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Appendix-B-Geotechincal-Report-1Appendix B Geotech n ical Report GMU GEOTECHNICAL,INC. Preliminary Geotechnical Study Report for San Ramon Canyon Storm Drain System, City of Rancho Palos Verdes,California Prepared For HARRIS &ASSOCIATES November 10,2010 GMU Project No.1 0-036-00 23241 Arroyo Vista Rancho Santa Margarita CA 92688 voice:949.888.6513 fax:949.888.1 380 web:www.gmugeo.com GMU·..·.· ,. GEOTECHNICAL,INC. TRANSMITTAL 23241 Arroyo Vista Rancho Santa Margarita CA 92688 voice:949.888.6513 fax:949.888.1380 web:www.gmugeo.com HARRIS &ASSOCIATES 34 Executive Park,Suite 150 Irvine,CA 92614 ATTENTION: SUBJECT: DATE:November 10,2010 PROJECT:10-036-00 Mr.Randall Berry Preliminary Geotechnical Study RepOli for San Ramon Canyon Storm Drain System,City of Rancho Palos Verdes ;WE ARE SENDING THE FOLLOWING: One (1)wet signature copy of our "Preliminary Geotechnical Study Report for San Ramon Canyon Storm Drain System,City of Rancho Palos Verdes,California,"dated November 10,2010. Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ran/oil Callyoll St01'11I Dmill Project,City ofRallcho Palos Verdes TABLE OF CONTENTS Description Page INTRODUCTION 1 SCOPE OF WORK 1 SITE LOCATION 2 EXISTING CONDITIONS AND HISTORY 2 PREVIOUS GEOTECHNICAL INVESTIGATIONS 3 PROPOSED DESIGN ALTERNATIVES 4 ALTERNATIVE 1 4 ALTERNATIVE 2 4 ALTERNATIVE B (OPTION FOR ALTERNATES 1 AND 2)5 GEOLOGIC EXPLORATION AND SURFACE MAPPING 5 FIELD EXPLORATION 5 Surface Mapping 5 Subsurface Exploration 5 Geophysical Testing 7 LABORATORY TESTING PROGRAM 7 GEOLOGIC FINDINGS 7 REGIONAL GEOLOGy 7 MATERIALS ENCOUNTERED 8 Topsoil 8 Recent Alluvium (Qal)8 Artificial Fill (Qaf)8 Older Alluvium (Qoal)9 Recent Landslide Debris (Qlsr)9 Ancient Landslide Debris (Qols)9 Altamira Shale Member,Monterey FOimation (Tma)9 LANDSLIDES AND GEOLOGIC STRUCTURE 10 EROSION 11 GROlfNDWATER 12 SEISMIC HAZARDS 12 Faulting,Ground Rupture,and Seismic Shaking .12 Seismically-Induced Landsliding 13 Liquefaction and Lateral Spreading 13 Tsunami.,13 Seiche ,13 Seismic Design ,13 November 10,2010 GMU Project 10-036-00 Mr.Randall Beny,HARRIS &ASSOCIATES Sail Ra1l/011 Cal1yol1 Storm Dl'flin Project,City ofRancllo Palos Verdes TABLE OF CONTENTS (continued) Description Page GEOTECHNICAL ENGU\JEERING CHARACTERISTICS 15 GEOPHYSICAL TESTING 15 GEOMECHANICS CLASSIFICATION (RMR)15 Uniaxial Compressive Strength 15 Rock Quality Designation (RQD)15 Joint or Discontinuity Spacing 16 Joint Condition 16 Groundwater Condition 16 Joint Orientation ~16 Overall RMR 16 GENERAL GEOTECHNICAL ENGrnEERING CHARACTERISTICS 17 SUMMARY OF SLOPE STABILITY ANALYSES 17 Tarapaca Landslide 18 Lower Switchback PVDE 18 Upper Switchback PVDE 18 Bluff Stability 19 PVDE SWITCHBACKS STABILITY DISCUSSION 19 CANYON WALL STABIL TY DISCUSSION 20 CONCLUSIONS :21 DESIGN ALTERNATIVE GEOTECHNICAL CONSIDERATIONS 22 ALTERNATIVE 1 22 Anticipated Construction Methods 22 Preliminaly Geotechnical Considerations for Open Trench Segments 22 Preliminaly Geotechnical Considerations for Tunnel Segments 23 Preliminary Geotechnical Considerations for Canyon Inlet Structure 24 Preliminary Geotechnical Considerations for Bluff Face Outlet Structure 25 ALTERNATIVE 2 26 Preliminaly Geotechnical Considerations for Open Trench Segments 26 Preliminary Geotechnical Considerations for Canyon Inlet Structure 27 Preliminaly Geotechnical Considerations for Canyon Outlet Structure/ Tie-In to City Inlet 28 ALTERNATIVE B (OPTION TO ALTERNATIVES 1 AND 2)28 Preliminaly Geotechnical Considerations for Open Trench Segments .28 Preliminary Geotechnical Considerations for Tie-In to Existing Outlet 29 November 10,2010 ii GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ramon Callyon Storm Drain Project,City ofRancho Palos Verdes TABLE OF CONTENTS (continued) Description Page FUTURE TASI(S 29 LIMITATIONS 29 SUPPORTING DATA .30 REFERENCES 31 PLATE 1 PLATE 2 PLATE 3 PLATES 4 and 5 PLATE 6 APPENDIX A APPENDIX A-I APPENDIX A-2 APPENDIXB APPENDIXC APPENDIXD November 10,2010 -Study Location Map -Study Area Map -Geotechnical Map -Geotechnical Cross-Sections -Design Alternatives -Exploration Logs -GMU Geotechnical Boring Logs -Exploration by Others -GMU Geotechnical Laboratory Test Results -Stability Analysis -Geophysical Testing Results iii GMU Project 10-036-00 INTRODUCTION This report is intended to provide a summary of our preliminary geotechnical investigation and evaluation of the feasibility of design altematives for the proposed San Ramon Canyon Storm Drainage System project within the City of Rancho Palos Verdes,California.Our repOli is based on our understanding of the design alternati ves prepared by Harris &Associates and presented in their conceptual plans,dated September,2010 (see References). SCOPE OF WORK Our scope of work for the preliminary geotechnical investigation and feasibility evaluation of the design alternatives was generally as described in our proposal to Harris &Associates,dated February 23,2010. 1.Background Review and Technical Study -including review of available geologic and geotechnical data and historical aerial photographs,surface mapping of San Ramon Canyon, preparation of geologic cross-sections,and attendance at team meetings. 2.Evaluation of Palos Verdes Drive East Switchbacks -including drilling two bucket auger borings on the outside of the switchbacks,completion of a laboratory testing program,and revision of the geologic cross-sections to incorporate the collected data. 3.Evaluation of Tunnel Design Alternative -including drilling two continuous core borings along the conceptual tunnel aligmnent and performing geophysical logging of the borings, completion of a laboratory testing program,and geotechnical analyses ofthe data collected. In addition to the scope described in our proposal,one additional bucket auger boring was drilled near the launch pit for the southernmost pOliion of the tunnel alignment,and corresponding additional laboratory testing and analyses were performed. 4.Evaluation of Canyon Design Alternatives -including drilling one hollow-stem auger boling within San Ramon Canyonjust upstream from 25 th Street,completion ofa laboratory testing program,revision of the geologic cross-sections as required,and geotechnical analyses ofthe data collected. 5.Deliverables and Technical SuppOli-including preparing both a draft and final preliminary geotechnical report (herein),and attendance at meetings as necessary to facilitate understanding and support of the project from goveming agencies. Mr.Randall Berry,HARRIS &ASSOCIATES Still RaJllon Canyon StOl''''DI'ain Project,City ofRancho Palos Verdes SITE LOCATION The proj ect site is located within the eastern portion ofthe City of Rancho Palos Verdes.In general, the site is bounded by Palos Verdes Drive East (PVDE)on the west,Calle A ventura and Tarapaca Road to the north,the City of Los Angeles boundary to the east,and the Pacific Ocean to the south. It should be noted that the site is bisected by Palos Verdes Drive South,which is named 25 th Street within the City of LA.For the purposes of this report,this street is referred to as "25 th Street".A Location Map showing the specific limits of the project site is included in this report as Plate 1. EXISTING SITE CONDITIONS AND HISTORY In general,the project site is in an undeveloped condition,except for the PVDE and 25 th Street roadways.Some areas that bound the site are developed,such as the residences upslope ofthe upper p01tions of San Ramon Canyon,and the Palos Verdes Shores mobile home park to the south of 25 th Street.The location of the park and other major features are shown on Plate 2. The major topographical feature within the project site is San Rarpon Canyon,which trends generally n01th-south.Prior to development,this canyon extended to the Pacific Ocean.However,during the construction of 25 th Street,the lower portion of the canyon was buried and the flow of water was collected into a storm drain system that begins at 25 th Street and extends down to the ocean. Currently,the inlet structure that was the upstream beginning of the system has been buried by debris. The remaining p01tions of the project site consist of gentle to very steep slopes,with the steeper slopes found within the canyon.The topography of the project site is generally controlled by the large ancient landslide that comprises the majority of the site.This landslide,the South Shores landslide,is considered dormant and is discussed in further detail in subsequent sections of this report. The need for this storm drain project has been prompted by the episodic flooding of 25 th Street that occurs during moderate to heavy rainfall periods and the concern for the stability of PVDE.The flooding of the 25 th Street area is primarily due to the clogged and buried storm drain inlet,which does not collect surface water.During a rain event,smface water flowing down the canyon is calTied downstream and directly onto the roadway.In addition,erosion of the canyon and slope movement are contributing to the problem,causing mudflows and debris to be washed down the canyon. Our review of historical aerial photographs (listed in References)indicates that 25 th Street and the associated storm drain under the roadway were constructed prior to 1954.Residential construction at the top of the canyon began in the late 1950s and continued intermittently through the 1990s. November 10,2010 2 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ralllon Canyon StOl'lII Dmin Project,City ofRancho Palos Verdes Residential construction south ofthe project site (Le.,south of25 1h Street)OCCUlTed in the 1970s.In addition,failure ofthe slope at the head of San Ramon Canyon and the subsequent repair OCCUlTed in the early 2000s.This failure,while outside the influence of the project site,is discussed in a subsequent section of this report. Areas of increased erosion within San Ramon Canyon were noted in the photos from 1970,1978, 1979,1988,and 1992.Surficial failures,slumps,and small landslides were noted on the photos within the canyon.The Tarapaca landslide,located on the east side of the canyon,is first noted on the photos in 1978 as increasing erosion,with scarps observed in the 1988 photos.Further detailed discussion of the Tarapaca landslide is included in subsequent sections of this report. The buildup of silt and debris within the lower portions ofthe canyon,upstream from 25 1h Street,is first observed within the 1988 photos and continues through the present.Based on the erosion observed within the photos and the currently observed site conditions,it appears the canyon has widened over time,with increasingly steepened side walls. PREVIOUS GEOTECHNICAL INVESTIGATIONS No site-specific investigations for a storm drain within San Ramon Canyon have been completed prior to the current geotechnical investigation by GMU Geotechnical,Inc.