HomeMy WebLinkAbout71-098-EG; Squires Dam No. 2 Foundation & Borrow Material; Squires Dam No. 2 Foundation & Borrow Material; 1972-03-10p^ GEOLOGIC AND SOILS INVESTIGATION
FOUNDATIONS AND BORROW MATERIALS
^ SQUIRES DAM NO. 2
[I CARLSBAD, CALIFORNIA
Conducted for:
CARLSBAD MUNICIPAL WATER DISTRICT
P. O. BOX 1095
CARLSBAD, CALIFORNIA 92008
In Cooperation with:
Woodside/Kubota & Associates
309 West Third Street
Santa Ana, California 92701
and
Benton Engineering, Inc.
6741 El Cajon Boulevard
San Diego, California 92115
Project No, 71-098-EG
March 10, 1972
FUGRO, Inc.
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CONSULTING ENGINEERS AND GEO
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Jack J. Schoustra, President
Jay L-Smith, Vice President
Ronald F. Scott, Sc.D., Consultant
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Woodside Kubota & Associates, Inc.
309 West Third Street
Santa Ana, California 92701
Subject: Project No. 71-098-EG
March 10, 1972
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Gentlemen:
Transmitted herewith is our feasibility report on Squires Dam No. 2.
Based on the geologic and foundation engineering studies, it is our
opinion that the proposed dam and reservoir can be safely constructed
at the site. The bedrock at the site will provide adequate foundation
support and is sufficiently impermeable so that a lining will not be
required. Except for riprap and filter material, there is a sufficient
amount of surficial and bedrock material at the site for construction
of the embankment and dikes.
The investigation was performed under the general supervision of
Jack J. Schoustra. The geologic studies were supervised by Jay L.
Smith and were conducted by John D. Scott. The engineering studies
were made by Stanley H. Madsen.
We appreciate the opportunity of working with you on this project and
will be glad to discuss the report with you at any time.
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Sincerely,
President
SHM/JJS/jm
LJ Encl. : a. s.
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FUGRO, INC. 730 East Third Street • P. 0. Box 2291 • Long Beach, California 90801
Telephone (213) 775-7642 and (213) 435-8351 • Cable: FUGRO LONG BEACH
Affiliated with N. V. FUGRO • Head Office: Leldschendam, Netherlands
Branch Offices: Arnhem • Eindhoven • Curasao • Paramaribo • Singapore
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& ^SSOCO^YES,
I. ,' .,.:! -J
ENGINEERS
309 West Third Street • Santa Ana, California 92701 • Phone: (714) 542-3987 MARCH 14, 1972
HONORABLE BOARD OF DIRECTORS • • • ••
CARLSBAD MUNICIPAL WATER DISTRICT '. '
SUBJECT: SQUIRES DAM ADDITION No. 2
GENTLEMEN: • . . '
ON NOVEMBER 30, 1971 WE MADE A PRELIMINARY REPORT ON THE FEASIBILITY OF
CONSTRUCTING SQUIRES DAM ADDITION No. 2 AND RECOMMENDED THAT THE PROPOSED
SITE UNDER CONSIDERATION BE ACQUIRED. THIS WAS BASED ON THE PRELIMINARY SOILS-'
AND GEOLOGICAL INVESTIGATIONS WHICH WERE AVAILABLE AT THAT TIME.
THE "FIELD TESTING AND SOILS ANALYSES" REPORT WAS COMPLETED ON JANUARY 24, 1972
BY BENTON ENGINEERING, INC. THE REPORT ON "GEOLOGY, SOILS INVESTIGATION, >
FOUNDATION, AND BORROW MATERIALS" WAS COMPLETED ON MARCH 10, 1972 BY FUGRO, INC.
THESE REPORTS AND THE CONCLUSIONS CONTAINED THEREIN SUBSTANTIATE OUR CONCLUSION
OF NOVEMBER 30, 1971 THAT THE SITE is SUITABLE FOR THE CONSTRUCTION OF SQUIRES
DAM ADDITION: No. 2 AS PLANNED. THESE REPORTS CONTAIN THE NECESSARY INFORMATION
FOR PREPARING ENGINEERING DESIGNS, .COST ESTI MATES, AND ^EVALUATIONS OF THE
VARIOUS ALTERNATES FOR A FINAL DESIGN.
THE REPORTS ALSO PROVIDE SUFFICIENT INFORMATION FOR EVALUATION OF THE SITE AS A
BORROW AREA' FOR ROAD CONSTRUCTION MATERIALS. THE WEATHERED GRANITIC ROCK ON
THE SITE IS SUITABLE FOR USE AS BORROW MATERIAL. MOST OF THE MATERIALS WILL MEET
THE SPECIFICATIONS FOR CLASS 3 SUBBASE OF THE STATE OF CALIFORNIA DIVISION OF
HIGHWAYS, CLASS 3 BASE FOR SAN DIEGO COUNTY, AND DISINTEGRATED GRANITE OF THE
STANDARD SPECIFICATIONS FOR PUBLIC WORKS CONSTRUCTION..
