HomeMy WebLinkAboutGEORGE T SANDERS COMPANY PUD - PRELIMINARY & FINAL - 76-88H - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTGEOTECHNICAL INVESTIGATION
FOR
GEORGE T. SANDERS PUD
FORT COLLINS, COLORADO
for
George T. Sanders Company
10201 West 49th Street
Wheatridge, CO 80033
PROJECT NO. 95-051T
SMITH GEOTECHNICALJEngineecing Consultants
1318 WEBSTER AVENUE
FORT COLLINS, COLORADO 80524
(303)-490-2620
July 21, 1995 D M a
C� Smith
Geotechnical
ENGINEERING CONSULTANTS
July 21, 1995
Mr. Tom Tooley
George T. Sanders Company
10201 West 49th Street
Wheatridge, CO 80033
Re: Geotechnical Investigation for George T. Sanders PUD, Preliminary Report
Dear Mr. Tooley:
SMITH GEOTECHNICAL/Engineering Consultants has completed a portion of the geotechnical
investigation for the above referenced project as requested. Enclosed is one (1) copy of our PRELIMINARY
REPORT for your review and we are forwarding four (4) copies of our report to Ripley Associates and one
(1) copy to WESTEC, Inc. Please note this is a draft copy as all of the consolidation testing has not been
completed at this time. Some of the results indicated in this report may be modified after all of the testing
is complete.
Should you have any questions, please feel free contact us.
Sincerely,
SMITH GEOTECHNICAL
Duane H. Smith, P.E.
w/enclosure
cc: Ripley and Associates (4)
WESTEC (1)
1318 Webster Ave. • Fort Collins, CO 80524 9 (970) 490-2620 • FAX (970) 490-2851
TABLE OF CONTENTS
Item Pate
Executive Summary I
A. INTRODUCTION 2
A.1 PROJECT INFORMATION 2
A.2 SCOPE OF SERVICES 2
A.3 SITE LOCATION AND DESCRIPTION 2
A.4 REPORT FORMAT 3
B. EXPLORATION RESULTS 3
B.1 SCOPE OF EXPLORATION 3
B.2 SUBSURFACE EXPLORATION PROCEDURES 3
B.3 SUBSURFACE CONDITIONS 4
BA GEOLOGY 5
C. ENGINEERING RECOMMENDATIONS 6
C.1 PROJECT DATA 6
C.2 DISCUSSION 6
C.3 FOUNDATION RECOMMENDATIONS 6
CA FILL REQUIREMENTS 7
C.5 PAVEMENT DESIGN 7
C.7 GENERAL RECOMMENDATIONS 8
D. OBSERVATION AND TESTING 10
E. STANDARD OF CARE 10
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APPENDIX A
Vicinity Map
Boring Locations
APPENDIX B
Key to Boring Logs
Unified Soil Classification
Description of Terms
Boring Logs
APPENDIX C
Summary of Laboratory Test Data
Consolidation/Swell Tests
Unconfined Compressive Strength Tests
Moisture/Density Curves
EXECUTIVE SUMMARY
The site investigated includes approximately 2.6 acres of undeveloped rolling land bordering Fossil
Boulevard on the east, Mill Brothers Nursery on the south, Burlington Northern Railroad right-of-way on
the west, and an undeveloped tract of land on the north. The site is approximately .6 mile south and .2
mile west of the intersection of College Avenue and Harmony Road in South Fort Collins, Colorado. The
site is currently covered with native forbes and grasses. There are no existing structures on the site.
Subsurface conditions include overburden clays with underlying weathered sandstone and sandstone
bedrock.
Swelling soils were encountered, however swell pressures were typically less than 500 pounds per square
foot. Conventional foundations with spread footings and pads may be used if designed for maximum
bearing pressures of 3000 pounds per square foot and minimum dead load pressures of 500 pounds per
square foot.
Groundwater was encountered during drilling operations in borings BH-1, and BH-3 at 13 to 15 feel
below grade. Two days after drilling groundwater was present in borings BH-3, BH-4 and BH-6 at 11
to 15 feet below grade.
A. INTRODUCTION
A.1 PROJECT INFORMATION
This report summarizes the subsurface exploration work, laboratory findings, conclusions, and
recommendations as prepared by SMITH GEOTECHNICAL for the proposed subdivision.
A.2 SCOPE OF SERVICE
The scope of service for this investigation was limited to the following:
Advancement of six (6) borings to depths of fifteen (15) feet below the ground surface with soil
samples obtained during drilling.
