HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.21.2023rcn f,xffil[1{ifffif*'"'s;''
**5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RI,SIDENCE
LOT t4, FTLTNG 1, PTNYON MESA
129 SAGE MEADOW ROAD
GARFTELD COUNTY, COLORADO
.JUl" 2 3 202tt
GARFIELD COIJNTY
COM?,{ U I.IITY DEI'ELCPMENT
PROJECT NO. 23-7-344
AUGUST 21,2023
PRT,PARED FOR:
MS SERVICES
ATTN: MIGUEL SALVIDREZ
274 CEDAR WAY
NEW CASTLE, COLORADO 81647
ms22services@email.com
$
.a\t
.$
-\\:5
aN
TABLE OF'CONTENTS
PURPOSE AND SCOPE OF STUDY ....
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 -SWELL-CONSOLIDATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
I
,...- 1 -
FIELD EXPLORATICN ...............- 2 -
1
7
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS .....................- 3 -
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM
4-
5-
-5-
Kumar & Associates, lnc. o Project No. 23-7-344
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot 14, Filing l, Pinyon Mesa, 129 Sage Meadow Road, 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 MS Services dated June 7,2023.
Subsurface evaluation consisting of an exploratory boring 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, expansion-compression potential 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, design recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
Development plans for the lot were conceptual at the time of our study. The proposed residence
is planned to be a two-story structure over a crawlspace with an attached garage. The garage
floor will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut
depths between about 3 to 8 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 property is vacant and vegetated with grass and weeds with sage brush on the northem part
of lot. The front part of the lot was graded for the road construction and vegetation was sparse.
The ground surface is moderately sloping in the northern part to gently sloping in the southern
building envelope area down to the southwest.
SUBSIDENCB POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Pinyon Mesa
Development. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone
and limestone with some massive beds of gypsum. There is a possibility that massive gypsum
deposits associated with the Eagle Valley Evaporite underlie portions of the property.
Kumar & Associates, lnc. @ Project No. 23-7-344
a-L-
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 River valley.
No evidence of subsidence or sinkholes was observed on the property or encountered in the
subsurface materials, however, the exploratory boring was relatively shallow, for foundation
design only. Based on our present knowledge of the subsurface conditions at the site, it cannot
be said for ceftain that sinkholes will not develop. The risk of future ground subsidence at the
site throughout the service life of the proposed structure, in our opinion is low, however the
owner should be a-ware of the potential fbr sinkhole clevelopment. I f lurther investigation of
possible cavities in the bedrock below the site is desired, we should be contacted.
F'IELD EXPLORATION
The field exploration for the project was conducted on June 7, 2023. An exploratory boring was
drilled at the location shown on Figure I to evaluate the subsurface conditions. The boring was
advanced with 4-inch diameter continuous flight augers powered by a truck-mounted CME-45B
drill rig. The boring was 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 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils, below about one foot of topsoil, consist of mixed sandy silt and clay with gravelto
about l0% feet underlain by sandy silty clay to about 2l feet. A 3-foot-thick layer of more
gravelly soils was encountered between 10% and 14 feet.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density and finer than sand size gradation analyses. Results o1'swell-consolidation
tests performed on relatively undisturbed samples taken lrom the boring, preseltted on Figure 3
typically show low compressibility under light loading and natural low moisture and moderate
compressibility under additional loading after wetting. The sample from 15 feet deep showed a
low expansion potential when wetted. The laboratory testing is summarized in Table l.
Kumar & Associates, lnc. @ Project No. 23-7-344
-3-
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
molst.
F'OUNDATION BEARING CONDITIONS
The upper mixed sandy silt and clay soils encountered in the boring at typical shallow foundation
depth are relatively low density and mainly tend to settle when they become wetted. The tested
sample from l5 feet deep indicated a low expansion potential but our experience on nearby lots
is that the subsoils are typically settlement prone. A shallow foundation placed on these soils
will have a risk of settlement if the underlying soils become weffed and care should be taken in
the surface and subsurface drainage around the house to prevent the soils from becoming wet. It
will be critical to the long-term performance of the structure that the recommendations for
surface grading and drainage contained in this report be followed. The amount of settlement, if
the bearing soils become wet, will mainly be related to the depth and extent of subsurface
wetting but may result in settlements of around I to 2 inches which could cause building distress.
