HomeMy WebLinkAboutSoils Report 07.08.2017GEOLOGIC REVIEW AND
SOILS ENGINEERING
LOT 23 RAPIDS VIEW LANE
NEW CASTLE, COLORADO
Prepared For:
Chronos Builders
Grand Junction, Colorado
Prepared By:
CAPSTONE
ENTERPRISES WEST, LLC
GEOTECHNICAL AND MINING ENGINEERING
TESTING AND INSPECTION SERVICES
618 PARTEE DRIVE
GRAND JUNCTION, CO 81504
PHONE (970) 250-3331
capstonewest@juno.com
July 8, 2017
Job No. 4100-2
CAPSTONE
ENTERPRISES WEST, LLC
GEOTECHNICAL AND MINING ENGINEERING
TESTING AND INSPECTION SERVICES
618 PARTEE WIVE
GRAND JUNCTION, C0.81504
PHONE (970) 250-3331 FAX (970) 241-9721
July 8, 2017
JOB # 4100-2
Attn:
Chronos Builders
637 25 Road
Grand Junction, CO 81505
Subject: Geologic Review and Soils Engineering Report
Lot 23 Rapids View Lane
New Castle, CO
At your request, Capstone Enterprises West, LLC directed the excavation of two
test pits dug on the aforementioned property. The purpose of our work was to
determine if the soils are suitable for support of the proposed foundation for the
structure. Or, if necessary, to provide recommendations to prepare a proper soil
sub grade for support of the proposed structure. Additionally one of the holes was
used as the profile hole for an Onsite Waste -water Treatment System (OWTS)
The following maps show the location of the parcel and the approximate location
of the excavations. The test results and the OWTS design are contained in a
separate report.
The following maps show the lot and test pit locations.
CAPSTONE ENTERPRISES WEST, LLC
JOB NUMBER 4100-2
Rifle
Silt
New Castle
0,
Site Location
e f
.•HH+lVP
STP -2
• TP -•1.
2.0114,1,07
SITE DESCRIPTION
Geologically, the bedrock in the area is the Molina Member of the Wasatch
Formation. This unit is made up of sandstone and mudstone. At this site the
bedrock has been capped with alluvial sediments from the Colorado River that
CAPSTONE ENTERPRISES WEST, LLC 3
JOB NUMBER 41.00-2
borders the subdivision to the north. The following image taken from the Garfield
County GIS website shows that this lot is outside- of the flood plain.
'
SUBSURFACE INVESTIGATIONS
The geologic logs of the test pits are presented on the following page. The
sediments overlaying the bedrock change gradation from gravel with boulders to
sandy silty day. The contacts betw-een the ,different soil types are quite distinct.
Ground water was encountered in TP -1 at 7.1 feet below the surface. There was
no evidence of a seasonal water table above this elevation. It should be noted
that runoff at the time was q tte high and the- river was near seasonal high.
TP -1
Topsoil- Silty Clap
Abundant Roots
Reddish Brown Silty Clay
wi Gravel
PI = 10
Sandy Gravel e, Cobbles
Pl=rip
Sandy Gravel w/ Boulders
Moist
Water Table 6/22/17
10
CAPSTONE ENTERPRISES WEST, LLC 4
JOB NUMBER 4100-2
TP -2
Topsoil- Silty Clay
Abundant Roots
Reddish Brown Silty Clay
e: Gravel
Sandy Gravel Cobbles
LABORATORY TESTING AND RESULTS
The suitability for foundation material is generally determined by two tests: the
Swell/Consolidation test and the Atterberg Limits test. The Swell/Consolidation
test consists of placing an undisturbed sample of material in a device that applies
a load to the soil. TIie specimen compacts or "consolidates". After the initial- toad
stabilizes, the specimen is saturated and the specimen will either swell or
consolidate further. The distribution of gravel in the silty clay made it impossible
to collect at intact specimen for Swell/Consolidation testing.
The Atterberg Limits Test gives an indication of the mechanical properties of fine
grained materials. The first part of the test is to determine the Plastic Limit of the
material. Then the Liquid Limit is determined. The difference between the Liquid
Limit and the Plastic Limit is defined as the Plasticity Index. Swell potential based
on the plasticity limit (PI) is shown on the following page.
Plasticity Index (PI)
Inherent Swelling Capacity
0-15
Low
10-35
Medium
20-55
High
35-F
Very 1-1 igh
(After Seed et al. 1962)
The results presented below indicate there is a low potential for swelling for both
the silty material and the fines in the gravel.
Material
Source
Depth I Liquid
Plastic
Plasticity Percent
j Limit
Limit
Index Passing
200 mesh
Red Brn. Silty Clay
TP -2
1-3 ft
28
18
10
52.7 %
Sandy Gravel
TP -1
2.5-
NP
NP
1.8 %
4.5ft
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JOB NUMBER 4100-2
Based on the gradations and Atterberg Limits TP -1 1' to 2' was classified as CL -
ML (Silty Clay or Clayey Silt). The gravel is classified as a well graded gravel
GW.
The Atterberg Limits Tests indicate the silty soil is suitable for foundation
structural fill. .
The strength of soils and aggregates is a function of their density. The denser a
given material is, the stronger it is. The maximum dry density of a material is
determined by running an ASTM D-698,, Moisture -Density Relation Test. This is
commonly called the Standard Proctor Test. Samples with different moisture
contents are compacted with equal forces and a curve of the moisture density
relationship is established. The result of the Standard Proctor for a composite
sample of the gravely, silty clay is presented on the following page.
