HomeMy WebLinkAboutRevised Geo Engineering Investigation 06.22.2020CTL ITHOMPSON
INCORPORATID
March 27, 2020
(Revised June 22, 2020)
G. H. Daniels & Associates, Inc.
140 G. H. Daniels Boulevard
Gypsum, CO 81637
Attention: Mr. Jody Daniels
Subject: Revised Geotechnical Engineering Investigation
Shop Building
Lot 5, Quicksilver Court Subdivision
Garfield County, Colorado
Project No. GS06392.002-120
CTL 1 Thompson, Inc. performed a geologic evaluation and preliminary ge-
otechnical investigation for the development previously referenced as Dan-
iels/Hasenberg Subdivision (Project No. GS05135-115; report dated January 11,
2008) to identify geologic conditions at the site and provide preliminary mitigation
for construction of single-family residence on Lots 1 - 7 of the development. Our
opinions and recommendations in the report were based on seven exploratory
borings drilled at the site (one on each of the seven lots) and pertinent laboratory
testing. Subsequently, we utilized our field and laboratory data obtained for our
report to provide a soils and foundation investigation for the seven lots in the sub-
division (Project No. GS05135-120; letter dated February 14, 2008). However,
building plans for residences on Lots 1 — 7 were not developed at the time of our
letter.
The information, conclusions, and recommendations presented in our re-
port and letter were based upon consideration of many factors including, but not
limited to, the type of structures proposed, the geologic setting, and the subsur-
face conditions encountered. Standards of practice continuously change in the
area of geotechnical engineering. Our recommendations are appropriate for
about three years. Because residences were not constructed at the site within
this time period, and because building plans were not known at the time of our
soils and foundation investigation, we recommended that our geotechnical engi-
neering letter be updated. This revised letter provides our geotechnical engi-
neering opinions and recommendations for the shop building proposed on Lot 5,
Quicksilver Court Subdivision.
234 Center Drive Glenwood Springs, Colorado 81
Telephone: 970-945-2809 Fax: 970-945-7411
Site Conditions
The subject site is Lot 5, Quicksilver Court Subdivision in Garfield County,
Colorado. Lot 5 is an approximately 10 -acre parcel northwest of the intersection
of Quicksilver Court and Quicksilver Way. A pond is at the east edge of the prop-
erty. No buildings were present on the subject lot at the time of our investigation.
A gravel road enters the lot from the east with a turn -around near the building en-
velope. An aerial photograph of the site is included as Figure 1. Ground surface
at the building site slopes gently down to the northwest at grades less than 10
percent. Steep slopes drop down to a natural drainage at the west side of the
property. Natural vegetation in the building area consists of sparse grasses with
scattered sage, juniper and pinyon.
Proposed Construction
A shop building is proposed adjacent to the existing driveway in the east
part of Lot 5 (approximate location of TP -1 and TP -2). We expect the building to
be a one-story, steel or wood -frame building with slab -on -grade floor. At this
writing, it is not known if cuts and fills will be made to construct the building pad.
We do not know if the building will have spanning roof joists or interior columns
and pads. Foundation loads are expected to be less than 3,000 pounds per lin-
eal foot of foundation wall.
A residence may be constructed at the crest of the steep slope in the fu-
ture (approximate location of TP -3 and TP -4). Plans for this building have not
been developed. This letter does not address the potential residence. If re-
quested, we can provide geotechnical/geo-structural recommendations for the
residence when plans are further developed.
Subsurface Condition
Subsurface conditions at the site were investigated by excavating four ex-
ploratory pits (TP -1 through TP -4) with a trackhoe at the approximate locations
shown on Figure 1. Exploratory excavation operations were directed by our rep-
resentative who logged the soils and obtained samples for laboratory testing.
Subsurface conditions encountered in our exploratory pits were about 6
inches of sandy clay topsoil, underlain by clay with cobbles, boulders, and lenses
of clayey sand to the total explored depth of 8 feet. Free ground water was not
encountered in our exploratory pits. The pits were backfilled immediately after
G. H. DANIELS & ASSOCIATES, INC.
LOT 5, QUICKSILVER COURT SUBDIVISION
PROJECT NO. GS06392.002.120
2
exploratory excavation operations were completed. Graphic logs of the soils en-
countered in our exploratory pits are presented on Figure 2.
