Santa Anita Canyon Site 2 Geotech Design Report_Final.pdf

SUBMITTED TO:

Jacobs Engineering Group, Inc.

9191 Jamaica Street Englewood, CO 80112

BY:

Shannon & Wilson, Inc.

100 North First Street, Suite 200 Burbank, CA 91502

(818) 543-4560 www.shannonwilson.com

GEOTECHNICAL DESIGN REPORT ADDENDUM NO. 2

CA FLAP LA CR2N40 (1)

SANTA ANITA CANYON ROAD SITE 2 EARTH RETAINING

STRUCTURE, LOS ANGELES COUNTY, CALIFORNIA

September 19, 2022

Shannon & Wilson No: 106401-003

Geotechnical Design Report Addendum No. 2

106401-003 September 19, 2022

PAGE INTENTIONALLY LEFT BLANK FOR DOUBLE-SIDED PRINTING

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Submitted To: Jacobs Engineering Group, Inc.

Subject:

9191 Jamaica Street Englewood, CO 80112 Attn: Berwyn Wilbrink

GEOTECHNICAL DESIGN REPORT ADDENDUM NO. 2, CA FLAP LA

CR2N40 (1), SANTA ANITA CANYON ROAD SITE 2 EARTH

RETAINING STRUCTURE, LOS ANGELES COUNTY, CALIFORNIA

Shannon & Wilson prepared this report and participated in this project as a subconsultant to Jacobs Engineering Group, Inc. (Jacobs). Our scope of services was specified in Professional Services Task Order Number 148035062 of Professional Services Master Agreement Number 148029282.

This report is Addendum No. 2 to our Geotechnical Design Report (Shannon & Wilson 2016a) for the project. We previously issued Addendum No. 1 (Shannon & Wilson, 2016b) to the report. This addendum presents additional subsurface explorations and laboratory testing results and provides geotechnical design criteria for the proposed earth retaining structure at Santa Anita Canyon Road at Site 2.

This is the final version of Addendum No. 2. We updated this addendum to provide the results of additional subsurface exploration and incorporate resolutions to review comments from the design team and the County of Los Angeles Department of Public Works, Geotechnical and Materials Engineering Division.

We appreciate the opportunity to be of service to you on this project. If you have questions concerning this addendum, or we may be of further service, please contact us.

Sincerely, SHANNON & WILSON, INC.

Stephen D. Diem PE, GE, PG, CEG Gregory R. Fischer, PhD Associate President

SDD: GRF/ady g

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CONTENTS

1 Project Information

2 Site Conditions

3 Subsurface Data

3.1 Subsurface Exploration

3.2 Laboratory Testing

3.3 Subsurface Data by Others

4 Subsurface Conditions

5 Conclusions and Recommendations

5.1 Mechanically Stabilized Earth Retaining Walls

5.1.1 Seismic Design Criteria

5.1.2 Global Stability

5.1.3 External Stability and Settlement

5.1.4 MSE Wall Geometry

5.2 Secant Pile Wall

5.2.1 Design Recommendations

5.2.1.1 Lateral Earth Pressures

5.2.1.2 Tiebacks

5.2.1.3 Axial Capacity

5.2.1.4 Long-Term Slope Surface for Design

5.2.2 Construction Considerations

5.3 Drainage

5.4 Temporary Excavations

6 Closure

7 References

Exhibits

Exhibit 2-1: General Site Conditions Exhibit 2-2: Existing Gabion Wall and Fill Slopes Exhibit 5-1: Ground Motion Parameters Exhibit 5-2: Summary of Material Shear Strengths v

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Figures

Figure 1: Vicinity Map Figure 2: Site and Exploration Plan, Site 2 Figure 3: Geologic Cross Section A-A’ Figure 4: Geologic Cross Section B-B’ Figure 5: Lateral Earth Pressures for Secant Pile Walls Figure 6: Recommended Surcharge Loading for Walls

Appendices

Appendix A: Subsurface Explorations Appendix B: Laboratory Testing Appendix C: Subsurface Data by Others Appendix D: Slope Stability Analyses Important Information

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1 PROJECT INFORMATION

This addendum provides geotechnical design criteria and construction considerations for a retaining structure along the outboard side of Santa Anita Canyon Road through Site 2, starting at an existing gabion wall. Our understanding of the improvements is based on:

Preliminary plans (Jacobs, 2017a, 2022)

Site 2: Debris and Sediment Basin Clarification memorandum (Jacobs, 2017b)

Los Angeles County FLAP Project: Santa Anita Canyon Road meeting summary (Jacobs, 2020)

Our communication with representatives of Jacobs and the County of Los Angeles Department of Public Works, Geotechnical and Materials Engineering Division (GMED)

The proposed improvements have evolved since the beginning of the project. The original Santa Anita Canyon Road project, as described in Shannon & Wilson (2016a), only included drainage crossing improvements at Site 2. The drainage crossing improvements consisted of constructing an attenuation basin with walls and cut slopes upslope of the roadway, and the installation of a pipe to transport water beneath the roadway to a flume drain outlet into the existing drainage channel. In February 2019, a storm event eroded a portion of the descending fill slope that supports Santa Anita Canyon Road through Site 2, adjacent to the existing gabion wall. Subsequently, GMED conducted a geotechnical investigation to provide design parameters for a secant pile wall to support the outboard side of the roadway. In December of 2020, the design team considered several retaining structure types to stabilize the outboard side of the roadway through the eroded portion of Site 2 (Jacobs, 2020). From those considered, the design team decided to evaluate two alternatives: 1) secant pile wall and 2) mechanically stabilized earth (MSE) wall.

We understand the top of the planned wall will be located to provide a roadway width of 15 feet from the proposed centerline and to allow for a 12-foot-wide lane, 1-foot-wide guard rail, and 2-foot-wide shoulder. If an MSE wall is selected, the bottom of the wall will coincide with the bottom of the existing gabion wall, with matching face batter. If a secant pile wall is selected, the wall will be vertical with the top located as indicated above.

