arema 2010 volume 1

13

2010

Manual for Railway Engineering

Volume 1

Track

Introduction

Foreword

Table of Contents

Chapter 1 Roadway and Ballast

(Chapters 3 and 10 were combined in 2000 to form Chapter 30)

Chapter 4 Rail

Chapter 5 Track

Chapter 30 Ties

General Subject Index

Copyright 2010by the

AMERICAN RAILWAY ENGINEERING AND MAINTENANCE-OF-WAY ASSOCIATION

All rights reservedNo part of this publication may be reproduced, stored in an information or data retrieval system, or

transmitted, in any form, or by any meanselectronic, mechanical, photocopying, scanning, recording, or otherwisewithout the prior written permission of the publisher. Photocopying or electronic reproduction

and/or distribution of this publication is a violation of USA and International Copyright laws and is expressly prohibited.

Correspondence regarding copyright permission should be directed to the Director of Administration, AREMA, 10003 Derekwood Lane, Suite 210, Lanham, MD 20706 USA.

ISSN 1542-8036 - Print Version

ISSN 1543-2254 - CD-ROM Version

1INTRODUCTION

The AREMA Manual for Railway Engineering contains principles, data, specifications, plans and economics pertaining to the engineering, design and construction of the fixed plant of railways (except signals and communications), and allied services and facilities. This material is developed by AREMA technical committees, is published on the AREMA web site for comments and then is approved for publication in the Manual by the Associations Board of Directors.

Designated as Recommended Practice1, the contents of the Manual are published as a guide to railways in establishing their individual policies and practices relative to the subjects, activities and facilities covered in the Manual, with the aim of assisting them to engineer and construct a railway plant which will have inherent qualities of safe and economical operation as well as low maintenance cost.

The AREMA Manual is not a maintenance manual per se since the development of standards or criteria for the maintenance of railway roadway, track and structures has always been considered to be the prerogative of the individual railways based on the nature and characteristics of their plant and operations and the specific characteristics of the geographical region or regions through which they operate.

The above statements also apply to the AREMA Portfolio of Trackwork Plans, which is a companion volume to the AREMA Manual. The plans in the Portfolio relate to the design, details, materials and workmanship for frogs, switches, crossings and other special trackwork and are prepared and maintained by Committee 5 Track, in addition to its Manual Chapter.

1 RECOMMENDED PRACTICE A material, device, design, plan, specification, principle or practice recommended to the railways for use 2010, American Railway Engineering and Maintenance-of-Way Association i

as required, either exactly as presented or with such modifications as may be necessary or desirable to meet the needs of individual railways, but in either event, with a view to promoting efficiency and economy in the location, construction, operation or maintenance of railways. It is not intended to imply that other practices may not be equally acceptable.

IntroductionTHIS PAGE INTENTIONALLY LEFT BLANK. 2010, American Railway Engineering and Maintenance-of-Way Association

ii AREMA Manual of Railway Engineering

2010, American Railway Engineering and Maintenance-of-Way Association iii

1

FOREWORD

This manual is current for the dates indicated on the title page of Volume I and is kept current by the issuance of annual updates.

The first two editions of the Manual were issued in 1905 and 1907 as the Manual of Recommended Practice for Railway Engineering and Maintenance of Way. Both were bound volumes and published by the Association under its original name American Railway Engineering and Maintenance-of-Way Association.

In 1911, the Association changed its name to the American Railway Engineering Association and issued the third edition of its Manual. This edition, and the next one in 1915, was called the Manual of the American Railway Engineering Association, and was also a bound volume. The final bound volumes were published in 1921 and 1929 under the name Manual of the American Railway Engineering Association for Railway Engineering. A number of Manual updates were issued between some of the bound volumes.

The first looseleaf edition of the AREMA Manual was issued in 1936 under the name Manual for Railway Engineering, the next in 1953. In 1961, the publication was reissued and called the Manual of Recommended Practice for Railway Engineering. The current title, Manual for Railway Engineering, was approved by the Board of Directors in 1970 and reverts to the former, simpler, more functional name although the contents are still recommended practice, as indicated in the preceding Introduction.

In 1996 the Manual was given a complete facelift. Not only was the manual available in paper form, it was also available in an electronic version stored on a CD-ROM. The Manual was enlarged to an 8 11 inch format, perfect bound and divided into four volumes. For our users convenience, the Manual returned to a loose leaf four volume set in 2000. Each volume covers one of four general areas: Track, Structures, Infrastructure and Passenger, and Systems Management. The CD-ROM contains a complete version of the manual, which can be run on several platforms (Windows, Macintosh, and Unix).

The Association also publishes the Portfolio of Trackwork Plans, which is a companion volume to the Manual for Railway Engineering. The Portfolio contains specifications and plans relating to the design of frogs, switches, crossings and other special trackwork. It was first issued about 1926 in cooperation with the Manganese Track Society.

As shown on the following Contents pages, the AREMA Manual for Railway Engineering is issued in four volumes, each volume divided into chapters with numbers corresponding to the numbers of the standing technical committees charged with the primary responsibility for developing and maintaining the chapters. In addition, each volume contains a General Subject Index which augments the separate Table of Contents provided with each Chapter and Part of the Manual.

To make the Manual easier to use and facilitate reference to parts of it, the committee identification number is carried throughout the publication by incorporating the number in the page numbering system. For complete information on the key features of the Manual, such as page numbering system, document dates, article dates, revision marks, and Proceedings references, the user is directed to the Introduction found in each Chapter.

As stated earlier, updates to the Manual normally are issued annually. Beginning in 2001, revision sets to the looseleaf books are available.

Foreword

2010, American Railway Engineering and Maintenance-of-Way Association

iv AREMA Manual of Railway Engineering

All holders of the Manual individual AREMA members, individual nonmembers, railways, universities, governmental agencies, consulting engineers, constructors, supply companies, or other firms are notified each year of the availability of the revised Manual and its cost.

Manuals ordered during the normal Association year will be furnished complete for the dates indicated on the title page.

Copies of the complete Manual may be purchased from Association Headquarters at the then current prices, which are subject to change without notice. To obtain current individual Chapters, please contact the Publications Department at AREMA at 301-459-3200.

2010, American Railway Engineering and Maintenance-of-Way Association v

TABLE OF CONTENTS

Current until publication of next edition

FOREWORD

This Manual is divided into four Volumes which are further subdivided into Chapters and Parts. Each volume contains a general subject index covering data found in all volumes. Each Chapter and Part are prefaced by a Table of Contents.

Because of numbering of Chapters to coincide in most cases with AREMA technical committees, there are no Chapters 3, 10, 19, 20, 21, 22, 23, 24, 25, 26, 29, 31 and 32. Committee 24 does not maintain a Manual Chapter.

