the concrete should be properly reinforced and jointed
Proposed 7-Eleven December 9, 2011
3045 West Prospect Road PSI Project No. 0532395
Fort Collins, Colorado Page 13 of 13
and should be constructed from a concrete mixture, which has a 28-day minimum
laboratory compressive strength of 4,000 psi. We recommend a maximum water cement
ratio of 0.45 and an air-entrainment specification of 5 percent (±1.5 percent) be followed.
Expansion joints should be sealed with a polyurethane sealant so that moisture
infiltration into the subgrade soils and resultant concrete deterioration at the joints is
reduced.
7.0 LIMITATIONS
The recommendations submitted are based on the available subsurface information
obtained by PSI and design details furnished by Ripsaw Development and 7-Eleven. If
there are revisions to the plans for this project or if deviations from the subsurface
conditions noted in this report are encountered during construction, PSI should be notified
immediately to determine if changes in the foundation recommendations are required. If
PSI is not retained to perform these functions, PSI will not be responsible for the impact of
those conditions on the project.
The geotechnical engineer warrants that the findings, recommendations, specifications, or
professional advice contained herein have been made in accordance with generally
accepted professional geotechnical engineering practices in the local area. No other
warranties are implied or expressed.
After the plans and specifications are more complete, the geotechnical engineer should be
retained and provided the opportunity to review the final design plans and specifications to
check that our engineering recommendations have been properly incorporated into the
design documents. At that time, it may be necessary to submit supplementary
recommendations. This report has been prepared for the exclusive use of 7-Eleven and
their consultants for the specific application to the proposed 7-Eleven Store located at 3045
West Prospect Road in Fort Collins, Colorado.
SC
CL
SC
15
9
7
18
10
1
2
3
4
5
12
12
12
12
12
DD = 110 pcf
-200 = 44.8%
DD = 113 pcf
LL = 24
PL = 13
DD = 117 pcf
-200 = 19.4%
DD = 112 pcf
LL = 30
PL = 14
DD = 128 pcf
-200 = 24.1%
7-6
N=13
3-9
N=12
9-12
N=21
10-10
N=20
12-18
N=30
ASPHALT - Approximately 3 Inches Thick
MAN-MADE FILL- Composed of Sand and
Clay, Fine to Coarse Grained Sand, Gravel in
Areas, Dark Gray to Dark Brown
CLAYEY SAND (SC) - Reddish Brown, Fine
to Medium Grained Sand, Moist, Medium Stiff
to Stiff
SANDY CLAY (CL) - Silty in Parts, Reddish
Brown, Fine to Medium Grained Sand, Moist,
Stiff
CLAYEY SAND (SC) - Tan, Fine to Coarse
Grained Sand, Moist, Very Stiff
PROJECT NO.: 0532395
PROJECT: 7-Eleven
Depth, (feet)
STRENGTH, tsf
Additional
Remarks
USCS Classification
0
SC
CL
SC
8
18
19
1
2
3
4
5
12
12
12
12
12
S(250) = 0.3%
-200 = 31.5%
DD = 122 pcf
-200 = 28.7%
DD = 111 pcf
-200 = 79.2%
DD = 110 pcf
LL = 31
PL = 14
10-12
N=22
6-6
N=12
7-9
N=16
7-10
N=17
6-10
N=16
ASPHALT - Approximately 3 Inches Thick
MAN-MADE FILL- Composed of Sand and
Clay, Fine to Coarse Grained Sand, Gravel in
Areas, Dark Gray to Dark Brown
CLAYEY SAND (SC) - Reddish Brown, Fine
to Medium Grained Sand, Moist, Medium Stiff
to Stiff
SANDY CLAY (CL) - Silty in Parts, Reddish
Brown, Fine to Medium Grained Sand, Moist,
Stiff
CLAYEY SAND (SC) - Tan, Fine to Coarse
Grained Sand, Moist, Stiff
PROJECT NO.: 0532395
PROJECT: 7-Eleven
Depth, (feet)
STRENGTH, tsf
Additional
Remarks
USCS Classification
0
Qp
Sample Type
2.0
0
Moisture, %
SC
10
1
2
12
12
LL = 27
PL = 16
S(250) = 1.2%
DD = 120 pcf
LL = 44
PL = 16
-200 = 41.5%
7-7
N=14
6-10
N=16
ASPHALT - Approximately 3 Inches Thick
MAN-MADE FILL- Composed of Sand and
Clay, Fine to Coarse Grained Sand, Gravel in
Areas, Dark Gray to Dark Brown
CLAYEY SAND (SC) - Reddish Brown, Fine
to Medium Grained Sand, Moist, Stiff
PROJECT NO.: 0532395
PROJECT: 7-Eleven
Depth, (feet)
STRENGTH, tsf
Additional
Remarks
USCS Classification
0
Qp
Sample Type
2.0
0
Moisture, %
Moisture
MATERIAL DESCRIPTION
STANDARD PENETRATION
TEST DATA
N in blows/ft
Qu
Sample No.
