B08_3 - CHOH 241450 - Basis of Design Report.pdf

REPORT COVER PAGE Basis of Design Report CHOH: Improve Visitor Safety and Remediate Rockfall Hazards

Oldtown, Maryland

June 26, 2020

Terracon Project No. EY195055

Prepared for:

VHB

Williamsburg, VA

Prepared by:

Terracon Consultants, Inc.

Germantown, Maryland

Terracon Consultants, Inc. 20401 Seneca Meadows Parkway Germantown, MD 20876 P (301) 354 6100 F (301) 354 6101 terracon.com

Professional Certification. I hereby certify that these documents were prepared or approved by me, and that I am a duly licensed professional engineer under the laws of the State of Maryland, License No. 45404, Expiration Date: 05/19/2020

REPORT C OVER L ETTER TO SIGN

June 26, 2020

VHB

351 McLaws Circle Williamsburg, VA 23185

Attn: Mr. Vikrant Desai, P.E.

P: (757) 279 2832 E: vdesai@vhb.com

Re: Basis of Design Report CHOH: Improve Visitor Safety and Remediate Rockfall Hazards Paw Paw Tunnel Oldtown, Maryland Terracon Project No. EY195055

Dear Mr. Desai, We have prepared a Basis of Design Report for rockfall mitigation solutions proposed at the Paw Paw Tunnel located in the Chesapeake & Ohio Canal National Historic Park (CHOH) in Oldtown, Maryland.

This report was performed in general accordance with National Park Service (NPS) IDIQ Task Order Authorization dated September 16, 2019. This report presents the technical basis used in the design of the pinned mesh, pattern and spot rock bolts, and shear blocks. Full details and engineering analyses are included to this report in the Appendices.

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

Sincerely, Terracon Consultants, Inc.

Tim Hastings, P.E. Nancy A. Straub, P.E., ENV SP, LEED AP Project Engineer Senior Associate

SME Review By: Eric B. Rehwoldt, P.E., P.G., Senior Principal

Kirk Beach, Assistant National Director

TABLE OF CONTENTS

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REPORT TOPICS

INTRODUCTION

BACKGROUND

REGIONAL GEOLOGY

GEOLOGIC HAZARD SUMMARY

ROCK MASS STRUCTURAL GEOLOGY

MECHANICAL STABILIZATION DESIGN

DESIGN METHODOLOGY

GENERAL COMMENTS

FIGURES

FIGURE 1 – SITE LOCATION MAP

APPENDICES

APPENDIX A – PINNED MESH DESIGN

APPENDIX B – PATTERN BOLTING DESIGN

APPENDIX C – SPOT BOLTING DESIGN

APPENDIX D – SHEAR BLOCK DESIGN

Note: Refer to each individual Appendix for a listing of contents.

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ROCKFALL GEOHAZARD EVALUATION REPORT

CHOH: IMPROVE VISITOR SAFETY AND REMEDIATE ROCKFALL HAZARDS

PAW PAW TUNNEL

OLDTOWN, MARYLAND

Terracon Project No. EY195055 June 26, 2020

INTRODUCTION

This report presents the results of a geotechnical evaluation of the rockfall at the Paw Paw Tunnel located in the Chesapeake and Ohio (C&O) Canal National Historic Park in Oldtown, Allegheny County, Maryland. This report presents:

an overview of the site and rock mass conditions in the 1,000-ft long C&O Canal prism north of the Paw Paw Tunnel, a discussion of the analyses performed, and an explanation of the design methodology used to develop the schematic design to mitigate the rockfall hazards.

BACKGROUND

The Paw Paw Tunnel is a 3,118-foot long historic canal tunnel located near Oldtown, Maryland as presented on the Site Location Map in Figure 1. The canal tunnel was constructed by the Chesapeake & Ohio Canal Company to allow boats to bypass a 6-mile-long sinuous stretch of the Potomac River near mile post 155, known as the ‘Paw Paw Bends’, and the adjacent steep cliffs on their way to Cumberland. The tunnel was constructed between 1836 and 1850 and remained in operation until 1924 when it fell into disuse. The canal was purchased by the Federal Government in 1938 and by the early 1950’s, plans were being developed to repurpose the canal into a non-motorized recreational trail. In the mid-1950’s, the National Park Service started making improvements to stabilize and repair the condition of the tunnel and the towpath, and these efforts continue today.

This section of the canal and the tunnel was designed to follow the valley of Mill Run, a former tributary of the Potomac River. Mill Run generally followed the alignment of a geologic fold axis (i.e. anticlinal fold) in the bedrock. North of the tunnel, the canal was created by deepening and widening the valley through predominantly shale bedrock. The excavation for the canal cuts across the anticlinal axis of the fold at an oblique angle exposing potentially unstable rock slope conditions on both the east and west sides of the canal prism. Historic landslides and rockfall events have occurred within the canal prism since its construction.

Basis of Design Report

Oldtown, Maryland June 26, 2020 Terracon Project No. EY195055

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The National Park Service recently took measures to stabilize the east slope of the canal prism in 2013 and 2019. In 2013, in response to a landslide at the north end of the canal prism, a barrier fence was installed. In 2019, stabilization efforts including rock scaling, and installation of rock bolts, shear blocks, draped mesh, and weep drains were completed. This project builds upon that project by stabilizing the west slope of the cut and providing additional stabilization support for the east slope.

REGIONAL GEOLOGY

Geologic Setting

The Paw Paw Tunnel is located in the Allegheny Plateau, and Valley and Ridge Physiographic province of western Maryland. Sedimentary rocks folded and faulted during the Alleghenian Orogeny (Appalachian mountain-building period approximately 300 to 250 million years ago) created the Broadtop Synclinorium, the largest fold structure of the region. The synclinorium consists of many secondary folds.

According to the Geologic Map of the Paw Paw quadrangle, Allegany, Maryland (Glaser, J.D.

1994), bedrock at the site consists of late Devonian-age (358 to 382 million years ago) Brallier Formation sedimentary rock. Brallier Shale is described as olive-gray to greenish-gray shale and siltstone formed from layers of mud deposited in the Kaskaskia Sea. In general, Brallier Shale is laminated and uniform, with approximately 40% to 50% of the shale formation interbedded with siltstones and fine-grained sandstones.

Based on a review of geologic maps available for the project site, the canal generally follows and obliquely crosses the axis of an anticlinal fold trending in a northerly direction. The axis of the anticline is overturned along the east wall of the canal prism and has been eroded or cut away leaving the east and west limbs of the anticline exposed. The alignment of the axis of the anticline appears to vary as it trends to the north, which changes how much of each limb of the anticline is exposed on the east slope face. The west slope face is incorporated in its entirety within the west limb of the anticline.