VOLUME 1 TRACK

IntroductionForewordTable of Contents

Chapter 1 Roadway and BallastPart 1 RoadbedPart 2 BallastPart 3 Natural WaterwaysPart 4 CulvertsPart 5 PipelinesPart 6 FencesPart 7 Roadway SignsPart 8 TunnelsPart 9 Vegetation ControlPart 10 Geosynthetics

Chapter 4 RailPart 1 Design of RailPart 2 Manufacture of RailPart 3 Joining of RailPart 4 Maintenance of RailPart 5 MiscellaneousPart 6 Commentaries

Chapter 5 TrackPart 1 Tie PlatesPart 2 Track SpikesPart 3 CurvesPart 4 Track Construction

Table of Contents


vi AREMA Manual of Railway Engineering

VOLUME 1 TRACK (CONT)

Part 6 Specifications and Plans for Track ToolsPart 7 Rail AnchorsPart 8 Highway/Railway Grade CrossingsPart 9 Design Qualification Specifications for Elastic Fasteners on Timber Cross TiesPart 10 Miscellaneous

Chapter 30 TiesPart 1 General ConsiderationsPart 2 Evaluative Tests for Tie SystemsPart 3 Solid Sawn Timber TiesPart 4 Concrete TiesPart 5 Engineered Composite Ties


VOLUME 2 STRUCTURESChapter 7 Timber Structures

Part 1 Material Specifications for Lumber, Timber, Engineered Wood Products, Timber Piles, Fasteners, Timber Bridge Ties and Recommendations for Fire-Retardant Coating for Creosoted Wood

Part 2 Design of Wood Railway Bridges and Trestles for Railway LoadingPart 3 Rating Existing Wood Bridges and TrestlesPart 4 Construction and Maintenance of Timber StructuresPart 5 Inspection of Timber StructuresPart 6 Commentary

Chapter 8 Concrete Structures and FoundationsPart 1 Materials, Tests and Construction RequirementsPart 2 Reinforced Concrete DesignPart 3 Spread Footing FoundationsPart 4 Pile FoundationsPart 5 Retaining Walls, Abutments and PiersPart 6 Crib WallsPart 7 Mechanically Stabilized EmbankmentPart 10 Reinforced Concrete Culvert PipePart 11 Lining Railway TunnelsPart 12 Cantilever PolesPart 14 Repair and Rehabilitation of Concrete StructuresPart 16 Design and Construction of Reinforced Concrete Box Culverts Part 17 Prestressed ConcretePart 19 Rating of Existing Concrete BridgesPart 20 Flexible Sheet Pile BulkheadsPart 21 Inspection of Concrete and Masonry StructuresPart 22 Geotechnical Subsurface InvestigationPart 23 Pier Protection Systems at Spans Over Navigable StreamsPart 24 Drilled Shaft FoundationsPart 25 Slurry Wall ConstructionPart 26 Recommendations for the Design of Segmental BridgesPart 27 Concrete Slab TrackPart 28 Temporary Structures for ConstructionPart 29 Waterproofing

Part 5 Track Maintenance

Table of Contents


AREMA Manual of Railway Engineering vii

VOLUME 2 STRUCTURES (CONT)

Chapter 9 Seismic Design for Railway StructuresPart 1 Seismic Design for Railway StructuresPart 2 Commentary to Seismic Design for Railway Structures

Chapter 15 Steel StructuresPart 1 DesignPart 3 FabricationPart 4 ErectionPart 6 Movable BridgesPart 7 Existing BridgesPart 8 MiscellaneousPart 9 CommentaryPart 10 Bearing DesignPart 11 Bearing Construction


VOLUME 3 INFRASTRUCTURE AND PASSENGER

Commuter, Transit and High Speed Rail - Unified Table of Contents and Common Elements of Planning, Design and Operations Analyses for Passenger Rail Systems

Chapter 6 Buildings and Support FacilitiesPart 1 Specifications and General Design Criteria for Railway BuildingsPart 2 Design Criteria for Railway Office BuildingsPart 3 Design Criteria for Spot Car Repair ShopsPart 4 Design Criteria for Diesel Repair FacilitiesPart 5 Energy Conservation and AuditsPart 6 Locomotive Sanding FacilitiesPart 7 Design Criteria for Railway Materials Management FacilitiesPart 8 Design Criteria for Railway Passenger StationsPart 9 Design Criteria for Centralized Maintenance-of-Way Equipment Repair ShopsPart 10 Design Criteria for Observation TowersPart 11 Design Criteria for CTC CentersPart 12 Design Criteria for a Locomotive Washing FacilityPart 13 Passenger Rail (Coach)/Locomotive Maintenance, Repair and Servicing FacilitiesPart 14 Selection and Maintenance of Roofing SystemsPart 15 Inspection of Railway BuildingsPart 16 Design Criteria for Main Line Fueling Facilities

Table of Contents


viii AREMA Manual of Railway Engineering

VOLUME 3 INFRASTRUCTURE AND PASSENGER (CONT)

Chapter 11 Commuter and Intercity Rail SystemsPart 1 IntroductionPart 2 Corridor Planning ConsiderationsPart 3 Track and Roadway ConsiderationsPart 4 Facilities and Structural ConsiderationsPart 5 Vehicle ConsiderationsPart 6 Signals, Communications, and Propulsion ConsiderationsPart 7 Maintenance of Way Considerations

Chapter 12 Rail TransitPart 1 IntroductionPart 2 Corridor Planning ConsiderationsPart 3 Track and Roadway ConsiderationsPart 4 Facilities and Structural ConsiderationsPart 5 Vehicle ConsiderationsPart 6 Signals, Communications, and Propulsion ConsiderationsPart 7 Maintenance of Way ConsiderationsPart 8 Embedded Track

Chapter 14 Yards and TerminalsPart 1 GeneralitiesPart 2 Freight Yards and Freight TerminalsPart 3 Freight Delivery and TransferPart 4 Specialized Freight TerminalsPart 5 Locomotive FacilitiesPart 6 Passenger FacilitiesPart 7 Other Yard and Terminal Facilities

Chapter 17 High Speed Rail SystemsPart 1 IntroductionPart 2 Corridor Planning ConsiderationsPart 3 Track and Roadway ConsiderationsPart 4 Facilities and Structural ConsiderationsPart 5 Vehicle ConsiderationsPart 6 Signals, Communications, and Propulsion ConsiderationsPart 7 Maintenance of Way Considerations

Chapter 18 Light Density and Short Line RailwaysPart 1 General EngineeringPart 2 TrackPart 3 BridgesPart 4 Communication and Signals

Chapter 27 Maintenance-of-Way Work EquipmentPart 1 GeneralPart 2 Roadway Machines

Table of Contents


AREMA Manual of Railway Engineering ix

VOLUME 3 INFRASTRUCTURE AND PASSENGER (CONT)

Chapter 33 Electrical Energy UtilizationPart 1 Factors to Consider in Making Electrification Economic StudiesPart 2 ClearancesPart 3 Recommended VoltagesPart 4 Railroad Electrification SystemsPart 5 Signal Compatibility with Alternating Current Railway ElectrificationPart 6 Power Supply and Distribution Requirements for Railroad Electrification SystemsPart 7 Rail BondingPart 8 Catenary and Locomotive InteractionPart 9 Ancillary Power SystemsPart 10 IlluminationPart 12 Power Supply and Electrification Systems


VOLUME 4 SYSTEMS MANAGEMENT

Chapter 2 Track Measuring SystemsPart 1 DefinitionsPart 2 Track Measuring VehiclesPart 3 Typical Uses of Data Collected by Track Measuring VehiclesPart 4 Measurement Frequency Practices for Track Geometry Measuring Vehicles

Chapter 13 EnvironmentalPart 1 IntroductionPart 2 Environmental Review ConsiderationsPart 3 Water and Wastewater CompliancePart 4 Air Quality CompliancePart 5 Waste Management

Chapter 16 Economics of Railway Engineering and OperationsPart 1 Railway LocationPart 2 Train PerformancePart 3 PowerPart 4 Railway OperationPart 5 Economics and Location of Defect Detector SystemsPart 6 Railway Applications of Industrial & Systems EngineeringPart 7 Public Improvements Their Costs and BenefitsPart 8 OrganizationPart 9 Programming WorkPart 10 Construction and Maintenance OperationsPart 11 Equated Mileage ParametersPart 12 AccountingPart 14 TaxesPart 15 Planning, Budgeting and Control

Chapter 28 ClearancesPart 1 Clearance Diagrams Fixed ObstructionsPart 2 Equipment DiagramsPart 3 Methods and Procedures

Table of Contents


x AREMA Manual of Railway Engineering

VOLUME 4 SYSTEMS MANAGEMENT (CONT)

AAR Scale Handbook (Included for Information Only)Part 1 Specifications for the Location, Maintenance, Operation, and Testing of

Railway Track ScalesPart 2 Basic Specifications for the Manufacture and Installation of Railway Track ScalesPart 3 Specifications for the Design and Installation of Low Profile, Pitless, and Instrumented

