HomeMy WebLinkAboutSubsoil Study1f+AKumar ni Associates, Inc.®
Geotechnical and Materials Engineers 5020 County Road 154
and Environmental Scientists Glenwood Springs, CO 81601
phone: (970) 945-7988
t
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
August 21, 2019
Revised August 29, 2019
Paul R. Cody
71 Windward Passage
North Chatham, MA 02650
(prcodyi(&aol.com)
Y( 4
Project No.18-7-625
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 32, Mountain
Springs Ranch, North Marsh Lane, Garfield County, Colorado
Gentlemen:
As requested, Kumar & Associates, Inc. performed a subsoil study and percolation test for
foundation and septic disposal designs at the subject site. The study was conducted in
accordance with our agreement for geotechnical engineering services to Paul R. Cody dated July
10, 2019. The data obtained and our recommendations based on the proposed construction and
subsurface conditions encountered are presented in this report.
Proposed Construction: The proposed residence will be a two-story wood frame structure
above a basement with attached garage located on the site as shown on Figure 1. Ground floor
will be slab -on -grade. Cut depths are expected to range between about 3 to 12 feet. Foundation
loadings for this type of construction are assumed to be relatively light and typical of the
proposed type of construction.
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.
Site Conditions: The subject site was vacant with a rough -cut driveway at the time of our field
exploration. The site is located on a hillside at an elevation of about 8090 feet, sloping down to
the east at moderate grades between 20 to 30%. Vegetation consists of oak brush, other brush
and grass.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 1 to 1 Meet of topsoil, consist of
relatively dense, silty, clayey gravel and sand with cobbles. Results of gradation analyses
performed on a sample of clayey gravel and sand (minus 5 -inch fraction) obtained from the site
are presented on Figure 3. No free water was observed in the pits at the time of excavation and
the soils were slightly moist to moist.
-2 -
Foundation Recommendations: 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 2,500
psf for support of the proposed residence. The fine-grained portion of the soils typically tend to
compress after wetting and there could be some post -construction foundation settlement.
Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns.
Loose and 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.
We should observe the completed excavation for foundation bearing conditions. Exterior
footings should be provided with adequate cover above their bearing elevations for frost
protection. Placement of footings at least 36 inches below the exterior grade is typically used in
this area. Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 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 45 pcf for the on-site granular soil as backfill.
Floor Slabs: The natural on-site granular soils, exclusive of topsoil, are suitable to support
lightly loaded slab -on -grade construction. Clay soils, if encountered, at slab subgrade level
should be evaluated for bearing properties and the need to remove them. 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
basement level 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 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.
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
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 1 %2 feet deep.
Kumar & Associates, Inc. Project No. 18.7-625
-3 -
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
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 covered with filter fabric and 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 residence.
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 5
feet from the building.
Percolation Testing: Percolation tests were conducted on August 2, 2019 to evaluate the
feasibility of an infiltration septic disposal system at the site. The percolation tests were not
performed in accordance with State Regulation #43 specifications. Two profile pits and three
percolation holes were dug at the locations shown on Figure 1. The logs of the profile pits are
shown on Figure 2. The test holes (nominal 12 -inch diameter by 12 -inch deep) were hand dug at
the bottom of shallow backhoe pits. The soils exposed in the percolation holes are similar to
those exposed in the profile pits and consist of loam and very gravelly sandy loam. Results of
USDA gradation tests are shown on Figures 4 and 5. The percolation test results are presented in
Table 2. A civil engineer should design the septic disposal system.
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
express 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
and to the depths shown on Figure 2, 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.
Kumar & Associates, Inc. 0�' Project No. 18-7-625
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
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,
Kumar & Associates, Inc.
Robert L. Duran, E. I.
Reviewed by:
Steven L. Paw
RLD/lkac
Attachments
Pits
Figure 2 — Logs of Exploratory Pits
Figures 3 through 5 — Gradation Test Results
Table I — Summary of Laboratory Test Results
Table 2 — Percolation Test Results
cc: Eric Rewinkel — (ericsopris(cgmail.com)
John Cody — (dirtfoxl gaol.com)
Kumar & Associates, Inc. 0 Project No. 18-7-625
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APPROXIMATE SCALE—FEET
dal 18-7-625 I Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1 PIT 2 PROFILE PIT 1 PROFILE PIT 2
EL. 8086' EL. 8080.5'
0 0
o:
1 GRAVEL=57 -
W - o " '•SAND=30 1 GRAVEL=9 w
5 � 0'.0
.o . SILT= 10 1 SAND=18
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_ ;':0 1 +4=49 CLAY=3 SILT=22 5
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- o.• o J -200=12 ::o CLAY=51 ~
0 0 'o w
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10 10 1
LEGEND
19 TOPSOIL, ORGANIC LOAM, FIRM, SLIGHTLY MOIST, DARK BROWN.
o GRAVEL AND SAND (GM -GC): COBBLES, SCATTERED SMALL BOULDERS, SILTY, CLAYEY,
DENSE, SLIGHTLY MOIST TO MOIST, MIXED TAN.
CLAY, STRONG BLOCKY, WITH SAND AND GRAVEL, VERY STIFF, MOIST, BROWN.
LOAM, MASSIVE, STIFF, SLIGHTLY MOIST, BROWN.
VERY GRAVELLY SANDY LOAM, DENSE, SLIGHTLY MOIST, MIXED TAN.
o• .o
DISTURBED BULK SAMPLE.
i
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 2, 2019.