THE BED ROCK AND DAM SECTIONS WOULD HAVE SUCH LOW PERMEABILITY THAT IMPERMEABLE
LINING OF THE RESERVOIR WOULD NOT BE NECESSARY.
CONCLUSION: ' .
THE SITE IS SUITABLE FOR THE CONSTRUCTION OF THE PROPOSED SQUIRES DAM ADDITION
NO. 2 AND .SUFFICIENT SOILS AND GEOLOGICAL INFORMATION IS AVAILABLE FOR PRELIMINARY
AND FINAL DESIGN, .! NCLUD I NG COST ESTIMATES.
RESPECTFULLY SUBMITTED,.
. . WOODS IDE/KUBOTA & ASSOCIATES, INC.
. ' CONSULTING ENGINEERS
BY
RDW/pjB>an Diego CouIn San Diego County, Carlsbad
R. D. WOODS IDE
CONSULTING ENGINEER
j ; ; . TABLE OF CONTENTS
Page
U 1. INTRODUCTION 1
H 2. SCOPE OF INVESTIGATION 2
2.1 FIELD AND LABORATORY STUDIES 2
'-' 2.2 EXTENT OF RECOMMENDATIONS 3
H 3. GEOLOGIC CONDITIONS 4
* ) v
3.1 TOPOGRAPHY AND DRAINAGE 4
*-" 3.2 BEDROCK LITHOLOGY 4
H 3.3 SURFICIAL MATERIALS 6
3. 31 Alluvium 6
3. 32 Slopewash Deposits 6
M 3.4 BEDROCK STRUCTURE 7i I
P, 3. 41 Joints 7
3.42 Faults . . 7
PI 3.5 REGIONAL SEISMICITY 9i I
,-, 3.6 GEOLOGIC CONCLUSIONS 10
M
4. AVAILABLE BORROW MATERIALS 11
nM 4.1 QUANTITIES 11
p. 4.11 General 11
u 4.12 Granitic Rock 11
(J 4.13 Torrey Sand 12
ri 4.14 Alluvium 12
4.15 Slopewash 12
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n TABLE OF CONTENTS (Cont. )
Page
U 4.2 PROPERTIES OF EMBANKMENT MATERIALS ... 13
H 4. 21 Gradation 13
4. 22 Permeability 14
Li 4.23 Unit Weight 14
|~| 5. TYPICAL SECTIONS 15
5.1 GENERAL 15n
L 5.2 CENTRAL CORE WITH BLANKET DRAIN 17
H 5.3 CENTRAL CORE WITH CHIMNEY DRAIN 17
5.4 HOMOGENEOUS SECTION WITH CHIMNEY DRAIN . 17
5.5 DISCUSSION 18
Fj 6. RECOMMENDATIONS ,. 19
6.1 EXCAVATIONS 19
^ 6.11 Stripping Depth - Main Dam 19
P, 6.12 Stripping Depth - Cutoff Trench 21
6. 13 Stripping Depth - Dikes 23
LI 6.2 MAXIMUM DENSITY TEST AND COMPACTION
CRITERIA . 24M
6. 21 Maximum Density Test 24
6.22 Compaction Criteria 24
p 6.3 GROUTING 24
6.4 RESERVOIR LINING 25
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I 6.5 INSTRUMENTATION 25
FUGRO, Inc.
TABLE OF CONTENTS (Cont. )
Page
6.6 BORROW MATERIAL FOR ROAD CONSTRUCTION . . 26
6. 61 Test Results and Specifications 26
6. 62 Conclusion 29
BIBLIOGRAPHY
TABLES, FIGURES, AND DRAWINGS
TABLE NO. 1 Quantities of Borrow Materials
TABLE NO. 2
TABLE NO. 3
TABLE NO. 4
TABLE NO. 5
Recommended Permeability Values
Unit Weight and Moisture Content
Stripping Depth for Embankment
Stripping Depth for Cutoff Trench
11
14
15
20
22
FIGURE NO. 1 Gradation of Available Borrow Materials
Following Page 13
DRAWING NO. 1
DRAWING NO. 2
Geologic Map
Geologic Sections
In Pocket
In Pocket
FUGRO, Inc.
-p 1. INTRODUCTION
PM This report presents the results of studies performed at the
pi site of proposed Squires Dam No. 2. The site covers an area slightly
larger than 50 acres and is located just north of the existing Squires Dam.
M The site is about five miles east of the city of Carlsbad and is easily
-f-j reached by a road branching off of El Camino Real about 1. 5 miles north
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of Palomar Airport Road. (See Location Map on Drawing No. 1)
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|_J The purpose of the study was to determine the feasibility of
•|~~] constructing a second dam, primarily with respect to geologic conditions,
suitability of surficial and bedrock materials for foundation support, and
\^J available borrow materials. The report also includes a discussion of
r~| design concepts and recommendations relating to stripping depths,u
compaction, grouting, reservoir lining and instrumentation. A secondary
j_J purpose of the study was to determine the feasibility of using a portion of
f~~j the reservoir area as a borrow pit prior to construction of the dam.