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GEOLOGIC HAZARD SUMMARY

Based on the rockfall hazard assessment and observations, explorations, and analyses described in the Rockfall Geohazard Evaluation Report dated April 15, 2020, there are two primary modes of slope failure occurring at the site depending on the local structural geology of the shale and siltstone rock mass, as well as the slope orientation within each segment of the canal prism.

These failure modes are described below:

Planar Failures – Potential planar failure in the rock mass exists where the orientation (i.e.

dip and dip direction) of persistent discontinuity planes within the rock mass (i.e. bedding joints, stress relief joints, geologic faults) are adverse to the orientation of the slope face.

Adverse orientation would be considered where the dip direction of the discontinuity is within 20 degrees of the dip direction of the slope face, and where the dip of the discontinuity planes is coincident or are flatter than the slope face (i.e. a ‘dip slope’ or

Figure 1 – Historic sketches of the general rock structure within the canal prism by William E. Davies (1999)

Responsive Resourceful Reliable 4 unsupported condition, respectively). A condition of potential failure exists when the frictional strength assumed between the discontinuity planes is less that the dip of the plane, and where the uplift pressures from groundwater are present below sliding rock blocks.

A condition of planar failure has been observed and calculated for both the west and east canal prism slopes. A ‘dip slope’ failure condition along bedding joints is present within the East Slope from approximately Sta 32+16 to Sta 40+50. We expect that continued failure of relatively thin bedding slabs (a few inches to 36 inches) will occur unless reinforced and protected. Unsupported sets of stress relief joint discontinuities are expected to continue to be a potential source of larger landslides into the canal prism on the West Slope and is considered to be the mode of failure triggering the 2016 landslide located at approximately Sta 37+66.

Toppling/Wedge Failures – Conditions for toppling and wedge failures occur in the upper portion of the East Slope and rock cuts above the north tunnel portal due to the differential weathering and raveling of the shale and siltstone rock mass where the bedding dips into the rock slope. Rockfall generated from the upper East Slope pose a significant hazard to trail users due to the fact that the rocks fall directly on the towpath from a great height.

Rockfall generated from above the tunnel portals are a potential hazard to trail users accessing the areas immediately below exposed rock cut face below and adjacent to the tunnel portals.

Rockfall generated from the West Slope poses a lower risk to trail users. The towpath where trail users are located is elevated above the canal prism basin. For rockfall generated from the West Slope to reach the towpath, it would need to cross the existing canal prism basin and then bounce above the height of the towpath.

ROCK MASS TRUCTURAL GEOLOGY

Based on the results of a field investigation as stated in the Rockfall Geohazard Evaluation Report, the following tables indicate the mean dip and dip direction of the identified bedding joint and joint sets present within the respective segments and slopes of the canal prism. Bedding joints associated with the east and west limbs of the anticline have been indicated in the tables.

Segment 1 (from Station 31+16 to Station 32+50) – East Slope Joint Set Description Mean Dip (deg) Mean Dip Direction (deg)

J1 Bedding Joint (west limb) 50 314

J2 Bedding Joint (east limb) 31 135

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J5 Joint 80 246

Due to the orientation of the East Slope face, there is a potential for planar failure of rock blocks along bedding planes and/or joint sets within the rock mass.

There is a potential for wedge sliding due to intersection of J2 (the bedding joint on the east limb of the anticline) and J5 within the slope face, which can be a source of rockfall.

There is a potential for toppling failures.

Segment 1 (from Station 31+16 to Station 33+50) – West Slope

J1 Bedding Joint (west limb) 59 313

J3 Joint 46 127

There is a potential for planar sliding of thin shale and siltstone beds along J3, which are unsupported in the West Slope. The bedding joint, J1, is exposed in many locations along the West Slope, where the planar sliding mass has separated from the rest of the rock mass along the bedding joint at the top of the slide.

A potential for wedge failure exists due to the intersection of the bedding joint (J1) and joint set (J3) within the slope face and can be a source of rockfall.

A potential for toppling failure exists due to the exposure of bedding joint set (J1) exposed within the slope as slabs of shale and siltstone slide into the canal along J3. This can be a source of rockfall.

Segment 2 (from Station 33+50 to Station 36+00) – East Slope

J1 Bedding Joint (west limb) 49 316

J5 Joint 70 243

J3 Joint 41 127

The bedding joint (J1) on the west limb of the anticline creates a ‘dip-slope’ condition on the lower portion of the East Slope. Continued planar sliding is expected along thin slabs of shale and siltstone onto the towpath, if unsupported.

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A potential for wedge sliding exists in the segment due to the intersection of joint sets J3 and J5 within the slope face. Rockfall resulting from wedge sliding is possible in this area.

A potential for toppling failures is expected, related to differential weathering of the upper portion of the slope face, where the bedding joint (J2) structures on the east limb of the anticline are exposed and dipping back into the hill slope. Rockfall related to differential weathering and toppling failures are expected in this area.

Segment 2 (from Station 33+50 to Station 36+00) – West Slope

J1 Bedding Joint (west limb) 59 313

J3 Joint 47 128

There is a potential for planar sliding along joint set J3, which is exposed and unsupported in the slope.

There is a potential for wedge sliding, with resulting rockfall.

There is a potential for toppling failures to occur. Toppling failure is associated with exposure of rock beds controlled by the J1 bedding joint in the slope, which creates a rockfall potential.

Segment 3 (from Station 36+00 to Station 43+16) – East Slope

J1 Bedding Joint (west limb) 44 315

J3 Joint 27 150

The bedding joint (J1) on the west limb of the anticline creates a ‘dip-slope’ condition on the lower portion of the East Slope. Continued planar sliding is expected along thin slabs of shale and siltstone onto the towpath, if unsupported.

A potential for wedge sliding exists in the segment due to the intersection of joint sets within the slope face. Rockfall resulting from wedge sliding is possible in this location

There is a potential for toppling failures to occur related to differential weathering of the upper portion of the slope face, where the bedding joint (J2) structures on the east limb of the anticline are exposed and dipping back into the hill slope. Rockfall related to differential weathering and toppling failures are expected in this location.