(GMU).However, numerous studies by geologists have been done on the South Shores landslide,and several geotechnical reports for single-family residences have been published for properties upslope of San Ramon Canyon.A complete list ofreports and publications reviewed as part ofthis investigation is included in the References section of this report.In addition,where appropriate,data from these previous investigations,as well as data from regional publications,have been incorporated into this preliminary geotechnical report. In general,the primary focus of previous studies in the area pertains to the South Shores landslide. These studies conclude that the landslide is approximately 16,200 years old (Ray,1982),and may have failed in one event.Various authors disagree on the eastern limits of the landslide,and different interpretations of the available data have resulted in several opinions as to the depth and toe ofthe landslide.Dibblee (1999)maps the toe of the landslide within the bluffface above sea level, while Ray (1982)and others map the toe below sea level and the current beach.It appears that the majority of authors on the subject of the South Shores landslide agree that the landslide is dOlmant and has not moved in historic time. Site-specific reports for single-family residential developments were also reviewed for this investigation,including reports by Ehlert (1997,1998),and T.I.N.Engineering Company (2006)for residences upslope of the project site.Geologic data from these reports,including boring and November 10,2010 3 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Stili Rallloll Canyon Storm Drain Project,City ofRallcho Palos Verdes trenching data,were included in our Geotechnical Map and Cross-Sections (Plates 3,4,and 5). However,much of the data shown on the geologic maps within thee rep0l1s references boring or trench logs that were not available for our review.Where available,these logs are included in Appendix A of this report.Logs that were not available are indicated on the legend of our Geotechnical Map,Plate 3. PROPOSED DESIGN ALTERNATIVES Based on our review of the conceptual plans by Harris &Associates (2010),we understand there are two main alternatives for this project,with a third alternative that is considered to be an option for the first two alternatives.These alternatives are described below,and shown generally on Plate 6. ALTERNATIVE 1 In order to significantly reduce the erosion and flooding within San Ramon Canyon from surface water,Alternative 1 proposes to construct an inlet structure within the canyon which will carry runoff water through a subsurface storm drain system to the west of the canyon,exiting through an outlet structure at the toe of the bluffs at the ocean.The storm drain system would be constructed with tunnel and open trench methods,and would be located entirely within the City ofRancho Palos Verdes.The general location of the storm drain system proposed for Alternative 1 is detailed in conceptual plans prepared by Han-is &Associates.In addition to the construction ofthe stOlID drain system,a gravity-type buttress would be constructed within the canyon in order to reduce the potential for future deep-seated movement within the actively failing portion of the canyon (i.e.,the Tarapaca landslide). ALTERNATIVE 2 This alternative includes construction of a subsurface drainage system within the canyon,with an inlet structure in approximately the same location as Alternative 1.This structure will collect surface water into a subsurface storm drain system consisting of a 48-inch-diameter pipe system with a 12-inch-diameter underlying subdrain system.Construction ofthe storm drain system would include placing fill within the majority ofthe canyon in order to restore the ground surface to "pre-erosion" conditions and to mitigate the over-steepened canyon walls and failing areas.This storm drain system would tie into the existing system that underlies 25 th Street.The general location and details of this alternative are presented in the conceptual plans prepared by Hal1'is &Associates. November 10,2010 4 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ramon Canyon Storm Drain Project,City ofRanclto Palos Verdes ALTERNATIVE B (OPTION FOR ALTERNATIVES 1 AND 2) The third alternative consists ofan optional upstream extension ofthe stonn drain system that would apply to either Alternative 1 or 2.This option would consist ofcOllilecting the proposed storm drain systems (either within the canyon or to the west ofthe canyon)to the existing storm drain system for the residences at the head of the canyon.The existing storm drain system cun'ently outlets into the canyon at the toe of the graded cut slope at the head of San Ramon Canyon. GEOLOGIC EXPLORATION AND SURFACE MAPPING FIELD EXPLORATION Our field exploration program was designed to provide preliminary data for evaluation of the feasibility ofthe design alternatives described above.In order to accomplish this,our investigation consisted of multiple types of subsurface exploration as well as surface geologic mapping.All aspects of our field investigation were performed by a Celtified Engineering Geologist. Surface Mapping Geologic mapping of exposed materials was performed across the project site.Exposures ofancient and recent landslide debris,alluvium,and bedrock were observed and geologic structure recorded where observed,generally within San Ramon Canyon and at the bluff descending to the ocean at the southern edge ofthe project site.Our geologic observations and mapping were incorporated into our data and analyses and are shown as mapped on the Geotechnical Map,Plate 3,and where appropriate on our Cross-Sections,Plates 4 and 5. Subsurface Exploration Our subsurface exploration program included drilling,sampling,and logging small-diameter hollow- stem,large-diameter bucket auger,and continuous diamond core borings.Each boring type was selected in order to provide the optimal data retrieval methods for the soil and bedrock conditions anticipated,and to provide the appropriate data type for the proposed alternative.Each method of subsurface exploration is discussed below,and geologic discussion of materials encountered is presented in a subsequent section of this report.Detailed logs of each boring are presented within Appendix A of this report.The approximate location of each of these borings is shown on our Geotechnical Map,Plate 3,and the associated geologic structure is shown on the Cross-Sections, Plates 4 and 5,where appropriate.Backfill of all exploratory borings was completed immediately after logging,and consisted of backfilling and tamping with native materials or backfilling with concrete sluny,where appropriate. November 10,2010 5 GMU Project 10-036-00 Mr.Randall Berry,HARRlS &ASSOCIATES Sail Ramol1 Callyoll Storm Draill Project,City of Rallcho Palos Verdes Small-diameter Hollow-Stem Auger Boring One hollow-stem auger boring was drilled within San Ramon Canyon,just north of 25 th Street, within the City of Los Angeles easement.This boring was drilled to a maximum depth of 46.5 feet, and was intended to evaluate the recently deposited alluvial materials at the upstream intersection of San Ramon Canyon and 25 th Street.Drive and bulk samples were collected and Standard Penetration Tests (SPTs)were performed in order to geotechnically evaluate the materials encountered. Large-diameter Bucket Auger Borings Three bucket auger borings were drilled as part ofour investigation.Boring DH-l was located in the southern portion of the proj ect site,near the proposed launch pit area for the stOlID drain alignment in Alternative 1,and was intended to evaluate the materials to be encountered at the launch pit as well as geologic structure of the materials exposed in the bluff face.This boring was drilled to approximately 103 feet,where refusal was encountered on very hard material.In addition,the boring was downhole logged by a Certified Engineering Geologist to about 93 feet. Boring DH-2 was located just east of the lower switchback of PVDE,adjacent to the descending slope to San Ramon Canyon,and was intended to evaluate the geologic structure of the materials underlying the switchback.This boring was drilled to 63 feet,where refusal was encountered due to severe caving of highly fractured material.In addition,the boring was downhole logged by a Certified Engineering Geologist to about 55 feet. Boring DH-3 was located adjacent to the upper switchback,on the east side ofthe roadway,and was intended to evaluate the geologic structure ofthe materials underlying the switchback.This boring was drilled to 60 feet,where refusal was encountered due to severe caving of highly fractured material.In addition,the boring was downhole logged by a Celtified Engineering Geologist to about 22 feet,where severe caving precluded fulther logging ofthe boring.Drive and bulk samples were collected in each of these bucket auger borings in order to geotechnically evaluate the materials encountered.These borings were backfilled with native materials and tamped in place to properly backfill the borings to minimize settlement potential. Continuous Diamond Core Borings Two continuous core borings were drilled as part ofour investigation.Boring C-I was drilled on the "inside"of the lower switchback of PVDE,near the conceptual storm drain alignment of Alternative 1.This boring was intended to primarily evaluate the materials within the South Shores landslide at the storm drain location and to evaluate the geologic structure ofthis area.This boring was drilled to approximately 149 feet.The continuous core samples collected during drilling were logged by a Certified Engineering Geologist,and geophysical testing of the borings was performed. November 10,2010 6 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sall Ramoll Ca11yoll Storm Dm;1l Project,City ofRa11cho Palos Verdes Boring C-2 was drilled on the southern shoulder of25111 Street adjacent to the