Railway Track ScalesPart 4 Rules for the Manufacture, Installation, Location, Operation and Testing of Railway

Master Track ScalesPart 5 Vehicle ScalesPart 6 Hopper Type ScalesPart 7 Belt Conveyor Scales (Amended 2009)Part 8 Mass Flow Meters (Added 2010)Part 9 Other Scales

Guide for SI Metrication


2010, American Railway Engineering and Maintenance-of-Way Association 1-i

1

3

1

CHAPTER 1

ROADWAY AND BALLAST1

TABLE OF CONTENTS

Part/Section Description Page

1 Roadbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-11.1 Exploration and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-31.2 Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-121.3 Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-381.4 Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-53

2 Ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-12.0 Substructure Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-42.1 Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-52.2 Scope (1991) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-92.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-92.4 Property Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-102.5 Production and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-132.6 Loading (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-132.7 Inspection (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-142.8 Sampling and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-142.9 Measurement and Payment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-152.10 Maintenance Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-152.11 Sub-ballast Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2-19

3 Natural Waterways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-13.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-43.2 Drainage Basin Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-53.3 Capacity of Waterway Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-73.4 Basic Concepts and Definitons of Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-203.5 Calculating Scour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-253.6 Protecting Roadway and Bridges From Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-603.7 Means of Protecting Roadbed and Bridges from Washouts and Floods . . . . . . . . . . . . . . . . 1-3-148

1 The material in this and other chapters in the AREMA Manual for Railway Engineering is published as recommended practice to railroads and others concerned with the engineering, design and construction of railroad fixed properties (except signals and communications), and allied services and facilities. For the purpose of this Manual, RECOMMENDED PRACTICE is defined as a material, device, plan, specification, principle or practice recommended to the railways for use as required, either exactly as presented or with such modifications as may be necessary or desirable to meet the needs of individual railways, but in either event, with a view to promoting efficiency and economy in the location, construction, operation or maintenance of railways. It is not intended to imply that other practices may not be equally acceptable.


1-ii AREMA Manual for Railway Engineering

TABLE OF CONTENTS (CONT)


3.8 Construction and Protection of Roadbed Across Reservoir Areas . . . . . . . . . . . . . . . . . . . . 1-3-1503.9 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-159

4 Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-14.1 Location and Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-64.2 Specifications for Placement of Reinforced Concrete Culvert Pipe . . . . . . . . . . . . . . . . . . . 1-4-94.3 Specifications for Prefabricated Corrugated Steel Pipe and Pipe-arches for Culverts,

Storm Drains, and Underdrains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-94.4 Specifications for Coated Corrugated Steel Pipe and Arches. . . . . . . . . . . . . . . . . . . . . . . . 1-4-174.5 Standard Specification for Corrugated Aluminum Alloy Pipe . . . . . . . . . . . . . . . . . . . . . . . 1-4-174.6 Specifications for Corrugated Structural Steel Plate Pipe, Pipe-arches, and Arches. . . . . 1-4-244.7 Specifications for Corrugated Structural Aluminum Alloy Plate Pipe, Pipe-arches,

and Arches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-264.8 Hydraulics of Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-294.9 Design Criteria for Corrugated Metal Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-564.10 Design Criteria for Structural Plate Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-654.11 Culvert End Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-684.12 Assembly and Installation of Pipe Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-704.13 Earth Boring and Jacking Culvert Pipe through Fills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-754.14 Culvert Rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-774.15 Specification for Steel Tunnel Liner Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-824.16 Construction of Tunnel Using Steel Tunnel Liner Plates . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-904.17 Culvert Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-914.18 Perforated Pipe Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4-100

5 Pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-15.1 Specifications for Pipelines Conveying Flammable Substances. . . . . . . . . . . . . . . . . . . . . . 1-5-35.2 Specifications for Uncased Gas Pipelines within the Railway Right-of-Way . . . . . . . . . . . 1-5-115.3 Specifications for Pipelines Conveying Non-Flammable Substances . . . . . . . . . . . . . . . . . 1-5-235.4 Specifications for Overhead Pipelines Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5-295.5 Specifications for Fiber Optic Route Construction on Railroad Right of Way . . . . . . . . 1-5-31

6 Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-16.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-36.2 Specifications for Wood Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-46.3 Specifications for Concrete Fence Posts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-66.4 Specification for Metal Fence Posts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-106.5 Specifications for Right-of-way Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-136.6 Stock Guards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-206.7 Methods of Controlling Drifting Snow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-216.8 Specifications for Snow Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6-24

7 Roadway Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7-17.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7-27.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7-47.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7-4


AREMA Manual for Railway Engineering 1-iii

1

3

4

TABLE OF CONTENTS (CONT)


8 Tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-18.1 Scope (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-28.2 Design (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-28.3 Construction (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-38.4 Measurement and Payment (1982). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-68.5 Lining (1982) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-68.6 Ventilation (1982) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-68.7 Increasing Clearances In Existing Tunnels (1982) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8-7

9 Vegetation Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-19.1 Rationale and Scope of Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-29.2 Preparing a Vegetation Control Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-29.3 Executing a Vegetation Control Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-119.4 Evaluating Results of a Vegetation Control Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-149.5 Glossary (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-169.6 Lead Agencies (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-179.7 Commentary (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9-20

10 Geosynthetics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10-110.1 Geotextile Specifications for Railroad Track Separation/Stabilization Applications . . . . . 1-10-310.2 Geotextile Specifications for Railroad Drainage Applications . . . . . . . . . . . . . . . . . . . . . . . 1-10-910.3 Geotextile Specifications for Railroad Erosion Control Applications . . . . . . . . . . . . . . . . . . 1-10-1510.4 Geocomposite Drainage System Specifications for Railroad Applications . . . . . . . . . . . . . . 1-10-2010.5 Cellular Confinement System Specification for Railroad Use . . . . . . . . . . . . . . . . . . . . . . . 1-10-2410.6 Geogrid Specifications for Ballast and Sub-Ballast Reinforcement . . . . . . . . . . . . . . . . . . . 1-10-28

Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-G-1

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-R-1


1-iv AREMA Manual for Railway Engineering

INTRODUCTION

The Chapters of the AREMA Manual are divided into numbered Parts, each comprised of related documents (specifications, recommended practices, plans, etc.). Individual Parts are divided into Sections by centered headings set in capital letters and identified by a Section number. These Sections are subdivided into Articles designated by numbered side headings.

Page Numbers In the page numbering of the Manual (1-2-1, for example) the first numeral designates the Chapter number, the second denotes the Part number in the Chapter, and the third numeral designates the page number in the Part. Thus, 1-2-1 means Chapter 1, Part 2, page 1.

In the Glossary and References, the Part number is replaced by either a G for Glossary or R for References.

Document Dates The bold type date (Document Date) at the beginning of each document (Part) applies to the document as a whole and designates the year in which revisions were last made somewhere in the document, unless an attached footnote indicates that the document was adopted, reapproved, or rewritten in that year.

Article Dates Each Article shows the date (in parenthesis) of the last time that Article was modified.

Revision Marks All current year revisions (changes and additions) which have been incorporated into the document are identified by a vertical line along the outside margin of the page, directly beside the modified information.

Proceedings Footnote The Proceedings footnote on the first page of each document gives references to all Association action with respect to the document.

Annual Updates New manuals, as well as revision sets, will be printed and issued yearly.

2010, American Railway Engineering and Maintenance-of-Way Association 1-1-1

1

3

1

Part 1

Roadbed1

2007

FOREWORD

Since the development of soil and foundation engineering as an important branch of civil engineering during the past few decades, earth and rock have come to be treated as construction materials. They have properties which can be evaluated and they are subject to strains and failures in the same way as other building materials.

Earth and rock are different, however, from such materials as steel and concrete in one fundamental way of which the designer should always be aware: each soil and rock deposit is extremely variable and has its own characteristics which reflect its origin and the factors affecting it since. As a result, investigation and testing are uniquely important if soils and rock are to be used economically and safely in engineering work.

