HomeMy WebLinkAbout; Maerkle Reservoir; Soils Report; 1993-03-26i M&T AGRA, Inc.
iformerly Moore & Tabed
Geotechnical & Environmental Services
GEOTJXHNICAL STUDY
Maerkle Reservoir
Carlsbad Municipal Water District
Carlsbad, California
CLIENT
John Powell & Associates
175 Calle Magdelena, Suite 101
Encinitas, California 92718
March 26, 1993
Job No. 693-103
16760 West Eiernardo Drive San Diego, CA 92127
619-487-2113
FAX 619-487-2357
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TABLE OF COh’TENTS
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1.0 INTRODUCI’ION .............................................. -l-
1.1 PROPOSED CONSTRUCI’ION ............................... -2-
1.2 SCOPE OF WORK ......................................... -3-
2.0 FIELD EXPLORATION AND LABORATORY TESTING ................ -4-
2.1FIELDEXPI.0RATION ..................................... -4-
2.2 LABORATORY TESTS ..................................... -4-
3.0 SITE CONDITIONS ............................................. -5
3.1 SURFACE CONDITIONS .................................... -5
3.2 GEOTECHNICAL CONDITIONS .............................. -7-
3.3 RESERVOIR BASIN CONDITIONS ............................ -8-
4.0 CONCLUSIONS AND RECOMMENDATIONS ........................ 9-
4.1 LINER REQUIREMENTS ................................... -9-
4.1.1 General ...................................... -9-
4.1.2 Permeability ................................. -lO-
4.1.3 Sediment Volumes ............................. -lO-
4.1.4 Core Desiccation .............................. -lO-
4.15 Grading Recommendation ....................... -ll-
4.1.6 Upstream Dam Face ........................... -12-
4.1.7 Settlement ................................... -12-
4.1.8 Excavatabiiity ...... ; ......................... -12-
4.1.9 Slope Stability ................................ -13-
4.1.10 Permeable and Nonpetieable Liner ............... -13-
4.2 FLOATING COVER REQUIREh4ENTS ....................... -16-
4.2.1 General ..................................... -16-
4.2.2 Access Service Road ........................... -17-
4.2.3 Footings ........... ......................... -17-
4.2.4 Rock Anchors ...... , ......................... -18-
4.3 SPILLWAY .............................................. -2O-
5.0 GEOTECHNICAL REVIEW ...................................... -21-
6.OCLOSURE.. ...................... ..1......................... -22-
REFERENCES ................................................... -23-
FIGURES IN TEXT
Figurel-VicinityMap ......................................... -6-
Figure 2 - Rock Anchor Detail ................................... -19-
Job No. 693-103 - March 26, 1993 @AGRA i
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PLATES
PLATBI-SITEPLAN
APPENDIX A
I In Pocket
SEISMICREFRACI’IONSURVEYDATA . . . . . . . . . . . . . . . . . . . A-ltoA-7
APPBNDIX B
LABORATORY TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-l to B-3
APPBNDIX c
JOINT MAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-l to C-7
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1.0 IN/FRODUCTION i-
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This report presents the results and recommendations developed from our geotechnical
study for the proposed covering and possible bottom lining of the Mae&e Reservoir. The
reservoir site is located approximately 2 miles northeast of Palomar Airport in Carlsbad,
California. Maerkle Reservoir, formerly Squires Reservoir, has a capacity of approximately
600 acre-feet and a surface area of about 16 acres. The proposed improvements include a
floating cover, possible installation of a permeable or impermeable basin liner, and spillway
improvements.
The purpose of this study was to explore’ and evaluate the general soil/rock, geologic, and
hydrogeologic conditions for the proposed reservoir improvements, and provide geotechnical
recommendations and designs to aid John Powell & Associates and the Carlsbad Municipal
Water District (CMWD) in the preparation of project plans and specifications.
The existing facility consists of an import water storage basin developed by damming a
natural drainage course with an approximately lOO-foot maximum height, zoned earth-fill
embankment. Dam construction materials were obtained on-site, resulting in a cut rock
impoundment basin. The facility is under the jurisdiction of the State Division of Safety of
Dams.
Reference was made to various documents in both the public and private domain Primary
sources of information are listed immediately following the text of this report.
1.1 PROPOSED CONSTRUCTION
Present plans call for the installation of a floating cover and possibly a liner system to
protect the CMWD drinking water supply from Maerkle Reservoir from contamination in
compliance with federal clean water regulations. Modification will also be made to the
existing spillway. Currently, consideration is being given to an impermeable geomembrane
liner or a permeable asphalt liner. However, it is possible that no liner will be required.
The floating cover will be restrained and suspended by a cast-in-place concrete footing at
the perimeter of the reservoir near the high-water line. A narrow service road or walkway
is being considered to access the cover and help control surface runoff from the surrounding
watershed.