City boundary,near the conceptual storm drain alignment of Altemative 1.This boring was also intended to primarily evaluate the materials within the South Shores landslide at the storm drain location and to evaluate the geologic stmcture of this area.This boring was drilled to approximately 104 feet.The continuous core samples collected during drilling were logged by a Certified Engineering Geologist, and geophysical testing of the borings was performed. Geophysical Testing The geophysical testing performed for Borings C-l and C-2 included caliper measurements,optical televiewer,and Suspension P-and S-wave velocities.It should be noted that during the logging of Boring C-l,water levels would not rise above 103 feet despite water added to the boring by the drillers via a gravity hose from a water tmck.Therefore,Suspension logging could not be pelformed above 103 feet.The results of the geophysical testing,performed by Norcal Geophysical Consultants,Inc.,are attached to this repOlt as Appendix D,and are incorporated into our findings, analyses,conclusions,and recommendations as discussed in this repOlt. LABORATORY TESTING PROGRAM Our laboratory program was designed to include testing on representative samples of all geologic materials encountered in order to provide a preliminary geotechnical database for the project site in light of the three alternatives.Our testing program included geotechnical index testing of typical onsite soils as well as direct shear testing of a variety of materials at critical locations to provide a compilation of strength values for the onsite materials.Detailed discussion of each type of testing performed as well as testing results are presented in Appendix B of this repOlt.In addition,further discussion of testing results is included in subsequent sections of this report. GEOLOGIC FINDINGS REGIONAL GEOLOGY Published regional data and our experience in the Palos Verdes Peninsula indicate the peninsula is underlain by Tertiary sedimentary units over basement rock ofthe Catalina Schist.These geologic materials have been uplifted over time through folding and faulting to create a large-scale anticline that comprises the peninsula,generally trending northwest-southeast.Tectonic uplift in the area may be primarily due to movement on the Cabrillo and Palos Verdes fault zones.Quaternary sediments overlie the Teltiary materials in much of the lower pOltions of the peninsula due to deposition of November 10,2010 7 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ramon Canyon Storm Drain Project,City of Rancho Palos Verdes sediments by wave action during uplift and through sediment deposition due to gravity,erosion,or in situ weathering. The geologic features of primary interest within the Palos Verdes Peninsula are the numerous landslides that exist mainly on the ocean (southwesterly)side of the peninsula,generally coincident with southwesterly dipping regional bedding.The two most significant landslide features in the Palos Verdes area are the Portuguese Bend landslide,located approximately 2 miles west of the project site,and the South Shores landslide,located paltially within the project site.Fm1her discussion oflandsliding and impacts to the project altematives are discussed in a subsequent section of this report. MATERIALS ENCOUNTERED Geologic soil and bedrock materials encountered during our field investigation are described below and within our boring logs.In addition,the lateral extent of these materials is shown on the Geotechnical Map,Plate 3.The geologic structure of these materials is shown on the Cross- Sections,Plates 4 and 5. Topsoil Topsoil was observed during our field investigation as a thin veneer across much of the project site. While topsoil was not encountered within our borings,it was ob;erved within drill pad and access road excavations,as well as during surface mapping of the site.Where observed,the topsoil consisted of dark brown silty clay,dry to damp,with no soil structure.Due to the thin nature of the topsoil (Le.,less than three feet in thickness),this geologic unit is not shown on our Geotechnical Map or Cross-Sections. Recent Alluvium (Qal) These materials are generally located within San Ramon Canyon,on the canyon floor and in a relatively thick deposit on the northern side of the intersection of the canyon and 25 th Street.Where encountered in Boring DH-4,and during surface mapping,the recent alluvium generally consisted of dark brown clay with fine-to medium-grained sand.These materials were generally moist,very soft to soft,with scattered to abundant bedrock fragments and organic materials (i.e.,plant debris).The thickest deposit of these recent alluvial materials was found to be about 31 feet thick. Artificial Fill (Qat) These materials are generally located underlying and adjacent to the paved roadways,PVDE,and 25 tl1 Street and,as such,were likely placed during grading of these roads pre-1950s.Where November 10,2010 8 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Stili Ramol/Cal/You Storm Draiu Project,City ofRancho Palos Verdes observed,these fill materials were dark brown,dry to damp,soft to film silty clay and sandy silt with fragments of bedrock.Visible lifts were not observed within the downhole logged boring,DH-3,nor were they observed within the core samples recovered within C-2.The maximum thickness ofthese fill soils was 0 bserved to be about 18 feet.However,there may be deeper fill soil deposits within the project site,paliicularly adjacent to or underlying roadway areas. Older Alluvium (Qoal) Deposits of older alluvium were observed within the upper portions of San Ramon Canyon during surface mapping.Where observed within the canyon bottom and sidewalls,these materials consisted on dark brown clayey silt with scattered to abundant bedrock fragments and rare charcoal fragments. These soils were moderately well-developed,with a blocky to columnar stmcture and local porosity. Structure within these soils was difficult to identify,with some local areas showing subtle textural layers.Given that no borings were drilled within the older alluvium,the maximum thickness of these deposits is unknown;however,it is estimated to be less than 50 feet. Recent Landslide Debris (Qlsr) Recently failed materials derived from bedrock and ancient landslide debris were observed during our field exploration on the east wall of San Ramon Canyon.These materials are refelTed to in geologic publications as the Tarapaca landslide.This landslide is considered to be actively moving. Where observed during surface mapping,the materials of the Tarapaca landslide consist of loose bedrock fragments up to cobble-sized with a soil matrix.Pockets oftopsoil with organic debris were observed within the landslide mass.FUliher discussion ofthis recent landslide is provided within the "Landslides and Geologic Stmcture"section of this report. Ancient Landslide Debris (Qols) These materials,known as the South Shores landslide,underlie the majority of the project site,and were encountered within all of our borings.Where observed,these materials consisted of remnant blocks of bedrock up to 10 feet thick within a silty clay matrix.These materials are varicolored,soft to hard,dry to moist,and contain blocks of siliceous siltstone that can be very hard.Further discussion ofthe South Shores landslide is provided within the "Landslides and Geologic Structure" section of this repOli. Altamira Shale Member,Monterey Formation (Tma) Bedrock ofthe Altamira Shale member ofthe Monterey FOlmation underlies the project site at depth, and is exposed within portions of San Ramon Canyon.Where observed,the Altamira Shale member consisted of interbedded siltstone and siliceous siltstone with tuffaceous siltstone,bentonitic tuff, and bentonite.These beds are generally thinly to thickly bedded,planar,with some local soft November 10,2010 9 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Still RtlmOIl COllY 011 Storm Droill Project,City ofROllcho Palos Verdes sediment deformation.The materials are generally gray to olive brown,damp to moist,firm to very hard,with scattered fracturing and jointing.Further discussion of the geologic structure of the bedrock underlying the project site is included in the section below. LANDSLIDES AND GEOLOGIC STRUCTURE Regional geologic publications and site-specific geotechnical rep0l1s for prope11ies adjacent to the project site indicate the area around the project site may form a geologic "bowl"structure.Bedding inclinations to the north ofthe site are generally oriented towards the south.Bedding inclinations to the east of the site are generally oriented to the west,and inclinations west of the site are generally oriented to the east.This synclinal geologic structure likely contributed to and controlled the lateral extent of the failure of the South Shores landslide,which dominates the project site. The South Shores landslide is considered to be approximately 16,200 years old,and failed as a block glide type failure (Ray,1982).While the authors ofpublications on the South Shores landslide agree the landside is dormant,there is some disagreement on the limits of the landslide,in particular the eastern edge of the landslide.Some geologists include the cUlTently active Tarapaca landslide as part of the South Shores landslide,while others map the active landslide as originating upslope of the limits of the dormant landslide mass. Our interpretation of the limits of the South Shores landslide are based on our review of existing geologic data,our observations during our field investigation,and our review of historic aerial photographs.All of our borings encountered the ancient landslide debris,with all three of the large- diameter borings excavated entirely within the landslide.Observations made during downhole logging suggest the South Shores landslide has variable composition,depending on location within the landslide mass.Borings drilled in the upper middle of the landslide (Borings DH-2 and DR-3) encountered large remnant blocks of siltstone and siliceous siltstone that appeared to be highly fractured,sheared,and laterally discontinuous.Continuous beds of bentonite or bentonitic tuffwere not observed within either ofthese two borings.The geologic structure within the landslide mass in the area of the lower switchback of PVDE generally consists of discontinuous remnant fragments and small blocks of bedrock within the