This Part of the Manual is prepared with recognition of the importance of geotechnical knowledge in the design, construction and maintenance of track. The subgrade is considered to be as important to track performance as the rail and ballast. Keeping this balanced point of view in mind, an engineered approach is presented for many roadbed problems rather than reference to standard practice.

The choice of available methods is given along with an evaluation of the judgment factors involved in many of the questions relating to the design and construction of new roadbed and the upgrading and maintenance of existing roadbed. Considerations such as drainage and slope stability which affect the roadbed directly but are centered outside its physical limits are included.

Because of the variety of foundation conditions which occur and their associated problems, a number of references are given. Details of methods are presented only when adequate information is hard to find elsewhere. Specialized help is advisable when a detailed appraisal of the suitability and performance of particular deposits is required.

1 References, Vol. 74, 1973, p. 55; Vol. 77, 1976, p. 237; Vol. 87, 1986, p. 35; Vol. 89, 1988, pp. 40, 41. Reapproved with revisions 1988.

Roadway and Ballast


1-1-2 AREMA Manual for Railway Engineering

TABLE OF CONTENTS

Section/Article Description Page

1.1 Exploration and Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-31.1.1 General (2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-31.1.2 Preliminary Exploration (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-31.1.3 Detailed Geotechnical Exploration in Soil (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-41.1.4 Detailed Geotechnical Exploration in Rock (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-61.1.5 Construction Material Sources (2000). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-8

1.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-121.2.1 General (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-121.2.2 Cuts (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-131.2.3 Fills (2002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-231.2.4 Drainage (2003) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-32

1.3 Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-391.3.1 General (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-391.3.2 Contract Documents (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-39

1.4 Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-551.4.1 Maintenance of Roadbed (2007). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-551.4.2 Maintenane of Rock Slopes (2007). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1-641.4.3 Maintenance of Earth Slopes (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-651.4.4 Widening of Cuts (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-671.4.5 Drainage and Erosion Control (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-681.4.6 Methods of Opening Snow Blockades (2007) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-70

LIST OF FIGURES

Figure Description Page

1-1-1 Cut and Fill Section Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-131-1-2 Width of Rock Cut Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-171-1-3 Variable Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-191-1-4 Uniform Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-201-1-5 Permanent Bench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-211-1-6 Temporary Bench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-211-1-7 Zoning of Rock Fill Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-291-1-8 Interception of Sidehill Seepage by Subdrainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-371-1-9 Lowering of Ground Water In a Wet Cut. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-371-1-10 Lowering of Ground Water in Cut to Fill Transition (Longitudinal). . . . . . . . . . . . . . . . . . . . . 1-1-381-1-11 Lowering of Ground Water in Cut to Fill Transition (Sidehill) . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-381-1-12 Example of Distorted Roadbed Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-571-1-13 Example Cross Section of Displaced Roadbed and Ballast Pocket . . . . . . . . . . . . . . . . . . . . . . . 1-1-571-1-14 Method of Marking Track for Treatment of Frost Heaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-631-1-15 General Approach to Rock Fall Hazard Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-65

Roadbed


AREMA Manual for Railway Engineering 1-1-3

1

3

4

LIST OF TABLES

Table Description Page

1-1-1 Sources of Site Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-81-1-2 Procedures for Soil Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-101-1-3 Standard Procedures for Soil Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-101-1-4 Technical Descriptions of Cores or Fresh Exposures of Rock . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-111-1-5 Typical Tests for Rock Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-121-1-6 Factors Affecting Width of Cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-141-1-7 Factors Affecting Base Width of Rock Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-171-1-8 Design Factors for Rock Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-221-1-9 Improvement of Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-271-1-10 Soil Groups, Their Characteristics and Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-301-1-11 Guidelines for Limiting Velocities to Prevent Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-331-1-12 Potential Methods for Stabilizing Earth Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1-66

SECTION 1.1 EXPLORATION AND TESTING

1.1.1 GENERAL (2000)

a. Roadbed construction and maintenance costs can be reduced by using an effective exploration and testing program as the first and most important step of the design process.

b. Site investigations are usually done in two phases:

(1) PRELIMINARY SITE INVESTIGATION - Review of information available from published sources and previous investigations, supplemented by site reconnaissance. Roadbed maintenance investigations should include a history of slow orders, surfacing operations, drainage condition changes, apparent failure mechanism, failure frequency, and apparent correlation with weather.

(2) DETAILED SITE INVESTIGATION - Collection and analysis of detailed information on soil, rock, groundwater, surface drainage, and topography determined by exploration, sampling, and laboratory testing. Detailed maintenance information should include investigation of the ballast roadbed interface, particularly "ballast pockets", their density and drainage.

1.1.2 PRELIMINARY EXPLORATION (2000)

1.1.2.1 Information Available

a. New Construction - Geological, topographic, climatic, and seismic information from published sources is useful in planning exploration work and interpreting site observations. See Table 1-1-1.

b. Maintenance - Review the information for new construction as noted in Table 1-1-1, supplemented by a performance history of the problem area. Include a review of the slow order history, surfacing operations, track geometry history, traffic density history, drainage conditions, apparent failure mechanisms, frequency of failure, and apparent correlation with weather. Some problem maintenance areas will become readily apparent when the above information is graphed with respect to time.

Roadway and Ballast



1.1.2.2 Photogrammetry

1.1.2.2.1 New Construction

a. Aerial photographs at various scales are available for most locations. Photo mosaics can be assembled and used in studying the site conditions. Photos on a large scale may be required for more detailed studies and can be obtained on order.

b. Stereo-optic viewing of overlapping aerial photographs assists inrecognizing land forms, landslides, general soil types, drainage, and erosional features. Photo interpretation can aid in supplementing ground observations and in planning an appropriate detailed site investigation program. Since aerial photographs only showconditions at or near the ground surface, they cannot be used independently to give detailed subsurface information for design.

c. Other techniques for obtaining general surface conditions and landform characteristics as well as more detailed information for track layout, drainage design, and asset location may include ground or aerial based LIDAR (Light Detection and Ranging) and video based surveying techniques.

1.1.2.2.2 Maintenance

Aerial photographs are not routinely utilized. Soil Conservation Service photographswith adjacent soil types superimposed on them may be useful. Site specific aerial photographs can provide useful information relative to the local surface drainage conditions.

1.1.2.2.3 Site Reconnaissance

1.1.3 DETAILED GEOTECHNICAL EXPLORATION IN SOIL (2000)

1.1.3.1 General Soil Exploration Criteria

Construction or maintenance of a roadbed frequently involves an interface with, or the excavation of, either naturally deposited or mechanically placed soils. The ultimate stability of the roadbed will be governed by the engineering characteristics and suitability of these soils. An adequate exploration program should be developed with the assistance of a qualified geotechnical engineer to define these parameters. Procedures utilized can include, but should not be limited to, those listed in Table 1-1-2.

1.1.3.2 Embankment (Fill) Foundations


a. Embankment foundations are explored so that the embankments are designed to avoid failure or compensate for settlement of the subsoil. The subsurface and surface drainage conditions must be

a. New Construction - A thorough reconnaissance of the site is necessary to assess the existing conditions and establish the need for appropriate detailed tests. Effective site reconnaissance requires close observation of apparent surface soil conditions and rock exposures, as well as ground surface and drainage patterns. Observation of nearby excavations may provide useful information. A particular warning is given by the presence of soft ground, soils, which become weak when disturbed, ground water seepage, and eroding soil banks.

b. Maintenance - A thorough reconnaissance of the existing roadbed is necessary to understand the true nature of the roadbed failure mechanism. This will include examination of the roadbed cross section, profile, alignment, track geometry, and surface drainage. Look for ground water seepage, roadbed erosion, track squeeze, slides, irregularity of the shoulder vegetation lines, and any site specific anomalies which may be influencing the site conditions. Trackside trees and pole line are excellent indicators of slope movement in a maintenance situation.