In order to facilitate the cover installation and maintenance, grading will be required to
provide more uniform shoreline and basin topography. Cut and fill earthwork will be
designed to remove prominences and fill re-entrant irregularities. If a liner system is
installed, regrading wiU also be used to create suitable basin subgrade conditions. The
spillway is currently poorly developed and will be upgraded.
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1.2 SCOPE OF WORK
The geotechnical investigation included sit
rock sampling, field and laboratory
formulation of design recommendations,
scope of work included of the following
. . .
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Review of original rese truction documents.
General site re mapping, and location of soil and rock
sampling site.
basin.
s for subsequent laboratory testing.
er photography of the reservoir
. . .
reservoir.
line around the perimeter of the
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Evaluation of local geology.
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Preparation of general reco endations for project regrading, excavatability,
site preparation, fill place and spillway suitability.
ommendations for rock anchors, underdrain
the work performed, the
designrecommendations.
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r 2.0 FIELD EXPLORATION AND LABORATORY TESTING
2.1 FIELD EXPLORATION
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Field exploration was completed’in February 1993, and included joint orientation and
frequency mapping, eight seismic refraction traverses (geophysical survey lines), rock
sampling along de shore of the reservoir, soil sampling of underwater reservoir sediments,
underwater photography and geologic mapping of exposed rock
The seismic refraction traverses were conducted to evaluate the seismic velocity profiles of
the subsurface earth materials and assess the depths to relatively unweathered rock.
Geophysical survey lines were 90 and 100 feet in length and their locations are plotted on
the site plan (Plate I).’ The traverses were performed using a GeoMetrics/Nimbus
Instruments Signal Enhancement Seismograph Model ES-125 Arrival times were plotted
directly onto a time/distance graph in the field. Best fit straight-line segments were drawn
through the plotted points and velocities in feet per second were calculated. Geophysical
data are summarix ed in Section 4.1.8 and presented in Appendix A.
Samples of the local rock having varying degrees of weathering were obtained along the
high-water line for subsequent laboratory testing. Sample locations are shown on the site
plan (Plate I) and laboratory test data can be found in Appendix B.
Sampling of the underwater sediments in the reservoir was accomplished by two certified
geotechnical divers who logged sediment thickness and obtained bulk samples of the bottom
sediments at the locations shown on Plate I. In addition to sampling, general reconnaissance
of the reservoir bottom was performed and underwater photographs were taken of the area
between underwater locations S-14 and S-5.
Geologic mapping of visible structural features on outcrops and excavated faces was
performed by an M&T AGRA engineering geologist to provide general information about
the extent of weathering; and the orientation, character and frequency of jointing and
fracturing.
2.2 LABORATORY TESTS
The following laboratory tests were performed to measure relevant physical and chemical
properties of selected earth materials.
o Grain Size Analysis
o Unconfined Compressive Strength
o Unit Weight of Rock Samples
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1 LOCATION MAP I - l.T.$.~;o.s.~~srds
Job No. 693-103
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MAERKLE REsEavolR
carlsbad Mouici~ watel Dishict
cadsbad,-
m3uRBl -vIcINlTYMAP
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Geoaechnicll & Bnvimmamtal services
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3.2 GEOTlKHNICAL CONDITIONS
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Earth materials exposed at the ground surface consist of weathered granitic rock associated
with the Santiago Peak Volcanics of the southern Califomia.Batholith. Diver examination
and sampling of the reservoir bottom indicates that all residual and alluvial soils were
removed during project grading thirty years ago. Currently, minor residual/alluvial soil
profiles (1 to 2 feet) are exposed at scattered locations above the high water elevation
throughout the site. Geophysical survey lines suggest the near surface weathered rock varies
between 15 and 20 feet in thickness. Weathered rock, in this case, is defined as granitic
rock with a seismic propagation velocity less than 5,000 feet per second. The weathered
rock is underlain by more sound rock with seismic velocity in excess of 5000 feet per second.
Three diamond core borings were drilled along the dam foundation in about 1961 and
resultant drilling logs show “decomposed granite” to depths of about 60 feet in all three
borings. Intact, sound rock was encountered below 60 feet. The fresh granitic rock is
interpreted to be represented by seismic velocities in the range of ~10,000 feet per second.
Typical outcrops expose small corestones visible within the weathered rock The granitic
bedrock is dense and has a coarsely crystalline texture. Weathering has resulted in
alteration along mineral grain boundaries so that mechanical disintegration produces a sandy
to blocky excavation product.
Joint orientation data were collected by means of a systematic scanline traverse at the south
comer of the reservoir and mapping along the remainder of the shoreline. The data
collected were plotted on a lower hemisphere, equal angle stereo-plot for evaluation.
Traverse data are included in Appendix C.
