HomeMy WebLinkAboutPreliminary Findings of Excavation Observation 05.1.2020I(+A
kurnar & ASEethitiS,
Geoterhnical and Materials Engineers
and Enviranmental Scientists
An Employee Owned Company
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
Fax.: (970) 945-8454
email: kaglenwoodgkumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Pon Collins, Glenwood Springs, and Summit County, Colorado
May 1, 2020
Saul Torres
940 Quicksilver Way
Rifle, Colorado 81650
saultorres Lees.com
pashelull(iyahoo.coin
Project No. 20-7-246
Subject: Preliminary Findings of Excavation Observation, Proposed Residence, Lot 68,
Ironbridge, 1198 River Bend Way, Garfield County, Colorado
Gentlemen:
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on April 30, 2020 for preliminary evaluation the exposed soils for foundation
support. The findings of our observations and recommendations for the foundation design are
presented in this report. Hepworth-Pawlak Geotechnical (now Kumar & Associates) previously
conducted a subsoil study for design of foundations at the site and presented the findings in a
report dated December 15, 2014, Job No. 114 522A. The current observation was conducted
according to our services agreement with Saul Torres dated April 29, 2020.
The proposed residence is similar to that described in the previous report with the garage at the
main level and the residence over a walkout lower level. The south part of the residence will be
above crawlspace. The foundation was designed to be supported on spread footings with an
allowable bearing pressure of 1,500 psf on compacted structural fill or with an allowable bearing
pressure of 2,500 psf on relatively dense river gravel soils encountered at depths of around 3 to
8 feet below natural ground surface.
At the time of our visit to the site, the foundation excavation was mostly complete (except for the
crawlspace area) and had been cut in multiple levels from 1 to 5 feet below the adjacent ground
surface. The soils exposed in the bottom of the excavation mostly consisted of sandy silt and
clay except in the basement area where river gravel soils were encountered in places. Results of
swell -consolidation testing performed on samples of silt and clay soils taken from the excavation
bottom, shown on Figures 1 and 2, indicate the soils are moderately to highly compressible under
conditions of loading and wetting. The laboratory test results are summarized in Table 1. No
free water was encountered in the excavation and the soils were relatively dry.
The soil conditions exposed in the excavation are consistent with those previously encountered
on the site. The silt and clay soils should be sub -excavated down to the river gravel soils and
structural fill placed back to design footing bearing level as described in the previous report. It
may be feasible to use the onsite soils as structural fill with extreme care since achieving proper
Saul Torres
May 1, 2020
Page 2
compaction can be difficult with silt and fine sand soils. We should observe the sub -excavated
areas for bearing conditions and evaluate the structural fill for adequate compaction on a regular
basis. Other recommendations presented in the previous report which are applicable should also
be observed.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation and the previous subsurface exploration at the site. Variations
in the subsurface conditions below the excavation could increase the risk of foundation
movement. We should be advised of any variations encountered in the excavation conditions for
possible changes to recommendations contained in this letter. 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.
If you have any questions or need further assistance, please call our office.
Sincerely,
Kumar & Associates, Inc.
Steven L. Pawl
Rev. by: DEH
SLP/kac
Attachments: Figures 1 an ' 2 — Swell -Consolidation Test Results
Table 1 — Summary of Laboratory Test Results
cc: Kurtz and Associates — Brian Kurtz (kurtzengineer cc yahoo.com)
Kumar & Associates, Inc. `s Project No. 20.7.246
1
0
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CONSOLIDATION - SWELL
—1
— 2
— 3
— 4
—5
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NATO..1.H.d. Th. I..Irn. report
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Kumar and A..ucenoptn,,Inc. S iJ
Canwtdouon (Wrap� M U SI6 accordant* .Nh
SAMPLE OF: Sandy Silt and Clay
FROM: West Wall of Garage
WC = 7.7 %, DD = 102 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE — KSF TO 100
20-7-246
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
Fig. 1
2
0
0
CONSOLIDATION - SWELL
— 2
— 4
— 6
— 8
—10
—12
—14
SAMPLE OF: Porous Sandy Silt
FROM: East Wall of South Part
WC = 5.1 %, DD = 87 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
t..f r..uns cepb eny 0
ittluO,.nhput pt'.*hnCeuScL.n6ati.nnp.. arel of
f
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In a Sr el:
Cen.oid0Y n.hdlno pofortn.d 'n
ecwedbnn ith A11 Q-4 46.
1.0 APPLIED PRESSURE - KSF 10 100
20-7-246
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
Fig. 2
K±A
i�tsQrar & Associates, Inc.
Gsotetnrcal and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Pro act No. 20-7-246
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pcf)
GRADATION
PERCENT
200 SIEVE PASSING NO.
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL OR
BEDROCK TYPE
BOTTOM OF EXCAVATION
GRAVEL
(%°0)
SAND
vie) i0)
LIQUID LIMIT
f %)
PLASTIC
INDEX
(/°)
West Wall of7.7
Garage
102
Sandy Silt and Clay
East Wall of South
Part
5 1
87
Porous Sandy Silt