HomeMy WebLinkAboutSoils Report 05.21.2019• Kumar & Associstn, inc.
Geotechnical and Materials Engineem 5020 County Road 154
and Envisonmental Scientists (iteilv,iood Springs, C.10 81601
phone: (970) 945-7988
fax: (970) 945-84-54
email
kagi en WO ocl(7kurnarusa.com
An Employe 4 Owned Cerndn's' wwv,,,kuraartisa Anon,
Offic,-; Locations: Denver tl1Q), Parke,r, Colorado Springs, Fon Collins, Glenwood Springs, and Snnialit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
PARCEL 217924300225
SIX LAZY K ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-238
MAY 21, 2019
PREPARED FOR:
COREY DEPAOLO
779 EAST 17TH STREET
RIFLE, COLORADO 81650
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
GEOLOGY -2-
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS -6-
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY PITS
FIGURE 2 - LOGS OF EXPLORATORY PITS
FIGURES 3 THROUGH 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Komar & Associates, Inc. Project No, i9-7.238
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at Parcel
217924300225, Six Lazy K Road, 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 Corey DePaolo dated April 16, 2019.
A field exploration program consisting of exploratory pits was conducted to obtain information
on the subsurface conditions. Samples of the subsoils and bedrock 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
Construction plans were not provided as part of this study. We assume that the proposed
residence will be a one to two story structure with a partial basement level. Ground floors could
be slab -on -grade or structural over crawlspace. Grading for the structure is assumed to be
relatively minor with cut depths between about 3 to 12 feet. We assume relatively light
foundation loadings, typical of the, proposed type of construction.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The lot was vacant at the time of the field exploration. The terrain was moderately sloping down
to the east and northeast at a grade of about 10% to 20%. Elevation difference across the
KUanar & Associates, Inc, Project No 19-7438
-2
building site is about 14 feet. Vegetation consisted of grass, weeds, scattered sage brush with
pinyon and juniper trees. An old gravel access road cuts across the site as shown on Figure 1.
Vacant land surrounds the site.
GEOLOGY
According to the Geologic Map of the Leadville 1 °x2° Quadrangle, Northwestern Colorado,
dated 1978, by Tweto, Moench, and Reed, the site is underlain by the Wasatch and Ohio Creek
Formations. The formation is described as variegated claystone, siltstone, sandstone, and
conglomerate.
FIELD EXPLORATION
The field exploration for the project was conducted on April 30, 2019. Two exploratory pits
were excavated at the locations shown on Figure 1 to evaluate the subsurface conditions. The
pits were dug with a mini -excavator. The pits were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with relatively undisturbed and disturbed sampling methods.
Depths at which the samples were taken are shown on the Logs of Exploratory Pits, 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 1/2 -foot of topsoil overlying stiff, silty, sandy clay and medium hard to
hard claystone bedrock. The claystone was weathered and became very hard with depth where
practical digging refusal was encountered.
Laboratory testing performed on samples obtained from the pits included natural moisture
content and density and percent fines (percent passing the No. 200 sieve). Results of swell -
consolidation testing performed on relatively undisturbed liner samples, presented on Figures 3
through 5, indicate low compressibility under light loading. The clay indicated low to moderate
compressibility when wetted and the claystone indicated low to moderate expansion when
wetted. The laboratory testing is summarized in Table 1.
Kui to r & Associates, inc, Project No. 19..7438
be designed for an allowable bearing pressure of 2,000 psf
-3
No free water was encountered in the pits at the time of exploration and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The sandy, silty clay soils encountered in the exploratory pits possess low bearing capacity and
generally low to moderate compressibility potential, especially when wetted. The underlying
weathered claystone bedrock generally has low to moderate expansion potential when wetted.
The assumed cut depth is expected to transition between the two material types. Shallow
footings appear to be feasible for foundation support of the residence with risk of movement and
distress. To reduce the risk of movement, we recommend the spread footings bear on a
minimum of 3 feet of compacted structural fill. Precautions should be taken to prevent wetting
of the natural bearing soils and bedrock below the structural fill. Sources of wetting include
excessive irrigation near the foundation, poor surface drainage adjacent to the foundation walls,
and utility leaks.
A lower risk of settlement foundation system is drilled piers or micro -piles bearing in bedrock
below an assumed wetted depth'(typically 15 to 20 feet). Provided below are recommendations
for spread footings bearing on compacted structural fill. We should be contacted if
recommendations for drilled piers or micro -piles are desired.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory pits and the nature of the
proposed construction, the building can be founded with spread footings bearing on a minimum
3 feet of compacted structural fill with a risk of movement and distress. The structural fill should
consist of imported well -graded granular soils such as road base.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on a minimum 3 feet of imported granular structural fill should
Based on experience,
€(� �n & Associates, Inc, .• Project No, 194-23
-4 -
we expect initial settlement of footings designed and constructed as discussed in
this section will be about 1 inch or less. There could be additional movement if
the underlying soil or bedrock become wetted. The magnitude of the additional
movement would depend on the depth and extent of wetting but may be on the
order of 1/2 to 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 heavily 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 also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) The topsoil, clay soil and loose disturbed soils should be removed down to at least
3 feet below footing bearing level. The exposed soils in footing area should then
be moistened and compacted. Structural fill should extend at least 11/2 feet
beyond footing edges and be compacted to at least 98% of standard Proctor
density at near optimum moisture content. The depth of sub -excavation could be
terminated where very hard cemented rock is encountered.