2. Advancement of two (2) borings to five (5) feet below ground surface to obtain samples for
pavement design thickness.
Visual classification of soil samples obtained.
4. Laboratory testing of soil samples.
5. Analysis of the results of soil classifications and laboratory testing to determine foundation related
recommendations, with regard to bearing capacities, swell potential, and settlement.
6. Analysis of the results of soil classifications and laboratory testing to determine pavement
thickness design.
A.3 SITE LOCATION AND DESCRIPTION
The site includes approximately 2.6 acres of undeveloped rolling land bordering Fossil Boulevard on the
east, Mill Brothers Nursery on the south, Burlington Northern Railroad right-of-way on the west, and an
undeveloped tract of land on the north. The site is approximately six -tenths mile south and two -tenths mile
west of the intersection of College Avenue and Harmony Road in South Fort Collins, Colorado.
A legal description of the site is as follows: A tract of land situated in the NE 1/4 of Section 2, Township
6 North, Range 63 West of the 6th P.M., which considering the East line of said Section 2 as bearing N
00047' East and with all bearings contained herein relative thereto is contained within the boundary lines
which begin at a point on the West right- of -way line of U.S. Highway No. 287 which bears N 00047'
East 2681.7 feet and again N 88045' W, 48.40 feet from the Southeast Corner of said Section 2 and run
Thence N 00°48' 35" E, 433.99 feet along the said West right-of-way line; Thence N 88°45'35" W, 913.46
feet to a point on the East right-of-way line of the Burlington Northern Railroad, said right-of-way line
being 100.00 feet from the centerline of the said railroad: thence S 00°53' W, 433.98 feet along the said
East right-of-way line; thence S 88°45' E, 914.202 feet to the POINT OF BEGINNING, County of
Larimer, State of Colorado. LESS THE Weberg, P.U.D.
A.4 REPORT FORMAT
The purpose of this report is to describe the subsurface investigations and laboratory test results, and to
provide engineering recommendations. Provided in the Appendix to this report is a Vicinity Map showing
the project location, Boring Location Plan showing boring locations with respect to property boundaries,
Boring Logs showing the type and depth of soil changes and water table location, and the results of the
laboratory testing conducted on specific samples retrieved from the borings. Also included in the
Appendix is a description of terms used for soil and rock characteristics.
B. EXPLORATION RESULTS
BA SCOPE OF EXPLORATION
The borings were drilled on July 19, 1995. Borings BH-1, BH-2, and BH-3 were advanced to 15 feet in
depth below existing grade within the envelope of the proposed G.T. Sanders Building. Borings BH-4,
BH-5, and BH-6 were advanced to a depth of 15 feet below existing grade within the envelope of the
proposed future building located at the southwest corner of the property. Boring PV-1 was advanced to
five feet in depth in line with the center line of Fairway Lane and approximately 30 feet west of the west
curb of Fossil Boulevard. Boring PV-2 was advanced to five feet in depth approximately 135 feet south
of Boring PV-1.
B.2 SUBSURFACE EXPLORATION PROCEDURES
The borings were advanced with a CME-55 drill rig using a 4-inch diameter solid stem flight auger.
Disturbed and relatively undisturbed samples were recovered from the borings for use in visual
classification (ASTM D-2488) in the field and for future laboratory testing.
Disturbed soil sampling was performed in accordance with ASTM D-1586, Standard Penetration Test
(SPT). Using this procedure, a 2-inch outside diameter split -spoon sampler was driven into the soil by
successive blows of a 140-pound weight falling 30-inches. After an initial set of 6-inches, the number
of blows required to drive the sampler an additional 12-inches was recorded as the "penetration resistance"
or "N value" in blows per foot (bpf). The N value is an index of the relative density of cohesionless soils
and the consistency of cohesive soils.
A limited number of undisturbed soil samples were recovered by use of 2'/Z-inch diameter thin walled
Shelby tubes in accordance with ASTM D 1587. These samples are relatively undisturbed and can be
used for strength and consolidation testing.
Some samples were also obtained using a California sampler which consists of a 2%-inch outside diameter
barrel with a 2-inch internal brass liner which is driven into the soil by successive blows of a 140-pound
weight falling 30-inches. These samples provide relatively undisturbed sample that can be used for
strength and consolidation testing. These samples are not as representative as the Shelby Tube samples
and the degree of disturbance must be considered when using the results from these samples.
