PRESCRIPTIVE MEASURES FOR MAN-MADE SLOPES …

1 GEO PUBLICATION No. 1/2009 PRESCRIPTIVE MEASURES FOR MAN-MADE SLOPES AND RETAINING WALLS GEOTECHNICAL ENGINEERING office Civil Engineering and Development Department The Government of the Hong Kong Special Administrative Region GEO PUBLICATION No. 1/2009 PRESCRIPTIVE MEASURES FOR MAN-MADE SLOPES AND RETAINING WALLS GEOTECHNICAL ENGINEERING office Civil Engineering and Development Department The Government of the Hong Kong Special Administrative Region 2 The Government of the Hong Kong Special Administrative Region First published, August 2009 Prepared by : Geotechnical Engineering office , Civil Engineering and Development Department, Civil Engineering and Development Building, 101 Princess Margaret Road, Homantin, Kowloon, Hong Kong.

2 Captions of Figures on the Front Cover Top Left : Soil Cut Slope at Princess Margaret Road, Homantin Top Right : Soil and Rock Cut Slope at Tin Hau Temple Road, North Point Bottom Left : Skin Wall at Heung Chung, Sai Kung Bottom Right : Soil Cut Slope at Wo Chung Street, Homantin 3 FOREWORD This Publication presents a recommended standard of good practice for the application of PRESCRIPTIVE MEASURES as improvement works on existing MAN-MADE SLOPES and retaining walls in Hong Kong.

3 The scope of application covers a range of PRESCRIPTIVE MEASURES items in the form of preventive maintenance works, upgrading works or repair works to landslides. Various types of PRESCRIPTIVE MEASURES have been developed for soil/rock cut SLOPES , fill SLOPES and masonry/concrete retaining walls. The findings and recommendations of the studies on the formulation of the PRESCRIPTIVE MEASURES framework are given in a series of technical reports and guidance documents published by the Geotechnical Engineering office from 1995 to 2007. This Publication integrates and rationalises the recommendations and provides a comprehensive guidance document on the application of PRESCRIPTIVE MEASURES to existing MAN-MADE SLOPES and retaining walls. This document was prepared by a team consisting of Dr Raymond Cheung, Ms Becky Lui and Mr Lawrence Shum, under the supervision initially of Mr Pun and later Mr Ken Ho.

4 Copies of a draft version of this document were circulated to local professional bodies, consulting engineers, academics and Government departments. Many individuals and organisations made useful comments, which have been taken into account in finalising this Publication. All contributions are gratefully acknowledged. Practitioners are encouraged to provide comments to the Geotechnical Engineering office at any time on the contents of this Publication, so that further improvements can be made in future editions. Chan Head, Geotechnical Engineering office August 2009 4 CONTENTS Page No. TITLE PAGE 1 FOREWORD 3 CONTENTS 4 LIST OF TABLES 7 LIST OF FIGURES 9 1. INTRODUCTION 11 PURPOSE AND SCOPE 11 2.

5 APPLICATIONS 12 GENERAL 12 DEVELOPMENT OF PRESCRIPTIVE MEASURES 12 AREAS OF APPLICATION 14 MERITS AND LIMITATIONS OF PRESCRIPTIVE MEASURES 14 TYPES OF PRESCRIPTIVE MEASURES 15 SELECTION OF PRESCRIPTIVE MEASURES 16 RECOMMENDED PROCEDURES FOR APPLICATION 18 QUALIFICATION REQUIREMENTS OF PERSONNEL 20 STATUS OF SLOPE FEATURES IMPROVED BY 23 PRESCRIPTIVE MEASURES 5 Page No. 3. TYPE 1 PRESCRIPTIVE MEASURES 24 GENERAL 24 TYPE 1 PRESCRIPTIVE MEASURES 24 Surface Protection 24 Surface Drainage 27 Local Stability 29 4. TYPE 2 PRESCRIPTIVE MEASURES 31 GENERAL 31 TYPE 2 PRESCRIPTIVE MEASURES 31 Subsurface Drainage 31 5.

6 TYPE 3 PRESCRIPTIVE MEASURES 41 GENERAL 41 PRESCRIPTIVE SOIL NAILS FOR SOIL CUT SLOPES 41 Qualifying Criteria 41 Soil Nail Layout 43 Soil Nail Head and Facing 46 Corrosion Protection 47 PRESCRIPTIVE SOIL NAILS FOR SOIL CUT SLOPES WITH 48 TOE WALLS Qualifying Criteria 48 Soil Nail Layout 52 Soil Nail Head and Facing 54 Corrosion Protection 54 PRESCRIPTIVE SOIL NAILS FOR CONCRETE OR MASONRY 54 RETAINING WALLS Qualifying Criteria 54 Soil Nail Layout 57 Soil Nail Head and Facing 60 Corrosion Protection 62 PRESCRIPTIVE SKIN WALLS FOR MASONRY RETAINING 62 WALLS Qualifying Criteria 62 6 Page No. Skin Wall Design 63 PRESCRIPTIVE CONCRETE BUTTRESSES FOR ROCK CUT 64 SLOPES PRESCRIPTIVE ROCK DOWELS FOR ROCK CUT SLOPES 64 Collection and Assessment of Discontinuity Data 64 PRESCRIPTIVE Rock Dowels 65 6.

