HomeMy WebLinkAboutSubsoil Study for Foundation Design 12.15.2021i ICrtflffilfiffifffiiri,"i**
An Employcc Ownad Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Par{<er, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
December 15,2021
Maria Ruiz
2307 Road l54,Trailer #l
Glenwood Springs, Colorado 81601
r o cioruiz23 07 @hotmail. c om
Job No. 2I-7-740
Subject: Subsoil Study for Foundation Design, Proposed Residence, Tract 2,Holgate
Parcels, Highway 133, Carbondale, Colorado
Dear Ms. Ruiz:
As requested, Kumar and Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated September 10,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The design for the proposed residence has not been determined, but is
assumed to be a one- or two-story, wood frame structure over crawlspace or with slab-on-grade
floor. Cut depths are assumed to range between about 2 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 site is vacant and vegetated with grass and weeds. The lot is bordered on
the west by the Rockford Ditch and Colorado Highway 133, and on the north by Roaring Fork
High School. The lot slopes gently down to the west. The ground surface appears natural and is
relatively flat with approximately 2 feet of elevation change across the lot.
Subsidence Potential: The Town of Carbondale is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under
certain conditions can cause sinkholes to develop and can produce areas of localized subsidence.
During previous work in the area, sinkholes were observed in the south and central portions of
the nearby River Valley Ranch development. Sinkholes were not observed in the immediate area
of the subject lot. Based on our present knowledge of the site, it cannot be said that sinkholes
will not develop. In our opinion, the risk of ground subsidence on the lot is low throughout the
service life of the residence and similar to other lots in the area, but the owner should be aware of
the potential for sinkhole development.
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Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. ln Pit 1, below about I foot of topsoil, an approximately I foot thick
layer of medium dense sandy, silty gravel and cobbles was encountered. This was underlain by a
layer of stiff sandy silt and clay with scattered gravel down to about 6% feet. Below the silt and
clay layer, a silty sand was encountered down to the explored depth of 8 feet. In Pit 2, below
about I foot of topsoil, an approximately 2 foot thick layer of medium dense sandy, silty gravel
and cobbles was encountered. Below the gravel layer a silty sand was encountered down to the
explored depth of 8 feet. Results of swell-consolidation testing performed on a relatively
undisturbed sample of the sandy silt and clay material, presented on Figure 4, indicate low
compressibility under existing moisture conditions and light loading and a low collapse potential
when wetted. Results of a USDA gradation analysis performed on a sample of the natural silty
sand obtained from the site are presented on Figure 5. No free water was observed in the pits at
the time of excavation and the soils were slightly moist.
Septic Disposal Area: The subsoil conditions in the planned septic disposal area were evaluated
by digging a Profile Pit at the location shown on Figure 1. The subsurface profile mainly
consists of a sandy loam. Results of a USDA gradation test performed on a sample of the soils
are shown on Figure 5. Based on these findings, the tested area appears suitable for an
infiltration septic disposal system. A Civil Engineer should be engaged to design the septic
disposal system.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
bearing on the natural soils or on compacted structural fill designed for an allowable soil bearing
pressure of 1,200 psf for support of the proposed residence. Post-construction foundation
settlement should be relatively low and around I to 2 inches mainly if the bearing soils are
wetted. Footings should be a minimum width of 20 inches for continuous walls and2 feet for
columns. Structural fill should consist of an imported granular material such as CDOT Class 6
specifications, placed in 6-inch thick lifts and compacted to at least 98 percent standard Proctor
density at a moisture content within 2 percent of optimum. We should observe the completed
foundation excavation for bearing conditions. 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 heavily reinforced top and bottom to span local anomalies such as by assuming an
unsupported length of at least 10 feet. Foundation walls acting as retaining structures should be
designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least
55 pcf for the on-site soil as backfill, excluding organics and rock larger than 6 inches.
Floor Slabs: The natural on-site fine-grained soils, exclusive of topsoil, are suitable to support
lightly loaded slab-on-grade construction with a risk of settlement and building distress if the
bearing soils are wetted. To reduce the effects of some differential movement, floor slabs should
Kumar & Associates, lnc. @ Project No, 21-7-740
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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 road base
should be placed beneath slabs for support. This material should consist of minus 2 inch
aggregate with less than 50Vo passing the No. 4 sieve and less than l2%o passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at least 95oh 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: It is our understanding the proposed finished floor elevation at the lowest
level is at or above the surrounding grade. Therefore, a foundation drain system is not required.