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Segment 3 (from Station 36+00 to Station 43+16) – West Slope

Joint Set Description Mean Dip (deg) Mean Dip Direction (deg)

J1 Bedding Joint (west limb) 48 316

J3 Joint 44 136

J4 Joint 84 64

There is potential for planar sliding to along joint set J3, which is exposed and unsupported in the slope. We expect that the existing landslide within this canal prism segment on the west side of the slope likely was controlled by a planar failure mode along J3.

There is potential for wedge sliding created by the intersection of joint sets within the slope face.

There is potential for toppling failures to occur on the West slope. Toppling failures likely would be associated with exposure of rock beds controlled by the J1 bedding joint in the slope, which creates rockfall potential.

MECHANICAL STABILIZATION DESIGN

This section presents the selected methods to mechanically stabilize the slope to reduce the geological hazards.

Method 1: Perform maintenance scaling of all slopes to remove loosened rock that threaten Park user’s safety. Scaling of loosened rock also provides protection to personnel installing mechanical stabilization.

Method 2: Remove fallen rock and accumulated talus from the canal area so that it can continue to function as a catchment ditch. During this activity, debris from the rock slope failure near Station 37+66 on the west side of the prism would be mechanically removed and transported for disposal.

Method 3: Within the upper slope on the east side of the canal prism (and within the east limb of the anticline axis), the rock structure is blocky and severely weathered. There is also no fall-out zone at the base of this section of the slope where rock debris can safely be contained and removed. For this area, we recommend a pinned mesh system anchored to the slope face to actively restrain rock fall occurrence. Pinned mesh is a system of anchors and steel rockfall mesh to improve the surficial rock face stability and maintain the debris/rock on place. The pinned mesh areas will terminate at least 20 ft above the tow path to discourage users from climbing the mesh.

Method 4: In areas where rock bolting reinforcement has recently been completed in the lower portion of the East Slope (within the west limb of the anticline), we recommend that supplemental rock bolting be provided in a spot bolting fashion in localized areas

Responsive Resourceful Reliable 8 where currently unsupported rock bedding slabs are demonstrating signs of cracking and distress.

Method 5A: In areas where wedge and planar failures are a potential failure mechanism, within the West Slope of the canal prism, pattern rock bolting and rock drains are recommended to increase the factor of safety against planar sliding.

Method 5B: In areas where previous landslides have left rock overhangs within the West Slope of the canal prism, we recommend installation of anchored shear blocks to underpin and support the existing rock ledges/overhangs and increase the factor of safety of the rock wedges above the overhang against sliding.

DESIGN METHODOLOGY

Pinned Mesh Design

The pinned mesh system was designed using the MacRo software developed by Maccaferri. The software uses a limit equilibrium approach, considering numerous variables including topography, rock mass properties, joint geometry and condition, mesh type, and related restraint conditions.

The design considers that the rock mass conditions exposed at the slope surface are weathered, heavily jointed, or otherwise disturbed. The weathered/disturbed rock mass layer at the slope surface is considered pseudo-continuous for purposes of calculation and will most frequently generate shallow instabilities and rockfalls.

The forces on the mesh and nails are passively generated when one of two conditions occur:

1. The whole surficial layer of weathered rock at the face of the slope starts to slide. The anchors will stabilize and reinforce this surface layer.

2. One or more blocks pop out of the rock surface in between the anchors. The mesh supports these localized rockfalls.

The rock mass of a slope naturally weathers, fractures, and weakens unevenly due to variations in inherent rock properties in combination with external factors such as fracture spacing and water exposure. These variations can impact the design of the pinned mesh system. To account for these variations, the design software allows safety and load factors to be applied to both the driving forces and stabilizing forces. Factors applied to the stabilizing forces are divisors (factors of safety) to reduce the stabilizing forces. Factors applied to the driving forces (load factors) increase the driving force by a multiplier. The rock mass features affect the size of the stabilizing forces, while the external conditions and slope morphology play an important role in the magnitude of the driving forces. Below is a table that summarizes the factors used, based on the program recommendations and the uncertainties for each component.

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Applied Factors of Safety Stabilizing or

Driving Forces Component Symbol Partial Factor of Safety/Load Factor Value

Stabilizing

Superficial Instability Thickness T 1.20

Rock Unit Weight W 1.05

Rock Weathering B 1.05

Driving Rock Morphology MO 1.20

External Loads OL 1.10

With these factors, the resultant global safety factor is on the order of 1.74.

Shear stresses and tensile stresses develop in the anchors primarily near the sliding joint. The anchor tensile stresses are estimated based on the sliding joint roughness using the Barton- Bandis sliding surface dilatancy. The anchor combined load is calculated using the maximum work principle, as a function of the anchor bar yield stress with a factor of safety of 1.67.

The anchor total length is then estimated by summing the thickness of the assumed weathered/unstable rock mass at the slope face, the length required to transfer the shear and tensile stresses to the bar, and the length required to transfer the tensile load from the bar to the stable mass through bond stress between the grout/resin and the rock.

The mesh strength requirements are calculated based on the size of the dislodged surficial rock blocks to be supported by the mesh. The rockfall causes the mesh to bulge between the anchors, loading it tangentially (tension), as well as to provide a radial confinement force. The resulting mesh tension is compared with the admissible tensile strength of the mesh considering a factor of safety of 2.5, and the resulting radial confinement force is compared with the experimental punching resistance of the mesh which is associated with a maximum bulging deformation before mesh failure occurs. The allowable bulging deformation is limited to the maximum bulging divided by a factor of safety of 1.5.

Pattern Bolting Design

Using the RocScience program RocPlane, a series of potential planar failures conditions within the West Slope were considered including water uplift pressures assumed over 30% of the slip surface length. RocPlane uses a limiting equilibrium formulation to calculate the sliding factor of safety. The basic inputs of the program are the rock discontinuity and slope geometry, unit weight of the rock, assumed shear strength parameters of the rock joint interface (interface friction angle

Responsive Resourceful Reliable 10 of 34 degrees and no cohesion), and the pre-stress of the proposed rock anchors. Based on FHWA guidance for slopes adjacent to highways and ‘important installations’ (FHWA Publication No. FHWA-TS-89-045, September 1989), a minimum factor of safety of 1.5 was used for calculation purposes in design for mitigating possible planar sliding. The required pre-stress of the rock anchor to increase the normal force on the sliding block was calculated by the program to achieve a target factor of safety of 1.5.

Additionally, we performed a hand calculation using the limit equilibrium approach on an assumed local sliding block measuring 4-ft thick x 6-ft long x 6-ft wide. The 6-ft long by 6-ft wide section was based on our assumed pattern bolt spacing and tributary area acting on each anchor. In this calculation, it was assumed that water is not present along the sliding plane or in the tension crack (assumed dry conditions) as drains are proposed to be installed in conjunction with the pattern bolting.

