HomeMy WebLinkAboutWOODLAND STATION PUD - PRELIMINARY - 18-94B - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTChateau Custom Builders, Inc.
ELI Project No. 20945028
TABLE OF CONTENTS (Cont'd)
Terracon
Page No.
APPENDIX A
Figure No.
SITEPLAN ......................................................... 1
Logs of Borings .......................................... Al thru A4
APPENDIX B
Summary of Test Results ......................................... B1
APPENDIX C: GENERAL NOTES
Drilling & Exploration ............................................ C1
Unified Soil Classification ......................................... C2
Laboratory Testing, Significance and Purpose ........................... C3
Report Terminology ............................................. C4
RILLING AND EXPLORATION
DRILLING & SAMPLING SYMBOLS:
R : Ring Barrell - 2.42" I.D., 3" O.D., unless otherwise noted
SS : Split Spoon - 1%" I.D., 2" O.D., unless otherwise noted
PS : Piston Sample
ST : Thin -Walled Tube - 2" O.D., unless otherwise noted
WS : Wash Sample
PA : Power Auger
FT : Fish Tail Bit
HA : Hand Auger
RB : Rock Bit
DB : Diamond Bit = 4", N, B
BS : Bulk Sample
AS : Auger Sample
PM : Pressure Meter
HS : Hollow Stem Auger
DC : Dutch Cone
WB : Wash Bore
Penetration Test: Blows per foot of a 140 pound hammer falling 30 inches on a 2-inch O.D. split spoon, except where
noted.
WATER LEVEL MEASUREMENT SYMBOLS:
WL : Water Level WS : While Sampling
WCI : Wet Cave in WD : While Drilling
DCI : Dry Cave in BCR : Before Casing Removal
AB :After Boring ACR : After Casting Removal
Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils,
the indicated levels may reflect the location of groundwater. In low permeability soils, the accurate determination of
groundwater levels is not possible with only short term observations.
DESCRIPTIVE SOIL CLASSIFICATION:
Soil Classification is based on the Unified Soil Classification system and the ASTM Designations D-2487 and D-2488.
Coarse Grained Soils have more than 50% of their dry weight retained on a #200 sieve: they are described as: boulders,
cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are
described as: clays, if they are plastic, and silts if they are slightly plastic or non -plastic. Major constituents may be
added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In
addition to gradation, coarse grained soils are defined on the basis of their relative in -place density and fine grained soils
on the basis of their consistency. Example: Lean clay with sand, trace gravel, stiff (CL); silty sand, trace gravel, medium
dense ISM).
CONSISTENCY OF FINE-GRAINED SOILS:
Unconfined Compressive
Strength, Qu, psf
Consistency
< 500
Very Soft
500 - 1,000
Soft
1,001 - 2,000
Medium
2,001 - 4,000
Stiff
4,001 - 8,000
Very Stiff
8,001-16,000
Very Hard
RELATIVE PROPORTIONS OF
SAND AND GRAVEL
Descriptive Term(s)
(of Components Also
Percent of
Present in Sample)
Dry Weight
Trace
< 15
With
15 - 29
Modifier
> 30
RELATIVE PROPORTIONS OF FINES
Descriptive Term(s)
(of Components Also
Percent of
Present in Sample)
Dry Weight
Trace
< 5
With
5-12
Modifier
> 12
RELATIVE DENSITY OF
COARSE -GRAINED SOILS:
N-Blows/ft.
Relative Density
0-3
Very Loose
4-9*
Loose
10-29
Medium Dense
30-49
Dense
50-80
Very Dense
80+
Extremely Dense
GRAIN SIZE TERMINOLOGY
Major Component
of Sample
Size Range
Boulders
Over 12 in. (300mm)
Cobbles
12 in. to 3 in.
(300mm to 75mm)
Gravel
3 in. to #4 sieve
(75mm to 4.75mm)
Sand
#4 to #200 sieve
(4.75mm to 0.075mm)
Silt or Clay
Passing #200 Sieve
(0.075mm)
Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
z,racon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
Other design and construction details, based upon geotechnical conditions, are presented in the
report.
We have appreciated being of service to you in the preliminary geotechnical engineering phase of
this project, and are prepared to assist you 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,
EMPIRE LABORATORIES, INC.
A Division of The Terracon Companies, Inc.
f�eil R. S ecrod�
Senior Engineering Geologist
Reviewed by:
Chester C. Smith, P.E.
Division Manager
NRS/CCS/cic
Copies to: Addressee (3)
AiPG i
Empire ' Laboratories, Inc.
A Division of The Terracon Companies, Inc.
