Am1_Geotechnical_Appendix_LSAR_Reach_9_PHASE_3.pdf

GEOTECHNICAL APPENDIX OF

DESIGN DOCUMENTATION REPORT

LOWER SANTA ANA RIVER CHANNEL

REACH 9 – PHASE III,

ORANGE COUNTY, CALIFORNIA

Prepared for:

TETRA TECH, INC.

17885 Von Karman, Suite 500

Irvine, California 92614

Project No. 602502-005

November 23, 2011 (Revised August 28, 2012)

November 23, 2011 (Revised August 28, 2012)

Project No. 602502-005

To: Tetra Tech, Inc.

17885 Von Karman, Suite 500 Irvine, California 92614

Attention: Ms. Patti Sexton

Subject: Geotechnical Appendix of Design Documentation Report for Lower Santa

Ana River Channel Reach 9 – Phase III, Orange County, California

In accordance with your request and authorization, Leighton Consulting, Inc. has prepared this geotechnical exploration report for the proposed slope protection for a reach of Santa Ana River downstream of the Prado Dam that is referred to as Reach 9

– Phase III. This report will be included as an appendix of the Design Documentation Report that Tetra Tech is preparing for U.S. Army Corps of Engineers.

This report was prepared based on review of available geologic information pertinent to the site, field exploration consisting of geologic mapping and borings to a maximum depth of 51 feet, and geotechnical analyses of the collected data. Slope stability analyses were performed for short-term and long-term conditions for several alternatives and configurations of slope protection system. A slope protection system consisting of a 10-foot wide soil-cement stabilization fill is feasible from a geotechnical standpoint and is the preferred alternative.

This report presents geotechnical conditions of the project site, describes subsurface exploration and laboratory testing performed for the site, evaluates current conditions of the study area, discusses geotechnical considerations for the proposed bank protection systems, and provides geotechnical recommendations for construction.

17781 Cowan | Irvine, CA 92614-6009

949.253.9836 | Fax 949.250.1114 | www.leightongroup.com

602502-005

- 2 -

If you have any questions regarding this report, please do not hesitate to contact this office. We appreciate this opportunity to be of service.

Respectfully submitted, LEIGHTON CONSULTING, INC.

Joe Roe, PG, CEG 2456 Project Geologist

Djan Chandra, PE, GE 2376 Senior Principal Engineer

JAR/DJC/lr

Distribution: (1) Addressee

- i -

TABLE OF CONTENTS

Section Page

1.0 INTRODUCTION

1.1 Purpose and Scope

1.2 Site Location and Proposed Project

2.0 FIELD EXPLORATION AND LABORATORY TESTING

2.1 Field Exploration

2.2 Laboratory Testing

3.0 GEOLOGY AND SEISMIC HAZARDS

3.1 Regional Geology

3.2 Topography and Drainage

3.3 Groundwater

3.4 Subsurface Soil Conditions

3.5 Soil Corrosivity

3.6 Faulting and Seismicity

3.7 Seismic Hazards

3.7.1 Fault Rupture

3.7.2 Ground Shaking

3.7.3 Liquefaction

3.7.4 Lateral Spreading

3.7.5 Seismically-Induced Inundation

3.7.6 Seiches and Tsunami

4.0 SLOPE STABILITY ANALYSES AND DISCUSSIONS

4.1 Methodology

4.2 Design Criteria

4.3 Shear Strength Parameters

4.4 Protection System Selection

4.5 Soil-Cement Stabilization Fill

5.0 GEOTECHNICAL RECOMMENDATIONS

5.1 Soil Cement Stabilization Fill

5.2 Headwall and Wingwall Foundation

5.3 Lateral Earth Pressures

5.4 Cement Type and Corrosion Protection

5.5 Seismic Deformation

6.0 CONSTRUCTION CONSIDERATIONS

6.1 Earthwork

6.1.1 Site Preparation

6.1.2 Excavation and Subgrade Preparation

6.1.3 Fill Placement and Compaction

TABLE OF CONTENTS (Cont’d)

Section Page

- ii -

6.2 Temporary Excavation and Shoring Design

6.3 Dewatering

6.4 Soil Cement Construction

6.5 Protection of Existing Improvements

6.6 Aggregate and Cement Sources

6.7 Trench Backfill

6.8 Geotechnical Observation and Testing

6.9 Limitations

7.0 REFERENCES

LIST OF TABLES, FIGURES AND APPENDICES

Table 1 – Summary of Field Exploration Page 4 Table 2 – Groundwater Level at Time of Drilling Page 9 Table 3 – Summary of Corrosivity Test Results Page 13 Table 4 – Results of Liquefaction Analysis Page 16 Table 5 – Design Water Levels and Criteria Page 20 Table 6 – Direct Shear Test Results Page 20 Table 7 – Design Shear Strength Parameters Page 21 Table 8 – Slope Stability Analyses for Various Slope Protection Schemes Page 22 Table 9 – Slope Stability Analyses for 1:1 Soil Cement Page 23 Table 10 – Lateral Earth Pressures Page 31 Table 11 – Concrete Aggregate Sources Page 33 Table 12 – Cement Sources Page 33

Figure 1 – Bank Protection Location Map Page 2 Figure 2 – Boring and Cross-Section Location Map Page 5 Figure 3a – Regional Geologic Map Page 7 Figure 3b – Geotechnical Map Page 8 Figure 4 – Santa Ana River Stream Flow and Rainfall Data Page 10 Figure 5 – Santa Ana River Stream Flow and Groundwater Data Page 11 Figure 6 – Geotechnical Cross-Section 1370+50 Page 24 Figure 7 – Geotechnical Cross-Section 1378+00 Page 25

Appendix A – Geotechnical Boring Logs Appendix B – Laboratory Test Results Appendix C – Liquefaction Analysis Appendix D – Slope Stability Analyses

- 1 -

1.0 INTRODUCTION

1.1 Purpose and Scope

The purpose of this exploration was to evaluate the geotechnical conditions and characteristics at the site and to provide recommendations for the design and construction of the proposed project. The scope of our work included the following tasks:

• Review of readily available geotechnical reports and geologic maps in our in-house library, including the reports that we prepared for the Santa Ana Regional Interceptor (SARI) relocation project. References used in preparation of this report are listed in Section 7.0.