We performed our study in accordance with the U.S. Department of Transportation, Federal Highway Administration (FHWA), Project Development and Design Manual (PDDM) (FHWA, 2012). Because the proposed basin and roadway are County of Los Angeles facilities, we performed our geotechnical analyses in accordance with County of Los Angeles guidelines (2013, 2020).

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2 SITE CONDITIONS

Beginning at Arno Drive in the residential developments of Sierra Madre, Santa Anita Canyon Road winds northward through mountainous terrain to the Chantry Flats parking lot and trail head. Site 2 is on Santa Anita Canyon Road, at the location shown in the Vicinity Map, Figure 1. At this location, the roadway crosses over canyon fill that was placed across a natural drainage. The existing grade inboard of the roadway rises at a gentle gradient where it joins the sloping natural topography. A guardrail and earthen berm are located on the inboard side of the roadway. The outboard side of the roadway is a steep fill slope that joins the natural topography below. Steep cut slopes are present on the inboard side of the roadway preceding and following the filled area of Site 2. These general site conditions are shown in Exhibit 2-1.

The outboard side of the roadway is supported by the existing gabion wall and fill slope.

The gabion wall was designed as rock filled baskets that were 3-foot-wide by 3-foot-tall by 6-foot-long with a layer of geogrid at the base of each basket. The wall has a maximum height of 24 feet and batter of 4 vertical to 1 horizontal (4V:1H) (City of Arcadia, 2000). The geogrid reportedly extended from the face of the wall back between 12.5 and 13.8 feet (City of Arcadia, 2000). The gabion wall is shown in Exhibits 2-1 and 2-2.

Exhibit 2-1: General Site Conditions. View of Site 2 looking north. Drill rig is setup on boring B-20. The existing gabion wall and fill slope are supporting the outboard side of the roadway. A guardrail and berm are present on the inboard side of the roadway.

Exhibit 2-2: Existing Gabion Wall and Fill Slopes. View of Site 2 looking southwest. The existing gabion wall and fill slope are supporting the outboard side of the roadway.

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3 SUBSURFACE DATA

3.1 Subsurface Exploration

We completed subsurface explorations at Site 2 in four stages throughout the design. The year, purpose and explorations include:

2015: proposed drainage improvements

- Borings B-5 and B-6

2016: proposed attenuation basin walls and cut slopes

- Borings B-15, B-16, and B-17

- Test pits TP-1, TP-2, and TP-3

2021: proposed earth retaining structure options, MSE wall and secant pile wall

- Borings B-19 and B-20

2022: proposed secant pile wall depth to bedrock

- Borings B-21, B-22, B-23, and B-24

The Site and Exploration Plan for Site 2 (Figure 2) presents the approximate locations of our subsurface explorations. Appendix A provides the exploration logs, in addition to a description of our field preparations, drilling and sampling procedures, review and classification of samples, and provides exploration photographs for all our subsurface exploration at Site 2.

During drilling we collected grab samples, Standard Penetration Test (SPT) samples, and ring samples using a modified California sampler. We used samples collected during the field exploration program for laboratory testing.

3.2 Laboratory Testing

We completed geotechnical laboratory testing in accordance with Association of American State Highway Transportation Officials (AASHTO) testing methods on selected samples collected during our subsurface explorations. A description of the AASHTO test methods is provided in Appendix B. Laboratory tests that were performed include natural moisture content, dry density, grain-size analysis, Atterberg Limits, compaction test, direct shear, R-value, and chemical analyses for corrosion potential.

3.3 Subsurface Data by Others

We incorporated subsurface data from GMED Geotechnical Investigation at Site 2, which consisted of two borings and associated laboratory testing. We have added the GMED

106401-003 September 19, 2022 boring locations to Figure 2. Appendix C presents the GMED boring logs and laboratory test data.

4 SUBSURFACE CONDITIONS

Santa Anita Canyon Road through Site 2 is underlain by artificial fill. In general, the artificial fill consisted of very loose to medium dense, poorly graded sand and silty sand.

The artificial fill was underlain by bedrock that consisted of very weak weathered quartz diorite. Groundwater was not encountered in the subsurface explorations.

The interpreted distribution of the geologic materials from mapping is provided in the Site and Exploration Plan, Figure 2. We generated two geologic cross sections to illustrate our interpretation of the subsurface conditions. Cross section A-A’ (Figure 3) is oriented along the presumed axis of the drainage channel. Cross section B-B’ (Figure 4) is oriented along the proposed wall alignment. In cross section A-A’, we interpret the thickest section of artificial fill will be located beneath the top of the fill slope. As indicated, we interpret that the fill thickness decreases towards the northwest and southeast, where it joins the natural hillside terrain. In cross section B-B’, the interpreted thickest section of artificial fill is in the vicinity of boring B-20. The interpreted fill thickness decreases toward the southwest and northeast.

Our description of the subsurface conditions in the cross sections is interpreted from materials observed in the explorations. Variations between the interpretation shown and actual conditions will exist.

5 CONCLUSIONS AND RECOMMENDATIONS

This section provides geotechnical design criteria for evaluation of the MSE wall and secant pile wall alternatives to support the roadway. Because ground conditions, including top-of-bedrock, are highly variable across the project site, Shannon & Wilson should review the alternative wall designs as they are developed by the project team for conformance with our design assumptions.

Note that gravity walls, such as an MSE wall, are not typically used to expand the shoulder of an existing roadway located on deep deposits of artificial fill. At this site, the fill is very loose to medium dense and (based on the relative density from in situ testing) was not likely placed in a controlled manner (e.g., it was likely non-engineered). Typically, all non-engineered fill would be removed below an MSE wall footprint prior to constructing the wall. We do not know if this design/construction approach was used to install the existing

106401-003 September 19, 2022 gabion wall or not. Constructing a gravity wall on very loose to medium dense undocumented fill has inherent risks that should be considered by the design team and project owner.

