CA.FLAP.SCR T5(1) (2).Monterey Bay Sanctuary Scenic Trail. Geotech Rpt FINAL.June 2023 with Appendic.pdf

MONTEREY BAY SANCTUARY SCENIC TRAIL

SANTA CRUZ COUNTY, CA

CA FLAP SCR T5(1) & (2)

FINAL Geotechnical Report

Prepared by Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch June 2023 ii

SIGNATURE SHEET

Report prepared by: ___________________________________________________________

Dominic Monarco, Geotechnical Engineer

Report reviewed by: ____________________________________________________________

James M. Arthurs, Ph.D., P.E., Senior Geotechnical Engineer

Approved for distribution by: _____________________________________________________

Devin Dixon, P.E., Lead Geotechnical Engineer

Digital Distribution

N:\CA\scrt5(1)\Geotech\7_FinalDocs

K:\TechServices\Geotech\1. Geotech Project Reports

Project Management

Project Development, Lead Designer

Technical Services, Hydraulic

DOMINIC J

MONARCO

Digitally signed by DOMINIC J

MONARCO

Date: 2023.06.27 12:17:37 -06'00'

DEVIN T DIXON

Digitally signed by DEVIN T

DIXON

Date: 2023.06.27 12:19:55 -06'00'

JAMES M

ARTHURS

Digitally signed by JAMES M

ARTHURS

Date: 2023.06.27 12:22:36 -06'00'

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TABLE OF CONTENTS

SECTION ONE - INTRODUCTION

1.1 Objective and Scope

1.2 Proposed Construction

1.3 Site Conditions

SECTION TWO - GEOLOGY AND SEISMICITY

SECTION THREE - SUBSURFACE INVESTIGATION

SECTION FOUR - ANALYSIS & RECOMMENDATIONS

4.1 Geotechnical Profile

4.1.1 Subsurface Material Parameters

4.1.2 Interpreted Groundwater & Soil Moisture Conditions

4.2 Embankments

4.2.1 Reinforced Soil Slopes

Armored Shotcrete Faced RSS

4.2.2 12

4.3 Permanent Cut Slopes & Crest Rounding

4.4 CUT SIDE ROCKERY DESIGN

4.4.1 Rockery analysis

4.5 Corrosion Potential

4.6 Construction Considerations

4.7 Disclaimer/Limitations Clause

SECTION FIVE - REFERENCES

TABLES

Table 1:- Estimated Material Parameters for Design Table 2:- Summary of Proposed RSS Dimensions & Slope Stability Table 3: -Summary of Proposed Cuts Table 4: - Recommended Safety Factors for Design of Rockeries Table 5- Material Properties used in the Analysis for Rockeries Table 6: - Minimum Required Rockery Geometry to Satisfy Safety Factors Table 7: - Minimum Base Rock Widths for Rockeries with a Given Height Table 8: - Rockery Base Width Requirements

FIGURES

Figure 1:- Railroad trestles beneath embankment along the trail alignment

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PLATES

Plate 1:- Vicinity Map Plate 2:- Project Location Map Plate 3:- Geologic Map Plate 4:- Regional Fault Map Plate 5:- Geologic Investigation Map

APPENDICES

APPENDIX A - “Monterey Bay Sanctuary Scenic Trail CA FLAP SCR T5 (1) & (2), Draft Geotechnical Data Report” July 2017

APPENDIX B - RSS Analysis APPENDIX C - Slope Stability APPENDIX D - Rock Rippability APPENDIX E- Rockery

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Monterey Bay Sanctuary Scenic Trail CA FLAP SCR T5(1) & (2) June 2023

SECTION ONE - Introduction

1.1 Objective and Scope

This report presents the results of the geotechnical investigation and analysis conducted for the Monterey Bay Sanctuary Scenic Trail, CA FLAP SCR T5 (1) and (2) project.

The Federal Highway Administration, Central Federal Lands Highway Division (FHWA- CFLHD), in cooperation with the Santa Cruz County Regional Transportation Commission (SCCRTC), is proposing the construction of a segment of the Monterey Bay Sanctuary Scenic Trail (MBSST) in Santa Cruz County, CA. The entire proposed trail network is about 50 miles broken up into several segments. The current proposed project is Segment 5 of the trail project. In 2012 SCCRTC took ownership of the 32-mile Santa Cruz Branch Railroad Line. Much of the proposed MBSST will run parallel to and within the railroad right of way.

The proposed project segment consists of constructing 7.4 miles of new multi-use trail for pedestrians and bicyclists north of Santa Cruz, CA alongside the existing rail line. The proposed trail and rail system parallels California Highway 1 beginning at Davenport, CA and proceeds south to the trail terminus at the Wilder Ranch State Park parking area. In addition, the proposed project includes improvements to the Yellowbank Beach parking lot and the Davenport parking lot. Improvements to pedestrian access to the trail from a third parking lot, the Bonny Doon parking area, are also planned.

This report summarizes the relevant findings of one previous investigation report and provides geotechnical recommendations pertaining to the 99 percent design plans dated December 2022.1 Pertinent field and laboratory information used in the development of the final recommendations were previously detailed in the following report, and must be read in conjunction with this report:

• U.S. Department of Transportation, Federal Highway Administration, Central Federal Lands Highway Division, Geotechnical Services Branch, “Monterey Bay Sanctuary Scenic Trail CA FLAP SCR T5 (1) & (2), Draft Geotechnical Data Report”, dated July 2017.

This data report is attached as Appendix A to this report.

1 U.S. Department of Transportation Federal Highway Administration Plans for Proposed CA FLAP SCR T5(1), Santa Cruz County, Length 7.3 miles. Preliminary 99 percent Plans Dated December 2022.

