HomeMy WebLinkAboutSoils Report 10.15.2018H-PKUMAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
October 15, 2018
Ralph Delaney
203 Haystack Road
Glenwood Springs, Colorado 81601
(drdel aney53 @gmail.com)
CEIVE
Project No. 18-7-558
Subject: Subsoil Study for Foundation Design and Percolation Testing, Proposed Cabin,
131 Black Bear Road, West of Lot 17, Mountain Springs Ranch, Garfield County,
Colorado
Dear Ralph:
As requested, H-P/Kumar performed a subsoil study and percolation testing for foundation and
septic disposal designs at the subject site. The study was conducted in general accordance with
our agreement for geotechnical engineering services to you dated August 31, 2018. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report. Evaluation of potential geologic hazard
impacts on the site are beyond the scope of this study.
Proposed Construction: The proposed cabin will be a 11/ story log structure over a walkout
basement located on the site as shown on Figure 1. The basement floor will be slab -on -grade.
Cut depths are expected to range between about 2 to 8 feet. Foundation loadings for this type of
construction are assumed to be relatively Light and typical of the proposed type of construction.
The septic disposal system is proposed to be located downhill to the west of the cabin.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
We also excavated a profile pit for a proposed shop building and performed percolation testing
near an existing hunting cabin located on the property about 500 feet to the west and downhill of
the proposed new cabin.
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Site Conditions: The site of the proposed cabin is located on a southwest -facing slope which
varies from about 10% grade in the building area to 40% grade below the building area.
Vegetation consists of oak brush and scattered pine trees with an understory of grass and weeds.
Basalt cobbles and boulders were observed on the ground surface.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits in the proposed cabin area and two profile pits in the septic disposal area at the
approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The
subsoils encountered, below about lh to 11 feet of topsoil, consist of relatively dense, basalt
cobbles and boulders in a sandy clay matrix down to the Pit 1 depth of 8 feet. Refusal to
backhoe digging was encountered in Pit 2 at 6 feet. Approximately 60% of the basalt rock
material was greater than 3 inches in size. Results of swell -consolidation testing performed on
relatively undisturbed samples of the clay matrix soils, presented on Figure 4, indicate low
compressibility under existing moisture conditions and light loading and a low to moderate
expansion potential when wetted. The samples were moderately compressible under increased
loading after wetting. The laboratory test results are summarized in Table 1. No free water was
observed in the pits at the time of excavation and the soils were slightly moist.
The subsoil conditions encountered in Profile Pit 3, located about 35 feet southeast of the
existing hunting cabin, consisted of about 1 foot of topsoil and 2 feet of stiff, silty sandy clay
overlying 5 feet of medium dense silty sand with scattered cobbles. Results of swell -
consolidation testing performed on a relatively undisturbed sample of the silty sand soils,
presented on Figure 5, indicate low compressibility under existing moisture conditions and light
loading and a minor collapse potential when wetted. The sample was moderately compressible
under increased loading after wetting. No free water was observed in Profile Pit 3 at the time of
excavation.
Foundation Recommendations (Proposed Cabin): Considering the subsoil conditions
encountered in the exploratory pits and the nature of the proposed construction, we recommend
spread footings placed on the undisturbed natural soil designed for an allowable soil bearing
pressure of 3,000 psf with a minimum dead load pressure of 800 psf for support of the proposed
H-P%KUMAR
Project No. 18-7-558
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cabin. The matrix soils tend to expand after wetting and there could be some post -construction
foundation movement. Footings should be a minimum width of 16 inches for continuous walls
and 2 feet for columns. The topsoil and loose disturbed soils encountered at the foundation
bearing level within the excavation should be removed and the footing bearing level extended
down to the undisturbed natural soils. Exterior footings should be provided with adequate cover
above their bearing elevations for frost protection. Placement of footings at least 42 inches
below the exterior grade is typically used in this area which is at about 8,100 feet elevation.
Continuous foundation walls should be reinforced top and bottom to span local anomalies such
as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining
structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit
weight of at least 50 pcf for the on-site soil as backfill.
Foundation Recommendations (Proposed Shop):
The proposed shop near the existing
hunting cabin can be supported on spread footing foundations placed on the silty sand soils
designed for an allowable soil bearing pressure of 2,000 psf.
