HomeMy WebLinkAboutObservation of Excavation 04.28.23l(tAffi*,ffi,Fsni'i:'i'*"5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945,7988
fax: (970) 945-84s4
email: kaglenwood@kumarusa.com
An Emplofao Ovmcd Compony www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
April28,2A23
Garvik Construction
Atfir: Quinn Garvik
P.O. Box 2257
Basalt, Colorado 81621
qgarvikfdgma.d.com
Project No.23-7-254
Subject:observation of Excavation, Proposed Addition to Existing Residence, 1434
County Road 107, Garfield County, Colorado
Dear Quinn:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on April 19,2023 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 were performed in accordance with our agreement for professional engineering services
to Garvik Construction dated April 18,2023.
The proposed addition will be a two-story wood-framed structure attached to the north side of
the existing residence. The ground floor will be structural over crawlspace. The addition has
been designed to be supported on spread footings sized for an allowable soil bearing pressure of
2,000 psf.
At the time of our visit to the site, the foundation excavation had been cut in one level from 2 to
3%feetbelow the adjacent ground surface. The soils exposed in the bottom of the excavation
consisted of generally medium dense, mixed sand and silt with scattered gravel. There was
evidence of foundation backfill near the existing foundation. Results of swell-consolidation
testing perforrred on a sample taken from the site, shown on Figure l, indicate the natural soils
are moderately compressible under conditions of loading and wetting. The results of a gradation
analysis performed on a disturbedbulk sample of the soils (minus 3-inch fraction) obtained from
the site are presented on Figure 2. The laboratory testing is summarizedtnTable 1. No free
water was encountered in the excavation and the soils were slightly moist.
Garvik Construction
April28,2023
Page 2
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an allowable
bearing pressgre of 2,000 psf can be used for support of the proposed addition with some risk of
settlement. The exposed soils tend to compress when wetted and there could be some post-
construction settlement of the foundation if the bearing soils become wet. The settlement would
likely be differential with respect to the existing structure which should be considered in the
design. Precautions should be taken to prevent wetting of the bearing soils.
Footings should be a minimum width of 18 inches for continuous walls and? feet for columns.
Loose disturbed soils in footing areas should be removed and the bearing level extended down to
the undisturbed natural soilso and the subgrade compacted. Exterior footings should be provided
with adequate soil cover above their bearing elevations for frost protection. Continuous
foundation walls should be heavily reinforced top and bottom to span local anomalies and resist
the effects of some settlement such as by assuming an unsupported length of at least 14 feet. The
fill near the foundation wall can probably be bridged by dowelling the proposed foundation into
the existing wall and reinforcing the continuous walls. Foundation walls acting as retaining
structures should also be designed to resist a lateral earth pressure based on an equivalent fluid
unit weight of at least 55 pcf for on-site soil as backfill. A perimeter foundation drain should not
be required for the proposed shallow crawlspace construction. Structural fill placed within floor
slab areas can consist of the on-site soils compacted to at least 95% of standard Proctor density at
a moisture content near optimum. Backfill placed around the structure should be compacted and
the surface graded to prevent ponding within at least 10 feet of the building. Landscape that
requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within 5
feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the tbundation 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
Garvik Construction
April28,2023
Page 3
variations in the subsurface conditions. ln 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, prevenlion 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,
K**rnr & Asg*e iate*, in*
James H. Parsons, P.E.
Rev. by: DAY
JHP/rjf
attachments Figure 1 - Swell-Consolidation Test Results
Figure 2 - Gradation Test Results
Table 1 - Summary of Laboratory Test Results T:
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SAMPLE OF: Silt ond Sond
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Fi1. 223-7-254 Kumar & Associates GRADATION TEST RESULTS
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Geotechnical and Materials Engineors
and Environmental Scientists
*5:
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23-7
LOCA
SD- 1
HD- 1
HD_2 20,5
13.0
5.7
phl
NATURAT
MOISTURE
CONTENT
97
83
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DRY
DEiISITY
55
(%)
GRAVEL
23
(%)
SAIID
GRADATION
55
22
PERCENT
PASSING NO,
200 slElrE
ATTERB
t%)
LIQUID UMIT PLASTIC
INDEX
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G LIMITS
IPSR
UNCONFINED
COMPRESSIVE
STRENGTH
Silt and Sand
Silt and sand
Silty Sandy Gravel
sorL oR
BEDROCK TYPE