Mitigation methods such as a deep foundation (piles or piers extending down around 20 feet
below existing ground surface) or removing and replacing the bearing soils as compacted
structural fill could be used to support the proposed house with a lower risk of settlement. If a
deep foundation is desired, we should be contacted to provide additional design
recommendations.
DESIGN RECOMMENDATIONS
FOL]NDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
natural soils at basement level with a risk of movement. Compacted structural fill should be
used for shallow depth footings such as for the garage or crawlspace.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the natural soils at basement level or on compacted structural
fill in shallower cut areas should be designed for an allowable bearing pressure of
J40 prf. The garage footing areas should be sub-excavated down about 7 feet
belowEEiinflground surface and the excavated soil replaced as compacted
structural fiIl back to design grade. The sub-excavation should extend down at
least 4 feet below the footing bearing level. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this section
will be about 1 inch or less. Additional differential settlements of about Yz to
1 inch could occur if the bearing soils are wetted.
Kumar & Associates, lnc. @ Project No. 23-7-344
4
3)
The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
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
atea.
Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupporled length of at least l4 feet.
The foundation should be configured in a box like shape to help resist differential
movements. 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.
The topsoil, sub-excavation depth and any loose or disturbed soils should be
removed below the foundation area. The exposed soils in footing areas after sub-
excavation should then be moistened and compacted. Structural fill should
consist of low permeable soil (such as the on-site sandy silt and clay soils)
compacted to at least 98% of standard Proctor density within 2% of optimum
moisture content. The structural fill should extend laterally beyond the footing
edges equal to at least %the fill depth below the footing.
A representative of the geotechnical engineer should evaluate the fill placement
for compaction and observe all footing excavations prior to concrete placement.
4)
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 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 earth pressure computed on the basis of an equivalent
fluid unit weight of at least 45 pcf for backfill consisting of the on-site fine-grained soils.
All foundation and retaining structures should be designed for appropriate hydrostatie 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 lbundation wall or retainirrg structure. An underdrairr
should be provided to prevent hydrostatic pressure buildup behind walls.
2)
s)
6)
Kumar & Associates, lnc, @ Project No. 23-7-344
5
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95o/o 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 eatth 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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 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 95o/o 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 with a settlement risk similar to the foundation if the underlying soils are wetted.
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 controljoints 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 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 50% retained on the No. 4 sieve and less than
2Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95%o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site soils devoid of vegetation and topsoil.
LTNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where clay soils are present, that local perched groundwater can develop during
Kumar & Associates, lnc, @ Project No. 23-7-344
-6-
times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a
perched condition. We recommend below-grade construction, such as retaining walls and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. An underdrain should not be provided around slab-at-grade garage and shallow
crawlspace areas to help limit potential wetting of bearing soils from shallow water sources.
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 lo/oto
a suitable gravity outlet or sump and pump. Free-draining granular material used in the
underdrain system should contain less than 2%o 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 1Yz feet deep. An impervious membrane such as 30 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 DRAINACtr
Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting
building settlement. The following drainage precautions should be observed during construction
and rnaintained continuously 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 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 from the foundation in all directions. We recommend a minimum
slope of l2 inches in the first l0 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
covered with filter fabric and capped with at least2 feet of the on-site soils to
reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill. Graded surface swales should have a minimum slope of 3%.
5) Landscaping which requires regular heavy irrigation should be located at least
5 feet from foundation walls. Consideration should be given to use of xeriscape
to reduce the potential for wetting of soils below the building caused by irrigation
Kumar & Associates, lnc. @ Project No. 23-7-344
-7 -
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this areaat the time of this study. 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 boring drilled at the location 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,
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 boring
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 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 verif' 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,
Kumar & Associates,
Daniel E. Hardin,
Reviewed by:
@-,/-
Steven L. Pawlak, P.E
SLPlkac
Kumar & Associates, lnc. s Project No. 23-7-344
I
..au
i
f
,
!
