HomeMy WebLinkAboutObservation of Excavation 04.19.2019It -A
karpim & Aasinialcc, Inc.
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
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
April 19, 2019
David Levine
2801 Glendale Road
Charlotte, North Carolina 28209
d!evine69C i inai1.corn
Subject:
Gentlemen:
Project No. 19-7-228
Observation of Excavation, Proposed Residence, Lot S-8, Saddleback Ridge, Aspen
Glen, 649 Saddleback Road, Garfield County, Colorado
As requested, a representative of Kumar & Associates observed the excavation at the subject site on
April 16, 2019 to evaluate the soils exposed for foundation support. The findings of our observations
and recommendations for 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 November 15, 2013, Job No. 113 420A.
The residence location and design appear similar as described in our previous report. The house will
be above crawlspace and the garage will be slab -on -grade. Spread footings sized for an allowable
bearing pressure of 1,200 psf were selected for the foundation support. Due to the compressible nature
of the near surface soils, an alternate deep foundation or using 3 feet of compacted bearing soil were
provided as ways to limit potential settlement and building distress risk.
At the time of our visit to the site, the foundation excavation had been cut in multiple levels from 1 to
7 feet below the adjacent ground surface, stepped down to the south and east with the ground surface
slope. The soils exposed in the bottom of the excavation consisted of sandy to very sandy silt and clay
with scattered gravel (alluvial fan deposit). Results of swell -consolidation testing performed on a
sample taken from the site, shown on Figure 1, indicate the soils are slightly compressible under
existing low moisture content and light loading and have low collapse potential (settlement under
constant load) when wetted with moderate compressibility under additional loading after wetting. The
laboratory test results are summarized in Table 1. No free water was encountered in the excavation
and the soils were slightly moist and moist.
Footings sized for 1,200 psf bearing pressure can be supported on the low bearing and compressible
soils exposed in the excavation with a potential for settlement and building distress. It will be critical
to prevent wetting below the building such as by eliminating landscape irrigation near the structure as
well as proper backfill compaction with properly graded perimeter slopes. Loose disturbed soils in the
footing areas should be moistened and compacted. Other recommendations presented in the previous
David Levine
April 19, 2019
Page 2
report which are applicable, especially those to keep the bearing soils dry, should also be observed. A
perimeter foundation drain should not be provided around the garage foundation. The foundation
drain around the crawlspace should be underlain with the recommended impervious membrane. The
onsite soils should be used as foundation wall backfill to create a tight, relatively impervious backfill
to minimize surface water infiltration to the bearing soils.
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. Pawlak
Rev. by: DEH
SLP/kac
Attachments:
Figure 1 — Swell -Consolidation Test Results
Table 1 — Summary of Laboratory Test Results
cc: WoodStone — Ken Smith (leenewoodstoneinc.net)
WoodStone — Alan Short (a1anL woodstaneinc.net).
Kumar & Associates, inc.
Project No. 19-7-228
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19-7-228
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 1
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Kornai & Associates, lac.
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Proiect No. 19-7-228
SAMPLE LOCATION
GRADATION
NATURAL
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
LIQUID LIMIT
(")
PLASTIC
(%)
COMPRESSIVE
STRENGTH
(PSF)
SOIL OR
BEDROCK TYPE
I1
1 1
BOTTOM OF EXCAVATION
NATURAL
MOISTURE
CONTENT
(%)
DRY
DENSITY
1 (pen
GRAVEL
aINDEX
(��)
SAND
(%)
North -Center
3.9
82
52
Very Sandy Silt and Clay
with Gravel
Northeast Corner
7.4
93
Sandy Silt and Clay with
Gravel
Southeast Corner
5.2
80
57
Very Sandy Silt and Clay
1 with Gravel
_
Middle
13.4
104L
.
Sandy Silt and Clay