5.1 Mechanically Stabilized Earth Retaining Walls

We evaluated the geometry and design parameters for an MSE wall to expand the outboard shoulder of Santa Anita Canyon Road through Site 2. MSE wall construction would consist of removing the existing roadway embankment to the bottom-of-wall elevation using temporary slopes around the wall excavation and then progressively installing layers of reinforcement and fill until the roadway grade is restored. Because of the thickness of artificial fill (up to approximately 40 feet), we assumed that all artificial fill could not be removed. We developed our conclusions and preliminary recommendations for the MSE wall in accordance with the PDDM and County of Los Angeles (2013) using guidance from the FHWA (Berg and others, 2009). The purpose of our analyses was to determine the minimum width of the reinforced zone to satisfy the required factor of safety values for external and global stability.

For our analyses, we assumed the following:

4V:1H face batter to match the existing gabion wall

24-foot-tall wall height to match the existing gabion wall

2-foot embedment below a bench in front of the wall

250 and 125 pounds per square foot (psf) traffic surcharge (for static and seismic global stability)

Drained shear conditions

No hydrostatic water pressure on the wall

No groundwater at the site (although we assumed the basin may temporarily fill after a rain event, we assumed this water will not infiltrate into the subgrade)

Base of the MSE reinforcement zone excavation is prepared in accordance with Section

7.2.4 of our Geotechnical Design Report for the Santa Anita Canyon Road Improvements (Shannon & Wilson, 2016a)

The results of our analyses indicate that a minimum reinforcement length equal to 2H (2 times the height of the wall) is needed to satisfy global stability, which is the critical design case. The internal stability and potential compound failures should be evaluated by the MSE wall designer and submitted for review prior to construction. Note that reinforcement lengths of twice the wall height are highly unusual and further indicate that a MSE wall is

106401-003 September 19, 2022 not ideal for this site. In addition, such lengths would extend well beyond the roadway limits and make any temporary detour difficult.

5.1.1 Seismic Design Criteria

We developed seismic design inputs for the MSE wall based on seismic design criteria in AASHTO (2020), which incorporates the 2014 United States Geological Survey (USGS) ground motion model (Peterson and others, 2014). The AASHTO (2020) criteria is for ground motions with a 7% probability of exceedance in 75 years (975-year return period).

We used interactive online maps by the USGS to evaluate the onsite ground motions for a Site Class D condition. We evaluated site class based on SPT N-values and soil/rock type found in the subsurface explorations.

Exhibit 5-1: Ground Motion Parameters

Period Mapped

Coefficients

Site Adjustment

Factor

Ground Motion

Parameter

Peak Ground Acceleration (PGA) PGA = 0.59 FPGA = 1.00 As = 0.59

Short Period (T = 0.2s) SS = 1.39 Fa = 1.00 SDS = 1.39

Long Period (T = 1.0s) S1 = 0.43 Fv = 1.57 SD1 = 0.68

NOTES:

s = seconds

AASHTO (2020) uses a horizontal seismic coefficient, kh, for pseudo-static global stability evaluation for wall design of one-half the As value. This design criterion conflicts with County of Los Angeles (2013), which uses a kh of 0.15, which is intended for slope design.

We used kh of 0.15 in our analysis for the MSE wall because the criterion is based on local experience and incorporates slope displacement mechanisms. AASHTO (2020) states their criterion is intended specifically for rigid walls, and that the criterion is conservative for MSE walls that can accommodate displacement.

5.1.2 Global Stability

We performed global slope stability analyses for the MSE wall using cross section A-A’ which was oriented along the presumed axis of the drainage and located to capture the deepest section of the existing artificial fill. We performed the stability analyses using two-dimensional limit equilibrium with the SLOPE/W tool in the GeoStudio software suite by Geo-Slope International. We evaluated the stability of existing and proposed conditions using circular failure surfaces with the Morgenstern-Price method of analysis.

We estimated the shear strength of subsurface materials using the results of previous laboratory testing (Geotechnical Soilutions, Inc., 2008), correlations using SPT N-values and

106401-003 September 19, 2022 material type, as well as back calculation of the existing conditions. The material shear strength properties used in our analyses are summarized below in Exhibit 5-2.

Exhibit 5-2: Summary of Material Shear Strengths

Geologic Unit Unit

Weight Cohesion

Angle of Internal Friction

Artificial Fill 125 pcf 150 psf 32

Reinforced Backfill 135 pcf 0 psf 36

Quartz Diorite Bedrock 125 pcf 840 psf 41

County of Los Angeles (2013) requires a minimum factor of safety of 1.50 and 1.10 for static and pseudo-static loading conditions, respectively. We performed our analyses by increasing the width of reinforcement behind the MSE wall face until our analyses yielded the required factors of safety. Based on our analyses, the MSE wall reinforcement should have a length of at least two times the height of the wall (e.g., 2H) and be spaced at two-foot intervals. The reinforcement should consist of TenCate Miragrid 20XT or approved equivalent.

Appendix D presents output figures from our slope stability analyses. The figures include the existing condition (i.e., back calculation assuming an existing factor of safety of 1.1), static and pseudostatic loading with the basin empty (permanent condition), and basin full of water (temporary condition).

5.1.3 External Stability and Settlement

External stability will be required for the proposed MSE wall. However, based on a reinforced length of twice the wall height, we do not anticipate that external stability will control the design.

We estimated the total settlement for the proposed MSE wall will be approximately 1 inch and be maximum near the face of the wall. We anticipate the top of bedrock will be near the heel of the MSE wall reinforced zone and settlement of the wall foundation on bedrock will be negligible. Therefore, the differential settlement across the width of the reinforced zone will be equal to the total settlement of the wall portion on soil. We anticipate the top of bedrock will be encountered in the MSE wall excavation toward the northeastern end;

therefore, the differential settlement along the MSE wall will be equal to the total settlement across the distance from the southwestern end of the wall to where the wall is supported on bedrock. We anticipate this distance will be about 50 feet.

