HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(+A Kumar & Assoeiatsso lns.@
Geotechnical and Materials Engineers
and Environmental $cientists
An f,mploycc Srynrd C*mpcny
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), Parker, Colorado Springs, Fort Collins, Glenrvood Springs, and Summit County, Colorado
March 2,2021
Christian Harra
0149 Lakenz Circle
Silt, Colorado 81652
miner914@'hotmail'com
project No. 21-7-171
Subject: Subsoil Study for Foundation Design, Proposed Pool, 30 feet Southwest of
Existing House, 0149 LaFrenzCkcIe, Silt, Colorado
Dear Christian:
As requested, Kumar & Associates, Inc. observed two backhoe pits to obtain soils information
for design of a proposed pool at the subject site. The study was conducted in accordance with
our agreement for geotechnical engineering services to you dated February 3,2021. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report.
Proposed Construction: The proposed in-ground pool will be 12 feet by 24 feet in plan size
and about 4 feet deep. The pool will have steel walls. The pool will be located about 30 to
40 feet off the southwest corner of the existing house.
Site Conditions: The existing house is a one-story wood frame structure over a walkout
basement level. The pool will be located in an existing, relatively flat, lawn area. The general
topography in the area slopes moderately down to the southwest.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits in the proposed pool area on February 5,2021. The subsoils encountered, below
about r/z foot of topsoil, consist of gravelly sandy clay to clayey sand and gravel down to the pit
depths of 6 feet. Results of a gradation analysis performed on a sample of very clayey sand and
gravel (minus 3-inch fraction) obtained from the site are presented on Figure 1. Atterberg limits
testing indicates the clay soils have low plasticity. Percent finer than sand size gradation
analyses indicate the silt and clay fraction of the soils varies from23 to 67 percent. No free
water was observed in the pits at the time of excavation and the soils were moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, the pool can be placed on the
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natural soils at this site, as planned. The soils are clayey and a drainage layer should be placed
below the pool. The drainage layer should consist of coarse sand or pea gravel protected by filter
fabric and sloped to drain to daylight. Loose and disturbed soils encountered at the pool bottom
within the excavation should be removed. The pool walls acting as retaining structures should be
designed to resist alatenl 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
should be separated 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.
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 '/o-inch aggregate with less than 50%o
passing the No. 4 sieve and less than2%o passing the No. 200 sieve.
A11 filI materials for support of slabs should be compacted to at least 95Yo of maximum standard
Proctor density at a moisture content near optimum. Required fill can consist of the on-site soils
devoid of vegetation, topsoil and oversized (plus 3-inch) rock.
Underdrain System: The pool underdrain should consist of a drainage layer placed below the
bottom of the pool and connected to a drainpipe sloped at a minimum lYo to 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 1 inch. The drain gravel backfill 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) Inundation ofthe pool excavations and underslab areas should be avoided during
construction. Drying could increase the expansion potential of the clay portion of
the soils.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%o of the maximum standard Proctor density in deck slab areas and to at
least90Yo 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.
Kumar & Associates, lnc, @ Project No. 21-7-17'l
-3-
LEmi€aticns: Ttris study has been candueted in accordance with geaerally accepted ge*technieal
engir:eering principles and practiees in this area at this time. We make no warranty eith*r
oxpr*ss or implied. The c*nclusions and recommendations submitted in this report are based
upcn th* data obtained frcm tlee explcratory pits, the proposed type of consbucti*n, and our
expcrienee in the area. Our findings include interpolation and extrapalaticn of the subsurfaee
*onditi*ns identified at the exploratary pits a"nd vartations irr the subsurface ccrediti*ns n:ay not
become evident until excavation is perfonned. If ccnditi*ns en**untered duri*g *cnstruction
appear different f,r*m thcse described in this repcrt, we should be notified at once so re-
evaluation af the recomfi:*ndations may be made.
This repcrt has been prepared far the exslusive use by our client far design purpos€s. We are not
resp*nsible for technical interpretaticns by *thers of our infbrmation. As th* pr*ject sr'*lves, we
shculd provide eontinued consultation and field serviees during s*i?structi*n t* review *nd
mcnitor the impl*meiatati** of our recommendations, and to veri$i that the recommendati*r:s
have been apprcpriat*ly interpreted. Signifieant design *hanges may require additional anaiysis
or madifications to the recsslmendations presented herein. We recommend on-site observati*n
of exeavations and foundation bearing strata and testing of structural fill by a representative of
the ge*technical engineer.
If y*u hav* any questions *r if wc may b* of fu*her assistan*e, please lct us knCIw"
Respectfully S*bmitt*d,
$(eEnpap" & "&ss*ciate*, 9ne,
Da$iel E. Hardin,
Rev. by: SLP
FEH/kac
attaehments
ce:
Figure I * Gradati*n Test Resu9ts
Table I - $urnmary of Laboratory Test Results
Lowell Walter lwalf*rr.$)behs:**r.*r*
,
Wurwar & &w**ciateg, lqxc. e Vrqe*tf{*" ?3-?-t?'$
Eg
*
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIUE RilDINGS
2,t HRS 7 HRS I CLEAR SAUARE OPEi{INGS
a/R. rfl. t 1 /r. ?,
U,S. STANDARO SERIES
l1
6
f,
H
ro0
go
ao
70
60
50
iao
30
20
to
0
o
to
20
30
&
50
60
70
EO
90
loo
tr
E
P
H
DIAMETER OF PARTICLES IN M RS
CLAY TO SILT COBBLES
GRAVEL 41 % SAND
LIQUID LIMIT
SAMPLE OF: Cloyey Sond ond Grovel
33%
PLASTICITY INDEX
SILT AND CLAY 23 %
FROM:Pit1O3'-4'
Thrtr brl rctullt opply only lo lhc
lomplss whlch v.ro lsshd. Tho
h3tlng roport Bhqll nol bt roproducld,
cxcrpl ln full, vllhoul lhc wrlilcn
opprcvol ol Kumor & Assoclotrs, lnc.
Slav. onolysls lGllng ls porfomcd ln
occordoncr wllh ASTM D6915, ASTM D7928,
ASTM Cl36 ond,/or ASIM D1140.
SAND GRAVEL
MEDTUM lCOlnSr FINE COARSEFINE
GRADATION TEST RESULTS Fig. 121-7 -171 Kumar & Associates
lcrt#l[ffiffi,If'****
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.21-7-171
Very Clayey Sand and
Gravel
Clayey Sand and Gravel
Very Clayey Sand and
Gravel
Sandy Clay
Sandy Clay
SOIL TYPE
(psfl
UNCONFINED
COMPRESSIVE
STRENGTH
(:/"1
PLASTIC
INDEX
JI
ATTERBERG LIMITS
(%l
LIQUID LIMTT
28
67
59
PERCENT
PASSING NO.
200 SIEVE
47
ZJ
46
JJ44
99
95
89
12.8
20.8
18.0
3-4
5
1
4
2
16.82%94
DEPTH
1
PIT
SAMPLE GMDATIONNATURAL
DRY
DENSTTY
NATURAL
MOISTURE
CONTENT
SAND
(:/,1
GRAVEL
%t