Pavement Hole samples were advanced with a 6-inch diameter continuous flight auger. Bulk soil samples
were taken from these test holes at locations PV-1 and PV-2 for testing Atterberg Limits, percent of
material passing the 4200 sieve, and moisture/density relationships using the Standard Proctor test.
As the samples were obtained in the field, they were visually classified by an Engineer from SMITH
GEOTECHNICAL. Representative portions of the samples were then returned to the laboratory for further
examination and verification of field classification. Boring logs indicating the depth and identification
of the various strata, the N value, ground water levels, and other pertinent information are included in the
Appendix. Charts illustrating the soil classification procedure and descriptive terminology and symbols
on the Boring Logs are also included in the Appendix.
B.3 SUBSURFACE CONDMONS
The subsurface conditions encountered in the borings have been used to infer the general
soil conditions at the site. We assume the soil conditions between borings are fairly
represented by the borings. During any repair or modification work, if conditions are
encountered other than that described below and as shown on the Borings Logs included
in the appendix to this Report, it is important that a geotechnical engineer be informed
to evaluate the exposed conditions with respect to their effect on our recommendations.
The following is a brief review of the various layers of soil encountered. All depths given are relative
to the ground surface at the time of drilling. Please refer to the Appendix for a more complete description
of soil conditions at outlined in the written bore logs.
The conditions found in the borings are as follows:
(1) Topsoil: A six (6") inch to twelve (12") layer of topsoil overlies the site and the site is well
vegetated with native grasses.
(2) Clay- A layer of tan, clay was found in all borings. This material extended from the below the
topsoil to a depth of six (6) to fourteen (14) feet. Typically more than 60% of the material passes
the # 200 sieve and is of medium to plasticity. The soil in its natural state is slightly moist to
moist with a water content of from ten (10) to twenty-two (22) percent.
(3) Sandstone: A layer of greenish Sandstone was encountered below the overburden clay in all six
deep borings. The Sandstone bedrock is overlain with a few inches of completely weathered
sandstone. The depth of the Sandstone bedrock varies from five (5) to fourteen (14) feet below
existing grade.
(5) Groundwater: Groundwater was encountered in borings BH-1 and BH-3 at the interface between
the overburden soil and the sandstone bedrock at a depths of 13.4 and 14.5 feet below grade
respectively, at the time of drilling. No groundwater was encountered in the other borings. At 2-
days after drilling boring BH-3 had standing water at 15 feet below the ground surface, BH-4 had
standing water at 13 feet below the ground surface and BH-6 had standing water at 11 feet below
the ground surface.
Groundwater levels do fluctuate seasonally and yearly and variations should be expected from the
groundwater readings noted in this report
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B.4 GEOLOGY
1. Physio rg anhy. The project site is located at the northern portion of the Colorado Piedmont
Section of the Great Plains Physiographic Province, east of the Southern Rockies Physiographic
Province, and southwest of the Great Plains Escarpment. The Colorado Piedmont is an elongated
trough in the Great Plains, adjacent to the Front Range of the Southern Rockies which has been
eroded due to uplift of the area in Miocene -Eocene times. Erosion has exposed bedrock stratum
next to the foot hills and outlying areas. The Colorado Piedmont and Great Plains are separated
by the Great Plains Escarpment or Tertiary Escarpment near the Colorado -Wyoming border.
Elevations in the Colorado Piedmont are in the order of 5,000 to 7,000 feet in this area.
A variety of geologic processes have formed the present natural surface including erosion and
deposition due to wind, water, and mass wasting. Land forms created from these processes in
this area include dip slopes, colluvial slopes, pediment gravels, deflation basins, and alluvial and
aeolian deposits. The folds of the bedrock strata in this area have had major influence on the
topography of the site.
2. Stratigraphy. The stratigraphy of the site consists of the Upper Cretaceous Pierre Shale
overlain by colluvial, alluvial, and aeolian deposits. The Pierre Shale was deposited in a shallow -
water marine environment from sediment derived from the land area to the west during late
Cretaceous times. The Pierre Shale consists of shales, claystones, siltstones, and sandstones with
a maximum thickness in this area of approximately 8,000 feet. Five sandstone units have been
described in the Pierre Shale; in ascending order they are the Hygiene, Terry, Rocky Ridge,
Larimer, and Richard Sandstone members.