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5.1.4 MSE Wall Geometry

The base of the MSE wall should coincide with the base of the existing gabion wall and maintain a constant elevation laterally along the wall until bedrock is encountered towards the northeast end. Where bedrock is exposed, the base elevation may be stepped up. The steps should be excavated into bedrock and have a height of two feet to match the reinforcement spacing. As the base elevation steps up, the height of the wall will be reduced. The reinforcement length of 2H should be maintained with the reduction in wall height. Where bedrock is encountered, the reinforcement length may be reduced (see recommendations below). The MSE wall batter should match the batter of the existing gabion wall.

For the MSE wall, we recommend the following:

Reinforcement:

- Type = TenCate Miragrid 20XT or approved equivalent

- Vertical spacing = 2 feet

- Length = 2H, starting at face of MSE wall and extending toward inboard side of roadway. Where bedrock is encountered before 2H, the reinforcement length may be reduced so that it extends past the fill to bedrock contact by at least 1 foot. However, the reinforcement length should not be shorter than 0.7H.

Backfill:

- Reinforced zone material = FP-14 section 704.08, select granular backfill (FHWA, 2014)

- Placement = FP-14 section 209.09 (FHWA, 2014)

- Compaction = FP-14 section 209.10 (FHWA, 2014)

5.2 Secant Pile Wall

A secant pile wall can be used to support the outboard side of Santa Anita Canyon Road through Site 2. We used geologic cross section A-A’ to develop recommendations for the proposed secant pile wall. The purpose of our analyses was to determine the lateral earth pressures, axial capacity, and tieback anchor capacity to be provided for design of the secant pile wall.

For our analyses, we assumed the following:

Maximum vertical exposed face of 24 feet

Drained conditions

250 and 125 psf traffic surcharge (for static and seismic global stability)

Tiebacks will be required to support the wall

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AASHTO (2020) will be used to calculate the seismic earth pressure increment on the wall

Our secant pile wall analyses do not consider hydrostatic pressures from groundwater. To avoid the buildup of hydrostatic pressures behind the wall, the wall design should include drainage. Drainage recommendations are provided in Section 5.3.

5.2.1 Design Recommendations

The project structural engineer should use the following design recommendations to determine the secant pile diameter, depth, and reinforcement, as well as the locations and lengths of tiebacks needed for lateral resistance.

5.2.1.1 Lateral Earth Pressures

The secant pile wall will be subject to lateral earth pressures from retained soil and surcharge loads, including construction or vehicle traffic. We estimated the lateral earth pressures for apparent earth pressure conditions behind the wall because tiebacks will be used to provide lateral support. We estimated earth pressure coefficients for the static and seismic cases using the Rankine and Mononobe-Okabe equations. We provide lateral earth pressures for the secant pile wall design in Figure 5 and equations to evaluate surcharge loading on the wall in Figure 6.

In determining the seismic earth pressure, we considered a peak ground acceleration with a 7-percent probability of exceedance in 75 years, in accordance with AASHTO LRFD (2020) Section 3.10.1. We recommend the seismic increment be applied as a uniform load. This approach is considered conservative in AASHTO LRFD (2020), which states a “combined static/seismic resultant location (e.g., 0.4h to 0.5h) may be considered, since there is limited evidence the resultant could be higher, especially for walls in which the impact of failure is relatively high.” See AASHTO LRFD section C11.6.5.3 for a discussion of the location of the seismic earth pressure resultant force.

5.2.1.2 Tiebacks

We estimated the tieback anchor capacity using guidance from the FHWA-IF-99-015 and the parameters of the geologic materials on site (Sabatini and others, 1999). For the tieback anchor capacity, we recommend using the nominal bond strength provided in Figure 5, Note 9, for design. The value provided assumes the tieback bond zone is located in bedrock.

The bond zone should be at least 15 feet long with a maximum bond zone length of 40 feet.

The bond strength assumes all tiebacks are proof tested in accordance with Recommendations for Prestressed Rock and Soil Anchors (Post-Tensioning Institute, 2014).

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The distance to bedrock could be estimated using the contact illustrated in cross section A-A’. For those tiebacks not located along cross section A-A’, the distance to bedrock could be estimated using the elevation bedrock was observed in the borings drilled within the existing basin. For cost estimating purposes, we recommend adding at least 5 feet to the estimated tieback length.

We recommend a representative of Shannon & Wilson observe the tieback installation to confirm the specified embedment into bedrock has been achieved. We should also observe proof testing to confirm the tiebacks meet the acceptance criteria and are locked-off at the specified load.

5.2.1.3 Axial Capacity

The secant pile wall will be subject to vertical loads from the vertical component of ground anchors. We estimated axial capacity using guidance from AASHTO LRFD (2020) and the parameters of the geologic units on site. We recommend axial capacity be evaluated using a coefficient of skin friction (i.e., ktanδ) between piles and bedrock of 0.32 and end bearing of 50 kips per square foot (ksf). These are nominal values that should be multiplied by a resistance factor of 0.55 and 0.50, respectively. We recommend neglecting skin friction in the soil overburden. We recommend a minimum pile embedment of 10 feet into bedrock.

The depth to bedrock could be estimated using the contact illustrated in cross section B-B’.

For cost estimating purposes, we recommend adding at least 2 feet to the estimated pile length to reach bedrock to account for the distance between cross section B-B’ and the secant pile wall alignment.

We recommend a representative of Shannon & Wilson observe the secant pile installation to confirm the specified embedment into bedrock has been achieved.

5.2.1.4 Long-Term Slope Surface for Design

Design of the secant pile wall should consider the fill slope that will be located outboard of the proposed secant pile wall after construction, i.e., long-term slope surface for design.

This slope surface should take into consideration construction activities, such as tieback installation and erosion/deterioration of the fill slope. We suggest the long-term slope surface be based on the friction angle of the fill soil, 32 degrees. We have added our recommended long-term slope surface for design to cross section A-A’, Figure 3. The slope intersects the proposed secant pile wall at an elevation of approximately 1262 feet. We anticipate all tiebacks will be located above this elevation. This slope surface is also shown on Figure 5, Lateral Earth Pressures for Secant Pile Walls.