Measured joint orientations cluster to reveal four joint sets, albeit with significant scatter
within each group. Representative orientations (strike/dip) of the four sets are 50/69SE,
65/75NW, 326/68SW and 340/71NE. These are all steeply dipping orientations with
northeastward and northwestward strikes. Few joints measured had dips shallower than 60”
and none significantly shallower than 45”.
The high dip angles of the great majority of joints makes joint-related (wedge) failure of the
rock supporting the reservoir cover footing very unlikely under the small loads that the cover
is understood to impose. Field inspection of footing excavations during construction should
reveal local, low-angle joints or other weakened surfaces which, together the prevalent joint
sets, could make specific areas vulnerable to loss of support.
Should the perimeter footing to support the reservoir cover be required to withstand
substantially greater loads than are anticipated at present, it is recommended that a
quantitative analysis of the potential for wedge-type failure be undertaken.
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3.3 RESERVOIR BASIN CONDITIONS
Sampling of bottom sediments and exposed weathered rock surface, reconnaissance, and
photography of the bottom of the reservoir were performed by two scuba divers with
geotechnical backgrounds. Sediment cover over cut rock is very limited, typically between
one and three inches thick. The thickest sediments were found at locations S-9 and S-14,
where about 12 to 15 inches of deposition was measured. One undisturbed sample of the
sediments was obtained at location S-9 using a 3-inch diameter Corps of Engineers tube
sampler. Samples of the exposed weathered granitics were also obtained at various
locations. These rock materials are essentially the same as in place “decomposed granite”
seen along the shoreline. The weathered granite typically consists of tine to coarse sand.
Sediment samples were found to be black, fine sandy silt typical of suspended solids
imported by Colorado River water. Grain sire distributions for a sample of the ftne
grained sediments and weathered granitics can be found in Appendix B.
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Recomiaissance of the reservoir bottom revealed little vegetation, with the exception of
limited amounts of eel grass near sample location S-9. Scattered cobbles and boulders up
to 4 feet in maximum diameter were seen over much of the basin bottom. Known boulder
locations include S-4, S-5, S-8, S-12, S-13 and the photographed area (Plate I). The boulders
appear to be deposited on the bottom rather than projecting corestones still embedded in
the weathered granitic matrix.
4.0 CONCLUSIONS AND RECOMMENDATIONS
4.1 IMPOUND~NT BASIN RECONFIGURATION
4.1.1 General - To facilitate the installation of the floating cover and placement of
an impermeable geomembrane liner or a permeable asphalt liner, the reservoir will be
drained and graded to create more uniform side slopes and bottom. Reconfiguration will
entail removal of shoreline irregularities along the southeast side of the reservoir, and fill
placement in major re-entrants and the basin floor. Additional improvements are
recommended to stabilize the steep slopes above the waterline along the north side of the
reservoir where recompaction of loose fill and shotcrete pavement of cut rock to prevent
surface erosion are warranted.
4.1.2 Hydrogeology - The outlet structure for the dam was originally positioned to
allow 10 acre-feet of storage below the outlet to retain any basin sediment. Therefore, the
remaining water will require pump dewatering. The dewatering system should be designed
by the contractor and reviewed by M&T AGRA.
Bank storage for the basin is estimated to total several acre-feet. The largest volume of bleed-back will occur within a few weeks of drawdown along discontinuities in the basin
rock. However, due to low gross rock permeability it should be anticipated that seeps and
small springs will continue to discharge water throughout the construction of the liner and
cover. The quantities will be fairly small but could be enhanced by local rainfall prior to
and during construction.
According to Carlsbad Municipal Water District records, when the reservoir is full only
minor leakage is observed at the downstream toe of the dam. It is unknown if the majority
of the discharge originates through the dam or its foundation. Background information and
past experience would indicate that the most probable water source is outflow from the low
permeability dam core that is captured and drained by the gravel chimney drain. In other
words, the zoned dam is functioning as per design
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Water pressure test data from the diamond core borings in 1961 produced in situ rock
permeabihties that ranged from “impermeable” to 50 feet per year (4 x lo-’ cm/set). These
data for maximum hydraulic conductivity indicate that basin loss from the unlined
impoundment is very low, a conclusion corroborated by District operating records.
Therefore, the native rock provides a very low permeability containment system for the
reservoir. In addition, the following geohydrologic and surface hydrology conditions
combine to create a very well protected environment against groundwater contaminants -
if any.
. The reservoir is positioned on a topographically elevated massif of granitic
rock (Mt. Hinton) out of the path of regional groundwater gradients - (See
Figure 1). . Stored water creates a positive hydraulic gradient into the rock.
. Surrounding terrain is generally of moderate relief which promotes run-off
and mGm.izes infiltration.
l A channel around the reservoir intercepts most of the run-off and directs it
to the spillway.
In light of these considerations, a reservoir liner will not provide substantially improved
groundwater cant aminant protection over existing conditions.
