HomeMy WebLinkAboutSubsoil Report for Foundation DesignT(+A Kurmr & Assoolate, lnc."
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.comAn Employcc Oryncd Gompony
Office Incations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
May 2,2023
TE Builders
Attn: Jimmy Terui
7380 County Road 100
Carbondale, Colorado 81623
jt@tebuilders.net
Project No. 23-7-177
Subject: Subsoil Study for Foundation Design, Proposed Residence, 237 Rusty Spur Trail,
Garfield County, Colorado
Gentlemen:
As requested, Kumar & 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 TE Builders dated March 6,2023. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed residence will be a2-story, slab-on-grade structure
located on the site as shown on Figure l. The existing building will be renovated and supported
by a new foundation. The second level deck will be supported by several new isolated piers.
Cut depths are expected to range between about 3 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 ground surface is gently sloping through the building site then moderately
sloping beyond the building site down to the northeast as indicated by the contour lines shown on
Figure 1. Vegetation consists of grass and weeds.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing two
exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about Yzfoot of topsoil or clay fill soil,
consist of very sandy silt and clay to very silty sand down to the pit depths of 8 feet. Results of
swell-consolidation testing performed on relatively undisturbed soil samples, presented on
Figures 3 through 5, indicate low compressibility under existing moisture conditions and light
loading and a low to moderate collapse potential (settlement under constant load) when wetted.
The laboratory test results are summarizedin Table 1. No free water was observed in the pits at
the time of excavation and the soils were slightly moist to moist.
N.q
\s\
\
-2-
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, spread footings placed on the
undisturbed natural soil designed for an allowable soil bearing presstlre of 1,000 psf can be used
for support of the proposed residence with a settlement risk. The soils are compressible mainly
after wetting and there could be post-construction foundation settlement of around I to 2 inches
depending on the depth and extent of wetting. Footings should be a minimum width of 24 inches.
Loose and disturbed soils and existing fill encountered at the foundation bearing level within the
excavation should be removed. The exposed soils should then be moisture treated to near
optimum and compacted. We should observe the completed excavation for bearing conditions
prior to placing footing forms and steel reinforcement. 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 14 feet. Foundation walls acting as retaining structures (if any)
should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at
least 55 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used 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 such as road base should be placed beneath slabs
for support. This material should consist of minus 2-inch aggregate with less than 50oh passing
the No. 4 sieve and less than lLYo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite soils devoid of vegetation, debris and topsoil.
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
and should not be provided. 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 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. A shallow crawlspace should not need to be protected
with an underdrain with proper foundation wall backfill and surface grading.
Kumar & Associates, lnc. @ Project No. 23-7-177
J
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: Proper surface grading and drainage will be critical to preventing subsurface
wetting and building distress. 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 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 irrigation should be located at least 10
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
express or implied. The conclusions and recommendations 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
Kumar & Associates, Inc. o Project No. 23-7-177
-4-
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verify 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, lnc.
Steven L. Pawlak, P
Reviewed by:
Daniel E. Hardin, P.E.
SLPlkac
Attachments: Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figures 3 through 5 - Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
cc: Evolve Structural Design - Steve Edmiston (stevefde.volvestructural.com)
I
U'15222
Kumar & Associates, lnc. o Project No. 23-7-177
TRACT 30
17.o2 ACRES
50 60
APPROXIMATE SCALE-FEET
23-7 -177 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
I
PIT 1
EL. 5,659'
Pt't 2
EL. 5,960'
0 0
WC=16.4
DD= 1 Ol F
LrJ
UJL-
IIFo-
Ldo
FlrJl^lL
I
:EFo-
LJo
5
WC=8.5
DD=92
WC=16.4
DD= 1 03
-2OO=57
5
WC=9.1
DD=96
-2OO=41
WC=5.6
DD=99
10 10
LEGEND
TOPSOIL; ORGANIC SANDY SILT, FIRM, MOIST, DARK BROWN.
FILL: SANDY SILTY CLAY WITH ORGANICS AND DEBRIS, FIRM, MOIST' BROWN.
5AND AND S|LT (SM-ML); SLIGHTLY CLAYEY, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST
TO MOIST, BROWN.
slLT AND CLAY (ML-CL); VERY SANDY, MEDIUM STIFF' MOIST' BROWN.
F
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON APRIL 6, 2023.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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 (PCI) (ASTU D 2216);
-2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1 1 4o).
23-7 -177 Kumar & Associates LOGS OF EXPLORATORY PITS Fis. 2
I
SAMPLE OF: Sondy Silt
FROM: Pit 1 Gt 5'
WC = 8.5 %, DD = 92 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
td
qffi 0-43i6.
2
0
2
-4
-6
-8
-10
-12
bq
JJ
lrJ
=tn
I
zo
F
o
=oaz.oo
PRESSURE - KSF t0
Fig. 3SWELL_CONSOLIDATION TEST RESULTS23-7 -177 Kumar & Associates
I
SAMPLE OF: Sondy Silt ond Cloy
FROM:Pit2(r.3'
WC = 16.4 %, DD = 101 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1
I
)
)
\
\
\
I
I
l
l
\\
\
\
I
t
l
t
I
I
l
l
I
I
l
l
llls tad @ub opPly dly b h
sfipb t.!trd, thc t-!n9 nFort
tEt rct ba raproduc.(t, .x6pt ln
tull, wfthout thc s,lthn opp'@l ol
(umor ond Alroolotc. 1rc. Smll
Cotulldltlon tstlng grtonn d ln
o@don6 rlth Astu 0-,+5{8.
1
0
1
2
5
-4
-5
-6
x
JJlrl
=a
I
z.o
F
o
=o
U'zo
C)
PRESSURE - KSF 10
Fig. 423-7 -177 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS
SAMPLE OF: Sondy Slll ond Cloy
FROM:Pit2@7'
WC = 5.6 %, DD = 99 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
{
I \\
\)
j
j
ot
dty
t.0 t00
2
0
N
J-| -z
LrJ
=th
t-4
zo
F
$-ooazoo-g
23-7 -177 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
I
€
I
l(+r\fffififfiffinr':;'i**
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23-7-177
Sandy Silt and Clay
Very Sandy Silt and Clay
Sandy Silt and Clay
SOILTYPELIQUID tIMTf
UNCONFINED
c0iltPRESstvE
STRENGTH
PTASTIC
INDEX
Sandy Silt
Very Silty Sand4l
57
PERCENT
PASSING NO.
200 srEvE
SAND
$t
GRADATION
(%)
GRAVEL
101
103
99
NATURAL
DRY
DENSITY
{ocfl
92
96
t6.4
5.6
{'/"1
NATURAL
MOISTURE
CONTENI
8.5
I9
16.4aJ
5
7
(ft)
DEPTH
5
7
SAIIPLE LOCATON
PlT
1
2