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5.2.2 Construction Considerations

Drilled shafts will be installed in a secant pile configuration. Construction of drilled shafts will require drilling through artificial fill and into very weak quartz diorite to provide the recommended embedment. Although we did not encounter difficult drilling in the bedrock, we anticipate the bedrock strength will increase with depth below the bottom of the borings.

The relative density and granular composition of the artificial fill at the site may necessitate the use of temporary excavation support during the drilling process. This could be accomplished by using temporary casing, drilling fluid, or a combination thereof.

5.3 Drainage

We recommend incorporating surface and subsurface measures to reduce the potential for water to flow over and erode the top of slope or infiltrate into the artificial fill. Finished grades should direct surface runoff away from the planned improvements and toward collection devices. The proposed basin should be designed to eliminate the potential for surface water to infiltrate the subgrade soils.

To reduce the potential for the buildup of hydrostatic pressure behind the MSE wall, we recommend installing a back drain at the heel of the reinforced zone. The back drain should consist of 4-inch diameter perforated PVC pipe, encased in gravel, and surrounded by a Class 2, Type E geotextile filter.

The secant pile wall should be drained, using weep holes or other methods, or designed for hydrostatic pressure. Drainage could also be provided by installing the non-structural secant piles to a depth just below the long-term slope surface for design, or one foot above the fill -bedrock contact, whichever is shallower. This approach would result in gaps in the wall below grade to allow unimpeded groundwater flow. If the wall is designed for hydrostatic pressures, the hydrostatic pressure should extend up to the level of the existing gabion wall backdrain or the existing ground surface, whichever is higher.

5.4 Temporary Excavations

We anticipate temporary excavations will be used during construction to provide access to the excavation to construct the MSE wall. The type of excavation support system selected for construction will depend on proposed depth of the excavation, proximity to existing structures, anticipated surcharge loads, and materials exposed during construction. For planning purposes, we recommend using the excavation criteria in U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) 29 CFR, Part 1926, Subpart P, Excavations (OSHA, 2022).

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Temporary, unbraced excavations should be sloped, as needed, to provide a safe, stable slope. Consistent with conventional construction practice, the Contractor should be responsible for temporary excavation slopes. The Contractor is continually at the site, can observe the nature and conditions of the subsurface materials encountered, and is responsible for the methods, sequence, and schedule of construction.

The County of Los Angeles (2013) requires a minimum factor of safety of 1.25 for temporary static condition. We assumed that 1V:1.5H temporary slopes will be needed to facilitate any excavation in the artificial fill. Steeper slopes should be possible in the bedrock.

6 CLOSURE

This addendum was prepared for the exclusive use of Jacobs and other members of the design team for specific application to this project. The preliminary recommendations in this addendum are provided to assist the design team in selecting and designing the wall for Site 2.

The analyses, conclusions, and recommendations contained in this addendum are based on our understanding of site conditions as they presently exist, and further assume that the explorations are representative of the subsurface conditions throughout the site; that is, the subsurface conditions everywhere are not significantly different from those disclosed by the existing explorations. Our addendum conclusions, and interpretations should not be construed as a warranty of subsurface conditions. If subsurface conditions different from those encountered in the explorations are encountered or appear to be present during construction, we should be advised at once so that we can review these conditions and reconsider our recommendations, where necessary. If there is a substantial lapse of time between the submission of this addendum and the start of construction at the site, or if conditions have changed because of natural forces or construction operations at or adjacent to the site, we recommend that we review our addendum to determine the applicability of the conclusions and recommendations.

Within the limitations of scope, schedule and budget, the analyses, conclusions and recommendations presented in this addendum were prepared in accordance with generally accepted professional geotechnical engineering principles and practice in this area at the time this addendum was prepared. We make no other warranty, either express or implied.

These conclusions and recommendations were based on our understanding of the project as described in this addendum and the site conditions as observed at the time of our explorations.

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The scope of our work did not include environmental assessments or evaluations regarding the presence or absence of wetlands, or hazardous or toxic substances in the soil, surface water, groundwater, or air, on or below or around this site, or for the evaluation or disposal of contaminated soils or groundwater should any be encountered.

7 REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), 2020, AASHTO LRFD bridge design specifications (9th ed.): Washington, D. C., AASHTO, 2 v.

Berg, Ryan R., Christopher, Barry R., Samtani, Naresh C., 2009, Design of and construction of mechanically stabilized earth walls and reinforced soil: Federal Highway Administration, Geotechnical Engineering Circular No. 11, FHWA-NHI-10-024 Washington D.C., 2v.

City of Arcadia, Public Works Services Department, 2000, Santa Anita Canyon Road, erosion repair, project no. 5233085, plans and specifications, dated July 24, 21 sheets and pages.

County of Los Angeles, 2013, Manual for the preparation of geotechnical reports: Report prepared by Geotechnical and Materials Engineering Division, County of Los Angeles, California, July 1, 163p: Available:

http://dpw.lacounty.gov/gmed/manual.pdf.

County of Los Angeles, Department of Public Works, Geotechnical and Materials Engineering Division, 2020, Administrative Manual, seismic earth pressures on retaining walls, S004.0, revised January 6, 2 p: Available:

http://dpw.lacounty.gov/gmed/permits/docs/policies/S004%20- %20Seismic%20Earth%20Pressures%20on%20Retaining%20Walls%207-18-17.pdf.

Geotechnical Soilutions, Inc., 2008, Update to geotechnical recommendations report for repair of landslides and distress to roadway along Santa Anita Canyon Road (Chantry Flat Road) in the City of Monrovia, California: Report prepared by Geotechnical Soilutions, Inc., Los Angeles, California, for the City of Monrovia, California, July 3, 106p.

Jacobs, 2017a, CA FLAP LA CR2N40(1), Santa Anita Canyon Road, Angeles National Forest, Los Angeles County: Plan prepared by Jacobs, Denver, Colorado, for U.S.

