HomeMy WebLinkAboutSoils Report 07.13.2020GEOTECHNICAL ENGINEERING REPORT
RESIDENCE ADDITION
877 COUNTY ROAD 229
SILT, COLORADO
July 13, 2020
Prepared By:
PO Box 1080
Silt, CO 81652
(970) 230-9208
Project No. 20 -023R -G1
Prepared For:
Mr. Richard Johnson
877 County Road 229
Silt, CO 81652
877 County Road 229 Project No. 20 -023R -G1
Silt, Colorado
TABLE OF CONTENTS
1.0 PROJECT INFORMATION 1
1.1 Purpose and Scope 1
1.2 Proposed Construction 1
1.3 Site Conditions 1
2.0 SITE INVESTIGATION 1
2.1 Subsurface Investigation 1
2.2 Subsurface Conditions 2
2.2.1 Groundwater 2
3.0 SITE GRADING 2
4.0 FOUNDATION RECOMMENDATIONS 3
4.1 Foundations placed on Natural Soils 3
5.0 SLABS -ON -GRADE 4
6.0 CONCRETE 4
7.0 SURFACE DRAINAGE 4
8.0 LIMITATIONS 4
LIST OF FIGURES
Figure 1 — Approximate Test Hole Location
Figure 2 — Test Hole Log and Legend
877 County Road 229 Project No 20 -023R -G1
Silt, Colorado
1.0 PROJECT INFORMATION
1.1 Purpose and Scope
This report presents the results of our geotechnical investigation and recommendations for
design and construction of an addition planned at 877 County Road 229 in Silt, Colorado. The
investigation was performed to provide foundation and construction recommendations for the
proposed addition.
The site investigation consisted of geologic reconnaissance and exploratory test hole drilling to
investigate subsurface conditions. Test hole drilling was observed by a representative of RJ
Engineering. Samples obtained during the field exploration were examined by the project
personnel and representative samples were subjected to laboratory testing to determine the
engineering characteristics of materials encountered. This report summarizes our field
investigation, the results of our analyses, and our conclusions and recommendations based on
the proposed construction, site reconnaissance, subsurface investigation, and results of the
laboratory testing.
1.2 Proposed Construction
We understand an addition is planned to be constructed at the northwest corner of the
residence behind the existing garage. The addition is planned as a single story over a
crawlspace.
1.3 Site Conditions
The site is relatively flat in the area of the proposed addition. The area around the garage is
partially landscaped with grasses and shrubs. The area around the residence is also
landscaped.
2.0 SITE INVESTIGATION
2.1 Subsurface Investigation
One test hole was drilled on July 3, 2020. The test hole was drilled in a non -landscaped area
near the northwest corner of the proposed addition. The approximate test hole location is
presented on Figure 1.
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877 County Road 229 Project No. 20 -023R -G1
Silt, Colorado
The test hole was advanced with a hand auger. Bulk samples were collected at depths
indicated on the test hole log presented on Figure 2.
2.2 Subsurface Conditions
Subsurface conditions encountered in test hole TH-1 consisted of natural sandy silt to a
maximum explored depth of 10 feet. The silt was clayey near the bottom of the test hole.
One natural silt sample had 83 percent fines (material passing the No. 200 sieve). Atterberg
limit testing indicated the silt was non -liquid and non -plastic. The silt sample classified as a
sandy silt (ML) according to the Unified Soil Classification System (USCS).
2.2.1 Groundwater
Groundwater was not encountered during drilling. The test hole was backfilled for safety
reasons and delayed measurements could not be obtained. Variations in groundwater
conditions may occur seasonally. The magnitude of the variation will be largely dependent upon
the amount of spring snowmelt, duration and intensity of precipitation, site grading changes, and
the surface and subsurface drainage characteristics of the surrounding area.
3.0 SITE GRADING
Fills may be planned at this site to achieve finished grades. Grading plans were not available at
the time of this investigation. Based on drilling and our observations, we believe that material
can be excavated by conventional construction equipment.
We recommend fill slopes be constructed at 2H:1V or flatter. Fill slopes should be protected
from erosion. Surface drainage should be directed around slopes. Surface water ponding
behind or flowing over the face of fill slopes may cause significant erosion and instability.
The on-site soils can be used in site grading fills provided the material is substantially free of
organic material, debris and particles are no larger than 6 inches. Areas to receive fill should be
stripped of vegetation, organic soils and debris. Topsoil is not recommended for fill material
below structural elements or slabs. Imported granular soils should contain less than 30 percent
fines (passing No. 200 sieve) and a maximum particle size of 6 inches. Fill should be placed in
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877 County Road 229 Project No. 20 -023R -G1
Silt, Colorado
thin, loose lifts of 8 inches thick or less. We recommend fill materials be moisture conditioned to
within 2 percent of optimum moisture content and compacted to at least 95 percent of maximum
standard Proctor dry density (ASTM D 698). Placement and compaction of fill should be
observed and tested by a geotechnical engineer.
4.0 FOUNDATION RECOMMENDATIONS
We believe that the natural silts encountered at the site are suitable for the proposed
construction. We judge the natural silt encountered at the site to exhibit low collapse potential.
Foundations should be placed on natural soils. Foundation recommendations for structures
supported by the natural soils are presented below.
4.1 Foundations placed on Natural Soils
Foundations should be constructed on undisturbed natural soils. Existing fill or loose, disturbed
soils encountered at foundation level should be removed and the foundation should be
extended to natural soils and/or replaced with properly compacted fill. We recommend fill be
placed in accordance with the specifications presented in section 3.0.
