HomeMy WebLinkAboutSubsoils Report for Foundation DesignI CA niffi fi'^Ttfflt:fn'i vi' * "
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
lax: (970) 945-8454
ernai I : kaglenwood@kumarusa.com. www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Surntnit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
435 BROOKIE
LOT M-10, ROARING FORK MESA
ASPEN GLEN
GARFIELD COUNTY, COLORADO
PROJECT NO.20-7-474
SEPTEMBER 25,2020
PREPARED FOR:
RM CONSTRUCITON
ATTN: BLAKE PILAND
5O3O COUNTY ROAD 154
GLENWOOD SPRINGS, COLORADO 81623
@
TABLE OF CONTENTS
PTJRPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION ..
SITE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS ..,
FOUNDATION BEARING CONDITIONS ...
DESIGN RECOMMENDATIONS ....
FOUNDATIONS .......
FOLINDATION AND RETAINING WALLS
FLOOR SLABS
LTNDERDRAIN SYSTEM
SURFACE DRAINAGE....
LIMITATIONS..
FIGTJRE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
1
1
1
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1
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Kumar & Associates, lnc. @ Project No. 20'7-474
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot M-10, Roaring Fork Mesa, Aspen Glen, 435 Brookie, 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 RM Construction dated August 21,2020.
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 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
The proposed residence will be a one or two story wood framed structure with attached garage.
Ground floor will be slab-on-grade or structural over crawlspace. Grading for the structure is
assumed to be relatively minor with cut depths between about 2 to 5 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 subject site was vacant at the time of our field exploration. The ground surface is sloping
down to the east at a grades between 5 and 10 percent with a steep slope of approximately
50 percent at the west end of the lot. Vegetation consists of grass.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen
development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and
Kumar & Associates, lnc. @ Project No. 20-7-474
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, several sinkholes were
observed scattered throughout the Aspen Glen development. These sinkholes appear similar to
others associated with the Eagle Valley Evaporite in areas of the Roaring Fork 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 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 M-10 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 August 24,2020. Two exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
The borings were advanced with 4 inch diameter continuous flight augers powered by a truck-
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
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
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 consist of about Yzfoot of topsoil (rootzone) overlying medium stiff, sandy clay to
between I0% and 15 feet further underlain by up to 4 feet of medium dense silty sand to depths
between 11 and 19 feet. Dense, silty sandy gravel was encountered below the sand to the
Kumar & Associates, lnc. @ Project No. 20-7-474
.J
maximum explored depth of 22 feet. Drilling in the dense granular soils with auger equipment
was difficult due to the cobbles and boulders and drilling refusal was encountered in Boring 1.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, density and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples, presented on Figure 4, indicate low to moderate
compressibility under existing moisture conditions and light loading and nil to low expansion
potential when wetted. Results of gradation analyses performed on small diameter drive samples
(minus \%-inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory
testing is summarizedrnTable 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The shallow clay soils encountered at the site possess a low bearing capacity and varied low
compressibility potential to low expansion potential when wetted. The expansion potential
exhibited by the sandy clay could be a localized anomaly and the expansion potential of the
subgrade clay soils should be further evaluated at the time of excavation.
DESIGN RE,COMMENDATIONS
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
on the natural soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 2,000 psf. Based on experience, we expect
settlementoffootingso.,lg;"duG;tructedasdiscussedinthissectionwill
be about I inch or less. The expansion potential of the clay soils should be further
evaluated at the time of construction.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
Kumar & Associates, lnc. @ Project No. 20-7-474
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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 least36 inches below exterior grade is typically used in this
area.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 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.
All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the relatively dense natural granular
soils. The exposed soils in footing area should then be moistened and compacted
If water seepage is encountered, the footing areas should be dewatered before
concrete placement.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
4)
s)
6)
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 50 pcf for backfill consisting
of the on-site fine-grained 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 eafth pressure computed on the basis of an equivalent
fluid unit weight of at least 40 pcf for backfill consisting of the on-site fine-grained 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
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 90Yo of the maxrmum
standard Proctor density at a moisture content slightly above optimum. Backfill in pavement and
walkway areas should be compacted to at least 95Yo of the maximum standard Proctor density.
Kumar & Associates, lnc. @ Project No. 20-7-474
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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 0.30. 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 a nonexpansive material compacted to at
leastg1%o of the maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, 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 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 should be placed beneath slabs for supporl. This material should
consist of minus 2-inchaggregate with at least 50% retained on the No. 4 sieve and less than
l2o/o passing the 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 fiIl can consist of an
imported granular soil such as'/o-inchroad base devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN 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 create a perched condition. We
Kumar & Associates, lnc. @ Project No. 20-7-474
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recommend below-grade construction, such as retaining walls, crawlspace and basement areas (if
any), 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 I foot below lowest adjacent finish grade and sloped at a minimum 7o/o to
a suitable gravity outlet or drywell. 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 I%feet
deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel
in a trough shape and attached to the foundation wall with mastic to prevent wetting of the
bearing soils.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) 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 95%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90Vo 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
capped with about 2 feetof 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
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
Kumar & Associates, lnc. @ Project No. 20-7-474
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from the exploratory borings drilled at the iocations 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 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 expioratory 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 reconlmendations may be made.
