HomeMy WebLinkAboutSubsoil Studylcrt Kumar & Associates, lnc.'
Geotechnical and Materials Engineers
and Environmental Scientists
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Ofiìce Locations: Denver (HQ), Parker, Colorado Springs, FoÍ Collins, Glenwood Springs, and Summit County, Colorado
January 4,2021
Shane David
David Electric
2241Dolores Way
Carbondale, Colorado 81623
s.david@davidelectric.us
Project No. 20-1 -230.0 1
Subject: Subsoil Study for Foundation Design, Proposed Swimming Pool, South of
Residence, 422La Casita Road (CR 162),Lot 21 Stirling Ranch, Garfield County,
Colorado
Dear Shane:
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 you dated October 20,2020. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report. The previous geotechnical investigation report by CTL Thompson dated
January 4,2019, their Project No, GS0631 1.000-120, contains recommendations for pool design
and construction.
Proposed Construction: The proposed pool will be located just south of the existing residence
(which is under construction) as shown on Figure 1. The in-ground pool will be 4%to 7 feet
deep. The pool will be roughly 20 feetby 50 feet in plan size. There will be pool decks on all
sides from 7 to 20 feet wide. Cut depths are expected to range between about 6 to 8 feet. 'We
assume that the pool will be constructed of reinforced shotcrete. 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 residence was under construction at the time of our site visit on
October 20,2020. The pool area had been stripped of topsoil and leveled to about 2%to 3 feet
lower than the nearby residence floor elevation.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
four exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about lYz to 2 feet of clay fill in Pits 1
"|
and 4, consist of medium stiff to stiff, sandy silty clay down to the maximum depth explored,
8/z feet. Results of swell-consolidation testing performed on relatively undisturbed samples of
the sandy silty clay, presented on Figures 3 to 5, indicate low compressibility under existing
moisture conditions and light loading and a low collapse potential (settlement under constant
load) when wetted. The clay soils were moderately compressible under increased loading after
wetting. The laboratory test results are summarized in Table 1. No free water was observed in
the pits at the time of excavation and the soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend the shotcrete pool
be placed on the undisturbed natural clay soil designed for an allowable soil bearing pressure of
1,200 psf for support of the proposed pool. The soils tend to compress after wetting and there
could be some post-construction foundation settlement. Loose and disturbed soils and existing
fill encountered at the pool bearing level within the excavation should be removed and the
bearing level extended down to the undisturbed natural soils. We should observe the completed
excavation for bearing conditions. Foundations should be protected against frost as needed.
Pool side walls should be reinforced top and bottom to span local anomalies such as by assuming
an unsupported length of at least 10 feet. The pool walls acting as retaining structures should be
designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least
50 pcf for the on-site soil as backfill.
Pool Deck 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, slabs-
on-grade should be separated from all bearing walls and columns with expansion joints which
allow unrestrained vertical movement. 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 free-draining gravel should be placed beneath pool deck slabs to facilitate drainage.
This material should consist of minus 2-inchaggregate with less than 50%o passing 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 least 95%o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site soils or imported granular material devoid of vegetation, topsoil and oversized rock.
Underdrain System: The pool should have a layer of free draining gravel under it which is
sloped to drain to a gravity outlet. Free water was not encountered during our exploration. The
Kumar & Associates, lnc. o Project No. 20-7-230.01
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drainage layer under the pool deck should also be connected to the underpool drain system. The
drains should consist of drainpipe placed in the bottom of the pool backfill surrounded above the
invert level with free-draining granular material. The drains should be placed at each level of
excavation and at least I foot below lowest adjacent f,rnish grade and sloped at a minimum lo/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%o passingthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel under the pool should be at least I foot deep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the pool has been completed:
1) lnundation 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 95o/o 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 pool should be sloped to drain
away in all directions. \üy'e recommend 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
pool deck and walkway areas. A swale may be needed uphill to direct surface
runoff around the pool.