Once the required anchor bolt pre-stress load was calculated for each method above, the necessary anchor bolt bar section and the required bond length were calculated. These calculations considered a factor of safety of 1.67 on the ultimate tensile strength of the bar and the working bond stress determined from the Pattern Bolting Design, as presented in Appendix B.

Spot Bolting Design Using a limit equilibrium approach, the required pre-stress of the rock anchor to increase the normal force on an assumed sliding block based on field measurement data and observations of past failures was calculated to achieve a factor of safety of 1.5. The potential sliding block used in the calculation was 4-ft thick x 10-ft long x 10-ft wide with an interface friction angle of 34 degrees and no cohesion. Since this method is to be applied to the east rock slope, and no evidence of water is observed on the rock discontinuities on the east side, it was assumed that no water was present along the sliding plane or in the tension crack (assumed dry conditions) for the purposes of the calculation. The resulting anchor pre-stress force is compared with the admissible rock anchor bar strength, considering a factor of safety of 1.67 on the ultimate tensile strength of the bar.

Once the required tension of the anchor bar was calculated, the necessary bond length was calculated using the working bond stress of 125 psi. The calculation of the working bond stress is included in the Pattern Bolting Design presented in Appendix B. Full details of shear bolting design can be found in Appendix C.

Shear Block Design Based on field observations, rock overhangs as large as 5 feet in vertical height are present in the west rock slope face as a result of previous rock slides, shear blocks are proposed to support the rock overhangs. The shear blocks are designed to support rock slabs approximately 7-ft thick and 14-ft long considering full water pressure along the slip plane and release surface. Using Limit Equilibrium analysis, the loading on the potential cast-in-place shear block was calculated

Oldtown, Maryland June 26, 2020 Terracon Project No. EY195055

Responsive Resourceful Reliable 11 by first determining the potential net sliding block force. Upon calculating the driving forces of the sliding block, a cast-in-place concrete shear block was analyzed considering the net sliding block forces, the friction along the base of the concrete shear block, and the normal forces provided by the pre-stressed rock anchors to achieve a sliding factor of safety of 1.5.

Once the required anchor bolt pre-stress load was calculated, the anchor bolt bar section and the required bond length were calculated. These calculations considered a factor of safety of 1.67 on the ultimate tensile strength of the bar and the working bond stress of 125 psi determined from the Pattern Bolting Design presented in Appendix B. Full details of shear block design can be found in Appendix D.

GENERAL COMMENTS

The analyses and recommendations presented in this report are based upon the data obtained at the indicated locations, or observations at the site, and from other information discussed in this report. This report does not reflect variations that may occur across the site or due to the modifying effects of weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing.

We have endeavored to prepare these calculations and report in accordance with generally accepted engineering practice and make no warranties, either express or implied, as to the professional advice provided under the terms of our agreement and included in this .

We appreciate the opportunity to be of service for this project. Please contact either of the undersigned if clarification is needed for any aspect of this report.

FIGURES

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

20401 Seneca Meadows Pkwy Germantown, MD 20876

PH. (301) 354-6100 FAX. (301) 354-6101

FIG No.SITE LOCATION MAP

Old own, Maryland

Project Manager:

Performed by:

Checked by:

Approved by:

NS

TH

NS

NS

Project No.

Scale:

File Name:

Date:

EY195055

See above

11/29/19

Approximate Limits of Project

Oldtown, Maryland June 26, 2020 Terracon Project No. EY195055

APPENDICES

Oldtown, Maryland June 26, 2020 Terracon Project No. EY195055

APPENDIX A – PINNED MESH DEIGN

DESIGN CALCULATION OR ANALYSIS COVER SHEET

Project Name: CHOH: Improve Visitor Safety and Remediate Rockfall Hazards Date: 2-20-2020

Terracon Project Number: EY195055 No. of Pages: 4

Calculation Description:

Pinned mesh system for rockfall protection in zones RF003, RF004, RF005, RF006, RF007, and RF008 Objective:

See next page Results:

Maccaferri SteelGrid HR30GP, or equivalent, is sufficient to contain the anticipated rockfall debris.

#8 all-threaded bars (Gr. 75) that are 6-ft long and spaced center-to-center 6-ft horizontally and 6-ft vertically should be used to anchor the pinned mesh drapery system to the slope using epoxy resin grout.

Item No. Description No. of Pages Revision 1 Pinned Mesh Design Calculations 4 0

Performed By: Tim Hastings, PE 02/20/2020

(Print Name) (Sign) (Date)

Checked By: Carlos Englert, PE 02/20/2020

(Print Name) (Sign) (Date)

Reviewed By: Eric B. Rehwoldt, PE, PG 03/23/2020 (Print Name) (Sign) (Date)

PE: Eric B. Rehwoldt (Print Name)

21356 (License Number)

09/26/2020 (Expiration Date)

Objectives:

Based on observations and analyses described in the Rockfall Geohazard Evaluation Report dated December 3, 2019, there is potential for rockfall debris from the existing upper East Slope to dislodge and impact the areas located directly below in zones RF003, RF004, RF005, RF005, RF006, RF007, and RF008, therefore, a pinned mesh system is proposed to be installed to control rockfall at these locations.

Below is the design of the pinned mesh system.

Design Methodology:

The pinned mesh system was designed using the MacRo software developed by Maccaferri. The software uses a limit equilibrium approach taking into numerous variables including topography, rock mass properties, joint geometry and properties, mesh type and related restrain conditions.

Assumptions:

The average angle of the slope in zones RF003, RF004, RF005, RF005, RF006, RF007, and RF008 is 65 degrees from horizontal.

The thickness of surficial instability of the slope is 4-ft.

Horizontal spacing between the anchors is 6-ft.

Vertical spacing between the anchors is 6-ft.

The most dangerous joint has an inclination of 20 degrees from horizontal.