Samples obtained from our pits were returned to our laboratory where
they were visually classified and typical samples were selected for testing. Two
samples selected for gradation analysis contained 54 and 75 percent gravel, 12
and 19 percent sand, and 6 and 34 percent silt and clay (passing the No. 200
Sieve). Gradation test results do not include rocks larger than 5 inches, which
are present in the in-situ soils. Engineering index testing on two samples indi-
cated the sandy clay matrix soils at the site have a liquid limit of about 37 to 38
percent and plasticity index of about 14 to 15 percent. Gradation test results are
shown on Figure 3. Laboratory test results are summarized on Table I.
Foundation
We judge that a footing foundation supported by the undisturbed, natural
clayey gravel soil is appropriate for the shop building proposed on Lot 5. The rec-
ommendations in the Surface Drainage section of this letter will be critical for per-
formance. Design and construction criteria for footings are presented below.
Footing foundations can be supported on the undisturbed, natural
clayey gravel soil. Soils loosened during excavation or the forming
process for the footings should be removed or the soils can be re -
compacted prior to placing concrete.
Footings on the undisturbed, natural clayey gravel should be de-
signed for a
maximum soil bearing pressure of 3,000 psf.
Continuous wall footings should have a minimum width of at least 16
inches. Foundations for isolated columns should have minimum di-
mensions of 24 inches by 24 inches.
Grade beams and foundation walls should be well -reinforced, top
and bottom. We recommend reinforcement sufficient to span an un-
supported distance of at least 10 feet.
5. The soils under exterior footings should be protected from freezing.
We recommend the bottom of footings be constructed at a depth of
at least 36 inches below finished exterior grades for frost protection.
The Garfield County building department should be consulted to ver-
ify the required depth.
G. H. DANIELS & ASSOCIATES, INC.
LOT 5, QUICKSILVER COURT SUBDIVISION
PROJECT NO. GS06392.002-120
3
Slab -on -Grade Construction
A slab -on -grade floor is likely for the shop building. The area below the
building footprint should be stripped of vegetation, organic soils and debris. We
do not know if excavation cuts and/or structural fill will be required to construct the
building pad. The on-site soils free of rocks larger than 3 inches in diameter, or-
ganic matter, and debris are suitable for use as structural fill below the floor slab.
The structural fill should be placed in loose lifts of 10 inches thick or less, moisture -
conditioned to within 2 percent of optimum moisture content, and compacted to at
least 98 percent of standard Proctor (ASTM D 698) maximum dry density. Mois-
ture content and density of fill should be checked by a representative of our firm
during placement. Observation of the compaction procedure is necessary.
Floor slabs should be separated from the building foundation (including in-
terior column pads) with slip joints which allow free vertical movement of the slabs.
These slabs should be well -reinforced to function as independent units. Move-
ments of these slabs should not be transmitted to the building. Frequent control
joints should be provided, in accordance with American Concrete Institute (ACI)
recommendations, to reduce problems associated with shrinkage and curling.
Below -Grade Walls
We do not know if the uphill wall of the shop building will retain earth. Walls
that will retain earth should be designed for lateral earth pressures. For a very
rigid wall where negligible or very little deflection will occur, an "at -rest" lateral earth
pressure should be used in design. For walls which can deflect or rotate 0.5 to 1
percent of wall height (depending upon the backfill types), lower "active" lateral
earth pressures are appropriate.
Our experience indicates that typical building walls that retain earth can de-
flect or rotate slightly under normal design loads, and that this deflection results in
satisfactory wall performance. Thus, the earth pressures on the walls will likely be
between the "active" and "at -rest" conditions. If the on-site soils are used as back-
fill, we recommend design of below -grade walls using an equivalent fluid density
of at least 45 pcf for this site. This equivalent density does not include allowances
for sloping backfill, surcharges or hydrostatic pressures.
Foundation Wall Backfill
Properly -placed backfill adjacent to foundation wall exteriors is important to
reduce infiltration of surface water and subsequent consolidation. This is espe-
cially important for backfill that will support exterior concrete flatwork, such as
driveway aprons. The on-site excavated soils can be used as foundation backfill,
G. H. DANIELS & ASSOCIATES, INC.
LOT 5, QUICKSILVER COURT SUBDIVISION
PROJECT NO. GS06392.002-120
4
provided they are free of organic matter, debris, and rocks larger than 3 inches in
diameter. Backfill should be moisture -conditioned to within 2 percent of optimum
moisture content and compacted to at least 95 percent of standard Proctor (ASTM
D 698) maximum dry density.