The investigation has been coordinated with Benton EngineeringnU who did much of the field work and all of the laborjitory testing. FUGRO,
j~| Inc. performed the geologic investigation, supervised the field and
laboratory investigation, made site inspections during the progress of
LJ the field work, evaluated the test data, made some preliminary calculations
[^~j concerning quantities of borrow materials, and prepared this report.
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The report includes data initially presented in a progress
report dated October 27, 1971. The field and laboratory studies per-
formed By Benton Engineering are included in a separate report dated
January 24, 1972 under Project No. 71-8-6A.
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fl 2. SCOPE OF INVESTIGATION
2. 1 FIELD AND LABORATORY STUDIES
P The investigation included:
1. Research of available geologic data, both published and
unpublished, and a review of large and small scale aerial
Pj photographs of the site and vicinity;
„ 2. Preparation of a geologic map of the site and geologic
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reconnaissance of the vicinity by an Engineering Geologist;
P1 3. Excavation of 25 backhoe-trenches on and off the site;
r—| 4. Excavation of 3 bulldozer-trenches in the abutment areas;
5. Drilling of three bucket-auger borings in the channel area
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I near the proposed dam;
pi 6. Drilling of five core-borings with water-pressure tests in
the abutments and channel bottom of the proposed dam; and
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! 7. Laboratory testing of representative samples of surficial and
j—I bedrock materials to determine their physical characteristics
and engineering properties.
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All of the field work was coordinated with Benton Engineering,
who performed rippability tests with the bulldozer (trenches 28 through
32) and obtained representative samples with the backhoe (trenches 22
through 27). Although not all trenches were excavated expressly for the
geologic investigation, all were inspected by an Engineering Geologist.
All of the laboratory tests were performed by Benton Engineering.
The results of these tests are included in their report dated January 24, 1972.
2.2 EXTENT OF RECOMMENDATIONS
The recommendations included in this report are limited to those
concerning foundations and available borrow materials. The recommendations
are based on field inspection of trenches, examination of cores, and results
of field and laboratory tests.
Because the report is primarily a feasibility report and because
maximum water elevation, reservoir area, and drawdown conditions have
not been definitely established, the report does not include any discussion
of stability. Strength tests and stability analyses will be performed at a
later date as required Likewise, there is no discussion of the outlet works
or spillway. Additional recommendations will be required as design
concepts are finalized.
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u 3. GEOLOGIC CONDITIONS:° v '; '. :
3. 1 TOPOGRAPHY AND DRAINAGE
The site is located in an area of gentle, rolling hills. There
D are two stream channels located within the site; the southern channel has
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n a westerly trend and the more northerly one has a southwesterly .trend. The
two channels converge near the west end of the site. Located between the
ni two channels is the most prominent ridge within the site; it has a maximum
^-, elevation of 547. 5 feet. The highest point (elevation 556) on the site is
located in the southeast corner where a narrow ridge separates the site
ni area from the existing reservoir of Squires Dam No. 1. The lowest point
G (elevation 443) is located in the channel at the west property line. Two
small peaks define the limits of the proposed dam. The northern peak
p1 (right abutment) has a maximum elevation of 506. 8 and the southerly peak
0 (left abutment) has a maximum elevation of 512. 8.
The only flow in the channels is that produced by runoff within
the drainage area which is limited almost entirely to the site area.
D 3. 2 BEDROCK LITHOLQGY
The dam -and-reservoir site is underlain by granitic rock
(quart/, (lioi'it'o) of tin; Southern California batholith. This crystalline rock
is upper Cretaceous in age and is the oldest, most competent rock exposed
at the site. Near the ground surface, the quartz diorite is commonly reddish
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brown, very weathered, moderately to very jointed, and moderately hard.
At depth the rock is light gray to bluish gray, slightly weathered or fresh,
hard, and moderately jointed. Depth of weathering varies locally and
appears to be controlled by the degree of jointing. According to core
borings, the depth to moderately weathered rock in the abutment areas
ranges from 23 to 31 feet on the ridges, and from 29 to 37 feet on the lower
slopes near the gullies. The degree of weathering is shown in the sections
I I . on Drawing No. 2.
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A relatively-thin veneer of Eocene sedimentary rocks (Torrey
Sand member of the LaJolla Formation) unconformably overlies the quartz
diorite (Dwg. No. 1). Most of this member has been eroded away leaving
only an elongate remnant in the canyon bottom along the north margin of
the site. Trenches and borings indicate the Torrey Sand member has a
0 maximum thickness of about 19 feet in the site and is commonly less than. .-•
_ 10 feet thick. The Torrey Sand member consists of light brown and gray
Li interbedded silty sandstone, sandy siltstone, and claystone with some
scattered lenses of clean uncemented sandstone. The rocks are moderately
,—, hard to hard and, with the exception of scattered lenses of loose, clean
sandstone, are relatively impermeable. The bedding planes are nearly
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I horizontal and the individual beds range in thickness from a few inches to-U
r-i a few feet.
