HomeMy WebLinkAbout3593-2; FARADAY AVENUE EXTENSION; AS-GRADED REPORT; 1999-12-09W ,
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ENGINEERING GEOLOGY REPORT
OF ROUGH-GRADING,
FARADAY AVENUE EXTENSION,
STATION 10+00 TO STATION 62+00,
CARLSBAD, CALIFORNIA
PROJECT NO. 3593
OR
LEIGHTON AND ASSOCIATES
Geotechnical and Environmental Engineering Consultants
SWAN
Leighton and Associates
A GTG Company GEOTECHNICAL CONSULTANTS
ENGINEERING GEOLOGY REPORT
OF ROUGH-GRADING,
FARADAY AVENUE EXTENSION,
STATION 10+00 TO STATION 62+00,
CARLSBAD, CALIFORNIA
PROJECT NO. 3593
Project No. 980118-003
November 5, 1999
Prepared For
CITY OF CARLSBAD
Engineering Department
2075 Palmas Drive
Carlsbad, California 92009-1576
3934 Murphy Canyon Road, #B205, San Diego, CA 9213-4425
(619) 292-8030. FAX (619) 292-0771 • www.leightongeo.com
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Leighton and Associates
I A GTG Company GEOTECHNICAL CONSULTANTS
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November 5, 1999
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Project No. 980118-003
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To: City of Carlsbad, Engineering Department
2075 Palmas Drive
Carlsbad, California 92009-1576
Attention: Ms. Sheri Howard
Subject Engineering Geology Report of Rough Grading, Faraday Avenue Extension,
Station 10+00 to Station 62+00, Carlsbad, California, Project No. 3593
I geotechnical observation services during rough-grading operations for the Faraday Avenue Extension
project; Station 10+00 to Station 62+00 in Carlsbad, California. The accompanying report summarizes
In accordance with your request and authorization, Leighton and Associates, Inc. has provided limited
I our observations of the geotechnical conditions encountered during rough-grading of the subject site.
If you have any questions regarding this report, please do not hesitate to contact this office. We appreciate
this opportunity to be of service. I . Respectfully submitted,
Y'
LEIG ON AND A OCIA S IN 1 1• NO.
I CERTIFIED • I ENGINEERING I
I t GEOLOGIST 1 Michael R. StewartQC$G 1349 (Exp. 12/31/99)
dentfPrincip3Geologist
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EXP 2.13 'i'?l
'P CIVI
NO. 54033 I
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Distribution: (4) Addressee
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3934 Murphy Canyon Road, #B205, San Diego, CA 9213-4425
(619) 292-8030 • FAX (619) 292-0771 • www.leightongeo.com
980118-003
TABLE OF CONTENTS
Section
1.0 INTRODUCTION .1
I 2.0 SUMMARY OF ROUGH-GRADING OPERATIONS ...............................................................................3
2.1 SITE PREPARATIONS AND REMOVALS ........................................................................................................3
2.2 SUBDRAINS AND PANEL DRAINS ...............................................................................................................4
3.0 ENGINEERING GEOLOGY SUMMARY..................................................................................................6
3.1 GENERAL ................................................................................................................................................6
I 3.2 GEOLOGIC UNITS....... ... ...........................................................................................................................6
3.2.1 Artificial Fill (by others, Map Symbol-Af) .......................................................................................6
3.2.2 Older Artificial Fill (by others, Map Symbol-Afc) ............................................................................ 6
3.2.3 Topsoil (Unmapped)........................................................................................................................7 I 3.2.4 Quaternary Alluvium (Map Symbol-Qal) .......................................................................................... 7
3.2.5 Quaternary Colluvium (Map Symbol - Qcol)...................................................................................7
I 3.2.6 Quaternary Landslide Deposits (Map Symbol-Qis) ..........................................................................
3.2.7 Quaternary Marine Sediments (Map Symbol - Qm) .........................................................................8
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3.2.8 Tertiary Santiago Formation (Map Symbols - Ts (ss), Ts(cs) and Ts. ...................................... . .......... 8
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3.2.9 Cretaceous/Jurassic Santiago Peak Volcanics (Map Symbol - Kfsp ................................................
