RETAINING - CEDD

1 GEOGUIDE 1 GUIDE TO RETAINING WALL DESIGN GEOTECHNICAL ENGINEERING OFFICE Civil Engineering Department The Government of the Hong Kong Special Administrative Region 2 The Government of the Hong Kong Special Administrative RegionFirst published, September 19821st Reprint, January 19832nd Reprint, July 19833rd Reprint, October 19854th Reprint, January 19875th Reprint, April 1990 Second Edition, October 1993 Reprinted with minor correction, November 1994 Reprinted, January 1998 Reprinted, August 2000 Prepared by:Geotechnical Engineering Office,Civil Engineering Department,Civil Engineering Building,101 Princess Margaret Road,Homantin, Kowloon,Hong Committee:E. W. Brand (before April 1989)A. W. MaloneK. C. Brian-Boys (before December 1988) Lam (before October 1989)J.

2 B. MasseyJ. C. Shelton (after December 1988)D. J. Howells (after October 1989)R. P. Martin (between April 1989 and January 1991)Y. C. Chan (after January 1991) Pang (after November 1991)This publication is available from:Government Publications Centre,Ground Floor, Low Block,Queensway Government Offices,66 Queensway,Hong orders should be placed with:Publications Sales Section,Information Services Department,Room 402, 4th Floor, Murray Building,Garden Road, Central,Hong in Hong Kong: HK$68 Price overseas: US$14 (including surface postage)An additional bank charge of HK$50 or US$ is required per cheque made in currenciesother than Hong Kong , bank drafts or money orders must be made payable toThe Government of the Hong Kong Special Administrative This Geoguide presents a recommended standard of good practice for the design of RETAINING walls in Hong Kong.

3 The first edition of the Gwguide was published in July 1982 and preparation for a second edition begun in 1985 with a consultation exercise to obtain the views of practitioners on the first edition. Work on the revision began in 1987. The Geoguide covers the types of RETAINING walls which are commonplace in Hong Kong, including conventional reinforced concrete walls, gravity walls such as crib walls, gabion walls and mass concrete walls, and cantilevered RETAINING walls. It does not aim to deal comprehensively with maritime structures nor structures used to support the sides of deep excavations, such as sheet pile walls. The recommendations given herein are also not intended for RETAINING wall design which is outside existing experience derived from practice in Hong Kong.

4 In giving recommendations on design this Geoguide adopts the limit state method with partial factors of safety. Reference has been made in preparing this Gwguide to the results of research on RETAINING walls and to various national codes and guidance documents. These include the UK draft revised CP2, the Canadian Foundation Engineering Manual, the Danish Code of Practice for Foundation Engineering, the US Navy Design Manual and , the then New Zealand Ministry of Works and Development's RETAINING Wall Design Notes and the draft Eurocode No. 7. The Geoguide was prepared by a team in the Special Projects Division of the Office led by Dr Pang under the overall supervision initially of Dr R. P. Martin and later Mr Y. C. Chan and including at various times Mr W.

5 T. Chan, Mr W. K. Pun and Dr C. Y. Yung. The membership of the Steering Committee at various times over the past five years is given on the opposite page. To ensure that the Geoguide would be considered a consensus document by interested parties in Hong Kong, a draft version was circulated locally and abroad for comment in early 1992. Those consulted included consulting engineers, contractors, academics, professional bodies and Government departments. Many individuals and organisations made very useful comments, which have been taken into account in finalising the Geoguide, and their contributions are gratefully acknowledged. As with other Geoguides, this document gives guidance on good engineering practice, and its recommendations are not intended to be mandatory.

6 It is recognised that experienced practitioners may wish to use alternative methods- to those recommended herein. Practitioners are encouraged to comment at any time to the Geotechnical Engineering Office on the contents of this Geoguide, so that improvements can be made to future editions. A. W. Malone Principal Government Geotechnical Engineer October 1993 [BLANK PAGE] 5 CONTENTS Page No. TITLE PAGE 1 FOREWORD CONTENTS 5 1. INTRODUCTION PURPOSE AND SCOPE 13 GENERAL GUIDANCE General Personnel Local Experience Geology 2. DESIGN CONSIDERATIONS 17 GENERAL 17 PERFORMANCE CRITERIA, LIMIT STATES AND DUCTILITY 17 Performance Criteria 17 Limit State Method 17 Ductility 18 SITE INVESTIGATION AND THE GEOLOGICAL MODEL 18 SELECTION OF TYPE OF RETAINING WALL 19 DURABILITY AND MAINTENANCE 19 AESTHETICS 20 PATENTS 20 3.