2. THE EXPLORATORY PIT LOCATIONS WERE DESIGNATED IN THE FIELD BY ERIC REWINKEL.
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.
9 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
s APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
e
6. GROUND WATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
+4 = PERCENTAGE RETAINED
ON NO.
4 SIEVE (ASTM
D 422);
s
-200= PERCENTAGE PASSING NO. 200
SIEVE (ASTM
D 1140);
GRAVEL = Percent retained on No. 10
Sieve
SAND = Percent passing No.
10 sieve
and retained
on No. 325 sieve
'm
SILT = Percent passing No.
325 sieve
to particle
size .002mm
m
CLAY = Percent smaller than
particle
size .002mm
18-7-625
Kumar & Associates
LOGS
OF EXPLORATORY PITSFig.
2
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as
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40
30
20
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_ 100
i B 4.75 8.3 19 38.1 76.2 127 00
,425 2.0
OF PARTICLES IN MILLIMETERS152
SAND GRAVEL _
FINE MEDIUM COARSE FINE COARSE l UCtlI tJ
GRAVEL 49 % SAND 39 % SILT AND CLAY 12 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Clayey Sandy Gravel FROM: Pit 1 ® 5'-6'
These test results apply only to the
samples which were tested. The
v testing report *hall not be reproduced,
o« except in full, without the written
approval of Kumar & Associates, Inc.
i Sieve analysis testing is performed In
accordance wkh ASTM D6913, ASTM D7928,
ASTM C136 an ASTM D1140.
a�
tp 18-7-625 Kumar & Associates GRADATION TEST RESULTS Fig. 3
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FINE MEDIUM COARSE FINE COARSE l UCtlI tJ
GRAVEL 49 % SAND 39 % SILT AND CLAY 12 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Clayey Sandy Gravel FROM: Pit 1 ® 5'-6'
These test results apply only to the
samples which were tested. The
v testing report *hall not be reproduced,
o« except in full, without the written
approval of Kumar & Associates, Inc.
i Sieve analysis testing is performed In
accordance wkh ASTM D6913, ASTM D7928,
ASTM C136 an ASTM D1140.
a�
tp 18-7-625 Kumar & Associates GRADATION TEST RESULTS Fig. 3
HYDROMETER ANALYSIS
SIEVE ANALYSIS
24
045
10
TIME READINGS U.S. STANDARD SERIES
HR. 1 HR 1 MIN
N. 15 MIN. — 60MM1 19MIN. 4MIN. #325 #140 #60 #35 #18 #10 #4
CLEAR SQUARE OPENINGS
3/8' 314' 1 112' 3' FT
8' 100
20
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30
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100
.001 .002 .005 .009 .019 .045 106 .025 .500 1.00 2.00 4.75
DIAMETER OF PARTICLES IN MILLIMETERS
9.5 19.0 37.5 762 152
203 0
CLAY
SILT SAND GRAVEL
V. FlNE FINE I MEDNM 1COAMEMODARM SMALL I MEDIUM I i APM I COBBLES
GRAVEL 57 % SAND 30 % SILT 10 % CLAY 3 %
USDA SOIL TYPE: Very Gravelly Sandy Loam FROM: Profile Pit 1 @ 3'-4'
18-7-625
Kumar & Associates
USDA GRADATION
TEST RESULTS
Fig.
4
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a'3
HYDROMETER ANALYSIS
I
SIEVE ANALYSIS
24
045MIIt
10
TIME READINGS I U.S. STANDARD SERIES CLEAR SQUARE OPENINGS
HR. 7 HR 1 hK
15 MN. 6M 19MR 4W #325 #140 #60- #35 #18 #10 #4 318' 3/4' 11/2' 3' 56'
8' 100
90
80
30
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.001 .002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152
DIAMETER OF PARTICLES IN MILLIMETERS
203 0
CLAY SILT
V. FINE I FINE
SAND GRAVEL
I MEDIUMCOARSE V.COAAS SMALL I MEDIUM LARGE COBBLES
GRAVEL 9 % SAND
USDA SOIL TYPE: Clay
18 % SILT 22 % CLAY 51 %
FROM: Profile Pit 2 @ 3.5'-4.5'
18-7-625
Kumar & Associates
USDA GRADATION TEST RESULTS
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If+AKumar ni Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
:1
TABLE 2
PERCOLATION TEST RESULTS
PROJECT NO. 18-7-625
HOLE
NO.
HOLE DEPTH
(INCHES)
LENGTH OF
INTERVAL
(MIN)
DEPTH OF
WATER IN
HOLE AT
START
(INCHES)
DEPTH OF
WATER IN
HOLE AT
FINISH
(INCHES)
DROP IN
WATER
LEVEL
(INCHES)
AVERAGE
PERCOLATION
RATE
(MINANCH)
1
30
15
8
77/.
%
80
7'/e
7%
%
7%
71/2
%
7'/2
7%
%
7%
7%
%
7%
7
%
7
63/4
1/4
2
27
15
Add Water
61/2
5%
%
30
5%
5'/4
3/8
5%
43/4
1/2
43/4
4%
3/8
4%
4
%
7
6%
3/4
6'/4
53/4
1/2
3
26
15
Add Water
4%
4
44
4
3%
3%
3
3
2 %
y4
4%
4%
%
4%
3%
3%2
E1Y43%
Note: Percolation test holes were hand dug and soaked on August 2, 2019. Percolation tests were
conducted on August 2, 2019. The average percolation rate is based on the last 4 readings of each
test.