3.3 GEOLOGIC STRUCTURE ............................................................................................................................8
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3.4 LANDSLIDES AND SURFICIAL FAILURES ......................................................................................................9
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3.5 FAULTING................................................................................................................................................9 I 3.6 GROUND WATER .....................................................................................................................................9
4.0 CONCLUSIONS AND RECOMMENDATIONS ......................................................................................10
1 4.1 REMOvALs ............................................................................................................................................10
4.2 SLOPE STABILITY ............................................................................. ....................................................... 10 4.3 CONSTRUCTION DELAY ... .......................................................................................................................10
I 4.4 SUPPLEMENTAL DESIGN RECOMMENDATIONS .........................................................................................10
4.5 SUBDRAIN OUTLETS ............................................................................................................................... 11
5.0 LIMITATIONS...........................................................................................................................................12
FIGURES
I FIGURE 1 - SITE LOCATION MAP - PAGE 2
PLATES
I PLATES 1 THROUGH 7 — AS-GRADED GEOTECHNICAL MAPS - IN POCKETS
I APPENDICES
APPENDIX A - REFERENCES
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1.0 INTRODUCTION
In accordance with your request and authorization, Leighton and Associates, Inc. (Leighton) has provided
limited geotechnical services during rough grading for the extension of Faraday Avenue, Station 10+00 to
Station 62+00 in Carlsbad, California (Figure 1). Rough grading for the project was conducted from July
1999 to September 1999. This report summarizes our observations of the geologic conditions encountered
during mapping of the rough-grading operations.
GO
ITY
)F SAN
I1ARCOS
FIGURE No. 1
CITY OF
OCEANSIDE
SITE LOCATION MAP
Faraday Avenue Extension
Carlsbad, California
ENCINITAS
PROJECT No. 980118-003
SCALE Not to scale
ENGR. /GEOL. SAC/MRS
DRAFTED By KAM
DATE October 1999
Leighton and Associates, Inc.
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2.0 SUMMARY OF ROUGH-GRADING OPERATIONS
Rough grading for the extension of Faraday Avenue was conducted from July 1999 through September
1999. Rough grading operations were performed by W.R. Connelly, Inc.. Geologic mapping, evaluation of
removals, recommendations for subdrain installation, and slope stability analysis were performed by
Leighton and Associates. Geotechnical observation of placement and testing of compacted fills was
provided by Kleinfelder under separate contract with the City of Carlsbad. A geologist from Leighton was
on site on an as-needed basis during the excavation activities of rough grading.
2.1 Site Preparations and Removals
Prior to grading, the areas of proposed development were stripped of surface vegetation and debris.
I Removals of unsuitable and potentially compressible soil, including undocumented fill, topsoil,
colluvium, alluvium, and highly weathered formational material, were generally made to competent
material. In areas, where ground water and saturated materials impeded further excavation in
I alluvial materials, removals were made to approximately 2 feet above the existing groundwater
elevation. Removals of the unsuitable and potentially compressible soil were performed in general
accordance with recommendations made in the project geotechnical report (Leighton, 1998) and
I field recommendations made during the course of grading. Approximate bottom elevations in the
removal areas are shown on the As-Graded Geologic Maps (Plates 1 through 7).
I In fill slope areas (including stability and buttress fills), remedial removals were made to allow for
placement of compacted fill within a 1:1 projection downward from the toe of slope. Except where
limited by biological constraints, these removals were completed to competent fonnational
I materials or, where encountered, to approximately 2 feet above ground water. The limits of fill
placement mapped along the margins of the work alignment identify the top of the temporary
backcuts that were made during rough grading. For this reason, compressible soils may underlie
I some fills placed during rough grading along the limits of work. Any future construction or
grading adjacent to the limit of work should include removal of unsuitable material beneath fill
along the margins of the project.
I To create sufficient fall on subdrains, some excavations were made outside the limits of work. For
these excavations, complete removal of compressible soils was not performed. The locations of
these partial removals are shown on the As-Graded Geologic Maps (Plates 1 through 7). Fill was I placed over installed subdrains in these areas only to restore original topography and should not be
considered competent, engineered fill. Before placement of additional fills or structural
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improvements in these areas, complete removals should be made.
In areas where clay, seams, landslide failure surfaces, or potential landslide failure surface were
encountered, removals were made to allow for buttressing of these surfaces to mitigate instability.