• Site reconnaissance to observe the current site conditions.

• Geotechnical analyses of the collected data.

• Preparation of this report documenting our findings, results of the analyses, and recommendations.

1.2 Site Location and Proposed Project

Slope protection has been constructed along several stretches of the Santa Ana River between Prado Dam and Weir Canyon Road by the U.S. Army Corps of Engineers (USACE), local agencies at freeway and railroad embankments, and at existing private developments adjoining the river. The existing slope protection includes riprap, grouted stone, soil cement, and sheet piles. Recently constructed and proposed slope protections along this reach of Santa Ana River are shown on Figure 1, Bank Protection Location Map.

The location of the slope protection addressed in this report is called Reach 9 – Phase III. It is approximately 1,600 feet long, located approximately 2,200 feet east of Gypsum Canyon Road as shown on Figure 1. A portion of the river bank at this location was previously improved with soil cement. The project will include several storm drain outlets for an existing 18-inch diameter corrugated metal pipe (CMP) and two existing 60-inch diameter reinforced concrete pipes.

Green River Golf Course

BANK PROTECTION LOCATION MAP

Orange County, California

FIGURE 1Proj: 602502-005 Eng/Geol: DJC/JAR

Scale: 1"= 2000' Date: October 2011

P:\Drafting\602502\005\GIS\Bank Protection Index Map Fig 1.mxd Printed By: jpflueger on 10/20/11 @ 1530 hrsPrepared By: JMP Checked By: DJC Leighton

2,000 0 2,0001,000 Feet

LEGEND

G ypsum

Canyon Road

STATE ROUTE 91

Active Channel Santa Ana River

A.T.S.F. RAILROAD

Proposed Bank Protection (USACE)

H ighw ay 71

STATE ROUTE 91

ST

AT

E R

O U

TE

C oa l C an yo n

R oa dW eir C anyon Road

SAVI Ranch

Yorba Linda

Chino Hills

Existing Bank Protection (USACE)

Recommended Bank Protection per Tetra Tech's Scour Study

SARI Proposed Alignment

Reach 9, Phase III

Reach 9, Phase IIB

Reach 9, Phase IIA

Reach 9, Phase IIB

Reach 9, Phase IIA

Reach 9, Phase I Extension

Reach 9, Phase I

- 3 -

2.0 FIELD EXPLORATION AND LABORATORY TESTING

2.1 Field Exploration

Leighton Consulting advanced 78 borings along the Santa Ana River banks between the Green River Golf Course and east of Weir Canyon Road for the SARI relocation project. Five of the borings were located adjacent to the Reach 9 – Phase III improvements and were used for this report. No additional borings were performed for this study.

The 8-inch diameter, hollow-stem auger borings were drilled in May of 2009 and March of 2010 to a maximum depth of 51 feet below the existing grade using CME-75 and CME-85 drill rigs. The borings were logged and sampled using Standard Penetration Test (SPT) and California Ring samplers at selected intervals. The California Ring sampler has an I.D. (inside diameter) of 2⅜ inches and an O.D. (outside diameter) of 3 inches. The SPT and Ring samplers were driven into the soil with a 140-pound hammer, free falling 30 inches. The number of blows was noted for every 6 inches of sampler penetration. Relatively undisturbed samples were collected from the borings using the Ring sampler.

The sampling procedures generally followed ASTM Test Method D 1586 and D 3550 for SPT and split-barrel sampling of soil. In addition to driven samples, representative bulk soil samples were also collected from selected borings. Each soil sample collected was described in general conformance with the Unified Soil Classification System (USCS). The samples were sealed, packaged, and transported to our soil laboratory.

After completion of the field exploration, the borings were backfilled with bentonite grout, except Boring MW-140+60B. This boring was converted to a groundwater monitoring well.

The boring information is summarized in Table 1. The boring logs are included in Appendix A and approximate location of our borings is shown on Figure 2, Boring and Cross-Section Location Map. To be consistent with Tetra Tech’s plan, elevations used in this report are relative to the National Geodetic Vertical Datum of 1929 (NGVD29), which is approximately 2.5 feet lower than the NAVD88.

- 4 -

Table 1 – Summary of Field Exploration

Boring No. Date of Drilling

Boring Elevation Total Depth

(feet) Top (feet) Bottom (feet)

B-124+20B 5/20/2009 383 337 46

B-129+20B 5/20/2009 387 340 47

B-134+30B 5/26/2009 388 341 47

B-225+50 3/25/2010 389 372 17

MW-140+60B* 5/27/2009 390 339 51

B-144+20B 5/20/2009 391 341 50

*Converted to groundwater monitoring well

2.2 Laboratory Testing

Laboratory tests were performed on representative samples to verify the field classification of the recovered samples and to evaluate the geotechnical properties of the subsurface materials. The laboratory tests performed include:

• In-situ moisture content and dry density (ASTM D 2216 and ASTM D 2937);

• Sieve analysis (ASTM D 422);

• Sand Equivalent (California Test Method 217);

• Direct shear (ASTM D 3080); and

• Corrosivity suite – pH, minimum resistivity, Sulfate content, and Chloride content (California Test Methods 532/643, 417 and 422).

The results of the in-situ moisture and density tests are presented on our geotechnical boring logs in Appendix A. The results of other laboratory tests are presented in Appendix B of this report.

