HomeMy WebLinkAboutSoils Report 12.08.2016H-P�KUMAR
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
December 8, 2016
Smith Brugger Construction
Attn: John Brugger
47 Elk Range Drive
Snowmass, Colorado 81654
(johnb@sopris.net)
Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado
Project No.16-7-585
Subject: Subsoil Study for Foundation Design, Proposed Residence, 420 County Road
122, Garfield County, Colorado
Dear Mr. Brugger:
As requested, H-P/Kumar performed a subsoil study for design of foundations at the subject site.
The study was conducted in accordance with our agreement for geotechnical engineering
services to Smith Brugger Construction dated November 10, 2016. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report. We previously observed an excavation for a residence on the ranch and
reported our findings April 6, 1999, Job No. 199 281.
Proposed Construction: The proposed residence will be one story modular construction above
a crawlspace and located on the site as shown on Figure 1. Cut depths are expected to range
between about 3 to 4 feet. Foundation loadings for this type of construction are assumed to be
relatively Tight 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.
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Site Conditions: The property has historically been used as ranch land. The building area is
located in an irrigated pasture and vegetated with grass and weeds. The ground surface is
relatively flat with a slight slope down to the south.
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'/2 feet of topsoil, consist of 1 to
2V2 feet of sandy clayey gravel with basalt cobbles overlying sandy silty clay down to the bottom
of the pits at 6 feet. Results of swell -consolidation testing performed on relatively undisturbed
samples of sandy silty clay, presented on Figure 3, indicate low to moderate compressibility
under wetting and loading. Results of a gradation analysis performed on a sample of clayey
sandy gravel (minus 3 inch fraction) obtained from the site are presented on Figure 4. No free
water was observed in the pits at the time of excavation and the soils were slightly moist to
moist.
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 1,500
psf for support of the proposed residence. The soils 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. 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 (if
any) 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 (if any)
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.
H -P = KUMAR
Project No. 16-7-585
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Floor Slabs: The natural on-site soils, 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 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 and
crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. Shallow crawlspaces, Tess than 4 feet below grade, should not need a perimeter drain
system.
If installed, 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 1V2 feet deep.
H -P KUMAR
Project No. 16-7-585
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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 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 recqmmend a minimum
slope of 6 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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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.
H -P ; KUMAR
Project No. 16-7-585
-5 -
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,
H -P* - KU AR
L uis Eller
Reviewed by:
Daniel E. Hardin, P.E.
DEH/kac
attachments Figure 1 — Location of Exploratory Pits
Figure 2 -- Logs of Exploratory Pits
Figure 3 — SwelI-Consolidation Test Results
Figure 4 — Gradation Test Results
Table 1 -- Summary of Laboratory Test Results
cc: Pattillo & Associates — Bob Pattillo (bob!
25 0 25 50
APPROXIMATE SCALE -FEET
16-7-585
H-Ptil{LIMAR
LOCATION OF EXPLORATORY PITS
Fig. 1
r
1
1
2
1
I
— 0
5
PIT 1
PIT 2
WC=10.8
DD=97
WC=17.6
DD=98
-200=92
0—�
10 10—
LEGEND
P
[-I
TOPSOIL; ORGANIC SANDY SILT AND CLAY WITH BASALT COBBLES, FIRM, MOIST, DARK BROWN.
BASALT GRAVEL AND COBBLES (GC); CLAYEY, SANDY, MEDIUM DENSE, SLIGHTLY MOIST TO
MOIST, BROWN.
CLAY (CL); SANDY, SILTY, STIFF, MOIST, BROWN.
HAND DRIVEN LINER SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINIEXCAVATOR ON NOVEMBER 11, 2016.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
BUILDING CORNERS STAKED IN THE FIELD.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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 EXCAVATING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (X) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM 0 1140).
16-7-585
H -P KUMAR
LOGS OF EXPLORATORY PITS
Fig. 2
J
J
W
5 0
CONSOUDATION -
CONSOUDATION - SWELL
— 1
—2
—3
0
- 1
— 2
— 3
— 4
— 5
6
}
SAMPLE OF: Sandy Silty Clay
FROM: Pit 1 0 5.5'
WC = 18.2 %, DD = 99 pcf
NO MOVEMENT UPON
WETTING
1.0 APPLIED PRESSURE — KSF
ID
100
SAMPLE OF: Sandy Silty Cloy
FROM: Pit 2 0 3'
WC = 10.8 %, DD = 97 pcf
mo' :'"• ./, uw., 'PNr.e n.tw«...k .
.A..r d
New Ors•KWN. K, i.A!
wwa
'aK. 7
1M ASUl 6 1346 n
NO MOVEMENT UPON
WETTING
16-7-585
5.0 APPLIED PRESSURE — KSF ID
H-P---LIKUMAR
SWELL -CONSOLIDATION TEST RESULTS
100
Fig. 3
100
00
BO
70
a0
Se
e0
10
0
HYGROMETER ANALYSIS
S EYE ANALY515
WA 0i.40.001
id Mil 1 Mee
41 M14 13,y. )0666 IT •471
I0
LI 3 114M*Ano SCRICE
l'00 f50 ■A0 610 01 !tail (4
S1:'
CCE4A 000M[ ORNIIKI
3!4' 1 {,/Y 1Y"
F
4 1
1 l !
I.017r
I I
I2 11
101
11i.1 l
1743C,yl_733*
112
Ll I I
11 }.1 1 j1.10
O! .007
.Goa
.Oaf
.a11 /
DIAMETER
,1 y0 -.100.idi 2 3 +
.4as7
OF PARTICLES IN MILLIMETERS
1 1
CLAY TO SILT
SAND
GRAVEL
FINE MEDIUM [COARSE FINE 1 COARSE
COBBLES
16-7-585
GRAVEL 81 X
LIQUID LIMIT
SAND 4 X
PLASTICITY INDEX
SILT AND CLAY 10 X
SAMPLE 0F: SY9hIly Clayey Slightly Sandy Gray.I FROM: PIF 1 O 3'-4'
H-P1KUMAR
10
20
30
43
30
•0
70
BO
f0
100
These 11,1 luwb 00417 0100 ,o 146
✓ umples width were Sued. The
Ie1nnp roper, she. Rol be reproduced.
e rcfpl 111 1.11, without the wr1U1on
opproro of Kumor A Auoaloleec, Ina.
Wets on/dyelf HON; Ie performed In
occardonc..fl! *STU 0422, *5344 C7313
and/or ASD4 Ot440
GRADATION TEST RESULTS
Fig. 4
HPEKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 16-7-585
SAMPLE LOCATION
NATURAL
NATURAL
DRY
DENSITY
(pc$
GRADATION
ATTERBERG LIMITS
SOIL OR
BEDROCK TYPE
PIT
DEPTH
(ft)
MOISTURE
CONTENT
(°)
GRAVEL
SAND
(1)
PERCENT
PASSING
NO. 200
SIEVE
LIQUID
LIMIT
(")
PLASTIC
INDEX
(°)
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
1
3-4
8I
9
10
Slightly clayey, slightly
sandy gravel
51/2
18.2
99
Sandy silty clay
2
3
10.8
97
Sandy silty clay
5'/
17.6
98
92
Slightly sandy silty clay