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3. 3 SURFICIAL MATERIALS
•3_._3_1 Alluvium
The two large canyons that converge near the west edge of the
site are covered by alluvium consisting of sandy silt, silty sand, and clayey
sand. These deposits are brown, firm, slightly porous to porous, and
contain organic debris. A maximum depth of 16 feet of alluvium was
encountered in Boring AB-2 near the upstream toe of the dam. Near the
center and downstream toe of the dam, the depth of alluvium ranges from
9 to 14 feet (DT-31 and AB-2). No water was observed in any of the trenches
or borings in the alluvial deposits.
3. 3Z Slopewash Deposits
Nearly the entire site is covered by a thick blanket of slopewash
deposits which ranges from 0. 5 to 2 feet thick on the ridges, to about 7. 5
feet on the lower slopes near trench 20. Drawing 1, the geologic map,
indicates the distribution of slopewash deposits where observed or estimated
to be greater than 4 feet thick. The slopewash deposits have been derived
from disintegrated quartz diorite and consist of reddish brown and grayish
brown silty sand. In some areas, portions of these deposits are classified
as sandy clay. They are dry, porous, and contain some organic debris.
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3.4 BEDROCK STRUCTURE
3.41 Joints
Joints are extensively developed in the quart diorite and are the
most common structural feature at the site. Prominent trends of joints
are N 40 - 60 E and N 20 - 40 W, forming a nearly perpendicular conjugate
set. Dips are steep and the joints have slight alteration or oxide staining
along some surfaces. As indicated by the core, joint spacing in the abut-
ments ranges from a few inches to a few feet.
Water pressure tests in the core borings indicate the joints are
tight and should not cause excessive leakage.
3.42 Faults
Trenching in the northern part of the site revealed a fault striking
N 55 to 60 degrees E and dipping 60 degrees N W. The fault is not well-
expressed in the topography but could be traced in the trenches from the
proposed right abutment (DT-30) through Trench 8 and is presumed to continue
eastward to the site boundary. The fault displaces the Torrey Sand member
10 feet vertically in Trench 8A, but no slickensides were observed and the
D sense or amount of slip could not be determined. The gouge zone is less.
than one inch wide and the rocks (diorite and Torrey Sand member) adjacent
to the fault are not noticeably fractured. In Trench DT-30 the fault is a thin
shear zone with little or no clay, and the diorite adjacent to the shear is not
fractured more than unfaulted rock in other parts of the trench.
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Core borings CB-5 and CB-2, in opposite abutments of the main
dam, revealed fault gouge at depths of 18 feet and 60 feet respectively.
These gouge zones consist of reddish brown, slickensided clay ranging in
thickness from 3 inches to 7 inches. These two small faults are not exposed
in the exploratory trenches on the abutments and they have not been observed
elsewhere at the site. Water pressure tests at these shear zones indicate
only negligible leakage, although the core recovered from the borings is
very fractured.
Backhoe trench 'A' was excavated beyond the site boundaries to
investigate a prominent northwest-trending lineation about 600 feet west
of the proposed dam. This lineation was first observed on small-scale
aerial photographs of the region and was suspected of representing a fault.
In the field, the lineation could be traced for 3 miles as a series of aligned
valleys and ridge-depressions. Trench 'A', which was 154 feet long,
was excavated across the lineation just outside the west boundary of the
site property. The trench revealed a near-vertical fault zone striking
N 15 W and corresponding closely in position and orientation to the lineation.
This fault zone is approximately one foot wide and is composed of numerous
shear surfaces with thin films of clay gouge. A few of the shear surfaces
have vertical slickensides but the total amount of slip could not be determined
because the fault was exposed only in the diorite. Several other shears were
noted in Trench 'A1 but these were significantly smaller and fewer in number
than the fault just described.
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No faults or shears parallelling the lineation were revealed
in trenches in the abutments or in the channel area of the main dam.
Other geologic maps of the region indicate that Tertiary
sedimentary rocks overlie the north and south end of the lineation
without displacement of the contact. This suggests no fault movement
since Tertiary time (Eocene). Our inspection of these same relation-
ships was not completely conclusive due to the poor exposures and the
uncomformable nature of the contacts. However, the contacts do appear
to be grossly continuous across the lineation and no evidence of
displacement was found. Presently there is no evidence to suggest that
the fault has moved in Holocene time or has been seismically active in
historic time.
3. 5 REGIONAL SEISMICITY
Historically the Oceanside-San Diego coastal area has been
relatively quite seismically. The Crustal Strain and Fault Movement
Investigation, Bulletin 116-2, by the Department of Water Resources,
and seismological information obtained from the California Institute of
Technology indicate no earthquake epicenters greater than magnitude 4
have occurred within a 15 mile radius of the site between 1934 and 1970.
The two nearest earthquake epicenters (magnitude 4. 0 - 4.4) have
occurred 17 and 25 miles from the site during that same time period.
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Some of these small earthquakes have probably been associated
•with the Elsinore fault zone, which is approximately 23 miles northeast
of Squires Dam No. 2 and is the closest large fault to the site. From
geologic and seismic evidence in the region, it is unlikely that earthquake
groundmotion of damaging intensity has occurred at the site during historic
time.
3.6 GEOLOGIC CONCLUSIONS
1. The geology of the dam and reservoir site is suitable in terms of
stability and impermeability.
2. The quartz diorite •will provide a relatively uncompressible and
impermeable foundation for the main dam.