P.O. Box 503 • 301 No. Howes
Fort Collins, Colorado 80522
(303) 484-0359
FAX No. (303) 484-0454
Chester C. Smith, P.E.
Neil R. Sherrod, C.P.G.
March 17, 1994
Chateau Custom Builders, Inc.
8101 East Prentice, Suite 815
Englewood, Colorado 80111
Attn: Mr. Brad Bennett
Re: Preliminary Geotechnical Engineering Report, Proposed Residential Development
Strachan Farm - County Road 9
Fort Collins, Colorado
ELI Project No. 20945028
Empire Laboratories, Inc. (ELI) has completed a preliminary geotechnical engineering exploration
for the proposed project to be located on County Road 9 south of Horsetooth Road in southeast
Fort Collins, Colorado. This study was performed in general accordance with our proposal number
D2094051 dated February 15, 1994.
The results of our preliminary engineering study, including the boring location diagram, laboratory
test results, test boring records, and the geotechnical recommendations needed to aid in the
design and construction of foundations and other earth connected phases of this project are
attached.
The subsurface exploration indicated conditions which are typical of soils commonly found in the
southeast Fort Collins area. The subsurface soils at the site consisted of lean clay with sand,
sandy lean clay, clayey sand and minor amounts of silty sand with gravel. The information
obtained by the results of field exploration and laboratory testing completed for this study
indicates that the soils at the site have low expansive potential and moderate bearing
characteristics.
Based on the preliminary geotechnical engineering analyses, subsurface exploration and laboratory
test results, we recommend that the proposed structures be supported on spread footing and/or
grade beam 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.
Offices of The Terracon Companies, Inc. Geotechnical, Environmental and Materials Engineers
Arizona. Tucson ■ Colorado. Colorado Springs. Denve, Ft. CoOms. Greeley. Longmont 0 Idaho: Boise g Illinois: Bloomington.
Chicago. Rock s:and ■ Iowa. Cedar Falls. Cedar=aoids. Davenport. Des Moines, Storm Lake ■ Kansas: Lenexa. Topeka.
Wichita ■ 1,imnesota: S! Paul ■ Missouri'. r,ansas City ■ Nebraska: Lincoln. Omaha ■ Nevada: Las Vegas
■ Okianoma. Oklancma City. Tulsa ■ Texas: Dauas ■ Utah: Salt Lake City ■ Wyoming: Cheyenne
QUALITY ENGINEERING SINCE 1965
PRELIMINARY GEOTECHNICAL ENGINEERING REPORT
PROPOSED RESIDENTIAL DEVELOPMENT
STRACHAN FARM - COUNTY ROAD 9
FORT COLLINS, COLORADO
ELI PROJECT NO. 20945028
Prepared for.
CHATEAU CUSTOM BUILDERS, INC.
8101 EAST PRENTICE, SUITE 815
ENGLEWOOD, COLORADO 80111
ATTN: MR. BRAD BENNETT
Empire Laboratories, Inc.
A Division of the Terracon Companies, Inc.
REPORT TERMINOLOGY
(Based on ASTM D653)
Expansive Potential
The potential of a soil to expand (increase in volume) due to absorption of
moisture.
Finished Grade
The final grade created as a part of the project.
Footing
A portion of the foundation of a structure that transmits loads directly to the
soil.
Foundation
The lower part of a structure that transmits the loads to the soil or bedrock.
Frost Depth
The depth of which the ground becomes frozen during the winter season.
Grade Beam
A foundation element or wall, typically constructed of reinforced concrete,
used to span between other foundation elements such as drilled piers.
Groundwater
Subsurface water found in the zone of saturation of soils, or within fractures
in bedrock.
Heave
Upward movement.
Lithologic
The characteristics which describe the composition and texture of soil and
rock by observation.
Native Grade
The naturally occuring ground surface.
Native Soil
Naturally occurring on -site soil, sometimes referred to as natural soil.
Optimum Moisture
The water content at which a soil can be compacted to a maximum dry unit
content
weight by a given compactive effort.
Perched Water
Groundwater, usually of limited area maintained above a normal water
elevation by the presence of an intervening relatively impervious continuing
stratum.
Scarify
To mechanically loosen soil or break down existing soil structure.
Settlement
Downward movement.
Skin Friction (Side
The frictional resistance developed between soil and an element of structure
Shear)
such as a drilled pier or shaft.
Soil (earth)
Sediments or other unconsolidated accumulations of solid particles produced
by the physical and chemical disintegration of rocks, and which may or may
not contain organic matter.
Strain
The change in length per unit of length in a given direction.
Stress
The force per unit area acting within a soil mass.
