HomeMy WebLinkAboutSubsoil StudyI Grt f;,'pii'trtf,'#r*:ff' å' * "
Ån Employea twnçd Company
5020 County Road 154
Glenwood Springs, CO 8160i
phone: (970) 945-7988
fax: (970) 945-8454
emai I : kaglenwood(@kumarusa.com
wrvw.kumarusa.com
Ofüce Locations: Denver (FIQ), Parkeq Colorado Springs, Fort Collins, Glenvood Springs, and Sununit Courty, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 20, CORYELL RANCH
70 CUTBOW LÄNE
GARFIELD COUNY, COLORADO
PROJECT NO. 21-7-160
MARCH 4,2021
PREPARED FOR:
RICK WALLACE
3539 N. VALLEY STREET
ARLINGTON, VIRGINIA 22207
(rgwallacei r@yahoo.com)
TABLB OF CONTBNTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
1
-1
.)
-L'
a
-3-FOLINDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS .......,...,...
FOLNDATIONS
FOTINDATION AND RETAINING WALLS .....
FLOOR SLABS
LTNDERDRAIN SYSTEM
SURFACE DR4IN4G8..........,.......
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORiNGS
FIGURE 3 - LEGEND AND NOTES
FIGI]RE 4 - GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 21-7-160
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil str-rdy for a proposed residence to be located on
Lot20, Coryell Ranch, 70 Cutbow Lane, 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 proposal for geotechnical engineering
services to Rick Wallace dated January 22,202I.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained dtiring the field
exploration were tested in the laboratory to deterrnine their classification and other engineering
characteristics. The results of the field exploration and laboratory testing were analyzed to
develop recommendations for foundation types, depths and ailowable pressures for the proposed
building foundation. This report summarizes the data obtained during this study and presents our
conclusions, design recomrnendations and other geotechnical engineering considerations based
on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a two-story wood-frame structure over a full basement with
attached 3-car garage. Ground floors will be slab-on-grade. Grading for the structure is assumed
to be relatively minor with cut depths between about 3 to 10 feet. We asslrme reiatively light
foundation loadings, typicai of the proposed type of construction.
If building loadings, location or grading plans change significantly frorn those described above,
we should be notified to re-evaluate the recommendations contained in this repoft.
SITE CONDITIONS
The subject site was vacant at the time of our fìeld exploration with approxirnateiy 6 inches of
snow cover. The ground surface was mostly level. Vegetation consists of grass and weeds. Dry
ditches border both the east and west lot boundaries. Two ponds are south of the lot connected
to the ditches.
SI]BSIDENCB POTBNTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies Coryell Ranch. These rocks
are a seqllence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds
Kumar & Associates, lnc. @ Project No. 21-7-160
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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 ancl can produce areas of localized subsidence.
During previous work in the area, several sinkholes were observed scattered throughor,rt the
lower Roaring Fork Valley. These sinkholes appear similar to others associated with the Eagle
Valley Evaporite in areas of the Eagle Valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratoly 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 20 throughout the service life ofthe 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 clesired,
we should be contactecl.
FIELD EXPLORATION
The field exploration for the project was conducted on Febrr"rary 1,2021. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advancecl with 4 inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates, lnc.
Samples of the subsoils were taken with a ItAinch I.D. spoon sampler. The sarnpler was driven
into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This
test is sirnilar to the standard penetration test described by ASTM Method D-l586. The
penetration resistance values arc an indication of the relative density or consistency of the
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 revier,v 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 l to 1% feet of topsoil ancl clayey fìlloverlying dense, slightly silty to
silty sandy gravel down to the maximum explored deptli of 16 feet. Drilling in the dense
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granulff soils with auger equipment was difficult due to the cobbles and boulders and drilling
refusal was encountered at 13%feet deep in Boring 2.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses perfonned on small diarneter drive
samples (minus 7lz-inch fraction) of the coarse granular subsoils are shown on Figure 4. The
laboratory testing is summarized in Table l.