Graphic Log
50
PL
Elevation (feet)
LL
4.0
25
Recovery (inches)
BENCHMARK: N/A
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1
DATE STARTED: 11/28/11 DRILL COMPANY: Dakota
DATE COMPLETED: 11/28/11
STATION: N/A OFFSET: N/A
LOGGED BY: CW
COMPLETION DEPTH 5.0 ft DRILL RIG: CME-55
DRILLING METHOD: 4" Solid Stem Auger
ELEVATION: 5124.2 ft
SC
9
1
2
12
12
LL = 30
PL = 16
S(250) = 0.4%
DD = 113 pcf
LL = 37
PL = 14
-200 = 27.3%
3-3
N=6
4-6
N=10
ASPHALT - Approximately 3 Inches Thick
MAN-MADE FILL- Composed of Sand and
Clay, Fine to Coarse Grained Sand, Gravel in
Areas, Dark Gray to Dark Brown
CLAYEY SAND (SC) - Reddish Brown, Fine
to Medium Grained Sand, Moist, Soft to
Medium Stiff
PROJECT NO.: 0532395
PROJECT: 7-Eleven
Depth, (feet)
STRENGTH, tsf
Additional
Remarks
USCS Classification
0
Qp
Sample Type
2.0
0
Moisture, %
Moisture
MATERIAL DESCRIPTION
STANDARD PENETRATION
TEST DATA
N in blows/ft
Qu
Sample No.
Graphic Log
50
PL
Elevation (feet)
LL
4.0
25
Recovery (inches)
BENCHMARK: N/A
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1
DATE STARTED: 11/28/11 DRILL COMPANY: Dakota
DATE COMPLETED: 11/28/11
STATION: N/A OFFSET: N/A
LOGGED BY: CW
COMPLETION DEPTH 5.0 ft DRILL RIG: CME-55
DRILLING METHOD: 4" Solid Stem Auger
Professional Service Industries, Inc.
Asphalt
KEY TO SYMBOLS
PSI Job No.:
Project:
Location:
0532395
7-Eleven
3045 West Prospect
Ft. Collins, CO
Professional Service Industries, Inc.
