HomeMy WebLinkAboutSoils Report 03.17.2020It+A
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 40, SPRING RIDGE RESERVE
HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-161
MARCH 17, 2020
PREPARED FOR:
FLOYD McADOW
P.O. BOX 129
GLENWOOD SPRINGS, COLORADO 81602
fcmcadow(a)comcast.net
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 - 5 -
UNDERDRAIN SYSTEM - 6 -
SITE GRADING - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
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 20-7-161
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
40, Spring Ridge Reserve, Hidden Valley Drive, Garfield County, Colorado. The project site is
shown on Figure 1. The purpose of the study was to develop recommendations for foundation
design. The study was conducted in accordance with our agreement for geotechnical engineering
services to Floyd McAdow, dated February 26, 2020.
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, recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed single-family residence will be single -story above crawlspace with an attached
slab -on -grade garage located as shown on Figure 1. We assume excavation for the building will
be cut about 2 to 6 feet below the existing ground surface. Foundation loadings for the structure
were assumed to be relatively light and typical of the proposed type of construction.
If building loadings, location or grading plans are significantly different from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The property was vacant with patchy snow cover at the time of our field exploration. The site is
vegetated with grass, weeds and sage brush. The ground surface slopes moderately down to the
Kumar & Associates, Inc. Project No 20-7-161
-2-
northeast with around 10 feet of elevation difference in the general building area. Maroon
Formation sandstone is exposed on the hillside to the west of the lot.
GEOLOGY
According to the Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado, by
Krikham, Steufert, Hemborg, and Stelling, dated 2014, the site is underlain by alluvium and
colluvium deposits of the Holocene age overlying Maroon Formation.
FIELD EXPLORATION
The field exploration for the project was conducted on March 4, 2020. 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 auger powered by a truck -
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with a 2-inch I.D. spoon sampler. The sampler was driven
into the subsurface materials 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
subsoils and hardness of the bedrock. 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 profiles encountered at the site are shown on Figure 2. Below
about 1 foot of organic topsoil, the subsoils consist of stiff to very stiff, sandy silt and clay with
scattered gravel underlain by very hard sandstone bedrock. In Boring 2, about 2V2 feet of medium
hard, weathered sandstone was encountered below the sandy silt and clay soil and overlying the
hard sandstone.
Laboratory testing performed on samples obtained during the field exploration included natural
moisture content and density and percent silt and clay (percent passing the No. 200 sieve).
Kumar & Associates, Inc. Project No 20-7-161
3
Swell -consolidation testing was performed on relatively undisturbed drive samples of the silt and
clay soils. The swell -consolidation test results, presented on Figures 4 and 5, indicate low
compressibility under relatively light surcharge loading and minor collapse to moderate
expansion potential when wetted under a constant light surcharge. The laboratory testing is
summarized in Table 1.
No free water was encountered in the borings at time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The subsoils encountered at the site possess variable low to moderate movement potential mainly
when wetted. The expansion potential measured in the sample from Boring 2 at 5 feet appears to
be an anomaly and the expansion potential should be further evaluated at the time of excavation.
Surface runoff, landscape irrigation, and utility leakage are possible sources of water which
could cause wetting. Footings placed on the natural soils can be used for foundation support
with the accepted risk of movement. Deep foundations, such as drilled piers or micro -piles, can
be used if the risk of movement cannot be tolerated. We should be contacted if deep foundation
recommendations are desired.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the residence can be founded with spread footings placed on
undisturbed natural soils with a risk of settlement mainly if the bearing soils are wetted.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils can be designed for an allowable
Based on experience, we expect initial settlement
bearing pressure of 1,500 psf.
of footings designed and constructed as discussed in this section will be up to
about 1 inch. Additional movement could be around % to 1 inch depending on
the depth of wetting.
Kumar & Associates, Inc. Project No 20-7-161
4
3) The footings should have a minimum width of 16 inches for continuous footings
and 24 inches for isolated pads.
4) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies and limit the risk of differential movement. One method of
analysis is to design the foundation wall to span an unsupported length of at least
12 feet. Below grade level are not currently planned. If a basement level is
planned, the foundation walls acting as retaining structures should also be
designed to resist a lateral earth pressure as discussed in the "Foundation and
Retaining Walls" section of this report.
5) 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 the exterior grade is typically used in this
area.
6) Prior to the footing construction, the topsoil and loose or disturbed soils should be
removed and the footing bearing level extended down to competent bearing soils.
7) A representative of the geotechnical engineer should observe all footing
excavations 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 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
Kumar & Associates, Inc. Project No 20.7.161
5
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 0.40. 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
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. There could be
differential settlement potential from wetting of the bearing soils
similar to that described above for footings. 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 relatively well graded sand and gravel such as road base should
be placed beneath slabs for support. This material should consist of minus 2-inch aggregate with
at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200 sieve.
Kumar & Associates, Inc. Project No 20-7-161
-6-
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 (plus 6-inch) rock.
UNDERDRAIN SYSTEM
Although groundwater was not encountered during our exploration, it has been our experience in
the area and where clay soils are present and 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. Therefore, we recommend below -grade construction,
such as crawlspace and basement areas (if provided),
be protected from wetting by an underdrain
system. The drain should also act to prevent buildup of hydrostatic pressures behind foundation
walls.