Roadbed



1

3

4

determined to avoid conditions such as sinkholes, springs under the fill, excessive pore water pressures in the foundation soils, and inadvertent interception of an underground aquifer.


The First order of business in a catastrophic failure on an existing railroad embankment is to get the railroad open for service. This usually doesn't allow sufficient time to do a thorough detailed site exploration prior to reconstructing the roadbed. Many troublesome maintenance failures are of a "creeping" type. These manifest themselves in a poor or degrading track alignment and surface. This type of failure often requires substantial exploration to determine the failure mechanisms. Failure mechanism exploration is site specific and may be very complicated. Borings are required of sufficient depth to intercept any failure planes, as a minimum at least below the embankment foundation or depth of failure plane whichever is greater. Exploration of maintenance failure mechanisms should not be limited solely to boring. Other methods may include any of the following; cross trenches or test pits, inclinometer, piezometer, or examination of the exposed failed embankment surfaces.

1.1.3.3 Cuts


a. Locations of proposed cut slopes are explored to design stable slopes and berms. In fine grained soils this requires suitable samples and appropriate laboratory tests to determine the shear strength characteristics of the materials. In cohesionless, disturbed samples and standard penetration test values are usually adequate. In cohesive soils it may be necessary to obtain undisturbed tube samples for tests which include classification, water content, and shear strength. Most importantly, exploration should be carried out at least below the bottom of the proposed cut or deeper if recommended by the geotechnical engineer.

b. The exploration should determine the level of the groundwater table and efforts should be made to determine whether or not a perched water table exists. This may require a rather elaborate investigation, including the installation of standpipes at selected locations. Particular care should be taken to identify cohesionless layers that might become water-bearing at certain times or seasons. These can be expected to erode back from the face of the cut, causing local instability or a build-up of excess water pressure leading to a failure.

c. Sufficient information should be obtained to classify the materials likely to be encountered, determining suitability of the materials for use in adjacent fills. A knowledge of the geology of the area is useful to indicate the necessity for additional tests of a specialized nature. Some geological formations have swelling characteristics and should be investigated.


Typical failures in an existing cut include filled or non-functional ditches, surface water eroding the slope, shallow ballast sections, and inadequate subgrade support. An initial means for assessing the potential cause of a problem begins with performing a field observation. The question to be answered is, "What has caused a previously stable slope to fail?" Examine the top of the slope. Check the slope for chemical changes in soil properties, seepage and drainage changes, and additional loading surcharge above the top of slope. Use cross trenches, inclinometer, aerial photography, and previous area history to help determine the failure mechanism.

b. Depending on the material conditions encountered, the exploration and sampling requirements can be quite different. When granular material is encountered in the embankment foundation the exploration and sampling may be less then that required for cohesive soils but should be sufficient to confirm the range of the strength parameters. The depth and number of borings should be sufficient to provide the design information required.

c. Areas of new construction immediately adjacent to existing track, such as new sidings and auxiliary main lines, do not require detailed exploration. These areas would normally require few widely spaced borings unless specific problem areas warrant further examination. On new construction to avoid major problems at tie ins attention should be paid to grubbing, stripping, and benching.

Roadway and Ballast



1.1.3.4 Laboratory Testing and Analysis

Appropriate laboratory tests and analysis methods will be dependent on the soils encountered, the desired construction or existing roadbed configuration, and the sampling methods utilized. These can include, but should not be limited to, the tests listed in Table 1-1-3.

1.1.4 DETAILED GEOTECHNICAL EXPLORATION IN ROCK (2000)1.1.4.1 General Rock Exploration Criteria



When roadbed maintenance problems exist as a result of existing rock cut slopes, or the failure of the embankment bedding structure, it may be necessary to assess the stability of the associated rock structures prior to undertaking corrective measures. Such assessments may require an intrusive study, but in many cases can be explored by a detailed site investigation of geologic surface features and a thorough review of original construction plans and exploration records.

1.1.4.2 Rock Exploration Methodology


a. The first step of the exploration process involves a detailed geological reconnaissance and mapping of site. Utilize visible outcroppings to predict the strike and dip of beds, as well as to identify obvious faults, discontinuities, jointing and fracture patterns. Utilize auger borings or test trenches through soil overburden, to determine initial rock surface profiles when rock is not visible.

b. From this information an exploration plan should be devised which will provide a continuity of data regarding structure of rock. Undisturbed rock samples should be obtained from fresh unweathered exposures at the site, or from core samples recovered from borings. To the extent possible, the subsurface exploration program should be designed in an attempt to reveal potential structural discontinuities. Core recovery should be monitored by a qualified Engineering Geologist, so that necessary changes may be made to maximize recovery of useful data. The spacing and depth of bores will be project specific. All bores should be advanced to a depth which is sufficient to verify the competency of the proposed subgrade. At minimum, this depth will be the proposed subgrade elevation. On cuts of significant depth, exploration should extend well outside the proposed centerline as significant discontinuities may exist which could affect design of the upper portions of slopes. Detailed drilling logs should be maintained and the recovered samples should be preserved for a mutually agreed upon period of time.

a. When construction of roadbed involves an interface with natural rock bedding (embankment fills), or requires rock excavation and slope design (rock cuts), it is imperative that adequate insitu and laboratory information is obtained on the structural nature of the rock. Beyond providing for sound design, preliminary information will provide realistic parameters for estimating both construction costs and schedules.

b. The methods of obtaining information on rock formations can be grouped into two (2) categories: 1) empirical - a study based solely on existing geological information and visible surface features, or 2) intrusive - a study in which existing information is supplemented by subsurface exploration and testing of the rock mass.

c. The ultimate stability of a roadbed engineered through rock will be defined by the nature of any structural discontinuities which may exist at the location. Major rock cuts will typically require detailed subsurface exploration. Minor rock cuts often may be designed by an experienced engineer without subsurface exploration. Both methods are valid provided that an educated decision is made for appropriateness. The planning and execution of this exploration should be conducted with the assistance of a qualified Engineering Geologist.

Roadbed



1

3

4

c. Undisturbed core samples are typically obtained using a standard diamond-tipped rock boring machine equipped with a continuous recovery tube. The minimum size for a recovery tube should be type BX (1-5/8"), with sizes NQ (2") and NX (2-1/8") being more commonly used. For projects in areas of suspected geologic irregularities use of even larger recovery tubes may be of value. Such a determination can be based on the preliminary geologic data for the site.


Exploration of rock as related to roadbed maintenance problems, will rely primarily on visual examination of exposed rock surfaces. When existing surface conditions do not obviously reveal the causes of the problem, it may be necessary to use intrusive exploration techniques to identify the depths at which competent material is present. This may reveal the presence of faults, fracture patterns, and structurally weak layers that could affect the stability of the associated rock mass.

1.1.4.3 Examination and Testing

a. Rock samples and cores provide an important record of visible structura information. Samples should be examined and a final geologic log accurately prepared. See Table 1-1-4 for a list of recommended descriptive terminology. The resulting data should be consolidated in a usable format which may include detailed boring logs, and cross-sectional mapping of the rock structure. In general this detailed information provides the primary tool for the Design Engineer in predicting the theoretical structural behavior of the rock mass. This base information provides only qualitative design values which are used in part for detailed strength and stability analysis .

b. Representative samples from the rock cores can be utilized to determine the strength and deformation characteristics of the rock as well as its potential for weathering. See Table 1-1-5 for a list of possible test methods. These tests can provide much more precise design values, but test suitability is job specific and should be determined with the assistance of an Engineering Geologist.

c. Since many variables exist regarding rock mechanics, providing the most comprehensive information available in a usable format will greatly assist the Design Engineer in development of a viable design or corrective scheme.