No free water was encollntered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The natural gravel soils below the topsoil and fill are adequate for supporl of spread footing
foundations. The topsoil and fill encountered in the borings was relatively shallow (less than
2 feet) and should be removed from beneath proposed foundation areas and the bearing grade
extended down to the granular sr¡bsoils.
DESIGN RECOMMENDATIONS
FOLINDATIONS
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
on the natural granular subsoils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placecl on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 2,500 psf. Based on experience, we expect
settlement of footings designed ancl constructed as discussed in this section will
be about %inch or less.
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.
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4)Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least i0 feet.
Foundation walls acting as retaining structures shoulcl also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
All existing fill, topsoil and any loose disturbed soils should be removed and the
footing bearing level extended down to the relatively dense natural granular soils
The exposed soils in footing areas should then be moistened and compacted.
A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation wails 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 45 pcf for backfili consisting
of the on-site granular soils. Cantilevered retaining structures which are separate from the
residence and can be expected to deflect sufficiently to rnobilize the full active eafih pressure
condition should be designed for a lateral eafth pressure computed on the basis of an equivalent
fluid unit weight of at least 35 pcf for backfill consisting of the on-site granular soils.
A1l for"rndation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressllres such as adjacent footings, traffic, construction materiais and equipment. The
pressllres recommended above assrÌffre drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface wili
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 r"rniforrn lifts and compactecl to at least 90%o of the maximum
standarcl Proctor density at a moisture content near optimum. Backf,rll in pavernent and walkway
areas should be compacted to at least 95o/o of the rnaxirnum standard Proctor density. Care
should be talçen 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 corectly, and could result in distress to
facilities constructed on the backfill.
The lateralresistance 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
s)
6)
Kumar & Associates, lnc. @ Project No. 21-7-160
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the side of the footing. Resistance to slicling at the bottorns of the footings can be calculated
based on a coefficient of friction of 0.50. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight o1425 pcf. The
coefÍicient of friction and passive pressure values recommended above assuffre ultimate soil
strength. Suitable factors of safety should be included in the design to lirnit 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 a granular rnaterial compacted to at ieast
95o/o of the maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil and fill, are suitable to support lightly loaded slab-
on-grade construction. 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 requilements 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 50olo retained on the No. 4 sieve
ancl less than2o/o passing the No. 200 sieve.
All fillmaterials for support of floor slabs should be compacted to at least95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site granular soils devoid of vegetation, topsoil and oversized rock.
We recommend vapor retarders confonn to at least the rninimum requirements of ASTME1745
Class C rnaterial. Certain floor types are lnore sensitive to water vapor transmission than others.
For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor
transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum
requirements of ASTM 81745 Class A material. The vapor retarder should be installed in
accordance with the manufacturers' recommendations and ASTM 81643.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that local pelched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. We
recommencl below-grade construction, such as retaining walls, crawlspace and basemettt areas,
be protected from wetting and hydrostatic pressure buildup by an underdrain system.
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The drains should consist of drainpipe placed in the bottorn of the wall backfill surounded above
the invert level with free-draining granular r-naterial. 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 lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo 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 7% feet deep.
SURFACE DRATNAGE
The following drainage precautions should be observed during construction and maintained at all
times after the has been compieted:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfrll should be adjustecl to near optimurn moisture and compacted to
at least 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90%o 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 fiom the foundation in all directions. We recomtnend a minimum
slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of
2Yz inches in the first 10 feet in paveci areas. Free-draining wall backftll should be
covered with filter fabric and capped with about 2leet of the on-site, finer graded,
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 5
feet from foundation walls.
LIMITATIONS
This study has been conductecl in accordance with generally accepted geotechnical engineering
principles and practices in this area at this tirne. 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 drilied at the locations indicated on Figure 1, the proposed type of
constrr-lction 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 freld of
practice should be consulted, Our findings include interpolation and extrapolation of the
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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 pu{poses. 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 veriô'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
ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
Respectfuily Submitted,
K¡¡rnar & Associateso Ïnc.
