HomeMy WebLinkAboutHEARTHFIRE (THE POND AT) SUBDIVISION - PRELIMINARY - 31-95B - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTPreliminary Geotechnical Engineering Exploration
Merrick & Company
TCW Project No. 20955191
Terracon
conditions encountered at the site, it is recommended that additional test borings be made
prior to final design. Samples obtained from the borings should be tested in the laboratory
to provide a basis for evaluating subsurface conditions.
This report has been prepared for the exclusive use of our client for specific application to
the project discussed and has been prepared in accordance with generally accepted
geotechnical engineering practices. No warranty, express or implied, is made. This report
has been prepared to aid in the evaluation of the property and to assist the architect and/or
engineer in the preliminary design of this project.
This report is for the exclusive purpose of providing preliminary geotechnical engineering
and/or testing information and recommendations. The scope of services for this project
does not include, either specifically or by implication, any environmental assessment of the
site or identification of contaminated or hazardous materials or conditions. If the owner is
concerned about the potential for such contamination, other studies should be undertaken.
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Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
U, = 15to25xD
Where: Up = the uplift force in kips, and
D = the pier diameter in feet
Basement Construction: Groundwater was encountered on the majority of the site at
depths of 6 to 14 feet below existing grade. Full -depth basement construction is
considered feasible on the site provided that basement subgrade is a minimum of 3 feet
above existing groundwater. Finished basement slabs should be placed a minimum of 3 feet
above the bedrock stratum. A complete dewatering system should be provided around the
basement area.
Perched groundwater may occur at times since the subsurface soils are relatively
impermeable and tend to trap water. Completion of site development, including installation
of landscaping and irrigation systems, will likely lead to perched groundwater development.
To reduce the potential for groundwater to enter the basement of the structure, installation
of a dewatering system is recommended. The dewatering system should, at a minimum,
include an underslab gravel drainage layer sloped to a perimeter drainage system.
Floor Slab Design and Construction: The variability of the existing soils at approximate slab
subgrade elevation could result in differential movement of floor slab -on -grade should
expansive soils become elevated in moisture content. Use of structural floor systems,
structurally supported independent of the subgrade soils, is a positive means of eliminating
the potentially detrimental effects of floor movement.
• Compliance: Recommendations for slabs -on -grade, foundations and pavement
elements supported on compacted fills or prepared subgrade depend upon
compliance with "Earthwork" recommendations. To assess compliance, observation
and testing should be performed under the direction of the geotechnical engineer.
PRELIMINARY GENERAL COMMENTS
It should be noted this was a preliminary investigation and the foundation systems
recommended in this report are based on preliminary tests. Due to variations in soil
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Preliminary Geotechnical Engineering Exploration
Merrick & Company
TCW Project No. 20955191
Terracon
4. On -site clay soils may pump or become unstable or unworkable at high water
contents. Workability may be improved by scarifying and drying.
Overexcavation of wet zones and replacement with granular materials may
be necessary. Lightweight excavation equipment may be required to reduce
subgrade pumping.
• Fill Materials:
1. On -site clay soils are suitable for use beneath slabs or as backfill.
2. On -site bedrock materials are not recommended for use beneath structural
ares of the site, or as backfill. Should bedrock materials be used for general
site grading, placement in fills at non-structural locations on the site is
recommended.
Foundation Systems: Due to the presence of moderate of high swelling soils on the site,
spread footing and/or grade beam foundations bearing upon undisturbed subsoils and/or
engineered fill are recommended for support for the proposed structures. Consideration
should be given to using drilled pier foundations for structures founded partly on the
bedrock stratum and partly in the clay soils. Additional testing should be done prior to final
design. Based on preliminary test results, footing and/or grade beams founded on the
undisturbed soil should be designed for a maximum allowable bearing capacity of between
2,000 to 4,500 pounds per square foot (dead load plus 1/2 live load). To counteract
swelling pressures which will develop if the subsoils be wetted, all footings should be
designed for a minimum dead load pressure of 500 to 1,500 per square foot.