Floor Slabs (Proposed Cabin): The on-site soils at the proposed cabin site possess an
expansion potential and slab heave could occur if the subgrade soils were to become wet. Slab -
on -grade construction may be used provided precautions are taken to limit potential movement
and the risk of distress to the building is accepted by the owner. A positive way to reduce the
risk of slab movement, which is commonly used in the area, is to construct structurally supported
floors over crawlspace.
To reduce the effects of some differential movement, nonstructural floor slabs should be
separated from all bearing walls and columns with expansion joints which allow unrestrained
vertical movement. Interior non-bearing partitions resting on floor slabs should be provided with
a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be
transmitted to the upper structure. This detail is also important for wallboards, stairways and
door frames. Slip joints which will allow at least 1' inches of vertical movement are
recommended. Floor slab control joints should be used to reduce damage due to shrinkage
cracking. Slab reinforcement and control joints should be established by the designer based on
experience and the intended slab use.
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Project No. 18-7-558
4
We recommend vapor retarders conform to at least the minimum requirements of ASTM E1745
Class C material. Certain floor types are more sensitive to water vapor transmission than others.
For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor
transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum
requirements of ASTM E1745 Class A material. The vapor retarder should be installed in
accordance with the manufacturers' recommendations and ASTM E1643.
Floor Slabs (Proposed Shop): The natural on-site soils at the proposed shop area, exclusive of
topsoil, are suitable to support lightly loaded slab -on -grade construction. To reduce the effects
of some differential movement, floor slabs should be separated from all bearing walls and
columns with expansion joints which allow unrestrained vertical movement. Floor slab control
joints should be used to reduce damage due to shrinkage cracking. The requirements for joint
spacing and slab reinforcement should be established by the designer based on experience and
the intended slab use. A minimum 4 inch layer of free -draining gravel should be placed beneath
slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with less than
50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in mountainous areas that local perched groundwater can develop during
times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also
create a perched condition. We recommend below -grade construction, such as retaining walls,
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
We assume that the proposed shop building will have a slab -at -grade
floor and should not require an underdrain.
The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above
the invert level with free -draining granular material. The drain should be placed at each level of
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Project No. 18-7-558
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excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to
a suitable gravity outlet. Free -draining granular material used in the underdrain system should
contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least 11/2 feet deep. An
impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough
shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the proposed cabin has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction. Drying could increase the expansion potential of the soils.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maximum standard Proctor density in landscape areas.
Free -draining wall backfill should be capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltration.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3
inches in the first 10 feet in pavement and walkway areas. A swale may be
needed uphill to direct surface runoff around the cabin.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least 10
feet from the building. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the building caused by irrigation.
Percolation Testing: Profile Pits 1 and 2 were dug near the proposed cabin site as shown on
Figure 1. The soils encountered in the pits, below about 1/2 foot of topsoil, consisted of extremely
gravelly loamy sand, see gradation shown on Figure 6.
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Project No. 18-7-558
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Profile Pit 3 and two percolation holes were dug near the proposed shop location. Percolation
tests were conducted on September 11, 2018 in the proposed shop area to evaluate the feasibility
of an infiltration septic disposal system at the site. The test holes (nominal 12 inch diameter by
12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with water.
The soils exposed in the percolation holes are similar to those exposed in Profile Pit 3 and
consist of slightly clayey, silty sand, see gradation shown on Figure 7. The percolation test
results are presented in Table 2.
Based on the subsurface conditions encountered and the percolation test results, the tested areas
should be suitable for a conventional infiltration septic disposal system. A civil engineer should
design the infiltration septic disposal systems.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. We make no warranty either
expressed or implied. The conclusions and recommendations submitted in this report are based
upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1,
the proposed type of construction and our experience in the area. Our services do not include
determining the presence, prevention or possibility of mold or other biological contaminants
(MOBC) developing in the future. If the client is concerned about MOBC, then a professional in
this special field of practice should be consulted. Our findings include interpolation and
extrapolation of the subsurface conditions identified at the exploratory pits and variations in the
subsurface conditions may not become evident until excavation is performed. If conditions
encountered during construction appear different from those described in this report, we should
be notified at once so re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on-site observation
H-P-45KUMAR
Project No. 18-7-558
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of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
H -P KU MARS
Daniel E. Hardin, P.E.