3. The Eocene sedimentary rocks are firm and suitable for support
j of the main dam fill; however, the permeability of the rocks varies
and the cut-off trench should extend into the quartz diorite.
4. The abutment and reservoir areas are free of landslides and are
not potentially unstable under anticipated conditions.
5. The faults observed to date in the abutment and reservoir areas
are not expected to affect the dynamic or static stability, or
water tightness of the proposed project.
i>. Tin.: :;c'i .sinic it y of the Carlsbad region is relatively low, and
earthquakes of damaging intensity are unlikely near the site.
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4. AVAILABLE BORROW MATERIALS
4. 1 QUANTITIES
4. 11 General
It is expected that, except for filter material and riprap, all of
the embankment materials can be obtained at the proposed dam and
reservoir site. Available materials include very weathered granitic rock,
Torrey sand, alluvium, and slopewash. The estimated quantities of each
of these materials is shown in the following table.
TABLE NO. I
QUANTITIES OF BORROW MATERIALS
Material
Very Weathered Granitic Rock
Torrey Sand
Alluvium
Slopewash Deposits
Quantity Available in
Site Area, cubic yards
>500, 000 *
55, 000 10, 000
20, 000 4, 000
7, 000 + 2, 000
* The entire site is underlain by granitic rock so that the quantity available
is governed only by the depth of excavation.
4. 12 Granitic Rock
Since the granitic rock underlies the entire site, there is plenty
of this material available for construction of the dam and dikes. The only
limiting factors are the depth to which the material can be easily excavated
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and the desired shape of the reservoir. The core borings do suggest that
the rock is more deeply weathered in the high areas and that excavations
in these areas will be easier than adjacent to existing channels.
4. 13 Torrey Sand
The Torrey sand is a good source of embankment material because
of its location and because it is a thick-enough unit to be processed. The
main problem with using this material is the change in lithology with depth.
It would be very difficult to separate silts and clays from the sands and,
thus, it would not be practical to plan on using only portions of this formation
in a particular zone of an embankment.
4. 14 Alluvium
Since the alluvium must be excavated within the embankment area,
it is logical to incorporate this material into the embankment. Additional
alluvium is available upstream of the.main dam; this material decreases in
thickness upstream but is generally thick enough to be processed.
4. 15 Slopewash
Slopewash has been mapped in those areas where it is estimated
to be greater than four feet thick. The volume of material shown in the
table is the estimated volume in the two broad belts in the western part of
the site for an assumed thickness of two feet. The actual thickness is quite
variable, and where the thickness is two feet or less, much of it will be
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removed daring stripping operations. All slopewash material not
containing organic debris can be used in., the .embankment..
4. 2 PROPERTIES OF EMBANKMENT MATERIALS
4. Zl Gradation
The weathered bedrock generally breaks down to the extent that
all of it passes the No. 4 sieve. For seven bulk samples on which mechanical
analysis tests were performed, the percent passing the No. ZOO sieve varied
between 5 and 12 percent. This percentage of silt and clay requires a dual
classification when using the Unified Soil Classification system. All of the ,
samples tested fall into the classification of SW - SM, indicating a well-
graded, fine to coarse, silty sand.
The alluvium contains practically no gravel. Of the seven samples
tested, the percentage of silt and clay varied from 21 to 42 percent. The
typical classification is fine to medium clayey-sand. The range in gradation
of both the alluvium and weathered granitic rock is shown in graphical form
on the following page. (Fig. No. I)
The Torrey sand has a wide range in gradation and includes
material coarser than the granitic rock and finer than the alluvium. Based
on visual inspection of trenches, it is concluded that 75 percent or more of
the Torrey sand has a classification comparable to or finer grained than
the alluvium.
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F i;.3o i /r
PROJECT NO.: rl-098-EG GRAIN-SIZE DISTRIBUTION
HYDROMETER
200
U.S. STANDARD SIEVE NUMBER
100 60 40 ~20 . . 10
STANDARD SIEVE OPENING
3/8" 3/4" .IVi" 3"
RANGE IN GRADATION
OF ALLUVIUM
RANGE IN GRADATION
OF WEATHERED GRANITIC
ROCK
.001 .05 0.1 . 0.5
GRAIN-SIZE IN MILLIMETERS
5.0 10.0 50.0
SILT OR CLAY SAND
MEDIUM
GRAVEL
FINE | COARSE
GRADATION OF AVAILABLE BORROW MATERIALS
SQUIRES DAM NO. Z
Figure No. 1
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4. 2Z Permeability
Benton Engineering performed five permeability tests on samples
of the weathered granitic rock. Three of the samples were compacted to
95 percent of the maximum density (DWR Test Designation S-10) and two
other samples were compacted to 98 and 99 percent of maximum density.
The range in permeability was between 9. 8 x 10-6 anc[ 4. 4 x 10-7.
It is recommended that for an embankment using weathered bedrock, the
values shown in Table No. 2 bo used.
Three permeability tests were performed on samples of alluvium.
The range in permeability was between 1. 5 x 10~7 and 3.0 x 10-7 cm/sec. .