Where drilled pier foundation systems are used, the piers would have minimum 12 to 15
foot lengths and extend a minimum of 5 feet into the bedrock stratum. Based on
preliminary test results, the piers should be designed for a maximum end bearing pressure
of between 15,000 to 30,000 psf and skin friction of 1,500 to 3,000 psf. For preliminary
design purposes, the uplift force on each pier can be determined on the basis of the
following equation.
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Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
• Site Clearing:
1. Strip and remove existing vegetation, debris, and other deleterious materials
from proposed building and pavement areas. All exposed surfaces should be
free of mounds and depressions which could prevent uniform compaction.
2. If unexpected fills or underground facilities are encountered during site
clearing, such features should be removed and the excavation thoroughly
cleaned prior to backfill placement and/or construction. All excavations
should be observed by the geotechnical engineer prior to backfill placement.
3. Stripped materials consisting of vegetation and organic materials should be
wasted from the site, or used to revegetate exposed slopes after completion
of grading operations. If it is necessary to dispose of organic materials on -
site, they should be placed in non-structural areas, and in fill sections not
exceeding 5 feet in height.
4. All exposed areas which will receive fill, once properly cleared and benched
where necessary, should be scarified to a minimum depth of 6 inches,
conditioned to near optimum moisture content, and compacted.
• Utility and Site Grading:
1. It is anticipated that excavations for the proposed construction can be
accomplished with conventional earthmoving equipment.
2. Excavations penetrating the well -cemented sandstone bedrock may require
the use of specialized heavy-duty equipment, together with drilling and
blasting, ripping or jack -hammering to facilitate rock break-up and removal.
3. Depending upon depth of excavation and seasonal conditions, groundwater
may be encountered in excavations on the site. Groundwater seepage should
be anticipated for excavations approaching the level of the bedrock. Pumping
from sumps may be utilized to control water within excavations. Well points
may be required for significant groundwater flow, or where excavations
penetrate groundwater to a significant depth.
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Preliminary Geotechnical Engineering Exploration
Merrick & Company
TCW Project No. 20955191
Terracon
Field and Laboratory, Test Results: Field and laboratory test results indicate the clay soils
are medium to very stiff in consistency and exhibit moderate to high bearing characteristics
and moderate to high swell potential. The bedrock is moderately hard to hard and cemented
to well cemented and exhibits very high bearing characteristics and low swell potential.
Groundwater Conditions: Groundwater was encountered in Boring 2 at the time of drilling
and when checked 1 to 10 days after drilling, groundwater was encountered in Borings 2
through 6 at approximate depths of 6 to 14 feet. Boring 1 remained dry. These
observations represent groundwater conditions at the time of the readings, and may not be
indicative of other times, or at other locations. Groundwater levels can be expected to
fluctuate with varying seasonal and weather conditions.
Zones of perched and/or trapped groundwater may also occur at times in the subsurface
soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the
bedrock materials. The location and amount of perched water is dependent upon several
factors, including hydrologic conditions, type of site development, irrigation demands on or
adjacent to the site, fluctuations in water features, seasonal and weather conditions.
Fluctuations in groundwater levels can best be determined by implementation of a
groundwater monitoring plan. Such a plan would include installation of groundwater
monitoring wells, and periodic measurement of groundwater levels over a sufficient period
of time.
The possibility of groundwater fluctuations should be considered when developing design
and construction plans for the project.
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS
Site Development Considerations: The site appears suitable for the proposed construction.
Although fill or underground facilities, such as septic tanks, cesspools, basements and
utilities, were not observed during site reconnaissance, such features might be encountered
during construction.
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JPreliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
The regional dip of the Pierre shale in this area is slight and in an easterly direction. Seismic
activity in the area is anticipated to be low; therefore, from a structural standpoint, the
property should be relatively stable. It is anticipated that the weathered bedrock and the
J majority of the firm bedrock may be excavated by conventional heavy-duty construction
equipment equivalent to a D-8 tractor and ripper or a large track -mounted backhoe.