4.13 Sediment Volumes Sediment thicknesses were typically 1 to 4 inches with two
locations having thicknesses of 12 to 15 inches. A conservative estimate for determining
sediment volumes would be 6 inches average over the entire basin area.
4.1.4 Core Desiccation If an impermeable liner is installed, there are concerns voiced by the Water District, that the core of the dam will become desiccated and crack,
leading to potential for water induced internal erosion. Aside from the fact that an
impermeable liner should obviate the need for a low permeability ductile core, desiccation
and cracking of the dam core is unlikely for the following reasons:
b Desiccation is typically experienced for only the upper 5 to 10 feet below the
ground surface.
. The borrow material is described in original reports as “nonplastic to slightly
plastic”, indicating low clay contents and low clay activity. Volume changes
which would cause cracking would be more likely in high plasticity clays.
. Impermeable liners are not 100 % impermeable. Typical installations have
lo-15 punctures per acre with an average size of 1 square centimeter.
Therefore, it should be anticipated that adequate water to preserve moisture
contents will be available from membrane leakage.
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Core moisture contents in the upper 10 feet could be monitored by installing two
tensiometers along the dam crest. If moisture contents show significant decreases, the
existing sprinkler system on the dam crest can be used as needed to replace soil moisture
of the upper 10 feet of the dam.
4.1.5 Grading Recommendation AU site cleanup and grading will be subject to the
approval of Carlsbad Municipal Water District and the Geotechnical Engineer. Cut and fill
earthwork is planned to produce a more regularly shaped and contoured basin to
accommodate the cover and, possibly, a liner. It is understood that compacted fill,
consisting of cut rock from prominances, will be placed at some of the small inlets along the
southeast and eastern sides of the basin as well as in the steep, deep central trough of the
reservoir to create requisite uniform bottom and maximum waterline topography.
The ground surface to be modified should be stripped of any soil, loose rock, or boulders
basin sediments, brush, trees and organic debris and disposed of off site. The resulting exposed surface will be firm weathered granitic rock.
On-site soils which do not contain roots or organic debris will generally be suitable for use
as compacted fill. It is anticipated that cut areas will be limited to prominances along the
southeast side of the reservoir and cuts to create a access road. Excavatibility of the
weathered rock is discussed in subsequent sections of the report. Minor processing of the
excavated rock will be required to provide suitable fill materials. Rock particles larger than
12 inches in maximum dimension will require additional processing or special handling for
disposal in the central basin fill.
On-site soil and rock used as compacted fill should be placed in lifts 8 inches or less in loose
thickness, moisture conditioned to within 0 to 4 percentage points above optimum moisture
content, and compacted to at least 90 percent relative compaction based on the ASTM D
1557 laboratory test method. Boulders from one to three feet in maximum dimension can
be placed in the fill at the deepest part of the basin provided they are 6 feet below finished
grades and are individually placed in windrows and clean gram&u soil (i.e. sand equivalent
greater than 30) is jetted or flooded around boulders so as to prevent nesting and creation
of voids around the boulders. Any rock exceeding three feet should be disposed of off-site.
Where unbuttressed fill is to be placed on slopes steeper than 5:1, a level, equipment width
toe bench should be established at the base of the fill. Benching into competent material
should continue as the fill progresses up-slope.
After completion of the fill, the slopes shall be dressed and graded so as to provide a
uniform surface and slope. All slopes shall be track-walked or rolled with equipment
approved by the Engineer. Existing fill slopes along the north shore of the reservoir will
also require dressing and compaction to the above standards prior to applying any protective
cover. Drainage should be provide behind gunned or shotcreted surfaces.
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4.1.6 Upstream Dam Face Riprap (1 foot to 2 feet diameter rock) covers the entire
upstream face of the dam. In order to provide a uniform surface for a liner system, it is
recommended that % inch crushed gravel be used to fill all voids around the riprap. The
riprap infill should cover the rock particles to a depth of at least six inches. The % inch
gravel should meet the specifications in Section 200-111 and 200-1.2 in Standard
Specifications for Public Works Construction. Depending on the geomembrane liner used,
a puncture-resistant geotextile may be needed between the crushed gravel layer and the
membrane.
4.1.7 Settlement Surface settlements are predicted for the deepest part of the basin
where substantial thicknesses of new fill will be placed. The settlements will occur as a
result of compression within the new fill itself. For a permeable or unlined bottom, total
ground surface settlements will be less than M inch. Maximum ground surface settlement
is predicted to be in the range of 1-M to 241 inches when the reservoir is filled if an
impermeable liner system is constructed over about 20 feet of fill and differential
settlements will develop in proportion to the fill thickness variations. If these adjustments
are considered unacceptable, relative compaction requirements can be raised to 95 percent
(based on ASTM D 1557), thereby reducing total and differential settlements to about 40
percent of those listed above.
