Geotechnical_Appendix.pdf

Los Angeles District Geotechnical Branch

Geotechnical Appendix, Design Documentation Report

Bradley Canyon Extension Santa Maria, Santa Barbara County, California

By US Army Corps of Engineers, Los Angeles District

Engineering Division, Geotechnical Branch 915 Wilshire Blvd, Los Angeles, CA 90017

August 2012

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Geotechnical Appendix, Design Documentation Report

Bradley Canyon Extension Santa Maria, Santa Barbara County, California

Report Prepared By:

Michael L. Leongson, PE Civil Engineer Soils and Materials Section, Geotechnical Branch, Engineering Division, Los Angeles District, US Army Corps of Engineers

With the Assistance of:

Chris A. Spitzer, PE Civil Engineer Soils and Materials Section, Geotechnical Branch, Engineering Division, Los Angeles District, US Army Corps of Engineers

Arturo Orozco, PG, CEG Geologist Geology Section, Geotechnical Branch, Engineering Division, Los Angeles District, US Army Corps of Engineers

Report Reviewed By:

Douglas Dahncke, PE, GE Soils Design & Material Section Chief Geotechnical Branch, Engineering Division, Los Angeles District, US Army Corps of Engineers iii

TABLE OF CONTENTS

1 INTRODUCTION

1.1 PROJECT BACKGROUND

1.2 PROPOSED CONSTRUCTION

1.3 AVAILABLE GEOTECHNICAL INFORMATION

1.3.1 Pertinent Geotechnical Investigations

1.3.2 Historical Aerial Photography

2 SUBSURFACE INVESTIGATIONS AND LABORATORY TESTING

2.1 SUBSURFACE INVESTIGATIONS

2.1.1 DYA 2009 Investigation

2.1.2 DYA 2010 Investigation

2.1.3 DYA 2011 Investigation

2.2 LABORATORY TESTING

3 SITE CONDITIONS AND SOIL DESIGN PARMETERS

3.1 SURFACE CONDITIONS

3.2 GEOLOGY AND FAULTING

3.2.1 Regional Geology

3.2.2 Local Geology

3.2.3 Suface Fault Rupture

3.2.4 Historical Seismicity

3.3 SUBSURFACE CONDITIONS

3.3.1 Generalized Subsurface Conditions

3.4 SOIL PERMEABILITY

3.5 GROUNDWATER CONDITIONS

4 SEISMIC/GEOLOGIC HAZARDS

4.1 SURFACE FAULT RUPTURE

4.2 GROUND ACCELERATION

4.3 LIQUEFACTION AND SEISMIC SETTLEMENT

4.4 LATERAL SPREADING

5 GEOTECHNICAL ANALYSIS

5.1 SELECTION OF CRITICAL CROSS SECTIONS USED IN DESIGN . 14

5.2 SOIL PARAMETERS

5.3 SCOUR

5.4 SEEPAGE ANALYSIS

5.4.1 Seepage Results

5.5 SLOPE STABILITY

5.5.1 Analysis Methodology

5.5.2 Summary of Results

6 DESIGN RECOMMENDATIONS

6.1 GENERAL

6.2 EARTHWORK CONSIDERATIONS AND RECOMMENDATIONS .. 20

iv

6.3 EMBANKMENT FILL

6.4 TOE EXCAVATION

6.4.1 Temporary Excavations

6.5 BORROW AREA

6.6 MISCELLANEOUS FILL

6.7 CONSTRUCTION CONSIDERATIONS

6.8 COMBI-WALL RETAINING SYSTEM

6.8.1 Design Parameters

6.8.2 Serviceability

6.8.3 Pile Driving Conditions

6.9 CORROSION

6.9.1 Concrete Corrosion

6.9.2 Combi-wall Corrosion

6.10 SOIL CEMENT EMBANKMENT

6.10.1 General

6.10.2 Soil Cement Mix Study

6.10.3 Construction Specifications

REFERENCES

v

List of Tables

Table Title

Page

Table 1: Generalized Subsurface Conditions Table 2: Soil Permeability Summary Table 3: Summary of Potentially Liquefiable Zones Table 4: Summary of Seismically Induced Settlements Table 5: Seepage Analysis Soil Parameters Table 6: Summary of Seepage Analyses Table 7: Minimum Slope Stability Factor of Safety Table 8: Summary of Slope Stability Analysis Table 9: Import Fill and Select Backfill Criteria Table 10: Corrosion Potential Test Summary

List of Figures

Figure

Title

Figure 1: Vicinity Map Figure 2: Typical Soil Cement Cross Section

List of Appendices

Appendix

Title

Appendix A: Geotechnical Sheets (Boring Location, Boring Logs, etc.)

Appendix B: Laboratory Data Appendix C: Geologic Conditions Appendix D: Seismic Analysis Appendix E: Seepage Analysis Appendix F: Slope Stability Analysis Appendix G: DYA 2010 Investigation Appendix H: Memorandum for Design – Geotechnical Considerations

1 INTRODUCTION

This report presents the result of the geotechnical and materials studies performed in support of the levee enhancements along the westerly channel of the Bradley Canyon Wash. This report follows upon numerous studies performed for the Santa Maria River levee improvement projects recently completed in 2010. An Addendum to the Supplemental Design Deficiency Report (ASDDR), dated November 2011, was prepared by the U.S. Army Corps of Engineers, Los Angeles District (LA District), recommended improvements to the Bradley Canyon Levee System.

1.1 PROJECT BACKGROUND

The Bradley Canyon Levee is located along the left (west) bank of the Bradley Canyon channel, upstream of the confluence of the Santa Maria River and the Bradley Canyon Wash in Santa Maria, California. The Bradley Canyon Levee project site is generally bounded by agricultural land to the east and west, the Santa Maria River to the north, and Foxen Canyon Road to the south. The Site Vicinity Map, presented on Figure 1, shows the location of the project. The Site Plan, presented in Appendix A, Sheet G1, depicts other locations described in this report such as boring locations, soil cement feasibility sample locations, and other pertinent geotechnical information.

