HomeMy WebLinkAbout; James Drive Extension; James Drive; 1985-09-01GEOTECHNICAL CONSULTANTS
STUDIES IN APPLIED EARTH SCIENCES
Project No. 183.1.1
September 1, 1985
Berryman & Stephenson, Inc.
16880 West Bernardo Drive
San Diego, California 92127
Attention: Mr. Ivan Fox
Subject: GEOTECHNICAL INVESTIGATION
James Drive Extension
James Drive & Basswood
City of Carlsbad, California
Gentlemen:
INTRODUCTION
This report presents the results of my soil and geological
investigation for an extension of James Drive from Basswood to
approximately 1,000 feet to the northwest. The purpose of this
investigation was to evaluate the geotechnical conditions along
the proposed alignment and to provide recommendations concern-
ing the soil and geological engineering aspects of the proposed
road development.
Based on my review of an undated plan entitled "James Drive
Assessment District No. 83-2," by Berryman & Stephenson, Inc.,
the proposed street will be almost entirely in cut resulting in
cut-slope heights of up to approximately 3 feet at a 2:1
(horizontal to vertical) inclination.
SCOPE
The scope of work performed in this investigation included a
geologic site reconnaissance, subsurface exploration, labora-
tory testing, engineering analysis of the field and laboratory
data and the preparation of this report. The data obtained and
the analyses performed were for the purpose of providing design
and construction criteria for site earthwork. In addition,
samples of the materials encountered at proposed finish grade
were tested to provide a street section.
2255 Fire Mountain Drive, Oceanside, CA 92054 • (619) 439-2497
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Geotechnical Investigation
James Drive Extension
Project No. 183.1.1
September 1, 1985
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SITE CONDITIONS
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A. Surface
The proposed road alignment extends from the intersection
of Basswood and James Drive to approximately 1,000 feet to
the northwest. Ground surface elevations along the align-
ment vary from a high of approximately el. 159 at the
intersection of Basswood and James Drive to a low of
approximately el. 155 at the proposed terminus of James
Drive. The ground surface is dominated by flat,
gently-sloping terrain. The natural slope along the
alignment is essentially flat. A moderate to heavy growth
of grass and low brush covers the road alignment.
B. Site Geology
The site bedrock is composed of nearly flat-lying sedimen-
tary rock units of the Lindavista Formation. These
materials consist of interbedded fine-grained sandstones
and siltstones. The sedimentary rocks are massive. No
faults were observed in the exploratory excavations made
for this investigation nor are any mapped in the area. No
landsliding is present or anticipated on the site.
C. Subsurface
A geologic reconnaissance and subsurface investigation was
performed by hand excavating three test pits to a maximum
depth of three feet. The test pit locations are indicated
on the site plan. Logs of the test pits are presented in
Appendix A. Details of the laboratory testing and the
laboratory test results are presented in Appendix B.
The materials encountered in the exploratory test pits
consisted predominantly of dense formational silty and
clayey sands to the depths explored.
Based on past experience with similar materials, the sandy
formational materials of the Lindavista Formation possess
only a negligible potential for expansion.
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Geotechnical Investigation
James Drive Extension
Project No. 183.1.1
September 1, 1985
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GEOTECHNICAL CONSULTANTS
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The test pit logs and related information depict subsurface
conditions at the specific locations shown on the site plan
and on the particular dates designated on the logs. Sub-
surface conditions at other locations may differ from
conditions occurring at these test pit locations. Also,
the passage of time may result in changes in the subsurface
conditions due to environmental changes.
D. Groundwater
Groundwater was not encountered in any of the exploratory
excavations made for this investigation and no surface
seeps were observed. It must be noted, however, that
fluctuations in the level of groundwater may occur due to
variations in surface topography, subsurface stratifica-
tion, rainfall and other possible factors which may not
have been evident at the time of my field investigation.
In addition, experience has shown that a groundwater con-
dition can and may develop in areas where no groundwater
condition existed prior to site development. Irrigation
from adjacent nurseries and poor drainage have created some
wet areas.
E. Seismic Considerations
Based on my site reconnaissance and a review of some
available published information including the City of San
Diego Seismic Safety Study Fault Location Map and the
County of San Diego Faults and Epicenters Map, there are no
active or potentially active faults known to pass through
the site. The faults generally considered to have the most
potential for earthquake damage in the vicinity of the site
are within the active Elsinore and San Jacinto Fault Zones
located approximately 22 and 45 miles northeast of the
site, respectively. The Rose Canyon Fault is located
approximately 12 miles southwest of the site. No earth-
quake epicenter clusters are associated with this system
and no faults associated with the Rose Canyon Fault Set are
classified as active under current criteria.