!< MW-140+60B

T.D. 50.5'

GW @ 17.3'

B-225+50 T.D. 16.5'

GW @ 16'

B-134+30B T.D. 46.5'

GW @ 18.6'

B-144+20B T.D. 51'

GW @ 18.2'

B-129+20B T.D. 46.5'

GW @ 18'B-124+20B

T.D. 46'

GW @ 15'

BORING AND CROSS-SECTION LOCATION MAP

Reach 9 - Phase III

Orange County, California

FIGURE 2Proj: 602502-005 Eng/Geol: DJC/JAR

Scale: 1"= 300' Date: 2/12

P:\Drafting\602502\005\GIS\Phase III Boring Map Fig 2.mxd Printed By: jpflueger on 2/20/12 @ 1400 hrsPrepared By: JMP Checked By: DJC Leighton

300 0 300150 Feet

LEGEND

STATE ROUTE 91

Active Channel Santa Ana River

!@( Approximate location of hollow-stem auger borings shown with total depth and depth to groundwater at time of drilling (Leighton, 2010)

Approximate location of monitoring well shown with total depth and depth to groundwater at time of drilling (Leighton, 2010)

Reach 9, Phase III

1370+50

1378+00

- 6 -

3.0 GEOLOGY AND SEISMIC HAZARDS

3.1 Regional Geology

The project site is located in the lower Santa Ana River Valley, below Prado Dam, which lies within a deeply incised gorge approximately 12 miles long with an average gradient of approximately 18 feet per mile. This area is between Riverside County to the northeast and Orange County to the southwest and between the northern Santa Ana Mountains and southern margin of the Puente Hills, part of the Peninsular Ranges geomorphic province of Southern California.

The Santa Ana Mountains and the Puente Hills formed a topographic high prior to the Santa Ana River entering the lower canyon from the Prado Dam basin.

Both the Puente Hills and the Santa Ana Mountains consist generally of sandstones and shale of Cretaceous to Tertiary age (65 million to 1.8 million years old) bedrock. The Puente Hills represent a complexly folded and faulted block of Tertiary age marine sediments uplifted between the Whittier fault on the southwest and the Chino fault to the northeast (Jennings and Bryant, 2010).

Both faults merge easterly of the project site to join with and continue southeast as the Elsinore fault zone (Glen Ivy Segment). The regional geology of the area is shown on Figure 3a and the local geology is shown on Figure 3, Geotechnical Map.

3.2 Topography and Drainage

Reach 9 of the lower Santa Ana River project is situated within the southeastern (Orange County) part of the Los Angeles basin, a broad alluviated lowland plain on the coast of southern California at the north end of the Peninsular Ranges province. Santa Ana River has its headwaters in the San Bernardino Mountains and flows across the upper Santa Ana Valley to Prado Dam. Downstream from Prado Dam, the Santa Ana River flows through the relatively narrow, steep-sided Santa Ana Canyon where the project site is located. The north side of the canyon is bounded by the rolling topography of the Chino Hills (also known as the eastern Puente Hills). On the south side, the more rugged, higher, and more geologically diverse Santa Ana Mountains bound the canyon. Elevations in the rolling hills to mountainous terrain range from 200 feet to more than 5,000 feet above sea level.

Coal

Green River Golf Course

Reach 9, Phase III

Savi Ranch

Santa Ana Mountains

Puente Hills

Canyon

Qw

Tt

Tsi

Qya

Tvs

Tch

Tpy

Qyf

Tsa

Tvs

Klbc

Tpsc

Tpy

Tpy

Tt

Tpy

Qvof

Qyf

Qyf

Tt

Klhs

Tpsq

Tpy

Tpy

Tpy

Qls?

REGIONAL

GEOLOGY

MAP Figure 3a

Project No.

602502-005

Date February 2012

\\GIS\Drafting\602502\005\GIS\Figure3a-RegionalGeologyMap.mxd

AÎ

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FEET

0 3,000 6,000

SCALE

Base Map: USGS Topographic Map, Prado Dam and Black Star Canyon Quadrangles, California 7.5' series, Orange, San Bernardino and Riverside Counties, 1979

Reach 9 - Phase III Orange County, California

USGS, 2006, Geologic map of the San Bernardino and Santa Ana 30'x60' quadrangles, California, Version 1.0, Open File Report 2006-1217

Tpsc Puente Formation, Sycamore Canyon Member

Tch Sandstone and conglomerate in southeastern Chino Hills

Qyls? Young landslide deposits?

Qvof Very old alluvial-fan deposits

Qw Very young wash deposits

Qyf Young alluvial-fan deposits

Tpsq Puente Formation, Soquel Member

Qya Young axial-channel deposits

Qls Very young landslide deposits Topanga Group, undiffferentiatedTt

Klbc Ladd Formation, Baker Canyon Conglomerate Member

Santiago Peak VolcanicsKvsp

Tsi Silverado Formation

Vaqueros and Sespe Formations, undifferentiated

Tvs

Williams Formation, Schulz Ranch MemberKwsr

Tpy Puente Formation, Yorba Member

Klhs Ladd Formation, Holz Shale Member

Old axial-channel depositsQoa Tsa Santiago Formation

Tplv Puente Formation, La Vida Member

LEGEND:

- 9 -

3.3 Groundwater

Groundwater at the site is primarily within the alluvium of the Santa Ana River floodplain, which is overall an unconfined aquifer type or condition. This is based on the geology of the river alluvium which is young age sediments that are porous, unconsolidated and laterally extensive, with no major confining layers present in the stratigraphy as known or mapped. This is also based on the water level records of the numerous observation wells and piezometers in the area that show quick response times (water level rises) with increased river discharge flows. This aquifer also contains groundwater that occurs as sporadic perched aquifer types on top of the lower permeability bedrock formations, as well as semi-confined types or conditions.

During our field exploration, groundwater was encountered in all of our hollow-stem-auger borings. Depths to groundwater were found to range from 15 to 19 feet below the existing grade, at elevations of 368 to 373 feet. The groundwater levels encountered in our borings are summarized in Table 2.

