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GE07ECHNICAL INVES77GA77ON FOR
THE PROPOSED 1301-it LOT
SFLVER OAKS SUEDIMON
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GEOTECHNICAL INVESTIGATION FOR
THE PROPOSED 130t LOT
SFLVER OAKS SURDIMON
Tri-Tmf 4Inc.
1a05 Timberline Road
Ft. Collins, CO 80524
Date: July 14 1992
Prcoct No.: 7WM-92052G-08-709
LANDMARK ENGINEERING LTD.
3521 W. EISENHOWER BLVD-
LOVELAND, CO 80537
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Landmark
LABORATORIES Ltd.
July 14, 7992
Project No. TRITR-92052G-08-709
Tri-Trend, Inc.
1505 Timberline Road
Ft. Collins, CO 80524
The enclosed report presents the results of a geotechnical investigation for the
proposed Silver Oak Subdivision, located in the City of Ft. Collins, Colorado.
If you have any questions or if we can be of further assistance, please feel free to
contact our office.
Sincerely,
Landmark Engineering Lid.
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Larry Miller
Geologist
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Enclosures
The above has beenll
David Shupe, Colo.
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e vr'o_vl�d under the direct supervision of
�fft: Loveland (303) 667-6286
3521 West Eisenhower Blvd. t�3.•. = Denver (303) 629-7124
Loveland, Colorado 80537
FAX (303) 667 6298
Geotechnical Investigations • Material Testing • Drilling • Inspections
Water & Wastewater Laboratory 0 Radon Testing & Mitigation • ACIL Laboratory
TABLE OF CONTENTS
Page
Letter of Transmittal ........................................ i
Table of Contents ......................................... it
Scope.................................................. 1
Site Location and Description ................................ 1
Field Investigation ......................................... 1
Laboratory Testing ........................................ 2
Subsurface Conditions ..................................... 2
Foundation Recommendations .............................. 3
Floor Slabs ............................................... 5
Basements.............................................. 6
Site Grading, Landscaping and Drainage ...................... 6
Pavement Thickness Design ................................. 7
Groundwater Evaluation ................................... 8
General Information ....................................... 8
Location of Borings .................................... Plate 1
Legend of Soils and Rock Symbols ........................ Plate 2
Boring Logs ................................... Plate No. 1 - 19
Consolidation - Swell Tests .................... Drawing No. 1 - 13
Summary of Test Results ............................... Table 1
Suggested Specifications For Placement of
Compacted Earth Fills and/or Bockfllls ................ Appendix A
' SCOPE
The following report presents the results of a geotechnical investigation on the
proposed 130± lot. Silver Oaks Subdivision located in Ft. Collins, Colorado.
The investigation was performed for Tri-Trend, Inc.
itThe purpose of this investigation was to obtain the technical information and
subsurface property data necessary for the design and construction of
foundations and pavement systems for the proposed Silver Oaks Subdivision. The
conclusions and recommendations presented in this report are based upon
analysis of field and laboratory data and experience with similar subsurface
conditions in the general vicinity.
it SITE DESCRIPTION
IThe 31 ± acre site is located at the Northwest corner of South Taft Hill Road & West
Horsetooth Road, Ft. Collins, Colorado. The site is presently vacant pasture land
except for a tree nursery located along the Northeast boundary of the properly.
The site is relatively flat, sloping very gently to the East. Pasture grasses, alfalfa
and weeds vegetate the site.
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IFIELD INVESTIGATION
The field investigation consisted of 17 borings at selected locations on the site.
The borings were advanced with on Acker AD-11 drill rig utilizing 4-inch diameter
continuous flight augers.
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As the boring operation advanced, an index of soils relative density and
consistency was obtained by use of the standard penetration test, ASTM Standard
' Test D-1586. The penetration test result listed on the log is the number of blows
required to drive the 2 inch split -spoon sampler twelve inches, or increments as
shown, into undisturbed soil by a 140-pound hammer dropped 30 inches.
ItUndisturbed samples for use in the laboratory were taken in 3" O.D. thin wail
samplers (Shelby), pushed hydraulically into the soil. Undisturbed and disturbed
samples were sealed in the field and preserved at natural moisture content until
time of test.
Complete logs of the boring operation are shown on the attached plates and
include visual classifications of each soil, location of subsurface changes,
standard penetration test results, and subsurface water level measurements at the
time of this investigation.
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LABORATORY TESTING
The laboratory testing program was undertaken to determine visual classification,
moisture contents, dry densities, swelling and consolidation characteristics,
plasticity, gradation and soluble sulfates.