Quaternary deposits overlie the Pierre Shale with colluvial, alluvial, and aeolian deposits. The
soils and subsoils encountered at the site are clays containing varying quantities of silt and sand
and derived from the nearby bedrock stratum. The upper zones of the soils are primarily
colluvial deposits with aeolian and alluvial processes involved. Residual clays are located over
the bedrock stratum.
3 Structural Geology. The reservoir lies on the western edge of the Denver Basin, a large
structural basin (or asymmetrical syncline) which is located from north of the Arkansas River,
adjacent to the mountain front, to just west of the Kansas and Wyoming borders. The Denver
Basin was formed as a down warping of sediments during late Cretaceous and early Cenozoic
as a result of the Laramide Orogeny, the last major uplift of the Front Range. Paleozoic and
Mesozoic rock strata located at the flanks of the uplifting mountains folded and faulted from the
pres§ures created during the orogeny resulting in the Front Range anticline or anticlinorium. The
strata once located over the mountainous areas had since been eroded exposing tilted strata of
sandstones and limestones (hogbacks) adjacent to the Front Range in an eastward dipping pattern.
4 Mineral and Energy Resources. No minable gravels or sands were located at the site during
this investigation.
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C. ENGINEERING RECOMMENDATIONS
C.1 PROJECT DATA
The engineering recommendations made in this report are based on our understanding of
the project as discussed in the following paragraphs. The recommendations are valid for
a specific set of project conditions. If the characteristics of the project should change from
those indicated in this section, it is important that we be informed so that we can
determine whether the new conditions affect our recommendations.
C.2 DISCUSSION
The site is relatively uniform consisting of overburden clays overlying a sandstone unit of the Pierre Shale
Formation. Testing of the soils recovered indicated only minor swelling with pressures less than 500
pounds per square foot with less than 1 percent volume change. Sandstone bedrock was encountered in
some of the borings and appears to be nonexpansive. Groundwater was encountered at the center of the
site and was at the interface between the overburden soils and sandstone bedrock.
The site is suitable for the construction of proposed structures if the recommendations of this report are
followed. Based on the conditions encountered in this investigation, we recommend the following
foundation types:
■ Spread footings or pads bearing on undisturbed soils.
C.3 FOUNDATION RECOMMENDATIONS
C.3.1 Spread Footings
Spread Footings consisting of conventional spread footings or pads may be used at the site. These
footings shall be designed for a maximum bearing pressure of 3000 pounds per square foot (full dead plus
live load) and shall be sized to ensure a minimum dead load pressure of 500 psf to resist the swell
pressures.
Void forms in general are not required, however, there is some minor swell potential at the site and areas
that would be susceptible to changes in moisture contents or damage due to movements should be
investigated for use of void forms if lightly loaded.
C.3.2 Basement Foundations
Basement foundations will be acceptable on most of the site as high groundwater was not encountered
during our investigation. The northwest corner of the site does have bedrock at approximately five (5)
feet below grade which would increase the construction costs for a basement depth foundation in this area.
This area also had groundwater at the interface between the overburden soil and bedrock.
C 3 3 Frost and Foundation Depth Considerations
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Footings should be placed at least 30-inches below the final exterior grade to provide proper protection
from frost damage.
CA FILL REQUIREMENTS
All fills supporting buildings or structures shall be designed by a geotechnical engineer. They shall be
compacted to a minimum of 98% of the maximum dry density at -2% to +2% of optimum moisture as
determined by a Standard Proctor test (ASTM D698). It is recommended that any fill required for
structural applications should be constructed using pit run or other granular, or approved nonexpansive
soils.
All overlot and roadway fills should be placed in nearly level lifts, not more than 12-inches in loose
thickness, and compacted with a sheepsfoot or segmented pad roller equivalent to a CAT 815 roller. Each
lift must be compacted before additional soil is added and shall be compacted to at least 95% of the
maximum dry density at -2% to +2% of optimum moisture as determined by a standard Proctor test
(ASTM D698).
All backfill around structures should be compacted to 92% to 95% of maximum density at -1% to +3%
of optimum moisture in accordance with ASTM D698 and should slope a minimum of 5% away from the
structure.
All fills should be tested by a geotechnical engineer to assure adequate and uniform densitti, is obtained
For no reason shall any structure rest upon any fill that has not been adequately compacted and tested to
assure as much.