NATIONAL PARK SERVICE / EY195055Client:

www.maccaferri.com pag. 1 of 2

Reinforced System Rock and Soil Slope Protection Design Software

MACRO 1

Safety coefficient to reduce stabilizing forces

Inclination [º]

Compressive Strength JCS [MPa]

Roughness coefficient JRC

Project Information Title:

Number:

PAW PAW TUNNEL - SCHEMATIC DESIGN

EY195055

NATIONAL PARK SERVICEClient:

Designer:

Description:

Assumed plasticization between rock and anchor [m]

Safety Coefficients

Slope inclination [º]

Input

Rock Slope

Thickness of the surficial instability [m]

Mesh type

Mesh ultimate tensile strength [kN/m]

Maximum design displacement [m]

Mesh

1.22 Density of the rock mass [kN/m³] 26.40

0.20

Most Dangerous Joint

52.00

Horizontal spacing between the anchors [m]

Vertical spacing between the anchors [m]

Inclination of bar to the horizontal [º]

Steelgrid HR 30 177.00

0.18

1.83

1.83

Anchor Bars

Geometry

Anchor Type pp_CTG pp_ADTi pp_CTG

Bar internal diameter [mm] Bar type

Bar external diameter [mm] Thickness of corrosion crown [mm]

Bar yield stress [MPa]

Rock-grout adhesion (Bond stress) [MPa]

25.4

0.86

#8 All Threaded Bar

Factors affecting the stabilizing forces Uncertainty of the thickness of surficial instability

Uncertainty of the rock mass unit weight 1.05

1.20

Uncertainty of rock behavior and weathering 1.05

Factors affecting the driving forces Slope surface morphology

External loads 1.10

1.20

Seismic Acceleration

Horizontal seismic coefficient

Safety coefficient to increase the driving forces

Global Safety Coefficient 1.74

1.32

Mesh Coefficient for the mesh tensile resistance

Coefficient for the maximum mesh displacement

Anchor type Coefficient for the steel bar yield stress

Coefficient for rock-grout adhesion (bound stress) 2.00

1.66

0.00

0.05

1.32

1.20

2.50

B

MACRO Studio | Copyright® Maccaferri 2012-2014 | 2.0.850d | 2014.MAR.14 | Notice: Maccaferri is not responsible for the drawings and the calculations transmited, since they should be intended as general design outlines and advice, aiming only to the best use of the produts.

NATIONAL PARK SERVICE / EY195055Client:

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Reinforced System Rock and Soil Slope Protection Design Software

MACRO 1

Angle between perpendicular to slope and bar axis [º]

Minimum acceptable steel yield stress [MPa]

Effective cross section of bar [mm²]

Potential unstable volume on joint - case A [m³/m]

Potential unstable volume on joint - case B [m³/m]

Potential unstable volume on joint - case C [m³/m]

Sliding plane stabilizing forces - per anchorage [kN]

Results

Satisfied Satisfied Satisfied

Stabilizing forces [kN]

Driving forces [kN]

Ratio Stabilizing/Driving forces

Bar design check Mesh design check Serviceability design check

Bar design

Minimum drilling diameter (NOMINAL) [mm]

1.16

126.86

6.52 1.001.16

146.87

5.00

301.20

506.71

40.40

Geometry

Nails Design Instability Model

Maximum pull-out force (total) [kN]

12.29

5.20

12.29

0.30

Minimum total bar length [m]

1.70

2.20

Mesh design

Admissible tensile stress of the mesh [kN/m]

Max. tensile stress within the mesh [kN/m]

Force-strength ratio 6.52

70.80

10.85

Punching forces acting on the mesh [kN]

35.53

18.24

8.74

11.17

5.78

0.00

0.46

0.89

1.35

Maximum acceptable displacement [m]

Calculated mesh displacement [m]

Displacement Ratio

Serviceability

1.00

0.15

0.15

Pressure on the average slip surface [MPa]

Initial dilatance of the most dangerous joint [º]

Total unstable volume controlled by each anchorage [m³]

Features of the instability

4.09

0.00

0.03

Total unstable weight controlled by each anchorage [kN] 107.86

79.64 Maximum rock volume that can slide between anchors

[m³/m]

Maximum rock weight that can slide between anchors [kN/m]

Sum of driving forces acting on the sliding plane [kN/m]

Sum of stabilizing forces acting on the sliding plane [kN/m]

Average angle between deformed mesh plane and rock surface [º]

(Slope SF)

Minimum length (bar) in the unstable rock mass [m]

Minimum bar length in the stable rock mass [m]

Anchor pull-out force due to global instability [kN]

Anchor pull-out force from load on the mesh [kN]

MACRO Studio | Copyright® Maccaferri 2012-2014 | 2.0.850d | 2014.MAR.14 | Notice: Maccaferri is not responsible for the drawings and the calculations transmited, since they should be intended as general design outlines and advice, aiming only to the best use of the produts.

APPENDIX B – PATTERN BOLTING DESIGN

DESIGN CALCULATION OR ANALYSIS COVER SHEET

Project Name: CHOH: Improve Visitor Safety and Remediate Rockfall Hazards Date: 2-20-2020

Terracon Project Number: EY195055 No. of Pages: 15

Calculation Description:

Calculate the necessary pattern bolting to stabilize large areas of rock slabs potentially unstable or subject to buckling to achieve a minimum sliding Factor of Safety of 1.5.

Objective:

To calculate the necessary bolt size and length to support a rock slab undergoing planar sliding if the bolts were installed and spaced every 6 ft vertically and horizontally.

Results:

The pattern bolting should consist of #8 all-threaded (Gr. 75) bars at 6 feet on centers installed using epoxy resin grout with a minimum 4 ft unbonded length and 6 ft bond length, and pre-stressed to 35 kips.

Item No. Description No. of Pages Revision 1 Pattern Bolting 13 0

Performed By: Tim Hastings, PE 02/20/2020

(Print Name) (Sign) (Date)

Checked By: Carlos Englert, PE 02/20/2020

(Print Name) (Sign) (Date)

Reviewed By: Eric B. Rehwoldt, PE, PG 03/23/2020 (Print Name) (Sign) (Date)

PE: Eric B. Rehwoldt (Print Name)

21356 (License Number)

Design Methodology:

Using the RocScience program RocPlane, a series of potential planar failure conditions within the West Slope were considered, including water uplift pressures assumed over 30% of the slip surface length. RocPlane uses a limiting equilibrium formulation to calculate the sliding factor of safety. The basic inputs of the program are the rock discontinuity and slope geometry, unit weight of the rock, assumed shear strength parameters of the rock joint interface (interface friction angle of 34 degrees and no cohesion), and the pre-stress of the proposed rock anchors. A target factor of safety of 1.5 was used for calculation purposes. Based on FHWA guidance (FHWA-TS-89-045) the required pre-stress of the rock anchor to increase the normal force on the sliding block was calculated by the program to achieve a factor of safety of 1.5.