Table 2 – Groundwater Level at Time of Drilling

Boring No. Date of Drilling

Groundwater

Depth (feet) Elevation (feet)

B-124+20B 5/20/2009 15 368

B-129+20B 5/20/2009 18 369

B-134+30B 5/26/2009 19 369

B-225+50 3/25/2010 16 373

MW-140+60B* 5/27/2009 17 372

B-144+20B 5/20/2009 18 372

*Converted to groundwater monitoring well

The groundwater table was also monitored in the monitoring well MW-140+60B installed during our field exploration. Fluctuations, generally on the order of one to four feet, were noted from several readings taken between July 6, 2009 and April 30, 2010. Factors such as seasonal rainfall, groundwater pumping at the Green River Golf Course and Canyon RV Park, irrigation, and discharge from Prado Dam will affect the groundwater level at the site.

- 10 -

During the time period between June 2009 and April 2010, the southern California region experienced several rainfall events that ranged from less than

0.1 inches to greater than 2 inches of rainfall within a 24-hour period. We collected groundwater table readings within a few days after the rain storms to evaluate the groundwater fluctuations due to the rainfall and release from Prado Dam. A direct correlation exists between the significant rainfall events and increased stream flow in the Santa Ana River below Prado Dam as plotted on Figure 4. It is clear that after significant rainfall events (≥ 1 inch of rain over a 24-hour period), an increase in storage release occurs from Prado Dam into the Santa Ana River channel by the USACE, thus increasing the stream flow in the Santa Ana River. Additionally, during significant rainfall events and increased releases in the Santa Ana River below Prado Dam, a rise in elevation of groundwater levels was measured in the monitoring well. The maximum rise in groundwater elevations was on the order of 4 feet (to a depth of 13 feet or an elevation of 377 feet) when approximately 5,000 cubic feet per second (cfs) of stream flow were released into the river (see Figure 5). The ground surface elevation at this groundwater monitoring well location is at 390 feet.

Figure 4 – Santa Ana River Stream Flow and Rainfall Data

- 11 -

Figure 5 – Santa Ana River Stream Flow and Groundwater Data

3.4 Subsurface Soil Conditions

The subsurface conditions subsequently described in this section of the report have been summarized for ease of interpretation. Detailed descriptions of the materials encountered in the borings and the approximate stratigraphy are presented on the boring logs in Appendix A. The project area is underlain by artificial fills, alluvium, and river terrace deposits. These units were briefly described below.

Artificial Fill (Af): Several generations of artificial fill underlie the site and adjacent areas. These fills, in part, consist of locally derived materials placed as levee and soil-cement embankment fills along the Santa Ana River, fills associated with the adjacent bike path and structural fills to support the placement of the 91 Freeway. The fill materials as encountered in our borings consist primarily of medium dense sands and silts with varying amount of gravels to depths of 5 to 17 feet. Based on our field observation, the soil cement extends slightly beyond the limit of Reach 9 – Phase III as shown on Figure 3. The thickness of the soil cement was estimated to be on the order of 5 to 10 feet.

- 12 -

Quaternary Wash Deposits (Qw): The Quaternary Wash deposits consist primarily of sands, gravels and cobbles ranging in size from 4 to 12 inches to boulders greater than 24 inches in size. These materials are unconsolidated deposits within the active channel of the Santa Ana River and within the low lying adjacent floodplain. The channel deposits observed within the main active channels and low lying floodplain of the Santa Ana River were not directly encountered in the borings. Considering the watershed boundaries and depositional environment related to the Santa Ana River, these active wash deposits are expected to be of similar composition relative to the adjacent elevated alluvial deposits.

Quaternary Alluvium (Qal): Earth materials locally encountered within and adjacent to the site occurs as elevated stream channel and river floodplain deposits. Generally, these deposits consist of an unconsolidated to semi-consolidated, interbedded mixture of medium dense to dense sands and gravels, locally containing cobbles and boulders up to and greater than 24 inches in size.

To a depth of approximately 25 to 30 feet, the material consisted mainly of medium dense to dense (SPT N-values of 10 to 48), poorly graded sand with gravel, silty sand, and gravel with isolated layers of medium stiff silt. Below a depth of 25 feet to the maximum depth explored, the material consisted predominantly of medium dense to very dense (SPT N-values of 36 to refusal), poorly graded sand with gravel, gravelly sand and gravel.

3.5 Soil Corrosivity

In general, soil environments that are detrimental to concrete have high concentrations of soluble sulfates and/or pH values of less than 5.5. Soils with chloride content greater than 500 ppm per California Test 532 are considered corrosive to steel, either in the form of reinforcement protected by concrete cover or plain steel substructures, such as steel pipes. Additionally, soils with a minimum resistivity of less than 1,000 Ohm-cm are considered corrosive to ferrous metal.

As a screening process, one representative soil sample from Boring B-124+20B was tested for corrosivity. Based on laboratory test results, the subsurface soils have low soluble sulfate contents and neutral pH values. Therefore, the potential for sulfate attack on concrete is considered low. Additionally, the tested soils are

- 13 -considered to have low corrosion potential to buried ferrous metal in direct contact with the soils and reinforcement steel protected by concrete cover.

Table 3 – Summary of Corrosivity Test Results

Test Parameter Test Results General Classification of Hazard

Water-soluble sulfate content 42 ppm

Negligible sulfate exposure to buried concrete (per ACI 318)

Water-soluble chloride content 61 ppm Non-corrosive to buried concrete (per

Caltrans Specifications) pH 7.9 Alkaline, relatively passive to buried metals

Minimum resistivity (in saturated condition) 8,770 Ohm-cm Low corrosivity to buried ferrous pipes

3.6 Faulting and Seismicity

Our review of available published geologic data indicates the presence of two active faults that trend towards this reach of Santa Ana River. The Elsinore fault zone (Glen Ivy Segment) is located approximately 1.8 miles to the southeast of the site, south of SR-91, and there is no currently available data showing the location of the fault trace north of SR-91. The fault trace is likely concealed beneath the alluvium of the Santa Ana River drainage. The Alquist-Priolo zone for the Whittier fault is located approximately 0.5 miles to the north of the site.

