HomeMy WebLinkAboutSubsoil StudyCIV CO Engine ering, fnc .
Civil Engineering Consultonts
P.O. Box t758
365 West 50 North, Suite W-l
Vernol, Utqh 84078
September 1,2021
Shawn Ruse
Clayton Homes
671 23 Road
Grand Junc{ion, CO 81505
DearShawn,
Sub¡ecü Soil lnrestigation - Hobon at TBD GR SfXl' Parachúq Gololado
I am writing this letter to report the findings of a soil investigation that was conducted at the proposed
site for the Hobson residence at TBD County Road 300, Parachute, Colorado. The investigation
entailed the analysis of one soil sample that was taken from the proposed construc{ion site at
approximately the bearing depth of the proposed foundation. Testing of the soil sample included a
sieve analysis and Atterbeg Limits testing. The results of the soil testing were used to classiff the soil
sample as 'ML - Silt with Sand' ae¡ording to the Unlfied Soil Classification System. A copy of the soil
data is included with this lefter.
ML soils are generally silts of low plasticity having nominal bearing capacities in the vicinity of 3000 psf
for medium to stiff soils. Recognizing that no specific testing was conduc'ted to determine the soils
actual bearing capacity, I recommend that a smaller bearing capacity of 1500 psf be used for design of
the home's foundation.
Over the years, a number of studies have been ænducted in an effort to conelate soil expansiveness
to atterberg limit data. According to one study, soils with Liquid Limits less than 50% and Plasticity
lndices that less lhan 25Yo, generally exhibit a low potential for expansion (Snethen, Johnson, and
Patrick, 1977). The soil sample tested was found to have no measurable Liquid Limit and no
measurable Plasticity lndex. Thus, according to the referenced study, the soil in question is anticipated
to have a low expansion potential. lt should be noted that Atterberg Limits testing does not address
miner:alogy and thus may have a limited ability to reliably predict soil expansion potential.
Though the Atter.berg Limits testing suggests a non-expansive soil, ML soils may be susceptible to frost
heave. Foundations should extend to below frost depth or be frost-protected by some other means.
Water should be kept away from the foundations. Walhltrays, driveways, and ground surfiaces should
be graded to flow away ftom the foundation. Gutter down-spout outlets should be kept at least fle feet
away from the foundation. Vegetation requiring significant watering should not be planted near the
foundation.
No testing was done to determine the soil's collapse potential. ln my experience, foundation failures
due to soil collapse are generally even more catastrophic than failures due to soil expansion. ln every
instance of soil collapse failure that I have investigated, the damaged home was located at the mouth
of a pronounced drainage, such as a canyon or gully where the soil has been deposited alluvially by
intermittent ru noff water fl ows.
Alluvially deposited soils are typically not very dense and derive their strength from mineral bonds that
form between soil particles. When these soils become wet, the mineral bonds dissolve, allowing the
soil particles to consolidate (collapse) under any load that is more than that which existed when the
mineral bonds originally formed.
Phone (435P89-544¡g * Fo< (435F89-4485
Emoil : vonceking@civcoengineeriqg.com
. Page2 September 1,2021
Veriff that the projec't slte ls not at the moufr of any obvious drainage. The previously mentioned
methods for lowering the risk of frost heave are also key to lessening the risk of soil collapse failure.
ln summary, the soil under the proposed foundation was not specifically tested to determine
expansiveness but was found to have properties consistent with soils having very little expansion
potential. Likewise, the soil was not specifically tested to determine bearing capacity but was found to
be of a type having characteristic bearing capacities in the range of 3000 psf. For design purposes, a
1500 psf bearing capacity is recommended. The homeowner should make every effort to keep
moisture from being introduced to the soil near the foundation. Any future purchaser of the home
should be apprised of the underlying soil characteristics and the importance of keeping moisture away
from the foundation.
This concludes my report. Please note that this investigation was performed for the purpose of
providing general information regarding the soil underlying the proposed home and makes no
prediction of foundational performance. This report should not be regarded as documentation of a
geotechnical investigation as I am not a geotechnical engineer, and this study was not conducted to
any generally accepted st¡andard of geotechnical engineering practice. Please contact me if you have
questions regarding this report.
Sincerely,
Vance V. King, PE
Engineer
CIVCO Engineering, lnc.
Enclosure
Cc: Project File
þ.l,Zl
35315
Q. C. Testing. lnc
2944 S 1500 E
VERNAL, UTAH 84078
Phone (435) 789-0220
Fax (435) 781-1876
SIEVE ANALYSIS AND ATTEBERG LIMITS
Civco-Hobson residence, Parachute, CO
Q- C- TTSTIHß
-
Project No. or Cl¡ent:
Material Type:
Distance from CL:
MF=
native
Depth: _ Date Sampled
Tested By TD
Stations:
Dato Tested 8t27t2021
AASHTO T{9 & T-90 Atterberg Limit
Liqu¡d Limit NV
Plastc Limit NP
Plâstic index NP
Classm€t¡on Ml'silt with sând
44 Moisture Data
wt.7.8
wt.7
H20 Wt.5.1
H20%
Washed DryWt.
AASHTO T-27 Coarse Gradation
Sieve
Size
Wo¡ght
Ret.7o Ret.
% Total
Passing
Sieve
Size Sp6cs
3" çrsmm¡3'',
2" (oomm)2"
'1.5" (37.smm)1.5"
1" (2smm)1
3/4" ¡smm¡ct4"
112" (12.5nñl 1t2"
3/8" (e.smm)3t8"
tl4 (4.75mm)F4
#4 (4.7smm)
WETWT.
+4 (4.7smm)
DRYWT.
Total
Fine Gradation
Sieve
Size
Weight
Ret.7o Ret.% Pass
þ4 (4.75mm)
Èt8 (2.36mm)
F10 (z.omn)
F16 lr.rsmm)
#20 (ssopm)0 0.0 100
Ë30 (eoor¡m)
F40 (425!m)'t.2 0.4 99.6
F50 (3oopm)
#60 (25opm)
É€0 (1gopm)
#100 (rsor¡m)
v200 66.3 21.9 77.7
#200 íSum)235.2 77.7
Total 302.7
Remarks