Additionally, a hand calculation using the limit equilibrium approach was performed on an assumed local sliding block measuring 4 ft thick x 6 ft long x 6 ft wide. The 6 ft long by 6 ft wide section was based on our assumed pattern bolt spacing and tributary area acting on each anchor.

In this calculation, it was assumed that water is not present along the sliding plane or in the tension crack (assumed dry conditions) as drains are proposed to be installed in conjunction with the pattern bolting.

Once the required anchor bolt pre-stress load was calculated for each method above, the necessary anchor bolt bar section and the required bond length were calculated considering a factor of safety of 1.67 on the ultimate tensile strength of the bar, and the working bond stress of 125 psi determined from the Lachel & Associates Rock Bolt Proof Test Data sheets performed on June 26, 2017 at the project site.

Assumptions:

For the RockPlane Analyses

Water is present along 30% of the sliding plane with peak pressure mid height.

Friction angle for the sliding plane is 34-deg (no cohesion present on sliding plane).

Unit weight of rock = 168 pcf

For the Hand Analyses

Sliding block is 4 ft thick x 6 ft long x 6 ft wide.

Water is not present along sliding plane or tension crack (dry condition).

Friction angle for the sliding plane is 34-deg (no cohesion present on sliding plane).

No external loading on the sliding block

Sliding surface has an average slope angle of 55 deg from horizontal

Unit weight of rock = 168 pcf

Pe ak

W at er P re ss ur e

0.

k sf

Sl op e H ei gh t

5.

ft

D is t.

to

S lo pe C re st

0.

ft

Te ns io n

C ra ck

.2 f t

U pp er F ac e

W id th

2.

ft

U pp er F ac e

H ei gh t

.2 f t

Fa ilu re P la ne

A ng le

6.

Sl op e

An gl e

.0

U pp er F ac e

An gl e

.0

Te ns io n

C ra ck A ng le

0.

D riv in g

Fo rc e

.9 ki ps

/ft

N or m al

F or ce

8.

k ip s/ ft

B ol t P ro pe rti es

A ng le

C ap ac ity

Le ng th A nc hL en gt h

.0 ki ps /ft

.0 f t

.9 f t

Fa ct or o f S af et y

1.

D riv in g

Fo rc e

.9 ki ps

/ft R es is tin g

Fo rc e

.6 ki ps

/ft W ed ge

W ei gh t

.6 ki ps /ft

W ed ge V ol um e

8.

ft ^3

/ f t

Sh ea r S tre ng th

0.

k sf

Sh ea r R es is ta nc e

.4 ki ps /ft

N or m al

F or ce

.8 ki ps

/ft Pl an e

W av in es s

.0

Ac tiv e Bo lt Fo rc e

.0 ki ps /ft

Ac tiv e Bo lt An gl e

.0

Pa ss iv e Bo lt Fo rc e

0.

k ip s/ ft

Pa ss iv e

Bo lt

An gl e 0.

0° W at er

F or ce o n Fa ilu re

P la ne 9.

k ip s/ ft W at er

F or ce o n Te ns io n C ra ck

0.

k ip s/ ft

100 80 60 40 20 0 -20

-6

-4

-2

An al ys is

De sc rip tio n Se gm en t 1 : W es t S id e

St a

Pl an ar S lid in g An al ys is Co m pa ny Te rr ac on Dr aw n

By T.

H as tin gs

Fi le

N am e Se gm en t 1

W es t S id e St a

.p ln

Da te

Fe br ua ry

, 2

Pr oj ec t

CH

OH

: I m pr ov e Vi sit or

S af et y

Re m ed ia te

R oc k Fa ll Ha za rd s (P aw P aw T un ne l)

RO

CP

LA

NE

.0

W at er P re ss ur e

0.

k sf

Sl op e H ei gh t

0.

ft

D is t.

to

S lo pe C re st

8.

ft

Te ns io n

C ra ck

.4 f t

U pp er F ac e

W id th

.0 f t

U pp er F ac e

H ei gh t

.6 f t

Fa ilu re P la ne

A ng le

9.

Sl op e

An gl e

.0

U pp er F ac e

An gl e

.0

Te ns io n

C ra ck A ng le

0.

D riv in g

Fo rc e

.9 ki ps

/ft

N or m al

F or ce

8.

k ip s/ ft

B ol t P ro pe rti es

A ng le

C ap ac ity

Le ng th A nc hL en gt h

.4 ki ps /ft

.0 f t

.1 f t

Fa ct or o f S af et y

1.

D riv in g

Fo rc e

.9 ki ps

/ft R es is tin g

Fo rc e

.5 ki ps

/ft W ed ge

W ei gh t

.4 ki ps /ft

W ed ge V ol um e

9.

ft ^3

/ f t

Sh ea r S tre ng th

0.

k sf

Sh ea r R es is ta nc e

.5 ki ps /ft

N or m al

F or ce

.9 ki ps

/ft Pl an e

W av in es s 0.

0° Ac tiv e

Bo lt

Fo rc e

.4 ki ps

/ft Ac tiv e

Bo lt

An gl e

.0

Pa ss iv e

Bo lt

Fo rc e 0.

k ip s/ ft Pa ss iv e Bo lt An gl e

0.

0°

W at er F or ce o n

Fa ilu re P la ne

3.

k ip s/ ft

W at er F or ce o n

Te ns io n

C ra ck 0.

k ip s/ ft

60 40 20 0 -20

-4

-2

An al ys is

De sc rip tio n Se gm en t 2 : E as t S id e

St a

Pl an ar S lid in g An al ys is Co m pa ny Te rr ac on Dr aw n

By T.

H as tin gs

Fi le

N am e Se gm en t 2

Ea st

S id e St a

.p ln

Da te

Fe br ua ry

, 2

Pr oj ec t

CH

OH

: I m pr ov e Vi sit or

S af et y

Re m ed ia te

R oc k Fa ll Ha za rd s (P aw P aw T un ne l)

RO

CP

LA

NE

.0

W at er P re ss ur e

1.

k sf

Sl op e H ei gh t

.0 f t

D is t.

to

S lo pe C re st

9.

ft

Te ns io n

C ra ck

.1 f t

U pp er F ac e

W id th

.0 f t

U pp er F ac e

H ei gh t

.5 f t

Fa ilu re P la ne

A ng le

7.

Sl op e

An gl e

.0

U pp er F ac e

An gl e

.0

Te ns io n

C ra ck A ng le

0.