Although research on earthquake prediction has greatly
increased in recent years, seismologists have not yet
reached the point where they can predict when and where an
earthquake will occur. Nevertheless, on the basis of
Geotechnical Investigation
James Drive Extension
Project No. 183.1.1
September 1, 1985
Page Four
GEQFACIFICA
GEOTECHNICAL CONSULTANTS
current technology, it is reasonable to assume that the
proposed road improvements will be subject to the effects
of at least one moderate earthquake during their design
life. During such an earthquake, the danger from fault
offset through the site is remote, but strong ground
shaking is likely to occur.
CONCLUSIONS AND RECOMMENDATIONS
From a soil and geological engineering standpoint, it is my
opinion that the site is suitable for construction of the
proposed road improvements provided the conclusions and
recommendations presented in this report are incorporated into
the design and construction of the project. Detailed recommen-
dations for the earthwork are presented in the following
paragraphs.
O A. Clearing and Stripping
The area of the road alignment should be stripped of all
surface vegetation and cleared of all obstructions
including any miscellaneous trash or debris that may be
present at the time of construction. The stripping depths
required to satisfactorily remove surface vegetation should
be determined in the field by the soil engineer's repre-
sentative at the time of construction. The cleared and
stripped materials should be disposed of off-site.
B. Preparation for Filling
After the alignment has been cleared and stripped, the
exposed subgrade soils in areas to receive fill should be
scarified to a depth of 6 inches, moisture-conditioned, and
compacted to the requirements presented in Item E, "Compac-
tion." In general, the natural surface soils are loose to
only shallow depths and as a result, the normal scarifica-
tion and recompaction process should be adequate to effec-
tively stabilize these soils.
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Geotechnical Investigation
James Drive Extension
Project No. 183.1.1
September 1, 1985
Page Five
GEQFACIFICA
GEOTECHNICAL CONSULTANTS
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C. Excavation
Based on the results of my exploratory excavations and my
experiences with formational soils similar to those present
on this site, it is my opinion that the on-site natural
formational soils can be excavated utilizing ordinary heavy
earthmoving equipment. The bidding contractors should not,
however, be relieved of making their own independent evalu-
ation of the excavatability of the on-site materials prior
to submitting their bids.
D. Materials for Fill
All existing on-site soils with an organic content of less
than 3 percent by volume are in general suitable for reuse
as fill. Fill material should in general, however, not
contain rocks or lumps over 12 inches in greatest dimension
and not more than 25 percent larger than 2-1/2 inches.
E. Compaction
All structural fill should be compacted to a minimum degree
of compaction of 90 percent based upon ASTM Test Designa-
tion D 1557-78. Any fill material should be spread and
compacted in uniform horizontal lifts not exceeding 8
inches in uncompacted thickness. Before compaction begins,
the fill should be brought to a water content that will
permit proper compaction by either: 1) aerating the fill
if it is too wet, or 2) moistening the fill with water if
it is too dry. Each lift should be thoroughly mixed before
compaction to ensure a uniform distribution of moisture.
F. Slopes
Based on the results of my soil and geological engineering
reconnaissance of the site, my past experience with similar
materials, and my engineering analysis, it is my opinion
that proposed 2:1 (horizontal to vertical) cut slopes will
mass instability (minimum static factor of
The cut slopes, however, should be
qualified engineering geologist at the time
to assure that no adverse geologic
which may not have been discovered in
be safe against
safety of 1.5).
inspected by a
of construction
conditions exist
connection with the work performed for this investigation.
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Geotechnical Investigation
James Drive Extension
Project No. 183.1.1
September 1, 1985
Page Six
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GEOTECHNICAL CONSULTANTS
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The on-site soils will be moderately susceptible to
erosion. Therefore, the project plans and specifications
should contain all necessary design features and construc-
tion requirements to prevent erosion of the on-site soils
both during and after construction. Slopes and other
exposed ground surfaces should be appropriately planted
with a protective ground cover.
