HomeMy WebLinkAboutObservation of Pit Excavations 10.11.2018H-P�KUMAR
Geotechnical Engineering I Engineering Geology
Materials Testing I Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
October 11, 2018
Tony Choma
40 Huebinger Drive
Glenwood Springs, Colorado 81601
t.eho 1 @yahoo.coni
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
H[(7,/irk )�
Project No. 18-7-578
Subject: Observation of Pit Excavations, Proposed Residence, Lot 21, Homestead Estates,
Foster Ridge Road, Garfield County, Colorado
Dear Tony:
As requested, the undersigned representative of H-P/Kumar observed the rough cut excavation
and several shallow pits within the rough cut excavation at the subject site on September 19,
2018 to evaluate the soils exposed for foundation support. The findings of our observations and
recommendations for the foundation design are presented in this report. The services were
performed in accordance with our proposal for professional engineering services to you, dated
April 11, 2018.
The proposed residence will be one story ICF Block walls with a slab -on -grade floor.
Foundations may consist of traditional footing and stem walls with an isolated interior slab. A
thickened edge slab foundation is also being considered.
At the time of our visit to the site, the building excavation had been rough cut in one, moderately
sloping level from 1 to 11/2 feet below the adjacent ground surface. The topsoil and root zone had
been removed. Several shallow pits were excavated with a mini -excavator backhoe into the
underlying soils to a depth of about 21/2 feet. Refusal on basalt rocks was encountered in all of
the pits. The soils exposed in the bottom of the building excavation and in the shallow pits
consisted of basalt cobbles and boulders in a slightly sandy silty clay matrix. The results of a
gradation analysis performed on a sample of the matrix soils (minus 6-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.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings (or thickened edge slab) placed on the undisturbed natural soil
designed for an allowable soil bearing pressure of 1,500 psf can be used for support of the
proposed residence. The exposed matrix soils tend to compress when wetted under load and
there could be some post -construction settlement of the foundation if the bearing soils become
wet. Footings or thickened edges should be a minimum width of 18 inches for continuous walls
and 2 feet for columns. Loose and disturbed soils in footing areas should be removed and the
exposed bearing soils moistened and compacted. The bearing soils should be protected against
Tony Choma
October 11, 2018
Page 2
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 reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 10 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 50 pcf for on -site soil as backfill excluding topsoil and rock larger than 6
inches. A perimeter foundation drain should be provided to prevent temporary buildup of
hydrostatic pressure behind any retaining walls and prevent wetting any below grade interior
levels. Structural fill placed below thickened slabs or floor slab areas should consist of imported
3/4-inch road base compacted to at least 98% of standard Proctor density at a moisture content
near optimum. Backfill placed around the structure can consist of the on -site soils and should be
compacted and the surface graded to prevent ponding within at least 10 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. 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,
H-PKUMAR
Daniel E. Har
Rev. by: SLP
DEH/ kac
attachment
din,
Ice 4
Y ' L '..)
;3 24443 z;
'ke:t.':$/oNAL 1..
Figure 1 — Particle Size Distribution Report
H-P KUMAR
Project No. 18-7-578
Glenwood Springs, Colorado
PERCENT FINER
10
9
80
70
60
50
40
30
20
10
c
Particle Size Distribution Report
0 0 0 0
0 0
0 '
n - :C ; a 6' Z 1 u as
--1-1
I
1
I
1
1
1
1 1
1 1
1 1
1
1
1
T
i
1
!
I
1
I
I
I
1
1 1!
i l
1 1
1
1
i
1
I
1
I
1 1
I 1
1
1
I
I
I
I
I
1
11
1
1
1 1
1
1
1
l
i
i
1
II
1 1
I I
IL
1
I
i
I
J
I
I
!
1
11
I
! 1
I I
I!
I
1
I
I
I
I
11
1
II
I
1
I
I
I
I
I
I!
I I
1
I
1
I
I
!
II
It
II
II
I
I
I
I
I
f
I
1
I
__
I T")
1 1
I
1
1
—I—
1
!
1
1
II
1 i
1 1
II--
t
I
1
1
I
!
1
4
1
I
I
1
I
1
1 f
I I
I 1—
1
"
I
I
I
-i
1
1
I
11
1 1 1
II
I
I
1
1
!
1
I
I
I I
1 1
I
I
I
J
7
1
i
1
1
I
1 1 11
1 1 1
l 11
1
1
!
m
I
1
i
1
1
r
I
1
1 1
11
1 1
I
I
I
!
!
i
I
11
I
1 1
I 1 1
1
i
!
1
!
I
1
I
1 1
I I!
I
l
I
I _
1
11
11
I
1 1 1
1 1 1
1 1 1
_.
1
1
1
1
1
1
1
1
1
I
1
! I
I 1
1 1
1
100 10 1
0
1 0.01 ❑ aro
GRAIN SIZE - mrn.
%+3"
31
% Gravel
Coarse Fine
3
1
% Sand
1
Coarse Medium T Fine
1 2 6
_ % Fines
Silt 1 Clay
56
SIEVE
SIZE
PERCENT
FINER
SPEC."
PERCENT
PASS?
(X=NO)
6
100
5
80
3
69
1.5
67
.75
66
.375
65
#4
65
#8
64
#16
63
#30
62
#50
61
#100
59
#200
56
(no specification provided)
Location: Pit 3 @ 2'-3' - Northeast Part of Residence
Sample Number: 276-18
Kumar & Associates, Inc. Client: Tony Choma
Project: Lot 21, Homestead Estates, TBD Foster Ridge Road, Garfield County,
Colorado
Project No: 18-7-578
Material Description
Slightly Sandy Silty Clay with Cobbles
(Matrix Soils)
PL=
D90= 139.1215
D50=
D 10=
USCS=
Atterberq Limits
LL= Pl=
Coefficients
D85= 132.9227
D3074
Cu-
Classification
AASHTO=
Remarks
D60= 0.2121
D15=
Cc=
Tested By: KO Checked By: DEH
Date: 9/19/2018
Figure