However, the sandstone becomes dense at lower depths. This dense sandstone at depth
7 may require the use of special heavy-duty excavation equipment or possibly blasting for
J excavation. Due to the relatively flat to gently -rolling nature of the site, geologic hazards
due to mass movement caused by gravity, such as landslides, mudf lows, rockfalls, etc., are
not anticipated. With proper site grading around structures and proper drainage for streets
and drive areas, erosional problems at the site should be minimal. It is recommended that
construction not be placed within the wet areas in the central portion of the site without
proper draining and filling.
The site is underlain by the Cretaceous Pierre Formation. The Pierre shale is not known to
contain economic deposits of coal, limestone, or quarry rock. Sand and gravel was not
encountered at the site, and economic deposits of these materials are not anticipated.
Background levels of radioactivity are anticipated to be low in this area. However, the
possibility does exist that abnormally high radiation rates may exist on the property. A
detailed study of radon gas or radiation hazards at the site is beyond the scope of this
report. It is suggested that a more detailed study be made prior to construction to more
accurately determine if radiation hazards exist at the site.
Soil and Bedrock Conditions: As presented on the Logs of Boring, the subsurface soils were
encountered in order of increasing depths.
• Silty Topsoil: The area tested is overlain by a 6-inch layer of silty topsoil. The
topsoil has been penetrated by root growth and organic matter.
• Sandy Lean Clay: This stratum underlies the topsoil and extends to the bedrock
it below and/or the depths explored. The sandy lean clay is plastic, dry to wet and
medium to very hard.
• Sandstone-Siltstone Bedrock: The bedrock was encountered in Borings 2, 5 and 6
at depths of '/Z to 13 feet and extends to greater depths. The upper 1 to 1'/z feet
of the bedrock is highly weathered; however, the underlying sandstone interbedded
with claystone is well -cemented and hard.
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Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
• Water content • Expansion
• Dry density • Atterberg limits
The significance and purpose of each laboratory test is described in Appendix C. Laboratory
test results are presented in Appendix B, and were used for the geotechnical engineering
analyses, and the development of foundation and earthwork recommendations. All
laboratory tests were performed in general accordance with the applicable ASTM, local or
other accepted standards.
SITE CONDITIONS
The site surrounds an existing lake and wetlands areas. The area is vegetated with native
grass and Russian olive and cottonwood trees and brush. Cattails were noted growing in
the wetlands area. Fences are located throughout the property along with several oil wells.
The site is bordered on all sides by fenced pasture land. Drainage, in general, is from the
north, south, east and west toward the lake and wetlands in the center of the project. The
property is bordered on the west by Larimer County Road 13, on the southwest by Richards
Lake, and on the north and east by open pasture.
SUBSURFACE CONDITIONS
Geoloay: The proposed area is located within the Colorado Piedmont section of the Great
Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and
Early Quaternary time (approximately 2,000,000 years ago), is a broad, erosional trench
which separates the Southern Rocky Mountains from the High Plains. Structurally, the site
lies along the western flank of the Denver Basin. During the Late Mesozoic and Early
Cenozoic Periods (approximately 70,000,000 years ago), intense tectonic activity occurred,
causing the uplifting of the Front Range and associated downwarping of the Denver Basin
to the east. Relatively flat uplands and broad valleys characterize the present-day
topography of the Colorado Piedmont in this region. The site is underlain by the Cretaceous
Pierre Formation. The Pierre shale at the site consists of sandstone and claystone. Bedrock
was encountered in Borings 2, 5, and 6 at depths of Yz to 13 feet, and it is anticipated it
underlies the remainder of the site at depths of 20 to 25 feet. The bedrock is overlain by
residual and alluvial clays of Pleistocene and/or Recent Age. A Geologic Map, Soil Map and
legend are included in Appendix A.
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Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
SITE EXPLORATION
The scope of the services performed for this project included site reconnaissance by a
geotechnical engineer and an engineering geologist, a subsurface exploration program,
laboratory testing and engineering analysis.
Field Exploration: A total of 6 test borings were drilled on July 6, 1987 and October 31,
1995 to depths of 15 feet at the locations shown on the Site Plan, Figure 1. The borings
were drilled within the area of proposed buildings. All borings were advanced with a truck -
mounted drilling rig, utilizing 4-inch diameter solid stem auger.