Department of Transportation, Federal Highway Administration, Central Federal Lands Highway Division, Lakewood, Colorado, printed May 5, 9 sheets.

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Jacobs, 2017b, CA FLAP LA CR 2N40(1) – Santa Anita Canyon Road, Site 2: Debris and Sediment Basin Clarification: Memorandum prepared by Jacobs, Denver, Colorado, for U.S. Department of Transportation, Federal Highway Administration, Central Federal Lands Highway Division, Lakewood, Colorado, May 5, 5 p.

Jacobs, 2020, LA County FLAP Project: Santa Anita Canyon Road: Meeting summary prepared by Jacobs, Denver, Colorado, for U.S. Department of Transportation, Federal Highway Administration, Central Federal Lands Highway Division, Lakewood, Colorado, December 1, 19 p.

Jacobs, 2022, CA FLAP LA CR2N40(1), Santa Anita Canyon Road, Angeles National Forest, Los Angeles County: Plan prepared by Jacobs, Denver, Colorado, for U.S.

Department of Transportation, Federal Highway Administration, Central Federal Lands Highway Division, Lakewood, Colorado, printed July 6, 6 sheets.

Petersen, M. D.; Moschetti, M. P.; Powers, P. M.; and others, 2014, Documentation for the 2014 update of the United States national seismic hazard maps: U.S. Geological Survey Open-File Report 2014-1091, 243 p.

Post-Tensioning Institute, 2014, Recommendations for prestressed rock and soil anchors (5th ed.): Phoenix, Ariz., Post-Tensioning Institute, 110 p.

Sabatini, P. J.; Pass, D. G.; and Bachus, R. C., 1999, Ground anchors and anchored systems:

Washington, D. C., U.S. Federal Highway Administration, report no. FHWA-IF-99- 015, Geotechnical Engineering Circular no. 4, 281 p.

Shannon & Wilson, Inc., 2016a, Geotechnical Design Report, CA FLAP LA CR2N40(1), Santa Anita Canyon Road Site Improvements, Los Angeles County, California: Report prepared by Shannon & Wilson, Inc., Glendale, California, job no. 23-1-01458-011, for Jacobs Engineering Group, Inc., Denver, Colorado, December 29, 108 p.

Shannon & Wilson, Inc., 2016b, DRAFT Addendum No. 1 to Geotechnical Design Report, CA FLAP LA CR2N40(1), Santa Anita Canyon Road Site Improvements, Los Angeles County, California: Report prepared by Shannon & Wilson, Inc., Glendale, California, job no. 23-1-01458-011, for Jacobs Engineering Group, Inc., Denver, Colorado, December 30, 65 p.

U.S. Department of Labor, Occupational Safety and Health Administration, accessed 2022, 29 CFR, Part 1926, Subpart P, Excavations, available from https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926SubpartPAppB.

106401-003 September 19, 2022

U.S. Department of Transportation, Federal Highway Administration, 2012, Federal Lands Highway Project Development and Design Manual, Chapter 6: U.S. Department of Transportation and Federal Highway Administration, available from https://flh.fhwa.dot.gov/resources/design/pddm/Chapter_06.pdf.

U.S. Department of Transportation, Federal Highway Administration, 2014, Federal Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14 English Units: U.S. Department of Transportation and Federal Highway Administration, available from http://flh.fhwa.dot.gov/resources/pse/specs/.

CALIFORNIA

F i l e n a m e

L a x f s v o l E

F L A

X s

S a n t a

A n i t a

C a n D r a f t i n g F

I G

V

I C

I N

I T

Y

M

A P d w

D a t e

L o g i n

L o u i s

L a r i o s

Sacramento

Los Angeles

FIG. 1

VICINITY MAP

Map adapted from aerial imagery provided by

Google Earth Pro, reproduced by permission granted by Google Earth ™ Mapping Service.

NOTE

Project

Location

TM

SCALE: 1"=4000'

4000 80002000

PROJECT

LOCATION

CA FLAP LA CR2N40(1)

Santa Anita Canyon Road Site Improvements

Los Angeles County, California

106401-003September 2022

AutoCAD SHX Text I-5

P

C

T

B-1

B-2

A

A'

Start Site 2

67+10

B-5 B-6

B-16

B-17

B-15 qd qd af

TP-1

TP-3

TP-2

qd

B-19

B-20 qd af qd

Qc

Qc

B-21

B-22

B-23

B-24

106401-003

FIG. 2

SITE AND EXPLORATION PLAN

SITE 2

F i l e n a m e

P

L A

X s

S a n t a

A n i t a

C a n D r a f t i n g F

S

I T

E

A

E

X P

L O

R A

T I O

N

M

A P r e v d t e g i n

L o u i s

L a r i s b f i

September 2022

SCALE: 1"=30'

30 6015

End Site 2

68+50

CA FLAP LA CR2N40(1)

Santa Anita Canyon Road Site Improvements

Los Angeles County, California

Existing Gabion Wall

Boring Approximate Location

(This Study)

Boring Approximate Location

(Shannon & Wilson, 2016 a, b)

Hand Auger Boring

Approximate Location

(Shannon & Wilson, 2016 a, b)

Boring Approximate Location

(County of Los Angeles, 2019)

Test Pit

Approximate Location

(Shannon & Wilson, 2016, b)

LEGEND

af qd

Artificial Fill

Quartz Diorite

Geologic Contact

Surficial Failure

GEOLOGIC UNITS

B

B'

PROPOSED

BASIN WALLS

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A

A p p r o x i m a t e l e v a t i o n n e t

M

S L

A'

A p p r o x i m a l e v a t i o n e t

M

S L

Road

C

L

Existing Ground

Surface

Intersection

Cross Section of B-B'

B-19

Basin Wall

Approximate

B-20

(Proj. 8' SW)

FIG. 3

GEOLOGIC CROSS SECTION A-A'

AT STATION 67+50

F i l e n a m e

P

L A

X s

S a n t a

A n i t a

C a n D r a f t i n g C r o s s s e c t i o n s d t e g i n

L o u i s

L a r i o s

1. See Figure 2 for Explanation

2. This subsurface profile is generalized from materials observed in borings. Variations may exist between this cross section and actual conditions.