debris matrix.The geologic structure ofthe landslide mass in the area of the upper switchback appears to be more continuous,but moderately to severely folded with some faulting and discontinuities. Our large-diameter boring DR-1 was drilled near the mapped toe of the South Shores landslide,at the top of the bluff above the beach.Observations made during downhole logging of this boring suggest this area is comprised of generally intact bedrock materials with continuous,planar bedding. The materials were moderately to rarely fractured,with little to no shearing observed.Bentonite or bentonitic tuff beds were not observed within this boring.Surface mapping along the bluff below indicates this continuous,intact bedrock material continues along the bluff face within the project November 10,2010 10 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Rail/oil CallY 011 Storll/Dmill Project,City of Rancho Palos Venles area.Based on this limited subsurface data and the surface geologic mapping,it appears that this lower area may be either a separate,older landslide that failed as a generally intact block,or intact bedrock that has not failed as previously thought.However,very limited data was collected during our investigation,and the presence of a deep-seated landslide rupture smface as previously published cannot be ruled out. Our Cross-Section 7-7'illustrates the general structure of the older landslide and the postulated rupture surfaces.At least two significant rupture surfaces may exist;one rupture surface at the base of the upper,chaotic debris,and a basal rupture surface at the postulated landslide/bedrock contact below the relatively continuous material noted in DH-I and the bluff face. The Tarapaca landslide appears to have failed on a continuous,planar bedding plane surface within the Altamira Shale bedrock east of the South Shores landslide.It is our opinion that the Tarapaca landslide is not a part ofthe South Shores landslide,as discussed above.As discussed in the "Slope Stability"section of this report,this bedding plane surface does not appear to be a bentonite bed, based on back-calculations performed ofthe landslide.The most likely scenario for the failure ofthe Tarapaca landslide is an over-steepening of the canyon walls,resulting in a "daylighted"adverse bedding condition.Given the steep nature ofthe failure plane,and the continuous erosion ofthetoe of the landslide by surface water flow down the canyon,movement of the Tarapaca landslide is expected to continue.This episodic movement and failure ofthe landslide material into the canyon bottom is causing increased erosion of the opposite canyon walls,as discussed below. The failme that occurred at the head ofthe San Ramon Canyon area in the early 2000s occurred due to undercutting of oversteepened bedrock,and was subsequently repaired by grading a buttress fill and installing a new storm drain system outlet.It should be noted that this failure area,while shown on our Geotechnical Map,is not within the project site.None of the proposed design alternatives will adversely impact this repaired area. EROSION While erosion due to wind and water is a common geologic phenomenon over all of southern California,the impacts of water-driven erosion are significant within the project site in the area of San Ramon Canyon.Erosion within this canyon ranges from moderate to severe.The areas of severe erosion are generally in the area of the Tarapaca landslide and downstream. The episodic and active downslope movement ofthe Tarapaca landslide is forcing the flowline ofthe canyon to shift westerly,causing increased erosion of the western walls ofthe canyon.These areas are directly downslope of the switchbacks ofPVDE,in particular the lower switchback.Erosional scars can be seen on the topographic map used as the base for our Geotechnical Map,Plate 3.Based on our review ofhistorical aerial photographs and our experience in the Palos Verdes area,it appears November 10,2010 11 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Canyoll Storm Drain Project,City ofRancho Palos Verdes that these areas of the canyon are eroding at an average rate of about 5 feet per year.Continued annual erosion of these areas may cause stability issues with PVDE.Further discussion of the current and future stability of PVDE is discussed in subsequent sections of this report. Moderate to severe erosion of the canyon walls and floor due to heavy flow of surface water and flash flooding during rains has caused deep cutting ofthe canyon,in some areas generating vertical cuts up to 30 feet in height.Instability ofthese cuts is triggering surficial failures and topple of the vertical walls.Further discussion of the impact oferosion on the Tarapaca landslide and the PVDE switchbacks is provided in other sections of this report. GROUNDWATER In general,groundwater was not observed during our investigation.Boring C-l encountered water at 103 feet;however,this water appeared to be seepage or a perched zone,as samples collected at lower depths were not saturated.The hollow-stem and bucket auger borings did not encounter significant seepage or groundwater.Surface mapping during our investigation did not encounter surface water within San Ramon Canyon;however,it is likely water flows in this canyon during the winter months.Further exploration will likely be required to evaluate the impact of groundwater on the proposed Alternative 1 storm drain alignment.The impact of ground and surface water on Alternatives 2 and 3 will be greatly dependent on the time of year work was performed and the rainfall patterns at the time of work. SEISMIC HAZARDS Faulting,Ground Rupture,and Seismic Shalting The site is not within an Alquist-Priolo Earthquake Fault Zone,and no lmown active faults are shown on current geologic maps as crossing the site.The nearest lmown active fault is the Palos Verdes fault,which is located approximately 5.4 kilometers from the site and is capable of generating a maximum emthquake magnitude (M w)of 7.3.The site is also located within 15.6 kilometers of the Newport-Inglewood fault,which is capable of generating a maximum earthquake magnitude (Mw)of 7.1.Given the proximity of the site to these and numerous other active and potentially active faults,the site will likely be subject to earthquake ground motions in the future. In order to evaluate to evaluate the likelihood offuture earthquake ground motions occuning at the site,a probabilistic seismic hazard analysis (PSHA)of horizontal ground shaking was performed using the commercial computer program EZ-FRISK vel'.7.43.The PSHA utilized seismic sources and next generation attenuation (NGA)equations consistent with the 2008 USGS National Seismic November 10,2010 12 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Callyoll Storm Draill Project,City of Rallcho Palos Verdes Hazard Mapping Project.Assuming a risk level of 10 percent probability of exceedance in 50 years (i.e.,~475 year ARP),the PHGA is 0.35g. Seismically-Induced Landsliding Given that the site is predominately underlain by a large,dormant landslide,and that the existing walls and slopes of San Ramon Canyon are generally over-steepened due to erosion,the potential for further landsliding due to a large seismic event is high.However,the three design alternatives proposed are intended to reduce the rate of erosion within the canyon,reduce the flow of water and debris down canyon,and reduce the movement ofthe Tarapaca landslide.Therefore,constmction of any of the design alternatives would likely reduce the potential impact of seismically-induced landsliding. Liquefaction and Lateral Spreading Given the depth to groundwater and the well-consolidated nature of the landslide and bedrock materials on site,the potential for liquefaction and lateral spreading of these materials is low. However,localized areas where the canyon is underlain by recent alluvium or colluvium may be subject to these seismic hazards should these surficial soils be saturated at the time of the seismic event. Tsunami Based on our review of the Tonance/San Pedro Quadrangle of the Tsunami Inundation Map for Emergency Planning prepared by the California Geological Survey (CGS,2009),the area at the toe of the bluff within the project site may be susceptible to tsunami inundation.Therefore,the stOlID drain outlet structure of Alternative 1 would be susceptible to impact by tsunami during a seismic event. Seiche Given that a seiche,by definition,is restricted to a confined body of water,and no confined or semi- confined bodies of water are found on the project site or upstream of the project site,the probability of impact from a seiche is considered to be nil. Seismic Design No active or potentially active faults are known to cross the site;therefore,the potential for primmy ground rupture due to faulting on-site is very low to negligible.However,the site wi11likely be subject to seismic shaking at some time in the future. November 10,2010 13 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Callyoll Storm Draill Project,City of Rallcho Palos Verdes Wall and Tunnel Design The above PSHA derived PGA should be considered in the design of tunnel and retaining elements at the site. Building Structure Design Site-specific seismic design parameters were determined using the USGS computer program titled "Seismic Hazard Curves and Uniform Hazard Response Spectra,Version 5.0.9a."The site coordinates used in the analysis were 33.7295°North Latitude and 118.3297°West Longitude. On-site structures should be designed in accordance with the following 2007 CBC criteria: Parametel'Factor Value Mapped Spectral Response Acceleration (0.2 sec Ss 1.61gPeriod) Mapped Spectral Response Acceleration (1.0 sec SI 0.66gPeriod) Site Class Site Class D Site Coefficient Fa 1.0 Site Coefficient Fy 1.5 Maximum Considered Earthquake Spectral SMS 1.61gResponseAcceleration(0.2 sec Period) Maximum Considered Earthquake SJIlctral SM1 0.98gResponseAcceleration(1.0 sec Period) Design Spectral Response Acceleration SDS 1.07g(0.2 sec Period) Design Spectral Response Acceleration Sm 0.66g(1.0 sec Period) It should be recognized that much of southern California is subject to some level ofdamaging ground shaking as a result of movement along the major active (and potentially active)fault zones that characterize this region.Design utilizing the 2007 CBC is not meant to completely protect against damage or loss