Figure 1: Vicinity Map

The Santa Maria River Levee System was originally constructed between 1959 and 1963. The system consisted of levees along the Santa Maria River and Bradley Canyon Wash composed of compacted fill embankments protected with riprap revetment. Approximately 17 miles of levees were constructed along the left (south) bank and 5 miles of levees along the right (north) bank of the Santa Maria River. Approximately 2.2 miles of levees were constructed along the left (west) bank of the Bradley Canyon Wash. The Bradley Canyon Levee refers to the levee on the left (west) of the Bradley Canyon Wash which is the subject of this document.

The LA District prepared a Supplemental Design Deficiency Report (SDDR) to remediate deficiencies inherent in the original design. The report was approved in August 2009. The original levee system design was intended to pass the Standard Project Flood (SPF) flows from the Santa Maria River and Bradley Canyon Wash using the complete channel cross-sections.

However, lower flood flows which don't use the complete channel cross-section meander across the channel resulting in flows directly impinging on the levee. Over the last four decades, this resulted in one complete breach and several near breaches of portions of the levee system that receive Santa Maria River flows. Therefore, a portion of the Santa Maria Levee was improved to address the failure mode of directly impinging flows. Approximately 6.2 miles of the left (south) bank of the Santa Maria Levee was improved utilizing soil cement to armor the levee face. In addition, sheet pile was also utilized as part of the repair at a selected location for protection of environmentally sensitive habitat.

The remediation along the Santa Maria Levee was performed along three (3) reaches. Reach 1 included a soil cement revetment located between Blosser Road and California State Highway 101 (Hwy 101). Reach 2 included soil cement revetment located between Hwy 101 and Suey Crossing Road. Reach 3 included soil cement revetment and sheet pile mitigation located between Suey Crossing Road and the confluence of the Bradley Canyon Wash with the Santa Maria River. Due to environmental constraints sheet pile mitigation was utilized at the upstream end of Reach 3, beginning of the confluence of the Bradley Canyon Wash with the Santa Maria River and extending downstream for approximately 1,700 lineal feet. The sheet pile mitigation consisted of a combi-wall system that utilized 60-inch diameter pipe piles with sheet piles in between. The construction of Reaches 1, 2, and 3 was recently completed in 2010. The Santa Maria Levee continues approximately 17,000 feet upstream of the confluence of the Santa Maria River and Bradley Canyon Wash.

The SDDR did not consider the impact to the Bradley Canyon levee if a breach along the 17,000-foot portion of the Santa Maria levee upstream of the end of Reach 3 were to occur. Should a breach or failure of the 17,000-foot portion of the Santa Maria levee upstream of the end of Reach 3 were to occur, it is possible the Bradley Canyon Wash levee could also fail. This secondary failure of the Bradley Canyon levee was not taken into account in the original SDDR and could potentially cause flooding in the City of Santa Maria. To provide the authorized level of flood risk reduction to the City of Santa Maria, an Addendum to the Supplemental Design Deficiency Report (ASDDR) was prepared and was has recently been approved on 4 June 2012.

The ASDDR recommended revising the corrective action presented in the SDDR by extending the revetment 3,380 feet along the Bradley Canyon Levee. Per the ASDDR, the improvement of the Bradley Canyon Levee would provide the City of Santa Maria with the authorized level of flood risk reduction if a breach were to occur in the 17,000 foot segment of the Santa Maria Levee upstream of Bradley Canyon Wash. Investigations into the original Bradley Canyon levee conditions and potential rehabilitation considerations were conducted concurrently with the ASDDR preparation. .

1.2 PROPOSED CONSTRUCTION

The anticipated improvements to the Bradley Canyon Levee include a 1000 lineal foot continuation of a combi-wall system from the confluence of the Santa Maria Levee Reach 3 and Bradley Canyon Levee. Approximately 2,380 lineal feet of soil cement protection similar to that constructed along Reaches 1, 2, and 3 will be constructed upstream of the proposed combi-wall, for a total levee improvement length of 3,380 lineal feet. The soil cement is anticipated to be about 8-feet thick with a river-side slope gradient of 2H:1V and will extend from the crest of the levee to the design soil cement toe elevation (below scour elevation). The levee crest width is anticipated to have a final width ranging from 16 to 20 feet with a 2 percent grade from the land side grade toward the river-side. Based on conversations with LA District Structural Engineering Section, the combi-wall system will consist of H-piles (this differs from the pipe piles used downstream in Reach 3) with sheet piles in between. In addition, a portion of the levee will be raised up to 1 foot to contain the SPF of the Santa Maria River flows.

1.3 AVAILABLE GEOTECHNICAL INFORMATION

1.3.1 Pertinent Geotechnical Investigations

Several subsurface investigations for the Bradley Canyon Levee were performed by Diaz Yourman and Associates (DYA). A subsurface investigation was performed in 2009. In addition a geotechnical investigation report was prepared for the Santa Maria Levee (Reach 3) and Bradley Canyon Levee (DYA 2009 Investigation). Another subsurface investigation was performed in 2010 by DYA (DYA 2010 Investigation) and was described in a geotechnical data report dated 19 November 2010 for the soil cement improvement on the Bradley Canyon Levee.

Most recently, a subsurface investigation was performed in 2011 by DYA (DYA 2011 Investigation) and described in a geotechnical data report dated 31 August 2011 for the portion of the Bradley Canyon Levee which will receive a combi-wall improvement. Refer to Appendixes G and I for the DYA 2010 Investigation and DYA 2011 Investigation, respectively.