Strip
To remove from present location.
Subbase
A layer of specified material in a pavement system between the subgrade and
base course.
Subgrade
The soil prepared and compacted to support a structure, slab or pavement
system.
Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
L. f
REPORT TERMINOLOGY
(Based on ASTM D653)
Allowable Soil
The recommended maximum contact stress developed at the interface of the
Bearing Capacity
foundation element and the supporting material.
Alluvium
Soil, the constituents of which have been transported in suspension by flowing
water and subsequently deposited by sedimentation.
Aggregate Base
A layer of specified material placed on a subgrade or subbase usually beneath
Course
slabs or pavements.
Backrill
A specified material placed and compacted in a confined area.
Bedrock
A natural aggregate of mineral grains connected by strong and permanent
cohesive forces. Usually requires drilling, wedging, blasting or other methods of
extraordinary force for excavation.
Bench
A horizontal surface in a sloped deposit.
Caisson (Drilled pier
A concrete foundation element cast in a circular excavation which may have an
or Shaft)
enlarged base. Sometimes referred to as a cast -in -place pier or drilled shaft.
Coefficient of
A constant proportionality factor relating normal stress and the corresponding
Friction
shear stress at which sliding starts between the two surfaces.
Clluuvium
Soil, the constituents of which have been deposited chiefly by gravity such as
at the foot of a slope or cliff.
Compaction
The densification of a soil by means of mechanical manipulation.
Concrete Slab -on-
A concrete surface layer cast directly upon a base, subbase or subgrade, and
Grade
typically used as a floor system.
Differential
Unequal settlement or heave between, or within foundation elements of a
Movement
structure.
Earth Pressure
The pressure or force exerted by soil on any boundary such as a foundation
wall.
ESAL
Equivalent Single Axle Load, a criteria used to convert traffic to a uniform
standard, 0 8,000 pound axle loads).
Engineered F171
Specified material placed and compacted to specified density and/or moisture
conditions under observations of a representative of a geotechnical engineer.
Equivalent Fluid
A hypothetical fluid having a unit weight such that it will produce a pressure
against a lateral support presumed to be equivalent to that produced by the
actual soil. This simplified approach is valid only when deformation conditions
are such that the pressure increases linearly with depth and the wall friction is
neglected.
Existing Fill (or
Materials deposited through the action of man prior to exploration of the site.
man-made rill)
Existing Grade
The ground surface at the time of field exploration.
Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
LABORATORY TESTS
SIGNIFICANCE AND PURPOSE
TEST
SIGNIFICANCE
PURPOSE
California
Used to evaluate the potential strength of subgrade soil, subbase,
Pavement
Bearing
and base course material, including recycled materials for use in
Thickness
Ratio
road and airfield pavements.
Design
Used to develop an estimate of both the rate and. amount of both
Foundation
Consolidation
differential and total settlement of a structure.
Design
Used to determine the consolidated drained shear strength of soil
Bearing Capacity,
Direct
or rock.
Foundation Design &
Shear
Slope Stability
Dry
Used to determine the in -place density of natural, inorganic, fine-
Index Property
Density
grained soils.
Soil Behavior
Used to measure the expansive potential of fine-grained soil and to
Foundation & Slab
Expansion
provide a basis for swell potential classification.
Design
Used for the quantitative determination of the distribution of
Soil
Gradation
particle sizes in soil.
Classification
Liquid &
Used as an integral part of engineering classification systems to
Soil
Plastic Limit,
characterize the fine-grained fraction of soils, and to specify the
Classification
Plasticity Index
fine-grained fraction of construction materials.
Oxidation-
Used to determine the tendency of the soil to donate or accept
Corrosion
Reduction
electrons through a change of the oxidation state within the soil.
Potential
Potential
Used to determine the capacity of soil or rock to conduct a liquid
Groundwater
Permeability
or gas.
Flow Analysis
Used to determine the degree of acidity or alkalinity of a soil.
Corrosion
pH
Potential
Used to indicate the relative ability of a soil medium to carry
Corrosion
Resistivity
electrical currents.
Potential
Used to evaluate the potential strength of subgrade soil, subbase,
Pavement
R-Value
and base course material, including recycled materials for use in
Thickness
road and airfield pavements.
Design
Soluble
Used to determine the quantitative amount of soluble sulfates
Corrosion
Sulphate
within a soil mass.
Potential
Used to determine the quantitative amounts of sulfides within a
Corrosion
Sulfide Content
soil mass.
Potential
To obtain the approximate compressive strength of soils that
Bearing Capacity
Unconfined
possess sufficient cohesion to permit testing in the unconfined
Analysis for
Compression
state.