6) A representative of the geotechnical engineer should observe all footing
excavations and test structural fill compaction prior to concrete placement to
evaluate bearing conditions.
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 fine-grained soils and at least 45 pcf for backfill consisting of imported granular
materials. Cantilevered retaining structures which are separate from the residence and can be
Kumar & Msociates, Inc, 'rojrct No S, IN2S
-5 -
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 fine-grained soils and at least 35 pcf for
backfill consisting of imported granular materials.
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 95% of the maximum
standard Proctor density at a moisture content slightly above 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.
We recommend imported granular soils for backfilling foundation walls and retaining structures
because their use results in lower lateral earth pressures and the backfill can be incorporated into
the underdrain system. Subsurface drainage recommendations are discussed in more detail in the
"Underdrain System" section of this report. Imported granular wall backfill should contain less
than 15% passing the No. 200 sieve and have a maximum size of 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 300 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
Kumar & Associates, Project No, 19-7438
-6 -
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 movement and distress. The silty clay soils are compressible and the
claystone bedrock is expansive when wetted. We should evaluate the need for a depth (typically
consisting of the on-site soils or road base, below the slabs at the time of
2 feet) of structural fill,
construction.
A lower risk movement alternative would be to use a structural floor above
crawlspace.
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. Slip joints at the bottom of non -load bearing
partition walls could also be needed depending on the subgrade expansion potential. 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 can consist of the on-
site soils devoid of vegetation, topsoil and oversized rock or imported gravel such as CDOT
Class 6 base course.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where bedrock is shallow 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,
Kumar & Associates, Inc. Project No. .
-7
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 1'/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.
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 use of xeriscape to
reduce the potential for wetting of soils below the building 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.
Kumar8 Associates, °c. 'Project No.194438
-8 -
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, 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 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.
Alico /4()
Shane J. Robat, P.E.
Project Manager
Reviewed by:
Steven L. Pawlak,
SJR/kac
Kumar & Asc
Project Na.19-N38
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19-7-238
Kumar & Associates
LOCATION OF EXPLORATORY PITS
Fig. 1
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PIT 1
EL. 5854'
WC=14.6
DD=102
—200=60
WC=10.0
DD=120
PIT 2
EL. 5850'
WC=1 3.5
DD=102
WC=7.8
DD=117
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5 —
10 10
_LEGEND_
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TOPSOIL; ORGANIC, CLAY AND SILT, DARK, FIRM, MOIST, BROWN.
CLAY (CO; SANDY TO VERY SANDY, SILTY, STIFF, SLIGHTLY MOIST, BROWN, LOW PLASTICITY.
WEATHERED CLAYSTONE; MEDIUM HARD TO HARD, SLIGHTLY MOIST, MULTI—COLORED.
WASATCH AND OHIO CREEK FORMATION.
N HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE,
t PRACTICAL REFUSAL WITH EXCAVATOR BUCKET.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A GACKHOE ON APRIL 30, 2019.
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 OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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. GROUND WATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXPLORATION. PITS
WERE BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM 0 2216);
00 = DRY DENSITY (pcf) (ASTM D 22.16);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
19--7-238
Kumar & Associates
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LOGS OF EXPLORATORY PITS
Fig. 2
2
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0
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19-7-238
SAMPLE OF: Weathered Claystone
FROM: Pit 1 @ 5'
WC = 10.0 %, DD = 120 pcf
1.8 APPLIED PRESSURE — KSF
Kumar & Associates
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
SWELL—CONSOLIDATION TEST RESULTS
Fig. 3
CONSOLIDATION - SWELL
—6
—10
SAMPLE OF: Sandy Silty Clay
FROM: Pit 2 @I 2.5'
WC = 13.5 %, DD = 102 pcf
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theme LN feWtea 0* W the
f xnoW Lllul Tke
s*o t be AAaaue0277,111
fun. wlthwrt the eaten epprnnI no(
Armor Ped A+epttPl n, re.C. 5141
Cce%lonffett t,niMa rg-t54d In
xcwaenc. wllh tSTh li'43l .
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
.:
19-7-238
1.0 APPLIED PRESSURE — KSF 10 100
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
CONSOLIDATION - SWELL
fi
3
2
1
—1
—2
—3
lhnfe led moth!, appy only So !MO
eempfoo reeled Th ussao 10.1
Wrap net be ropooSoond, amp! In
fall, rNheW the .in( oppfovd of
k s,,r and M.oeIelltl, lK• S.eSl
eeidolfon Iep1Hg grfelr.Hd In
cccOrdonce with /°IM 11-4346.
SAMPLE OF: Weathered Claystone
FROM: Pit 2 @ 5'
WC = 7.8 %, DD = 117 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - 1(SF 10
100
19-7-238 r Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 5
Kumar & Associates, irtc.°
Gotedmicat and Maienals Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 19.7-238
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
1 DENSITY(%)
1 (pcfl
GRADATION
PERCENT
P200 SIEVNO. E
ATTERBERG
LIQUID LIMB
(%)
LIMITS
PLASTIC
INDEX
(%]
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
SOIL TYPE
PIT
DEPTH
(ft)
GRAVEL
SAND
(%)
2
14.6
102
60
Sandy Silty Clay with
Gravel
5
10.0
120
Weathered Claystone
2
21/2
13.5
102
Sandy Silty Clay
5
7.8
117
Weathered Claystone