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1.2 Proposed Construction

The proposed project will construct a multi-use trail that includes an 8- to 12-foot-wide asphalt paved trail and a variable width unpaved, aggregate surfaced trail. As of the 99 percent design plans, dated December 2022, the typical trail cross section will be 20 feet wide and consist of the following:

• 12-foot asphalt paved path

• 6-foot aggregate path on the coastal side of the paved path

• 2-foot aggregate shoulder on the inland side of the paved path

The widths of the asphalt and aggregate shoulder portions of the trail will vary in locations to either accommodate farm equipment or to reduce impacts to resources.

In several locations, the existing railway bench will be widened using cuts or fills to accommodate the proposed trail. In these locations, fill slopes will be used depending on the geometry of the site and any sensitive resources in the area. Proposed trail widening and reinforcement includes common embankment fill slopes and reinforced soil slopes (RSS). RSS embankment fills require geosynthetic reinforcement, back drains, and rock shear keys to resist seepage forces and improve stability. RSS will be constructed to blend into the environment to the greatest extent possible.

Where RSS or embankments can be vegetated, native vegetation will be utilized.

1.3 Site Conditions

Monterey Bay Scenic Trail Segment 5 travels from Davenport to Wilder Ranch State Park parking area, approximately 3.5 miles outside of Santa Cruz. The trail traverses farmland, generally following the coastline, on dirt roads and parallels an abandoned rail line. Private landowners and CA State Parks occupy the properties on both sides of the trail. Both overhead and underground utilities run along the trail.

The rail line paralleling the MBSST was constructed by cutting through slopes and filling drainage areas with the cut material. Existing cuts in the project area generally range from 5 to 20 feet in height and have slope ratios that range from 1V:1.2H to nearly vertical. Fills have a maximum height of approximately 50 feet with slope ratios up to 1V:1.25H. Existing cuts are performing with obvious weathering, requiring re-grading and enhanced drainage. Fill areas are generally performing well apart from the fill slope near Station 33+00.

Near Davenport (approximately station 33+00 to 34+70) the embankment fill is actively failing due to wave action causing erosion at the embankment toe. The embankment fill was placed around a wooden trestle during the construction of the railroad. Sections of the embankment that remain vegetated do not show evidence of failure. Reinforcement of this section of fill is proposed to

Page | 3 stabilize the slope. In addition, the lower portion of the slope will be hardened with a shotcrete facing to reduce the potential for future erosion.

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SECTION TWO - Geology and Seismicity

Refer to Section Two of the Draft Geotechnical Data Report, (Appendix) for discussions on:

• Geology- Section 2.1

• Geologic Hazards- Section 2.2

• Seismicity- Section 2.3

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SECTION THREE - Subsurface Investigation Refer to Section Three of the Draft Geotechnical Data Report, (Appendix A) for discussions on:

• Subsurface Exploration Program- Section 3.1

• Laboratory Testing Program- Section 3.2

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SECTION FOUR - Analysis & Recommendations

The construction of the MBSST consists of extensive embankment work including reinforced soil slopes, permanent cut slopes, utility relocation, and drainage improvements. In addition, temporary cut slopes, shoring, and barriers may be required to maintain access through construction. Shoring needs are at the discretion of the contractor for a given site and the contractors elected construction methods.

Subsurface characterization and geotechnical profiles were developed based on the subsurface materials encountered during the subsurface investigations and laboratory test results of samples taken along the route for use in the design of cuts and fills. Recommendations regarding cut slopes and embankment fills, corrosion potential, material shrink/swell, and construction considerations are discussed in the following sections. All foundations and structures are designed in accordance with the American Association of State Highway and Transportation Officials (AASHTO) probabilistic Load and Resistance Factor Design (LRFD), 8th edition, 20172.

4.1 Geotechnical Profile

Site observations, back-analysis modeling of existing conditions, and empirical correlation of index properties to strength characteristics of like materials were used in modeling the existing and proposed conditions along the site. Geotechnical profiles consist of estimated subsurface material parameters, anticipated design geomaterials, and interpreted groundwater and soil moisture conditions.

4.1.1 Subsurface Material Parameters

Subsurface conditions encountered can be simplified as existing roadway and train embankment fill, native overburden soil, and rock. Overburden soils generally consisted of alluvium, colluvium, and residual soils from in-place weathering of bedrock. Bedrock generally consisted of one geologic unit, Santa Cruz Mudstone, as discussed in the Draft Geotechnical Data Report, Appendix A. The description contained herein provides a general classification of materials for clarifying chosen material parameters used in design. Refer to the boring logs for a detailed description of subsurface conditions.

2 American Association of State Highway and Transportation Officials (AASHTO), 2017, AASHTO LFRD Bridge Design Specifications, 8th Edition

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Embankment fill encountered was predominantly coarse grained; typically, poorly graded gravel to clayey gravel with variable percentages of fines, sand, gravel, and cobble/boulder. The average depth of existing fill along the mainline alignment was approximately 15 feet; however, fills of over 30 feet were encountered in multiple borings. Fills on the order of 50 feet do exist along the alignment specifically in the larger drainages. Fill soils encountered were primarily dry to moist and loose. Locally, roots and wood fragments were encountered in the fill material or at the transition from fill to native material.

Native and engineered geo-material parameters estimated for design are based on field investigations, results of laboratory testing, and known empirical strength characteristics of like materials. In addition, slope stability analysis was conducted from observations of site conditions to calibrate estimated material values of the overburden. A range of selected design values for soil unit weight (γ), internal friction angle (φ), and cohesion intercept (c) are shown in Table 1. Local specific design parameters were determined for anticipated application and conditions on a site-by-site basis as presented in the analysis and slope stability contained in Appendices B, C and E.