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 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 identif,red 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 pu{poses. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
Kumar & Associates, lnc. o Project No. 20-7-230.01
-4-
should provide continued consultation and field services during construction to review and
monitor the implønentation of our recofirmendations, and to veriff 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.
Respectfully Submitted,
Kumar & Associates, Inc.
Daniel E. Hardin, P
Rev. by: SLP
DEH/kac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figures 3 to 5 - Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
Kumar & Associates, lnc. i Project No. 20-7-230.01
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-
PIT 1 PIT 2
RESIDENCE
PIT 4 PIT 5
E 0 0
APPROXIMATE SCALE-FEET
PROPOSED
POOL
20-7-230.01 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
I
PIT. 1
EL.97.6'
PIT 2
EL. 97.6'
PIT 5
EL. 97'
PIT 4
7.EL.I 5
rì 0
F-tiJ
L¡J
LL
I-F
o_t¡lo
WC= 13.9
DD= 1 07
I
F
L¡J
l¡JtL
I-F
o_
l¡JÕ
q Ã
WC=19.0
DD=89
WC= 1 6.6
DD=89
10
LEGEND
'10
FILL: SLIGHTLY SANDY SILTY CLAY WITH SCATTERED ORGANICS AND DEBRIS, MEDIUM STIFF
TO STIFF, SLIGHTLY MOIST, BROWN.
cLAy (cL), sLtcHTLy sANDY TO SANDY, STLTY, MEDIUM STIFF TO STIFF, SLIGHTLY MOTST,
BROWN, SLIGHTLY CALCAREOUS.
F
t
HAND DRIVEN 2_INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON OCTOBER 20, 2O2O
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM
FEATURES ON SITE.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
THE RESIDENCE FLOOR LEVEL AS 1OO" ASSUMED.
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. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
Wc = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216).
20-7-230.01 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
SAMPLE OF: Slighlly Sondy Silty Cloy
FROM:Pitl@8'
WC = 19.0 %, DD = 89 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
3holl not
t6t€d.
bê
full. without th8
Coßdidol¡on
1
\o
JJ
l¡J
=UI
I
z.otr
o
=oØzoO
0
-1
-2
-3
-4
-5
-6
APPLIED PRESSURE - KSF 10 100
20-7 -230.01 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig.3
ı
ı
¡
SAMPLE OF: Sondy Silty Cloy
FROM:Pit3@3'
WC = 13.9 %, DD = 1O7 pcl
sholl not
full, without th6 rñtt6n dpprovol ol
Kumor ond ksoc¡otè, lñc. Swoll
Con8olidotio¡ t€st¡ng p€ñomod in
occordoncê w¡th AW D-4546.
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1
JJ
t¡J
=tt',
I
z.otr
ô
=olnz.o(J
0
-1
-2
-3
-4
1.0 APPLI 100
20-7 -230.01 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
ã
I
I
SAMPLE OF: Slighlly Sondy Silty Cloy
FROM:Pit4@7'
WC = 16.6 %, DD = 89 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
2
ñ
JJ
UJ
=U''
I
zo
1-
o
Jo
UIz.o()
0
2
4
6
I
-10
-12
1,0 APPLIED PRESSURE - KSF 10 100
20-7 -230.01 Kumar & Associates SWELL-CONSOLIDATION TEST RISULTS Fig. 5
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rcnKumar & Asmciates, lnc.@Geotechnical and Materials Engineersand Environmental ScientistsTABLE ISUMMARY OF LABORATORY TEST RESULTSNo.20-7-230.01SOIL TYPESlightly Sandy Silty ClaySandy Silty ClaySlightly Sandy Silty Clay(psflUNCONFINEDCOMPRESSIVESTRENGTHPlolPLASTICINDEXATTERBERG LIMITS(%lLIQUID LIMITPERCENTPASSING NO.200 stEVE(%lGRAVELSAMPLE LOCATIONDEPTHPITSANDtf/"|NATURALDRYDENS]TYNATURALMOISTURECONTENT89r078919.013.916.6aJ781IJ4