The characteristics of these two faults are discussed below.

Other known regional active faults that could produce significant ground shaking at the sites include the Chino, Puente Hills Blind Thrust and San Jose faults among others. These faults are located approximately 3.2, 11.5 and 14.8 miles from the sites, respectively. Several inactive faults, including the Scully Hill fault, are also present to the north and south of the proposed projects.

Elsinore Fault Zone (Glen Ivy Segment): The Elsinore fault zone is a segmented 250 kilometers (155 miles) long zone of faulting that can be traced from Los Angeles to northern Baja California (Mexico). It is one of the major right-lateral strike slip faults of the Peninsular Ranges. The Glen Ivy segment of the Elsinore Fault Zone is approximately 36 kilometers (22 miles) long extending from near Corona southward to Lake Elsinore. This segment bifurcates northwestward into

- 14 -the west-northwesterly striking Whittier fault. The Glen Ivy Segment is a right lateral strike slip fault with an estimated slip rate of approximately 5 mm/year (Millman and Rockwell, 1986) making it the fourth most active fault in the State.

The maximum moment magnitude earthquake along the Elsinore fault zone (Glen Ivy Segment) is estimated to be 6.8 Mw (Frankel et al., 2002; Petersen et al., 1996). The fault is considered to be a Class A fault according to CDMG (Frankel et al., 2002; Petersen et al., 1996).

Whittier Fault: The Whittier fault is the northwestward extension of the Elsinore fault zone (Glen Ivy Segment). The Whittier fault is considered a strike slip fault along most of its length with a component of vertical thrust. This fault is approximately 40 km (25 miles) long, and extends from the Whittier Narrows section of the San Gabriel River southeastward to the Santa Ana River where it is concealed beneath the alluvium. The Whittier fault separates the Puente Hills on the north from the Santa Ana Mountains to the south. In the area of the Santa Ana River, based on offset of stream terrace deposits (Gath, 1992 and 1995;

Rockwell et al., 1988 and 1990), the Whittier fault is considered to have a slip rate of approximately 2 to 3 mm/year. The estimated maximum earthquake to occur along the Whittier fault is 6.8 Mw (Petersen et al., 1996). The fault is classified as a Class A fault by CDMG (Frankel et al., 2002; Petersen et al., 1996).

3.7 Seismic Hazards

3.7.1 Fault Rupture

No active faults are known or mapped as crossing the Reach 9 - Phase III site. However, the Whittier-Elsinore fault zone and Whittier fault, trend towards the Santa Ana River and potentially crosses the river east of Coal Canyon Road. If a 6.8 Mw earthquake occurs on these faults, the fault rupture will likely cause displacement at the ground surface. Due to the projected distance, fault rupture is not expected to affect the proposed improvements.

3.7.2 Ground Shaking

The site is likely to be subjected to strong ground shaking during the life of the project. The intensity of ground shaking depends primarily upon the

- 15 -earthquake magnitude, the distance from the source, and the site response characteristics. Peak Horizontal Ground Accelerations (PHGA) is generally used to measure the intensity of ground shaking resulting from an earthquake. Per EM 1110-2-2100, the seismic events to be considered in design should consist of an Operational Basis Earthquake (OBE) with a 50 percent chance of being exceeded in 100 years (144-year return period) and a Maximum Design Earthquake (MDE). The MDE is a seismic event with a 10 percent chance of being exceeded in 100 years (950-year return period) or the Maximum Credible Earthquake (MCE) based on a deterministic seismic analysis, whichever is higher.

A probabilistic seismic hazard analysis was performed using the deaggregation program developed by the United States Geological Survey (USGS) National Seismic Hazard Mapping Program (2011). Results of the analysis indicate peak horizontal ground accelerations of 0.30g and 0.65g for return periods of 144 years and 950 years, respectively. The deterministic analysis was performed using EZ-FRISK (Risk Engineering, 2009) and the result indicated a peak horizontal ground acceleration (84TH percentile value) of 0.78g from a 6.8 Mw earthquake on the Whittier fault.

As such, the design peak horizontal ground accelerations of 0.30g and 0.78g were selected for the OBE and MDE seismic events, respectively.

3.7.3 Liquefaction

The site is located within an area designated as potentially liquefiable on the California Seismic Hazard Zone Map (CDMG, 2001). Liquefaction is a seismic phenomenon in which loose, saturated, fine-grained granular soils behave similarly to a fluid when subjected to high-intensity ground shaking. Liquefaction occurs when three general conditions exist: 1) shallow groundwater; 2) low density, fine, clean sandy soils; and 3) high-intensity ground motion. Effects of liquefaction can include sand boils, ground surface subsidence/settlement, slope instability and bearing capacity failures below structural foundations.

The three general conditions for liquefaction occurrence exist at the site.

The current and historically high groundwater levels along the alignment vary from 10 to 30 feet below the existing ground surface. Based on our borings, the subsurface soils below the groundwater tables consist predominantly of loose to very dense sand and gravel with isolated layers

- 16 -of soft to hard clay. Additionally, the site is likely to experience strong ground shaking from an earthquake along the active faults in the region.

We have performed liquefaction analysis of the soil profiles encountered in our hollow-stem auger borings. The liquefaction analysis was performed using procedures outlined by Youd et al. (2001) and in accordance with the guidelines in the Special Publication 117A and 2010 CBC. The peak ground acceleration used in the liquefaction analysis is based on the MDE seismic event of 0.78g and an earthquake magnitude of 6.8 Mw.

The results of our evaluation indicated that several layers of the soils between depths of 10 to 30 feet below grade are potentially susceptible to liquefaction. The effect of liquefaction is expected to be settlement due to the post-liquefaction consolidation of the soils that experience liquefaction in response to the seismic event. The liquefaction induced settlement was calculated based upon the procedure described by Tokimatsu and Seed (1987). The seismically induced settlement of these strata consisted of liquefaction settlement below groundwater table and dynamic settlement of loose sand above groundwater table. The settlement was estimated to result in a cumulative settlement on the order of 1 to 3 inches at the ground surface. The results of our liquefaction analysis are presented in Appendix C and summarized in Table 4.

