HomeMy WebLinkAboutSoils Report 12.31.2019' Gemla*t lic Areas, Materials En
—}-- Ge nit:alent lScientists
5020 County Road 154
and Environmental Sc;ienlia' Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
�—� email: kaglenwood@kumarusa.com
An Employes Owned Company www,kunarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 35, FOUR MILE RANCH
225 MAROON DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-705
DECEMBER 31, 2019
PREPARED FOR:
DON & DEE MOORE
25 BUCKSKIN CIRCLE
NEW CASTLE, COLORADO 81647
ti tmoorec o(w gm a il.co m
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS -3-
FOUNDATION AND RETAINING WALLS ...... - 5 -
FLOOR SLABS -6-
UNDERDRAIN SYSTEM - 6 -
SITE GRADING - 7 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 8 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19-7-705
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 35, Four Mile Ranch, 225 Maroon Drive, Garfield County, Colorado. The project site is
shown on Figure 1. The purpose of the study was to develop recommendations for the
foundation design. The study was conducted in accordance with our agreement for geotechnical
engineering services to Don & Dee Moore dated November 25, 2019.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzed to develop recommendations for foundation types, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conclusions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
Building plans for the lot had not been developed at the time of our study. In general, we assume
the proposed residence will be a one- to two-story wood frame structure with a walkout
basement level and attached garage located in the building envelope shown on Figure 1. Ground
floors could be slab -on -grade or structural over crawlspace. Cut depths are assumed to range
between about 3 to 10 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 property is currently vacant. The site grading is mostly natural with minor fills in the
northern part of the lot due to the water tank construction located north of the site and minor cut
Kumar & Associates, Inc. Project No. 19.7.705
2
and fill grading along the water tank access road along the northwest edge of the lot. The lot
slopes down to the southwest at a grade of between around 10 to 15 percent. There is about
15 feet of elevation difference across the building envelope. Vegetation consists of native grass,
weeds and sage brush.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Four Mile Ranch
subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsum and limestone. There is a possibility that massive
gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot.
Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can
produce areas of localized subsidence.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot 35 throughout the service life of the proposed residence, in our
opinion, is low; however, the owner should be made 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.
FIELD EXPLORATION
The field exploration for the project was conducted on December 6, 2019. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4 inch diameter continuous flight augers powered by a truck -
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
Kumar & Associates, Inc. ¢' Project No. 19-7-705
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subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 1 foot of topsoil overlying 8 to 10 feet of generally very stiff, silty
sandy clay. Dense, clayey sandy gravel with cobbles and probable boulders was encountered at
depths of 9 and 11 down to the maximum depths drilled of 15 and 12'/z feet in Borings 1 and 2,
respectively. Drilling in the coarse granular soils with auger equipment was difficult due to the
cobbles and boulders and drilling refusal was encountered in Boring 2 at 12'/2 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density. Results of swell -consolidation testing performed on relatively undisturbed
drive samples of the silty sandy clay, presented on Figures 4 and 5, indicate low to moderate
compressibility under conditions of loading and a minor collapse or expansion potential when
wetted under a constant 1,000 psf surcharge load. The laboratory testing is summarized in
Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The upper natural clay soils possess a
potential when wetted. Shallow spread footings placed on the upper fine-grained soils could
have a movement potential and could result in building distress especially where foundations
low bearing capacity and a low collapse or expansion
transition different bearing soils. Lower risk options include removal of a minimum of 3 feet of
the natural fine-grained soils below the footings and replacement with compacted structural fill
and extending the footings down to the underlying dense granular soils.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
Kumar & Associates, Inc. Project No. 19-7-705
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on the natural soils, a minimum of 3 feet of compacted structural fill or the underlying natural
dense granular soils.
The design and construction criteria presented below should be observed for a sprcad footing
foundation system.
1) Footings placed on the undisturbed natural fine-grained soils should be designed
for an allowable bearing pressure of 1,500 psf with a risk of movement and
building distress.
Footings placed on a minimum of 3 feet of properly placed and
compacted structural fail or on the natural dense gravel mils should he designed
for an allowable bearing pressure of 3,000 psf. Based on experience, we expect
settlement of footings placed on the natural fine-grained soils could be up to about
1 to 2 inches and footings placed on the dense gravel soils or 3 feet of structural
fill could be up to about 1 inch.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) 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 also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) The topsoil and any loose or disturbed soils should be removed from the footing
bearing level. The exposed soils in footing area should then be moistened and
compacted to at least 95% of the standard Proctor. Structural fill (if used) should
be compacted to at least 98% of the standard Proctor density near optimum
moisture content and extend to at least 1 % feet beyond footing edges.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & Associates, Inc. cr, Project No. 19-7-705
-5-
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 on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on -site soils. Cantilevered retaining structures which are separate from the residence and
can be expected to deflect sufficiently to mobilize the full active earth pressure condition should
be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight
of at least 45 pcf for backfill consisting of the on -site soils.