4.1.8 Excavatability Anticipated excavation conditions are indicated by the seismic
refraction data presented in Appendix A. As a general statement, heavy weight hydraulic
excavators (such as the Caterpillar Model 245) experience difficulty when digging
homogenous rock-like materials having seismic propagation velocities (P-wave) greater than
4000 feet per second (f.p.s.). The upper limit of excavatability can be taken to about 5000
f.p.s. Large, single shank ripper-equipped bulldozers can successfully excavate materials in
the 6,000 to 8,000 f.p.s. range, depending on rock structure.
Review of the fundamental geophysical data listed in the following table shows the
weathered granitics typically have seismic velocities of 2200 to 4800 feet per second and the
more sound rock at depths of 15 to 20 feet have p-wave velocities of 7000 to 11,000 feet per
second. Geophysical survey data indicate little to moderate excavating difficulty to the
depths of about 15 feet below current grades. Potentially unexcavatable rock will be
encountered below these depths. The contractor should anticipate local bouldery masses
which will need to be broken by explosives, heavy-duty demolition tools or impactors in the
upper 15 feet.
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SUMMARY OF GEOPHYSICAL DATA
Seismic Approx. Apw=- Refraction
Line
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SR-1
SR-2
SR-3
SR-4
SR-5
SR-6
SR-7
First Second
Layer Layer
velocitv la&! (feet/set) (feet/set)
2600 9800*
1600-2800 4800
2200-3500 8500
2300-3000 11,000
3800 7100
3100 11,000
1500 3500
* Reverse survey traverse considered unreliable
Estimate
Depth to
Second
gy ee
19
3
16
19
14
21
3
4.1.9 Slope Stability Analyses were performed to assess the stability of the
proposed side slopes along the banks. Fill soil strength parameters were selected based on
experience with the materials to be excavated from the banks. On this basis, properly
compacted fill slopes as steep as ltil (horixontahvertical) can be used. Final fill slopes
with slopes of 1M:l have a calculated overall static factor of safety greater than 1.5. Under
pseudo-static conditions, a factor of safety greater than 1.2 was calculated. However, if it
is decided that no liner will be required, submerged slopes no steeper than 3:l are
recommended because fill slopes wilt be mainly comprised of granular soils which are
susceptible to surface erosion from rainfall during construction or cover leaks and adverse
pore pressure during rapid drawdown.
4.1.10 Permeable and Nonpermeable Liner Both liner systems will require a firm,
unyielding subgrade. The subgrade materials will consist of compacted fill or weathered
granitic rock Subgrade soils should be compacted to a minimum of 90 percent relative
compaction based on ASTM D 1557. b-regularities in the surface of the weathered granitics
should be removed. If there is a concern that irregularities could puncture a geomembrane
liner, consideration should be given to the use of a puncture-resistant geotextile between the
subgrade and geomembrane or overexcavation of the irregular rock surface and refill with
compacted fill to reestablish final grade.
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Because the existing reservoir has experienced very limited seepage loss, consideration could be given to a partial soil-cement liner system. After final grading, the reservoir surface
would either consist of dense decomposed granite in cut areasor an 8-i& thick soil cement
layer in fill areas. In fill areas, fill would be compacted to a minimum of 90 percent relative
compaction to within 8-inches of final grade. The final surface would consist of soil-cement
placed in two lifts, each 4-inches thick It is estimated that a 6 to 8 percent cement content
by weight, mixed with on-site decomposed granite would provide an adequate final surface.
A partial soil-cement liner system would be more economical than a geomembrane liner
system but it is not known if such a system would be accepted by jurisdictional agencies.
If such a system was approved, it would be necessary to conduct tests on soil-cement
specimens to determine the cement content for design
A nonpermeable (geomembrane) liner system will require an underdrain. From a technical
standpoint, 6 inches of Caltrans Class 2 Permeable Material will provide adequate drainage.
Construction specifications should call for a minimum 6-inch drainage blanket and adequate
verification to ensure compliance of finished thiclmess subsequent to rolling to consolidate
and smooth the gravel. Depending on which liner product is selected, it may be necessary
to provide further protection against puncture. An 8-ounce or lO-ounce, nonwoven
geotextile should be adequate for geomembrane liners with moderate puncture resistant
properties.