Table 4 – Results of Liquefaction Analysis

Boring No.

Historically High

Groundwater (feet)

Depth of Liquefiable

Layers (feet)

Seismically Induced Settlement1 (inches)

B-124+20B 10 None 1.0 B-129+20B 10 10-25 3.1 B-134+30B 10 10-25 2.5

MW-140+60B 10 10-25 3.1

B-144+20B 10 20-30 1.9

1 Includes liquefaction settlement below groundwater and dry settlement above groundwater

3.7.4 Lateral Spreading

Seismically-induced lateral spreading involves primarily lateral movement of earth materials along liquefied soils due to ground shaking. Empirical

- 17 -models for estimating lateral spreading have been developed for both sloping ground and free face conditions. However, for the case of a relatively steep slope, a more applicable evaluation of lateral movement is a slope deformation analysis that considers the post-liquefaction residual shear strength, slope geometry and seismicity parameters (Newmark method).

Analysis was performed on a representative cross-section near Boring B- 129+20B for a pseudo-static condition. A yield acceleration (ky) corresponding to a factor of safety of 1.0 was estimated. Based on this yield acceleration, the lateral displacement was calculated using the built-in design earthquake time histories in the Java program developed by USGS. The acceleration-time histories were scaled to a uniform peak horizontal ground acceleration corresponding to the OBE and MDE seismic events. The lateral spreading was estimated to be negligible for the OBE and on the order of 8 inches for the MDE.

3.7.5 Seismically-Induced Inundation

Strong seismic ground motion can cause dams and levees to fail, resulting in damage to structures and properties located downstream. Prado Dam is located upstream of the project site, approximately 3.6 miles east of the project site. The potential for seismically-induced inundation exists if Prado Dam failed during a large earthquake.

3.7.6 Seiches and Tsunami

Tsunamis are tidal waves generated in large bodies of water by fault displacement or major ground movement. Tsunamis affect coastal areas with large waves, some of which can crest at heights of more than 100 feet and strike with devastating force. Considering the inland location of the site, the potential for a tsunami to affect the site is considered negligible. Seiches are large waves generated in enclosed bodies of water in response to ground shaking. Under certain circumstances, seiches could occur within the Prado Dam retarding basin; however, the potential for seiches to affect the site is considered low.

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4.0 SLOPE STABILITY ANALYSES AND DISCUSSIONS

4.1 Methodology

The slope stability analyses were conducted using the computer program SLIDE v6.008 (Rocscience, 2011). SLIDE performs stability calculations using two-dimensional (2D) limit equilibrium techniques based on vertical slice equilibrium.

The analyses were conducted using circular surfaces based on the Simplified Bishop Method considering the generally isotropic strength model of the material.

The analysis typically included generating 5,000 trial surfaces using the search technique programmed into the software based upon specific search parameters input to the program. The critical surface (lowest factor of safety) of each analysis was plotted on the computer output included in Appendix D.

EM 1110-2-1902 and EM 1110-2-1913 provide various methods to analyze slopes for stability against shear failure. These documents also provide the various loading conditions to which a slope and its foundation may be subjected.

We have considered these loading conditions along with other conditions that we deemed appropriate as listed below.

End of Construction: Temporary re-routing of the Santa Ana River and dewatering will be required for construction of the proposed slope protection. We have assumed in our slope stability analysis for the end-of-construction case that the dewatering has stopped and the groundwater level rises to the long-term condition.

Long-Term Condition: This represents full saturation of the slope and a condition where steady-state seepage occurs. An elevation of 370 feet was used to represent the steady water flow in the river. Based on the groundwater monitoring data presented on Figure 5, a long-term groundwater table at elevation 373 feet was used in the analyses.

Full Flood Stage: Based on the analysis performed by Tetra Tech, the water level in the Santa Ana River for a full flood stage is at an elevation of 382 feet.

We have used this water level and the highest groundwater elevation of 377 feet as measured in the groundwater monitoring well to represent the steady-state seepage condition for the full flood stage.

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Sudden Drawdown: This represents the case where the water in the river is rapidly drained after a steady seepage condition is developed within the slope.

The supporting effect of the water pressures is removed as the level of water is lowered. This condition is not considered likely to occur since the soils at site are highly permeable as evidenced by the groundwater monitoring readings that fluctuated with the water level in the Santa Ana River. Nonetheless, slope stability analyses were performed for this condition where the groundwater table is taken at elevation 377 feet with no water in the river.

Scour Condition: A scour study conducted by Tetra Tech indicates the depth of scour within this reach of Santa Ana River could potentially extend to elevations of 356 to 364 feet. We understand that USACE considers scour as a long-term condition. The groundwater elevation for the long-term condition was used for this analysis and the water in the river was assumed to be 4 feet deep (an elevation of 363 feet). A full flood stage was analyzed using a surface water level at an elevation of 378 feet as provided by Tetra Tech. An analysis was also performed for a sudden drawdown case after scour has occurred.

Earthquake: Earthquake loading was evaluated using the water levels for the long-term condition. A horizontal coefficient KH of 0.15 was used for the pseudo-static analysis. The earthquake loading was not evaluated concurrently with flood loading nor scour conditions.

Post Liquefaction: As indicated in Section 3.7, the upper 25 to 30 feet of the soils are susceptible to liquefaction during a strong earthquake. The soils may lose some of their shear strength immediately after an earthquake. The water levels for the long-term condition and the residual shear strength of the sandy soils were used for the post-liquefaction analysis.

The design water level in the Santa Ana River and the design groundwater table for each loading condition are presented in Table 5.