NOTES

SCALE: 1"=30'

30 6015

50/5

USCS

Symbol

Groundwater

Standard Penetration Test

Blows/Foot or

Blows/Inches Driven

Grab Sample

Approximate Geologic

Contact

Bottom of Boring

B-7

(Proj. 22' NW)

Boring Designation

Projection Distance in

Feet and Direction

LEGEND

af qd

Artificial Fill

Quartz Diorite

GEOLOGIC UNITS

*See Boring Logs in Appendix A for additional details af qd

CA FLAP LA CR2N40(1)

Santa Anita Canyon Road Site Improvements

Los Angeles County, California

106401-003September 2022

Debris Basin

Assumed Long-Term Slope Surface for Design

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SDD

Text Box Face of Proposed Secant Pile Wall

SDD

Rectangle

SDD

Line

SDD

Line

SDD

Polygon

SDD

Line

Intersection of

Cross Section A-A'

B

A p p r o x i m a t e

E l e v a t i o n i n

F e e t

M

S L

B'

A p p r o x i m a t e

E l e v a t i o n i n

F e e t

M

S L

(Proj. 3' SE)

B-6

(Proj. 2' SE)

B-20

B-2

Approximate

Location of

Existing

Gabion Wall

B-21

B-22

(Proj. 2' NW)

B-23

(Proj. 3' NW)

B-24

(Proj. 8' NW)

50/6

50/6

B-1

FIG. 4

GEOLOGIC CROSS SECTION B-B'

F i l e n a m e

P

L A

X s

S a n t a

A n i t a

C a n D r a f t i n g C r o s s s e c t i o n s d t e g i n

L o u i s

L a r i o s

1. See Figure 2 for Explanation

2. This subsurface profile is generalized from materials observed in borings. Variations may exist between this cross section and actual conditions.

NOTES

SCALE: 1"=30'

30 6015

50/5

USCS

Symbol

Groundwater

Standard Penetration Test

Blows/Foot or

Blows/Inches Driven

Grab Sample

Approximate Geologic

Contact

Bottom of Boring

B-7

(Proj. 22' NW)

Boring Designation

Projection Distance in

Feet and Direction

LEGEND

af qd

Artificial Fill

Quartz Diorite

GEOLOGIC UNITS

*See Boring Logs in Appendix A for additional details qd

106401-003September 2022

CA FLAP LA CR2N40(1)

Santa Anita Canyon Road Site Improvements

Los Angeles County, California af qd

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GRAB

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50/5"

Fi le na m e:

C

:\U se rs \k w s\

D es kt op

\1

1-

Fi g.

LE

Ps

R ev

1.

dw at e:

8-

-2 og in : K

W S

RECOMMENDED EARTH PRESSURES

A B C

Active

LEGEND

Total Wall Height above long term slope surface for design, feet

Depths of Embedment of Strata, feet

Total Embedment Depth below long term slope surface for design, feet

Earth Pressure Factors; See Table

Active and Passive Earth Pressure Coefficients

Effective Friction Angle

Cohesion

Unit Weight of Soil, pcf

H

D1,D2

D

A, B, C...

Ka, Kp f' c g

The recommended pressure diagrams are based on a continuous wall system. For structural secant piles below the bottom of the non-structural piles, apply active pressure over the width of the piles and apply passive resistance over three times the diameter of the piles or the spacing of the piles, whichever is smaller.

Surcharge loads, including construction equipment loadings and traffic surcharges, are not included on this diagram. Surcharge loading is provided in Figure 6. The total lateral earth pressure is the sum of the appropriate active or at-rest earth pressure, surcharge pressure, and seismic pressure.

Active earth pressures assume the wall is allowed to deflect greater than 0.001(H).

All earth pressures are in units of pounds per square foot.

1.

2.

3.

4.

We have assumed drained conditions.

Passive pressures are nominal values. Apply a resistance factor of 0.75 and 0.67 to passive resistance for static and seismic conditions, respectively. Nominal passive pressures include a reduction factor of 1.5 for strain compatibility and account for the sloping ground in front of the piles.

Wall embedment (D) should be determined by satisfying horizontal static equilibrium about the bottom of the pile.

Minimum recommended embedment is 10 feet into bedrock.

Diagrams are not to scale.

Tiebacks should penetrate bedrock. Assume a nominal tieback bond strength of 10 kips per foot. This value should be confirmed by proof testing during construction. AASHTO (2020) recommends applying a resistance factor of 1 if proof tests are conducted during construction.

5.

6.

7.

8.

9.

NOTES

Passive --

LATERAL EARTH PRESSURES

FOR SECANT PILE WALLS

FIG. 5Geotechnical and Environmental Consultants

SHANNON & WILSON, INC.

106401-002

CA FLAP LA CR2N40(1)

Santa Anita Canyon Road Site Improvements

Los Angeles County, California

September 2022

Recommended Earth Pressures for Multiple Tieback Wall

Wall

SE

EARTH PRESSURE PARAMETERS

Ka g

(pcf)

0.31 115

- 140 f'

32o

41o

Kp

1.65

Fill

Bedrock

35 H

Bedrock

D1

D2

D

Fill

Wall

Long term slope surface for design

H1

Hn+1

3H1

3(Hn+1)

No L oa d

Zo ne fo r T ieb ac ks

Uppermost Tieback Aeq

A * H 1.5H - 12H1 - 12Hn+1

Aeq =

60°

190 D1 + 2000

230 D2 --

13 H

Lowermost Tieback

SE

SEISMIC

INCREMENT

c (psf)

Recommended Earth Pressures for Single Tieback Wall

Wall

PASSIVE

EARTH

PRESSURE

Bedrock

ACTIVE

EARTH

PRESSURE

B

D1

D2

D

C

Fill

H = elevation 1262 or bedrock, whichever is shallower

Wall

Long term slope surface for design

H1

3H1

3(H-H1)

No L oa d

Zo ne fo r T ieb ac ks

35' Min.

