HomeMy WebLinkAboutSoils Report 11.02.2016H-P�KUMAR
Geotechnical Engineering t Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkgtenwood®kumarusa.com
November 2, 2016
Ismael Argueta
129 Sunflower Loop
Carbondale, Colorado 81623
Office Locations: Parker, Glenwood Springs, and Siiverthome, Colorado
Project No.16-7-487
Subject: Subsoil Study for Foundation Design, Proposed Shop Building, Lot 54, Cerise
Ranch, 129 Sunflower Loop, Garfield County, Colorado
Gentlemen:
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 you dated September 27, 2016. The data obtained and our recommendations based
on the proposed construction and subsurface conditions encountered are presented in this report.
Proposed Construction: The proposed shop will be a single -story building about 30'x40' in
plan size cut into the hillside and 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 14 feet. Foundation
loadings for this type of construction are assumed to be relatively light and typical of the
proposed type of construction. The uphill foundation will act to retain the hillside and be
eccentrically loaded from lateral earth pressure.
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 shop site is located northeast of the residence as shown on Figure 1. The
ground surface is moderately sloping down to the southwest with about 14 feet of elevation
difference across the shop site. The slope to the southwest at the residence is gentle and the
hillside to the north is steep. Vegetation consists of grass, weeds and scattered brush and trees in
the shop site with pinon and juniper trees on the steep hillside. Basalt cobbles and boulders were
observed on the ground surface.
Subsurface Conditions: The subsurface conditions at the shop site were evaluated by drilling
one exploratory boring at the approximate location shown on Figure 1. The log of the boring is
presented on Figure 2. The subsoils encountered, below about 21/2 feet of topsoil, consist of
sandy silt and clay to clayey sand with gravel down to about 15 feet where medium dense, silty
-2 -
clayey sand and gravel with basalt cobbles was encountered to the boring depth of 21 feet.
Results of swell -consolidation testing performed on relatively undisturbed samples of the silt and
clay soils, presented on Figures 3 and 4, indicate low compressibility under existing moisture
conditions and light loading and a low collapse potential (settlement under constant load) when
wetted and high compressibility under additional loading. Results of testing performed on a
sample of clayey sand with gravel at 15 feet, shown on Figure 5, showed relatively low
compressibility under conditions of loading and wetting. The laboratory test results are
summarized in Table 1. No free water was encountered in the boring at the time of drilling and
the soils were slightly moist to moist.
Foundation Recommendations: The soils encountered to a depth of about 15 feet have low
bearing capacity and are compressible especially when wetted under Load. Shallow spread
footings placed on the natural soils can be used for the building support with a risk of settlement
and building distress. The settlement potential can be reduced by extending the bearing level
down to the gravel and cobble soils or replacement of the compressible soils compacted to at
least 98% of standard Proctor density at near optimum moisture content.
Provided the risk of building settlement and distress is accepted by the owner, spread footings
placed on the undisturbed natural soil and designed for an allowable uniform bearing pressure of
1,500 psf can be used for support of the proposed shop building. Eccentrically loaded (retaining
wall) footings can be designed for a maximum bearing pressure of 2,000 psf. The soils tend to
compress after wetting and there could be post -construction foundation settlement on the order
of 1 to 2 inches. Footings should be a minimum width of 24 inches for continuous walls and 3
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. The exposed soils should then be moistened and compacted. We
should observe the foundation excavation for bearing conditions prior to placing footing forms.
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 15 feet. Foundation walls
acting as retaining structures should be designed to resist a lateral earth pressure as discussed
below in the "Foundation and Retaining Wall" section of this report.
Foundation and Retaining Walls: Foundation walls and retaining structures which are
laterally supported and can be expected to undergo only a slight amount of deflection should be
designed for a lateral earth pressure computed based on an equivalent fluid unit weight of at least
50 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are
separate from the building and can be expected to deflect sufficiently to mobilize the full active
earth pressure condition should be designed for a lateral earth pressure computed based on an
equivalent fluid unit weight of at least 40 pcf for backfill consisting of the on-site soils. Backfill
should not contain organics or rocks larger than about 6 inches.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
H -P t KUMAR
Project No. 16-7-487
-3 -
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at near optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least 95% of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded
slab -on -grade construction with a risk of settlement if the bearing soils are wetted. 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
below grade 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 the area 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 below grade
building 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
H -P KUMAR
Project No. 16.7-487
-4 -
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 feet deep. An
impervious membrane such as 30 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 after the building 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 at least 2 feet of the on-site,
finer graded soils to reduce surface water infiltration.
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 will be
needed uphill to direct surface runoff around the shop building.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should not be used at the
site. Xeriscape may be used to limit potential wetting of soils below the
foundation caused by irrigation.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at the time of this study. 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 boring drilled at the location 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 boring
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
H -P z KUMAR
Project No. 16.7-487
-5 -
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`- KUMAR
Steven L. Pawlak, P.E.
Reviewed by:
Daniel E. Hardin, P.E.