James H. Parsons, E.I
Reviewed by:
JHPlkac
Kumar & åssociates, lnc. @ Project No.2l-7-1tû
21 -7 -1 60 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1
:
\,lC=2.4
+4=40
-2OO=1 4
so/ 1
BORING 1
EL. 100.0'
BOR¡NG 2
EL. 100.2'
0 0
53/ 12 50/5
5
46/12 50/1
WC=2.4
-/uu=l /
5
COMBINED
50/2
FtJ
t¡JL
IIl-
o_
TJô
10 10
F-
Lrl
l!
L
ITt-
o_tJÊ
66/12 50/6
t3 15
50 /2
20 20
21 -7 -1 60 Kumar & Associates LOGS OF IXPLORATORY BORINGS Fig.2It
LEGEND
TOPSOIL: CLAY, SANDY, GRAVELLY, SCATTERED BOULDERS, ORGANICS, FIRM, MOiST, BROWN
FILL: CLAY, SAND, SCATTERED GRAVEL, HARD' SLIGHTLY MOIST' BROWN
GRAVEL (GM): SANDY, SILTY, DENSE, SLIGHTLY MOIST, MIXED BROWN
i DRTVE SAMPLE, 1 3/B-rNCH l^D. SPLIT SPOON STANDARD PENETRATION TEST
,.I"^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 43 BLOWS OF A 14o_POUND HAMMER+r/ t¿ FALLTNc Jo TNcHES WERE REQU|RED To DRtvE THE SAMPLER 12 lNcHES.
f nnacrrcll AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON FEBRUARY 1,2021 WITH A 4_INCH-DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE TOCATIONS 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 MEASURED BY INSTRUMENT LEVEL AND
REFER To THE BORING I GROUND ELEVATION = 1 00 FEET.
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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTU OOSIS);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
21 -7 -1 60 Kumar & Associates LTGTND AND NOTES Fig.3
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6
100
90
80
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50
40
30
20
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10
20
30
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50
60
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90
=f
100
,oo1 .oo2 .600 r.18 I 2,36 1,75
2,OIN M¡LLIMETERS
9.5 3B.f
DIAMETER OF PA
CLAY TO SILT COBBLES
GRAVEL 40 % SAND
LIQUID LIMIT
SAMPLE 0F: Sllly Sond ond Grovel
46%
PLASTICITY INDEX
SILT AND CLÄY 14%
FROM: Borîng1 @ 4' & '10' (Combined)
Th6s6 losl rosulls opply only'lo lho
somples whlch wore losled. Tho
t6sllng rôporl sholl nol b. roproducâd,
oxcepl în lull, wllhoul lhe wrlH6n
dpprovol of Xumor & Assoclolôs, lnc.
Sl6vô onolysls losllng ls porformod ln
occordqhco wlth ASTM 06913, ASIM 07928,
i\STIJ C136 qnd/or ASTM 01140.
SIEVE ANALYSISHYDROMETER ANALYSIS
U,S. STANDARD SER]ES CLüRTJME READINGS
24 HRS 7 HRS
GRAVELSAND
FINE COARSEFINEMEDTUM ICoARSE
21 -7 -160 Kumar & Associates GRADATION TTST RESULTS Fis.4
lGrtåffii,milfffifniiü'"-"TABLE 1SUMMARY OF LABORATORY TEST RESULTSect No. 21-7-160Silty Sand and GravelSilry Sand and GravelSOIL TYPElpsflUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEX(%\ATTERBERG LIMITS("klLIQUID LIMITPERCENTPASSING NO.2OO SIEVE4I27(k\SAND46GRADATIONGRAVEL%t40locf)NATURALDRYDENSTTY(%lNATURALMOISTURECONTENT1A1A4 and i0combined4tft)DEPTHSAMPLË LOCATIONBORING12