The bedrock encountered, Santa Cruz Mudstone, was generally highly to slightly weathered, very weak to weak, with plastic clay joint infilling. The average depth to rock encountered during the subsurface exploration was approximately 30- to 35-feet below the intended trail alignment with bedrock found as shallow as 5 and deeper than 40 feet. Bedrock was observed in many of the existing cut slopes near or at the ground surface.

Table 1:- Estimated Material Parameters for Design

Source Material Unit Weight γ (pcf)

Cohesion c (psf)

Friction Angle φ (deg)

Analysis Application

Existing On- Site

Materials

Fill (SM/GP-GC or better) 110 0 34

Native Geomaterial

Stability Analysis RSS and Rockery

Native (SM) 110 20 32

Native (SC-SM/ SM) 110 0 34

Wind-Blown Beach Sand 125 0 34

Bedrock (Weathered Mudstone)

120 500 35

RSS Fill 125 20 30-32 RSS

Imported Material Rock Inlay 150 0 48 Rock Shear Key

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4.1.2 Interpreted Groundwater & Soil Moisture Conditions

Groundwater was not detected during the subsurface investigation for the trail alignment; however, the site can vary significantly within short distances, and the volume of groundwater flow may fluctuate between seasons. Monitoring wells installed during the preliminary investigation indicate groundwater seasonally ranges between 2- and 4-feet from top of bedrock. Monitoring well locations are not necessarily indicative of groundwater levels throughout the trail, and drilling observations indicated that groundwater is, at minimum, seasonally not observable. Low piezometric surfaces were included in stability analysis as most site materials are free draining and seismicity is anticipated to control design. Springs and seeps in the native slopes, cut slopes, and roadway inboard ditch have been observed and areas of heavy vegetation are noted in drainage areas. The springs and seeps were noted within existing through cuts with many found directly below agricultural ponds. Flows from groundwater are not anticipated to be significant during construction; however, dewatering/water diversion and special slope cutting methods to control the movement rates and prevent failures may be required.

4.2 Embankments

Trail construction requires embankments associated with the trail alignment, widening, and property approaches. It is recommended that proposed embankments be constructed at 1V:2H slopes or flatter to maintain slope stability and facilitate vegetation growth. As an alternative, embankments can be steepened when mitigation treatments such as reinforced soil slopes (RSS) are applied. In general, RSS can be constructed at 1V:1H with proper seeding and erosion control and steeper with slope armoring such as rock inlay or revetment mattress. It is recommended that embankments be benched into existing slopes, contain drainage systems on every bench, and the toe of embankments be constructed with special rock embankment for RSS that are taller than 15 feet. RSS are discussed below.

4.2.1 Reinforced Soil Slopes

The proposed alignment requires the construction of slopes at over-steepened angles requiring reinforcements. Reinforced Soil Slopes (RSS) were selected over conventional embankments constructed at flatter slope ratios to lessen right-of-way and the environmental impacts of construction near the ocean.

Analyses of the RSS were performed using RESSA and Slide 2 (SLIDE), two-dimensional, limit equilibrium computer programs from ADAMA Engineering and RocScience, respectively. The Simplified Bishop method of slices was used with isotropic soil parameters. The analysis conducted for RSS design consisted of external, compound, and internal stability in accordance with AASHTO “LRFD Bridge Design Specifications” (8th edition), and FHWA Publication NHI-

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10-024 and NHI-10-025, Volumes 1 and 2, respectively, entitled “Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes” dated November 2009.

Preliminary RSS analyses was performed to develop minimum trial reinforcement lengths and spacings at the top and bottom of the proposed RSS. The trial length and spacing were modeled in RESSA and SLIDE2 to determine final embedment length, spacing, and tensile strength required of the geosynthetic reinforcement for a desired minimum static factor of safety of 1.30 and a seismic factor of safety check exceeding 1.1 in accordance with the Caltrans Geotechnical Manual for slopes and walls that do not impact other structures. A 250 pound per square foot traffic surcharge was applied in the long-term static stability analysis to account for maintenance vehicles.

For RSS where the reinforced slope height was 15 feet or greater, global stability was checked using SLIDE 2.

It is recommended the RSS be constructed using woven geotextile reinforcements at 1-foot vertical spacing with a minimum 1,000 or 2,000 pound per foot factored long-term tensile strength, see Table 2.

On-site materials are generally suitable for RSS fill but should be limited to A1, A-2-4, and A-2- 5 soils, to achieve estimated design strength parameters and to limit deformations. Geocomposite sheet drains, with 30 percent minimum coverage, should be installed on each lift of embankment benching and outlet at low points and every 100 feet. Outlets should be staggered between rows.

Topsoil, seeding, and rolled erosion control product or hydraulic soil admixtures and mulching designed for the site conditions are imperative for vegetation growth and long-term performance of RSS.

To obtain a Factor of Safety of 1.1 in the Seismic Condition, it was found that using a rock buttress in the shape and dimensions as outlined in the contract documents will provide sufficient shear resistance while remaining hidden for the design life of the slopes. Factors of safety are presented for RSS where the height was 15 feet or greater.

Table 2 below summarizes the proposed RSS locations, dimensions, and global stability, if applicable. Results of the RSS design analyses global stability modeling are attached to this report in Appendices B and C, respectively.

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Table 2:- Summary of Proposed RSS Dimensions & Slope Stability

Stationing Side

(LT/RT)

Slope Ratio (V:H)

Max Height

(ft.)

Min Length of Reinforcement

(ft.)

Reinforcement Spacing (ft.)