1.3.2 Historical Aerial Photography

A review of readily available historic aerial photography of the site was performed to evaluate the characteristics of the site compared to its original construction. Based on the most historic aerial photography from Google Earth in 1994 it appears the site had not been graded, re-aligned, or any significant changes have been made since 1994. As-built plans were not available, however design plans dated December 1958 depict conditions similar to the 1994 photos. In addition, based on review of USACE permit files for the Santa Maria Levee, no permits were found for construction of modifications to the originally constructed Bradley Canyon Levee.

Therefore, based on the aerial photographs and the absence of historical USACE permits, it appears there have been no modifications to the Bradley Canyon Levee since its original construction in 1963.

SUBSURFACE INVESTIGATIONS AND LABORATORY TESTING

2.1 SUBSURFACE INVESTIGATIONS

As previously discussed, three (3) subsurface investigations for the Bradley Canyon Levee have been performed. For the DYA 2009 and DYA 2011 investigations, samples were collected from the borings at selected depths by driving a 2.5-inch inside diameter (I.D.) spilt barrel sampler (Modified California drive sampler) containing brass liners with a 140-pound automatic hammer free falling a distance of 30 inches. In addition, samples of the subsurface material were obtained using a 1.4-inch I.D. standard penetrometer test (SPT) sampler without liners driven 18 inches in accordance with ASTM D1586 test procedures. Resistance to sampler penetration was noted as the number of blows per foot over the last 12 inches of sampler penetration on the boring logs. The DYA 2010 Investigation utilized hand sampling methods to obtain bulk samples in the river bed.

The following sections provide a brief summary of the DYA investigations.

2.1.1 DYA 2009 Investigation

The purpose of the DYA 2009 investigation was to provide initial geotechnical data for the preliminary design of the Santa Maria Levee (Reach 3) and the Bradley Canyon Extension project. DYA’s scope of services included conducting a field investigation, performing geotechnical laboratory tests on select soil samples, performing engineering analyses (including seismic hazard, seepage, and slope stability analyses), providing geotechnical recommendations and a report. The DYA report was dated 22 January 2010.

DYA performed a subsurface investigation for the Santa Maria Levee (Reach 3) and the Bradley Canyon Levee between July 15 and 21, 2009. The subsurface investigation consisted of drilling 15 borings (DYA09-1 through DYA09-15) along the crest of the levee. Of the 15 borings drilled, three (3) were drilled along the Bradley Canyon Levee (DYA09-1 through DYA09-3) and were utilized in the development of the conclusions and recommendations presented in this Geotechnical Appendix. The borings DYA09-1 through DYA09-3 were drilled to depths ranging from 41.5 to 43.5 feet below the levee crest at the time of drilling. The locations of the borings are provided on Appendix A, Sheet G1 through G6.

2.1.2 DYA 2010 Investigation

The purpose of the DYA 2010 investigation was to provide geotechnical data for preliminary evaluation of the soil cement portion of the Bradley Canyon Extension project. DYA’s scope of services included collecting representative bulk soil samples from the river bed, performing geotechnical laboratory tests, performing a soil cement design study, and preparation of a report.

The DYA report is dated 19 November 2010 and is included in Appendix H.

Three (3) representative soil samples were collected for the soil cement study by a DYA designated independent subcontractor on 26 August 2010. The sample locations were collected in the river bed, approximately 20 feet from the toe of the slope and approximately 2 to 3 feet below the ground surface (bgs). The approximate sample locations are provided in Appendix A, Sheets G1 through G6.

2.1.3 DYA 2011 Investigation

The purpose of the DYA 2011 investigation was to provide geotechnical data to assist in the design of the combi-wall portion of the Bradley Canyon Extension project, which is to be conducted by the LA District’s Structural Engineering Section. DYA’s scope of services included performing a subsurface investigation, laboratory testing, and preparation of a report.

The DYA report was dated 31 August 2011.

The borings were drilled between July 18 and 20, 2011 and consisted of drilling five (5) borings (DYB11-1 through DYB11-5) along the crest of the levee. The borings were drilled to depths ranging from 80.5 and 83 feet below the levee crest at the time of drilling. The approximate locations of the borings are provided on Appendix A, Sheets G1 through G6.

2.2 LABORATORY TESTING

Laboratory tests were performed on select soil samples to evaluate their physical characteristics for the DYA 2011 Investigation. The following laboratory tests were used to develop the design geotechnical parameters:

• Moisture Content (ASTM D2216)

• Unit Weight (ASTM D2937)

• Gradation with Hydrometer (ASTM D422)

• Atterberg Limits (ASTM D4318)

• Direct Shear (ASTM D3080)

• Soluble Sulfate Content (California Test Method No. 417)

• Soluble Chloride Content (California Test Method No. 422)

• pH and Minimum Resistivity (California Test Method No. 532)

• Maximum Density/Optimum Moisture (ASTM D1557)

• Moisture Density (ASTM D558)

• Compressive Strength (ASTM D1633)

A compilation of laboratory test data performed for the DYA Investigations are provided in Appendix B.

SITE CONDITIONS AND SOIL DESIGN PARMETERS

3.1 SURFACE CONDITIONS

The Bradley Canyon Levee embankment is on average approximately 15 feet high measured from the thalweg to the crest of the levee. The crest of the levee was observed to be relatively level. The river-side slopes of the levee had an approximate gradient of 2H:1V (horizontal:vertical), and is covered with armor rock composed of subangular boulders approximately 12 to 24 inches in diameter. The land-side slopes of the levee were observed to have a gradient of at least 2H:1V. Generally, the terrain beyond the land-side toe of the levee is relatively level. Both the land side levee slope and areas beyond the toe are lightly vegetated with low lying grasses and low shrubs. Low height earthen berms with organic and plant debris were observed along portions of the riprap face.