offunction.Therefore,the preceding parameters should be considered as minimum design criteria. November 10,2010 14 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Canyon Storm Draill Project,City ofRancho Palos Verdes GEOTECHNICAL ENGINEERING CHARACTERISTICS GEOPHYSICAL TESTING P-wave velocities from the geophysical testing performed for Borings C-l and C-2 ranged from 3458 fps to 5860 fps (Appendix D).These velocities are characteristic of weathered shale. Structural data obtained from geologic logging of the core samples and the OPTV Image logs was utilized in the determination of a Rock Mass Rating (RlVIR). GEOMECHANICS CLASSIFICATION (RMR) The geomechanics classification ofthe rock mass rating (RMR)system was developed on the basis of experience in shallow tunnels in sedimentary rocks.The purpose of the RMR is to classify the rock into groups with specific characteristics relative to tunnel performance and support requirements.RMR values are based on six parameters:1)uniaxial compressive strength of the intact rock material,2)rock quality designation,3)joint or discontinuity spacing,4)j oint condition, 5)groundwater condition,and 6)joint orientation (i.e.,relative to the tunnel alignment).Points are assigned for each category and added numerically to obtain an overall RMR for the rock mass that can be con-elated with several tunneling characteristics. Uniaxial Compressive Strength Based on Schmidt hammer readings talcen from the rock cores,unconfined compressive strengths for the remnant blocks ofsiltstone within the South Shores landslide and intact siltstone ofthe Altamira Shale member of the Monterey Formation is expected to range from about 100 to about 7000 psi depending on the degree of weathering and disturbance.This c011'esponds to RMR ratings ranging from 0 to 7. The above uniaxial compressive strengths are not representative of hard siliceous zones within the South Shores landslide which may be encountered during tunneling and excavation.These zones may have unconfined compressive strengths of in the range of7,500 to 15,000 psi. Rocl{Quality Designation (RQD) Calculated values ofRQD are contained on the logs for the continuous core borings.RQD values range from 0 to 86.In general,the upper 40 to 60 feet indicates RQD values of zero with a range of higher values below.This is summarized in the following table. November 10,2010 15 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Callyon Storm Dralll Project,City ofRallcho Palos Ven!es Core Hole Tunnel Inveli Depth Range RQD Range Weighted RQD Depth Average C-l -0-39 feet 0-13 1 C-l 88 39-149 0-86 33 C-2 50 0-58 0 0 C-2 -58-104 0-44 19 Based on the above table,RMR ratings for RQD would range from 3 to 8 (i.e.,corresponding to weighted RQD values ranging from 0 to 33). Joint or Discontinuity Spacing Joint spacing ranges from about 6 inches to about 2 feet in the area of the proposed tunnel for Alternative 1.Consequently an RMR rating of 8-10 can be assumed. Joint Condition The joint condition ranges from "slightly rough and moderately to highly weathered,wall rock surface separation <lmm"to "slickensided wall rock surface or l-5mm thick gouge or l-5mm wide continuous discontinuity".These conditions cOll'espond to RMR ratings of 10-20. Groundwater Condition Boring and core logs indicate the landslide debris and bedrock materials are dry in the area of the proposed tunnel (Alternative 1).Consequently,a groundwater rating of 15 may be applied. Joint Orientation For the purposes ofjoint orientation,all geologic structural data (i.e.,from bedding,joints,fi:actures, etc.)were treated the same.Based on a comparison of structural attitudes determined from the aPTV logs,the geologic structure is considered favorable.This results in an RMR rating of (-)2. OverallRMR Based on the above individual ratings,the overall RMR for the older landslide debris of the South Shores landslide ranges from 34 to 58.This corresponds to a classification of poor to fair rock. Additional continuous core borings should be performed to better define the range of RMR values along the final tunnel alignment should this design alternative be selected. November 10,2010 16 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Rall/ol/Cal/yoll Storm Dmil/Project,City ofRal/cllo Palos Verdes GENERAL GEOTECHNICAL ENGINEERING CHARACTERISTICS Based on the results of our field investigation and laboratOly testing,preliminmy geotechnical propeliies ofthe onsite soils are anticipated to be as discussed below.Additional exploration along the selected design altemative is recommended to further evaluate these construction conditions. •In general,we anticipate all onsite soil and bedrock materials can be excavated with conventional trenching and tunneling methods.Hard to velY hard and oversize materials may be encountered in local areas. •Based on our preliminary laboratory testing,we anticipate the onsite soils will be highly expansive.These materials include recent and older alluvium,existing atiificial fill,recent and ancient landslide debris,and bedrock. •Based on our preliminary laboratory testing (See appendix B),we anticipate the onsite soils and rock will have the following corrosion potential: o Potential Soil Corrosion to Concrete •Recent/Older AlluviumlTopsoil-negligible •Existing Artificial Fill -negligible •Recent!Ancient Landslide Debris and bedrock -negligible o Potential Soil Corrosion to Fen-ous Metals •Recent/Older Alluvium -severe •Existing artificial Fill -severe •Recent/Ancient Landslide Debris and bedrock -severe •Based on our preliminary laboratOly testing,we anticipate the onsite surficial soils (i.e.,alluvium,older alluvium,topsoil,etc.)will be moderately to highly compressible. Removal and re-compaction of these materials will likely be required in local areas, depending on the design altemative selected.It is anticipated the landslide debris and bedrock will be generally slightly to non-compressible. SUMMARY OF SLOPE STABILITY ANALYSES The following project areas were analyzed for slope stability;Tarapaca landslide,descending slope below the switchbacks ofPVDE,and the bluff area along the beach at the proposed outlet structure location for Altemative 1.Slope stability results along with details of the strength model used at November 10,2010 17 GMU Project 10-036-00 Mr.Randall Beny,HARRIS &ASSOCIATES Stili Ramoll Callyon Storm Dmill Project,City ofRancho Palos Verdes each section are contained in Appendix C.A summalY of the results of the analyses is contained below. Tarapaca Landslide To evaluate how much fill is required in the canyon bottom to act as a gravity buttress,Cross- Sections 2-2'and 3-3'(drawn tlu'ough the Tarapaca landslide)were analyzed with various gravity buttress heights.The results of these analyses indicate that approximately 10 to 20 feet of fill (10 feet at the upper end and 20 feet at the lower end)will be required to obtain a safety factor of approximately 1.25.Approximately 20 to 30 feet of fill placed in the canyon at the toe of the landslide would be required to obtain a safety factor of approximately 1.5.Given the relatively small fill height differential required to obtain a 1.5 safety factor,it is recommended that strong consideration be given to designing a buttress that achieves the 1.5 safety factor. The fill could be placed in various configurations to obtain the required safety factors.The exact configuration of the buttress fill will be developed at the design stage of the project and once the final safety factor is decided upon. Lower Switchback PVDE Cross-Section 3-3'was analyzed to evaluate the existing slope stability safety factor at the lower switchback ofPVDE and to estimate how much additional erosion would be required to impact the existing roadway (i.e.,a safety factor of 1.0).Based on the strength model and assumptions provided in Appendix C,a safety factor of approximately 1.4 was obtained for existing conditions.Parametric analyses were performed by progressively moving the existing canyon wall and slope face back until a safety factor of 1.0 was achieved.These analyses indicate that the existing slope face would have to be eroded back approximately 35 feet before the roadway would be in a state of imminent failure. The probability that the existing slope face would be eroded back 35 feet should be evaluated by the project civil engineer to determine if any remediation is wan-anted.Based on our prelimimuy analyses and erosion rate assumptions,it appears that it would take approximately 7 years for the roadway to be impacted by erosion.It should be noted that the existing sewer line and utility easement would be impacted prior to this distance and time.Given the poor quality of the as-built sewer plans on file at the City,the exact location of the sewer line is not known;however,it appears this line is located between 5 and 10 feet closer to the canyon than the roadway. Upper Switchback PVDE Cross-Section 1-1'was analyzed to evaluate the existing slope stability safety factor at the upper switchback ofPVDE and to estimate how much additional erosion would be required to impact the existing roadway (i.e.,a safety factor of 1.0).Based on the strength model and assumptions provided in Appendix C,a safety factor of approximately 1.3 was obtained for existing conditions.Parametric November 10,2010 18 GMU Project 10-036-00 Mr.Randall Berry,HARRlS &ASSOCIATES Sail Ramoll Cal/yoll Storm Draill Project,City ofRancho Palos Vel'des analyses were performed by progressively moving the existing canyon wall and slope face back until a safety factor of 1.0 was achieved.These analyses indicate that the existing slope face would have to be eroded back approximately 40 feet before the roadway would be in a state of imminent failure. The probability that the existing slope face would be eroded back 40 feet should be evaluated by the project civil engineer to determine if any remediation is wan-anted.Based on our preliminary analyses and erosion rate assumptions,it appears that it would take approximately 8 years for the roadway to be impacted by erosion.The existing sewer line and easement are located very close to the currently eroding areas,as shown on our Geotechnical Map,Plate 3.We strongly recommend this active line be protected from damage as soon as possible by the pipeline owner to prevent damage to the line. Bluff Stability The existing bluff conditions were analyzed for deep seated