1070 West 124th Avenue, Suite 800
Westminster, CO 80234
Telephone: (303) 424-5578
Fax: (303) 423-5625
Fill
Clayey Sand
Sandy Clay
SSA = Solid Stem Auger
HSA = Hollow Stem Auger
CFA = Continuous Flight Auger
SPT = Standard Penetration Test
MC - Modified California Sampler
SS = Split-spoon Sampler
ST = Shelby Tube Sampler
RC = Rock Core
DD = Dry Density
MC = Moisture Content
LL = Liquid Limit
PL = Plastic Limit
-200 = Percent Passing the
No. 200 Sieve (%)
S(250) = Swell under 250 psf
surcharge pressure (%)
S(500) = Swell under 500 psf
surcharge pressure (%)
S(1000) = Swell under 1000 psf
surcharge pressure (%)
Qu = Unconfined Compressive
Strength
RQD = Rock Quality Designation
REC'D = Rock Core Recovery Percentage
PID = Photo Ionic Detector (ppm)
The borings were advanced into the ground using 4 inch solid stem augers. At regular intervals throughout the boring
depths, soil samples were obtained with either a 1.4-inch I.D., 2.0-inch O.D., split-spoon sampler or a 2.0-inch I.D., 2.4-inch
O.D. Modified California sampler. The samplers were first seated 6-inches to penetrate any loose cuttings and then driven
an additional foot where possible with blows of a 140 pound hammer falling 30-inches. The number of hammer blows
required to drive the sampler each 6-inch increment is recorded in the field. The penetration resistance "N-value" is
redesignated as the number of hammer blows required to drive the sampler the final foot and, when properly evaluated, is
an index to cohesion for clays and relative density for sands. The split-spoon sampling procedures used during this
exploration are in general accordance with ASTM Designation D 1586.
APPENDIX A
Laboratory Test Results
US SIEVE OPENING IN INCHES HYDROMETER
GRAVEL SAND
COBBLES COARSE FINE CRS MED FINE SILT OR CLAY
Specimen I.D. Description USCS AASHTO Group Index LL PI PL
B4 @ 0-5 FEET SC A-6 3 37 23
B3 @ 0-5 FEET CL A-7-6 11 44 28
Specimen I.D. D100 D60 D30 D10 Cc Cu %Gravel %Sand %Silt&Clay
B4 @ 0-5 FEET 37.50 0.93 21 43
B3 @ 0-5 FEET 19.00 0.14 7 40
JOB NO.
Clayey Sand
Sandy Clay
US SIEVE NUMBERS
7-Eleven - Fort Collins, CO
GRADATION CURVES
0532395
FIGURE NO. A-1
14
53
16
36
0
10
20
30
40
50
60
70
80
90
100
1000 100 10 1 0.1 0.01 0.001
GRAIN SIZE (mm)
%
F
I
N
E
R
by
W
E
I
G
H
T
1.5 3/4 3/8 4 10 16 30 40 100 200
118 pcf
2.5 feet 10.4 %
Sample Description 0.3 %
USCS Classification 1,000 psf
JOB NO.
FIGURE NO.
Sample Location
Sample Depth
B2 Dry Density
Moisture Content
CL
Sandy Clay
7-11 - Fort Collins
SWELL - CONSOLIDATION TEST
532395
A-2
Volume Change
Swell Pressure
SWELL-CONSOLIDATION TEST
-4
-2
0
2
4
6
8
10
100 1000 10000 100000
109 pcf
2 feet 9.2 %
Sample Description 1.2 %
USCS Classification 2,000 psf
JOB NO.
FIGURE NO.
7-11 - Fort Collins
SWELL - CONSOLIDATION TEST
532395
A-3
Volume Change
Swell Pressure
Sample Location
Sample Depth
B3 Dry Density
Moisture Content
CL
Sandy Clay
SWELL-CONSOLIDATION TEST
-4
-2
0
2
4
6
8
10
100 1000 10000 100000
113 pcf
2 feet 14.8 %
Sample Description 0.4 %
USCS Classification 1,400 psf
JOB NO.
FIGURE NO.
Volume Change
Swell Pressure
Sample Location
Sample Depth
B4 Dry Density
Moisture Content
CL
Sandy Clay
7-11 - Fort Collins
SWELL - CONSOLIDATION TEST
532395
A-4
SWELL-CONSOLIDATION TEST
-4
-2
0
2
4
6
8
10
100 1000 10000 100000
ELEVATION: 5123.4 ft
REVIEWED BY: See Figure No. 2
EFFICIENCY N/A East Parking lot Area
HAMMER TYPE: Manual BORING LOCATION:
0
5
N/A
While Drilling
Upon Completion
Delay
5120
LATITUDE: 40.567723°
LONGITUDE: -105.133262°
FIGURE: 6
LOCATION: 3045 West Prospect
Not Encountered
Not Encountered
Water
REMARKS:
DRILLER: Nick BORING B4
Professional Service Industries, Inc.