1.1.5 CONSTRUCTION MATERIAL SOURCES (2000)

1.1.5.1 Site Sources

Borrow areas for soil embankment fill construction are often preliminarily explored by auger boring. The suitability of such soils can be further verified by utilizing the sampling and testing procedures outlined elsewhere in this section.

1.1.5.2 Commercial Sources

Select granular fill materials supplied by off-site commercial sources for use in embankment fill construction are typically produced to defined specifications and should be tested to ensure consistent quality control.

Roadway and Ballast



Table 1-1-1. Sources of Site Information

Type of Information and Usage Source

Geological Surveys:National: Indexes to existing geologic mapping

and exploration.Detailed maps of Topography, Surface and Subsurface structural information.Correlation and characteristics of geological deposits.

Localized: Maps, bulletins, and reports on locally unique subjects.

National:United States - U.S. Geological SurveyCanada - Canadian Geological SurveyMexico - Colegio de Ingenieros de

Mineros, Metalurgistas y Geologos de Mexico

Localized:State and Provincial Geological Surveys and Societies

Other:Independent Geologic Societies

Existing & Historical Land Use:Maps and documents available on exploration and use of mineral and geologic resources.Information on the structural nature of deposits, and identification of subsurface excavations and discontinuity.

United States - Bureau of Land Management,Department of Surface Mining,Department of Mine Reclamation,American Petroleum Institute

Canada - Department of Energy, Mines & Resources (DEM&R)

Mexico - Com. de Fomento Minero Instituto Nacional de Statistica Geografica Informativa (INEGI)

Generalized Soil Information:Maps and reports on surface conditions with summaries of subsurface geological conditions.

National:United States - Department of

Agriculture Soil Conservation Service

Canada - DEM&R, Environment Canada

Mexico - ENEGILocalized:

State and Provincial Conservation and Agricultural Agencies

Aerial Photographs:See Section:1.2.2

National:United States - Department of

Agriculture Soil Conservation Service

Canada - DEM&R, Environment Canada

Mexico - ENEGI, Cia Topografica, Ingenieria y Aerofotogrametri

Localized:State and Provincial Agricultural or Economic Development Agencies

Roadbed



1

3

4

Atomospheric Conditions:Information on rainfall and temperature variation necessary for the analysis of drainage, weathering and frost penetration

National:United States - National Oceanic &

Atmospheric Administration, National Weather Service

Canada - Environment CanadaMexico - Servicio Meteorologico,

Servicio a la Navegacion en el Espacio Aereo Mexicano

Localized:State and Provincial Conservation and Agricultural Agencies

Building and Seismic Design Codes:Information on construction methods or design requirements.Seismic considerations.

United States - State and Municipal Building Code Agencies

Canada - National Building CodeMexico - Departamento del Distrito Federal

Table 1-1-1. Sources of Site Information

Type of Information and Usage Source

(Continued)

Roadway and Ballast



Table 1-1-2. Procedures for Soil Exploration

Procedure ASTM Method

Site Characterization for Engineering, Design & Construction Purposes D 420

Soil Investigation and Sampling by Auger Borings D 1452

Penetration Test and Split-barrel Sampling of Soils D 1586

Thin-wall Tube Geotechnical Sampling of Soils D 1587

Field Vane Shear Test in Cohesive Soils D 2573

Deep, Quasi-Static, Cone & Friction Cone Penetration Tests of Soil D 3441

Table 1-1-3. Standard Procedures for Soil Testing

Procedure ASTM Method

Material Finer than No. 200 Sieve in Mineral Aggregates by Washing C 117

Particle Size Analysis of Soils D 422

Laboratory Compaction Characteristics of Soil using Standard Effort D 698

Specific Gravity of Soils D 854

Laboratory Compaction Characteristics of Soil using Modified Effort D 1557

Density and Unit Weight of Soil in Place by the Sand-Cone Method D 1556

Unconfined Compressive Strength of Cohesive Soil D 2166

Density and Unit Weight of Soil in Place by the Rubber-Balloon Method D 2167

Laboratory Determination of Water (moisture) Content of Soils & Rock D 2216

One-Dimensional Swell or Settlement Potential of Cohesive Soils D 4546

Classification of Soils for Engineering Purposes D 2487

Description & Identification of Soils (visual-manual procedure) D 2488

Liquid Limit, Plastic Limit, and Plasticity Index of Soils D 4318

Maximum Index Density & Unit Weight of Soils Using a Vibratory Table D 4253

Minimum Index Density & Unit Weight of Soils and Calculation of Relative Density D 4254

Consolidated-Undrained Triaxial Compression Test of Cohesive Soils D 4767

Roadbed



1

3

4

Table 1-1-4. Technical Descriptions of Cores or Fresh Exposures of Rock

Feature Description or Occurrence Importance

Discontinuity- Type

- Position

- Surface

JointsFaultsBedding Planes (as in Sedimentary Rock)Cleavage Planes (as in Slates)Fracture with Striations or Slickenslides

(from past movement)

Closeness and Orientation of JointsThickness of Bedding LayersLength of Core Pieces (as influenced by

drilling techniques)Dip or Angle of Inclination from

Horizontal

Fit of Surfaces - Tight or OpenShape - Plane, Curved, or IrregularTexture - Slick, Smooth, or Rough

Influence on Permeability, Strength, and Deformation of the Rock Mass.

Of Major Importance in Cut Slopes and Tunnels.

Governs amount of Interlocking and Apparent Shearing Resistance along Fractures.

Filling Material Properties - Type, Hardness, Thickness, Variations

Origin - Derived from Rock by Alteration, or from External Source

May Govern Movement along Discontinuities.

Rock Type and Texture

Geologic Name Based on Mineral Composition, Texture and Origin

Size and Angularity of Grains, Type of Fracture, Luster, Lamination

Texture - Interlocking Grains Cemented or Laminated - Foliated, Preferred Orientation

Rock Hardness Relative hardness (give basis of comparison)

Variations Due to Changes in Rock Type, Weakened Rock, Weathering or Decomposition Products

Severe Design and Construction Problems may Arise when Hardness of Parts of Rock Mass Differ Radically from Average Value.

Core Recoverability

Total Core Recovery (%)Rock Quality Designation (RQD)

Identifies Weak CoreClassifies Relative Strength

Roadway and Ballast



1.2.1 GENERAL (2002)

a. This section describes material and drainage issues that need to be evaluated as part of the design of cuts and fills along railroad roadways. It is assumed that the general project alignment has been selected, field exploration and soil sampling have been performed, and laboratory testing is completed prior to commencing with the final design. Issues for consideration in design include horizontal and vertical alignments and typical sections all of which are influenced by traffic considerations, topographical features, drainage, and soils and rock data. Environmental conditions such as drainage, wetlands and contaminated soils also influence the design.

b. Subjects which could be common to both design and maintenance are found in Section 1.4, Maintenance. These subjects include unstable subgrade conditions, frost heaving of tracks, rock falls, both cut and fill slope failures, and erosion control. The issues which are discussed in Section 1.2, Design, address how soils and drainage influence cuts and fills.

1.2.2 CUTS (2002)

1.2.2.1 General

a. Definition: Cuts are made when excavations are required through hills to provide roadbed grades and to acquire materials for use when constructing fill sections. Materials encountered in cuts can consist of cohesive soils, cohesionless soils, rock or combinations thereof. The general components of a cut (and fill)

Table 1-1-5. Typical Tests for Rock Samples

Procedure ASTM Method Comments

Specific Gravity and Absorption of...- Coarse Aggregate- Fine Aggregate

C 127C 128

Soundness of Aggregates by use of Sodium Sulfate or Magnesium Sulfate

C 88 To Indicate Rocks Resistance to Weathering

Resistance to Degradation by Impact and Abrasion using the Los Angeles Machine of...

- Large Size Coarse Aggregate- Small Size Coarse Aggregate

C 535C 131

To serve as a measure of degradation of mineral aggregates from a combination of actions including abrasion or attrition, impact and grinding.