SLP/ksw
Attachments: Figure 1— Location of Exploratory Boring
Figure 2 — Log of Exploratory Boring
Figures 3-5 -- Swell -Consolidation Test Results
Table 1— Summary of Laboratory Test Results
cc: Shaver Construction — George Shaver (georgeshaver1836@gmai1.c om)
Pattillo Associates Engineers — Bob Pattillo (bob@pacneineers.com)
H -P t KUMAR
Project No. 16.7-487
1
's
,S
ax
If
LOT 54
3.45 AC +/-
01511114 NOUSE
r
if tlRROPi.l.tLeerr
i
30 0 30 60
APPROXIMATE SCALE—FEET
BORING 1 t
CAMAE7[ ante vss
•
U3
PROPOSED
Lot 53
ere
1 t °ae5far 4
+w.sarur raxt
16-7-487
H-PKUMAR
LOCATION OF EXPLORATORY BORING
Fig. 1
w
0
a
BORING 1
EL 1002'
1005
— 1000
— 995
— 990 ----
— 985
----- 980
5/12
•
15/12
/l WC=18.0
• 00=99
//
%
i
/ 22/12
WC=6.6
00=100
r.- APPROXIMATE PttOR"
s
e1
t r 17/12
WC=11.0
00=116
Y.
v
t•
q 29/12
WC=7.3
00=126
-200=48
LEGEND
7
•
—7
1
i
TOPSOIL; ORGANIC SANDY SILT AND CLAY, LOOSE/SOFT,
SLIGHTLY MOIST, DARK BROWN.
SILT AND CLAY (ML -CL); SANDY, SCATTERED GRAVEL,
MEDIUM STIFF TO STIFF, SLIGHTLY MOIST, DARK BROWN.
SAND AND CLAY (SC -CL); SILTY, GRAVELLY, MEDIUM
DENSE/STIFF, SLIGHTLY MOIST, DARK BROWN.
SAND AHD GRAVEL (SC -GC); SILTY, CLAYEY COBBLES, MEDIUM
DENSE, SLIGHTLY MOIST. GRAY -BROWN, BASALT ROCK
FRAGMENTS.
il DRIVE SAMPLE, 2 -INCH 1.0. CAUFORNIA LINER SAMPLE.
5/12 DRIVE SAMPLE BLOW COUNT. INOICATES THAT 5 BLOWS OF
A 140 -POUND HAMMER FALLING 30 INCHES WERE REQUIRED
TO DRIVE THE SAMPLER 12 INCHES.
NOTES
I. THE EXPLORATORY BORING WAS DRILLED ON SEPTEMBER 29,
2016 WITH A 4 -INCH DIAMETER CONTINUOUS FLIGHT POWER
AUGER.
2. THE EXPLORATORY BORING WAS LOCATED BASED ON THE
APPROXIMATE BUILDING CORNERS STAKED BY OTHERS.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED
BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN
PROVIDED.
4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD
BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY
THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL
6. GROUNDWATER WAS NOT ENCOUNTERED 1N THE BORING
AT THE TIME OF DRIWNG.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (X) (ASTII 0 2216);
DO = DRY DENSITY (pef) (ASTM 0 2216);
-200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140);
16-7-487
H-P� KUMAR
LOG OF EXPLORATORY BORING
Fig. 2
Si'
1
0
W -1
g
1 -2
z
0
a
SI —3
a
vs
z
a
0 —,1
—5
SAMPLE OF: Sandy SW and Clay with Gravel
FROM: Baring 1 0 5'
WC = 18.0 X. OD = 99 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
.M�ew w1s arta qy r w
uR .emr1 IN "NW MA▪ NI id
l • wI M4 Yr. i.d
▪ w
CwrMlwn Iwo wA 04t
.w.rn...iw p1Y a-wa
.1
1.0 APPLJtD PRESSURE — KSF
10 100
16-7-487
H-P:tKUMAR
SWELL—CONSOLIDATION TEST RESULT
Fig. 3
1
0
—1
x .. —2
ti
— 3
— 4
— 5
— 6
— 7
CONSOLIDATION - SWELL
SAMPLE OF: Silly Clay and Sand with Gravel
FROM: Baring 1 0 10'
WC = 6.6 X, DD = 100 pef
Wes WI WA. 1.40memo UAW. Ur Wig Well
rqi r M
1.0 WM44.4. WWI
nil..rrM 4r •raes fi- r
'C..VY�iw/r..YMr r. !.r
r
arnvr.e wit" o-o4a
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
.1
1.9 APPLIED PRESSURE - KSF 10 100
16-7-487
H -Pk KUMAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 4
F
t
1
0
V
CONSOLIDATION - SWELL
SAMPLE Or: Silty Clayey Sand with Grave
FROM: Boring 1 0 15'
WC = 11.0 X. DD = 116 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
Dm, 6M moi! Ep// - Wmaples Saud. TN twang mort
tlr
u oho r..UI...-w.w r
farrier .d rrwM-. r_ 7.1
a...rru.n INV w�.n�w r
..wr.w..rr o-�sfa
1.0 APPLIED PRESSURE - KSF 10
100
16-7-487
H -P* KUMAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 5
Project No. 16-7-487
co
J
co
w
w
w
O
JO
02 ca
a,
o
g
2
N
d
Q• Y
5(.
0u.• x
w
m
03
y
FA Vg
e
0.
ATTERBERG UMITS
oh
00
GRADATION
1
g
0 • 8
N
lg
<00
zm0
SAMPLE LOCATION
a-
u°i
0
0
o6
in
0
0
r
0
N
2
0