Foundations
Water
Used to determine the quantitative amount of water in a soil mass.
Index Property
Content
Soil Behavior
Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
°
UNIFIED SOIL CLASSIFICATION SYSTEM
Soil Classification
Criteria for Assigning Group Symbols and Group Names
Using Laboratory Testd`
Group
Symbol
Group Name'
Coarse -Grained
Gravels more than
Clean Gravels Less
Cu > 4 and 1 < Cc <3°
GW
Well -graded gravel`
Soils more than
50% of coarse
than 5% finest
50% retained on
fraction retained on
No. 200 sieve
No. 4 sieve
Cu < 4 and/or 1 > Cc > 31
GP
Poorly graded gravel`
Gravels with Fines c
more than 12% fines
Fines classify as ML or MH
GM
Silty gravel,G,H
Fines classify as CL or CH
GC
Clayey gravel`•O"
Sands 50% or more
Clean Sands Less
Cu > 6 and 1 < Cc < 31
SW
Well -graded send'
of coarse fraction
than 5% fines'
passes No. 4 sieve
Cu < 6 and/or 1 > Cc > 3'
SP
Poorly graded sand'
Sands with Fines
Fines classify as ML or MH
SM
Silty sand°•"•'
more than 12% fines
Fines Classify as CL or CH
SC
Clayey sand'-H,'
Fine -Grained Soils
Silts and Clays
inorganic
PI > 7 and plots on or above "A line'
CL
Lean clay""'
50% or more
Liquid limit less
passes the
than 50
PI < 4 or plots below "A" line'
ML
Silt"'""
No. 200 sieve
organic
Liquid limit -oven dried
".L.M.11
Organic clay
< 0.75
OL
Liquid limit - not dried
Organic sift"A'•O
Silts and Clays
inorganic
PI plots on or above 'A" line
CH
Fat clay"•L"'
Liquid limit 50
or more
PI lots below "A" line
MH
Elastic Silt' "
organic
Liquid limit - oven dried
Organic clay""'•"
< 0.75
OH
Liquid limit -not dried
Organic silt"M•°
Highly organic sails Primarily organic matter, dark in color, and organic odor
ABased on the material passing the 3-in.
(75-mm) sieve
"If field sample contained cobbles or
.•Cu-D10/D2p Cc f/1°)2
D30�1x Dco
boulders, or both, add "with cobbles or
boulders, or both" to group name.
cGravels with 5 to 12% fines require dual
`if soil contains > 15% sand, add "with
symbols:
sand" to group name.
GW-GM well -graded gravel with silt
°If fines classify as CL-ML, use dual symbol
GW-GC well -graded gravel with clay
GC -GM, or SC-SM.
GP -GM poorly graded gravel with silt
"If fines are organic, add "with organic fines'
GP -GC poorly graded gravel with clay
to group name.
°Sands with 5 to 12% fines require dual
1f soil contains > 15% gravel, add "with
symbols:
gravel' to group name.
SW-SM well -graded sand with silt
If Atterberg limits plot in shaded area, soil is
SW -SC well -graded sand with clay
a CL-ML, silty clay.
SP-SM poorly graded sand with silt
SP-SC poorly graded sand with clay
w
PT Peat
'if soil contains 15 to 29% plus No. 200, add
.with sand' or "with gravel", whichever is
predominant.
4f soil contains > 30% plus No. 200
predominantly sand, add "sandy" to group
name.
MY soil contains > 30% plus No. 200,
predominantly gravel, add "gravelly" to group
name.
"PI > 4 and plots an or above "A" line.
°PI < 4 or plots below "A" line.
"PI plots on or above "A" line.
°PI plots below "A" line.
rr tl°�IkOM "1 /M-prvMG Wb
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LIQUID LIMIT (LL)
Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
SUMMARY OF TEST RESULTS
PROJECT NO. 20945028
rStrength
,
Pressure
IndexROW,.AASHTO
r
,
:,
SUMMARY Or TEST RESULTS
PROJECT NO. 20945028
Boring
No.
Depth
Ft.
Moisture
%
Dry
Density
(PCF)
Compressive
Strength
(PSF)
Swell
Pressure
(PSF)
Soluble
Sulfates
%
pH
Liquid
Limit
%
Plasticity
Index
%
Group
Index
Classification
AASHTO
USCS
Resistivity
(OHM -CM)
Penetration
Blow/In.'
