HomeMy WebLinkAboutGeotechnical Investigation Report 05.22.2025GEOTECH NICAL INVESTIGAilON REPORT
New Cabin Project
Parcel 239925400082, CR 313-East Divide Creek Road
New Castle, Colorado
Geo Quest Project No.:25-119
May 22,2025
Prepared for:
Dustin Cheney
3360 County Road 233
Rifle, CO 81650
d ustin @ava la ncheexcavation. net
970-379-5258
.N
N
s.
$'
s
Geo,Quesf
Geoteehsi(al Engineering - Te*ting
{970} 818-fi?S4
FS tsox t*?2
Rifle,0O *tS6&
geoq*art*o@pm.rrrs
t
2
3
4
5
Table of Contents
Purpose and Scope of Study
Proposed Construction
Site Conditions
Field lnvestigation
Subsurface Conditions
5.1 Laboratory Test Results
Earthwork.
Recommendations
7.L Foundations
7.2 Below-Grade Walls
7.3 ConcreteSlabs................
7.4 DrainageConsiderations.
8 Limitations..........
Figures
Figure 1 - Project and Approximate Test Pit Location Map.
Figure 2 - Test Pit Excavation
Figure 3 - Typical Engineered Fill Section
Tables
Table L -Test Pit 1 Laboratory Test Results and Relative Density........
Table 2 - Compaction Criteria
6
7
L
L
L
2
3
4
4
5
5
6
7
7
8
5
2
3
5
Geo,Quesf
Geotechnical Engineensrg - Terting
ts?sl818-s?84
F* 3sx ?*?3
Rifte"*S *tSSe
**nqr:*etrs@pm"rris
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No.25-119
s/22/2s
L Purpose and Scope ofStudy
This report presents the results of our geotechnical investigation for the planned construction of a new
cabin on Parce|239925400082 along Garfield County Road 313 also known as East Divide Creek Rd, New
Castle, Colorado. The purposes of this investigation were to evaluate the subsurface conditions at the site
and to develop geotechnical recommendations to assist in design and construction. This report is not a
foundation design and cannot be used as such. The type, thickness, reinforcing and other aspects of
foundation elements should be designed by a structural engineer. Our scope of services included the
following:
Using excavated test pits, observe the subsurface conditions and collect soil samples to identify
and assess the material layers at the proposed building site.
Estimate soil parameters including allowable bearing pressure, approximate depth to bearing
stratum, and estimated foundation movement.
Discuss earthwork, including recommendations for fill placement and compaction, suitability of
the site soilfor reuse as engineered fill, and subgrade preparation.
2 ProposedConstruction
The project proposes the construction of a small cabin with up to two levels above ground. Geo Quest
(GQ) assumes a typical shallow foundation with concrete footings and stem walls and a concrete slab on
grade forthe floor or structuralfloor over a crawlspace. The location of the project site is presented in
Figure 1, Project ond Approximate Test Pit Location Mop. GQ was supplied with a preliminary site plan for
the cabin location on the lot. lf the proposed construction details change from those above, GQ should be
contacted for review and re-evaluation of the recommendations in this report.
3 Site Conditions
The property is located approximately 18 miles south/southeast of the town of Silt on a 4O-acre parcel.
County Road 313 cuts through the parcel with half of the property on the east and half on the west side
of the road. The proposed cabin site lies in the bottom of a draw along East Divide Creek. The area
surrounding the cabin is heavi[ vegetated with oak brush, bushes and large, mature evergreen trees.
a
a
a
L
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No. 25-119
s/22/2s
NeliCas,ttg,
Froiect Sit€.
AFprqr.ifiato TeEt Fil 1 Loastisn
\
rd
r lN
.!
I :
:.
1u,
Figure 1 - Project and Approximate Test Pit Location Map
4 Field lnvestigation
On May 8, 2025, GQ was at the property and one test pit was excavated to a depth of 7.5 feet below the
ground surface using a Caterpillar 306 excavator. The site and approximate test pit location are presented
in Figure 1.
Bulk samples of the subsurface materials were obtained from the test pit at select depths for testing and
identification of each material layer. The excavation was backfilled with the excavated soil when
completed.
2
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No. 25-119
s/22/2s
Figure 2 - Test Pit Excavation
5 Subsurface Conditions
The test pit encountered approximately 18
inches of topsoil over 3.5 feet of very loose to
loose clayey sand over 2.5 feet of loose silty
sand. These upper soils were wet to saturated
and bucket refusal was encountered at 7.5
feet on cobbles and boulders.
Significant ground water was encountered at a depth of 4 feet. Variations in groundwater conditions may
occur seasonally. The magnitude of the variation will be largely dependent upon the amount of spring
snowmelt, the flow in East Divide Creek, duration and intensity of precipitation, site grading changes, and
the surface and subsurface drainage characteristics of the surrounding area. Perched water tables may be
present but were not encountered in the test pit. Figure 2 presents photos of the soil layers and
groundwater in the excavation.