4.2 Design Criteria

EM 1110-2-1902 and EM 1110-2-1913 provide a guideline on the required factor of safety for some of the loading conditions mentioned above. In addition, USACE considers scour as a long-term condition. For temporary conditions, a factor of safety of 1.1 is considered as the minimum design criterion. The

- 20 -minimum factors of safety considered for each of the loading conditions are summarized in Table 5.

Table 5 – Design Water Levels and Criteria

Condition Analyzed Santa Ana River Water Elevation

(feet)

Groundwater Elevation (feet)

Minimum Required Factor of Safety End of Construction 363 373 1.3

Long-Term Condition 370 373 1.4 Full Flood Stage 382* 377 1.4

Sudden Drawdown 363 377 1.1 Scour Condition, Long Term 363 373 1.4

Scour Condition, Full Flood Stage 378* 377 1.4

Scour Condition with Sudden Drawdown 359 377 1.1

Earthquake 370 373 1.1 Post Liquefaction 370 373 1.1

*Provided by Tetra Tech

4.3 Shear Strength Parameters

Direct shear tests were performed on three undisturbed samples collected from the borings. The samples were tested under a saturated condition. Considering the granular nature of the soils and the strain rate, the test results are representative of consolidated, drained strengths. The test results are presented in Appendix B and the peak and post-peak strengths at 12 percent strain are summarized in Table 6.

Table 6 – Direct Shear Test Results

Boring No. Depth (feet)

Peak Shear Strength Shear Strength at 12% Strain ø ’ (degree) c’ (psf) ø ’

(degree) c’ (psf)

B-124+20B 15 39 230 33 500 B-134+30B 5 47 610 46 0 B-144+20B 5 41 230 33 180

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In addition, the friction angles of the soils were evaluated using correlation with SPT blowcounts and relative density in NAVFAC DM-7.1. To a depth of 25 to 30 feet below the ground surface (an approximate elevation of 360 feet), the SPT blowcounts ranged from 10 to 48 and results of the correlation, presented in Appendix D, indicate friction angles that are consistently higher than 33 degrees.

As such, a friction angle of 33 degrees and cohesion of 0 psf were conservatively selected for the upper 25 to 30 feet of the onsite soils. Materials for compacted fill are expected to be generated mostly from the onsite soils and, therefore, the same shear strength parameters were used for compacted fill. Below an elevation of 360 feet, the SPT blowcounts ranged from 36 to refusal. Based on these blowcounts, a friction angle of 38 degrees were used.

Post-earthquake residual strength of soils susceptible to earthquake is estimated using the chart developed by Seed and Harder (1990) based on the equivalent clean sand SPT blowcounts of the alluvium. A lower-bound estimate of residual shear strength of 300 psf was selected and applied to the liquefiable soils for the post-liquefaction analysis.

Grouted stone and soil cement were considered for the slope protection. The shear strength of the grouted stone was considered to be the same as the onsite soils as required by USACE. The soil cement was assumed to have a friction angle of 42 degrees and cohesion of 1,000 psf. The shear strength parameters used in the slope stability analyses are summarized in Table 7.

Table 7 – Design Shear Strength Parameters

Material Shear Strength Residual Strength ø ’ (degree) c’ (psf) ø ’ (degree) c’ (psf)

Alluvium above Elevation 360 feet 33 0 0 300

Alluvium below Elevation 360 feet 38 0 Not Applicable

Compacted Fill 33 0 Not Applicable Grouted Stone 33 0 Not Applicable Soil Cement 42 1,000 Not Applicable

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4.4 Protection System Selection

Preliminary slope stability analyses were performed on the conceptual plans and profiles provided by Tetra Tech to evaluate feasibility of various type and configuration of slope protection systems. Results of the analyses for the long-term scour condition, which represents the most critical case where the exposed slope is highest and the required minimum factor of safety is 1.4, are summarized in Table 8. A 1:1 soil cement stabilization fill is the preferred protection system, the analyses of which are discussed in Section 4.5.

Table 8 – Slope Stability Analyses for Various Slope Protection Schemes

Alternative Factor of Safety for Scour Condition

1½:1 Grouted Stone 0.9 2:1 Grouted Stone 1.2 1:1 Soil Cement 1.4

4.5 Soil-Cement Stabilization Fill

Two representative cross-sections were prepared through the river bank. The cross-sections, presented on Figures 6 and 7, show the existing profiles, proposed profiles, and the approximate contact of the alluvium and fill. The locations of the cross-sections are shown on Figures 2 and 3. The existing and proposed profiles and the geology of the two cross-sections are similar. Cross-section 1370+50 was selected for the slope stability analyses because this cross-section was considered more critical due to the slope height and proximity of the SR-91 embankment to the river bank. The scour depth at this cross-section location was estimated to extend to an elevation of 359 feet. Results of the analyses indicate factors of safety greater than the required minimum for each loading condition and are summarized in Table 9.

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Table 9 – Slope Stability Analyses for 1:1 Soil Cement

Condition Analyzed Factor of Safety End of Construction 1.7

Long-Term Condition 1.7 Full Flood Stage 2.3

Sudden Drawdown 1.5 Scour Condition, Long Term 1.4

Scour Condition, Full Flood Stage 1.5 Scour Condition with Sudden Drawdown 1.1

Earthquake 1.2 Post Liquefaction 1.1

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5.0 GEOTECHNICAL RECOMMENDATIONS

5.1 Soil Cement Stabilization Fill

Based on our slope stability analyses, soil cement may be used for slope protection along this reach of Santa Ana River. The soil cement stabilization fill may be constructed at a slope gradient of 1:1 with a minimum width of 10 feet.

The soil cement fill should extend to a minimum depth of 5 feet below the estimated scour bottom.

A subdrain system should be installed behind the soil cement to reduce buildup of hydrostatic pressure. The subdrain system should consist of a 4-inch diameter perforated pipe surrounded by a minimum 3 cubic feet per linear foot of gravel and wrapped in filter fabric. The subdrain system should be provided with outlets consisting of 4-inch diameter solid pipes installed through the soil cement stabilization fill at a horizontal spacing of approximately 100 feet. Each pipe should be sloped at a minimum gradient of two percent and provided with an outlet on the slope face. The outlets should be located at the lowest elevation as practical on the slope face.