The drainage blanket should be planned for all reservoir bottom surface having a finished
slope of 3:l or flatter. Steeper slopes can be covered with the geotextile underlayment for
puncture protection and drainage. One of the following geotextiles or their equivalent
should be used for the slopes and over the underdrain:
American Engineering Fabrics AEF 880 or 1080
hloco Amoco 4508 or 4510
Phillips Supac 8NP or 1ONP
A network of perforated collector pipes and tightline outlet should be embedded in the
gravel blanket to accumulate and discharge seepage from both the liner and any minor
groundwater inflow. Herring bone pattern collectors radiating from a central outlet is
suggested. All piping should be equivalent to schedule 40 P.V.C., and placed in graded V-
ditches with the drainage material used as backfill. Perforated collectors should be spaced
approximately 150 feet on center. Minimum 3-inch diameter collectors and a 6-inch outlet
is recommended. The outlet should terminate in a sump for pump discharge or penetrate
the dam for gravity flow. If the latter option is selected, the pipe boring annulus should be
sealed by grouting after pipe installation to ensure a positive waterstop.
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An alternative liner of impermeable asphalt is also under consideration Specifications for porous asphalt base can be found in Caltrans Standard Specifications Section 29,29-1.02A (Asphalt Treated Permeable Base). In conversation with several local asphalt mix
designers, the Caltrans Standard Specifications were suggested. Since the Caltrans material
is intended to be protected by a low permeability , high density wear layer; the mix may
have a limited service life. Therefore, it is recommended that a permeable surface course be used over the Caltrans permeable base or a drainage layer complying with the criteria
on the following page. This dual layer should provide an excellent liner system with very
low maintenance.
It is understood that a more economical porous asphalt design consisting of a single 34nch layer of porous asphalt, has successfully been used on several reservoirs in southern
California. It is not known if these reservoirs have been in service long enough to evaluate the long term stability of this design
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MIX COMPOSITIONS FOR FORMED IN PLACE ASPHALT LININGS
Sieve Size
1ilL %in.
Min. s/sin.
No. 4
No. 8
No. 16 No. 30 No. 50 No. 100 No. 200
Asphalt cement*, percent by weight of total
mix
MixType
Minimum Recommended
Compacted Depth
Recommended Usage
Percen
100 95-100
85-95 --
44-56
30-40
U-22
3-8 l-4
5.0-6.0
Permeable
(Medium Voids)
3 inches
Permeable Surface
Passing
100
93-100
35-65
5-25
2-15
O-7
O-3
2.0-4.0
Open-Graded (High Voids)
3 inches
Drainage Layer
*AC-20, or equivalent AR- or penetration grade, recommended (Asphalt Institute, Asphalt and Hydraulics, Manual Series #12)
Detailed subgrade preparation and lay-down requirements for a permeable asphalt liner
system can be provided if needed.
4.2 FLOATING COVER RRQUIREMRNTS
4.2.1 General The cover will be anchored at its perimeter by a continuous cast-in-
place concrete footing located at high water line. Liner loads can be supported by vertical and passive resistance of bearing rock (and possibly Eli), and where additional restraint is needed, rock anchors. Preliminary planning envisions a perimeter access road adjacent to most of the cover footing to facilitate construction and maintenance, and help control local
drainage. Excavatibility of the existing rock for the footing and access and required grading has been discussed in Section 4.1.8 and 4.1.5, respectively.
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4.2.2 Access/Service Road Construction of the access service road on the upstream
dam face at an elevation near the high-water line should be performed so as not to disturb the impervious core. Several options appear feasible:
1. The access road can be constructed entirely of fill, using the cover footing as
an earth retaining wall to support the approximately 2.5 feet of fill needed to provide an &foot wide roadway.
2. Composite cut and fill grading could be designed to minim&e the retaining wall height.
3. Providing a paved surface sloped (shoulder to shoulder) at approximately the existing 3!4zl dam f&e gradient.
Actual design may also be influenced by whether a liner system is installed and its
construction features.
Along most of the perimeter of the reservoir the accessway will be excavated into weathered granitic rock, except for the area along the northwest shore, north of the inlet pipe where the topography is too steep to build a new road. Due to the steep bank at this location, a narrow walkway will likely be provided with stairs descending from the existing storm water
diversion channel. These steep slopes may be gunited or shotcreted to control erosion, and
recommendations for slope preparation are presented in Section 4.1.5.
4.2.3 Footings In the upstream dam face and any local areas where the cover footing will be founded on compacted fill, the following recommendations can be used.
Allowable Vertical Bearing = 2500 psf Ultimate Passive Resistance = 2:l slope; I.50 psf/ft 5:l slope; 350 psf/ft Coefficient of Friction = 0.5
Footings bearing in firm undisturbed weathered rock can be designed for the following
allowable capacities:
Allowable Vertical bearing =
Ultimate Passive resistance =
Coefficient of Friction =
3500 psf
2:l slope; 250 psf/ft 5:l slope; 500 psf/ft 0.6
Resistance to lateral loads on the footing may be provided by friction at its base and passive earth pressure against the side of the footing. Linear interpolation can be used for passive resistance at intermediate gradients. The upper foot of compacted fill and the riprap section
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should not be relied upon for passive pressure or vertical bearing. If adequate factors of safety for overturning or sliding cannot be obtained, short piles or grouted anchors may be required. A typical pile would be 12 to 18 inch diameter and about 5 feet long. Geotechnical design recommendations can be provided if needed. It is assumed that
grouted anchors will extend through the fill into weathered rock; except in the dam section,
and recommendations are provided in the following section.