1070 West 124th Avenue, Suite 800
Westminster, CO 80234
Telephone: (303) 424-5578 Ft. Collins, CO
SAMPLING METHOD: Modified California
REVIEWED BY: See Figure No. 2
EFFICIENCY N/A South Parking Lot Area
HAMMER TYPE: Manual BORING LOCATION:
0
5
N/A
While Drilling
Upon Completion
Delay
5120
LATITUDE: 40.567723°
LONGITUDE: -105.133262°
FIGURE: 5
LOCATION: 3045 West Prospect
Not Encountered
Not Encountered
Water
REMARKS:
DRILLER: Nick BORING B3
Professional Service Industries, Inc.
1070 West 124th Avenue, Suite 800
Westminster, CO 80234
Telephone: (303) 424-5578 Ft. Collins, CO
SAMPLING METHOD: Modified California
Moisture
MATERIAL DESCRIPTION
STANDARD PENETRATION
TEST DATA
N in blows/ft
Qu
Sample No.
Graphic Log
50
PL
Elevation (feet)
LL
4.0
25
Recovery (inches)
BENCHMARK: N/A
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1
DATE STARTED: 11/28/11 DRILL COMPANY: Dakota
DATE COMPLETED: 11/28/11
STATION: N/A OFFSET: N/A
LOGGED BY: CW
COMPLETION DEPTH 20.0 ft DRILL RIG: CME-55
DRILLING METHOD: 4" Solid Stem Auger
ELEVATION: 5122.8 ft
REVIEWED BY: See Figure No. 2
EFFICIENCY N/A Northeast Corner of Building
HAMMER TYPE: Manual BORING LOCATION:
0
5
10
15
20
N/A
While Drilling
Upon Completion
Delay
5120
5115
5110
5105
LATITUDE: 40.567723°
LONGITUDE: -105.133262°
FIGURE: 4
LOCATION: 3045 West Prospect
Not Encountered
Not Encountered
Water
REMARKS:
DRILLER: Nick BORING B2
Professional Service Industries, Inc.
1070 West 124th Avenue, Suite 800
Westminster, CO 80234
Telephone: (303) 424-5578 Ft. Collins, CO
SAMPLING METHOD: Modified California
Qp
Sample Type
2.0
0
Moisture, %
Moisture
MATERIAL DESCRIPTION
STANDARD PENETRATION
TEST DATA
N in blows/ft
Qu
Sample No.
Graphic Log
50
PL
Elevation (feet)
LL
4.0
25
Recovery (inches)
BENCHMARK: N/A
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1
DATE STARTED: 11/28/11 DRILL COMPANY: Dakota
DATE COMPLETED: 11/28/11
STATION: N/A OFFSET: N/A
LOGGED BY: CW
COMPLETION DEPTH 20.0 ft DRILL RIG: CME-55
DRILLING METHOD: 4" Solid Stem Auger
ELEVATION: 5123.5 ft
REVIEWED BY: See Figure No. 2
EFFICIENCY N/A Southwest Corner of Building
HAMMER TYPE: Manual BORING LOCATION:
0
5
10
15
20
N/A
While Drilling
Upon Completion
Delay
5120
5115
5110
5105
LATITUDE: 40.567723°
LONGITUDE: -105.133262°
FIGURE: 3
LOCATION: 3045 West Prospect
Not Encountered
Not Encountered
Water
REMARKS:
DRILLER: Nick BORING B1
Professional Service Industries, Inc.
1070 West 124th Avenue, Suite 800
Westminster, CO 80234
Telephone: (303) 424-5578 Ft. Collins, CO
SAMPLING METHOD: Modified California