Reinforcement Nominal

Long-Term Strength

(pounds per foot)

Factor of Safety

Remarks Static Seismic

(0.33As)

33+00 To 34+70 RT 1:1.25 49.5 34.7 1 2000 1.54 1.10

Top 6 layers of reinforcement to extend full-width of trail, Construct Shotcrete

Armoring on lower RSS Face

40+10 To 41+60 RT 1:1 6.2 4.3 1 1000 62+80 To 62+90 RT 1:1 8 5.7 1 1000 82+40 To 82+70 RT 1:1 3 2.1 1 1000 83+80 To 84+00 RT 1:1 5 3.5 1 1000 84+60 To 84+70 RT 1:1 7.4 5.2 1 1000 85+10 To 85+45 RT 1:1 9.0 6.3 1 1000

114+15 To 115+10 RT 1:1 30.1 21.1 1

1.47 1.12 Construct Rock Buttress below

Toe of RSS 129+10 To 129+40 RT 1:1 5.6 3.9 1 1000 174+50 To 175+10 RT 1:1 2 1.4 1 1000 215+90 To 216+60 RT 1:1 12 8.4 1 1000 226+10 To 227+90 RT 1:1 9.8 6.9 1 1000 231+00 To 232+50 RT 1:1 4.5 6.7 1 1000

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236+40 To 237+60 RT 1:1 15.5 10.9 1

1.57 1.20 Construct Rock Buttress below

Toe of RSS

284+60 To 292+40 RT 1:1 16.7 11.7 1

1.49 1.17 Construct Rock Buttress below

Toe of RSS

298+90 To 301+70 RT 1:1 20.4 14.3 1

1.46 1.11 Construct Rock Buttress below

Toe of RSS

325+40 To 328+50 RT 1:1 30 21 1

1.47 1.10 Construct Rock Buttress below

Toe of RSS

331+40 To 332+20 RT 1:1 25.3 17.7 1

1.45 1.18 Construct Rock Buttress below

Toe of RSS

335+80 To 336+80 RT 1:1 27.1 19 1 1000 1.49 1.13 Construct Rock Buttress below

Toe of RSS

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4.2.2 Armored Shotcrete Faced RSS

As outlined in previous project memoranda to the California Coastal Commission dated November, 2021, slope protection will be installed to limit potential impacts from wave erosion with the following major highlights of the proposed work:

• The slope protection will extend from Elevation 8 to 25 feet between Sta. 33+00 to 34+70 and will include wire baskets installed into the slope face of the RSS. The welded wire baskets will have a similar structural capacity as a mechanically stabilized earth (MSE) wall welded-wire face system.

• The welded-wire baskets will provide a means for the shotcrete slope protection to be attached.

• Sculpting and staining of the shotcrete facing will be performed to mimic adjacent bedrock outcrops.

• Rock dowels are proposed to secure the shotcrete facing to the rock outcrop on the down-station end.

• The number and layout of the rock dowels will be determined by the contractor’s submitted and approved drawings as described in the contract documents.

• The rock dowels should be installed at a maximum 5-foot on centers spacing (both horizontal and vertical) with a minimum 5-foot penetration into bedrock. Using Table C10.9.3.5.2-1 in AASHTO 2017, the bedrock at the site is conservatively assumed to have a grout-to-ground bond strength of 4 kips/square foot (ksf).

As previously stated, the shotcrete armoring is to be limited to the zone between Elevation 8 and 25 for a maximum height of 17-feet. Limited deviations outside these elevations to better blend into adjacent outcrops are anticipated. The contractor is responsible for providing the final RSS and shotcrete armor geometry, including rock dowel layout, in their installation drawings.

The Contractor will be responsible for submittals as outlined in Sections 257, 260, 261, and 566 of the FP-14 and project specific SCRs. This includes, but is not limited to, RSS and shotcrete layout drawings, drilling and grouting methods to meet the specified bond strength, personnel, and equipment. Section 566 also requires field trials for shotcrete performance and aesthetic treatments.

4.3 Permanent Cut Slopes & Crest Rounding

Recommended slope ratios are based on observed conditions at the existing cut face, investigation data, and anticipated slope height. In general, weathered bedrock slopes can be cut at 1V:1.5H and highly weathered bedrock and non-saturated colluvium can be cut at 1V:2H. Cut slope recommendations are presented below.

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Table 3: -Summary of Proposed Cuts

Stationing Side Slope Ratio Max Height

(LT/RT) (V:H) (Ft.)

65+00 To 68+00 RT 1:2 9

88+25 To 89+50 RT Rockery 13

89+70 To 95+50 RT 1:2 8.5

110+00 To 113+50 RT 1:2 11

151+40 To 155+50 RT 1:1 5

233+00 To 236+00 RT 1:2 8

264+50 To 268+50 RT 1:2 4.5

298+50 - 302+00 RT 1:2 5.5

302+00 To 304+50 RT 1:2 7.5

306+25 To 309+00 RT 1:2 5

320+00 To 324+40 RT 1:2 7

383+00 To 385+60 RT 1:2 10

386+00 To 386+50 LT 1:1.5 8.5

396+50 To 399+50 LT 1:1.5 11.5

396+75 To 399+50 RT 1:2 12

Most existing slopes appear rippable, due to the degree of weathering and jointed nature of the rock mass. Determining rippability involves many factors, including equipment and tooling, and is the responsibility of the contractor. Additional discussion of rippability is presented in Appendix D.

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4.4 CUT SIDE ROCKERY DESIGN

Proposed rockery locations to retain soil cuts is identified at one location. Rockeries are earth retaining gravity walls constructed of large interlocking, dry-stacked rocks typically placed without mortar or reinforcement. These structures rely on the weight, size, shape, and interface friction of the individual rocks to resist earth pressures and provide overall stability. Rockeries have been recently utilized on many FHWA projects as context sensitive solutions preserving scenic, aesthetic, historic and environmental resources, while maintaining safety and mobility.