1
.5-1.5
22.9
8/12
4-5
21.0
1
4/12
7-8
26.8
79.2
920
8-9
20.8
4/12
14-15
19.5
5/12
2
.5-1.5
22.9
12/12
3-4
14.4
81.8
1220
240
4-5
15.2
5/12
7-8
20.8
34.8
11.2
2.5
A-6(3); SC -SW
5/12
8-9
5/12
14-15
15.6
20/12
3
.5-1.5
20.3
11/12
34
12.5
90.9
710
29.2
11.9
4.0
A-6(4); CL
4-5
9.7
8/12
7-8
18.8
6/12
8-9
5/12
14-15
10.8
13/12
4
.5-1.5
20.6
12/12
4-5
9.7
8/12
7-8
13.0
185
LOG BORING No. 4
Page 1 of 1
CLIENT
ARCHITECT/ENGINEER
Chateau Custom Builders Inc.
SITE County Road 9
PROJECT
Fort Collins, Colorado
Strachan Farm
SAMPLES
I
TESTS
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DESCRIPTION
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LEAN CLAY WITH SAND
Lt. brown/tan, moist
1
SS
12"
12
20.6
Medium to stiff
CL
2
SS
12"
8
9.7
5
6.0
185
3
ST
12"
I13.0
SANDY LEAN CLAY_
CL
4
SS
12"
14
WITH TRACE GRAVEL
111.3
Tan/red, moist
Medium to very stiff
10
5
SS
12"
10
23.6
15.0
15
BOTTOM OF BORING
THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES
BETWEEN SOIL AND ROCK TYPES: IN -SITU, THE TRANSITION MAY BE GRADUAL.
WATER LEVEL OBSERVATIONS
Empire Laboratories
Incorporated
Division of Te[racon
BORING STARTED 2-22-94
�I
g None W.D.
= None A.B.
BORING COMPLETED 2-22-94
WL
I
RIG CME-55
FOREMAN DAR
`�
Water checked 2 days A.B.
APPROVED NRS
JOB q 20945028
LOG BORING No. 3
Page 1 of 1
CLIENT
ARCHITECT/ENGINEER
Chateau Custom Builders Inc.
SITE County Road 9
PROJECT
Fort Collins, Colorado
Strachan Farm
SAMPLES
TESTS
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DESCRIPTION
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0.5 6" TOPSOIL
1
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12"
11
20.3
SANDY J.FAN CLAY
Lt. brown/tan, moist, medium
29/17/12
CL
2
ST
12"
12.5
91
710
4.5
5--
3
SS
12"
8
9.7
CLAYEY SAND
Red/tan, moist
Loose to medium dense
4
SS
12"
6
18.8
SC
5
SS
12"
5
10
13.0
SILTY SAND WITH GRAVEL
Red/tan, moist, medium dense
SM
6
SS
1 12"
13 110.8
15.0
15
BOTTOM OF BORING
THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES
BETWEEN SOIL AND ROCK TYPES: IN -SITU, THE TRANSITION MAY BE GRADUAL.
WATER LEVEL OBSERVATIONS
Empire Laboratories
Incorporated
Division of Terracon
BORING STARTED 2-22-94
L
g None WD•
= None A.B.
BORING COMPLETED 2-22-94
L
r
RIG CME-55
FOREMAN DAR
L
Water checked 2 days A.B.
APPROVED NRS
JOB a 20945028
LOG BORING No. 2 Page 1 of 1
CLIENT
ARCHITECTIENGINEER
Chateau Custom Builders Inc.
SITE County Road 9
PROJECT
Fort Collins, Colorado
Strachan Farm
SAMPLES
TESTS
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0.5 6" TOPSOIL
SANDY LEAN CLAY
Lt. brown/tan, moist, medium
1
SS
12"
12
22.9
CL
2
ST
12"
14.4
82I
1220
3
SS
12"
5
15.2
5
6.0
35/24/11
4
SS
12"
20.8
CLAYEY SAND
SC
5
SS
12"
5
Tan, moist, loose
10
5
SS
12"
20
15.6
15.0
15
BOTTOM OF BORING
THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES
BETWEEN SOIL AND ROCK TYPES: IN -SITU, THE TRANSITION MAY BE GRADUAL.
WATER LEVEL OBSERVATIONS
Empire Laboratories
BORING STARTED 2-22-94
WL
g None WD
IT None A.B.
BORING COMPLETED 2-22-94
Incorporated
Division of Terracon
WL
RIG CNE-55
FOREMAN DAR
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Water checked 2 days A.B.
APPROVED NgS
Jos a 20945028
LOG BORING No. 1
Page 1 of 1
CLIENT
ARCHITECTIENGINEER
Chateau Custom Builders Inc.