stability.The results of the analyses indicate that the blufflikely has a safety factor ranging from about 1.2 to over 1.4.Given that a slope failure would have to cut across large blocks of intact siltstone and siliceous siltstone and that the strength ofthese materials was not considered in the analyses,the actual safety factor is likely closer to the higher end of the range.Slope instability of the bluff face is not considered to be a geotechnical constraint for the project.However,surficial instability in the form of local slumps or "pop outs"may occur and will require further evaluation should this design alternative be selected. PVDE SWITCHBACKS STABILITY DISCUSSION As discussed in previous sections ofthis report,our analyses indicates an additional lateral erosion of the canyon walls of 35 to 40 feet will result in a reduction of stability of the switchbacks to the point of incipient failure.In addition,lesser erosion is necessary to impact the existing 8-inch sewer line that is located between the canyon and the switchbacks.Regardless ofthe anticipated rate of erosion in this area,the existing sewer line should be protected by the owner as soon as possible in order to prevent failure of the line,particularly in the area of the lower switchback,where the line appears to be very close to the top of the eroded canyon wall. If hydraulic calculations indicate the switchbacks will require stabilization prior to construction of the chosen design alternative for the StOlID drain system,three potential repair solutions are discussed below: •Installation of caissons (CID H piles)on the outside ofthe switchbacks -this option would be the most costly due to the constmction materials,staging and construction area grading,and the difficulty of drilling in the ancient landslide debris.The bucket-auger borings in these areas encountered very difficult drilling due to hard zones and severe caving,and ultimately November 10,2010 19 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ramon CallY on Storm DmjJl Project,City ofRaJlcho P(flos Verdes were abandoned due to refusal by the drilling equipment.However,this work would be within the City's propel1y,and environmental constraints may be minimal. •Installation of riprap or similar type of revetment in the canyon bottom -this option would be significantly less costly than caissons;however,the riprap would require grouting,and the flow velocities in the canyon may cause damage to the riprap in a major storm.In addition, continued failure ofthe Tarapaca landslide would likely bury the riprap,causing additional maintenance,repairs,or replacement.Finally,access to the area of the canyon with equipment to install the riprap would be difficult. •Installation of a gravity buttress at the toe of the Tarapaca landslide with a flexible pipe system -this option would include installation of a flexible pipe (i.e.,butt-fused,high strength HDPE)along the canyon bottom between the upper switchback and the boundary with the City of Los Angeles,with fill placement above the pipe to reduce movement of the Tarapaca landslide and erosion ofthe western canyon wall.This option would likely reduce the erosion in this area,significantly reduce (and potentially ultimately stop)the movement ofthe Tarapaca landslide,and significantly reduce the debris moving down canyon towards 25 1h street.It should be noted that this option differs from Alternative 2 in that there is no permanent storm drain relocation solution. Should the City wish to pursue one ofthese options,additional geotechnical analyses would likely be required in order to provide detailed recommendations for construction. CANYON WALL STABILITY DISCUSSION The results of the stability analyses for the slopes below the switchbacks indicate that where continuous adversely oriented bedding planes are not exposed in the bluff face,the in situ safety factor of the canyon walls is likely in the range of 1.3 to 104.Where adversely oriented bedrock exists relative to the canyon wall-such as in the area of the Tarapaca landslide -failure has either already occurred or the current safety factor is in the range ofjust above 1.0 to 1.2.In addition,local OCCU11'ences of adversely oriented planar bedrock surfaces may also result in local small failures. November 10,2010 20 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Stilt Ramon Canyon Storm Drain Project,City ofRaJ/cho Palos Verdes CONCLUSIONS Based on the results of our investigation and analyses,we present the following conclusions: 1.Design Alternatives 1,2,and 3 are considered to be feasible,provided the design considerations and recommendations for additional work presented in this report are followed. 2.The site is predominately underlain by the South Shores landslide,an ancient,dormant landslide complex. 3.The site includes the Tarapaca landslide,a cunently failing mass that appears to have failed along continuous adversely oriented bedding due to erosion of the canyon wall. 4.N one ofthe design alternatives will adversely impact the repaired San Ramon Canyon failure area,located offsite to the north. 5.Groundwater should not be a significant impact to any of the design altematives for the project. 6.The site will be subject to seismic hazards in the future;however,none of the design alternatives will increase the likelihood or magnitude of these impacts. 7.The Tarapaca landslide can be stabilized with a reduction of erosion at the toe and constmction of a gravity-type buttress. 8.The switchbacks ofPVDE are currently considered to have safety factors at or greater than 1.3.Approximately 35 to 40 feet oflateral erosion/failure would occur before the factor of safety is reduced to 1.0 (imminent failure). 9.The existing 8-inch sewer line should be relocated as soon as possible in order to avoid damage to the line from canyon wall erosion. 10.The conceptual access road will require significant corrective grading and/or stabilization of the cuts.Should these constmction constraints become cost prohibitive,consideration should be given to relocation of the road to a more favorable site. November 10,2010 21 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Stili Ramon Callyon Stol'm Drain PI'oject,City ofRancho Palos Verdes DESIGN ALTERNATIVE GEOTECHNICAL CONSIDERATIONS ALTERNATIVE 1 As discussed in a previous section ofthis report,Alternative 1 consists of constructing a storm drain system to diveli runoff water to the west of San Ramon Canyon,as shown on Plate 6 and in the Hanis (2010)plans.It is our understanding this storm drain system would be constructed with a combination of open trench and tunneling methods. In addition,excavation spoils and any local impOli would be utilized to grade a "gravity-type" buttress at the toe of the Tarapaca landslide.As discussed in our "Slope Stability"section,it is anticipated that up to 30 veliical feet of engineered fill would be required in order to reduce the movement of the landslide to static levels and bring the factor of safety up to 1.5. Anticipated Construction Methods We understand the open trenchmethod would be utilized in the pOliion of the system adjacent to the inlet structure in the canyon,and in the portion south of 25 th Street.Tunneling methods would be utilized in the remaining pOliions of the system,including near the bluff,connecting to the outlet structure.In addition,the system will require construction of an inlet structure within the upper San Ramon Canyon and an outlet structure at the toe of the bluff ascending from the ocean.It is anticipated the entire system will encounter ancient landslide debris of the South Shores landslide. Pipe Design Considerations The South Shores landslide is considered to be dormant,and has not shown signs of movement in historic time.However,design of the pipe and appUlienant structures (i.e.,manholes,etc.)should take into consideration potential movement ofthe landslide mass,pmiicularlyduring a seismic event. Minor movement along internal rupture or shem'surfaces within the landslide mass may occur during the life of the storm drain system.Consideration should be given to choosing a high-strength flexible pipe material without joints (such as Butt-fused High Density Poly Ethylene Pipe)that can accommodate these possible minor movements. Preliminary Geotechnical Considerations for Open Trench Segments Trench Excavation Based on our preliminary evaluation and the results of our field exploration,variable stability conditions will be encountered in the trench walls during construction.Some local areas may be temporarily unstable,particularly within the deeper areas of the trench;therefore,shoring or trench November 10,2010 22 GMU Project 10-036-00 MI'.Randall BeITY,HARRIS &ASSOCIATES Sail Ramoll Cal1yoll St0l'111 Dra;n Project,City ofRallcho Palos Venles wall lay-back will likely be required.Further exploration and analyses will be required in order to provide detailed shoring and temporary stability recommendations.However,for preliminary design alternative evaluation purposes,trench walls excavated at 1:1 (horizontal to vertical)should be anticipated to be temporarily stable. Backfill and Pipe Bedding We anticipate the onsite soils will be suitable for backfill ofthe trench above the pipe bedding zone. Some oversize materials will likely be encountered,and will not be suitable for placement within the backfill. Preliminary Geotechnical Considerations for Tunnel Segments Based on the RMR,visual observations and geophysical logging of cores,downhole geologic logging,and geologic observations of older landslide debris exposed in the canyon walls,the following preliminary observations can be made.Fm1her evaluation ofthese considerations may be warranted,if this alternative is selected. •Currently,the geologic structure is oriented favorably with respect to the tunnel alignnlent. Any modifications to the tunnel alignment should consider the geologic structure.Fm1her core holes are recommended to fm1her define the geologic structure along the tunnel alignment. •Groundwater is not anticipated to be encountered during tunneling.However future borings drilled below the tunnel invel1 elevation are recommended to further evaluate this condition. •The overall RMR ratings do not consider the presence ofhard siliceous zones which may be encountered during tunneling.Hard siliceous zones or blocks ofmaterials should be expected to be encountered during tunneling. •Some