Petrographic Examination of Aggregate

C 295 See text

Compression- Uniaxial

- Triaxial Stength of Undrained Rock Core Specimens without Pore Pressure Measurements

Special

D 2664

To Classify Rock for Strength and Deformation Properties.Utilizes Diamond Drilled Cores.

To Find Angle of Shearing Resistance of Weak Rock Material with Random Orientation of Joints.Range of Normal Stresses Occurring in Field are Applied.

SECTION 1.2 DESIGN

Roadbed



1

3

4

section consist of the back slope(s), benches (if required), foreslope(s), ditches, and the top of subgrade (track roadbed) as presented in Figure 1-1-1. The cut width is the total of the backslope(s), ditches, foreslope(s) top of subgrade widths, and interceptor ditches where required for the section(s). The purpose of each of these segments are defined in Table 1-1-6.

Figure 1-1-1. Cut and Fill Section Components

Roadway and Ballast



b. Cut Section Design Requirements: The track roadbed (top of subgrade) portion of a cut should remain stable during the excavation and track laying operations, and once the railroad line has been placed into operation. Cut section design issues also include providing back slopes and foreslopes that will not fail. Drainage ditches need to be sized to accommodate surface runoff and subsurface water which may seep from the backslope face. Ditches made within rock cuts may need to be designed having additional width for catchment of rock materials which may fall from the backslope face. Primary consideration when designing this catchment width is to position the toe of slope at a point that will not allow falling rock fragments to bounce into the track area. The working width required by ditch cleaning machines is important. The materials that will be encountered in the cut must be evaluated for excavatability. Cuts may need to be designed with flat slopes to facilitate self-cleaning by prevailing winds and minimize snow storage. Benching of the backslope may be required to accommodate drainage and to catch falling rocks.

1.2.2.2 Back Slopes in Cuts

Slope stability analysis should be performed to aid in selecting the steepest safe backslope section. Cross-sections should then be drawn transverse to the proposed track alignment to determine if safe cuts can be made within the right-of-way lines or if additional right-of-way or soil slope reinforcement will be required for the project. Soils and rock materials having varying strengths may necessitate that the backslope be cut at varying slopes. Subsurface water that seeps from the face of the backslopes can facilitate embankment instability. Vertical interceptor drains and horizontal drains may need to be designed into the backslope to intercept subsurface groundwater flow and reduce hydrostatic pressures which could cause embankment instability.

1.2.2.3 Drainage Ditches in Cuts

Ditches designed for drainage and catchment (as shown in Figure 1-1-2) should be designed to have the capacity to handle regional surface water runoff, snow storage and talus. The capacity is influenced by the width, depth and gradient of the ditch. Reference should be made to Article 1.2.4 which provides specific ditch design guidelines.

SEGMENT PURPOSE WHERE PROVIDED WIDTH & PROFILE

A. Top of Subgrade To provide a base for sub-ballast, ties, rails and service roads.

Throughout cut and fill sections.

Standard width.

B. Foreslope To safely support track and road subgrade. To place subgrade at safe height above maximum design drainage levels.

Throughout cut and fill sections.

Standard width.

C. Ditch To carry run-off from watershed served and seepage entering cut while preventing development of unstable track subgrade conditions.

In all cuts. Width as required to accomodate hydraulics. Profile may need to be different than track profile in long level cuts.

D. Backslope Resultant excavation face located between outer ditch line and natural ground line.

In all cuts. Variable width depending on slope, height of cut face, soil stability, maintenance and erodibility.

E. Interceptor Ditches To carry runoff from the watershed served and prevent surface runoff from entering the cut.

Above cut slope. Width as required to accommodate hydraulics.

Table 1-1-6. Factors Affecting Width of Cut

Roadbed



1

3

4

1.2.2.4 Track Bed Performance in Cuts

Track performance is enhanced by providing uniform stable subgrade conditions through out a given cut. Providing drainage of the immediate subgrade materials generally improves subgrade stability by increasing the materials strength while reducing the detrimental effects of frost action. Longitudinal and transverse drains can be designed to facilitate subgrade drainage.

1.2.2.5 Cuts in Soil

1.2.2.5.1 General

1.2.2.5.2 Cuts in Cohesionless Soils (Sands and Gravels)

a. Sands and gravels that are located above the ground water level generally will stand safely at a slope 2(H):1(V) or flatter. Steeper slopes may be able to be excavated and stand for short periods of time, but will eventually try to assume a flatter slope. Finished slopes in sand-gravel materials that are exposed to groundwater flow or seepage from the backslope face will routinely have to be cut flatter than would be required for the same cohesionless soil cut in a non-saturated state. In areas of loose saturated cohesionless soils, special provisions may be required to avoid liquefaction.

b. The stability of slopes in sand is generally improved as the density of the cohesionless soil increases.

1.2.2.5.3 Cuts in Cohesive Soils (Silts and Clays)

a. Cuts in cohesive soils need to be designed with caution. Previously stable slopes have been known to fail. Cuts in cohesive soils should be designed using slope stability analysis. Local long-term experience may prove to be an indicator of a stable slope for a particular soil profile. A slope of 2(H):1(V) or flatter generally proves stable in cohesive soils. Clay slopes over 10 to 15 feet in height should be designed on the basis of laboratory tests and slope stability analysis. In general, the higher the cut section becomes the flatter the slope will have to be to remain stable. Highly plastic clay soils require flatter slopes than those discussed above.

b. The stability of clay slopes can be increased by the installation of drains and by flattening the cut slope.

c. Cut slopes in areas where it is known that slides are inevitable may be designed to allow for slope movement (failure) without interference to traffic.

1.2.2.5.4 Cuts in Non-Uniform Soils

Cuts in soils which are layered or contain seams of varied soil types should be designed on the basis of a slope stability analysis. The seams that contain cohesionless (granular) soils are often water bearing during some part of the year and drainage of these seams should be provided. Effective drainage may stabilize an otherwise unstable slope if the soil properties of the unsaturated (drained) embankment soils are adequate.

a. Considerations such as the proposed slope angle, drainage conditions, and moisture conditions and strength of the soils encountered in a cut are the most significant factors that influence the stability of earth slopes. All sloping soils have a tendency to move under the influence of gravity. Slope stability evaluations should generally be made to select the cross-section for cuts over 15 feet deep. Observations of nearby cuts in similar soils and natural slopes in the project locale can aid in slope design.

b. It is important that the cut cross-section be wide enough to provide side ditches for interception of surface water. Where it is not practical to collect surface drainage with adequate ditches, buried drainage pipes can be provided. It may be very important to relieve subsurface water pressure in sloping ground to avoid slope failures. The subsurface water pressure may be reduced by installing interceptor ditches or drains above the slope, or horizontal buried drainage pipes at critical depths within the slope either longitudinal or transverse to the cut face. In rare cases, vertical wells may be required.

Roadway and Ballast



1.2.2.5.5 Cuts in Loess

In site specific cases cuts in loess can be designed with near-vertical or flatter slopes based upon the engineering properties of the soils and the findings of slope stability analysis. Cuts in loess that are designed to have a near-vertical face should be carefully drained at the foot and top of the face. Loess soils possess a natural cementation that is soluble, a uniform grading, and a vertical root hole structure. Deep cuts can be made with near vertical faces and berms, but it is critical to the stability of the backslope that drainage be carefully designed and maintained so that water does not accumulate atop the benches.

1.2.2.5.6 Cut Slope Summary

For every soil type it is necessary to maintain a safe and stable cut section. This should be the primary consideration during design. Berms, drainage, erosion protection, filter layers, vegetation and proper selection of the finished cut slope angle should be used as a means of achieving this end. Discussion is provided in Article 1.4.3 and Article 1.4.5. Cribs or retaining walls may be used in troublesome sections where berms and other less costly means of providing a stable cut slope are unable to be installed. Details for the design of crib and retaining walls are given in Chapter 8, Concrete Structures and Foundations. While slope control structures and techniques add to costs, they will pay dividends in reduced requirements for slope restoration and ditch cleaning.