The rockery walls are designed in accordance with the guidelines provided in the Central Federal Lands publication, “Rockery Design and Construction Guidelines” (FHWA 2006). No geotechnical investigations were conducted at the rockery wall sites; therefore, a conservative design approach was followed requiring both foundation and retained material property verification during wall excavation prior to rockery construction. In lieu of soil testing, presumptive soil strength properties for retained and foundation soils were assumed for observed on-site soils. Static lateral earth pressures were applied to the back of the rockery; however passive earth pressure was neglected at the toe of the wall. The design was checked for adequate factors of safety against sliding, overturning, and bearing capacity. The recommended factors of safety for static and seismic rockery design are presented in Table 4.

Table 4: - Recommended Safety Factors for Design of Rockeries

Failure Mode Static

Factor of Safety

Sliding 1.5 Overturning 2.0

Bearing 3.0

Rockeries were designed for a maximum back slope ratio of 1.0(V):1.5(H) with no surcharge loads. Assumed material properties used in the design of the rockeries are presented in Table 5.

Rockery geometries for the critical section height of 15 feet to meet the minimum safety factor as presented in Table 4 above are shown in Table 6.

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4.4.1 Rockery analysis

Table 5- Material Properties used in the Analysis for Rockeries

Retained and

Foundation Soil

Friction Angle, θ

Retained Soil Unit Weight, ɣs

Foundation Soil Unit Weight, ɣs

Retained Soil

Cohesion, C

Foundation Soil

Cohesion

C

Rockery Face

Friction Angle, θ

Rockery Face Unit Weight, ɣr

Rockery Face

Cohesion, C

34 degrees 125 pcf 120 pcf 0 psf 500 psf 45 degrees 150 pcf 0 psf

Table 6: - Minimum Required Rockery Geometry to Satisfy Safety Factors

Minimum Base Width, B

Maximum Height, H

Minimum Embedment, Df

Backslope Angle, ß

Surcharge

(psf)

Face Batter, V:H

Back Cut Inclination, V:H

8.0 ft 13.0 ft 1.0 ft 35 degrees 0 4:1 8:1

Constructing the rockery base with individual rocks wider than 5.5 feet will be too heavy for conventional earth-moving equipment to move and place according to specification and geometry shown in the plans. Therefore, the criteria as displayed in Tables 7 and 8 have been developed to assist in the constructability of the rockery walls.

Table 7: - Minimum Base Rock Widths for Rockeries with a Given Height

Total Wall Height (1)

(Ft)

Minimum Base Rock Width “B”

(Ft)

13 to > 12 8

≤ 12 to > 11 7

≤ 11 to > 9 6

≤ 9 to > 7 5

≤ 7 to > 5 4

≤ 5 to ≥ 3 3**

(1) Includes 1-foot Embedment ** Absolute Minimum Base rock width

Page | 16

Table 8: - Rockery Base Width Requirements

All Rockery

Heights Height greater than 8 Feet: Heights less than or equal to 8 Feet

A maximum tolerance of 6 inches may be applied toward the total base rock width “B”. Use rock with an “L” Dimension that is no more than 1-foot less than base rock “B” dimension. Do not consecutively place base rocks with widths less than “B”.

A maximum of 2 rocks is permitted for a composite base width “B”. A ratio of 60:40, front rock: back rock is required. Offset joints in composite base rocks a minimum of 6 inches.

Do not consecutively place composite base rocks. A ratio of 60:40, front rock: back rock is required.

Given the criteria as outlined in Tables 4 through 8 factors of safety were calculated for sliding, overturning and bearing capacity and are presented in Table 9 below. Refer to Appendix E for the Rockery Calculations.

Table 9: - A Summary of Calculated Factors of Safeties for Rockeries (1)

Case Factors of Safety Sliding Factor of

Safety Overturning Factor of Safety Bearing Capacity Factor of Safety

1 Static 1.98 4.7 23.3

2 Seismic 1.2 2.2 12.1

(1) Maximum Rockery wall height = 13 feet

4.5 Corrosion Potential

Electrochemical tests were conducted on selected samples to determine if soils may have detrimental effects on concrete and buried metals. In the interest of brevity, please refer to Section 3 of the Draft Geotechnical Data Report dated July 2017 for discussions on Corrosion Potential and testing performed, (Appendix A).

Given the proximity to the Pacific Ocean this project should consider sacrificial thickness or epoxy coating on metaling elements intended for high salinity, corrosive environments.

4.6 Construction Considerations

Trail excavations are anticipated to encounter both bedrock and soil containing cobbles and boulders (1-foot in diameter or larger). The contractor will be required to make the final determination on the rippability characteristics of encountered material based on review of the

Page | 17 boring logs and equipment capabilities. Further discussions of rippability are presented in Appendix D.

Maintaining stability and safety of temporary excavations is the responsibility of the Contractor.

If adverse conditions are encountered, the Contractor will need to develop shoring methods to stabilize any excavations that are deemed unstable.

Buried historic railroad trestles are thought to exist beneath the embankments and drainage crossings along the trail alignment. The trestles are believed to exist predominantly in the existing through fill embankments and drainage channels. Of note is the embankment surrounding the RSS/Shotcrete armoring near Station 34+00. Historic photos show a trestle being buried (Circa 1906, Figure 1) at the Davenport Beach area. Extreme care should be taken during all construction phases to not damage or expose the historic trestles. There may be voided areas near the trestles due to the side-cast (unconsolidated) nature of the historic fill construction.

Figure 1:- Railroad trestles beneath embankment along the trail alignment. Slope in photo is near Davenport, CA

Photo credit: Sandy Lydon (http://www.sandylydon.com/new-page-2) http://www.sandylydon.com/new-page-2

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Do not drill directly through the basket face and RSS to install the rock dowels into the rock outcrop near Station 33+70. Drilling through the constructed RSS presents a risk of entanglement and damage of the RSS reinforcements. The contractor should provide installation details for rock dowels through the RSS face to prevent damage and displacement of the welded wire mesh facing and geosynthetic reinforcement.

