HomeMy WebLinkAboutSoils Report 01.25.2017H-PI<U MAR
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
January 25, 2017
Jeff Bader
420 AABC, APT. E
Aspen, Colorado 81611
(jbader311 @me.coin)
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
Project No.17-7-125
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 7, Kings Row,
Garfield County, Colorado
Dear Mr. Bader:
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 proposal for geotechnical engineering services
to you dated January 12, 2017. 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 one and two story wood frame
construction above a crawlspace with an attached garage. The building area is located on the site
as shown on Figure 1. Garage floor will be slab -on -grade. Cut depths are expected to range
between about 3 to 4 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 vacant lot was covered with about 1 foot of snow at the time of our
exploration. Vegetation consists of grass and weeds with sage brush on the eastern side of the
lot. The ground surface is relatively flat with a slight slope down to the north.
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Subsidence Potential: Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the
Kings Row Subdivision. These rocks are a sequence of gypsiferious shale, fine-grained
sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that
massive gypsum deposits associated with the Eagle Valley Evaoprite underlie portions of the
property. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and
can produce areas of localized subsidence.
No evidence of sinkholes were observed on the property or encountered in the subsurface
materials, however, the exploratory pits were relatively shallow, for foundation design only.
Based on our present knowledge of the subsurface conditions at the site, it can not be said for
certain that sinkholes will not develop. The risk of future ground subsidence at the site
throughout the service life of the structure, in our opinion is low and similar to other lots in the
area, however the owner should be aware of the potential for sinkhole development. If further
investigation of possible cavities in the bedrock below the site is desired, we should be
contacted.
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 one foot of topsoil, consist of
sandy silty clay overlying basalt cobbles and boulders in a sand, silt and clay matrix. No
boulders and only scattered cobbles were encountered at Pit 1 with depth. Results of swell -
consolidation testing performed on relatively undisturbed samples of sandy silty clay, presented
on Figures 3, 4 and 5 indicate low compressibility under existing moisture conditions and light
loading. A sample tested from Pit 1 at 3 feet showed a minor expansion potential when wetted.
The other two samples showed a moderate collapse potential (settlement under constant load)
when wetted. 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 foot
placed on the undisturbed natural soil designed for an allowable soil bearing pressur
psf for support of the proposed residence. The soils typically tend to compress after 1,
there could be some post -construction foundation settlement. Care should be taken to avoid
wetting of the bearing soils. It will be critical to the long term performance of the structure to
follow the recommendations in the `Surface Drainage' section of this report. Footings should be
a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed
soils and existing fill 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
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Project No. 17-7-125
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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 14 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 onsite soil as backfill.
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 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 deep
crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. Shallow crawlspaces (less than 4 feet) and slab -at -grade areas should not need an
underdrain.
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 l'/2 feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the
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Project No. 17-7-125
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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 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 (if any) 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.
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 foundation caused by irrigation.
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.
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
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Project No. 17-7-125
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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 MAR
Louis E. Eller
Reviewed by:
/4;„. ,
a
9 :0 244 3 F
Daniel E. Hardin, P.E. ` ' `
LEE/kac
attachments
441-e.io+VAI.
Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figures 3, 4 and 5 — Swell -Consolidation Test Results
Table 1 — Summary of Laboratory Testing
H P;KUMAR
Project No. 17-7-125
•
•
•
•
• •
\ \
\ \
` ••
\L0T8
` PIT 2 i
• \ \
LOT 5 ` ` O,o BUILDING 0
i \ F,4, \ AREA PIT 1
i
OF
•
1 \• \\
i` • LOT 7
/ \\ \\ '
/ \ \
•
LOT 6 \ \ /
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111.
50 0 50 100
SCALE -FEET
17-7-125
LOCATION OF EXPLORATORY PITS
Fig. 1
E
Lqg
5e
1—
w
w
w
I
x
F-
a
w
-- • 0
5
PIT 1
WC=9.9
DD=101
WC=17.3
DD=79
PIT 2
WC=7.8
DD=97
WC=8.6
DD=76
0 —
5-
10 —
10 10
LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN.
CLAY (CL); SANDY, SILTY, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST TO MOIST, BROWN,
POROUS.
`SILT AND CLAY (ML—CL), SANDY WITH GRAVEL, SCATTERED COBBLES, MEDIUM STIFF, MOIST,
.,1LIGHT BROWN, CALCAREOUS.
BASALT COBBLES AND BOULDERS, (GM); IN A SAND, SILT AND MATRIX, DENSE, SLIGHTLY
MOIST, LIGHT BROWN, CALCAREOUS.
N HAND DRIVEN LINER SAMPLE.
4 PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JANUARY 18, 2017.
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 NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH. PIT 2 WAS ABOUT 1 FOOT LOWER THAN PIT 1.
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 (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216).
17-7-125
H -P- KU MAR
LOGS OF EXPLORATORY PITS
w
w
I
x
1-
w
0
Fig. 2
These leel results apply only to the
. omplee leeted. The testing report
nlylt not be fepreduCed, except In
51.11, wIITOVt the wrlllen approval of
%timer and Mnoclatee, Inc. Swell
Eaneolidatwn (sitting performed In
accordance with ASFN 1:1-45 .18.
SAMPLE OF: Sandy Silty Clay
FROM: Pit 1 ® 3'
WC = 9.9 %, DD = 101 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
17-7-125
1.9 APPLIED PRESSURE - KSF 10 100
H-PtiKUMAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 3
2
.. —2
—4
w
—6
z
0
1-
2 —8
J
O
<n
z
O
(-)-10
— 12
— 14
Thebe 1.4et refuel opply, oNy
omelet. Iaeted, Th, Ieetlnq report
ehof reel be Ieproduced, except In
rue, without the mitten opprerd of
xumor and Aawclatee, Ix. Seel/
Commedalerm testing performed h
occardance rah ASPM D-4546.
17-7-125
SAMPLE OF: Sandy Silt and Clay
FROM: Pit 1 CO 7'
WC = 17.3 %, DD = 79 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPUED PRESSURE - KSF 10 100
H-PvKUMAP
SWELL -CONSOLIDATION TEST RESULT
Fig. 4
Threw Leet neulte cooly ant/ W the
wmplee tested. The testing report
mild{ not be reproduced, except In
loll, without the written approval of
Kumar and Meoclatee, Inc. Swell
Cana detlen tesUng performed In
accordonce with ASTM 0-4648.
SAMPLE OF: Sandy Silty Clay
FROM: Pit 2 CSD 2'
WC = 7.8 %, DD = 97 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
17-7-125
1.0 APPLIED PRESSURE - KSF 10 100
H -P- KUNIAR
SWELL—CONSOLIDATION TEST RESULT
Fig. 5
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-125
SAMPLE LOCATION
E NATURAL 1 NATURAL
1 MOISTURE I DRY
CONTENT DENSITY
Wu) (pcf)
GRADATION
PERCENT
PASSING
NO. 200
SIEVE
1 ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL TYPE
PIT
DEPTH
(fL)
GRAVEL SAND
(%) (%)
LIQUID
LIMIT
roi
PLASTIC
INDEX
(%)
1
3
9.9
1 101
Sandy Silty Clay
7
17.3
79
Sandy Silt and Clay
2
2
7.8
97
Sandy Silty Clay
4
8.6
76
Sandy Silty Clay
r
f