3
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No. 25-119
s/2212s
5.1 Laboratory Test Results
Collected soil samples were classified by the geotechnical engineer in accordance with the Unified Soil
Classification System (USCS) as described in ASTM D-2488 and ASTM D-2487. Laboratory tests were then
performed on select samples to evaluate the pertinent engineering properties of the soil. The laboratory
testing was conducted in general accordance with the American Society for Testing and Materials (ASTM)
test procedures. The following laboratory tests were performed for this evaluation and presented in
Table 1:
ln-Situ Moisture Content ASTM D-2216
Soil Particle Analysis ASTM D-422
Plastic and Liquid Limits ASTM D-4318
Test Results and Relative
*Values measured with pocket penetrometer and correlated to relative density
6 Earthwork
Geo Quest anticipates that fill placement, outside of foundation excavation areas, will be minor. Areas to
receive fillshould be stripped of vegetation, organic soils and debris. The on-site soils encountered in the
test pit should not be used below structure foundations but may be used around the structure perimeter
and other areas. lf used as fill, these soils should first be dried to a workable state and be free of organic
matter, debris and rocks larger than 3 inches. lf weak, saturated and unsuitable soils are encountered at
subgrade elevations below concrete slabs on grade or other areas, the material should be removed and
replaced with imported granular material, to provide a suitable platform for construction.
We recommend that coarse granular material such as roadbase or an approved pitrun be imported for
use below structure foundations. lf pitrun is selected it should have no more than 15 percent passing the
200 sieve, a liquid limit not exceeding 35 percent and plasticity index not exceeding 6 percent.
Fill should be placed in loose lifts of 8 inches thick or less, moisture conditioned and compacted to at
least 95 percent of the maximum proctor dry density as shown in Table 2. Placement and compaction
should be observed and tested by the geotechnical engineer.
a
a
a
Table 1- Test Pit 1 Laborato
4
2 2s.2 73 37
31 LL
77 Pt
Very loose
45 38 LL
15 Pr
Very Loose to
Loose436.2 55
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No. 25-119
s/22/2s
Table 2 - Com Criteria
Care should be used when compacting soil next to foundation walls, utilities or other sensitive areas to
prevent damage. lf utility trenches are backfilled with granular soil, a clay plug of adequate thickness
should be placed in the trench adjacent to the building to reduce the potential for water flowing through
the trench back under the structure. Placement and compaction of fill should be observed and tested by
a representative of the geotechnical engineer.
7 Recommendations
7.t Foundations
The proposed cabin site is slightly lower in elevation than the test pit and closer to East Divide Creek. lt is
likely that the foundation excavation will encounter the very dense cobble/boulder layer at a shallower
depth than in the test pit. The clayey soil in the top 5 feet of the test pit was close to the liquid limit and
is not suitable for direct foundation support. GQ recommends that the foundation excavation be taken
down to the very dense layer of cobbles and boulders.
Coarse, granular material such as roadbase or approved pitrun should be placed with moisture and
compaction control directly on the cobble and boulder layer up to the bottom of footing elevation. All fill
should be placed with proper moisture and compaction control as described in Section 6. This will create
an engineered fill section that should extend laterally beyond all footing edges for a distance that is at
least half the thickness of engineered fill or a minimum of 12 inches as represented in Figure 3.
lf the dense layer is encountered at a very shallow depth GQ recommends that a minimum of 6 to t2
inches of roadbase be placed and compacted to fills low spots and create a smooth, level construction
platform for concrete footings.
The following design and construction details should be observed for footings placed on the engineered
fillsection.
1. Weak, disturbed or unsuitable material encountered at the subgrade elevation at the base of
foundation excavations should be removed and replaced with properly compacted fill or the
subgrade should be extended to undisturbed soils.
2. Footi for a maximum allowable soil pressure of 2,500 pounds
per square foot (when constru t e esc bed
a ove.
3. Continuous wall footings should have a minimum width of at least 15 inches. Foundation pads
for isolated columns should have a minimum dimension of 24 inches.
5
95% minimum Standard (ASTM D698)+ 2% of optimum
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No. 25-1-19
s/22/2s
4. Resistance to sliding at the bottom of the footing can be calculated based on a coefficient of
friction of 0.50. Passive pressure againstthe side of the footings should not be considered due
to the generally soft and wet soil at the site.
5. Grade beams and foundation walls should be reinforced to span undisclosed loose or soft soil
areas. We recommend reinforcement designed to span an unsupported distance of at least
14 feet.
6. The soils below exterior footings should be protected from freezing. Foundation footings
should be constructed at least 36 inches below finished exterior grade for frost protection or
as required by local municipalcode.
7. All foundation excavations should be observed by a representative of the geotechnical
engineer prior to placement of concrete.