SITE County Road 9
PROJECT
Fort Collins, Colorado
Strachan Farm
SAMPLES
TESTS
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15
BOTTOM OF BORING
THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES
BETWEEN SOIL AND ROCK TYPES: IN -SITU, THE TRANSITION MAY BE GRADUAL.
WATER LEVEL OBSERVATIONS
Empire Laboratories
BORING STARTED 2-22-94
W-
Q None W.D.
= None A.B.
BORING COMPLETED 2-22-94
Incorporated
wti
RIG CME-55
FOREMAN DAR
Division of Turecon
WL
Water checked 2 days A.B.
APPROVED NRS
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Empire Laboratories, Inc.
A Division of The Terracon Companies, Inc.
Terracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
Beneath pavements ............................ 95
Utility trenches below building & paved areas .......... 95
Utility trenches below grassed areas ................. 90
Imported fill:
95
Beneath foundations ............................
Beneathslabs ................................
95
Beneath pavements ............................
95
Utility trenches below building & paved areas ..........
95
Utility trenches below grassed areas .................
90
Miscellaneous backfill................................ 90
5. If a well defined maximum density curve cannot be generated by impact compaction
in the laboratory for any fill type, engineered fill should be compacted to a minimum
of 80 percent relative density by determined by ASTM D4253, D4254.
6. On -site clay soils should be compacted within a moisture content range of optimum
moisture to 2 percent above optimum. On -site clay soils below pavement and
imported soils should be compacted within a moisture range of 2 percent below to
2 percent above optimum.
• 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
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 design
of this project. It should be noted that this was a preliminary investigation and the bearing
capacities recommended in this report are based on preliminary tests. Due to variations in soil
conditions encountered at the site, it is recommended that additional test borings be made prior
to construction. Samples obtained from the borings should be tested in the laboratory to provide
a basis for evaluating subsurface conditions.
w
M
Terracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
• general site grading • exterior slab areas
• foundation areas • pavement areas
• interior floor slab areas • foundation backfill
2. Select granular materials should be used as backfill behind walls which retain earth.
3. Frozen soils should not be used as fill or backfill.
4. Imported soils (if required) should conform to the following:
• Gradation (ASTM C136):
percent finer by weight
6"................................................... 100
3"................................................ 70-100
No.4 Sieve .......................................... 50-100
No.200 Sieve ....................................... 35(max)
• Liquid Limit ......................................... 35 (max)
• Plasticity Index ...................................... 15 (max)
• Placement and Compaction:
1. Place and compact fill in horizontal lifts, using equipment and procedures that will
produce recommended moisture contents and densities throughout the lift.
2. Uncompacted fill lifts should not exceed 10 inches loose thickness.
3. No fill should be placed over frozen ground.
4. Materials should be compacted to the following:
Minimum Percent
Material Compaction (ASTM D6981
On -site soils:
Beneath foundations ............................ 95
Beneath slabs ................................ 95
�3
Terracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
2. Depending upon depth of excavation and seasonal conditions, groundwater may be
encountered in excavations on the site. 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.
• Slab Subgrade Preparation:
1. Where existing clay soils will support floor slab, the soils should be scarified,
moisture -conditioned and compacted to a minimum depth of 8 inches.
2. A minimum 4-inch layer of clean -graded gravel should be placed beneath slabs.
3. A minimum 8-inch layer of free -draining gravel should be placed beneath basement
floor slabs in conjunction with the underslab drainage system.
• Pavement Sub4rade Preparation:
1. The subgrade should be scarified, moistened as required, and recompacted for a
minimum depth of 8 inches prior to placement of fill and pavement materials.
2. 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.
Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a
stabilization technique. Laboratory evaluation is recommended to determine the
effect of chemical stabilization on subgrade soils prior to construction.
• Fill Materials:
1. Clean on -site soils or approved imported materials may be used as fill material for
the following:
7
erracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
Earthwork:
• General Considerations: The conclusions contained in this report for the proposed
construction are contingent upon compliance with recommendations presented in this
section.
Although fills or underground facilities, such as septic tanks, cesspools, basements, and/or
utilities, were not observed during site reconnaissance, such features might be encountered
during construction.
• 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. Sloping areas steeper than 3:1 (horizontal: vertical) should be benched to reduce the
potential for slippage between existing slopes and fills. Benches should be level and
wide enough to accommodate compaction and earth moving equipment.
4. The site should be initially graded to create a relatively level surface to receive fill
and to provide for a relatively uniform thickness of fill beneath proposed building
structures.