The underdrain system should consist of a drainpipe surrounded by free -draining granular
material placed at the bottom of the wall backfill. The drain lines should be placed at each level
of excavation and at least 1 foot below lowest adjacent finish grade, and sloped at a minimum
1 % grade to a suitable gravity outlet. Free -draining granular material used in the drain system
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. The drain gravel should be at least 1 Yz feet deep. An
impervious liner such as 20 mil PVC should be placed below the drain gravel in a trough shape
and attached to the foundation wall with mastic to keep drain water from flowing beneath the
wall and to other areas of the building.
SITE GRADING
The risk of construction -induced slope instability at the site appears low provided cut and fill
depths are limited. We assume cut and fill depths for foundation construction will not exceed
about 5 to 6 feet. 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 the portions of
the hillside exceeding 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.
Kumar & Associates, Inc. Project No 20-7-161
-7-
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to prevent wetting of the bearing
soils and limiting building settlement and distress. The following drainage precautions should be
observed during construction and maintained at all times after the residence has been completed:
1) Excessive wetting or drying 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 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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfil 1.
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
prevent wetting of bearing soils from landscape 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 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 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 borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
Kumar & Associates, Inc. Project No 20-7-161
-8-
during construction appear to be 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 of 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.
Steven L. Pawla
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
Kumar & Associates, Inc. Project No 20-7-161
i2l71 Subeoll Study, !'royuaad Rae.cuic•WelaNn0,2971131.—ut4.9
N
0
Cri
saleloossy '9 Jewn>
SONId08 ) Oldd0ldX3 JO NOI1d001
9
1333-31VOS 31VWIXOdddd
sz
T
r
0
01
- - I 1/
_ + I I
-
r _____I___-
ll_+ - i/ I 1
r _ 1
T
Oi
I-- _
_ J+ i o
1 11
II n
! i m
III -<
1 11 v
I z
j -, I 1 rri
'a
0
BORING 1
EL. 6458'
9/12
WC=6.5 DD=101
5 /
23/12
WC=5.4
DDf 20 110
—0=20054
30/12
15
] 50/2
7
0
20
/1 30/2, 10/0
10
BORING 2
EL. 6452'
.21 20/12
19/12
!^ WC=9.0
DD=106
/
34/12
/r WC=8.4
DD=107
—200=77
36/12
50/1
0 —
5
10
15 —
20 —
— 25 25 ---
20-7-161
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
7
/
TOPSOIL; ORGANIC SANDY SILT, BROWN, MOSTLY FROZEN.
SILT AND CLAY (ML—CL); SANDY TO VERY SANDY, SCATTERED GRAVEL, STIFF TO VERY STIFF,
SLIGHTLY MOIST, RED —BROWN.
WEATHERED SANDSTONE; MEDIUM HARD, SLIGHTLY MOIST, RED.
SANDSTONE BEDROCK; VERY HARD, SLIGHTLY MOIST, RED. MAROON FORMATION.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
9/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 9 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 4, 2020 WITH A 4—INCH—DIAMETER
CONTINUOUS —FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY TAPING
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);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
20-7-161
Kumar & Associates
LEGEND AND NOTES
Fig. 3
1
0
J —1
N
O
0 —4
—5
SAMPLE OF: Sandy Silt and Clay
FROM: Boring 1 ® 2.5'
WC = 6.5 %, DD = 101 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
/
I
.
IIII
Mao* Lill naill eppy eny 1e 1110
.emple� 1n1.d. the !..ling rep,(
NH. l411 tie r.predye.d, prma 1n
NH. land ur..nu.n eppmrol et
larmar and A.loclel.f. Via. 9rr.tl
Cen.a&Jnn l.ning pprlar,n.d 1n
eecardence .111, �y 0-4518.
1 0 APPLIED PRESSURE - KSF
10
100
1
20-7-161
Kumar & Associates
SWELL -CONSOLIDATION TEST RESULTS
Fig. 4
March 13. 2020 — 09:22am
YMI+a!xIa‘0020,20-7—I61 Submil S1cer Prypaard 4 rrIernarAQry111rr 207I61-04 14 05,a.p
N
0
salepossy Jewn}1
S11f1S3? 1S31 NOI1V011OSN00-113MS
r
0
N
N
m
0
CONSOLIDATION - SWELL (%)
01
Then tent re.alte eppfY ono' Iq the
femtien (..I d. The feeling r.pert
EMU not p. reprepogd, .XC.pt In
full, without Ih..AI4n apprary of
Kurnar and F..odol.., I,u. Sire!
COntrillciohon tenting performed in
oucordmoo with ASTM D-4549.
-411
\
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 ® 5'
WC = 9.0 %, DD = 106 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
K+A
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 20-7-161
SAMPLE
LOCATION
DEPTH
ft)
1NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(PC)
GRADATION
SAND
(%)
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
SOIL TYPE
BORING
GRAVEL
o
CA)
LIQUID LIMIT
(%)
PLASTIC
INDEX
(T.,)
1
2V2
6.5
101
Sandy Silt and Clay
5
5.4
110
54
Very Sandy Silt and Clay
2
5
9.0
106
Sandy Silty Clay
10
8.4
107
77
Sandy Silt and Clay