Sequencing cut and fill excavations during periods of dry weather for efficient material handling and foundation preparation is highly recommended. Groundwater is possible in excavations for RSS embankments. Temporary containment of groundwater flow may be required to meet the water quality requirements specified in Section 157 of the FP-14. Dewatering and stabilization methods for foundation construction will depend on conditions encountered. It is recommended that all foundation excavations be evaluated by a CFL geotechnical representative to verify conditions assumed in design.

Based on conditions encountered during the geotechnical investigation, it is not anticipated that a significant depth of topsoil will be present at the project site. For estimating purposes, it should be assumed that limited topsoil will be stripped and stockpiled for re-use on the project. Topsoil is anticipated to be imported for the project.

4.7 Disclaimer/Limitations Clause

The recommendations in this report are based on the data obtained from exploratory borings, field review, and the laboratory test results. The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface variations across the site are likely and may not become evident until excavation is performed. The Analysis and Recommendations sections in this report include interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

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SECTION FIVE - References

American Association of State Highway and Transportation Officials (AASHTO), 2017, LFRD BRIDGE DESIGN SPECIFICATIONS, 8th Edition

ACI, 2005, “Building Code Requirements for Structural Concrete (ACI 318-05) and Commentary (318R-05)”.

ADAMA Engineering, Inc, Computer Program, ReSSA, Version 3.0, Copyright 2008.

Berg, R. R., Christopher, B. R., & Samtani, N. C. (2009). Design and construction of mechanically stabilized earth walls and reinforced soil slopes. US Department of Transportation, Federal Highway Administration, National Highway Institute.

California Department of Transportation (Caltrans), Office of Earthquake Engineering. 2007 Fault Database.

Caltrans, ARS Online (v2.3.06) http://dap3.dot.ca.gov/ARS_Online/ and ARS Online Appendix B.1 http://www.dot.ca.gov/hq/esc/earthquake_engineering/sdc/

Caltrans, Geotechnical Manual, Various Dates from 2012 to 2015, http://www.dot.ca.gov/hq/esc/geotech/geo_manual/manual.html

Caltrans, 2013, “Seismic Design Criteria Version 1.7”, dated April 2013.

Duncan J.M., Wright S.G., “Soil Strength and Slope Stability,” John Wiley & Sons, Inc, Hoboken, New Jersey, Copyright 2005.

Federal Highway Administration (FHWA), 2007, LRFD for Highway Bridge Substructures and Earth Retaining Structures, Publication FHWA-NHI-05-094, dated January.

Federal Lands Highways (FLH), 2006, “Technical Guidance Manual (TGM)”, A geotechnical supplement to the FLH Project Development and Design Manual.

FHWA, 2006, Soils and Foundations, Publication No. FHWA-NHI-06-088, dated December.

FHWA, 2008, Federal Lands Highway Project Development and Design Manual (PDDM), dated March.

Lydon, Sandy, 2021 Sandy Lydon’s Central Coast Secrets, http://www.sandylydon.com/new-page-2 http://dap3.dot.ca.gov/ARS_Online/ http://www.dot.ca.gov/hq/esc/earthquake_engineering/sdc/ http://www.dot.ca.gov/hq/esc/geotech/geo_manual/manual.html

Page | 20

RocScience Geotechnical Software, Computer Program, SLIDE2 with SLIDE INTERPRET Build

9.019 , Copyright 1998-2021

Rogers, J. David. Environmental & Engineering Geoscience, Vol. XII, No. 2, May 2006, pp.161-

179. “Subsurface Exploration Using the Standard Penetration Test and the Cone Penetrometer Test.”

United States Geological Survey (USGS), 2008, “National Seismic Hazard Map”, website:

http://earthquake.usgs.gov/research/hazmaps.

http://earthquake.usgs.gov/research/hazmaps

Monterey Bay Sanctuary Scenic Trail CA FLAP SCR T5(1) & (2) May 2023

APPENDIX A

Monterey Bay Sanctuary Scenic Trail CA FLAP SCR T5 (1) & (2), Draft Geotechnical Data Report

Monterey Bay Sanctuary Scenic Trail

CA FLAP SCR T5 (1) & (2)

Draft Geotechnical DATA Report

Prepared by:

Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch

July 2017 i

CA FLAP SCR T5(1) & (2) MONTEREY BAY SANCTUARY SCENIC TRAIL Page i

Table of Contents

SECTION ONE --INTRODUCTION

1.1. PROPOSED CONSTRUCTION

SECTION TWO --GEOLOGY AND SEISMICITY

2.1. GEOLOGY

2.2. GEOLOGIC HAZARDS

2.3. SEISMICITY

SECTION THREE -FIELD EXPLORATION

3.1. SUBSURFACE EXPLORATION PROGRAM

3.2. LABORATORY TESTING PROGRAM

SECTION FOUR --LIMITATIONS

SECTION FIVE --REFERENCES

FIGURES

Figure 1: Location Map

Figure 2: Geology Map

Figures 3-11: Geotechnical Boring Locations

APPENDICES

Appendix A: Field Exploration Program

Appendix B: Laboratory Test Results

Appendix C: Photos

CA FLAP SCR T5(1) & (2) MONTEREY BAY SANCTUARY SCENIC TRAIL July 2017

SECTION ONE--INTRODUCTION

This data report presents the results of the geotechnical investigation conducted for the Monterey

Bay Scenic Sanctuary Trail, CA FLAP SCR T5 (1) and (2) project. as Also included are documentation of projects assumptions used during the design hiatus due to right-of -way issues.