C.5 PAVEMENT DESIGN
C.5.1 Recommended Pavement Thickness
Flexible pavement was designed using guidelines from the City of Fort Collins, DESIGN CRITERIA
AND STANDARDS FOR STREETS, July, 1986 and from The Asphalt Institute, THE DESIGN,
CONSTRUCTION AND MAINTENANCE OF ASPHALT PARKING LOTS. Using the average soil
conditions found in the borings, a Group Index (ASTM D3282-92) of ?? was determined based on the
Atterberg Limits and percent passing the 200 sieve. The pavement thicknesses were determined for an
Industrial/Commercial street and a parking lot.
The minimum recommended pavement sections are listed in the table below. We do not recommend an
asphalt thickness of less than 3-inches as we have not seen acceptable results for thinner sections in a
commercial application.
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MINIMUM RECOMMENDED PAVEMENT SECTIONS
C.5.2 Roadway Construction
All paving should have a minimum slope or crown of 2% for drainage. All subgrades for roads and
driveways shall be proof rolled and compacted to 95% of the maximum dry density at -2% to +2% of
optimum moisture as determined by a standard Proctor test (ASTM D698). Onsite materials may be
utilized for roadway fill for pavements. Any imported materials shall be tested and approved
nonexpansive materials. Road base materials should be Class 6 in accordance with CDOT standards and
asphalt materials shall meet CDOT and City of Fort Collins standards.
Roadway fills should be placed in ne uiy level lifts, not more than 12-inches in loose thickness, and
compacted with a sheepsfoot or segmented pad roller equivalent to a CAT 815 roller. Each lift must be
compacted before additional soil is added and shall be compacted to at least 95% of the maximum dry
density at -2% to +2% of optimum moisture as determined by a standard Proctor test (ASTM D698).
A11 fills should be tested by a geotechnical engineer to assure adequate and uniform density is obtained.
For no reason shall any structure rest upon any fill that has not been adequately compacted and tested to
assure as much.
C.7 GENERAL RECOMMENDATIONS
1.) Provide proper drainage around all structures to minimize infiltration of water. Slope a minimum
of 5% away from the structure.
2.) Provide all downspouts with extensions to assure that rain runoff is not directed into the
foundation backfill.
3.) Do not plant shrubs or trees in the backfill zone adjacent to the foundation that require significant
amounts of watering or that have large root systems.
4.) Do not place sprinkler systems in the backfill zone adjacent to the foundations where the potential
for water line breaks or leakage will saturate the foundation area.
5.) All plumbing that penetrates slabs should be isolated with flexible expansion material to minimize
I
the potential for damage due to slab heaving.
6.) All concrete slabs should be a minimum of 4-inches in thickness and all exterior concrete slabs
should contain fibermesh reinforcement to resist expansion and contraction forces. All structural
slabs should be designed for the loading conditions expected and contain reinforcing steel. All
slabs should have control joints at 10-foot spacings with a depth of 1/4 of the slab thickness. All
exterior slabs adjacent to structures should have a minimum 2% slope away from the structure.
All slabs should be isolated from structures and allowed to "float". Expansion joint material
should be used to isolate slabs from all structural components.
7.) All concrete should use TYPE II or TYPE I -II cement. We recommend all structural concrete
have a minimum cement content of 564 pounds per cubic yard, a 6% air content, and 1-inch
maximum size aggregate with fine aggregate content in the range of 40% to 501/o.
1
D. OBSERVATION AND TESTING
Since a project of this nature requires many soil related judgements and decisions, we recommend that
an experienced geotechnical engineer be retained as part of the re -constriction team. We strongly
recommend that all footing trenches be visually inspected by a geotechnical engineer or trained technician
prior to placing concrete. Any unsuitable or wet soil conditions existing at footing level can then be
delineated for removal and replacement. We also recommend that a limited number of compaction test
(approximately one test for every 100 cubic yards of fill placed) be performed to document the degree
of compaction obtained in backfill and structural fill. SMITH GEOTECHNICAL is equipped for, and
would be pleased to provide, the recommended quality assurance testing of concrete and construction fills
for the proposed project.
E. STANDARD OF CARE
The recommendations contained in this Report represent our professional opinions. These opinions were
arrived at in accordance with currently accepted engineering procedures at this time and location. Other
than this, no warranty, either expressed or implied, is intended.
Prepared and submitted by:
SMITH GEOTECHNICAL
/Duane H. Smith, P.E.
APPENDIX A
Vicinity Map
Boring Locations
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