Subsurface Drainage
Water from rain, snow melt and surface irrigation frequently flows through
relatively permeable backfill placed adjacent to a building and collects on the sur-
face of relatively undisturbed soils at the bottom of the excavation. This can cause
wetting of foundation soils after construction, which results in movement of foun-
dations and floor slabs. To mitigate this concern, we recommend provision of a
foundation drain adjacent to the footing of walls that retain earth.
The foundation drain should consist of a 4 -inch diameter, slotted pipe en-
cased in free draining gravel. A prefabricated drainage composite should be
placed adjacent to foundation walls. Care should be taken during backfill opera-
tions to prevent damage to drainage composites. The drain should lead to a pos-
itive gravity outfall, or to a sump pit where water can be removed by pumping.
Gravity outlets should not be susceptible to clogging or freezing. Installation of a
clean-out along the drain pipe is recommended.
Surface Drainage
Surface drainage is critical to the performance of foundations, and concrete
flatwork. Surface drainage should be designed and constructed to provide rapid
runoff of surface water away from the building. Proper surface drainage and irriga-
tion practices can help control the amount of surface water that penetrates to foun-
dation levels and contributes to settlement or heave of soils and bedrock that sup-
port foundations and slabs -on -grade. Positive drainage away from the foundation
and avoidance of irrigation near the foundation also help to avoid excessive wetting
of backfill soils, which can lead to increased backfill settlement and possibly to
higher lateral earth pressures, due to increased weight and reduced strength of
the backfill. We recommend the following precautions be observed during con-
struction and maintained at all times after the building is completed:
1. The ground surface surrounding the exterior of the building should
be sloped to drain away from the building in all directions. We rec-
ommend providing a slope of at least 12 inches in the first 10 feet
around the building.
Backfill around the exterior of foundation walls should be placed in
accordance with recommendations in the Foundation Wall Backfill
section.
G. H. DANIELS & ASSOCIATES, INC.
LOT 5, QUICKSILVER COURT SUBDIVISION
PROJECT NO. GS06392.002.120
5
3. The building should be provided with roof gutters and downspouts.
Roof downspouts and drains should discharge well beyond the limits
of all backfill. Splash blocks and downspout extensions should be
provided at all discharge points.
Landscaping should be carefully designed to minimize irrigation.
Plants used near foundation walls should be limited to those with low
moisture requirements; irrigated grass should not be located within 5
feet of the foundation. Sprinklers should not discharge within 5 feet
of the foundation and should be directed away from the building.
Impervious plastic membranes should not be used to cover the
ground surface immediately surrounding the building. These mem-
branes tend to trap moisture and prevent normal evaporation from
occurring. Geotextile fabrics can be used to control weed growth and
allow some evaporation to occur.
Geotechnical Risk
The concept of risk is an important aspect of any geotechnical evaluation.
The primary reason for this is that the analytical methods used to develop ge-
otechnical recommendations do not comprise an exact science. The analytical
tools which geotechnical engineers use are generally empirical and must be tem-
pered by engineering judgment and experience. Therefore, the solutions or rec-
ommendations presented in any geotechnical evaluation should not be consid-
ered risk-free and, more importantly, are not a guarantee that the interaction be-
tween the soils and the proposed structure will perform as desired or intended.
What the engineering recommendations presented in the preceding sections do
constitute is our estimate, based on the information generated during this and
previous evaluations and our experience in working with these conditions, of
those measures that are necessary to help the building perform satisfactorily.
The information, conclusions, and recommendations presented herein are
based upon consideration of many factors including, but not limited to, the type of
structure proposed, the geologic setting, and the subsurface conditions encoun-
tered. The conclusions and recommendations contained in this letter are not valid
for use by others. Standards of practice continuously change in the area of ge-
otechnical engineering. The recommendations provided in this letter are appro-
priate for about three years. If the proposed project is not constructed within
three years, we should be contacted to determine if we should update this letter.