The Federal Highway Administration, Central Federal Lands Highway Division (FHWA-CFLHD), in cooperation with the Santa Cruz County Regional Transportation Commission (SCCRTC), is proposing the construction of a segment of the Monterey Bay Sanctuary Scenic Trail (MBSST) in

Santa Cruz County, CA. The entire proposed trail network is about 50 miles broken up into several segments. The current proposed project is Segment 5 of the trail project. In 2012 SCCRTC took ownership of the 32-mile Santa Cruz Branch Railroad Line, which much of the proposed MBSST would run parallel to and within the railroad right of way.

The proposed project consists of constructing 7.4 miles of new multi-use trail for pedestrians and bicyclists north of Santa Cruz, CA that would run alongside the existing rail line. The proposed trail and rail system parallels California Highway 1 beginning at Davenport, CA and proceed south to its terminus at the Wilder Ranch State Park parking area. In addition, the proposed project would include improvements to the Yellowbank Beach parking lot and the Davenport parking lot.

Pedestrian access to the trail from a third parking lot, the Bonny Doon parking area are also planned for improvements.

1.1. PROPOSED CONSTRUCTION

The proposed project would construct a multi-use trail that includes an 8- to 12-foot wide asphalt paved trail and a variable width unpaved, decomposed granite trail. The typical trail cross section would be 20 feet wide and would consist of the following:

12-foot asphalt paved path

6-foot aggregate path on the coastal side of the paved path

2-foot aggregate shoulder on the inland side of the paved path

However, the widths of the asphalt and aggregate shoulder portions of the trail may vary in locations to either accommodate farm equipment or to reduce impacts to resources.

In several locations, the existing railway bench will be widened using cuts or fills to accommodate the proposed trail. In these locations, retaining walls or fill slopes will be used depending on the geometry of the site and any sensitive resources in the area. Walls may be constructed as soldier pile with timber lagging, mechanically stabilized earth (MSE), or segmental precast concrete wall system with a façade with architectural treatments. Walls would be designed to blend into the environment to the greatest extent possible. Where walls or embankments can be vegetated, native vegetation would be planted. Near Davenport (station 33+00), the embankment fill is actively eroding through wave action at the embankment toe and several options are being considered to support the trail: slope construction using wire mesh baskets; a retaining wall; or re-establishing the portion the embankment using standard embankment slopes or reinforced soil slopes. In all scenarios, coastal armoring must be established at the base of the slope to minimize or eliminate further erosion that potentially compromise the trail stability.

Near Station 114 + 00 the bench must be widened specifically in areas where the slopes are steep.

A Retaining wall, reinforced soil slope, or a narrow bridge to span the ravine are also considered for this location to reduce the impacts to the surrounding environment. Bridge details are not known but it is anticipated that approximately 16 feet wide bridge will be required to support bicyclists and pedestrians and potentially providing access for emergency vehicles.

SECTION TWO--GEOLOGY AND SEISMICITY

2.1. GEOLOGY

The MBSST lies within the Coast Range geomorphic province of California. The Santa Cruz

Mountains consist of Tertiary-age sedimentary rocks that have been folded and faulted by movements along the San Andreas Fault system. The MBSST trail traverses a marine, wave-cut terrace (Santa Cruz Terrace) formed at a sea-level high stand in the Late Pleistocene. The Santa

Cruz Terrace is the lowest and youngest of a series of marine terraces on the southwest flank of the

Santa Cruz Mountains that formed during regional uplift and varying sea levels (Weber and

Allwardt, 2001). The surface of the Santa Cruz Terrace is underlain by Santa Cruz Mudstone covered with a veneer of Quaternary terrace deposits and colluvium. The unconsolidated terrace deposits and colluvium are described as comprising silt, sand, and gravel with some clay. A geologic map is shown in Figure 2 and a description of the soil and rock encountered from the borings is discussed in more detail in Appendix A.

2.2. GEOLOGIC HAZARDS

Soil settlement due to Static Loading: The embankments spanning the major drainages are comprised of under-consolidated fills placed by side-casted waste material generated from the cuts during the construction of the railroad corridor. Loads from reinforced soil, walls or standard embankments should incorporate some degree of settlement analysis.

Earthquakes and Fault Rupture: See Section below regarding seismicity at the site.

Liquefaction, lateral Spreading and Seismic Settlement: Based on maps provide by the County of

Santa Cruz, high to very high liquefaction potential exist where the proposed trail crosses deep drainages on existing rail embankments. A potential for seismic settlement likely exists due to the unconsolidated nature of these liquefiable layers. In addition, a potential for lateral spreading exists due to the sloping nature of the area. These phenomena’s will increase the overall project cost substantially.

Deep Erosion Hazard: Along the coast and extending up some of the larger creeks, there is a potential for erosion due to wave action, per the County of Santa Cruz (SCC, 2010). The toe of the existing rail embankment may be subject to erosion.

Organic Soils: Basin deposits mapped in the floor of the wider creek drainages crossed by the

MBSST include organic estuarine deposits.

2.3. SEISMICITY

The MBSST is in a relatively active seismic area; however, the site is not located in a designated

Earthquake Fault Zone (EFZ). The Santa Cruz Mountains are cut by several active faults, of which the San Andreas is the most important. Along the coast, the ongoing tectonic activity is most evident in the gradual uplift of the coastline, as indicated by the series of uplifted marine terraces that sculpt the coastline (City of Santa Cruz, 2011). In addition to the San Andreas fault, the

Zayante-Vergeles and San Gregorio faults and the Monterey Bay – Tularcitos fault zone are associated with Holocene activity (movement in the last 11,000 years) and are active. The nearby mapped faults include:

• Unnamed Fault: An unnamed late Quaternary fault is mapped approximately 3 miles east of the southern end of the proposed trail and trends north-south. The USGS Quaternary Fault Database

(USGS, 2012) indicates that the age of this fault is less than 130,000-years old and exhibits slip rates of less than 0.2 mm per year.