The recommended values for alluvium are included in Table No. 2
TABLE NO. 2
RECOMMENDED PERMEABILITY VALUES
Material
Weathe red
Granitic Rock
Alluvium
Vertical
Pe rmeability
c m / s e c
1. 0 x lO-6
2. 0 x 10 -7
Horizontal
Permeability
c m / s e c
9- 0 x lO-6
18. 0 x 10-7
4. 23 Unit Weight
Because the maximum dry density and optimum moisture
content of the alluvium and granitic rock are nearly identical, the same
value can be used for both materials. The recommended values are
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shown in Table No. 3.
TABLE NO. 3
UNIT WEIGHT AND MOISTURE CONTENT
Material
W e a th e r e d
G rani tic
Rock or
Alluvium
Dry Unit
Weight, pcf
119. 0
Optimum
Moisture
Content, %
10. 0
Moist
Unit
Weight, pcf
131. 0
Submerged
Unit
Weight, pcf
74. 0
'5. TYPICAL SECTIONS
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5. 1 GENERAL
Both the alluvium and the Torrey Sand could be used as core
material and the quantities of these materials at the site appear to be
sufficient for the main dam section. In determining a design, consideration
should be given to both a centra.! core section and a homogeneous section.
The following three sections are considered feasible and art; illustrated
on the following page.
1. Central core with blanket drain.
2. Central core with chimney drain.
.3. Homogeneous section with chimney drain.
The final selection will depend on the maximum water level and
a cost evaluation of the different alternatives. A brief discussion of each
section follows. Since all of the sections will require wave orotection on
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SECTION I
CENTRAL CORE WITH BLANKET DRAIN
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SECTION II
:ENTRAL CORE WITH CHIMNEY
SECTION III
HOMOGENEOUS SECTION WI i'H r;HIMKEY DRAIN
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the upstream slope, the discussion will not include materials required
for this protection.
5. 2 CENTRAL CORE WITH BLANKET DRAIN•
The advantage of this section is that the only material that has
to be imported is the blanket drain and it can be placed in one operation
during an early phase of construction.
The disadvantage is that the core material has to be carefully
selected to insure that there are no pervious zones along which piping
could develop. Very close field inspection would be required. Because
of this selection and control, construction work would be slowed down.
5. 3 CENTRAL CORE WITH CHIMNEY DRAIN
The advantage of this section is that, with the chimney drain,
^— ' the selection and control of the core material is not as critical. Thus,
more liberal specifications could be used and less selection of materials
would be required.D The disadvantage is that the chimney drain would have to be
select import material, which would have to be trucked in throughout most
of the construction period.
[I 5-4 HOMOGENEOUS SECTION WITH CHIMNEY DRAIN
«—, The advantage of this section is that all of the available materials,
including the Torrey sand and alluvium, can be used throughout the embankment
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section. Such a procedure would tend to speed up construction of the
embankment since there would be no selective use of the available
materials.
The disadvantage is the same as that mentioned above for a
central core section with chimney drain.
5. 5 DISCUSSION
Based on preliminary data, the homogeneous section with chimney'
drain appears to be the preferable section. Using this section and the
permeability values included in Section 4, preliminary estimates of
seepage through the embankment of the main dam are on the order of five
acre feet per year. Even if the embankment included a core zone and t
the seepage were reduced to one-fifth this amount, it is doubtful that the
additional expense of constructing a zoned dam is warranted. Because of
the expected low seepage without a core, it does not appear logical to
consider a core unless it provides some other additional advantage other
than a reduction of seepage. The only other apparent advantage would be
if the chimney drain could be eliminated, resulting in a section similar to
Section 1 on page 16.
In order to eliminate the chimney drain, the entire core section
would have to have a sufficient percentage of fines to insure that the core
was impervious. There would also have to be assurance that there was a
sufficient quantity of core material meeting the specifications. The limited
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U testing done to date is not adequate to determine these factors. A much
more thorough investigation would have to be made of the alluvium and
Torrey sand. An economic study may reveal that such an investigation
LJ is warranted because of the potential savings if the chimney drain can be
M eliminated.
LJ 6. RECOMMENDATIONS
nL 6.1 EXCAVATIONS
n
6.11 Stripping Depth - Main Dam
D To provide adequate foundation support for the embankment,
.
excavations must remove all of the soil cover, slopewash deposits, and
P alluvium, and extend at least two feet into weathered granitic rock or at
least four feet into the Torrey sand. The recommended depth of stripping
required at trench and boring locations in the embankment area to meet
u the above requirement is given in the following table. The stripping
depth is also shown on the lower half of Drawing No. 2. The line
representing the recommended, stripping depth has been smoothed out
in some areas and does not always represent exact depths as given in
I the table.