Total foundation movement is estimated to be on the order of one (1) inch or less. Differential
movement is anticipated to be on the order of %to % of the estimated total movement. These estimated
foundation movements are dependent on proper construction practices, drainage and following the
recommendations in this report. Therefore, proper drainage should be provided in the final design and
during construction.
Figure 3 - Typical Engineered Fill Section
7.2 Below-Grade Walls
The foundation walls should be designed for lateral earth pressure of the surrounding soil where backfill
is not present to the same level on both sides of the wall. For walls that can deflect or rotate about 0.5 to
6
Engineered Filt Secti0n
Claysy Ssnd
4" di_a^ rigid, perforet€d
drainpipe in f ree drai*ing gravel
surraunded with geoteltile
dEiinag€/separation tabric on'
top and exterior.
Engin€ered Fitt Sectioh
Cobbles, Bouldcrs
12 lnc min either side of footing
Ground Surface
E
4
c)
N
36 lnches Frost Protection
a
:9
(o
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No. 25-119
s/22/2s
1 percent of the wall height, the wall can be designed for "active" earth pressure conditions. For a very
rigid wall where negligible deflection can occu4 an "at-rest" lateral earth pressure condition can be used
Typically, below-grade walls for residences can rotate under normal design loads, and this deflection
results in acceptable performance.
lf on-site soils are used as backfill we recommend using an equivalent fluid density of 40 pcf for design of
below grade walls for "active" conditions. This value assumes that some minor cracking is acceptable. lf
this is unsuitable, then a higher ("at-rest") equivalent fluid density should be used for design. For "at
rest" conditions, an equivalent fluid density of 50 pcf can be used for design. These equivalent fluid
densities do not account for sloping backfill, surcharges or hydrostatic pressure.
7.3 lnterior Concrete Slab
lf a concrete slab is selected for the interior cabin floor, we recommend creating an engineered fill section
that is at least 12 inches thick as described in Section T.l Foundations and shown in Figure 3. Additional
slab design and construction recommendations are as follows:
. Positive separations and/or isolation joints should be provided between slabs and all foundations,
columns, or utility lines to allow independent movement.
r Controljoints should be provided in slabs to control the location and extent of cracking.
. lnterior trench backfill placed beneath slabs should be properly compacted in accordance with
Table 2.
r Slabs should not be constructed on frozen subgrade.
. GQ recommends the use of a moisture barrier below interior concrete slabs due the locally high
ground water levels to protect moisture sensitive floor coverings.
7.4 Drainage Considerations
This location has elevated ground water levels and a foundation drain should be constructed. A robust
drain system should consist of a 4-inch diameter; rigid perforated pipe encased in free draining gravel
and surrounded with geotextile drainage/separation fabric. The gravelfabric cross section should be at
least 18 inches square with%to 1.5-inch washed rock and less than 5 percent fines. The rigid pipe is
useful to maintain slope and avoid sags and low spots.
The pipe should be sloped at a minimum of 2 percent and installed 12 to 18 inches away from the
foundation footing and outside the engineered fill section. The top of the pipe should be at an elevation
equal to the bottom of footing at the high point. The drain should be provided with a gravity discharge to
daylight or sump pit where water can be removed by pumping.
We recommend the ground surface surrounding the building be sloped to drain awav from the structure
with a minimum slope of 10 percent or a drop of 12 inches in the first L0 feet for landscape areas. We
recommend a slope of 2 percent away from the structure beyond this. We recommend that roof drain
downspouts discharge a minimum of 5 feet away from the structure and beyond all structure backfill
zones. These recommendations may require raising the overall structure elevations.
7
Soil Report-New Cabin Project
CR 313 New Castle, CO
Geo Quest No.25-119
s/22/2s
I Limitations
The analyses and recommendations presented in this report are based upon our data obtained from the
test pit, field observations, soil classifications and our understanding of the proposed construction and
other information as discussed in this report. lt is possible and likely that subsurface conditions may vary
outside of the limits explored. The nature and extent of such variations may not become evident until
construction. We should review the report if the scope of the proposed construction, including the
proposed loads, finished elevations or structure locations, change from those described in this report,
and provide supplemental recommendations as necessary.
It is important to note that the recommendations herein are intended to reduce the risk of structural
movement and/or damage associated with volume change of the subsurface materials. However, GQ
cannot predict the long-term changes in subsurface moisture conditions and/or the extent of potential
damaging effects. Where significant increases in subsurface moisture occur due to grading changes,
utility line break, leaks from any source, excess irrigation or other causes, excessive movement is
possible.
This report was prepared in substantial accordance with the generally accepted standards of practice for
geotechnical engineering as exist in the site area at the time of our investigation. No warranties, express
or implied, are intended or made. These recommendations are based on the assumption that GQ will
conduct an adequate program of testing and observation to evaluate compliance with our
recommendations.
Respectfully submitted,
Geo Quest
Kevin E. Dye, P.E.
Founder
8
57139