• San Gregorio Fault Zone: This fault zone is located as close as approximately 3 to 4 miles west of the north end of the proposed trail and trends north/northwest-south/southeast. The USGS

(2012) indicates that the age of this fault is less than 15,000-years old and exhibits slip rates of greater than 5 mm per year.

• Monterey Bay – Tularcitos Fault Zone: This fault zone is as close as approximately 5 miles south of the south end of the proposed trail and trends north/northwest-south/southeast. The USGS

(2012) indicates that the fault is less than 15,000-years old and exhibits slip rates of 0.2 to 1 mm per year.

• Zayante-Vergeles Fault Zone: This fault zone is located approximately 10 to 11 miles east of the proposed trail and trends northwest-southeast. The USGS (2012) indicates that fault is less than

130,000-years old and exhibits slip rates of 0.2 to 1 mm per year.

• San Andreas Fault Zone: This fault zone is located approximately 13 to 14 miles east of the proposed trail and trends northwest-southeast. The USGS (2012) indicates that fault is less than

150-years old and exhibits slip rates of greater than 5 mm per year.

Refer to the map of known faults in the Santa Cruz area in the Appendix.

Based upon the geologic setting and anticipated subsurface conditions, the site will likely be classified as Site Class D. The design response spectrum parameters based on 7 percent probability of exceedance in 75 years (1,000-year return period), USGS mapping, and anticipated site class are shown below.

2009 AASHTO SEISMIC PARAMETERS (SITE CLASS D)

Seismic Parameter

Peak Ground

Acceleration Short Period 1-second Period

Mapped SRA PGAR = 0.542 g Ss = 1.273 g S1 = 0.559 g

Site Coefficients FPGA = 1.0 Fa = 1.0 Fv = 1.5

Design SRA AS = 0.451 g SDS= 1.273 g SD1= 0.838 g

Earthquake Magnitude 6.9

Notes:

Earthquake Magnitude = Mean value from PSHA deaggregation for 5% exceedance in 75 years PSHA = Probabilistic Seismic Hazards Analysis Fa = short-period site factor

FPGA = PGA site factor Fv = long-period site factor g = acceleration of gravity PGA = peak ground acceleration PGAR = mapped PGA value for soft rock AS = design PGA = 0.4*SDS S1 = long-period spectral acceleration SD1 = long-period maximum spectral acceleration SDS = short-period design spectral acceleration Ss = short-period spectral acceleration

Based on the long-period acceleration, a Seismic Zone 4 should be applied for all structural designs.

SECTION THREE-FIELD EXPLORATION

3.1. SUBSURFACE EXPLORATION PROGRAM

The Central Federal Lands Highway Division (CFLHD) Geotechnical Section completed a field exploration program for CA FLAP SCR T5 (1) (2), between August 23 and 25, 2016. The scope of work included drilling a total of fourteen (14) exploratory borings and installing seven (7) monitoring wells. Each field exploration program component was coordinated and observed by a

Geotechnical Engineer from CFLHD. Field exploration location plans, and individual boring logs are attached. These logs represent a compilation of field and laboratory data and description of the soil samples by CFLHD Geotechnical personnel. The methods used to conduct the field exploration program are described below. Photos of drilling equipment and field exploration activities are included in the attachments. Representative soil and rock samples collected during the field exploration program were transported to the CFLHD Materials Laboratory in Lakewood, Colorado for testing. A summary of the laboratory testing program is provided in Appendix B.

3.2. LABORATORY TESTING PROGRAM

Laboratory test were completed on select soil and rock samples recovered for the field exploration program in general accordance with the American Association of State Highway and

Transportation Officials (AASHTO) and ASTM testing methods. The laboratory testing program was completed to provide data for engineering studies and to classify the materials into similar geologic groups. The testing program included index tests and geotechnical engineering property tests. Individual test results are presented in Tables B-1 through B-3 contained in Appendices B.

SECTION FOUR--LIMITATIONS

The recommendations in this report are based on the data obtained from exploratory borings, field review, and laboratory test results. The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface variations across the site are likely and may not become evident until excavation is performed. The Analysis and Recommendations sections in this report include interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

SECTION FIVE--REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), 2014, LFRD

BRIDGE DESIGN SPECIFICATIONS, 7th Edition.

Brabb, Earl E, 1997, “Geologic Map of Santa Cruz County, California” U.S. Geological Survey, scale 1:62,500.

Federal Highway Administration (FHWA), 2008, Federal Lands Highway Project Development and Design Manual (PDDM), dated March.

Santa Cruz County Regional Transportation Commission, “Master Plan for the Monterey Bay

Sanctuary Scenic Trail” Dated 2013

U.S. Department of Transportation, Federal Highway Administration, 2016, “Plans for Proposed

CA FLAP SCR T5(1) & T5(2) Monterey Bay Sanctuary Scenic Trail”, dated November

2016.

http://geohazards.usgs.gov/cfusion/qfault/query_main_AB.cfm http://geohazards.usgs.gov/cfusion/hazfaults_2014_search/query_main.cfm

“National Seismic Hazard Map”, United States Geological Survey (USGS), 2008, website:

http://earthquake.usgs.gov/research/hazmap http://geohazards.usgs.gov/cfusion/qfault/query_main_AB.cfm http://geohazards.usgs.gov/cfusion/hazfaults_2014_search/query_main.cfm http://earthquake.usgs.gov/research/hazmap

Figures

Dominic.Monarco Text Box

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