Limitations
Our exploratory pits provide a reasonable estimate of subsurface condi-
tions in the area of the proposed building. Actual conditions below the building
G. H. DANIELS & ASSOCIATES, INC.
LOT 5, QUICKSILVER COURT SUBDIVISION
PROJECT NO. GS06392.002-120
6
will vary. Our representative should be called to observe subsurface conditions
exposed in the completed foundation excavation to confirm that conditions are as
anticipated from our geotechnical engineering investigation.
This geotechnical engineering investigation does not address the future
residence proposed on Lot 5. If requested, we can provide geotechnical/geo-
structural engineering recommendations for the residence when plans are further
developed.
This geotechnical engineering investigation was performed in a manner
consistent with that level of care and skill ordinarily exercised by geotechnical en-
gineers currently practicing under similar conditions in the locality of this project.
No warranty, express or implied, is made. We are available to discuss the contents
of this letter. If you have questions or need additional information, please call
Very Truly Yours
CTL 1 THOMPSON, INC. Reviewed By:
Ryan W. DeMars, E.I.T.
Staff Engineer
RWD:JDK:ac
G. H. DANIELS & ASSOCIATES, INC.
LOT 5, QUICKSILVER COURT SUBDIVISION
PROJECT NO. GS06392.002-120
-2
ames D.
ivision Mana er
7
0 100 200
SCALE: 1" = 200'
LEGEND:
TP --1 APPROXIMATE LOCATION OF
a EXPLORATORY PIT
_____ APPROXIMATE PROPERTY
BOUNDARY GARFIELD COUNTY GIS
NOTE: IMAGE FROM GOOGLE EARTH
G. H. Daniels & Associates, Inc.
Lot 5, Quicksilver Court Subdivision
Project No. GS06392.002-120
Aerial
Photograph
FIg. 1
1-
w
w
u_
x
1-
a
w
0
0
TP -1
5
10
SHOP
—15
LEGEND:
0 TOPSOIL, CLAY, SANDY, MOIST, BROWN.
771
• -•/
GRAVEL, CALYEY, COBBLES AND
BOULDERS, LENSES OF GRAVELLY CLAY,
MEDIUM DENSE TO DENSE, SLIGHTLY
MOIST TO MOIST, TAN. (GC, CL)
}
IHI INDICATES BULK FROM EXCAVATED SOILS
G. H. DANIELS & ASSOCIATES, INC.
LOT 5
PROJECT UICKSILVER NO. GS0639COURT 120UBDIVISION
TP -3
;;`
TP -4
NOTES:
2.
3.
4.
RESIDENCE
0
5
10
15
DEPTH - FEET
EXPLORATORY PITS WERE EXCAVATED
WITH A TRACKHOE ON FEBRUARY 26, 2020.
PITS WERE BACKFILLED IMMEDIATELY
AFTER EXPLORATORY EXCAVATION
OPERATIONS WERE COMPLETED.
FREE GOUNDWATER WAS NOT FOUND IN OUR
EXPLORATORY PITS AT THE TIME OF
EXCAVATION.
LOCATIONS OF EXPLORATRY PITS ARE
APPROXIMATE.
EXPLORATORY PITS ARE SUBJECT TO THE
EXPLANATIONS, LIMITATIONS AND
CONCLUSIONS CONTAINED IN THIS
REPORT.
Summary Logs of
Exploratory
Pits
FIG. 2
Sample of GRAVEL, CLAYEY (GC)
From TP - 1 AT 6 - 7 FEET
GRAVEL 75 % SAND
SILT & CLAY 6 % LIQUID LIMIT
PLASTICITY INDEX
19 %
OA
L HYDROMETER ANALYSIS 1 SIEVEANALYSFS 1
25 HR. 7 HR TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS
45 MIN. 15 MIN. 60 MIN. 19 MIN, 4 MIN. 1 MIN. '200 '100 50 '40 '30 16 '10 '8 4 3/8" 3/4" 1%" 3" 5'6. 8'
Inn ..
PERCENT PASSING
o 0 0 0 co 0 0 co 0
• •i 1 !I I.. i!
i o 0 0 '0 0 0 0
PERCENT RETAINED
N �PERCCNT PASSINQC
0 0 0 0 0 0 0
CD 0 0 0 0 0 0 0 0
PERCENT RETAINED
I
I
I
,�
--
—
= I:
—
_
_
au
-1
10
.� _—
�.
10
0
_ _
1 .-
r — -
._ —
..—�.-'��
._
_.
