HomeMy WebLinkAboutObservation of Excavation 02.17.2023lcrtHmmffü"*5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employcc OwrËd ComPonY www.kumarusa.com
Office Locations: Denver (HQ), Parke¡ Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
February 17,2023
Jordan Kobielusz
3602 County Road 108
Carbondale, Colorado 81 623
icservices2l@yahoo'com
project No. 23-7-14g
Subject: Observation of Pit Excavations, Proposed Residence, 3602 County Road 108,
Garfield County, Colorado
Dear Jordan:
As requested, the undersigned representative of Kumar & Associates observed the pit
excavations at the subject site on February 10,2023 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 you dated February 10,2023.
The proposed residence will be one-story modular house over a crawlspace. The proposed leach
field will be located south of the residence. The site is located on a broad low ridge in a pinon
forest. An existing driveway provides access to the site. There were parked vehicles and
equipment at the site to the north of the building area.
At the time of our visit to the site, the site had been cleared of pinon trees. Three pits were
excavated with a Bobcat E45 mini-excavator. The subsurface conditions observed in the three
pits were similar and consisted of about 1 foot of organic silty sand topsoil overlying 3 to 4 feet
of reddish-brown, relatively dense, silty sandy gravel with scattered cobble-size sandstone rock
fragments (weathered sandstone/siltstone). Refusal to backhoe digging was encountered in all
three pits at about 4 to 5 feet on sandstone/siltstone bedrock of the Maroon Formation. The
results of gradation analyses performed on samples of silty sandy gravel (minus 5-inch fraction)
obtained from the site are presented on Figures 1 and 2. No free water was encountered in the
excavations and the soils were slightly moist to moist.
Considering the conditions exposed in the pit excavations and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an allowable
soil bearing pressure of 2,500 should be adequate for support ofthe proposed residence. The
exposed soils were dense and post-construction settlement of the foundation should be
less than I inch. Footings should be a minimum width of 16 inches for continuous walls and
2 feet for columns. Loose and disturbed soils in footing areas should be removed and the bearing
level extended down to the undisturbed natural soils. 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
Jordan Kobielusz
February 17,2023
Page2
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 (if any) should also be designed to resist alateral earth pressure based on an equivalent
fluid unit weight of at least 45 pcf for on-site soil as backfill. A perimeter foundation drain
should be provided to prevent temporary buildup of hydrostatic pressure behind the crawlspace
walls and prevent wetting of the crawlspace. Structural filIplaced
can consist of the on-site soils compacted to at least 95% of standard Proctor density at a
moisture content near optimum. Backfill around the structure and
the surface graded to prevent wl at least 10 feet of the building.
Based on the subsurface conditions encountered in the profile pit (1 foot of topsoil overlying
4 feet of gravelly sandy loam), the proposed septic area should be suitable for a shallow
conventional infiltration septic disposal system. We recommend the infiltration area be
oversized due to the relatively shallow weathered sandstone. A civil engineer should design the
infiltration septic disposal system.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the pit excavations. The risk of foundation movement may be greater than indicated in
this report because of possible variations in the subsurface conditions. We should observe the
completed foundation excavation at the time of construction. 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,
Daniel E. Hardin,
Rev. by: SLP
DEHlkac
attachments Figurc 1- Gradation Test Results
Figure 2 - USDA Gradation Test Results
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Kumar & Associates, lnc. @ Project No. 23-7-148
SIEVE ANALYSISHYDROMETER ANALYSIS
I
CLEAR SOUARE OPENIT{GS
s/a' 3/a' I 1/2' 3'
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2.O
ETER OF PARTICLES IN M
CLAY TO SILT COBBLES
GRAVEL 21 % SAND
LIQUID LIMIT
SAMPLE OF: Very Silty Grovolly Sond
10%
PLASTICITY INDEX
SILT AND CLAY 36 %
FROM: Plt 1 @ 2' to 3'
Th6so l€sl r€sulls opp¡y only lo lho
sqmples wh¡ch w€rs l€slsd. Tho
losl¡ng roporl sholl not b6 r€producod,
excepl ln full, wllhoul lhe wrlllsn
opprovol of Kumor & Assocloles, lnc'
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occordoncã wlth ASTM 06913, ASTM D7928,
ASTM c156 ond/or ASIM Dl1,lo.
GRAVELSAND
MEDIUM COARSE FINE COARSEFINE
23-7-1 48 Kumar & Associates GRADATION TEST RESULTS Fig. 1
SIEVE ANALYSISHYDROMETER ANALYSIS
TIME READINGS SERIES CLEAR UARE
2AHR. 7HR 1 MIN,
.#325 #140 #60 #35 #18 #'10 #4 3/8' 314" 1 112',5b ð
^45U
MIN,100
10 90
20 80
30 70
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50 50
60 40
70 30
80 20
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100 106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152 203.001 .002 ,005 ,009 .019 .045
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY COBBLES
GRAVEL 35 o/o SAND 26 %SILT 31 o/o CLAY 8 %
USDA SOIL TYPE: Gravelly SandY Loam FROM: Profile Pit at 4 to 5 feet
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V. FINE FINE
SAND
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23-7 -1 48 Kumar & Associates USDA GRADATION TEST RESULTS Fig.2