I The limits of the keyways for stability and buttress fills are shown on the As-Graded Geologic
Maps (Plates 1 through 7). '
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2.2 Subdrains and Panel Drains
I Subdrains were installed along the heel of stability and buttress fills and along canyon fills. The
approximate locations of these drains are shown on the accompanying As-Graded Geologic Maps
(Plates 1 through 7). Buttress and canyon subdrains consisted of 4-inch and 6-inch diameter
I perforated pipe surrounded by 3/4 inch gravel wrapped with filter fabric.
The following table contains a summary of the locations where subdrains were extended from
I below the roadway and into the area of the proposed golf course. Preliminary grading plans were
reviewed and the subdrain outlets located such that they could be extended during the golf course
grading. In several areas, the subdrain outlet was left below grade and a temporary vertical outlet
I was installed. These temporary outlets should be removed and the drain extended as part of future
grading.
Installed Suhdrains Requiring Connection to Suitable Outlet
Flowline Elevation at Connection to Station Vertical Outlet (feet msl)
25+45 36.5
30+50 55
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35+50 52.5
37+00 60.5
41+00 90
44+40 65
50+40 80
I In addition to the subdrain pipes, vertical panel drains were installed at regular intervals along the
backcut of selected slope buttress fills. Backdrains consisted of 4-foot wide panels of J-Drain 302
placed on approximate 20-foot centers. Vertical panel drains were spaced along the backcuts at
I the following stability and buttress fill locations on the north side (uphill) of the roadway
alignment.
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Several subdrams were installed and extended to proposed storm dram structures. Subdrams should be
connected to the dram structures as part of the continuing roadway construction. These subdrain outlets
are located as follows:
Station 21+30 Brow Ditch
Station 50+80 Storm Drain Box
Station .55+03 Storm Drain Box (2 drains)
Station 56+00 Storm Drain Box
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3.0 ENGINEERING GEOLOGY SUMMARY
3.1 General
I A summary of the geologic conditions including geologic units, geologic structure, and faulting is
presented below. The as-graded geologic conditions of the site are presented on the As-Graded
Geologic Maps. (Plates 1 through 7).
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3.2 Geologic Units
The geologic units encountered during the rough grading of Faraday Avenue project consisted of
the following: recent and previously placed artificial fill, topsoil, alluvium, colluvium, Quaternary
I Landslide Deposits, Tertiary Santiago Formation, and Cretaceous/Jurassic Santiago Peak
Volcanics. The approximate limits of the geologic units encountered during rough-grading are
presented on the As-Graded Geologic Maps (Plates 1 through 7), and are briefly described below.
3.2.1 Artificial Fill (by others. Map Symbol-Afi
I Soils derived from on site excavations were used as fill material to achieve design grades,
and to construct stability and buttress fills. These soils were placed by W.R. Connelly,
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Inc., under the observation and testing services of Kleinfelder. As encountered during
grading these soils generally consisted of light brown to dark brown, gray and greenish
gray, sands, silts and clays. These fill soils are differentiated on the geotechnical maps
from the existing fill soils from the previous phases of adjacent grading.
I 3.2.2 Older Artificial Fill (bwothers, Map Symbol-Afc)
Older artificial fill soils were encountered at the intersection of Faraday and Cannon Road
I at Station 10+00 and at the end of the existing Faraday Avenue near Station 62+00.
According to review of previous reports, the soils at Cannon Road were placed under the
observation and testing services of Geopacifica, (1996). Desiccated, loose and disturbed
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portions of existing fills were removed before placement of additional fill material. These
fill soils are differentiated on the geologic maps from the fill soils place during the current
phase of grading. .
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Topsoil (Unmapped)
Topsoil consisting of dry, loose, silty and clayey sands and clays, generally on the order of
2 to 4 feet in thickness and locally up to 6 feet in thickness, was encountered on portions of
the site where no grading had previously been completed. These soils were considered
potentially compressible and unsuitable to receive improvements in their existing condition.
Where situated within the limits of work, these soils were removed and recompacted during
rough grading operations, except at the margins where temporary backcuts blend to the
existing grade.
Quaternary Alluvium (Map Symbol-Oal)
Quaternary alluvium was encountered in the lower portions of all the drainages at the site.
As encountered, this material generally consisted of light to dark brown, moist, loose to
medium dense, porous, clayey to silty, fine to coarse sand. Abundant roots and rootcasts
were also visible within this unit. Where possible within the limits of work, this material
was completely removed during grading to competent formational material. Where
saturated conditions were encountered, removals were made to approximately 2 feet above
the groundwater table. Saturated alluvial soils that were left in place beneath the roadway
prism are mapped from Station 16+25 to Station 19+50 (approximate) and Station 35+50
and Station 36+00 (approximate). Due to the potential for consolidation settlements, we
have recommended installation of settlement monuments and monument surveying in these
areas.