1.2.2.6 Cuts in Rock

1.2.2.6.1 General

The design of a rock cut is predicated on obtaining the lowest balanced construction and maintenance cost consistent with safety. The ratio between construction and maintenance costs will vary with individual situations and should be developed for each project.

1.2.2.6.2 Assembly of Design Information

a. Factors which should be evaluated when designing rock cuts are the 3-dimensional competence of the rock and overburden, and the depth and length of the cut.

b. The first steps in design are the preparation of profiles and cross sections on which are plotted data obtained during site investigation, test borings and laboratory testing, interpreted with the aid of geological maps, groundwater surveys and aerial photographs. Knowledge of the behavior of similar rock in comparable cuts can prove to be valuable design information.

c. In layered formations, where dip or strike of the bedding planes is not normal to the center of the cut, it may be desirable to evaluate sections on the dip of the bedding planes to aid in examining the stability of the cut slope.

d. As the characteristics of bedrock often vary greatly (over short distances) it is fundamental for economy that the slope be fitted to the material and exposure on each side of the cut at each location. A uniform slope in one segment of rock is not necessarily appropriate throughout the length of a cut if the condition of the rock (i.e., strike and dip of bedding planes, fracturing, etc.) changes.

Roadbed



1

3

4

1.2.2.6.3 Width of Base of Cut in Rock

The base width of a rock cut is determined by the total width of zones A, B, and C, shown in Figure 1-1-2 and described in Table 1-1-7. Refer also to Article 1.2.2.6.7.

Table 1-1-7. Factors Affecting Base Width of Rock Cuts

1.2.2.6.4 Stability of Rock Slopes

a. Safe slopes are governed by the characteristics of the rock in the slope. Slope angles should be chosen independently even in the same cut for sound rock, weathered or shattered rock, and overburden. See Figure 1-1-3, Figure 1-1-4, Figure 1-1-5 and Figure 1-1-6.

SEGMENT PURPOSE WHERE PROVIDED WIDTH & PROFILE

A. Roadbed To provide base for supporting ballast, ties and rail.

Throughout cut. Standard width.

B. Drainage Ditch To carry run-off from watershed served, seepage entering cut, and for service road.

Throughout cut. Standard width with profile that may have to be steeper than track profile in long level cuts.

C. Catchment Ditch (Optional)

To contain material which may fall from faces of cut, and for service and maintenance access.

Within broken or rapidly weakening rocks cuts.

Of variable width depending on slope and height of cut face, size and rate of fall fragments and desirable frequency of ditch cleaning. Primary consideration in setting width is to position the toe of slope at a point which will not allow falling fragments to bounce into track area. Working width required by ditch cleaning machines is important.

Figure 1-1-2. Width of Rock Cut Base

Roadway and Ballast



b. For each rock material the slope is governed to a major degree by bedding planes, joints which are usually perpendicular to the bedding, fracture patterns and faulting, all of which tend to make the rock perform as a number of segments rather than as a mass. The influence of each of these characteristics should be carefully assessed in analyzing slope stability. It should be noted that the slope of such discontinuities, as entered on cross-sections, and profiles will not necessarily show their true angle of interception with the cut slope, which should be considered in design.

c. Stability of rock slopes can be analyzed using 3-D slope stability analysis with use of a stereo net software program, or by the method of slices (when appropriate) as used with soil slopes, but it should be realized that the surface of sliding will follow rock joints and defects where possible. Values of shear strength (friction angle and cohesion) are chosen accordingly. Cohesion is usually neglected as its value along joints in rock may be small. Experience is needed to design major slopes with safety and economy.

d. Design factors for the more common rock conditions are discussed in Table 1-1-8. The effects of water (hydrostatic) pressure in fissures is of primary importance in all cases.

e. Rock falls and slides commonly occur during or soon after heavy rains, which is an indicator of the major importance of seepage pressures on slope stability. Water has the dual effect of increasing shear stresses in the slope by its weight and hydrostatic pressure, and at the same time decreasing the shear strength of rock materials by weathering, freezing and expansion. Hence, it is important to keep water out of the slope if possible.

Figure 1-1-3. Variable Slope

Roadbed



1

3

4

Figure 1-1-4. Uniform Slope

Roadway and Ballast



Figure 1-1-5. Permanent Bench

Figure 1-1-6. Temporary Bench

Roadbed



1

3

4

Table 1-1-8. Design Factors for Rock Slopes

f. In most rock masses, the ground water table cannot be lowered economically. However, intercepting surface ditches at the top of the slope or horizontal relief drains in the face or at the toe of the slope may have benefits in certain cases (see Section 1.4, Maintenance).

1.2.2.6.5 Effect of Blasting

Uncontrolled blasting tends to open up cracks near the face of rock slopes, allowing an increase in the rate of weathering, infiltration of water and consequent deterioration of the slope. Such blasting may facilitate excessive rock falls for many years. A decision on the type of blasting should be part of the design procedure. The technique of pre-splitting by blasting a line of drill holes on centers less than 4 feet apart can produce a slope surface with minimum disturbance and negligible overbreak. Preservation of the rock segments in their pre-construction position allows valid design assumptions to be made and minimizes ultimate maintenance costs.

1.2.2.6.6 Use of Benches on Rock Slopes

a. Benches in rock cuts are used to catch falling rock, to prevent undermining of hard strata by differential weathering, to reduce pressures at the toe of cuts and to handle drainage. Principles applying to the choice of rock slopes and benches are illustrated in Figure 1-1-3, Figure 1-1-4, Figure 1-1-5, and Figure 1-1-6. Where permanent benches are used to intercept falling rock, as shown in Figure 1-1-5, access should be provided for periodic removal of debris. The width of such benches should be adequate for machine access after weathering of the softer rock has taken place. A minimum width of 20 to 30 feet may be required.

b. In shales and other soft-rock cuts, temporary benches may be designed to contain all debris from a steep slope.

c. A typical arrangement is shown in Figure 1-1-6. Debris from the top of the steep slope accumulates on the bench to form a protective zone for the toe of the slope, while the upper portion of the steep slope weathers back to its angle of repose. Provision for access to such slopes may not be required.

d. Benches used to reduce the effects of differential weathering are located at the top of the weaker rock where the stronger rock is set back to form the bench. The width of the bench is governed by the weathering characteristics of the weaker rock and the height and angle of its slope. Provision for access may not be required.

e. In deep rock cuts, where weaker rock appears in the base of the cut, it may be necessary to introduce benches to relieve the toe pressure. Such benches may serve other purposes, as noted above, to increase safety and reduce maintenance costs.

Condition of Rock Design of Slope

Hard rock with random joints

Providing there are no adverse bedding planes or joint systems, ground water pressures are low and blasting is presplit, slopes of 70 degrees are stable.

Layered rock An accurate joint survey is important. If rock dips with the slope, and dip angle is greater than angle of friction, critical slope is at angle of dip. If bedding is horizontal, stability is as for massive rock. If bedding dips into slope, critical slope is between 70 degrees and 90 degrees; local rock falls may be frequent.

Fractured or weathered rocks

Stability can be analyzed using shear strength parameters derived from field observations. Angle of friction for angular crushed rock varies between 45-50 degrees.

Clay-shale rocks Specialist advice is required as unloaded shale tends to decrease in strength with time.

Roadway and Ballast



f. A permanent bench may be required for accommodating longitudinal drainage from surface run-off or subsurface seepage. Such an arrangement is usually complicated and expensive and should be avoided, except in special circumstances.

g. Drainage of benches is best accomplished by sloping them to the face of the cut thus moving water off the bench as quickly as possible. Where rock on the surface of the bench presents open joints or fractures, water may be prevented from entering the rock mass by covering the bench with a layer of clay or ot