I SUBSURFACE CONDITIONS
ISubsurface conditions encountered over the site were fairly erratic. A brief
Idescription of encountered soils follows.
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' A one (7) to two and one half (2-112) feet layer of brown clay, slightly sandy,
blankets the entire site. The top six inches (6") to one foot (I') of this material
' contains organics and should be stripped prior to construction.
' Following the topsoil layer a red clayey sand was encountered in all of the
borings. The presence or absence of gravel, however, varied throughout each
boring. This material proved to offer moderate bearing capacities while
possessing a low to moderate swell potential.
In a majority of the borings, the red clayey sand or red sholy gravels continued
throughout the remainder of the borings. However, in borings No. 1, 2, 11, 12, 13
& 16 a tan -brown silty clay was found at varying depths and thicknesses.
' Laboratory and field test data indicated that this material possesses moderate
bearing capacities and moderate swell potential when subjected to wet loading.
k FOUNDATION RECOMMENDATIONS
tThe selection of the foundation type for a given situation and structure is
governed by two basic considerations. First, the foundation must be designed so
as to be safe against shear failure in the underlying soils and/or rock; and second,
differential settlement or other vertical movement of the foundation must be
controlled at a reasonable level.
Two basic controls are available to us in selecting the foundation type and
' allowable loads. These are the standard penetration test and consolidation -swell
z testing. The ultimate bearing capacity of the foundation soil depends upon the
isize and shape of the foundation element, the depth below the surface, and the
physical characteristics of the supporting soil or rock.
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' Continuous Spread Footing Foundations
' Where the foundation will be placed on the natural undisturbed clayey sands and
sandy gravels, the foundation should be a continuous spread footing foundation
' designed for a maximum allowable bearing capacity of 1500 pounds per square
foot (dead load plus full live load) and a minimum dead load of 750 pounds per
square foot to help counteract swelling should the subsoils become wetted. All
footings should be placed a minimum of thirty inches (30") below finished grade
for frost protection. Foundation walls should be reinforced with rebor to span an
unsupported length of ten feet (10) or as required by the Engineer. Splicing and
' placement should comply with AC1-318 or as required by the Engineer.
Pad and Grade Beam Foundations
' Where the foundation will be placed on the natural, undisturbed silty clays, the
foundation should be a pad and grade beam foundation designed for a
maximum allowable bearing capacity of 30100 pounds per square foot (dead load
plus full live load) and a minimum dead load of 1500 pounds per square foot to
help counteract swelling should the subsoils become wetted. All pads shall be a
minimum of thirty inches (30') below finished grade for frost protection. Grade
beams should be reinforced to span unsupported lengths between pads as
' determined by the Design Engineer. Four inch (4") void form shall be located
under the grade beams, between pads, os that no part of the grade beam will
bear on the soil, bearing only on the pads.
' The following recommendations should be followed in the design of the
foundation system:
1. All footings and pads should bear on or in the some type of soil.
Foundation components bearing on the earth should not be placed on
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frozen ground, topsoil, or inadequately compacted or unsuitable fill
material.
2. Areas of habitable space located below finished grade should be
protected by a perimeter drain system.
3. Partition walls should not be placed directly on concrete slabs. They should
be hung from the floorjoists, or other approved method which will allow the
slab to heave unimpaired for a vertical distance of 2 inches. Foundations
shall be provided for all bearing walls.
4. Laboratory test results indicate that soluble sulfates are 750 parts per million.
Therefore, a Type 11 cement should be used for all concrete exposed to the
' soils.
5. The bottom of all foundation components (except piers) should be placed
' at least three feet (3) above subsurface water levels.
' 6. The completed open excavation should be inspected by an experienced
soils engineer or technician to confirm the subsurface conditions described
in this report and observe any variations which may affect construction at
the site.
FLOOR SLABS
The slabs placed on the natural ground at the site should be anticipated to
' heave to some degree due to swelling of the subsoils. Therefore, slabs should be
constructed to be "free-floating", isolated from all bearing members, utilities, and
partitions so that the slab can move unimpaired without producing architectural
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' or structural damage. Generally, slabs should be underlain with a four -inch (4")
layer of washed rock to help distribute floor loads, provide a capillary break, and
' provide a pathway for potential infiltrating water to be directed toward sump
areas. However, upper level slabs in the area of Test Hole 5 should eliminate the
' gravel underloyment, as should basement slabs in the area of Test Hole 11.