,i.
i
I
:
.'
i
it,
I
II
1
.{
t
$
!
I
I
t
1
I
It
I
l
I
I
IJ
.H-fG-F*f(-D
o
BORING 1
rttn -lrt alrrt g;] afl fl
1 29 SAGE MEADOW ROAD
l1
I
I
I
I
I
I
I
I
I
NOT TO SCALE
23-7 -344 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1
E
a
BORING 1 LEGEND
N
TOPS0|L; ORGANIC SANDY SILTY CI,AY, SCATTERED GRAVEL,
SOFT, MOIST, DARK BROWN.
10/12
WC=5.4
DD=94
-200=56
CLAY (CL); SILTY, SANDY, SCATTERED GRAVELLY LAYERS,
SLIGHTLY CALCAREOUS, STIFF TO VERY STIFF AT DEPTH,
SLIGHTLY MOIST, LIGHT BROWN.
5
14/12
WC=6.3
DD= 1 00
GRAVEL (GM); SANDY, SILTY, WITH POSSIBLE C0BBLES, MEDIUM
DENSE, SLIGHTLY MOIST, BROWN.
i DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
10 8/6, 50/5
WC=6.9
DD=88
-200=73
rnr,oDR|VE SAMPLE BLOW COUNT. INDICATES THAT 10 BLOWS 0F
'ut '' A 14o-pouND HAMMER FALLTNG Jo rNcHEs WERE REQUTRED
TO DRIVE THE SAMPLER 12 INCHES.Ft!
LrllL
I-F(L
LJo
15 NOTES
24/12
WC=6.0
DD=1 10
THE EXPLORATORY BORING WAS DRILLED ON JUNE E, 2023 WITH
A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER,
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE
SITE PI,AN PROVIDED.
20
30/12 3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT
MEASURED AND THE LOG OF THE EXPLORATORY BORING IS
PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED
ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
25 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE
TIME OF DRILLING.
7, LABORATORY TEST RESULTS:
WC = WATER OONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
-200 = PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1 1 4o).
Fig, 223-7 -344 Kumar & Associates LOG OF EXPLORATORY BORING
SAMPLE OF: Slliy Sondy Cloy
FROM:Boringl@5'
WC = 6.3 %, DD = 100 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING--
L
)
t00
100
10PRESSURE - KSF
1
0
-1
-2
-3
-4
1
0
-1
JJ
LJ
=a
I
zo
L
o
=oaz.oo
Jtrl
=a
I
zotr
o
Joaz.oo
SAMPLE OF: Sondy Silly Cloy
FROM: Boring 1 @ 15'
WC = 6.0 "1, DD = 1 10 pcf
l
l
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
:
:
I
l
l
+
i
I
I
I
j
r nda tan Eu[! oPPry onDr ro th.
Bqmpl€ l6td. lhe tQting r.pod
lholl not b rop.du6d, .rc.pt in
full, xithout th6 vrihn oppdol ot
Kum. ond As6iob, lnc, Sr.ll
bnlolidotion tdtiq tsrfomd in
offidoncc slth relM D-S48.
23-7 -344 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
E
I
rcn liffif;ffi:ffiii:'i**
:'
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23-7-344
sailpt F I ocATtoN GRA ATION ATTERBERG LIMITS
PERCENT
PASSING NO.
200 stEvE
LIQUID LIMIT
tot"l tol
PLASTIC
INDEX
tnrll
UNCONFINED
COMPRESSIVE
STRENGTH SOIL TYPEBORING
lftt
DEPTH
Iokl
NATURAL
MOISTURE
CONTENT
(ocfl
NATURAL
DRY
DENSITY
GRAVEL
("h\
SAND
$t
94 56 Gravelly Sandy Silty
Clay125.4
Silty Sandy Clay56.3 100
73 Sandy Silty Clayl06.9 88
l5 6.0 1r0 Sandy Silty Clay