It has been our experience in the arcathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan create aperched
condition. We recommend below-grade construction, such as retaining walls and basement
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall
drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
l) Inundation ofthe 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 95o/o 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 l0 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 inigation should be located at least
5 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
Kumar & Associates, lnc. @ Project No. 21-7-740
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express or implied. The conclusions and recorlmendations submitted in this report are based
upon the data obtained from the exploratory pits excavated at the locations indicated on Figure I
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 recommendationso and to veriff 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.
Respectfu lly Submitted,
Kumar & Associates, Inc.
David A. Noteboom, Staff Engineer
Reviewed by:
Steven L. Pawlak,
attachments Pits
Figure
Figure
Pits
Figure 4 - Swell-Consolidation Test Results
Figure 5 - USDA Gradation Test Results
Table I - Summary of Laboratory Test Results
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3-Notes
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Kumar & Associates, lnc.6 Project No. 21-7-740
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50 0
APPROXIMATE SCALE_FEET
21 -7 -7 40 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1
EL. 1 01'
PIT 2
EL. 102'
PROFILE PIT
EL. 1 03'
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10
SAND=62
SILT=25
CLAY= 1 5 10
WC=6.2
DD=97
WC=6.5
DD=78
-200=56
21 -7 -7 40 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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TOPSOIL; ORGANIC SANDY SILT AND CLAY, BROWN.
CLAY AND SILT (CL-ML); SANDY, WITH SCATTERED GRAVEL, STIFF, SLIGHTLY MOIST, BROWN,
SLIGHTLY POROUS.
SAND (SM); SILTY, SCATTERED GRAVEL, SLIGHTLY CLAYEY, SLIGHTLY MOIST, MEDIUM DENSE,
BROWN, SLIGHTLY CALCAREOUS.
GRAVEL (CV); CnnVEL AND COBBLES, SANDY, SILTY, MEDIUM DENSE, SLIGHTLY MOIST,
BROWN.
F
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HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON OCTOBER 8,2021.
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 MEASURED BY HAND LEVEL AND REFER TO
GROUND LEVEL AT THE WELL ON THE NORTH PROPERTY LINE AS ELEVATION 1 OO" 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 EXCAVATION
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCt) (NSTV D 2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140);
GRAVEL = PERCENT RETAINED ON NO. 10 SIEVE;
SAND = PERCENT PASSING NO.10 SIEVE AND RETAINED ON NO.325 SIEVE;
SILT = PERCENT PASSING NO. 525 SIEVE TO PARTICLE SIZE .002MM;
CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM.
21 -7 -7 40 Kumar & Associates LEGEND AND NOTES Fig. 3
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SAMPLE OF: Sondy Silt ond Cloy
FROM:Pitl@4'
WC = 6.2 %, DD = 97 pcf
ln
t {cd. ftc
not bc raproducad,
without thc srittcn opprovol of
ond A38ociotca, lnc, Sscll
in
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1
0
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1,0 APPLIED PRESSURE _ KSF t0 r00
21 -7 -7 40 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME READINGS SERIES
#18 #10
CLEAR SOUARE OPENINGS
1 MIN.
*325 #140 #60 #3s #4 3/4', 1 112', 3' 5"6" I'
100
10
20 80
30 70
o
lrJz.aF
lJJu
Fz.
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40 60
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z.na
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50
60 40
70 30
80 20
90 10
100 0.001 .002 .005 ,009 .019 ,045 .106 .025 .500 1.00 2,00 4.?5 9,5 19.0 37,5 76.2 152 203
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY COBBLES
GRAVEL 2 %SAND 62 %SILT 23 o/o CLAY 13 "/"
USDA SOIL WPE: Sandy Loam FROM: Pit'l @ 7'-8'
.
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SAND
MEDIU|\ilSILT
21 -7 -7 40 Kumar & Associates USDA GRADATION TEST RESULTS Fig. 5
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.21-7-740
Sandy Silt and Clay
Very Sandy Silt and
SOIL TYPE
Sandy Loam
CLAY
vt
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SILT
(%)
64
(%)
SAND
USDA SOIL TEICIURE fivdrometer)
GRAVEL
(%)
SILT&CLAY
(%)
56
SAND
(/"1
GRADATION
(%)
GRAVEL
NATURAL
DRY
DENSITY
(pc0
97
78
NATURAL
MOISTURE
CONTENT
(Y"l
6.2
6.5
(ft)
DEPTH
4
6
7to8
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SAMPLE LOCATION
PIT