The soil cement mixture should have a minimum strength that meets or exceeds the design parameters of a friction angle of 42 degrees and cohesion of 1,000 psf. Soil cement mixture is typically tested using unconfined compressive tests.

From a slope stability standpoint, the soil cement mixture should have a minimum unconfined compressive strength of 100 psi. Higher strength of the soil cement mixture may be required for other reasons such as resistance to impact from river flow. Such evaluation is beyond the scope of this report.

5.2 Headwall and Wingwall Foundation

Several storm drain outlets will be constructed for the existing 18-inch and 60-inch diameter reinforced concrete pipes. Foundation for the headwalls and wingwalls of the outlet structures should be supported on firm, competent subgrade. The foundation should have a minimum depth of 18 inches and the bottom edge of the foundation should have a minimum horizontal distance of 5 feet from the slope face. An allowable bearing capacity of 3,000 psf may be used for the foundation design. The allowable bearing capacity may be increased by one third when considering loads of short duration.

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5.3 Lateral Earth Pressures

Headwalls and wingwalls of the outlet structures may be designed using lateral earth pressures of 36 pcf and 55 pcf for active condition and at-rest condition, respectively. These lateral earth pressures were calculated using an angle of internal friction of 33 degrees and a soil unit weight of 120 pcf.

Lateral loads may be resisted by friction between the footings and the supporting subgrade, and passive resistance of properly compacted backfill and/or undisturbed native soils, in combination. A friction coefficient of 0.4 may be used at the soil-concrete interface for calculating the sliding resistance. A passive pressure based on an equivalent fluid pressure of 360 pcf may be used for calculating the lateral passive resistance. The lateral passive resistance can be taken into account only if it is ensured that the soil against embedded structures will remain intact with time.

5.4 Cement Type and Corrosion Protection

Based on the results of laboratory testing, concrete structures in contact with the onsite soil are expected to have negligible exposure to water-soluble sulfates in the soil. Common Type II cement may be used for concrete construction onsite and the concrete should be designed in accordance with CBC or ACI requirements.

Based on our laboratory testing, the onsite soil is not considered corrosive to ferrous metals in direct contact with the onsite soil.

5.5 Seismic Deformation

As discussed in Section 3.7, seismic deformation caused by the OBE event is expected to be minimal. Seismic deformation caused by the MDE event due to the combined effects of liquefaction-induced settlement and slope deformation is estimated to be on the order of 9 to 11 inches. This level of deformation is not expected to cause collapse or widespread damage to the soil cement slope;

however, it could induce stresses and cause potential damage to underground utilities that penetrate the slope (proposed storm drain outlets) or are adjacent to the slope (proposed SARI Line). It is recommended that a thorough inspection of

- 28 -the soil cement slope and underground utilities be implemented following a significant seismic event. Any open cracking within the soil cement or damage to underground utilities should be promptly repaired.

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6.0 CONSTRUCTION CONSIDERATIONS

6.1 Earthwork

Earthwork should be performed in accordance with the recommendations in this report and the requirements of the local municipalities.

6.1.1 Site Preparation

Prior to construction, the site should be cleared of all topsoil, organic material, vegetation and debris. The existing soil cement will interfere with construction of the slope protection and should be removed. Cleared and grubbed material and rubble waste encountered or generated from demolition should be disposed of offsite.

6.1.2 Excavation and Subgrade Preparation

The alluvial soils at the site can be excavated with conventional heavy construction equipment in good working condition. Some cobbles and boulders were encountered during our field exploration and observed along the Santa Ana River. These materials are expected to be rippable without use of explosives. Use of large dozers equipped with rippers is recommended. We recommend that exposed surfaces at the bottom of the excavations be uniform in composition and free of loose soil or debris.

Prior to placing fill materials or soil cement, the subgrade should be scarified to a minimum depth of 6 inches, moisture conditioned, and proofrolled. Any soft and/or unsuitable materials encountered at the bottom of the excavations should be removed and replaced with fill material. Wet and pumping soils may be encountered in the excavation for the soil cement bank protection. If such soils are encountered, the excavation bottoms may need to be stabilized by working crushed and broken rock in 3- to 6-inch layers into the soil until a firm base is established on which fill can be placed. The minimum recommended thickness of crushed and broken rock layer is 12 inches to stabilize the wet and pumping soils. The wet soils will need to be air dried and/or mixed with dry material prior to placement as compacted fill. Field evaluation of the stability and support characteristics of the subgrade is recommended to be performed by the geotechnical engineer prior to fill placement.

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6.1.3 Fill Placement and Compaction

The onsite soils to be used as compacted structural fill should be free of organic material or construction debris. The soils may require air drying or mixing with drier materials prior to placement as compacted fill. Any imported fill soil should be approved by the geotechnical engineer prior to placement as fill. Where fills or soil cement is to be placed on ground with slopes steeper than 5:1 (horizontal:vertical), the ground should be stepped or benched. The benches for compacted fill and soil cement should be excavated a minimum width of 6 feet and 4 feet, respectively, into competent material or as otherwise recommended by the geotechnical engineer. Fill soils should be placed in loose lifts not exceeding 8 inches, moisture-conditioned as necessary to at least two percent above moisture optimum and compacted to a minimum of 90 percent of the maximum dry density as determined by ASTM Test Method D 1557.

6.2 Temporary Excavation and Shoring Design

All temporary excavations should be performed in accordance with project plans, specifications, and all OSHA requirements. Excavations 5 feet or deeper should be laid back or shored in accordance with OSHA requirements before personnel are allowed to enter. Groundwater should be dewatered to a depth below the excavation bottom prior to excavation. We analyzed the stability of a temporary excavation with a slope gradient of 1½:1 (horizontal:vertical) and a dewatered condition.