4.2.4 Rock Anchors Rock anchors will likely be required to secure the cover retaining footing to the existing slope around portions of the reservoir perimeter and may
be useful for shotcrete support along the steep north slopes. Unconfined compression testing was performed on six specimens of rock obtained at the surface near de high water hue at the locations shown on Plate I to aid in anchor design Specimens with varying degrees of weathering were tested. Test results are presented in Appendix B.
Design recommendations are as follows:
An allowable grout to rock bond stress of 3.1 kips per square foot (ksf) can be used in the weathered rock. For anchors greater than 10 feet in length, 4.5 ksf can be used below 10 feet (see Figure 2).
For anchors less than 10 feet in length, resistance in the upper 2 feet of the anchor should be neglected.
A minimum bond length of 5 feet is recommended.
Anchors systems should be provided with double corrosion protection.
Anchor design should be reviewed by the geotechnical consultant.
A test program should be initiated which includes testing 10% of the grouted
anchors to 200% of the design load. The anchor should be rejected if: the anchor cannot hold test load without continued displacement and/or more than 0.1 inch total displacement occurs in 5 minutes of loading.
Anchor lock-off load should be 125% of design.
Anchors for shotcreted slopes do not require proof testing.
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AnchorShortesthan lOfeet
Anchor~~~lofeet
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~GURE 2 - ROCK ANCHOR DETAIL
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4.3 SPILLWAY
The spillway transmits flow to a natural drainage course northwest of the dam along the right abutment. Runoff from the existing perimeter interceptor ditch/roadway also drains
into the spillway drainage course. Reconnaissance of the spillway and natural channel indicates two visible erosion control concrete structures; one located as a spillway weir at the reservoir high water elevation and the other at the top of the slope transition to the natural drainage. The drainage course is in fairly competent weathered granitics and erosion appears to be quite minor. A topographic map from 1960, prior to dam construction indicates that the drainage course is a natural feature. Based on available information, it does not appear that erosion of the drainage course will redirect water toward the dam embankment and the existing spillway improvements are adequate from a geotechnical perspective. However, issues related to the hydraulic capacity of the spillway and associated drainage course are beyond the scope of this study.
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5.0 GEOTECHNICAL REVIEW
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Geotechnical review is of paramount importance in engineering practice. The poor performance of many foundations and pavements has been attributed to inadequate review
prior to construction.
The geotechnical engineer should review the completed project plans and specifications prior to bidding and construction. Such review is necessary to determine whether the
geotechnical recommendations have been effectively incorporated into construction documents. This office is best qualified to make professional interpretations based on the
work already performed. The review should be verified in a written report by the geotechnical engineer.
Observations and testing should be performed by representatives of the geotechnical engineer of record during earthwork constructions. It should be anticipated that the substrata exposed by construction may locally differ from that encountered during the geotechnical investigation. Reasonably continuous construction observations during site grading allows evaluation of the exposed soil, rock and geohydrologic conditions, and confirmation or revision of the assumptions and extrapolations made in formulating the
design parameters and recommendations.
Site preparation, removal of unsuitable soils, approval of any imported earth materials if
needed, fill placement, proper moisture conditioning, and other ground preparation operations, along with footing excavations, anchor and pile installation should be observed and tested by the geotechnical engineer.
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6.0 CLOSURE
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This report is based on the project as described and the information obtained from limited exploration at the locations indicated on the plan. Resultant findings are based on the field, laboratory, and office studies, combined with an interpolation and extrapolation of soil and rock conditions between and beyond the test locations, or surface exposures. The results reflect our interpretation of the limited direct evidence obtained. Our firm should be notified of any pertinent change in the project plans. If conditions are found to differ from those described, a re-evaluation of the recommendations may be required.
Our recommendations for this site are, to a high degree, dependent upon proper quality control for problematic soil removal, fill placement, and footing and anchor installation. Consequently, recommendations are made contingent on the oppottuuity for M&T AGRA to observe grading operations and anchor construction. If parties other than M&T AGRA are engaged to provide such services, they must be notified that they will be required to assume complete responsibility for all phases (design and construction) of the project within the purview of the geotechnical engineer. They should notify in writing the owners, designers, appropriate governmental agencies, and this office that they concur with the recommendations in the report and any subsequent addenda or will provide alternative recommendations.
This document has not been prepared for use by parties or projects other than those named
or described above, as it may not contain sufficient information for other parties or other
purposes. This report has been prepared in accordance with generally accepted geotechnical
practices and makes no other warranties, either express or implied, as to the professional advice or data included.