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TABLE NO. 4
STRIPPING DEPTH FOR EMBANKMENT
Location
Left
Abutment
Channel
Right
Abutment
Boring or
Trench No
DT 32
T 19
T 20
DT 31
CB 3
AB 2
AB 1
T 17
T 18
T 16
AB 3
T 14
T 12
T 15
T 13
DT 30
(1) (2)
Surface Recommended Depth Elevation After
Elevation of Stripping, feet Stripping
478 - 513
474 - 480
450 - 458
450 - 456
451
448
492
475
470
464
462
470
468
466
476 - 483
479 - 504
5 473
5 469
6 - 9 444
11 439
12 439
16 432
18 474
4 471
4 466
(> 458
7 455
8 462
8 ? (3) 460
5 461
S 47 1
(.. 473
- 508
- 475
- 449
- 445
- 478
- 498
(1) Where two elevations are given, it is the elevations at either end of the trend
(2) Where two elevations are given, it is the elevation after stripping at either
end of the trench.
(3) Trench only 4. 5' deep. Probably Torrey sand in bottom foot of trench.
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6.12 Stripping Depth - Cutoff Trench
It is recommended that the main dam include a cutoff trench
which extends into the granitic rock. The trench should extend at least
five feet into granitic rock in the abutments and at least three feet into the
granitic rock beneath the Torrey sand and alluvium. After excavating, the
trench should be inspected by an engineering geologist to see if there are
any zones of highly fractured rock where the trench may need to be
deepened.
The recommended excavation depths are based primarily on the
results of the water pressure tests which indicate that even the very
weathered granitic rock is quite impervious. In Core Borings 1,2,4, and
5 the water pressure tests performed nearest to the surface were in rock
classified as "very weathered" and in all of these tests there was no flow
or neglibible flow.
In Core Boring 3, there was only one foot of very weathered rock
in contrast to the 20 feet or more of very weathered rock in the abutments.
Because of the good quality of the rock within a foot or two of the bedrock-
alluvium contact, it is anticipated that the cutoff trench will not have to
extend more than three feet into the bedrock in the existing channel area.
The recommended depth of excavation for the cutoff trench
is given in the following table.
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TABLE NO. 5
STRIPPING DEPTH FOR CUTOFF TRENCH
Recommended Depth Elevation of
Boring or Surface of Excavation for Base
Location Trench No. Elevation Cutoff Trench, feet of Trench
Left
Abutment DT 32 478 - 513
Channel DT 31 450 - 456
AB 3 46 Z
T 14 470
Right
Abutment T 13 476 - 483
DT 30 479 - 504
7 471 - 506
12 438 - 444 .
22 440
14* Below 456.
8 468 - 475
9 470 - 495
* Trench did not penetrate into bedrock.
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A comparison of Tables No. 4 and 5 indicates that in the abutments
the cutoff trench needs to be about three feet deeper than the stripping depth
for the rest of the embankment. In the channel area, the cutoff trench will
be as much as 15 feet deeper than the stripping depth for the rest of the dam.
V •-;•'....
The reason for this increase is that the cutoff trench must penetrate through
the Torrey sand. The Torrey sand has adequate strength for foundation
support but because it is nearly horizontally bedded and has lenses of
relatively clean sand, it is locally quite permeable. ;
For the height of the dam being considered, the width of the cutoff
is governed mainly by ease of construction. A base width of 15 feet is
recommended. The side slopes should be no steeper than 1:1.
6.1_3 Stripping Depth - Dikes .
At the present time the location and height of dikes is not known
and no field work has been done in the probable dike locations. Nevertheless,
it is likely that the geologic and foundation conditions are quite similar
throughout the site area and, therefore, a stripping depth of two feet into
bedrock should be adequate. No cutoff trench should be necessary. After
stripping for the dikes, a careful inspection should be made by an engineering
geologist to see if any very fractured zones or other conditions are revealed
that would require deeper excavations.
A review should be made of final dike locations to see if there are
any locations where additional field studies are considered necessary.
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D
6. 2 MAXIMUM DENSITY TEST AND COMPACTION CRITERIAQ —
_ 6>. 21 MaXL mum Den sity Test
It is recommended that the Department of Water Resources
(DWR) Test Designation S-10 b.e used to determine the maximum density
i_1 and optimum moisture content of embankment materials. It is anticipated
that all of the embankment materials will break down to pass the No. 4 sieve
nj so that Method A can be used. The data on this method is as follows:LJ
nI Size of Mold 1/20 cubic foot
pi Hammer Weight 10 pounds
Height of Drop 18 inches
Number of Layers 5
p Number of Blows per Layer ... 13
Energy per Cubic Foot 19, 500 ft. Ibs.
6^. 22 Compaction Criteria
p
It is recommended that the following compaction criteria be used:
D a. Average Percent Compaction - at least 95%
b. Minimum Percent compaction, any test - 93%
I c. Allowable number of tests below the average for any
pi three consecutive working days - 10%
U 6. 3 GROUTING
p The results of the water pressure tests indicate that grouting will
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not be necessary. Even at pressures of 150 percent of the estimated
maximum hydrostatic head, there was no flow or negligible flow.
It is anticipated that slush grouting in the bottom of the cutoff
trench will not be necessary. It should be possible to produce a
sufficiently smooth bottom surface so there will be an adequate bond with
the embankment materials. Slush grouting would be required locally only
if there is an irregular-shaped zone of more resistant rock.