A

SE

SEISMIC

INCREMENT

PASSIVE

EARTH

PRESSURE

BC

60°

Tieback

Fill

A

ACTIVE

EARTH

PRESSURE

35' Min.

A

0.76

Fill

H = elevation 1262 or bedrock, whichever is shallower

(see Note 9) (see Note 9)

RECOMMENDED SURCHARGE

LOADING FOR WALLS

FIG. 6SHANNON & WILSON, INC.

F ile

C

U se rs

\jz b\

O n eD ri ve

S ha nn on

W ils o n In c\ D e sk to p\

R

G D

R A d d

N o

2\

D ra ft\ F ig u re s\

-0

F ig .6

S ur ch ar ge

.d at e:

1-

-2 ut ho r:

J Z

B

W a ll

PLAN VIEW

sH

HH

2.0B

) (psf) cos (1.1' = s s 2 q q

1.5B

D e p th

, Z

1.0B

0.0B

0.5B

W a ll

Z

Wall Line

= H s p s

L/B =

L/B = 0.25

L/B = 0.5 L/B = 1

UNIFORM SURCHARGE

H s s= (0.4)q pH =s q2 a b

< 15 FeetH

EARTH BERM

(psf)s q

(0.4) (H ) (g ) s

Note: y < 33°

H

H z=nH

Bottom of Excavation x = mH Q

Point Load in Pounds s (psf)H

ELEVATION VIEW

x = mH

H

Bottom of Excavation

W a ll z=nH s (psf)H

Line Load in Pounds/Foot lQ

B) LATERAL PRESSURE DUE TO LINE LOAD

i.e. NARROW CONTINUOUS FOOTING

PARALLEL TO WALL

C) LATERAL PRESSURE DUE TO STRIP LOAD

(b - sin b cos2a) (psf)

W a ll

W a ll s

W a ll

A) LATERAL PRESSURE DUE TO POINT LOAD

i.e. SMALL ISOLATED FOOTING OR WHEEL LOAD y

D) LATERAL PRESSURE DUE TO EARTH BERM

OR UNIFORM SURCHARGE

Bottom of Excavation

Bottom of Excavation

E) LATERAL PRESSURE DUE

TO ADJACENT FOOTING

0 0.5 1.0 q

L

B

NOTES

Figures are not drawn to scale.

Applicable surcharge pressures should be added to appropriate permanent wall lateral earth and water pressure.

If point or line loads are close to the back of the wall such that m £ 0.4, it may be more appropriate to model the actual load distribution (i.e., Detail E) or use more rigorous analysis methods.

W a ll

Bearing Pressure q (psf)

1.

2.

3.

I , Influence Factor

(I ) q p

Lateral Footing Pressure on Wall

(derived from NAVFAC DM 7.2, 1986; and Sandhu, Earth Pressure on Walls Due to Surcharge, 1974)

(derived from Poulos and Davis, Elastic Solutions for Soil and Rock Mechanics, 1974; and Terzaghi and

Peck, Soil Mechanics in Engineering Practice, 1967)

(NAVFAC DM 7.2, 1986)

(derived from Fang, Foundation Engineering Handbook, 1991)

(NAVFAC DM 7.2, 1986)

= 1.28 (psf)H

H

2m nlQ

(m + n )H 2 2 2

(0.16 + n ) lQ

H n

2 2 = 0.20 (psf) (see Note 3)For m < 0.4: s

For m > 0.4: s = 1.77 (psf)H

H

2m npQ

(m + n )H 2 2 3

(0.16 + n ) pQ

H

2n

= 0.28 (psf) (see Note 3)For m < 0.4: s

For m > 0.4: s p

Point Load in Pounds g = Unit Weight of Earth Berm s

Qp

Bearing Pressure

Earth Berm sH sH' s = Lateral PressureH sH' in radians

ELEVATION VIEW

s

(see Note 3) (see Note 3)

106401-003

CA FLAP LA CR2N40(1)

Santa Anita Canyon Road Site Improvements

Los Angeles County, California

September 2022

106401-003 September 19, 2022 A-i

A

PP

EN

D

IX

A

: S U

B

SU

R

FA

C E

EX

PL

O R

A

TI

O N

S Appendix A: Subsurface Explorations

Appendix A

Subsurface Explorations

CONTENTS

A.1 Field Preparations ................................................................................................................. A-1

A.1.1 Underground Utility Locates .................................................................................... A-1

A.1.2 Los Angeles County Coordination ........................................................................... A-1

A.2 Borings .................................................................................................................................... A-1

A.2.1 Backfill Procedures...................................................................................................... A-2

A.2.2 Sampling Procedures .................................................................................................. A-2

A.2.2.1 Sampling Interval ........................................................................................... A-2

A.2.2.2 Standard Penetration Test (SPT) .................................................................. A-3

A.2.2.3 Modified California Sampler (MCS) ............................................................ A-3

A.2.2.4 Rock Coring ..................................................................................................... A-4

A.3 Test Pits ................................................................................................................................... A-4

A.4 Review and Classification of Samples ................................................................................ A-4

A.4.1 Field Observations ...................................................................................................... A-4

A.4.2 Soil Classification System........................................................................................... A-5

A.4.3 Geologic Units and Descriptions .............................................................................. A-5

A.4.4 Exploration Logs ......................................................................................................... A-5

A.5 References .............................................................................................................................. A-5

Figures

Figure A-1: Soil Description and Log Key Figure A-2: Rock Classification Figure A-3: Log of Boring B-5 Figure A-4: Log of Boring B-6 Figure A-5: Log of Boring B-15 Figure A-6: Log of Boring B-16 Figure A-7: Log of Boring B-17 Figure A-8: Log of Boring…