7 CONSTRUCTION CONSIDERATIONS IN DESIGN 2 1 GENERAL 2 1 Page No. SELECTION AND USE OF BACKFILL General Types of Backfill FILTER AND DRAINAGE MATERIALS Granular Filter and Drainage Materials Geotextile Filter Materials CONSTRUCTION METHOD AND SEQUENCE TEMPORARY WORKS - GENERAL ASPECTS Responsibility for Temporary Works Design Standard of Temporary Works Design Influence of Temporary Works on RETAINING Wall Design TEMPORARY EXCAVATION AND FOUNDATION WORKS Excavation Works Foundation Works Groundwater Control PLACEMENT AND COMPACTION OF BACKFILL SERVICES USE OF PRESTRESSED GROUND ANCHORS 4. VERIFICATION OF SAFETY AND SERVICEABILITY GENERAL PRINCIPLES DESIGN SITUATIONS CALCULATION METHODS Available Approaches to Design Calculations Design Calculation Models Loadings, Geometric and Geotechnical Parameters Factors of Safety Structural Design PRESCRIPTIVE MEASURES THE OBSERVATIONAL METHOD GEOTECHNICAL DESIGN REPORT 5.

8 GEOTECHNICAL PARAMETERS Page No. GENERAL GEOTECHNICAL INVESTIGATION Content of Site Investigation evaluation of Geotechnical Parameters DETERMINATION OF SELECTED VALUES OF DESIGN PARAMETERS UNIT WEIGHT SOIL SHEAR STRENGTH PARAMETERS General Design Soil Strength Model and Parameters Compacted Fill Soils Derived from Insitu Rock Weathering Colluvium Granular Sedimentary Soils Cohesive Sedimentary Soils SOIL DEFORMATION PARAMETERS General Deformation Parameters for the Linear Elastic Continuum Model Deformation Parameters for the Winkler Model SOIL permeability AND CONSOLIDATION PARAMETERS permeability Coefficient of Consolidation ROCK STRENGTH PARAMETERS Strength of Intact Rock Shear Strength of Rock Joints Shear Strength of

9 Rock Mass ROCK DEFORMATION PARAMETERS ROCK permeability 1 WALL FRICTION AND ADHESION General Wall Friction for Active Earth Pressure Calculations Wall Friction for Passive Earth Pressure Calculations BASE SHEARING RESISTANCE 6. EARTH PRESSURE GENERAL RELATIONSHIP BETWEEN MOVEMENT AND EARTH PRESSURE States of Stress Modes of Movement EARTH PRESSURES FOR DIFFERENT LIMIT STATES EARTH PRESSURE AT REST ACTIVE EARTH PRESSURES Rankine Earth Pressure Theory Rankine-Bell Equation Effect of Tension Cracks Coulomb Earth Pressure Theory Caquot & Kerisel Charts Trial Wedge Method PASSIVE EARTH PRESSURES INFLUENCE OF LIMITED BACKFILL EARTH PRESSURE DUE TO COMPACTION EARTH PRESSURE BASED ON SOIL-STRUCTURE INTERACTION ANALYSIS 7.

10 EFFECTS OF SURCHARGE AND SEISMIC LOAD TYPES OF SURCHARGE DESIGN SURCHARGE LOADINGS General Nominal Surcharge Loads Page No. 56 ASSESSMENT OF EFFECTS OF SURCHARGE General Uniformly-Distributed Loads Line Loads Point Loads Area Loads Horizontal Loads SEISMIC LOADS 8. EFFECTS OF WATER GENERAL DESIGN WATER PRESSURES Design Condition evaluation of Water Pressures EFFECTS OF WATER ON EARTH PRESSURES General Gravity and L- or Inverted T-shaped RETAINING Walls Cantilevered RETAINING Walls DRAINAGE PROVISIONS General Design Aspects GRANULAR AND GEOTEXTILE FILTER DESIGN Performance Criteria Design Criteria for Granular Filters Design Criteria for Geotextile Filters DESIGN AGAINST HYDRAULIC FAILURE 9.