Access points to the Bradley Canyon Levee Extension Project are at two locations; from a gate owned by the Santa Maria Landfill located west-northwest of the Levee and from Foxen Canyon Road which crosses the Bradley Canyon Levee approximately 5,400 feet upstream of the Bradley Canyon Extension. Based on field observations and conversations with the County of Santa Barbara, the levee crest is used as a vehicle maintenance road. It should be noted that based on field observations and aerial photographs, a portion of the levee near Station 359+00 (referenced in Appendix A, Sheet G3) is being utilized as a vehicle crossing between agricultural lands bisected by the levee.

3.2 GEOLOGY AND FAULTING

3.2.1 Regional Geology

The project is located along the Bradley Canyon Channel near its confluence with the Santa Maria River which flows on the northern edge of the Santa Maria Valley in the Southern Coast Ranges geomorphic province of California. This province comprises a number of northwest-trending mountain ranges and large structural valleys and basins. In the last 24 million years (Neogene time), transform tectonics created en-echelon, compressional basins of deposition; en-echelon folds; and northwest-trending strike-slip faults.

The Santa Maria Basin is a large structural syncline that has filled with alluvial sediments derived from the faulted anticlinal structures that form the San Rafael and the Santa Ynez Mountains to the north-northeast and south respectively (Tennyson, 1992). The alluvial floor of the Santa Maria Valley was created when sediments from the Cuyama and Sisquoc Rivers filled the Santa Maria Valley Syncline. These two rivers are confluent in the eastern portion of the valley and form the Santa Maria River that flows west across the valley to the Pacific Ocean.

The base of the alluvium of the Santa Maria Valley can be more than 2,000 feet bgs and averages 1,000 feet bgs (Miller et al., 1966). Underlying the alluvial sediments are Tertiary-age (65 million to 1.8 million years), sedimentary rocks of the Monterey, Point Sal, Obispo, Rincon, and Vequero formations, which unconformably overly the Cretaceous (145.5 to 65.5 million years) and Jurassic (200 to 65.5 million years) rocks of the Jalama formation, and Franciscan Complex (Tennyson, 1992). A portion of the Geologic Maps of the Santa Maria and Twetchell Dam Quadrangles are used as the Regional Geologic Map. The Regional Geologic map is provided in Appendix C.

3.2.2 Local Geology

The local geologic environment shown on the Geologic Maps (Sheets G2 through G5 in Appendix A) and Geologic Cross-sections (Sheet G6 in Appendix A) is based on the interpretations of earth materials encountered in the borings drilled by DYA (DYA 2009 and 2011 investigations) and a site observation of the geologic conditions by the LA District’s Geologist on 17 February 2012. The LA District’s civil drawings were used as base maps to generate the Geologic Maps. Sheet G1 in Appendix A is the Plan of Exploration showing the location of all the borings drilled along the planned Bradley Canyon Extension. An aerial photograph of the site is used as a base map for the Plan of Exploration (Sheet G1). In general, the Santa Maria Valley is of low topographic relief and slopes gently toward the coast. The northwest- to westerly-draining Santa Maria River and Santa Maria Valley were created by the erosion of the mountainous areas and ongoing uplift of the region. The site consists mainly of alluvial units of flood-plain and channel deposits and delineated on the Geologic maps with the map symbol “Qal.” The existing Bradley Canyon Levee rests on Holocene age (younger than 11,000 years) river channel deposits and floodplain alluvium. The levee embankments, roadways and other man-made structures are underlain by compacted fill and are delineated on the Geologic maps with a map symbol “Caf.” Rip Rap materials also exist on the river side slopes of the embankment.

3.2.3 Suface Fault Rupture

The current tectonic framework of the region is controlled by the transpressional junction between the Pacific and North American plates, namely the San Andreas fault system. The seismically active faults of this system closest to the project levee are the offshore trace of the Hosgri-San Simeon fault system located approximately 20 miles west, the Santa Ynez River fault located approximately 20 miles to the south, and the Oceanic-West Huasna fault zone located approximately 2 miles northeast of the project. The San Andreas fault is located about 40 miles northeast-east of the project. Based on Hart and Bryant (1997) and California Geological Survey (2012), the site is not located within an Alquist-Priolo Earthquake Fault Zone where special studies addressing the potential for surface fault rupture are required. The nearest known potentially active fault is the Santa Maria River fault system (also known as the San Luis Range fault system). The San Luis Range fault is a reverse fault about 64 km long with a maximum moment magnitude Mw 7.2 and a slip rate of 0.2 ± 0.1 mm/yr., and is located approximately 0.4 mile (2,100 feet) north of the project site (U.S. Geological Survey, 2006). Although inactive the Bradley Canyon fault is located approximately 500 feet east of the levee. A Fault Activity Map is provided in Appendix C.

3.2.4 Historical Seismicity

The project site and its vicinity is an area traditionally characterized by high seismic activity.

Based on research of historic earthquakes in proximity to the project site a wide variety of earthquake epicenters have been felt with magnitudes ranging from 5.0 to 6.5 within a radial distance of 125 miles (200 km). Some of the significant earthquakes that have occurred were earthquakes with magnitudes of 6.0 and 6.5 located approximately 58 miles (93 km) and 61 miles (98 km) from the site, and occurred in 2004 and 2003, respectively.

The Advanced National Seismic System (ANSS) catalog is a worldwide earthquake catalog which is created by merging the master earthquake catalogs from contributing ANSS member networks and then removing duplicate events, or non-unique solutions from the same event. The ANSS network includes the Northern and Southern California Seismic Networks, the Pacific Northwest Seismic Network, the University of Nevada, Reno Seismic Network, the University of Utah Seismographic Stations, and the United States National Earthquake Information Service.

The earthquake database also consists of earthquake records between 1800 and 1900 from Seeburger and Bolt (1976) and Toppozada et. al. (1978, 1981).