Quaternary Colluvium (Map Symbol - Ocol)
Quaternary colluvium was encountered thiFoughout the site in areas situated at elevations
above the alluvial drainages. Colluvial soils generally consisted of light to dark brown,
damp to moist, loose to medium dense, silty to clayey sand and soft to firm, silts and clays.
The colluvial soils were typically porous and potentially compressible. These soils were
removed and recompacted where encountered within the limits of work.
Quaternary Landslide Deposits (Map Svmbol-Qls)
Quaternary landslide deposits were encountered across the alignment of the road from
Station 23+00 to 27+00 (approximate). This unit consisted of soils derived from topsoil,
alluvium, colluviurn, and Santiago Formation materials. A landslide failure surface that
consists of remolded or highly sheared plastic clay seam generally underlies this unit.
Highly weathered and disturbed portions of the landslide were removed during the grading
operations. Stabilization of the landslide included the construction of buttress keys as
shown on the geotechnical map. A portion of unexcavated slide material that was left in
place underlies the roadway from Station.23+00 to 27+00. Based upon our analysis of the
as-graded conditions in this area, a factor of safety of at least 1.5 was attained for this
material and the as-graded slopes.
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3.2.7 Ouaternary Marine Sediments (Map Symbol - Om)
The Pleistocene-aged marine and lagoonal sediments were observed to be of limited areal
I extent overlying Santiago Formation materials near the intersection with Cannon Road.
As encountered during grading, this unit generally consists of finely bedded, sandy clays
and silts, interbedded with fine-grained sands.
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3.2.8 Tertiary Santiago Formation (Map Symbols - Ts (ss). Ts(cs) and T
I The Eocene-aged Santiago Formation, as encountered during grading, generally consists of
three distinct divisions: a massive, fine to medium grained, white to light gray sandstone; a
I massive, randomly fissured, sandy siltstone and claystone; and a fine to medium gramed
sandstone, interbedded with sandy silts and clays. The dominant locally observed type has
been mapped on the As-Graded Geologic Maps (Plates 1 through 7). Clay seams or
I potential landslide surfaces observed within this unit commonly divide differing sub-units
or are found near changes in lithology.
3.2.9 Cretaceous/Jurassic Santiago Peak Volcanics (Map Symbol - KJsp
The basement geologic unit observed on the project is the Cretaceous and Jurassic-aged
Santiago Peak Volcanics. This volcanic rock varies somewhat in composition, but is
primarily dacites and andesite. The weathered rock encountered during grading was
typically light to dark red-brown in color. Weathering of this unit is generally controlled by
fractures and jointing, which are typically at right angles. We observed that the uppermost
metavolcanic rock is generally moderately to highly fractured (fracture spacing on the
order of 2 to 6 inches) with a moderate to high amount of fines generated during the
removals. Below these depths, fracturing is believed to be more widely spaced.
3.3 Geologic Structure
Based on our geologic mapping during the rough-grading operations, bedding on site varies
considerably along the alignment. Generalized mapped bedding plane strike and dip attitudes are
presented in the As-Graded Geotechnical Maps. It should be noted that due to the undulatory
nature of the bedding contract, significant local variation can exist.
3.4 Landslides and Surficial Failures
Based on our review of the preliminary geotechnical report (Leighton, 1998), and our mapping
during rough grading operations, there were no additional indication of landslides or other surficial
failures within-the site other than those landslides that were previously discussed. However, during
a review of pertinent aerial photographs, several features, which may be related to mass movement,
can be seen in the immediate vicinity. Therefore, we recommend that prior to any development
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outside the limits of this phase of grading, a thorough evaluation with regard to landslides or other
mass movement be completed by a qualified geotechnical engineer and engineering geologist.
Faulting
Inactive Miocene-aged normal faults that offset the Santiago Formation were identified during site
grading and our previous investigation. These faults are attribUted to Miocene extension and are
not believed to present a significant constraint to the project.
No evidence of active faulting was encountered nor anticipated during rough-grading operations at
the site. No evidence of surface faulting was observed during grading operations on site or during a
review of pertinent aerial photographs.