D riv in g

Fo rc e

.0 ki ps

/ft

N or m al

F or ce

0.

k ip s/ ft

B ol t P ro pe rti es

A ng le

C ap ac ity

Le ng th A nc hL en gt h ki ps /ft

.0 f t

.5 f t

Fa ct or o f S af et y

1.

D riv in g

Fo rc e

.0 ki ps

/ft R es is tin g

Fo rc e

.6 ki ps

/ft W ed ge

W ei gh t

.5 ki ps /ft

W ed ge V ol um e

3.

ft ^3

/ f t

Sh ea r S tre ng th

0.

k sf

Sh ea r R es is ta nc e

.4 ki ps /ft

N or m al

F or ce

.7 ki ps

/ft Pl an e

W av in es s

.0

Ac tiv e Bo lt Fo rc e

.0 ki ps /ft

Ac tiv e Bo lt An gl e

.0

Pa ss iv e Bo lt Fo rc e

0.

k ip s/ ft

Pa ss iv e

Bo lt

An gl e 0.

0° W at er

F or ce o n Fa ilu re

P la ne

.4 ki ps

/ft W at er

F or ce o n Te ns io n C ra ck

0.

k ip s/ ft

150 100 50 0 -50

-1

-5

An al ys is

De sc rip tio n Se gm en t 2 : W es t S id e

St a

Pl an ar S lid in g An al ys is Co m pa ny Te rr ac on Dr aw n

By T.

H as tin gs

Fi le

N am e Se gm en t 2

W es t S id e St a

.p ln

Da te

Fe br ua ry

, 2

Pr oj ec t

CH

OH

: I m pr ov e Vi sit or

S af et y

Re m ed ia te

R oc k Fa ll Ha za rd s (P aw P aw T un ne l)

RO

CP

LA

NE

.0

W at er P re ss ur e

0.

k sf

Sl op e H ei gh t

0.

ft

D is t.

to

S lo pe C re st

3.

ft

Te ns io n

C ra ck

.4 f t

U pp er F ac e

W id th

.0 f t

U pp er F ac e

H ei gh t

.7 f t

Fa ilu re P la ne

A ng le

4.

Sl op e

An gl e

.0

U pp er F ac e

An gl e

.0

Te ns io n

C ra ck A ng le

0.

D riv in g

Fo rc e

.3 ki ps

/ft

N or m al

F or ce

7.

k ip s/ ft

B ol t P ro pe rti es

A ng le

C ap ac ity

Le ng th A nc hL en gt h

.9 ki ps /ft

.0 f t

.4 f t

Fa ct or o f S af et y

1.

D riv in g

Fo rc e

.3 ki ps

/ft R es is tin g

Fo rc e

.6 ki ps

/ft W ed ge

W ei gh t

.9 ki ps /ft

W ed ge V ol um e

1.

ft ^3

/ f t

Sh ea r S tre ng th

0.

k sf

Sh ea r R es is ta nc e

.6 ki ps /ft

N or m al

F or ce

.5 ki ps

/ft Pl an e

W av in es s 0.

0° Ac tiv e

Bo lt

Fo rc e

.9 ki ps

/ft Ac tiv e

Bo lt

An gl e

.0

Pa ss iv e

Bo lt

Fo rc e 0.

k ip s/ ft Pa ss iv e Bo lt An gl e

0.

0°

W at er F or ce o n

Fa ilu re P la ne

3.

k ip s/ ft

W at er F or ce o n

Te ns io n

C ra ck 0.

k ip s/ ft

60 40 20 0

-4

-2

An al ys is

De sc rip tio n Se gm en t 3 : E as t S id e

- P la na r S lid in g An al ys is Co m pa ny Te rr ac on Dr aw n

By T.

H as tin gs

Fi le

N am e Se gm en t 3

Ea st

S id e St a

.p ln

Da te

Fe br ua ry

, 2

Pr oj ec t

CH

OH

: I m pr ov e Vi sit or

S af et y

Re m ed ia te

R oc k Fa ll Ha za rd s (P aw P aw T un ne l)

RO

CP

LA

NE

.0

W at er P re ss ur e

0.

k sf

Sl op e H ei gh t

0.

ft

D is t.

to

S lo pe C re st

0.

ft

Te ns io n

C ra ck

.4 f t

U pp er F ac e

W id th

.0 f t

U pp er F ac e

H ei gh t

.5 f t

Fa ilu re P la ne

A ng le

2.

Sl op e

An gl e

.0

U pp er F ac e

An gl e

.0

Te ns io n

C ra ck A ng le

0.

D riv in g

Fo rc e

.6 ki ps

/ft

N or m al

F or ce

8.

k ip s/ ft

B ol t P ro pe rti es

A ng le

C ap ac ity

Le ng th A nc hL en gt h

.9 ki ps /ft

.0 f t

.9 f t

Fa ct or o f S af et y

1.

D riv in g

Fo rc e

.6 ki ps

/ft R es is tin g

Fo rc e

.3 ki ps

/ft W ed ge

W ei gh t

.3 ki ps /ft

W ed ge V ol um e

4.

ft ^3

/ f t

Sh ea r S tre ng th

0.

k sf

Sh ea r R es is ta nc e

.2 ki ps /ft

N or m al

F or ce

.5 ki ps

/ft Pl an e

W av in es s

.0

Ac tiv e Bo lt Fo rc e

.9 ki ps /ft

Ac tiv e Bo lt An gl e

.0

Pa ss iv e Bo lt Fo rc e

0.

k ip s/ ft

Pa ss iv e

Bo lt

An gl e 0.

0° W at er

F or ce o n Fa ilu re

P la ne

.6 ki ps

/ft W at er

F or ce o n Te ns io n C ra ck

0.

k ip s/ ft

100 50 0

-7

-5

-2

An al ys is

De sc rip tio n Se gm en t 3 : W es t S id e

- P la na r S lid in g An al ys is Co m pa ny Te rr ac on Dr aw n

By T.

H as tin gs

Fi le

N am e Se gm en t 3

W es t S id e St a

.p ln

Da te

Fe br ua ry

, 2

Pr oj ec t

CH

OH

: I m pr ov e Vi sit or

S af et y

Re m ed ia te

R oc k Fa ll Ha za rd s (P aw P aw T un ne l)

RO

CP

LA

NE

.0

Paw Paw Tunnel - Pattern Bolting Design

EY195055 TH CE1/20/20

7 15

*Since the sliding block is assumed to be 4 ft thick, and our required bond length is 5 ft, a total of 9 ft is required. Based on standard com-mercially available rock bolts, a 10 ft total length of bolt will be used.