The borings were located in the field by pacing from property lines and/or existing site
features. Elevations were taken at each boring location from a topographic map prepared
by Merrick & Company. The accuracy of boring locations and elevations should only be
assumed to the level implied by the methods used.
Continuous lithologic logs of each boring were recorded by the geotechnical engineer during
the drilling operations. At selected intervals, samples of the subsurface materials were
taken by means of pushing thin -walled Shelby tubes, or driving split -spoon samplers.
Penetration resistance measurements were obtained by driving the split -spoon into the
subsurface materials with a 140-pound hammer falling 30 inches. The penetration
resistance value is a useful index to the consistency, relative density or hardness of the
materials encountered.
Groundwater measurements were made in each boring at the time of site exploration, and
1 to 10 days after drilling.
Laboratory Testing: All samples retrieved during the field exploration were returned to the
laboratory for observation by the project geotechnical engineer, and were classified in
accordance with the Unified Soil Classification System described in Appendix C. Samples
of bedrock were classified in accordance with the general notes for Bedrock Classification.
At that time, the field descriptions were confirmed or modified as necessary, an applicable
laboratory testing program was formulated to determine engineering properties of the
subsurface materials. Boring logs were prepared and are presented in Appendix A.
Selected soil and bedrock samples were tested for the following engineering properties:
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PRELIMINARY GEOTECHNICAL ENGINEERING REPORT Terracon
THE POND AT HEARTHFIRE
DOUGLAS ROAD AND COUNTY ROAD 13
FORT COLLINS, COLORADO
TCW Project No. 20955191
April 22, 1996
INTRODUCTION
This report contains the results of our preliminary geotechnical engineering exploration for
the proposed first filing of The Pond at Hearthfire located at the southeast corner of Larimer
County Road 13 and Douglas Road, northeast of Fort Collins, Colorado. The site is located
in the West 1 /2 of Section 30, Township 8 North, Range 68 West of the 6th Principal
Meridian.
The purpose of these services is to provide preliminary geotechnical engineering information
relative to:
• subsurface soil and bedrock conditions
• groundwater conditions
• earthwork
• preliminary foundation systems
• basement construction
• preliminary floor slab design and construction
• utilities
The conclusions and recommendations contained in this report are based upon the results
of limited field and laboratory testing, engineering analyses, and experience with similar soil
conditions and structures and our understanding of the proposed project. Prior to final
design, additional studies will be required.
PROPOSED CONSTRUCTION
The site will be developed as a residential subdivision with single-family and multifamily
housing. Residential streets will be constructed throughout the project area. Grading plans
were not available at the time of preparation of this report, and it is anticipated that some
cut and fill will be required.
Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
TABLE OF CONTENTS (Cont'd)
APPENDIX A
Figure Nos
SitePlan ................................................. 1
GeologicMap ............................................. 1
SoilsMap ................................................ 1
Logs of Borings ..................................... Al thru A6
Legend.................................................. 7.
APPENDIX B
Summary of Test Results .................................... B1
APPENDIX C: GENERAL NOTES
Drilling & Exploration ........................................ C1
Unified Soil Classification .................................... C2
Bedrock Classification, Sedimentary Bedrock ....................... C3
Laboratory Testing, Significance and Purpose ...................... C4
Report Terminology ........................................ C5
Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
TABLE OF CONTENTS
Page No.
Letter of Transmittal ............................................... ii
INTRODUCTION ................................................ 1
PROPOSED CONSTRUCTION ....................................... 1
SITE EXPLORATION ............................................. 2
Field Exploration .......................................... 2
Laboratory Testing ......................................... 2
SITE CONDITIONS .............................................. 3
SUBSURFACE CONDITIONS ....................................... 3
Geology................................................ 3
Soil and Bedrock Conditions .................................. 4
Field and Laboratory Test Results ............................... 5
Groundwater Conditions ..................................... 5
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS .................. 5
Site Development Considerations ............................... 5
Site Clearing ........................................ 6
Utility and Site Grading ................................. 6
Fill Materials ........................................ 7
Foundation Systems ........................................ 7
Basement Construction ...................................... 8
Floor Slab Design and Construction ............................. 8
Compliance ......................................... 8
PRELIMINARY GENERAL COMMENTS ................................ 8
Preliminary Geotechnical Engineering Exploration Terracon
Merrick & Company
TCW Project No. 20955191
Preliminary earthwork considerations are presented in the report.