5. All exposed areas which will receive fill, once properly cleared and benched where
necessary, should be scarified to a minimum depth of twelve inches, conditioned
to near optimum moisture content, and compacted.
• Excavation:
1. It is anticipated that excavations for the proposed construction can be accomplished
with conventional earthmoving equipment.
L
Terracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
• spread footings and/or grade beams bearing on undisturbed soils; and
• spread footings and/or grade beams bearing on engineered fill.
Preliminary design and construction recommendations for foundation systems and other earth
connected phases of the project are outlined below.
Foundation Systems: Due to the presence of non- to low -swelling soils on the site, spread footing
foundations bearing upon undisturbed subsoils and/or engineered fill are recommended for support
for the proposed structure. Based on preliminary test results, the footings may be designed for
a maximum bearing pressure of between 1,000 to 1,500 psf. In addition, the footings should be
sized to maintain a minimum dead -load pressure of between 250 to 500 psf. Exterior footings
should be placed a minimum of 30 inches below finished grade for frost protection. Interior
footings should bear a minimum of 12 inches below finished grade.
Foundation excavations should be observed by the geotechnical engineer. If the soil conditions
encountered differ significantly from those presented in this report, supplemental recommendations
will be required.
Basement Construction: Groundwater was not encountered on the site to the maximum depth
of exploration, 15 feet. Therefore, full -depth basement construction is considered acceptable on
the site.
High moisture contents indicate groundwater may occur at times. Completion of site
development, including installation of landscaping and irrigation systems, may lead to groundwater
development.
To reduce the potential for groundwater to impact foundation bearing soils and enter the basement
of the structures, installation of perimeter drainage systems is recommended.
Floor Slab Design and Construction: Low -swelling natural soils or engineered fill will support the
floor slab. Some differential movement of a slab -on -grade floor system is possible should the
subgrade soils become elevated in moisture content. Such movements are considered within
general tolerance for normal slab -on -grade construction. To reduce any potential slab movements,
the subgrade soils should be prepared as outlined in the earthwork section of this report.
5
I L
7erracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
• Lean Clay with Sand: This stratum was encountered below the topsoil in Borings 1 and
4 and extends to depths of 6 feet. The lean clay with sand is brown, moist and medium
to stiff.
• Sandy Lean Clay: This stratum was encountered below the topsoil and upper clays in all
borings and extends to depths of 4Y2 to greater than 15 feet below the surface. The tan
to red sandy lean clay is moist and medium to very stiff.
• Sand: This stratum was encountered in Borings 2 and 3 at depths of 4Yz to 6 feet and
extends to depths of 13 to greater than 15 feet. The sand contains varying amounts of
clay, is loose to medium dense and moist in situ.
• Silty Sand and/or Silty Sand With Gravel: This stratum was encountered in Borings 1 and
4 at a depth of 13 feet and extends beyond the depths explored. The sand is moist and
loose to medium dense in situ.
Laboratory Test Results: The soils bedrock at anticipated foundation bearing depth have moderate
load bearing capability. Laboratory test results indicate that the clay subsoils at shallow depth
have low expansive potential.
Groundwater Conditions: Groundwater was not encountered in any test boring at the time of field
exploration, nor when checked two days after drilling. These observations represent only current
groundwater conditions, 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.
Based upon review of U.S. Geological Survey maps (ZHillier, et al, 1983), regional groundwater
is expected to be encountered in unconsolidated alluvial deposits on the site, at depths ranging
from 10 to 20 feet below the existing ground surface at the project site.
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS
General Considerations: Because of variations in the engineering properties of the on -site soils,
foundation bearing levels, structural loads, and possible final grades, the following foundation
systems were evaluated for use on the site:
'Hillier, Donald E.; Schneider, Paul A., Jr.; and Hutchinson, E. Carter, 1983, Depth to Water Table (19791 in the Boulder -Fort
Colfrns-Greeley Area, Front Range Urban Corridor, Colorado, United States Geological Survey, Map 1-855-I.
4
Chateau Custom Builders, Inc.
ELI Project No. 20945028
SITE CONDITIONS
Terracon
The site consists of a vacant tract of land vegetated with cut alfalfa. The property is irrigated
with several irrigation laterals running in an east -west direction across the site. The area is
relatively flat and has minor drainage to the northeast toward a natural drainage in the northeast
corner of the site. The property is surrounded by pine and deciduous trees on the northeast and
west sides and on the south by shrubs. An existing residence and outbuildings are located in the
southwest corner of the site.
SUBSURFACE CONDITIONS
Geology: The project 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. It is estimated the Pierre shale underlies the site
at depths of approximately 20 to 30 feet below existing grade. The Pierre shale is overlain by
residual and alluvial soils of Pleistocene and/or Recent Age.