— •
_—
j1
—..—
—. •
—
_`
— -
- __ 100
001 0 002 .005 .009 019. .037 ,074 .149 .297 .590 19 2 0 2,38 4 76 9 52 19.1 36,1 76.2 127 200
0.42 152
DIAMETER OF PARTICLE IN MILLIMETERS
CLAY (PLASTIC) TO SILT (NON -PLASTIC)
SANDS
GRAVEL
r
��—
FINE r MEDIUM f COARS
FINE I COARSE 1 COBBLES
—/
900
--
..
r
.
--
:
_ -
— L
.001
0 002 .005 009 .019 A37 .074 .149.2970 42.590 1 19 2.0 2.38 4.76 9 52 19.1 36.1 76.2 127 200
152
DIAMETER OF PARTICLE IN MILLIMETERS
CLAY (PLASTIC) TO SILT (NON -PLASTIC)
GRAVEL
iSANDS
FINE 1 MEDIUM I COARS
FINE I COARSE J COBBLES
Sample of GRAVEL, CLAYEY (GC)
From TP - 1 AT 6 - 7 FEET
GRAVEL 75 % SAND
SILT & CLAY 6 % LIQUID LIMIT
PLASTICITY INDEX
19 %
OA
Sample of GRAVEL, CLAYEY (GC)
From TP - 4 AT 6-7 FEET
G. H. Daniels & Associates, Inc.
Lot 5, Quicksilver Court Subdivision
PROJECT NO. GS06392.002-120
GRAVEL 54 % SAND
SILT & CLAY 34 % LIQUID LIMIT
PLASTICITY INDEX
Gradation
Test Results
12%
FIG. 3
HYDROMETER ANALYSIS SIEVE ANALYSIS
25 HR 7 HR, TIME READINGS U.S STANDARD SERIES CLEAR SQUARE OPENINGS
45 MIN. 15 MIN. 60 MIN. 19 MIN, 4 MIN 1 MIN. •200 '100 50 '40 '30 '16 '10 •8 .4 3/8" 3/4" 1'/::" 3" 5 6' B'
inn n
N �PERCCNT PASSINQC
0 0 0 0 0 0 0
CD 0 0 0 0 0 0 0 0
PERCENT RETAINED
,�
--
—
= I:
—
_
_
-1
10
.� _—
�.
90
0
_ _
1 .-
r — -
._ —
..—�.-'��
._
_.
— •
_—
j1
—..—
—. •
—
_`
— -
- __ 100
001 0 002 .005 .009 019. .037 ,074 .149 .297 .590 19 2 0 2,38 4 76 9 52 19.1 36,1 76.2 127 200
0.42 152
DIAMETER OF PARTICLE IN MILLIMETERS
CLAY (PLASTIC) TO SILT (NON -PLASTIC)
SANDS
GRAVEL
r
FINE r MEDIUM f COARS
FINE I COARSE 1 COBBLES
—/
Sample of GRAVEL, CLAYEY (GC)
From TP - 4 AT 6-7 FEET
G. H. Daniels & Associates, Inc.
Lot 5, Quicksilver Court Subdivision
PROJECT NO. GS06392.002-120
GRAVEL 54 % SAND
SILT & CLAY 34 % LIQUID LIMIT
PLASTICITY INDEX
Gradation
Test Results
12%
FIG. 3
TABLE 1
SUMMARY OF LABORATORY TESTING
PROJECT NO. GS06392.002-120
EXPLORATORY
PIT
DEPTH
(FEET)
MOISTURE
CONTENT
(%)
DRY
DENSITY
(PCF)
ATTERBERG LIMITS
LIQUID
LIMIT
(%)
PLASTICITY
INDEX
(%)
SOLUBLE
SULFATES
(%)
PERCENT
GRAVEL
(%)
PERCENT
SAND
(%)
PASSING
NO. 200
SIEVE
(%)
DESCRIPTION
TP -1
3-4
38
15
48
TP -1
TP -2
6-7
3-4
0.14
75
19
6
CLAY, GRAVELLY (CL)
GRAVEL, CLAYEY (GC)
TP -3
TP -4
TP -4
6-7
3-4
6-7
37
14
GRAVEL. CLAYEY (GC)
57
0.00
CLAY, GRAVELLY (CL)
GRAVEL, CLAYEY (GO)
_ 54
12
34
GRAVEL. CLAYEY (GC)
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