Reviewed by:
Steven L. Pawlak, P.E.
DEH/kac
attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 — Legend and Notes
Figures 4 and 5 - Swell -Consolidation Test Results
Figures 6 and 7 — USDA Gradation Test Results
Table 1 — Summary of Laboratory Test Results
Table 2 — Percolation Test Results
H -P KUMAR
Project No. 18-7-558
PROFILE PIT 1
■
3
• PIT 1
O
Pine
10' Radius Drip Line
_— Found Rebar
\PROFILE PIT 2
0
0
11
PIT 2
10 0 10 20
APPROXIMATE SCALE -FEET
18-7-558
H-PvKUMAR
7
.7
NOTE: PROFILE PIT 3 AND PERCOLATION
TESTS ARE LOCATED NEAR EXISTING
CABIN ABOUT 500 FEET DOWNHILL AND
WEST OF THIS PROPOSED CABIN.
LOCATION OF EXPLORATORY PITS
Fig. 1
— 0
- 5
10
-- 5
10
PROFILE PIT 1
EL. 8104'
PIT 1
EL. 8110'
-1 GRAVEL=78
1
-I SAND=5
SILT=9
CLAY=8
PROFILE PIT 2
EL. 8105'
PIT 2
EL. 8105'
WC=16.6
DD=98
PROFILE PIT 3
tI
Pl; WC=15.6
0
DD=91
Al
0
5
10
r -
w
La
1.1-
i I
1.---
0-
La aw
0
0
GRAVEL=1
SAND=55
SI LT=37
CLAY=7
5
10
1---
w
W
w
I
1-
a_
w
0
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H-PtiKUMAR
LOGS OF EXPLORATORY PITS
Fig. 2
LEGEND
MTOPSOIL, ORGANIC SANDY SILTY CLAY WITH BASALT COBBLES, FIRM, SLIGHTLY MOIST, DARK
BROWN.
BASALT COBBLES AND BOULDERS (GC): IN SANDY CLAY MATRIX, DENSE, SLIGHTLY MOIST,
:. 7 DARK BROWN.
CLAY (CL): SILTY, SANDY WITH SCATTERED COBBLES, STIFF, MOIST, BROWN, SLIGHTLY
ORGANIC. PROFILE PIT 3 ONLY.
SAND (SM): SILTY, WITH COBBLES, SLIGHTLY CLAYEY, MEDIUM DENSE, MOIST, BROWN.
PROFILE PIT 3 ONLY.
N HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE.
t PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 11, 2018.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DIGGING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
GRAVEL= PERCENT RETAINED ON No. 10 SIEVE
SAND= PERCENT PASSING No. 10 SIEVE AND RETAINED ON NO. 325 SIEVE
SILT= PERCENT PASSING No. 325 SIEVE TO PARTICLE SIZE .002mm
CLAY= PERCENT SMALLER THAN PARTICLE SIZE .002mm
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H-PtiKUMAR
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
2
1
0
—1
— 2
— 3
2
J
J
w
1
CONSOLIDATION
SAMPLE OF: Sandy Clay Matrix
FROM: Pit 1 0 5'
WC = 17.8 %, DD = 95 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
0
— 1
— 2
— 3
1.0 APPLIED PRESSURE — KSF
hozete,t recons a:WY 0.111r W the
samples lellsd Ike intim; report
shall np= be fspadyted. ,seep! In
r.{heal Me•ei11M app.ara, of
Kumar and Anaoatec. MC Seen
CoeiaQalian (M.nry
accordance nth AL7st n .45ao
10 100
SAMPLE OF: Sandy Clay Matrix
FROM: Pit 2 ® 4'
WC = 16.6 %, DD = 98 pcf
1.0 APPLIED PRESSURE — KSF 10
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
100
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SWELL -CONSOLIDATION TEST RESULTS
Fig. 4
CONSOLIDATION - SWELL
SAMPLE OF: Clayey Silty Sand
FROM: Profile Pit 3 ® 5'
WC = 15.6 %, DD = 91 pcf
Tim 1111 nlwlte apply Mb N 11,1
eomNee tested- Th. 1e14wq lepa1
.1,111 net W IIp+SWlld, l.eept .n
t & nthw{ [w .e ltln opprora of
xump ped NlePelm etc, 5.1
CansoWC:En letting pedlamee Ln
ecceldeeu wth 7611l 0-4114.
