HomeMy WebLinkAboutObservation of Excavation 04.25.2022lGrtiffififfiffinåäå'*"5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Em$oyue Ourned Compony www.kumarusa.com
Offlce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
Aprit25,2022
Jimmy Nakagawa
t70l County Road 103
Carbondale, Colorado 81623
nakaf¡aI/aj (glhotmail. com
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Project No. 2l-7-885
Subject: Observation of Excavation, Proposed Detached Garage, 1701 County Road 103,
Garfi eld County, Colorado
Dear Jimmy:
As requested, the undersigned representative of Kumar & Associates observed the excavation at
the zubject site on April 22,2022 to evaluate the soils exposed for foundation support. The
findings of our observations and recommendations for the foundation support are presented in
this report. The services wereperformed in general accordance with our agreement for
professional engineering services to you dated November 23,2021.
The proposed 30' by 40' detached garage is located east of the existing reside,nce. The garage
will be a tall one-story structure with a slab-on-grade floor.
We observed several pits that were dug on Novemb æ 25,2A21 in the proposed garage area. It
quickly became apparent that there was significant old undocumented fill in the proposed garage
area up to 6 or 7 feet deep. We recommended that the extent and depth of fill be fi¡rther
investigated and removed and it was likely that imported structural fill would be needed to re-
establish footing and slab iubgrade.
'We returned to the site on April 22,2022 and observed that the proposed garage area had bee,n
completely subexcavated to depths of 3% feet in the nortlreast corner andTtA feet in the
southwest corner. All the old fill had been removed from below the building area. The soils
exposed in the bottom of the excavation consisted of white, sandy silt with basalt gravel and
cobbles and scattered basalt boulders. No free water was encountered in the excavation and the
soils were slightly moist.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, we recommended the existing subgrade be moistened and compacted prior to
placement of structural fill. The client stated that he planned to place compacted minus 4-inch
'þit run" material as structural fill below the building. The foundation will likely be a thickened
slab. The thickened edge portion of the slab place on the proposed fill should be designed for an
allowable soil bearing pressure of 2,000 ryþhich can be used for support of the proposed
garage. The exposed natural maiñxffitend to compress when wetted and the fill may settle
over time and there could be some post-construction settlement of the foundation particularly if
Jimmy Nakagawa
April 25,2022
Page2
the bearing soils become wet. The thickened edge portion of the slab (footing) should be a
minimum width of 16 inches for continuous walls and2 feet for columns (if any). Loose and
disturbed soils in underslab areas should be removed and the bearing level extended down to the
well-compacted fill soils. Exterior footings should be provided with adequate soil cover above
their bearing elevations for frost protection or should be insulated. Structural fill placed below
the floor slab and thickened areas can consist of the on-site soils compacted to at least 98Yo of
standard Proctor density at a moisfure content near optimum. We should observe the compaction
of the fill placed for support of the garage as fill placement progresses to verifu the compaction
process. Backfill placed around the structure should be compacted and the surface graded to
prevent ponding within at least l0 feet of the building.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation and do not include subsurface exploration to evaluate the
subsurface conditions within the loaded depth of foundation influence. This study is based on
the assumption that soils beneath the footings have equal or better support than those exposed.
The risk of foundation movement may be greater than indicated in this report because of possible
variations in the subsurface conditions. In order to reveal the nature and extent of variations in
the subsurface conditions below the excavation, drilling would be required. It is possible the
data obtained by subsurface exploration could change the 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 ofñce.
Sincerely,
I(urnar & Associates, [nc.
I
Daniel E. Hardin, P.E.
Rev. by: SLP
DEHlkac
Kumar & Associates, lnc. Ð Project No. 21.7-885