HomeMy WebLinkAboutSoils Report 12.13.2018H-P----tiKUIMAR
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
December 13, 2018
Jep Bracey and Julie Ferrero
4406 Autumn Mist Court
Katy, Texas 77450
Project No. 18-7-709
Subject: Subsoil Study for Preliminary Foundation Design, Proposed Residence, Lot 23,
Filing 9, Elk Springs, Kingbird Court, Garfield County, Colorado
Dear Jep and Julie:
As requested, H-P/Kumar performed a subsoil study for preliminary design of foundations at the
subject site. The study was conducted in accordance with our agreement for professional
services to you dated November 27, 2018. The data obtained and our recommendations based on
the general proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: Development plan for the proposed residence were not available at the
time of our study. We understand the residence will be located within the upper, northern part of
building envelope shown on Figure 1. We assume the structure will be one or two stories with a
structural floor over crawlspace or slab -on -grade. Cut depths are assumed to range between
about 3 to 6 feet. Foundation loadings for this type of construction are assumed to be relatively
light and typical of the proposed type of construction.
When building location, grading and foundation loadings have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
Site Conditions: The site is currently vacant and located on the downhill side of a broad ridge
trending from west to east. The site slopes from around 10 to 15 percent, generally down to the
southeast. Vegetation at the site consists of native grass, sage brush and juniper and pinon frees.
About% foot of snow covered the lot at the time of our study.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
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presented on Figure 2. The subsoils encountered, below about 1/2 foot of topsoil and 1 to 11/2 feet
of sandy silt and clay, consist of basalt cobbles and boulders in a calcareous sandy silt matrix.
Results of swell -consolidation testing performed on relatively undisturbed sample of the silty
clay, presented on Figures 3 and 4, indicate low initial compressibility under existing low
moisture conditions and light loading and a low collapse (settlement under constant load) or low
swell potential when wetted. No free water was observed in the pits at the time of excavation
and the soils were slightly moist.
Preliminary 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, basalt rock soils designed for an allowable soil
bearing pressure of 2,000 psf for support of the proposed residence. The upper clay soils have
variable compression/expansion potential after wetting and should be removed from below
footing areas. Footings should be a minimum width of 16 inches for continuous walls and 2 feet
for columns. The topsoil, clay soils 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 basalt rock soils. Voids created from boulder removal at footing
grade should be backfilled with concrete or a structural material such as road base compacted to
at least 98 percent of standard Proctor density at a moisture content near optimum. 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 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 excluding organics
and rock larger than 6 inches.
Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded
slab -on -grade construction. The clay soils should be evaluated for expansion potential at the
time of construction and may need to be removed and replaced with structural fill. 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
H-P%KIJMAR
Project No. 18-7-709
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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 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 11/2 feet deep.
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.
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Project No. 18-7-709
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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 will 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
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
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
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Project No. 18-7-709
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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 -Pt KUMAR
Steven L. Pawlak, P.E.
Reviewed by: ,pRI�
( ' ( U.) F 6-A130.
Daniel E. Hardin, P. E.
SLP/kac
attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figures 3 and 4 — Swell -Consolidation Test Results
Table 1 — Summary of Laboratory Test Results
cc: DM Neuman Construction Company — Jason Neuman (jn n@clmncuny n.com)
H-P',KUMAR
Project No. 18-7-709
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LEGEND
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PIT 1
EL. 100'
PIT 2
EL. 99'
WC=10.1
DD=78
TOPSOIL; ORGANIC SANDY SILT AND CLAY, DARK BROWN, FROZEN.
PIT 3
EL. 90'
WC=1 1 .0
DD=106
CLAY AND SILT (CL—ML); SANDY, BASALT ROCKS, VERY STIFF, SLIGHTLY MOIST, WHITE TO
BROWN, MODERATELY CALCAREOUS, BLOCKY AT PIT 3.
BASALT COBBLES AND BOULDERS (GM); CALCAREOUS SANDY SILT MATRIX, MEDIUM DENSE TO
DENSE, SLIGHTLY MOIST, GRAY AND WHITE. SUBANGULAR ROCK.
Sl HAND DRIVEN 2"—DIAMETER LINER SAMPLE.
_i
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON DECEMBER 4, 2018.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
PIT 1 AS ELEVATION 100', ASSUMED.
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).
18-7-709
H-PvKUIV1AR
0
DEPTH -FEET
5
LOGS OF EXPLORATORY PITS Fig. 2
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— 2
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— 6
— 8
—10
—12
CONSOLIDATION - SWELL
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if 18-7-709
SAMPLE OF: Calcareous Sandy S111 and
Clay
FROM: Pit 2 0 1'
WC = 10.1 %, DD = 78 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.6 APPLIED PRESSURE — XSF ID 10t)
H-P�KUMAR
SWELL -CONSOLIDATION TEST RESULTS
fig. 3
CONSOLIDATION - SWELL
2
1
—1
—2
—3
—4
lYrr 1..1 mole epeb. o.Y 1e 11..
we.pM. 11110. ln. 1.01.1 epee
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%wea. e.d N6ecA1... 1 . 4.."
Lpnq.6ntlen I.e1 w+lemye 1n
ecce0QAN .Iln 15 P-IMM6
1 SAMPLE OF: Sandy Clay, Blocky
FROM: Pit 3 0 1.5'
WC = 11.0 %, DD = 106 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1,0 APPLIED PRESSURE - KSF 10 100
18-7-7091 H-Pk4KUMAR
SWELL -CONSOLIDATION TEST RESULTS
Fig. 4
HPKUMAP
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 18-7-709
SAMPLE LOCATION
' GRADATION ATTERBERG LIMITS
UNCONFINED
SOIL
PIT
DEPTH
NATURAL I NATURAL •
MOISTURE DRY GRAVEL
CONTENT DENSITY (%)
1 (/°) (Dcfl
SAND
(%)
PERCENT
PASSING
NO.200
SIEVE
LIQUID
LIMIT
(%)
PLASTIC
INDEX
(%)
COMPRESSIVE
STRENGTH
(psfl
2
1
10.1 78
-
-
Calcareous Sandy Silt and
Clay
-
-
-
3
11/2
11.0
106
Sandy Clay, Blocky