ofthe Altamira Shale member bedrock cores swelled after being exposed to the air for several days.The swelling is attributed to air drying and potentially secondary mineral crystal growth.The swelling will create pressure on the ground supp011s installed for the tunnel construction. •Tunneling may also encounter local zones of adversely oriented geologic discontinuities that may be lined with bentonite.These zones may produce local stability problems during tunneling. November 10,2010 23 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Callyoll Storm Draill Project,City ofRallcho Palos Verdes •Based on the RMR ratings: o The proposed tunnel will be excavated through Fair to Poor rock. o Approximate stand-up time during tunneling is expected to range from: •10 hours to 1 week for an 8-foot to 15-foot span. Preliminary Geotechnical Considerations for Canyon Inlet Structure Design Considerations Based on our understanding of Alternative 1 and our review of the conceptual plans by Hanis & Associates (2010),the conceptual location of the inlet structure is anticipated to be founded on bedrock or ancient landslide debris.Design of this structure should take into consideration the geotechnical characteristics of these materials (i.e.,high expansion,etc.).In addition,further investigation at the location of the structure may be required in order to evaluate temporary stability of excavations and to provide site-specific design values for the structure walls as well as recommendations for foundation design and wall drainage. Temporary Stability and Shoring While the canyon slopes in the area of the possible inlet structure location may be grossly stable during construction (see "Upper Switchback"portion of the "Slope Stability"section,above), surficial slumping or localized "pop outs"are likely to occur.Fmther investigation of the inlet structure location will be required in order to provide specific recommendations in regards to temporary stability.However,for the purposes ofthis study of Alternative 1,it can be assumed that shoring or other stability methods (i.e.,caissons,sheet piles,etc.)will likely be required for temporary stability. Maintenance Regular maintenance of the inlet structure will be critical to keep the drain system clear.A maintenance schedule should be established and followed regularly with,at a minimum,annual inspection,repair,and cleanout of the structure.Additional inspections should be considered after heavy rain events. Access Road and Retaining Wall Construction Based on our review of the Han'is (2010)conceptual access road plans,it is our understanding that an access road would be constructed from the cul-de-sac of Tarapaca Road to the inlet structure in order to provide maintenance access.The Harris (2010)plans indicate this road would be mostly in cut bedrock materials,and would require a retaining wall against the ascending cut slope.Cross- Sections 8-8'and 9-9'were drawn to illustrate the conceptual road location and the subsmface November 10,2010 24 GMU Project LO-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ramon Canyon Storm Drain Project,City ofRancho Palos Venles geologic structure.Based on our review ofprevious geotechnical repOlis for adjacent properties (see Reference list),bedding orientations in this area will result in adversely oriented bedrock exposed during grading ofthis road.In addition,this road would be located upslope of the currently moving Tarapaca landslide,and directly downslope of existing residential development. Wall design will need to accommodate adverse structure,and temporary instability will require c011'ective grading,shoring,and structural support such as tiebacks.In addition,alternative paving may be considered,including concrete,pavers,or other designs that may accommodate the expansive soils and slope creep.Fmiher field investigation and analyses of this area will be required for this possible access road location in order to obtain site-specific geologic and geotechnical data to evaluate these potential issues. Should these construction measures become cost prohibitive,consideration should be given to relocating this road to an area with more favorable geologic conditions,such as the westem side of the canyon near the existing PVDE switchbacks. Preliminary Geotechnical Considerations for Bluff Face Outlet Structure Design Considerations Based on our understanding of Alternative 1 and our review of the conceptual plans by Hanis & Associates (2010),the conceptual location ofthe outlet structure at thetoe ofthe bluffis anticipated to be founded on bedrock or ancient landslide debris (Cross-Section 6-6').Design of this structure should take into consideration the geotec1mical characteristics of these materials (i.e.,high expansion,etc.).In addition,further investigation at the location of the structure will likely be required in order to evaluate temporary stability ofexcavations and to provide site-specific design values for the structure walls as well as recommendations for foundation design and wall drainage. Tempormy Stability and Shoring While the bluff in the area of the possible outlet structure location may be grossly stable during construction (see "Slope Stability"section,above),minor surficial slumping or localized "pop outs" may potentially occur.These local instabilities are anticipated to be less significant than those ofthe canyon inlet structure due to the generally intact bedrock materials exposed in the bluffface.Further investigation of the outlet structure location may be required in order to provide specific recommendations in regards to temporary stability.However,for the purposes of this study of Alternative 1,it can be assumed that shoring or other stability methods (i.e.,caissons,sheet piles, etc.)may be required for temporary stability of the bluff face during construction. November 10,2010 25 GMU Project 10-036-00 MI'.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll CallYOII Storm Dmill Project,City ofRa/lcho Palos Ve,.des ALTERNATIVE 2 As discussed in a previous section of this repoli,Alternative 2 consists of constmcting a storm drain system to collect runoff water in upper San Ramon Canyon,as shown on Plate 6 and in the reference (1)plans,and carry it via storm drain piping to the existing inlet structure under 25 th Street. It is our understanding this storm drain system would likely be constructed using open trench and suppOliing grading methods.It is anticipated this construction would encounter ancient landslide, bedrock,and alluvial soils.Based on our preliminary data,the majority of the pipe trench would be founded on bedrock or ancient landslide debris.It should be noted that significant trenching within the canyon bottom is not anticipated for this alternative. In addition,construction of the storm drain system within the canyon would include construction ofa "gravity-type"buttress at the toe of the Tarapaca landslide,similar to Alternative 1. Pipe Design Considerations Design of the pipe and appurtenant structures (i.e.,manholes,etc.)should take into consideration potential movement of the South Shores landslide mass and the adjacent Tarapaca landslide, pmticularly during a seismic event.Consideration should be given to choosing a flexible pipe material without joints (such as butt-fused HDPE pipe)that can accommodate these possible minor movements. Preliminary Geotechnical Considerations for Open Trench Segments Trench Excavation Based on our preliminary evaluation and the results of our field exploration,variable stability conditions will be encountered in the trench walls during construction.Some local areas may be temporarily unstable,pmticularly within the deeper areas ofthe trench;therefore,shoring will likely be required.In addition,our slope stability analyses indicate the canyon walls are likely to be grossly stable;however,surficial slumps and local failures may occur during constmction.Efforts should be made to design the pipe and trench such that excavation into the bedrock within the canyon bottom is kept to a minimum.Fmiher exploration and analyses will be required in order to provide detailed shoring and temporary stability recommendations. Backfill and Pipe Bedding We anticipate the onsite soils will be suitable for backfill ofthe trench above the pipe bedding zone. Some oversize materials will likely be encountered,and will not be suitable for placement within the backfill. November 10,2010 26 GMU Project 10-036-00 Mr.Randall Beny,HARRIS &ASSOCIATES Sail Ramoll Callyoll Storm Draill Project,City ofRancho Palos Verdes Preliminary Geotechnical Considerations for Canyon Inlet Structure Design Considerations Based on our understanding of Alternative 2 and our review of the conceptual plans by Harris & Associates (reference (I»,the conceptual location ofthe inlet structure is the same as Alternative 1, and is anticipated to be founded on bedrock or ancient landslide debris.Design of this structure should take into consideration the geotechnical characteristics ofthe soil (i.e.,high expansion,etc.). In addition,further investigation at the location of the structure may be required in order to evaluate temporary stability ofexcavations and to provide site-specific design values for the structure walls as well as recommendations for foundation design and wall drainage. Temporary Stability and Shoring While the canyon slopes in the area of the possible inlet structure location may be grossly stable during construction (see "Slope Stability"section,above),surficial slumping or localized "pop outs" may potentially occur.Fmiher investigation ofthe inlet structure location will be required in order to provide specific recommendations in regards to temporary stability.However,for the purposes of this study ofAlternative I,it can be assumed that shoring or other stability methods (i.e.,caissons, sheet piles,etc.)will likely be required for temporary stability. Access Road and Retaining Wall Construction Based on our review of the Harris (2010)conceptual access road plans,it is our understanding that an access road would be constructed from the cul-de-sac of Tarapaca Road to the inlet structure in order to provide maintenance access.The Harris (20 I 0)plans indicate this road would be mostly in cut bedrock materials,and would require a retaining wall against the ascending cut slope.Cross- Sections 8-8'and 9-9'were drawn to illustrate the