A Final Design Documentation Report titled “Santa Maria Valley Levees South Levee Improvement Project Reach 3 (Suey Crossing Bridge to Bradley Canyon Confluence) Volume 2” was prepared by HDR and CDM for the LA District. The purpose of the referenced DDR was to provide analyses and calculations for the design of Reach 3 of the Santa Maria South Levee Improvement Project. Based on the referenced DDR it references significant earthquakes that have occurred within the vicinity of the Santa Maria Levee. Considering the near vicinity of the levees with respect to each other, it is assumed it could also apply to the Bradley Canyon Levee.

It states the following under the heading Seismicity:

“In addition to the individual seismogenic sources, we also allow for background seismicity that accounts for random earthquakes between M 5 and 8 using the exponential method. The project site and its vicinity is an area traditionally characterized by high seismic activity. Historically, the most significant activity in this area was a magnitude 7.9 earthquake occurred in 1857 at a distance of 65 km to the project site. The closest historical earthquake was about 5.8 km away from the project site with a magnitude of 5.8, and occurred in 1928. The earthquake database used contains in excess of 5,500 seismic events and covers the period from 1800 through March 2005. The earthquake database is principally comprised of an earthquake catalog for the State of California prepared by the Division of Mines and Geology (CDMG).”

3.3 SUBSURFACE CONDITIONS

The subsurface conditions encountered in borings DYA09-01 through DYA09-03 (DYA 2009 Investigation) and borings DYB11-1 through DYB11-5 (DYA 2011 Investigation) generally consist of a layer of embankment fill underlain by native soils. The fill soils predominantly consist of sand and silty sand with occasional gravel with a relative consistency of very loose to dense. Native soils encountered below the fill soils predominantly consist of silty sands and sands with a relative consistency of medium dense to very dense.

The above is a general description of the earth material profile. A more detailed representation of the conditions and materials at the specific exploration locations are provided on the boring logs in Appendix A, Sheets G8 through G22.

It should be noted that within boring DYB11-1, at a depth of approximately 7 feet below the levee crest, a blow count of zero (0) blows per foot (bpf) was recorded and described by DYA as a “very loose sample (almost a void)”. A piece of polythene bag was noted on the boring logs within the drill cuttings at the same depth. The first California Modified drive sample was taken at 0.5 feet below the levee crest within this boring. Drilling within this borehole continued to 8.5 feet and another Modified California drive sample was taken. An uncorrected SPT blow count of 18 bpf at this depth was recorded indicating a medium dense soil. This boring was then advanced to a depth of 82.5 feet and samples were taken at 5 foot intervals. Another boring was advanced approximately 5 feet downstream (north) of boring DYB11-1 referenced as DYB11- 1A to further evaluate the extent of the ‘void’ encountered. A Modified California drive sample was taken at a depth of 7 feet below the levee crest and an uncorrected SPT blow count of 25 bpf was recorded indicating a relative density of medium dense. Regardless of cause of this ‘void’, based on our interpretation the additional boring indicates that the ‘void’ does not extend further downstream.

3.3.1 Generalized Subsurface Conditions

DYA (2009) estimated soil design parameters for the Bradley Canyon Extension Project. A total unit weight of 115 pcf and friction angle of 31 degrees was provided for the fill; and a total unit weight of 120 pcf and friction angle of 32 degrees was provided for the native soils. Based on the borings drilled for the DYA 2009 and 2011 Investigations the soils appear to be relatively uniform throughout the Project site. Therefore, to simplify the design, and utilizing data provided in the 2010 and 2011 DYA reports, USACE produced Table 1, Generalized Subsurface Conditions table which includes design soil parameters for the Bradley Canyon Extension Project.

Table 1: Generalized Subsurface Conditions

Depth

(ft) USCS Material Average

SPT N

Total Unit

Weight (pcf)

Saturated Unit Weight

(pcf)

Friction Angle (deg)

0 to 13 Silty Sand (SM) / Poorly Graded Sand (SP) – Fill

20 115 130 32

>13 Silty Sand (SM) / Poorly Graded Sand (SP) – Native

30 115 130 32

Based on the DYA investigations, a friction angle of zero (0) and cohesion of 86,400 psf were estimated for the soil-cement revetment. The shear strength of the proposed miscellaneous fill material to be backfilled in front of the soil cement revetment was assumed to have the same shear strength parameters as the levee embankment fill material.

3.4 SOIL PERMEABILITY

Soil permeability tests were not performed on the DYA 2011 Investigation soil samples, but were performed on the DYA 2009 Investigation soil samples. DYA estimated the vertical permeability (Kv) in their 2009 report using correlations suggested by Kozeny-Carmen. Table 2 summarizes the vertical saturated permeability (Kv) range of each soil layer, and provides the design vertical permeability (Kv) value used by DYA for each soil type in the seepage analyses.

In Section 5.4 a supplemental seepage analysis was performed by the LA District Geotechnical Branch as a part of this report. Based on the DYA 2009 Investigation a horizontal to vertical permeability ratio (Kh/Kv) of 5 and 10 were evaluated. However, a conservative value of Kh/Kv of 10 was considered in the supplemental analysis. Detailed saturated permeability calculations for each soil sample tested are presented in the DYA 2009 Investigation.

Table 2: Soil Permeability Summary

Soil Layer Vertical Permeability, Kv (feet/second)

Permeability Value1 Design Value

Embankment fill and the fill in front of the soil-cement 1.8 x 10-5 to 7.0 x 10-5 5 x 10-5

Native material 8.5 x 10-5 8.5 x 10-5 Soil Cement2 -- 3 x 10-5 Notes:

1. Based on permeability correlations from the DYA 2009 Investigation

2. A lower value than the native soil was assigned

3.5 GROUNDWATER CONDITIONS

Groundwater was encountered at the time of drilling at depths ranging from 35 to 43 feet (these depths correspond to 267 and 255 feet MSL, respectively, as reported by DYA) below the levee crest (DYA 2011 Investigation). Groundwater was not encountered in the borings drilled for the DYA 2009 Investigation. Research utilizing the California Department of Water Resources (DWR) website (http://www.water.ca.gov/waterdatalibrary/index.cfm) shows the nearest well with publically available records to be within 0.3 miles from the project site (Well No.