Ground Water
Ground water was encountered during rough grading operations of the site and symbols identifying
observed locations and elevations are presented on the As-Graded Geotechnical Map. It should be
noted that the majority of this phase of grading lacks a shallow ground water or widespread
perched ground water condition. Subdrains and/or panel drains were installed in areas of observed
seepage and in areas where future seepage is anticipated. Groundwater does not appear to be a
significant constraint to proposed improvements provided the improvements are constructed with
appropriate consideration to address surface and subsurface infiltration. Areas of additional
localized seepage may Occur after period of heavy rainfall or irrigation of upsiope properties. If
areas of additional seepage are noted, this office should be notified in a timely manner so that
additional recommendations can be provided.
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I. 4.0 CONCLUSIONS AND RECOMMENDATIONS
1 4.1 Removals
Removal of compressible soils during rough grading for Faraday Avenue was performed in general
accordance with the project geotechnical reports, geotechnical recommendations made during the
course of grading, and the City of Carlsbad requirements.
Slope Stability
Based on our geologic observation, engineering analysis and testing, it is our opinion that the
slopes constructed of properly mixed and compacted fills (Leighton, 1998) at inclinations of 2:1
(horizontal to vertical) or flatter. possess a factor of safety of 1.5 or greater to resist deep-seated
and surficial 'instability. We recommend that all graded slopes be landscaped with drought-
tolerant, slope stabilizing vegetation as soon as possible to minimize the potential for erosion.
Erosion control fabric/measures should be considered while vegetation becomes established.
Design of surface drainage provisions are within the purview of the project civil engineer.
Construction Delay
We have recommended that settlement monitoring be performed for the two areas where saturated
alluvium was left-in-place beneath the roadway fill prism from Station 16+25 to Station 19+50 and
from Station 35+50 to Station 36+00. We recommend this office be provided with settlement
monitoring data for review prior to construction of improvements in these areas.
Supplemental Design Recommendations
It is our understanding that the City's testing laboratory will be performing additional tests
throughout the remainder of the project to confirm that design assumptions agree with as-graded
conditions. Supplemental design recommendations may be warranted based on observations and
test results. This office should be contacted to provide additional recommendations where
conditions differ from those assumed during the preliminary design phase.
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4.5 Subdrain Outlets
The site grading included the construction of several subdrain systems that will require the
construction of outlets. These outlets should be constructed and the drains connected as part of the
installation of the storm drain system. Care should be taken to not damage the outlets during
future construction. In addition, several drains were extended to the proposed golf course area and
temporary outlets constructed. These drains should be extended during future construction or be
allowed to drain freely.
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5.0 LIMITATIONS
The presence of our field representative at the site was intended to provide the owner with professional
advice, opinions, and recommendations based on observations of the exposed geologic conditions. We do
not guarantee the contractor's work or services provided by other consultants, nor do our services relieve
the contractor or his subcontractors of their responsibility if defects are subsequently discovered in their
work. Our responsibilities did not include any supervision or direction of the actual work procedures of the
contractor, his subcontractors, or the City of Carlsbad's designated testing laboratory.
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APPENDIX A
REFERENCES
City of Carlsbad, Contract Documents and Special Provisions for Faraday Avenue Extension, Contract
No. 3593, dated January 5, 1999:
Geopacifica, 1990, As-Graded Geotechnical Report, Kelly Ranch Phase 1, Carlsbad Tract No. 83-30,
Carlsbad, California, Project No. 160.1.4, dated January 10, 1990.
Leighton and Associates, Inc., 1998, Geotechnical Investigation for the Proposed Faraday Avenue
Extension, Alternate 8 Split, Carlsbad, California, Project No. 980118-003, dated July 1,
1998.
1999a, Summary of Settlement Monitoring at Surcharge No. 1, Faraday Avenue Extension,
Carlsbad, California, Project No. 980118-003, dated September 2, 1999.
1999b, Geotechnical Review of Improvement Plans for Faraday Avenue Extension, Carlsbad,
California, Project No. 980118-003, dated September 13, 1999.
1999c, Method of Documenting Stability Fill Geometries and Keyway Elevations, Faraday
Avenue Extension, Carlsbad, California; Project No. 980118-003, dated September 13, 1999.
PLANS
O'Day Consultants, 1999, Grading and Drainage Plans for Faraday Avenue, Project No. 3593, Sheet 1-15,
dated-June 10, 1999.
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