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
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 a moisture content near optimum. 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. Backfill should not contain organics, debris or rock larger
than about 6 inches.
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 350 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
Kumar & Associates, Inc. Project No. 19-7-705
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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 upper fine-grained soils have variable compressibility/expansion when wetted and there is a
risk of slab movement and distress if the bearing soils become wetted. Slabs -on -grade can be
supported on
2 feet of compacted structural fill where needed to reduce the risk of movement such as in living
areas of the residence. Structural floors should be used in areas where movement cannot be
tolerated.
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 at least 50% retained on 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 should consist of
imported granular 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 and where there are clay soils 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
Kumar & Associates, Inc. v Project No. 19-7-705
7
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 Y2 feet deep.
SITE GRADING
Embankment fills should be compacted to at least 95% of the maximum standard Proctor density
near optimum moisture content. Prior to fill placement, the subgrade should be carefully
prepared by removing all vegetation and topsoil and compacting to at least 95% of the maximum
standard Proctor density. The fill should be benched into slopes that exceed 20% grade.
Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter
and protected against erosion by revegetation or other means. This office should review site
grading plans for the project prior to construction.
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.
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 paved areas. Free -draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on -site soils to
reduce surface water infiltration.
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 foundation walls. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irrigation.
Kumar & Associates, Inc. Project No.19-7.7O5
-8-
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 reconunendations submitted in this report are based upon the data obtained
from the exploratory borings drilled at the locations 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 concemed 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 borings 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 so
that 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
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar& Associates, Inc.
htat,
Shane J. Robat, P.E.
Reviewed by:
Steven L. Pawlak,
SJR/kac
Kumar & Associates, Inc. Project No. 19-7-705
' ..I,
1 i!
LOT 36
19-7-705
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APPROXIMATE SCALE —FEET
LOCATION OF EXPLORATORY BORINGS
Fig. 1
_VtAlfjj7�-Qj I+ •
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1-
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w
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BORING 1
EL. 6197'
BORING 2
EL. 6188.5'
6200 6200
6195
6190
6185
— 6180
— 6180
I 36/12
//
/
I 38/12
//•' WC=13.8
DD=112
/
/
14/12
22/12
WC=10.6
DD=88
62/12
6195 —
6190
6185--
6180 ---
6180
1-
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w
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Z
0
w
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w
19-7-705
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
r
TOPSOIL, CLAY AND SILT, SANDY, FIRM, MOIST, DARK BROWN, ORGANIC.
CLAY (CL); SANDY, SILTY, STIFF TO HARD, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS,
LOW TO MEDIUM PLASTICITY.
GRAVEL (GC); CLAYEY, SANDY, WITH COBBLES AND PROBABLE BOULDERS, DENSE,
SLIGHTLY MOIST, BROWN. SUBANGULAR TO ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
1111 DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
36/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 36 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
t PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 6, 2019 WITH A 4—INCH—DIAMETER
CONTINUOUS —FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING 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 BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (pcf) (ASTM D2216).
19-7-705
Kumar & Associates
LEGEND AND NOTES
Fig. 3
ae
CONSOLIDATION - SWELL
2
1
0
—1
—2
—3
SAMPLE OF: Sandy Clay
FROM: Boring 1 ® 5.
WC = 13.8 %, DD = 112 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
Thom I..l re.uilo up* only to on
Motpl.. %wrd 'IM Inane rmpori
.hull not bo reproduced, nmrpl In
uP, ubbOtel ino wdMn upyurol or
burner end Mo eieirt_ I - Stroll
xmlI7almn l aiIng order d In
donor with ufu O--1et6.
1.0 APPLIED PRESSURE - KSF 10 10
19-7-705
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
Fig. 4
CONSOLIDATION - SWELL
— 2
—3
— 4
—5
— 6
.ahott rat a I.preac.d, a.cnc cf.f. .rorovti ih...tn.n ooaro OI l
Kumar end h,actotn, Inc. Steil
canaeireetke taring o.++emvd 4n
accardarc..hh r.STN D-4541
SAMPLE OF: Sandy Clay
FROM: Boring 2 ® 5'
WC = 10.6 %, DD = 88 pcf
i I
1 III
j L.
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE - KSF 10 100
19-7-705
Kumar & Associates
SWELL -CONSOLIDATION TEST RESULTS
Fig. 5
I(+A
Kumar & Associates, kic.
Geatechnkal and Mst>?riels Engines,
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Profect No. 19-7-705
t SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
r%)
NATURAL
DRY
DENSITY
(pcfl
GRADATION
PERCENT
PASSING NO.
200 SIEVE
1 ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
080
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
MI
SAND
rip)
LIQUID LIMB
P%)
PLASTIC
INDEX
eA)
1 1
5
13.8
112
Sandy Clay
2
5
10.6
88
Sandy Clay