Mapping completed by the Colorado Geological Survey ('Hart, 1972), indicates the site in an area
of "Moderate Swell Potential". Potentially expansive materials mapped in this area include
bedrock, weathered bedrock and colluvium (surficial units).
Soil Conditions: As presented on the Logs of Boring, the subsurface soils were encountered in
order of increasing depths as follow:
• 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.
'Hart, Stephen S., 1972, Potentially Swelling Soil and Rock in the Front Range Urban Corridor, Colorado, Colorado
Geological Survey, Environmental Geology No. 7.
3
erracon
Chateau Custom Builders, Inc.
ELI Project No. 20945028
of the proposed construction. All borings were advanced with a truck -mounted drilling rig, utilizing
4-inch diameter solid stem auger.
The location of borings were positioned in the field by r s from existing property lines
and topographic features. The accuracy of boring locations and elevations should only be
assumed to the level implied by the methods used to determine each.
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 by driving split -spoon samplers.
Penetration resistance measurements were taken with each sampling with the split -spoon by
driving the sampler with a 140-pound hammer falling 30 inches. When properly interpreted, the
penetration resistance is a useful index to the consistency, relative density or hardness of the
materials encountered.
Groundwater conditions were evaluated in each boring at the time of site exploration, and two
days after drilling.
Laboratory Testing: All samples retrieved during the field exploration were returned to the
laboratory for evaluation by the project geotechnical engineer, and were classified in accordance
with the Unified Soil Classification System described in Appendix C. At that time, the field
descriptions were confirmed or modified as necessary, final boring logs prepared, and an applicable
laboratory testing program was formulated to determine engineering properties of the subsurface
materials. Boring Logs for the project are presented in Appendix A.
Selected soil samples were tested for the following engineering properties:
• Water content • Expansion
• Dry density • Plasticity
• Compressive strength
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.
2
t
erracon
PRELIMINARY GEOTECHNICAL ENGINEERING REPORT
PROPOSED RESIDENTIAL DEVELOPMENT
STRACHAN FARM - COUNTY ROAD 9
FORT COLLINS, COLORADO
ELI PROJECT NO. 20945028
MARCH 17, 1994
INTRODUCTION
This report contains the results of our preliminary geotechnical engineering exploration for the
proposed project to be located on County Road 9 south of Horsetooth Road in southeast Fort
Collins, Colorado. The site is located in the Northwest 1 /4 of Section 33, Township 7 North,
Range 68 West of the 6th Principal Meridian.
The purpose of these services is to provide information and geotechnical engineering
recommendations relative to:
• subsurface soil conditions
• groundwater conditions
• preliminary foundation design and construction
• basement construction
• floor slab design and construction
• earthwork
The conclusions and recommendations contained in this report are based upon the results of field
and laboratory testing, engineering analyses, and experience with similar soil and structural
conditions.
PROPOSED CONSTRUCTION
The project as we understand it will be construction of single-family residences along with
residential streets. Minor amounts of site grading are anticipated.
SITE EXPLORATION
The scope of the services performed for this project included site reconnaissance by a
geotechnical engineer, a subsurface exploration program, laboratory testing and engineering
analyses.
Field Exploration: A total of four test borings were drilled on February 22, 1994 to depths of 15
feet at the locations shown on the Site Plan, Figure 1. The borings were drilled within the area
Chateau Custom Builders, Inc.
ELI Project No. 20945028
TABLE OF CONTENTS
Terracon
Page No.
Letterof Transmittal................................................... ii
INTRODUCTION..................................................... 1
PROPOSED CONSTRUCTION ........................................... 1
1
SITEEXPLORATION ..................................................
1
FieldExploration ...............................................
2
Laboratory Testing ..............................................
SITECONDITIONS ................................................... 3
SUBSURFACE CONDITIONS ............................................
3
3
Geology......................................................
SoilConditions .................................................
3
4
Laboratory Test Results ..........................................
4
Groundwater Conditions ..........................................
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS ....................... 4
GeneralConsiderations ........................................... 4
Foundation Systems ............................................. 5
Basement Construction ........................................... 5
Floor Slab Desiqn and Construction .................................. 5
Earthwork....................................................
6
General Considerations ......................................
6
Site Clearing .............................................
6
Excavation..............................................
6
Slab Subgrade Preparation ....................................
7
Pavement Subgrade Preparation ................................
7
Fill Materials .............................................
7
Placement and Compaction ...................................
8
Compliance..............................................
9
PRELIMINARY GENERAL COMMENTS .....................................
9