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JOB NUMBER 4100-2
Chronos Builders MOISTURE -DENSITY RELATION IASTM D-698)
Rapids View
Job 4100
Composite Gravely Silty Clay
125.0
123.0
119.0
120.4 pcf @ 11.8% MOISTURE
117.0
115.0
/
5% 7/0 9/0 1 % 1 3% 1 5%
MOISTURE CONTENT%
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JOB NUMBER 4100-2
DESIGN CONSIDERATIONS
As mentioned earlier, the Molina Member of the Wasatch Formation is the
bedrock unit in this area. Any swelling potential in the mudstones would have
been stabilized years ago from the Colorado River's inundation of the gravels
blanketing the bedrock. The altuvial- sediments are suitable for structural fig when
properly compacted.
DESIGN RECOMMENDATIONS
FOUNDATIONS
We recommend this structure be constructed on a conventional stemwall and footer
or slab on grade foundation system resting on a compacted fill mat. The mat
should be 2 feet thick and the subgrade should be compacted before constructing
the mat.
A maximum bearing load of 2,000 psf should not be exceeded.
EXCAVATION
The topsoil should be removed and stockpiled for landscaping. The footprint of the
foundation should be excavated approximately 2 feet below the surface to the top of
the sandy gravel The excavation should extend laterally 3 feet from the footprint of
the foundation.
SUBGRADE PREPARATION
Once the over -excavation has been completed, the subgrade should be moisture
conditioned and compacted. Any soft spots noticed during compaction should be
removed or reconditioned. Ideally the moisture conditioning should allow the water
to soak in overnight.
BACKFILL
All structural fill should consist of non -expansive, granular material with a PI of less
than 10. The native soils meet these requirements. The material should be
moisture conditioned and placed in 6 inch lifts. The structured fill should be
compacted to at least 95 percent of the maximum standard Proctor density at a
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JOB NUMBER 4100-2
moisture content (±)2% of optimum.
We recommend that Capstone staff be
contracted to perform field moisture density testing to confirm compaction is being
obtained. Tests should be performed after the 1 foot of fill is compacted and at the
final grade. The relatively fine texture of the native clayey silt is prone to break up
under traffic; therefore,, Capstone recommends that once the silt is compacted it be
capped with a more traffic resistant material such as -3/8" crusher fines, if the forms
cannot be placed within a day or two of pad completion.
SLAB CONSTRUCTION
Slab -on -grade construction may be used if the same subgrade preparation as
described earlier is used:
• 2 foot excavation below foundation
• Moisture condition bottom of excavation (preferably overnight)
• Compact subgrade and backfill to greater than 95% of Standard Proctor at
+1- 2% of optimum moisture
• Cap silty fill with -3/8" crusher fines
Slabs should be provided with control joints to reduce damage due to shrinkage
cracking. It is recommended control joints be spaced at 15 feet on centers or Tess.
WATER SOLUBLE SULFATES
Gypsum crystals were observed in the sediments. This indicates a sulfate content
of in excess of 2000 ppm. This concentration of water soluble sulfates represents a
severe degree of sulfate attack on concrete exposed to these materials. Based on
this observation,, sulfate resistant cement -(Type 11 modified) should be used in all
concrete exposed to the on-site soils.
SURFACE DRAINAGE AND LANDSCAPING
The success of shallow foundations and slab -on -grade systems is contingent upon
keeping the subgrade soils at more or less constant moisture content, and by not
allowing surface drainage a path to the subsurface. Positive' surface drainageaway
from structures and exterior slabs must be maintained at all times. Landscaped
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JOB NUMBER 4100-2
areas should be designed and built such that irrigation and other surface water will
be collected and carried away from foundation elements.
The final grade of the foundations backfill and any overlying concrete slabs or
sidewalks should have a positive slope away from.foundation walls on all sides. We
recommend a minimum slope of 12 inches in the first 10 feet; however, the slope
can be decreased to 4 inches in 10 feet if the ground surface adjacent to
foundations is covered with concrete slabs or sidewalks.
Backfill material should consist of non -expansive, non -free draining granular
material. Backfill material should be placed near optimum moisture content and
compacted to at least 90% of maximum standard Proctor density in landscaped
areas and to at least 95% maximum standard Proctor density beneath structural
areas (sidewalks, patios, driveways, etc.). All roof downspouts and faucets should
discharge well beyond the limits of all backfill. Irrigation within ten (10) feet of
foundations and driveway slabs should be carefully controlled and minimized. The
collapsing soils are very sensitive to moisture changes. Thus, control of watering
and downspouts next to foundation members is essential.
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JOB NUMBER 4100-2
LIMITATIONS
The analysis and recommendations submitted in this report are based in part upon
the data obtained from the excavations and field observations. The nature and
extent of variation may not become evident until construction. If variations then
appear, it will be necessary to reevaluate the recommendations in this report.
It is recommended that the geotechnical engineer be provided the opportunity for
general review of the final design and specifications in order that earthwork and
foundation recommendations may be properly interpreted and implemented in the
design and specifications. It is also recommended that the geotechnical engineer,
or a qualified geo-technician under his supervision, be retained to provide
continuous engineering services during construction of the foundation, excavations,
and earthwork phases of the work. This is to observe compliance with the design
concepts, specifications, or recommendations and to modify these
recommendations in the event that subsurface conditions differ from those
anticipated.
This report, does not constitute a warranty either expressed or implied, as no one
can predict the long -tern changes in subsurface moisture conditions resulting from
improper grading, excessive irrigation by the home owner or neighbors or other
causes during and after construction.
If you have any questions, or if we may be of further assistance, please do not
hesitate to contact us.
Respectfully Submitted:
CAPSTONE ENTERPRISES WEST, LLC
Martin W. Chenoweth, PE
Registered Professional Engineer
MWC
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JOB NUMBER 4100-2