6.4 RESERVOIR LINING
Based on the performance of the existing Squires Dam, the results
of the water pressure tests, and an examination of trenches, it is
concluded that a reservoir lining is not necessary. The bedrock conditions
are comparable to those at the existing Squires Dam. The records show that
the seepage losses at this dam are less than one half acre-foot per year.
Such low seepage is indicative of the imperviousness of the granitic bedrock.
6. 5 INSTRUMENTATION
It is concluded that a minimum amount of instrumentation will be
needed for the proposed dam. Surface survey markers and a few
piezometers should be adequate. The number and location of piezometers
should be determined after design details are known.
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6.6 BORROW MATERIAL FOR ROAD CONSTRUCTION
6.61 Test Results and Specifications
Consideration is being given to using a portion of the reservoir
area as a borrow pit, using the available weathered granitic rock. Such
a procedure will bring in additional revenue as well as enlarge the
capacity of the reservoir. To evaluate the suitability of the rock as base
course for road construction, 'RJ value tests, sand equivalent tests,
p
I and sieve analysis were performed on samples obtained from trenches
I— , DT28 and DT29. The results of the tests are summarized as follows:
Percentage Passing No. 4 . . . 98 - 100
Percentage Passing No. 200 . . 5-10
p, 'R' Value ......... 79
Sand Equivalent ...... 45-59
Based on these test results, the weathered granitic rock in the reservoir
D area meets the specifications for subbase and base course of the following
agencies and specifications:
D
Agency: California Division of Highways
n
[_j Standard: Standard Specifications , January 1971
D Section 25 Aggregate Subbases
The granitic rock meets the specifications for
(J Class 3 aggregate subbase.
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Section 26 Aggregate Bases
The granitic rock does not meet the specifications
for Class 1 and 2 aggregate base. Class 3
aggregate base must conform to the requirements
of the special provisions. It will depend on the
requirements of the special provisions, whether
or not the granitic rock can be used as Class 3
aggregate base.
Agency: San Diego County
According to the assistant materials engineer of San
Diego County, Class 3 aggregate base must meet
the following specifications:
Gradation
Sieve Size
1-1/2
1
No. 4
No. 30
No. 200
Percent Passing
100
90 - 100
50 - 100
25 - 55
5-18
Sand Equivalent -- Minimum of 30
R Value -- Minimum of 73
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The weathered granitic rock in the reservoir area of
proposed Squires Dam No. 2 does meet these specifications. Locally,
there may be areas where the percent passing the No. 200 sieve is
greater than 18 percent and would not meet the specifications.
Specification: Standard Specifications for Public Works
Construction, 1970 Edition
Part 2 - Construction Materials
Section 200 - Rock Materials
The granitic rock meets the specifications of
Disintegrated Granite, Section 200 - 2. 6.
In this specification, the percent passing the No.
200 sieve shall not be greater than 16 percent.
Locally the granitic rock may have more
than 16 percent passing the No. 200 sieve
and not meet these specifications.
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6.62 Conclusion
It is concluded that the weathered granite in the reservoir
area of proposed Squires Dam No. 2 can be used as a borrow pit.
The rock is weathered to a sufficient depth so that adequate quantities
of material can be obtained by blading and ripping. Most of the materials
obtained will meet the specifications for the Class 3 subbase of the
California Division of Highways, Class 3 base for San Diego County,
and disintegrated granite of the Standard Specifications for Public Works
Construction.
SHM/JDS/JJS/JLS/jm
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D
BIBLIOGRAPHY
Abbot, Patrick, 1963, Geology of the Vista Region, San Luis Rey and
San Marcos Quadrangles, San Diego County; unpublished Senior
Project, San Diego Stale College.
Brooks, Baylor, I960, Geologic Conditions at Squires Canyon Damsite,
Carlsbad, California, Unpublished geologic report for the Carlsbad
Municipal Water District.
Department of Water Resources, 1964, Crustal Strain and Fault Movement
Investigation, Bulletin No. 116-2.
Jahns, R.H. et al, 1954, Generalized Geologic Map of the Penninsular
Range Province, Southern California. Plate 3, Chapter II,
California Division Mines Bulletin 170.
Jones, B.F. , 1959. Geology of the San Luis Rey Quadrangle. Unpublished
M.S. Thesis, U.S. C.
Larsen, E.S. , Jr. , 1948; Batholith and Associated Rocks of Corona,
Elsinore, and San Luis Rey Quadrangle, Southern California,
Geol. Soc. America, Mem. 29, 182 pp.
Merriarn, R.H. , 1951; Groundwater in the bedrock in Western San Diego
County, California, in Cal. Div. Mines Bull. 159, p. 117-128
Weber, F. Harold, Jr. , 1961, Economic Geology of San Diego Region;
Geol. Soc. Am., Cordilleran Sect. Field Trip Guide Book, San
Diego County, California, March 1961.
Weber, F. Harold, Jr. , 1963, Geology and Mineral Resources of San
Diego County, California; Calif. Div. Mines & Geol. County Report
3, 309 pp.
Woodford, A.O. , I960; Bedrock Patterns and Strike Slip Faulting in
Southwestern Calif. , Am. Jour. Sci. , Bradley, Volume 0. 258-A,
p. 400-417.
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