HomeMy WebLinkAboutSubsoil Studyl(+rtirJþilfi'åìÌ'fË:i'[iË;å'*"
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
ernail : kaglenwood@kumarusa.com
wwwkumarusa.com
Office Locations: Denver (HQ), Parke¿ Colorado Springs, Fort Collins, Glenwood Springs, and Surnmit County, Cololado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT H-8
47 SPIRE RIDGE WAY
ASPEN GLEN SUBDIVISION
GARFIELD COUNTY, COLORADO
PROJECT NO. 21-7-852
JANUARY 17,2022
PREPARED FOR:
SMITH MOUNTAIN BUILDERS
ATTN: ZACHSMITH
1011 HERITAGE DRIVE
CARBONDALE' COLORADO 81623
smith mountainbuilders@.sm ail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL...
FIELD EXPLORATION...
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS .
FOUNDATIONS
FLOOR SLABS
IINDERDRAIN SYSTEM ....
SURFACE DRAINAGE...............
LIMITATIONS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
1
a
3-
6-
-3 -
-J-
-3-
5
5
-6-
FIGURE I - LOCATION OF EXPLORATORY BORINGS
1
1
1
Kumar & Associates, lnc. @ Project No. 21-7-852
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot H-8 within Aspen Glen Subdivision, 47 Spire Ridge Way, 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 general accordance with our agreement for
geotechnical engineering services to Smith Mountain Builders dated October 28,2021
A freld 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 analyzedto 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
Development plans for the proposed residence were not available at the time of our study. V/e
assume similar construction to that in the area which typically consists of a I or 2-story structure
with an attached garage. The ground floors will be structural over crawlspace or slab-on-grade.
Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 5
feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The site was vacant and vegetated with grass and weeds at the time of our field exploration. The
terrain ranges from relatively flat to gently sloping down to the east, north, and west with around
3 feet of elevation difference across the general building envelope. Spire Ridge Way is to the
Kumar & Associates, lnc, @ Project No. 21-7-852
1
east, a vacarÍ lot is to the south, Aspen Glen golf course is to the west, and a single-family
residence is to the north.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian-age Eagle Valley Evaporite underlies the subject site. 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.
During previous work in the area, sinkholes have been observed scattered throughout the lower
Roaring Fork Valley. The nearest mapped sinkhole is about 1,000 feet southeast of this lot.
These sinkholes appear similar to others associated with the Eagle Valley Evaporite in this area.
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 H-8 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 November I0,202I. 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-458 drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with l%-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
subsoils. Depths at which the samples were taken and the penetration resistance values are
Kumar & Associates, lnc. @ Project No.21-7-852
-3 -
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, below about I foot of topsoil, consist of about 4/zto 6/zfeet of stiff, sandy silty clay,
underlain by dense, silty cobbly sandy gravel with probable boulders. Drilling in the dense,
coarse granular soils with auger equipment was difficult due to the cobbles and probable small
boulders and drilling refusal was encountered in the deposit at depths of about 9 and 1 1 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and swell-consolidation. Results of a swell-consolidation testing performed on a
relatively undisturbed drive sample of the clay soil, presented on Figure 4, indicate low
compressibility under existing low moisture conditions and light loading and moderate to high
compressibility after wetting under increased loading. The natural moisture content and
relatively low dry density indicates the clay soils may be prone to settlement (collapse potential)
when wetted. Our experience in this area indicates the soils typically have a low collapse
potential when wetted under load. The laboratory test results are summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The natural sandy silty clay soils within about the upper 5%to7/zfeet are typically low density
and compressible especially when wetted. The underlying coarse granular soils possess a
moderate bearing capacity and a relatively low settlement potential. At assumed excavation
depths, we expect the subgrade will expose sandy silty clay soils and, possibly, sandy, cobbly
gravel soils. Spread footings should be feasible for foundation support of the residence with a
risk of settlement if the clay soils become wet.
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, lnc. o Project No, 21-7-852
-4-
on the natural soils or properly compacted structural fill. The bearing level could be extended
through the clay soils down to the underlying dense, coarse granular soils to reduce the
settlement potential and should be fuither evaluated at the time of construction.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural clay soils should be designed for an
allowable bearing pressure of 1,500 psf. Footings placed entirely on the natural
granular soils or compacted structural fill should be designed for an allowable
bearing pressure of 3,000 psf. Based on experience, 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 settlement of around lzto I inch if the clay
bearing soils are wetted.
2) The footings should have a minimum width of 18 inches for continuous walls and
2 feel 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 12 feef.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
55 pcf for the on-site fine-grained soil as backfill.
5) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the natural soils. The exposed soils in footing
area should then be moistened and compacted to a minimum of 95Yo of the
standard Proctor density. If needed, structural hll used to reestablish design
footing bearing level in sub-excavated clay soil areas should consist of imported
3/o-inch road base and extend at least I% feet beyond footing edges and be
compacted to at least 98% of standard Proctor density at near optimum moisture
content.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & Associates, lnc. @ Project No. 2'l-7-852
5
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction with the accepted risk of movement with clay soil subgrade. The risk of movement
can be reduced by placing slabs-on-grade on a minimum of 2 feet of compacted structural fill or
by using structural floors over crawlspace, which is commonly done in the area. The structural
fill should consist of CDOT Class 5 or 6 base course material.