10N33W16N001S). Based on the groundwater elevation data collected at this well, a groundwater depth was recorded at 40.5 feet bgs in 2005, corresponding to an approximate elevation of 292 feet MSL (based on the DWR website).

To be consistent with the previous investigations a design water level of 3 feet below the crest of the levee was considered for static stability and steady state seepage conditions. For pseudo-static and temporary stability conditions, a design groundwater level 20 feet below the river bed was assumed. It is possible that groundwater conditions at the site could change at some time in the future due to variations in rainfall, groundwater withdrawal, regional agricultural production, construction activities, or other factors not apparent at the time the test borings were drilled.

Fluctuations in the groundwater level could occur due to the irrigation of the surrounding agricultural land. Groundwater is not anticipated to have any effect on project design or construction. However, should excavations exceed a depth of 20 feet below the levee river-side toe, dewatering should be planned on.

SEISMIC/GEOLOGIC HAZARDS

The DYA 2009 Investigation has already performed seismic/geologic hazard analyses.

Therefore, this will be utilized in order to be consistent with the design of the project.

Consequently, the following seismic/geologic hazard analyses are based on the DYA 2009 Investigation.

Current USACE seismic design practice is outlined in ER 1110-2-1806. However, the LA District is in the process of updating those requirements in coordination with the Risk Management Center (RMC) and Headquarters (HQUSACE). Therefore, future seismic evaluations will need to incorporate those revised guidelines.

4.1 SURFACE FAULT RUPTURE

As discussed in 3.2 above, no known active faults are located within the project site boundaries, nor is the site located within a mapped earthquake fault zone (also known as an Alquist-Priolo Earthquake Fault Zone) (APEFZ; CDMG, 1999). Therefore, the possibility of surface rupture at the project site is considered low.

4.2 GROUND ACCELERATION

The site, like most of Southern California, will be subject to strong ground shaking during major earthquakes. The peak ground acceleration (PGA) considered for the design was based on an earthquake with a 475-year average return period (10 percent probability of exceedence in 50 years), and was estimated using the available USGS (2008) Probabilistic Seismic Hazard Assessment (PSHA) model. The PSHA model indicated a PGA of 0.26g expected at the site for a 475-year return period. A modal moment magnitude (Mw) and modal hypocentral distance for the design earthquake located on the San Andreas Fault were estimated to be 7.8 and 38 miles

(61 kilometers), respectively, based on the deaggregation of the USGS PSHA model. A deaggregation plot for the design earthquake is presented in Appendix C. It was determined that the San Andreas Fault with an estimated Mw of 7.8 and a modal hypocentral distance of 38 miles (61 kilometers) would have a more significant impact on the liquefaction and seismic settlement analyses in Section 4.3 below.

The seismic parameters developed and summarized are only used to evaluate liquefaction, settlement and slope stability with a design earthquake corresponding to a 475-year average return period. However, with respect to the combi-wall segment, the slope stability does not include the temporary scour condition in which approximately 27 to 30 feet of soils are eroded (from the crest of the levee to scour elevation) and the combi-wall is to be inspected, repaired if needed, and grades restored. It is anticipated that the repairing period is temporary and will be less than a 12-month period, therefore, seismic design for such a short duration temporary condition is not recommended.

It should be noted that a slight change in location coordinates was utilized in the ground acceleration analysis for this analysis with respect to the DYA 2009 Investigation. This is because the DYA 2009 Investigation also included a more specific Santa Maria Levee coordinate location and for this geotechnical appendix a more site specific coordinate location for the Bradley Canyon Levee was used. Although there was a slight change to the location coordinates this did not change the peak ground acceleration compared to the DYA 2009 Investigation.

However, the recent location resulted in a change of the modal hypocentral distance from 38.5 miles to 38 miles (62 kilometers to 61 kilometers, respectively).

4.3 LIQUEFACTION AND SEISMIC SETTLEMENT

DYA calculated soil liquefaction and seismically induced settlement potential based on subsurface data in their 2009 report, but did not provide similar calculations in their 2011 report.

This section evaluates liquefaction and seismically induced settlement potential utilizing subsurface data from the DYA 2011 Investigation and summarizes the results of the DYA 2009 analyses.

The potential for soil liquefaction at the site was evaluated using procedures recommended by Youd et al. (2001) and Boulanger et al. (2003; 2006), which summarize recent advances in liquefaction engineering topics based on recent databases. The liquefaction analyses were based on a PGA of 0.26g, a corresponding earthquake moment magnitude of 7.8, and a design groundwater depth approximately 20 feet below the existing river bed. Critical SPT N-values below which soil liquefaction is likely to occur were calculated for the design-level earthquake.

Based on the analyses, some of the loose to medium-dense sands and silts below the groundwater are anticipated to liquefy as a result of the design-level earthquake. Table 3 below summarizes the potentially liquefiable soil zones.

Table 3: Summary of Potentially Liquefiable Zones

Location Depth to Potentially Liquefiable Soils (feet)1

DYA09-01 33 to 38 DYA09-02 34 to 40 DYA09-03 38 to 43

DYA11-01 --2

DYA11-02 35 to 46

DYA11-03 --2

DYA11-04 --2

DYA11-05 --2

Note:

1. Measured from crest of levee.

2. Potentially liquefiable soil not encountered and settlement presented is seismically-induced dry sand settlement.

Another type of seismically induced ground failure, which can occur as a result of seismic shaking is seismic settlement. Calculations for liquefaction and dry sand settlement, attached in Appendix D, indicated a combined (liquefaction and dry sand) settlement of up to approximately 4-inches.

Seismically induced settlements at each boring location are summarized in Table 4. Additional details of potentially liquefiable soils and seismically induced settlement evaluation analysis are presented in Appendix D.