This report has been prepared for the exclusive use by our client fbr 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 reconlmendations, and to veri$z that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
l{ils$ar' & Assceiat*s, 6rxe"
H. Parsons, E.I.
Reviewed by:
Daniel E. Hardin,
JHPikac
cc: RM Gr qir(tt) tlul I i'i u1lilr r r.r1,eqqi)
Kumar & Associates, lne" "'[ircjer:t No. ?S"7-474
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f:
LOT M- 1O
o
BORING 1
o
BORING 2
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EROOK/E
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APPROXIMATE SCALE-FEET
20-7 -47 4 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1
EL. 105.5'
BORING 2
EL. 1 01 .5'
0 0
33/12
5 5e/12
WC=11.0
DD= 1 09
-2QO=74
18/ 12
WC=8.0
DD=110
10 10
F
LJ
trJ
LL
IIFo-
LJo
7/12
WC=13.1
DD=98
16/ 12 F
LJ
trJu-
ITF(L
LrJo
15 15
1O/ 12 so/3.5
20 2063/6
WC=1.9
+4=58
-200=1 1
25 25
20-7 -47 4 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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x:
LEGEND
TOPSOIL; ROOTZONE, SAND, SILTY, CLAYEY, ORGANICS, SCATTERED GRAVEL, FIRM, SLIGHTLY
MOIST, BROWN.
CLAY (CL); SANDY, SLIGHTLY SILTY, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST TO MOIST,
DARK RED/BROWN.
SAND (SM); SILTY, LOOSE, MOIST, BROWN
W
!
i
GRAVEL (CV); SANOY, SILTY, DENSE, SLIGHTLY MOIST TO MOIST, BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
DRTVE SAMPLE, 1 s/S-tNCH t.D. SPLIT SPOON STANDARD PENETRATIoN TEST
zz/it DRIVE SAMPLE BLOW COUNT. INDICATES THAT 55 BLOWS OF A 14O-POUND HAMMERrrl t z FALLTNG Jo TNcHES wERE REQUTRED To DRtvE THE sAMpLER 12 tNcHES.
PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 24, 2O2O 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 MEASURED BY HAND LEVEL AND REFER
TO THE GROUND SURFACE AT THE PHONE BOX AS 1OO'ESTIMATED.
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 (PCt) (ISTV D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6915);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140).
t
LEGEND AND NOTES Fig. 320-7 -47 4 Kumar & Associates
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:i
I
SAMPLE OF: Sondy Cloy
FROM: Boring 1 @ 10'
WC = 13.1 %, DD = 98 pcf
NO MOVEMENT UPON
WETTING
JJ
Ld
=a
I
zo
F
o
=ov,z.oo
1
0
-1
2
-3
-4
t,0 APPLIED PRESSURE - KSF 10 100
JJIJ
=a
I
zotr
o
Jo
UIz.o()
2
1
0
-1
-2
1.0 APPLIED 100
SAMPLE OF: Sondy Cloy
FROM:Boring2@5'
WC = 8.0 %, DD = 110 pcf
ln
to th.
t.!t d. fte
not b! raprcduc€d,
Yithout thr rrittrn opprovol ot
ond furociotr!, lnc. Sr€ll
ln
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
20-7 -47 4 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
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HYDROMETER ANALYSIS SIEVE ANALYSIS
TIMS READINCS
24 HRS 7 HRS #n rln Jad
CLEAR SQUARE OPENINOS
a/e" a//' I 1 /r' !i 5"6' I
/
/
/',
ti
l;
I
6
E
too
90
ao
70
8o
50
10
50
20
t0
0
'to
20
50
at)
50
60
70
so
90
too
zI
ei
0 .I
.o0t .oo2 .o05 .oo9 .ol9 5a.t 127
-125 2.O 152
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 3A % SAND 51
LIQUID LIMIT
SAMPLE OF: Slightly Sllty Grovel ond Sond
%
PLASTICITY INDEX
SILT AND CLAY 11 %
FROM:BorlnglO2O'
fh€so l€sl r€sulh opply only lo th!
somple! whlch wsre lo!16d. The
hlllng roporl eholl nol b! roproduccd,qxcrpt ln full, wlthoul lhe wrltlsn
opprovol of Kumqr & Asloclolos, lnc,
Slev. qnqlylls lesllng ls plrformld ln
occordqnc€ wlih ASTil 06915, ASTM D7928,
ASTM C156 ond/or ASTM Dl1110.
SAND GRAVEL
MEDTUM lCOlnSE FINE COARSEFINE
20-7 -47 4 Kumar & Associates GRADATION TEST RESULTS Fis. 5
rcn Xurmr & Associates, lne.@
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No. 20-7-474
Slightly Silty Gravel and
Sand
SOIL TYPE
Sandy Clay
Sandy Clay
Sandy Clay
(osfl
UNCONFINED
COMPRESSIVE
STRENGTH
(olol
PLASTIC
INDEX
74
ATTERBERG LIMITS
(%l
TIQUID LIMIT
PERCENT
PASSING NO.
200 stEVE
I1
f/t
SAND
15
GRADATION
(%)
GMVEL
38
(ocfl
NATURAL
DRY
DENSITY
109
98
110
9I
8.0
{%)
NATURAL
MOISTURE
CONTENT
11.0
1
aJ1l0
20
5
(ft)
DEPTH
5
SAMPLE LOCATION
BORING
1
2