Using the RocScience program RocPlane, a series of potential planar failure encompassing the whole slope height considering water uplifting pressures over 30% of the slip surface length were performed. RocPlane uses limiting equilibrium formulation to calculate the sliding factor of safety.

The basic inputs of the program are the rock discontinuity and slope geometry, unit weight of the rock, shear strength parameters of the rock surface (interface friction angle of 34 degrees and no cohesion), and the pre-stress of the proposed rock anchors. A required factor of safety of 1.5 was used for calculation purposes. Once the required pre-stress of the rock anchor to increase the normal force on the sliding block was calculated by the program to achieve a factor of safety of 1.5.

Additionally, a hand calculation using the limit equilibrium approach was performed on an assumed local sliding block measuring 4 ft thick x 6 ft long x 6 ft wide. The 6 ft long by 6 ft wide section was based on our assumed pattern bolt spacing and therefore, the tributary area acting on each anchor. In this calculation, it was assumed that water is not present along the sliding plane or in the tension crack (assumed dry conditions) as drains are proposed to be installed in conjunction with the pattern bolting.

Once the required anchor bolt pre-stress load was calculated for each method above, the necessary anchor bolt bar section and the required bond length were calculated considering a factor of safety of 1.67 on the ultimate tensile strength of the bar and the working bond stress determined from the Lachel & Associates Rock Bolt Proof Test Data sheets performed on June 26, 2017 at the project site.

Assumptions:

For the RockPlane Analyses

Water is present along 30% of the sliding plane with peak pressure mid height.

Friction angle for the sliding plane is 34-deg (no cohesion present on sliding plane).

Unit weight of rock = 168 pcf

For the Hand Analyses

Sliding block is 4 ft thick x 6 ft long x 6 ft wide.

Water is not present along sliding plane or tension crack (dry condition).

Friction angle for the sliding plane is 34-deg (no cohesion present on sliding plane).

No external loading on the sliding block

Sliding surface has an average slope angle of 55 deg from horizontal

9 15

CE

11 15

14 15

15 15

APPENDIX C – SPOT BOLTING DESIGN

DESIGN CALCULATION OR ANALYSIS COVER SHEET

Project Name: CHOH: Improve Visitor Safety and Remediate Rockfall Hazards Date: 2-20-2020

Terracon Project Number: EY195055 No. of Pages: 5

Calculation Description:

Stabilize an unstable block with assumed dimensions of 4 ft thick x 10 ft long x 10 ft wide to achieve a sliding Factor of Safety of 1.5.

Objective:

Calculate the necessary spot bolt required to stabilize an unstable block.

Results:

The spot bolting should consist of #11 all-threaded (Gr. 75) bars installed using epoxy resin grout with a minimum 5 ft unbonded length and 10 ft bond length, and pre-stressed to 85 kips.

Item No. Description No. of Pages Revision 1 Spot Bolting 0

Performed By: Tim Hastings, PE 02/20/2020

(Print Name) (Sign) (Date)

Checked By: Carlos Englert, PE 02/20/2020

(Print Name) (Sign) (Date)

Reviewed By: Eric B. Rehwoldt, PE, PG 03/23/2020 (Print Name) (Sign) (Date)

PE: Eric B. Rehwoldt (Print Name)

21356 (License Number)

Assumptions:

Sliding block is 4 ft thick x 10 ft long x 10 ft wide.

Water is not present along sliding plane or tension crack (dry condition).

Friction angle for the sliding plane is 34-deg (no cohesion present on sliding plane).

No external loading on the sliding block Sliding surface has an average slope angle of 55 deg from horizontal

Paw Paw Tunnel - Spot Bolting Design

Paw Paw Tunnel - Spot Bolting Design

APPENDIX D – SHEAR BLOCK DESIGN

DESIGN CALCULATION OR ANALYSIS COVER SHEET

Project Name: CHOH: Improve Visitor Safety and Remediate Rockfall Hazards Date: 2-20-2020

Terracon Project Number: EY195055 No. of Pages: 10

Calculation Description:

Design of a cast-in-place shear block to prevent planar sliding of unstable rock ledges present in zones RF011, RF012, and RF013 Objective:

To design a cast-in-place concrete shear block that will be used to support sections of rock in zones RF011, RF012, and RF013 on the West Side of the canal prism that are at risk of dislodging due to planar sliding.

Results:

Cast-in-place concrete shear blocks, up to 7 ft wide by 7 ft high at 10 ft on centers, supported with two anchors per block conformed by #9 all-threaded (Gr. 75) bar using epoxy resin grout with a minimum 5 ft unbonded length and 10 ft bond length, and pre-stressed to 60 kips.

Item No. Description No. of Pages Revision 1 Shear Block Design Calculations 8 0

Performed By: Tim Hastings, PE 02/20/2020

(Print Name) (Sign) (Date)

Checked By: Carlos Englert, PE 02/20/2020

(Print Name) (Sign) (Date)

Reviewed By: Eric B. Rehwoldt, PE, PG 03/23/2020 (Print Name) (Sign) (Date)

PE: Eric B. Rehwoldt (Print Name)

21356 (License Number)

Based on field observations, rock overhangs as large as 5 ft in vertical height are present in the West Slope rock face resulting from previous rock slides, Shear blocks are proposed to support the rock overhangs, as well as the slope above the rock overhang locations. The shear blocks are designed to support rock slabs approximately 7 ft thick and 14 ft long considering full water pressure along the slip plane and release surface. Using Limit Equilibrium analysis, the loading on the potential cast-in-place shear block was calculated by first determining the potential net sliding block force. Upon calculating the driving forces of the sliding block, a cast-in-place concrete shear block was analyzed considering the net sliding block forces, the friction along the base of the concrete shear block and the normal forces provided by the pre-stressed rock anchors to achieve a sliding factor of safety of 1.5.

Once the required anchor bolt pre-stress load was calculated, the necessary anchor bolt bar section and the required bond length were calculated considering a factor of safety of 1.67 on the ultimate tensile strength of the bar, and the working bond stress of 125 psi determined from the Lachel & Associates Rock Bolt Proof Test Data sheets performed on June 26, 2017 at the project site.

Assumptions:

The mean dip of Joint Set J1 is 44-deg from horizontal.

The mean dip bedding joint is -48-deg from horizontal.

Water is 100% present on the sliding plane and in the tension crack.

Friction angle for the sliding plane is 34-deg (no cohesion present on sliding plane).

Height…