Table 4: Summary of Seismically Induced Settlements

Location Seismically Induced Settlement

(inches) Total1

DYA09-01 3

DYA09-02 1

DYA09-03 1

DYA11-01 3

DYA11-02 4

DYA11-03 2

DYA11-04 3

DYA11-05 2

Notes:

1. Includes liquefaction induced settlement and seismically induced dry sand settlement.

4.4 LATERAL SPREADING

Liquefaction-induced lateral spreading is defined as the finite, lateral displacement of gently sloping ground as a result of pore pressure buildup, or liquefaction in shallow underlying deposits during an earthquake. Liquefaction beneath moderate to steep slopes such as levees can result in extensive flow slides involving tremendous downslope movements of completely broken soil over relatively long distances. However, the liquefaction analysis indicated that liquefaction occurs at the site at depths well below the fill embankments and along zones that are laterally discontinuous. Therefore, lateral spreading of the fill embankments is considered low.

GEOTECHNICAL ANALYSIS

Geotechnical analyses (e.g. seepage and slope stability) for the proposed project were performed by DYA based on the DYA 2009 Investigation. Additional geotechnical analyses was performed by the LA District’s Geotechnial Branch based on data provided in the DYA 2011 Investigation and where appropriate. This was performed to be consistent with the analysis performed for the DYA 2009 Investigation. Consequently, the subsequent sections provide geotechnical analyses in addition to what has already been performed for the project.

The DYA 2009 investigation did not provide analyses for the transient seepage condition and the associated slope stability. However, the steady state condition was analyzed. Evaluating the levee due to the steady state condition produces a higher exit gradient when compared to the transient condition, therefore, the evaluation due to the steady state condition is considered conservative. To be consistent with the DYA 2009 analyses additional seepage and slope stability analyses were performed using the steady state condition.

5.1 SELECTION OF CRITICAL CROSS SECTIONS USED IN DESIGN

Cross sections at Stations 355+00, 358+00, and 380+00, were selected to represent the critical areas for seepage and slope stability on the levee. Factors taken into account in selection of the cross section locations include embankment height, slope gradient, and the elevation difference between the design water surface elevation (WSE) and the crest of the levee. Other factors in the selection of the cross section locations include the position and depth of the sheet pile segment in relation to the levee. A detail of the cross sections with station numbers and subsurface geologic conditions are shown on Appendix A, Sheet G7. The locations of the cross sections analyzed are shown on Appendix A, Sheets G1 through G6. A brief description about these three cross sections is presented below.

Cross Section 1-1’ at Station 355+00 (Combi-wall segment)

: a width of 14 feet at the crest of the levee, 10-foot high on river-side and 13-foot on land-side, with an approximate slope gradient of 1.5H:1V on the river-side and 2.5H:1V on the landside.

Cross Section 2-2’ at Station 358+00 (Soil cement segment)

: an approximate width of 12.5 feet at the crest of the levee, 11-foot high on river-side and 8.5-foot high on landside, with an approximate slope gradient of2H:1V on the river-side and 3H:1V on the landside.

Cross Section 3-3’ at Station 380+00 (Soil cement segment)

: an approximate width of 13 feet at the crest of the levee, 10-foot high on river-side and 6-foot high on landside, with an approximate slope gradient of 2H:1V on the river-side and 2.5H:1V on the landside.

5.2 SOIL PARAMETERS

The soil parameters utilized in the seepage and slope stability analysis were based on the borings drilled during the DYA 2011 investigation. The cross sections were modeled under saturated permeability conditions, using the design permeability values provided the DYA 2009 Investigation. The soil parameters listed in Table 5 below were utilized in the seepage and slope stability analysis.

Table 5: Seepage Analysis Soil Parameters

Soil Description Soil Type Unit Weight (pcf)

Soil Friction Angle

(degrees)

Cohesion (psf) kv(ft/s)

Embankment Fill Silty Sand (SM) 115 32 0 0.00005

Miscellaneous Fill Poorly Graded Sand with Silt (SP-SM) 115 32 0 0.00005

Soil Cement Revetment -- 145 0 86,400 0.00003

Native Material Silty Sand

(SM)/Poorly Graded Sand (SP)

115 32 0 0.0001

5.3 SCOUR

A scour depth of 15 feet below the elevation of the lowest flow level of the river (thalweg) was assumed based on the attached Hydrology and Hydraulics Appendix. Verification of this assumption in design phases is critical as it directly relates to the conditions modeled for this

DDR.

5.4 SEEPAGE ANALYSIS

A seepage analysis was previously performed for the proposed project based on the attached DYA 2009 Investigation. The analysis was performed to evaluate the potential for piping at the toe of the embankment due to excessive hydraulic gradients caused during a design-level flood event. Based on the DYA 2009 Investigation it was considered that the potential for piping at the toe of the embankment is considered minimal.

The U.S. Army Corps of Engineers (USACE) performed a refined seepage analysis based on the more recent and site specific DYA 2011 Investigation. Seepage analysis was performed on three

(3) cross sections (Cross Section 1-1’, Cross Section 2-2’, and Cross Section 3-3’) to evaluate the steady-state groundwater flow conditions through the levee embankment during a design-level flood event. Section 5.1 provides descriptions of each of the cross sections.

Seepage analyses were performed using the computer program SEEP/W 2001 (GEO-SLOPE, 2007). SEEP/W analyzes seepage flow through saturated and unsaturated soil media under steady-state and transient flow conditions using the finite-element method of analysis. The program is capable of producing pore pressure, pressure head, and total head distributions across a soil profile under given flow conditions, and can also estimate flow gradients across individual elements of the discretized mesh.