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 sand and gravel base
course should be placed beneath floor slabs-at-grade for support. This 4-inch thickness can be
included in the recommended2 feet of base course below the slabs. A minimum 4-inch layer of
free-draining gravel should be placed beneath basement level slabs (if any) to facilitate drainage.
This material should consist of minus 2-inch aggregate with at least 50o/o retained on the No. 4
sieve and less than 2Yo passingthe No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill, below the
recommended depth of base course, can consist of the on-site soils devoid of debris, topsoil and
oversized rocks þlus 4-inch).
I.INDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can also create a perched condition. We
recommend below-grade construction, such as retaining walls and deep crawlspace areas, be
protected from wetting and hydrostatic pressure buildup by an underdrain system. An
underdrain should not be placed around shallow crawlspace areas to help limit the potential for
wetting the bearing soils.
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
Kumar & Associates, lnc, @ Project No. 21-7-852
-6-
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/o passingthe 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 llz feet deep.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be very important to limiting potential
wetting of the bearing soils and potential building movement and distress. 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 95o/o of the maximum standard Proctor density in pavement and slab areas
and to at least 90To 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. V/e recommend a minimum
slope of 6 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
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
5 feet from foundation walls.
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 l, 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
Kumar & Associates, lnc, o Project No, 21-7-852
-7 -
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 recoÍlmendations 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 verifu that the recoÍrmendations
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. fnc.
Mark Gayeski,
Reviewed By:
Daniel E.
DEHlkac
T
e:r(>øf>
Kumar & Associates, lnc.'l Project No.21-7-852
\
\
'.E
BORING 1o
Êi
Ë
,ìt
Ét
È
6ocÞ
""é
åi!
ê
)
,606Àt
'ts
Þo,
\l
¡
)-:
tì
rÀ
r,i
s
qô.,4t
%
':,:"
BORING 2o
""d,
t.'tr
1.,''l
i'.'.
[. 1
''I
4
uñ'
%o,
-!
6
I*::
!
t
ï--
.it
¡t
'-È
:È
':.
:
i¡.
15 0 15 30
APPROXIMATE SCALE_FEET
I
s
\\
¡\
s
21 -7 -852 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
ı
.;
É
BORING 1
EL. 6063.5'
BORING 2
EL. 6062'
0 0
5 Ã
!-
LJ
L'JtL
I-t"-
o_t¡lo
13/ 12
WC= 1 0.0
DD=92
11 /6, 35/6 F-
t¡J
t¡JtL
ITF
o_
LJÕ
50/ 4.s
10 1050/5.s
15 15
21 -7 -852 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
9
I
I
Ê
¡
8,,'
JIrÌ
,i
5'í
5s
LEGEND
TOPSOIL; CLAY, SANDY, SILTY, FIRM, MOIST, BROWN TO DARK BROWN
CLAY (CL); SILTY, SANDY, STIFF, SLIGHTLY MolST, BROWN, TRACE POROSITY AND TRACE
CALCAREOUSNESS.
GRAVEL (GM); SANDY, SILTY WITH COBBLES AND PROBABLE SMATL BOULDERS, DENSE,
SLIGHTLY MOIST, TAN AND LIGHT GRAYISH-TAN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
i DR|VE SAMPLE, 1 5/8-rNCH l.D. SPLIr-SPOoN STANDARD PENETRATION TEST
A2I ^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 15 BLOWS OF A 14o-POUND HAMMERtr/ tz FALLTNc Jo TNcHES wERE REQUIRED To DRtvE THE sAMpLER 12 tNcHES.
I PRACTICAL AUGER REFUSAL.
NOTES
THE EXPLORATORY BORINGS WERE DRILLED ON NOVEMBER 10, 2021 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.
5. 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 TRANSIÏIONS 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 (PCt) (ISTV D2216),
21 -7 -852 Kumar & Associates LEGEND AND NOTES Fig.3
E
ò
I
SAMPLE OF: Sondy Silty Cloy
FROM:Boringl@5'
WC = 1O.O %, DD = 92 pcf
NO MOVEMENT UPON
WETTING
in
tæt rdultg
tdt d. ftg
w¡th
1
J)
t¡J
=tt1
I
z.otr
ô
=o
t/1zo()
0
-l
-2
-5
-4
-5
-6
-7
t PRESSURE - KSF 10 100
21 -7 -852 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
I (+rt irffi [åifËfni':,Í å *' "TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.2l-7-852Sandy Silty ClaySOIL TYPElpsf)UNCONFINEDCOMPRESSIVESTRENGTH("/"1PLASTICINDEXATTERBERG LIMITS(ololLIQUID LIMITPERCENTPASSING NO.200 stEvESAND(%)GRADATION$tGRAVELlpcf)NATURALDRYDENSI'fY10.092IololNATURALMOISTURECONTENT(fr)DEPTH5SAMPLE LOCATIONBORING1