It should be the grading contractor's obligation to take
all measures deemed necessary during grading to provide
erosion control devices in order to protect slope areas and
adjacent properties from storm damage and flood hazard
originating on this project. It should be made the
contractor's responsibility to maintain slopes in their
as-graded form until all slopes, berms, and associated
drainage devices are in satisfactory compliance with the
project plans and specifications.
G. Trench Backfill
Pipeline trenches should be backfilled with compacted
fill. Backfill materials should be placed in lift thick-
nesses appropriate to the type of compaction equipment
utilized and compacted to a minimum degree of compaction of
90 percent by mechanical means. In pavement areas, that
portion of the trench backfill within the pavement section
should conform to the material and compaction requirements
of the adjacent pavement section.
H. Drainage
With regard to the need for subsurface drainage provisions,
no conditions were encountered during the field investiga-
tion phase of my geotechnical investigation work which
would suggest the need for subsurface drains for intercept-
ing and disposing of free groundwater. However, the need
for such drainage provisions can normally best be
determined during the site preparation and earthwork opera-
tions based on a close examination of the soil, geological,
and groundwater seepage conditions being exposed. If con-
ditions are encountered during construction that suggest
the need for subsurface drains, I can at that time provide
specific recommendations for their installation.
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Geotechnical Investigation
James Drive Extension
Project No. 183.1.1
September 1, 1985
Page Seven
GEOTECHNICAL CONSULTANTS
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I. Construction Observation
Variations in soil conditions are possible and may be
encountered during construction. In order to permit
correlation between the preliminary soil data and the
actual soil conditions encountered during construction and
so as to assure conformance with the plans and specifica-
tions as originally contemplated, it is essential that the
soil engineer be retained to perform on-site review during
the course of construction. All earthwork should be per-
formed under the direction of the soil engineer's repre-
sentative to assure proper site preparation, selection of
satisfactory fill materials, as well as placement and
compaction of the fills.
J. Street Section
Based upon the R-Value obtained, I recommend that the pro-
posed street section be 3 inches of AC on 8 inches Class II
aggregate base.
If you have any questions, please call.
Very truly yours,
GEOPACIFICA
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JAMES F. KNOWLTON
C.E.G. 1045
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APPENDIX A
BACKHOE COMPANY: BUCKET SIZE: Hati d Excavated DATE: 8-8-85
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SOIL DESCRIPTION
TEST PIT NO. ! ELEVATION
TOPSOIL: Light Brown Silty Sand, dry, loose
BEDROCK: Lindavista Formation, Light brown
and reddish brown sandstone, slightly moist,
T.D. 3'
No Water
No Caving
TEST PIT NO. 2 ELEVATION —
5 —
10 —
15 —
TOPSOIL: Brown silt, dry, loose
BEDROCK: Lindavista Formation, Light brown
and brown silty sandstone, slightly moist,
dense
T.D. 3'
No Water
No Caving
LOG OF TEST PITS
PROJECT NO. 183.1.1 JAMES DRIVE EXTENSION FIGURE NO A-l
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RACKHOE COMPANY: BUCKET SIZE : Han d Excavated DATE: 8-8-85
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5200
SOIL DESCRIPTION
TEST PIT NO. ELEVATION
TOPSOIL: Brown sandy silt, dry, loose
BEDROCK: Lindavista Formation, Brown to
reddish brown, sandstone, slightly moist, dense
T.D. 3'
No Water
No Caving
TEST PIT NO.ELEVATION
10
15
LOG OF TEST PITS
PROJECT NO. 183.1.1 JAMES DRIVE EXTENSION FIGURE NO.A-2
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APPENDIX B
Sample
No.
Tl-2
Sample
No.
Tl-2
Sample
No.
*Tl-2
Summary of Laboratory Compaction Test Results
ASTM D1557-70
Description
Brown, Silty SAND
Maximum Dry
Density
pcf
117.1
Optimum
Moisture
% Dry Wt,
11.2
Summary of Laboratory Expansion Index
Test Results
Moisture Content
Before
Test
9.3
After
Test
17.3
Dry
Density
pcf
112.8
Expansion
Index
0
Summary of Direct Shear Test Results
Dry
Density
pcf
105.0
Moisture
Content
11.7
Unit
Cohesion
psf
270
Angle of
Shear
Resistance
Degrees
31
*Sample remolded to approximately 90 percent of maximum dry
density at near optimum moisture content.
JAMES DRIVE EXTENSION
JOB NO.:183.1.1 DAT E.-September 1,1985 FIGURE:B-l