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
18-7-558
1.0 APPLIED PRESSURE - KSF 10
H-P--14KUMVIAR
SWELL -CONSOLIDATION TEST RESULTS
100
Fig. 5
PERCENT RETAINED
0
10
20
30
40
50
60
70
80
90
100
.001
HYDROMETER ANALYSIS
TIME READINGS
24 HF. 7 HA 1 MIN.
SIEVE ANALYSIS
U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS
n.... .a.,...
w." IWPM
..err.
77-0C.J xiru rev WOO 4'1 IV1L3 14 3B' 314' 1 1/2° 3' 5' 6' 0
/
1
/.."......."....°.
.002
.005 .009
.019
.045
.106
.025
.500
1,00
2.00 4.75 9.5 19.0 37.5 76,2 152 203
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY I SILT
18-7-558
GRAVEL 78 %
®EIMI
SAND
MEDIUM
SAND 5 %
GRAVEL
SMALL I MEDIUM 1 _LARGE f COP'
SILT 9 % CLAY 8 %
USDA SOIL TYPE: Extremely Gravelly Loamy Sand FROM: Profile Pit 1 @ 2-31
H -P1,KU MAR
r -
USDA GRADATION TEST RESULTS
100
90
80
70
60
50
40
30
20
10
0
Fig. 6
PERCENT PASSING
PERCENT RETAINED
HYDROMETER ANALYSIS
24 HR. 7 H
04514. 15m.
10
20
40
70
TIME READINGS
9MII. MIN. 4A4N.
1002
#325
SIEVE ANALYSIS
U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
40 460 035
8 #10 #4 318 314 1112' 3' 6'8'
100
90
80
100
601
70
50
40
20
-- 10
712 .005 .009 .019 .046 .106 .025 .500 1,00 2.00 4.75 99 19.0 3/.b 70.2
DIAMETER OF PARTICLES IN MILLIMETERS
0
152 203
CLAY SILT
SAW
MEDIUM COARSE
vMWL
SMALL ® LABGE
COBBLES
GRAVEL 1 %
SAND 55 % SILT 37 %
USDA SOIL TYPE: Very Sandy Loam
CLAY 7 %
FROM: Profile Pit 3 @ 44.5'
PERCENT PASSING
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H-PvKUMAR
USDA GRADATION TEST RESULTS
Fig. 7
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL
' MOISTURE
PIT DEPTH � CONTENT
(ft)
(%)
3
NATURAL I GRADATION
DRY
DENSITY GRAVEL SAND
(pcf) I
(%)
(°i°)
PERCENT
PASSING
NO. 200 I GRAVEL
SIEVE
Project No.18-7-558
USDA SOIL TEXTURE
1 5 17.8 95
SAND SILT
(%) (%)
(%)
CLAY
(%)
SOIL TYPE
Sandy Clay Matrix
2 4
16.6
98
Profile
Pit 1
2-3
78
5
9
Sandy Clay Matrix
8
Profile
Pit 3
4-4'
Extremely Gravelly
Loamy Sand
1
55
37
7
Very Sandy Loam
5
15.6
91
Clayey Silty Sand
H-PKUMAP
TABLE 2
PERCOLATION TEST RESULTS
HOLE NO. HOLE LENGTH
DEPTH INTERN
(INCHES) (MIN)
PROJECT NO. 18-7-558
OF
aL
- - -
WATER
DEPTH AT
START OF
INTERVAL
(INCHES)
-
WATER
DEPTH AT
END OF
INTERVAL
(INCHES)
DROP IN
WATER
LEVEL
(INCHES)
AVERAGE
PERCOLATION
RATE
(MIN./INCH)
91/4
9
'/4
40
9
8g/
%
8%
81/4
3/9
81/4
8
1/4
8
73/4
1/4
_ 73/4
71/2
1/4
22
71/4
63/4
1/2
6%
61/4
1/2
61/4
53/4
1/2
5%
5'/e
%
5%
434
1/2
Note: Percolation test holes were hand dug in the bottom of backhoe pits and
percolation tests were conducted on September 11, 2018. The average
percolation rates were based on the last three readings of each test.