We appreciated being of service during the preliminary geotechnical engineering phase of
this project, and are prepared to assist during the final geotechnical phase as well. If you
have any questions concerning this report or any of our testing, inspection, design and
consulting services, please do not hesitate to contact us.
Sincerely,
TERRACON CONSULTANTS WESTERN, INC.. L�
Empire Division P"�r�SSa '
Prepared by:
Senior Engineering Geologist
Reviewed by:
William J. Attw&rM P.E. °
Assistant Office Managee l-6,5O
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Copies to: Addressee (2)
Jim Sell Design (1)
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CONSULTANTS WESTERN, INC.
EMPIRE DIVISION
P.O. Box 503 •301 N. Howes
Fort Collins, Colorado 60522
(970) 484-0359 Fax (970) 484-0454
Larry G. O'Dell, P.E.
Neil R. Sherrod, C.P.G.
April 22, 1996
Merrick & Company
2450 South Peoria Street
Aurora, Colorado 80014
Attn: Mr. Glen Tulk
Re: Preliminary Geotechnical Engineering Report, The Pond at Hearthfire
Douglas Road and County Road 13, Fort Collins, Colorado
TCW Project No. 20955191
Terracon Consultants Western, Inc., Empire Division, has completed a preliminary
geotechnical engineering exploration for the proposed Filing 1 of The Pond at Hearthfire to
be located on Larimer County Road 13 south of Douglas Road, northeast of Richards Lake
and northeast of Fort Collins, Colorado.
The results of our engineering study, including the boring location diagram, laboratory test
results, test boring records, and the preliminary geotechnical recommendations needed to
aid in the preliminary design and construction of foundations and other earth connected
phases of this project are attached.
The subsurface soils at the site consist of sandy lean clays underlain by sandstone-
claystone bedrock. The information obtained by the results of field exploration and
laboratory testing completed for this study indicate the soils at the site exhibit moderate to.
high swell potential and moderate to high bearing characteristics. The bedrock at the site
exhibits high bearing characteristics and low swell potential. The soils at anticipated
foundation bearing depths exhibit medium to stiff consistency, and the bedrock varies from
medium hard to very hard to cemented and well cemented.
Based on the preliminary geotechnical engineering analyses, subsurface exploration and
laboratory test results, we recommend the proposed residences be supported on a
conventional -type spread footing and grade beam and/or straight shaft pier foundation
systems. Slab -on -grade may be utilized for the interior floor system provided that care is
taken in the placement and compaction of the subgrade soil. If no movement can be
tolerated, 'a structural floor system should be specified.
Offices of The Terracon Companies, Inc. Geotechnical, Environmental and Materials Engineers
Arizona ■ Arkansas ■ Colorado ■ Idaho ■ Illinois ■ Iowa ■ Kansas ■ Minnesota
Missouri ■ Montana ■ Nebraska ■ Nevada ■ Oklahoma -- ■ Texas ■ Utah ■ Wyoming
QUALITY ENGINEERING SINCE 1966
PRELIMINARY GEOTECHNICAL ENGINEERING REPORT
THE POND AT HEARTHFIRE
DOUGLAS ROAD AND COUNTY ROAD 13
FORT COLLINS, COLORADO
TCW PROJECT NO. 20955191
April 22, 1996
Prepared for
MERRICK & COMPANY
2450 SOUTH PEORIA STREET
AURORA,COLORADO 80014
ATTN: MR. GLEN TULK
Prepared by.
Terracon Consultants Western, Inc.
Empire Division
301 North Howes Street
Fort Collins, Colorado 80521
Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
PRELIMINARY GEOTECHNICAL ENGINEERING REPORT
THE POND AT HEARTHFIRE
DOUGLAS ROAD AND COUNTY ROAD 13
FORT COLLINS, COLORADO
TCW PROJECT NO. 20955191
April 22, 1996
Irerracon