Conditions should be verified by open excavation inspection at time of
construction. Positive drainage should be provided for the excavation subgrade
to prevent pooling of water beneath the slab. The slabs should be reinforced with
1 wire mesh, or equivalent. The slabs should be jointed to a depth of at least one -
quarter (114) of the slab thickness in dimensions not to exceed fifteen feet (75)
1 or 225 square feet and at areas of potential cracking. Exterior slabs exposed to
de-icing chemicals or extreme weathering should be constructed using Type ll
cement with higher air contents and higher compressive strengths.
BASEMENT
Basement construction is deemed feasible at this site if a perimeter drain is
' installed to protect all below grade habitation, and appropriate construction
' techniques are employed to control cracking in on -grade slabs.
SITE GRADING LANDSCAPING & DRAINAGE
Every precaution should be taken to prevent wetting of the subsoils and
percolation of water down along the foundation elements. Water infiltrating
along side the foundation may result in architectural or structural damage due
to weathering or swelling at the subsoils. Bockfill around the outside perimeter of
the structure should be compacted at optimum moisture, or above, to at least
90 percent of Standard Proctor Density as determined by ASTM Standard Test D-
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698. A suggested specification for placement of bockfills is included as Appendix
A. Bockfrll material should be relatively impervious and non -swelling. The bockfill
should be free of frozen soil, large dried clods, and organic matter. Bockfilling
should only be accomplished when concrete strength and adequate support to
foundation walls are applied and acceptable to the Foundation Engineer. It is
our opinion that the natural soils at the site could be used for backfill material.
Finished grades should be sloped away from the structure on all sides to give
positive drainage. A minimum of 6 inches fall in the first 10 feet is recommended
and should be maintained throughout the life of the structure. Sprinkling systems
should not be installed within 10 feet of the structure. Downspouts are
recommended and should be arranged to carry drainage from the roof at least
5 feet beyond the foundation walls. Should landscaping plants be located next
to the structure, we recommend the use of varieties of plant life which require
little watering.
PAVEMENT THICKNESS DESIGN
in conjunction with the subsurface soils investigation, this office also performed
pavement thickness designs for the streets within the subdivision. These designs
have been performed in accordance with the A.A.S.H.T.O. Guide For Design of
Pavement Structures. A subgrode sample was obtained and testing revealed on
R-value of 6. Using these figures along with a DTN of 5, on Overall Standard
Deviation (50) of 0.44, a reliability of 80%, and a design serviceability loss of
(A P.S.I.) of 2, a structural number (SN) of 2.7 was obtained from the nomograph.
Using this number as a solution in the equation SN = o,D,+02D2M2 the pavement
thickness sections of Hot Bituminous Pavement (H.B.P.) and Class V Aggregate
Base Course (A.B.C.) are listed in the table below. These thickness are based on
the H.B.P. having an R-value of 95 or better and the A.B.C. having an R-value of
78-83. The M2 factor is based on the quality of drainage being good (within I
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day) and the percent of time the pavement section is exposed to moisture levels
approaching saturation being one to five percent.
PAVEMENT THICKNESS H.B.P. A.B.C.
Full Depth 6-1/2" 0*
3" 3" 9-1120
2-112" 2-112" 110
2" 2" 720
GROUNDWATER EVALUATION
Three temporary groundwater monitor tubes were installed in test hole boring
numbers 1, 11 and 17. These monitors were randomly spaced throughout the site
to determine subsurface water levels. No water was encountered in any of these
borings or any additional borings during the time of drilling. Monitoring since
drilling indicates the water table to be at least 13' below the surface. These
observations, coupled with the relatively good rate of permeability in the area
soils indicate little likelihood of development of subsurface drainage problems in
' the general area. Proper site grading techniques as listed above should be strictly
observed, however, to minimize individually -caused local problems.
' GENERAL INFORMATION
' The data presented herein were collected to help develop designs and cost
estimates for this project. Professional judgements on design alternatives and
criteria are presented in this report. These are based on evaluation of technical
information gathered, partly on our understanding of the characteristics of the
proposed single family residences, and partly on our experience with subsurface
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' conditions in the area. We do not guarantee the performance of the project in
any respect, only that our engineering work and judgements rendered meet the
' standard of care of our profession.
' The test holes drilled were spaced to obtain a reasonably accurate picture of
subsurface conditions for design purposes. Variations from the conditions
' portrayed frequently occur. These variations are sometimes sufficient to
necessitate modifications in design.
We recommend that construction be continuously observed by a qualified soils
technician trained and experienced in the field to take advantage of all
opportunities to recognize different conditions and minimize the risk of having
some undetected condition which might affect the performance of the
' foundation elements.
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Loveland, CO. 80537 (303) 667-6286