1. Footings should be placed on undisturbed natural soils. Foundations can be designed
for a maximum allowable soil pressure of 1,500 psf. Based on experience, we anticipate
settlement of footings designed and constructed as recommended will be about 1 -inch or
less.
2. Continuous footings should have a minimum width of 18 inches and isolated pads
should have a minimum dimension of 2 feet.
3. The soils below foundations should be protected from freezing. We recommend the
bottom of foundations be constructed at least 3.0 feet below finished exterior grade or as
required by local municipal code.
4. Continuous foundation walls shall be reinforced to span anomalies by assuming an
unsupported distance of 10 feet. Foundation walls acting as retaining structures should
be designed to resist lateral earth pressures as discussed in section 5.0 below.
5. All foundation excavations should be observed by a representative of a geotechnical
engineer prior to placement of concrete.
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877 County Road 229 Project No. 20 -023R -G1
Silt, Colorado
5.0 SLABS -ON -GRADE
The natural on-site soils are suitable to support lightly loaded slab -on -grade construction such
as garage floor slabs and patios. To reduce distress associated with minor differential
movement, slabs should be separated from all bearing walls with expansion joints which provide
unrestricted vertical movement. A minimum 4 -inch layer of free draining gravel should be
placed beneath slabs -on -grade such as slabs and patios. The free draining gravel should have
less than 2 percent passing the No. 200 sieve, less than 50 percent passing the No. 4 sieve and
have a maximum size of 2 inches. All fill placed below floor slabs should be moisture
conditioned and compacted in accordance with the recommendations in section 3.0.
6.0 CONCRETE
Based on our experience, the silt soils encountered at the site are typically low in water soluble
sulfate. This concentration is considered negligible/low (Class 0 exposure) degree of sulfate
attack for concrete exposed to these materials. The degree of attack is based on a range of
0.00 to less than 0.10 percent water-soluble sulfates as presented in the American Concrete
Institute Guide to Durable Concrete. Due to the negligible/low degree, no special requirements
for concrete are necessary for this site.
7.0 SURFACE DRAINAGE
Surface drainage is crucial to the performance of foundations and flatwork. We recommend the
ground surface surrounding the garage and retaining walls be sloped to drain away. We
recommend a slope of at least 6 inches in the first 10 feet for landscape and unpaved areas and
a minimum slope of 2 percent for paved areas. Irrigation should not be discharged within 5 feet
of foundation walls. Backfill around foundations should be moisture conditioned and compacted
as recommended in the section 3.0. Drains should discharge beyond the wall backfill areas.
8.0 LIMITATIONS
This study was conducted in accordance with generally accepted geotechnical engineering
practices in this area for use by the client for design purposes. The conclusions and
recommendations submitted in this report are based upon the data obtained from exploratory
test holes, field reconnaissance and anticipated construction. The nature and extent of
subsurface variations across the site may not become evident until excavation is performed. If
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877 County Road 229 Project No. 20 -023R -G1
Silt, Colorado
during construction, conditions appear to be different from those described herein; this office
should be advised at once so reevaluation of the recommendations may be made. We
recommend on-site observation of excavations by a representative of the geotechnical
engineer.
The scope of services for this project did not include, specifically or by implication, any
environmental or biological (e.g., mold, fungi, and bacteria) assessment of the site or
identification or prevention of pollutants, hazardous materials or conditions or biological
conditions. If the owner is concerned about the potential for such contamination, conditions or
pollution, other studies should be undertaken.
The 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.
Respectfully Submitted,
RJ Engineering & Consulting,
Richard D. Johnson, P.E.
Principal
5
cr
X
Reception No. 899819
4,. yJ
S 67°,41
04 90
365.5' —
–
Tract 17
Antlers Orchard
S 89°3642" W
173.97'
Proposed AddWon
Irrigation Structurep�
(Typical) /
15.0' Irrigation Easement
Boundary Line Adjustment --
Reception No. 899817
126.1'
TH-1
N
Approximate
J
Welt House
Waterline Location
(To Be Relocated)
SEI/4SE1/4NE1/4
Section 5
9.996 t Acres
LEGEND:
T: 1 Indicates approximate test hole location
NOTES:
1. Base plan by Bookcliff Survey Services dated 06-03-2020.
tJ b
Reception No. 899820
X
Fence (Typical)
x x * I+
x
Parcel 2
Antonelli Exemption
Reception No. 338010
Parcel 1
Antonelli Exemption
Reception No. 358010
`\III Buried
Propane x
Tank
41
IX x n
x
Gravel
x X
Found #5 Rebar and
1-1/4" Yellow Plastic Cap
Skimped "PLS #13501"
Parcel 1
Pollard Exemption Plat
Reception No. 648136
0
u �,y
41
r V Parcel 2
~.. Pollard Exemption Plat
Reception No. 648136
X-
50
100
SCALE: 1" = 100'
PROJECT NO:
20 -023R -G1
PROJECT:
877 County Road 229, Silt, CO
Approximate
Test Hole Location
Figure
1
0
5
10
15
(1)
ov
20
25
30
35
40
TH-1
0
10
15
aa)
20
25
30
35
40
Sample Types
® Bulk sample obtained from auger cuttings at depths indicated.
Soil Lithology
nSILT, clayey to sandy, soft to medium stiff, dry to slightly moist,
brown, light brown, tan (ML)
NOTES:
1. The test hole was drilled on July 3, 2020 with 3 -inch diameter hand
auger.
2. Groundwater was not encountered during drilling. The test hole was
backfilled for safety reasons.
3. Test hole descriptions are subject to explanations contained in this
report.
LOG OF EXPLORATORY BORING
877 County Road 229
Silt, Colorado
Project No.:
20 -023R -G1
Figure 2