Steady state seepage analysis was conducted as part of this DDR to be consistent with analyses performed on downstream segments of the Santa Maria River Levee. However, if steady state conditions develop, a water differential height developed during a rapid drawdown condition (water on the landside and scour and drawdown on the channel side) would impart structural demands on the combi-wall system that for a design, would be costly and uneconomical. As such, the Geotechnical Branch performed a transient seepage analysis in an effort to model a more appropriate seepage condition to be utilized for structural design. In addition, based on the Hydrology and Hydraulic Appendix the runoff in the Santa Maria Watershed is termed as “flashy” because it attains its peak, or maximum flow, in a few hours and subsides with similar rapidity. Because the climatic and drainage area characteristics are not conductive to continuous runoff, very little stream flow occurs except during and immediately following rainfall. As such transient seepage analysis was determined to be a more appropriate approach. The transient seepage analysis mentioned above and subsequent findings are presented in Appendix H.

5.4.1 Seepage Results

Based on the design-level flood event, the groundwater level used for the seepage analyses was taken at 3 feet below the crest of the levee for each cross section. Based on the DYA 2009 investigation a Kh/Kv of 5 and 10 were evaluated. However, a conservative value of Kh/Kv of 10 was considered for this analysis. A summary of the maximum hydraulic gradients for each cross section for Kh/Kv permeability ratio of 10 is provided in Table 6. The results of the seepage analysis are provided in Appendix E. Also included in Appendix E are the seepage results from the DYA 2009 Investigation.

Table 6: Summary of Seepage Analyses

Location Exit Gradient1 Factor of Safety Against Sand Boiling/Piping

Cross Section 1-1’ 0.28 3.8 Cross Section 2-2’ 0.3 3.6 Cross Section 3-3’ --2 --2 Cross Section 3-3’3 0.35 2.8

Notes:

1. Steady seepage state with the assumed water level at an approximate depth of 3 feet below the levee crest level.

2. No exit gradient on land side.

3. Based on the DYA 2009 Investigation.

USACE EM 1110-2-1913 does not provide minimum FS requirements against piping/sand boiling. Therefore, a minimum FS of 2 was adopted for the current design based on the recommended value provided in U.S. Navy Design Manual 7.1. Based on our analyses, the potential for sand boiling/piping at the toe of the embankment is considered minimal.

5.5 SLOPE STABILITY

Slope stability analyses previously performed for portions of the Bradley Canyon Levee are presented in the DYA 2009 Investigation and are in Appendix F. Based on the DYA 2009 Investigation, the slopes under varying conditions were considered to be stable.

Supplemental slope stability analyses were performed by the LA District based on the critical cross sections specified in Section 5.1. The analyses utilized the same computational methods as was performed in the DYA 2009 Investigation. The temporary stability of the levee slopes during construction was analyzed. In addition, the stability of the permanent slopes was analyzed for the following conditions:

• Levee under steady-state seepage conditions,

• Full scour conditions with the upstream grades similar to short term excavation near the levee toe area with groundwater approximately 20 feet below channel grade.

• Short-term seismic (pseudo-static) condition with the groundwater approximately 20 feet bgs

The required minimum factor of safety (FS) for the slope stability analyses are summarized in Table 7.

Table 7: Minimum Slope Stability Factor of Safety Stability Condition Minimum Factor of Safety

Long-term static stability of levee under steady-state seepage conditions 1.41

Scour condition at the toe of the levee 1.1-1.32 Temporary stability during excavation Short-term seismic (pseudo-static) conditions 1.12 Notes:

1. Based on USACE EM 1110-2-1913.

2. Based on standard of practice.

5.5.1 Analysis Methodology

Analyses were performed using the computer program SLOPE/W (GEO-SLOPE, 2007).

SLOPE/W calculates the FS for slope stability by using two-dimensional, limit equilibrium analysis methods. The Spencer method which satisfies both force and moment equilibrium, was used in the analyses for this appendix to the DDR. The computed pore-water pressures from SEEP/W as described in Section 5.4 were incorporated in the stability analyses.

Cross Section 1-1’ through Cross Section 3-3’, as described in Section 5.1, represent the critical areas for slope stability at the site. Design strength parameters for soil and soil-cement used in our analyses are discussed in Section 5.2.

5.5.2 Summary of Results

Based on the results of the stability analyses performed, both the combi-wall segment and the portion to receive the soil cement revetment of the levee is stable under static, pseudo-static and steady-state loading conditions.

Results of the slope stability analyses are summarized in Table 8. Plots of the analysis results are shown on Appendix F. Also included in Appendix F is the slope stability analysis performed for the DYA 2009 Investigation. Following the recommended procedure in the Guidelines for Implementing the State Special Publication No. 117 (Blake et al., 2002), the seismic coefficient is estimated to be 0.15g to be applied horizontally in the SLOPE/W model. The calculated pseudo-static factor of safety is at least 1.1 for an earthquake having a return period of 475 years.

This factor of safety meets the requirement as presented in Table 8.

Table 8: Summary of Slope Stability Analysis

Cross Section1

Permeability Ratio (kh/kv)

FS for Static Loading

Conditions (river-side)2

FS for Static Loading

Conditions (land side)2

FS for Psuedostatic

Loading Conditions (river-side)3

FS for Psuedostatic

Loading Conditions (land side)3

FS for Temporary Excavation and Scour Condition

FS for Rapid Drawdown Condition

1-1’ 10 2.0 1.4 --7 --7 --7 1.2 2-2’ 10 6.5 1.4 3.04 1.14 1.24,5 1.0 3-3’ 10 4.2 1.6 2.74 1.14 1.34,5 1.0

3-3’8 5 5.1 1.5 2.94 1.34 1.34,5 -- 10 5.2 1.4 --4 --4 --4 --

Notes:

1. See Appendix A, Sheets G4 through G6 for cross section location.

2. Steady state seepage considered for static loading conditions based on a design water level of 3 feet below levee crest.

3. A horizontal seismic coefficient (k) of 0.15g was used based on SCEC…