conceptual road location and the subsurface geologic structure.Based on our review ofprevious geotechnical reports for adjacent propelties (see Reference list),bedding orientations in this area will result in adversely oriented bedrock exposed during grading ofthis road.In addition,this road would be located upslope of the currently moving Tarapaca landslide,and directly downslope of existing residential development. Wall design will need to accommodate adverse structure,and temporary instability will require corrective grading,shoring,and structural support such as tiebacks.In addition,alternative paving may be considered,including concrete,pavers,or other designs that may accommodate the expansive soils and slope creep.Fmther field investigation and analyses of this area will be required for this possible access road location in order to obtain site-specific geologic and geotechnical data to evaluate these potential issues. November 10,2010 27 GMU Project 10-036-00 Mr.Randall Beny,HARRIS &ASSOCIATES &11I Ramoll Callyoll StOl'11I Dmill Project,City ofRallcho Palos Verdes Should these construction measures become cost prohibitive,consideration should be given to relocating this road to an area with more favorable geologic conditions,such as the western side of the canyon near the existing PVDE switchbacks. Preliminary Geotechnical Considerations for Canyon Outlet Structure/Tie-In to City Inlet The area of the canyon where the Alternative 2 stonn drain system connects to the existing City system is underlain by recent alluvium over landslide debris ofthe South Shores landslide.Should this alternative be selected,it is likely the alluvial soils underlying the pipe trench and the connection area will require corrective grading to remove compressible alluvial soils.However,futiher detailed investigation of this area may be required to fully evaluate the alluvial soils below the pipe depth. ALTERNATIVE B (OPTION TO ALTERNATIVES 1 AND 2) As discussed in a previous section ofthis report,Alternative B consists of extending the storm drain systems described within Alternatives 1 and 2 up the canyon to connect to the existing storm drain system that outlets at the head of the canyon.Geotechnical considerations for this alternative are similar to that ofAlternative 2.However,for ease ofevaluation,these considerations are reproduced below. Pipe Design Considerations Design of the pipe and appurtenant structures (i.e.,manholes,etc.)should take into consideration potential movement of the South Shores landslide mass and the adjacent Tarapaca landslide, pmiicularly during a seismic event.Consideration should be given to choosing a flexible pipe mat~rial without joints (such as butt-fused HDPE pipe)that can accommodate these possible minor movements. Preliminary Geotechnical Considerations for Open Trench Segments Trench Excavation Based on our preliminary evaluation and the results of our field exploration,variable stability conditions will be encountered in the trench walls during construction.Some local areas may be temporarily unstable,particularly within the deeper areas ofthe trench;therefore,shoring will likely be required.In addition,our slope stability analyses indicate the canyon walls are likely to be grossly stable;however,surficial slumps and local failures may occur during construction.Efforts should be made to design the pipe and trench such that excavation into the bedrock within the canyon bottom is kept to a minimum.Fmiher exploration and analyses will be required in order to provide detailed shoring and temporary stability recommendations. November 10,2010 28 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Callyoll Storm Dm;1I Project,City ofRallcho Palos Verdes Backfill and Pipe Bedding We anticipate the onsite soils will be suitable for backfill ofthe trench above the pipe bedding zone. Some oversize materials will likely be encountered,and will not be suitable for placement within the backfill. Preliminary Geotechnical Considerations for Tie-In to Existing Outlet The area of the canyon where this alternative system would tie into the existing outlet is anticipated to be underlain by bedrock of the Altamira Shale.Should this alternative be selected,field investigation at this location may be required to evaluate the underlying materials and any temporaly construction slopes and/or trench walls. FUTURE TASKS Once the design alternative is selected,we recommend our office be retained to perform future geotechnical investigations to provide design-level geotechnical recommendations for final design and construction of the chosen alternative.These future tasks will include: •Additional field exploration at the chosen storm drain system alignment,including drilling additional borings and perfonning additional laboratory testing; •Further specific quantitative analyses offoundation and retaining wall design,slope stability, surficial stability,temporary stability,and shoring design; •Preparation of a final design report to supp01i the chosen design alternative final plans. LIMITATIONS All parties reviewing or utilizing this report should recognize that the findings,conclusions,and recommendations presented represent the results of our professional geological and geotechnical engineering efforts and judgements.Due to the inexact nature of the state of the ali of these professions and the possible OCCUlTence of undetected val'iables in subsurface conditions,we cannot guarantee that the conditions actually encountered during grading will be identicalto those observed and sampled during our study or that there are no unknown subsurface conditions which could have an adverse effect on the use of the property.We have exercised a degree of care comparable to the standard of practice presently maintained by other professionals in the fields of geotechnical engineering and engineering geology,and believe that our findings present a reasonably November 10,2010 29 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES San Ramo11 Canyon Storm Drai11 Project,City ofRancho Palos Verdes representative description of geotechnical conditions and their probable influence on the grading and use of the property. SUPPORTING DATA The following Plates and Appendices that complete this report are listed in the Table of Contents. Respectfully submitted, GMU GEOTECHNICAL,INC. November 10,2010 30 GMU Project 10-036-00 Mr.Randall Beny,HARRIS &ASSOCIATES Sail Ramoll CallY 011 Storm Draill Project,City ofRancho Palos Verdes REFERENCES Califol11ia Emergency Management Agency,California Geological Survey,University of Southel11 California,"Tsunami Inundation Map for Emergency Planning,Tonance Quadrangle/San Pedro Quadrangle,"dated March 1,2009. Dibblee,T.W.,1999,"Geologic Map of the Palos Verdes Peninsula and Vicinity,Redondo Beach, Torrance,and San Pedro Quadrangles,Los Angeles County,California," Dibblee Geologic Foundation map DF-70,scale 1:24,000. Ehlert,Keith W.,"Geological Investigation for Proposed Residential Development,Undeveloped Lot 2700 Y2 San Ramon Drive,Rancho Palos Verdes,Califol11ia,"dated February 17,1997. Ehlert,Keith W.,"Additional Geologic Information 30764 Tarapaca Road,Rancho Palos Verdes, CA,"dated April 9,1998. Ehlig,Peny L.and Ehlert,Keith W.,1978,"Engineering Geology of a Pleistocene Landslide in Palos Verdes,"in Geologic Guide and Engineering Geology Case Histories,Los Angeles Metropolitan Area.Association of Engineering Geologist,First Annual California Section Conference.pp.159-166. Ehlig,Perry,and Ehlert,Keith,W.,1979,"South Shores Landslide,Palos Verdes Hills,A Condensation,"inField Trip Guide,Landslides of Southern California,Japanese-American Conference. Engineering Service Corporation,"Profile Alignment and Grade of Sanitary Sewers to be Constructed in Outfall for Tract No.25051 in Sanitary Sewer R/W,"dated September 1959. Harris &Associates,"San Ramon Storm Drain Alternative 1,City of Rancho Palos Verdes,"dated September 2010. Harris &Associates,"San Ramon Storm Drain Alternative 2,City of Rancho Palos Verdes,"dated September 20 I O. Harris &Associates,"San Ramon Storm Drain Option Upstream Extension for Alt.I and 2,"dated September 2010. T.I.N.Engineering Company,"Limited Combined Soil and Geologic Engineering Investigation and Report for Proposed up to 5-Foot High Retaining Wall at 30760 Tarapaca Road,Rancho Palos Verdes,California,"dated June 3,2006. November 10,2010 31 GMU Project 10-036-00 Mr.Randall Berry,HARRIS &ASSOCIATES Sail Ramoll Callyoll Storm Draill Project,City ofRallcho Palos Venles Miyake,T.T.,Vakili,1.,Steiner,E.A.,and Ayas,M.,1990,"Investigation of Sea Cliff Stability ,"in Rock Mechanics Contributions and Challenges,Hustrulid and Johnson.pp.849-856. Pipkin,Bernard,W.,1974,"Field Guide Engineering Geology Palos Verdes Peninsula,"in Guidebook to Selected Features of Palos Verdes Peninsula and Long Beach,California, South Coast Geological Society. Ray,Monte,E.,1982,"Geologic Investigation,Grading Stabilization Measures,and Development of the South Shores Landslide,"in Landslides and Landslide Abatement,Palos Verdes Peninsula,Southern California,volume and guidebook for the 78 th annual Cordilleran Section GSA meeting. Saucedo,George,1.,Greene,H.,Gary,Kennedy,Michael,P.,and Bezore,Stephen,P.,2003, "Geologic Map of the Long Beach 30'x 60'Quadrangle,California,"California Geological Survey,California Conservation. Stark,T.D.,Choi,H.,and McCone,S.,2005,"Drained Shear Strength Parameters for Analysis of Landslides,"in Journal of Geotechnical and Geoenvironmental Engineering,ASCE. Steiner,E.A.,and Lippus,C.S.,1990,"Use of Downhole Geophysical Methods in a Geotechnical Investigation of the South Shores Landslide,Rancho Palos Verdes,California,USA,"in Rock Mechanics Contributions and Challenges,Hustrulid and Johnson.pp.857-862. SWN Soiltech Consultants,Inc.,"Addendum,Report of Soil Engineering Investigation,Proposed Residential Development,Lot 8,Tract 20856,30760 Tal'apaca Road,Rancho Palos Verdes, California,"dated December 27,1996. AERIAL PHOTOGRAPHS Date Flight No.Frame No.Date Flight No.Frame No. 8-31-54 19K 16,17,18 1-27-86 F 363,364 2-20-58 CAA-9 14,15 7-7-88 nla 19275,19279 9-18-68 8-4 79,80,81 1-24-92 C85-9 34,35 1-31-70 6]-9 185,186 5-14-93 C91-11 122 2-16-73 121M 18-01,19-01 1-28-95 C102-37 4,5 11-6-74 152G 3-1 10-16-97 Cl18-37 4,5 3-17-78 78049 202,203 2-24-99 C134-37 205,206 5-12-79 FCLA-12 139,140 November 10,2010 32 GMU Project 10-036-00