M&T AGRA, Inc.
Joseph J. Vettel [$x6*’ Project Engineer
2zczF%
Donald W. Clark Principal Engineering Geologist REG No. 1091
JJV/SHM/DWC/jr Distribution: (2) Client \ I
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BIBLIOGRAPHY
American Water Works Association, AWWA Standard for Flexible-Membrane-Lining and Floating-Cover Materials for Potable Water Storage, ANSI/AWWA D130-87 (First
Edition), 1987.
Asphalt Institute, Asphalt and Hydraulics, Manual Series No. 12.
Boyle Engineering, Inc., Design of Squires Dam and Appurtenant Structures for Carlsbad
Municipal Water District, February 1961.
County of San Diego, Orthophoto Topographic Survey, Sheet 358-1689, scale 1:2400, July 25, 1979.
County of San Diego, Topographic Survey, Sheet 358-1689, scale l2400, July 1960.
Fugro Consulting Engineers and Geologists, Site Inspection and Instrumentation Evaluation at Squires Dam, May 28, 1980.
Hoak, E. and Bray, J.W., Rock Slope Engineering, The Institution of Mining and Metallurgy London, 1981.
Rogers, Thomas, H., Geologic Map of California, SANTA ANA SHEET, 1965.
U.S. Geological Survey, 7.5 minute Quadrangle Series, Topographic, San Luis Rey Quadrangle, scale 1:24,000, 1968, photorevised 1975.
U.S. Geological Survey, 7.5 minute Quadrangle Series, Topographic, San Luis Rey
Quadrangle, scale 1:24,000, 1948.
Weber, F. Harold, California Divisions of Mines and Geology, Geology of Mineral Resources of San Diego County, California, County Report 3, 1963
Xanthakos, Petros, P., Ground Anchors and Anchored Structures, John Wiley & Sons, 1991.
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APPENDIX B
LABORATORY TRSTING
The laboratory test program was designed to fit the specific, needs of this project and was limited to testing on-site materials. A brief description of each type of test is presented
below. Specific results are given on the following pages.
Strength characteristics of the rock were determined in the laboratoxy by unconGned compressive strength tests performed on several samples. All samples were cut and ends
mitred using a masomy saw. The samples were oriented to break against the structural grain of the rock. All unconfined compressive strength tests were performed in general accordance with ASTM D 2938-86.
The grain size distributions for 2 samples were determined in general accordance with
ASTM D 422. Results of these tests are plotted in this appendix.
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TABLE B-l
SUMMARY OF LABORATORY
UNCONFINBD COMPRESSIVE STRBNGTH TEST RESULTS (ASTM D 2938-86)
Sample Na.
R-l R-2 R-3 R-4
R-S R-6
171 321
300
200
9624
876
. . mt We eht
(P4l
145.2 145.8 141.0
145.2
163.5
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APPENDIX C MAPPING DESCRIPTIONS
Rock Hardness
R-O R-l
R-2
R-3
R-4
R-5
R-6
Aperture
Extremely weak rock. Indented by thumbnail.
Weak rock. Crumbles under firm blows with points of geological hammer,
can be peeled by a pocket knife.
Weak rock. Can be peeled by a pocket knife with difficulty, shallow indentations made by firm blow with point of geological hammer. Medium strong rock. Cannot be scraped or peeled with pocket knife, specimen can be fractured with single firm blow of geological hammer, Strong rock. Specimen requires more than one blow of geological hammer to fracture it.
Very strong rock. Specimen requires many blows of geological hammer to
fracture it.
Extremely strong rock. Specimen can only be chipped with geological hammer.
co.1 mm Very Tight
0.1-0.25 mm Tight
0.25-0.5 mm Partly Open
“Closed Features”
05-2.5 mm Open 2.5-10 mm Moderately Wide “Gapped Features” >lOmm Wide
l-10 cm Very Wide
lo-100 cm Extremely Wide “Open Features”
>lm Cavernous
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Joint Weathering
I
II
III
Iv
V
VI
Fresh - No visible sign of rock material weathering; perhaps slight
discoloration on major discontinuity surfaces.
Slightly Weathered - Discoloration indicates weathering of rock material and discontinuity surfaces. All rock material may be discolored by weathering and
may be somewhat weaker than in its fresh condition
Moderately Weathered - Less than half of the rock material decomposed and/or disintegrated to a soil. Fresh or discolored rock is present either as a continuous framework or as corestones.
Highly Weathered - More than half of the rock material decomposed and/or
disintegrated to a soil. Fresh or discolored rock is present either as a
discontinuous framework or as corestones.
Completely Weathered - All rock material decomposed and/or disintegrated to a soil. The original mass structure is still largely intact.
Residual Soil - All rock material is converted to soil. The mass structure and material fabric is destroyed. There is a large change in volume but the soil
has not been significantly transported.
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