HomeMy WebLinkAboutObservation of Excavation 04.05.2022I(r'T lftmar & Assoclates, lnc.@
Geotechnical and Materials Engineers 5020 County Road 154
and Environmental Scientists Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
An Employcc Owntd Compony www.kumarusa.com
Offce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
April 5,2022
Matt Stinson
96 River Ridge Drive
Glenwood Springs, Colorado 81601
Matt. stinson.pa@ gmail. com
Project No.22-7-258
Subject: Observation of Excavation, Proposed Detached Garage, Lot 3, Rover Ridge PIJD,
96 River Ridge Drive, Glenwood Springs, Colorado
Dear Matt:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on March 30 and April 1, 2020 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 Matt Stinson dated March 30,2022.
We understand that the proposed garage has been designed to be founded on spread footings
bearing on the natural granular soils and sized assuming an allowable bearing pressure of
2,000 psf. The ground floor will be slab-on-grade.
At the time of our visit to the site on March 30,2022, the foundation excavation had been cut in
one level from 3 to 4 feet below the adjacent ground surface. The soils exposed in the bottom of
the excavation consisted mainly of relatively dense, slightly silty sandy gravel and cobbles. The
results of a gradation analysis performed on a sample of the sandy gravel soils (minus 5-inch
fraction) obtained from the site are presented on Figure 1. No free water was encountered in the
excavation and the soils were slightly moist to moist. Previously placed fill material consisting
of concrete rubble was encountered in the north-west corner of the excavation. It was
recommended that the concrete rubble be removed down to native granular soils and footing
grade reestablished with compacted structural fill consisting of the on-site granular soils devoid
of any vegetation or topsoil. At the time of our visit to the site on April 1,2022, the concrete
rubble had been removed from the northwest comer of the excavation down a depth of about
9 feet to native sandy gravel soils.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural granular soils or compacted
structural fill on the granular soils designed for an allowable soil bearing pressure of 2,000 psf
can be used for support of the proposed garage. There could be a low risk of post-construction
differential settlement of the foundation for footings placed partially on natural granular soils and
pafüally on compacted structural fill. The differential settlement across the building could be up
to about Ilzinches. Footings should be a minimum width of 16 inches for continuous walls and
2 feú for columns. Loose and disturbed soils and existing old fill in footing areas should be
removed and the bearing level extended down to the undisturbed natural soils or reestablished
with compacted structural fill. The bearing soils should be protected against frost and concrete
should not be placed on frozen soils. Exterior footings should be provided with adequate soil
cover above their bearing elevations for frost protection. Continuous foundation walls should be
Matt Stinson
Apnl 5,2022
Page ?
reinforced top and bottom to span local anomalies such as by assuming an unsupported length of
at least l0 feet. 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 45 pcf for on-site
granular soils aSbackfill. Struotural fill placed within floor slab areas can consist of the on-site
granular soils compacted to at least 95% of standard Proctor density at a moisture c¡ntent near
optimum. Structural fill placed beneath footing areas should consist of the on-site granular soils
placed in 8-inch maximum loose lifts and be compacted to at least 98% 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 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 movemelrt may be greater than indicated in this report because of possible
variations in the subsurface conditions. In order to reveal the natwe 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 ñrture. If the client is concemed 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'& Assocíatesu
Robert L. Duran. P
Reviewed by:
David A.
RLD/kac
P.E.
attachment Figure 1 - Particle Size Distribution Report
Kumar & Associates, lnc. ú)Project No.22-7-258
Particle Size Distribution Report
c o ru:: -N Sè *
t
t¡Jz
TL
Fz
UJOÉtufL
100
90
80
70
60
50
40
30
20
10
GRAIN SIZE - mm.
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?/. +3"
o/o Gravel % Sând % Fines
Coarse F¡ne Coarse Medium Fine sitt Clay
4.0 31.0 20.0 5.0 18.5 t4.2 7.3
(no specification provided)
Location: Native Soils
Sample Number: 043-22 Date: 313012022
SIEVE
stzE
PERCENT
FINER
sPEC.*
PERCENT
PASS?
(X=NO)
5
3
1.5
.75
.375
#4
#8
#t6
#30
#s0
#100
#200
100.0
96.0
82.0
65.0
53.0
4s.0
41.0
37.0
27.0
16.0
10.0
7.3
Soil Description
Sandy Gravel
PL=
Don= 56.6164DiX= 7.337s
Diö= o.tsoo
USCS=
Atterberg Limits
LL=
Coefficients
Daç.= 44.2009
DXX= 0.73s0
cüY ss't+
Glassification
AASHTO=
Remarks
Pl=
Dan= 14.2774Dii= 0.26'13cå: o.zs
Kumar & Associates, lnc.
Glenwood Sprinqs. Golorado
Glient: Matt Stinson
Project: Lot 3 River Ridge PUD, 96 River Ridge Drive, Glenwood Springs,
Colorado
Proiect No: 22-7-258 Fisure I
Tested By:KO Ghecked By:RLD