7 OTHER CONSIDERATIONS 67 GENERAL 67 SLOPE APPEARANCE AND LANDSCAPING 67 TREE PRESERVATION 67 BUILDABILITY 68 WORKS IN THE VICINITY OF SENSITIVE STRUCTURES 68 CONSTRUCTION SUPERVISION AND CONTROL 68 CONSTRUCTION REVIEW 68 MAINTENANCE 69 REFERENCES 70 GLOSSARY OF SYMBOLS 74 7 LIST OF TABLES Table Page No. No. Common Applications of Different Types of PRESCRIPTIVE 16 MEASURES Items of Type 1 PRESCRIPTIVE MEASURES 24 PRESCRIPTIVE Use of Vegetation Cover for Soil SLOPES 25 Items of Type 2 PRESCRIPTIVE MEASURES 31 Items of Type 3 PRESCRIPTIVE MEASURES 41 Qualifying Criteria for Application of PRESCRIPTIVE Soil 42 Nails to Soil Cut SLOPES Stability Enhancement for Application of PRESCRIPTIVE Soil 44 Nails to Soil Cut SLOPES Standard PRESCRIPTIVE Soil Nail Layouts for Soil Cut 45 SLOPES Sizing of PRESCRIPTIVE Soil Nail Heads 47 Additional Qualifying Criteria for Application of 48 PRESCRIPTIVE Soil Nails to Soil Cut SLOPES with Toe Walls as Upgrading Works Classification of Condition of Masonry Retaining Walls 49 Guidelines for Evaluation of the State of Masonry 49 Retaining Wall Deformation Qualifying Criteria for

8 Application of PRESCRIPTIVE Soil 54 Nails to Concrete or Masonry Retaining Walls as Upgrading Works Standard PRESCRIPTIVE Soil Nail Layouts for Concrete or 59 Masonry Retaining Walls Qualifying Criteria for Application of PRESCRIPTIVE Skin 62 Walls to Masonry Retaining Walls as Upgrading Works 8 Table No. Page No. Qualifying Criteria for Application of PRESCRIPTIVE Rock Dowels to Rock Cut SLOPES as Upgrading Works 66 9 LIST OF FIGURES Figure Page No. No. Schematic Diagram of Typical PRESCRIPTIVE MEASURES for 17 MAN-MADE Slope Features Record Sheets for PRESCRIPTIVE MEASURES on MAN-MADE 21 Slope Features Alternative Flat Drainage Channel Details to Minimise 28 Excavation in Rock No-fines Concrete Backfill to Local Areas 30 Raking Drains at Upper Part of Slope 32 Raking Drains at Lower Part of Slope 33 Toe Drain 35 Counterfort Drains at Upper Part of Slope 36 Drainage for Hard Surface Cover (with No-fines 37 Concrete Toe) Drainage for Hard Surface Cover (with Relief Drains)

9 38 No-fines Concrete Cover 40 PRESCRIPTIVE Soil Nails on a Soil Cut Slope 46 Types of Concrete Retaining Walls covered by the Scope 48 of Application of PRESCRIPTIVE Soil Nails Simplified Geometry of a Slope Feature Incorporating a 50 Soil Cut and a Mass Concrete or Masonry Retaining Wall at Toe Simplified Geometry of a Slope Feature Incorporating a 51 Soil Cut and a Reinforced Concrete Retaining Wall at Toe PRESCRIPTIVE Soil Nails on a Soil Cut Slope with Toe Wall 53 Simplified Geometry of a Mass Concrete or Masonry 55 Retaining Wall Feature 10 Figure Page No. No. Simplified Geometry of a Reinforced Concrete Retaining 56 Wall Feature Minimum Required Thickness of Concrete or Masonry 58 Retaining Walls where No Type 3 PRESCRIPTIVE MEASURES are Needed PRESCRIPTIVE Soil Nails on a Retaining Wall 60 PRESCRIPTIVE Skin Walls to Masonry Retaining Walls 63 PRESCRIPTIVE Rock Dowels on Rock Cut SLOPES 66 11 1.

10 INTRODUCTION PURPOSE AND SCOPE The purpose of this document is to give guidance on the application of PRESCRIPTIVE MEASURES to existing MAN-MADE slope features, MAN-MADE cut SLOPES , fill SLOPES and retaining walls, in Hong Kong. The document is aimed at professionally qualified engineers, who are conversant with the relevant geotechnical engineering principles. PRESCRIPTIVE MEASURES comprise pre-determined, experience-based and suitably conservative modules of works prescribed to MAN-MADE slope features to improve stability, or reduce the risk of failure, without the need for detailed ground investigations and design analyses. The guidelines set out in this document cover the application of PRESCRIPTIVE MEASURES to existing MAN-MADE slope features including soil cut SLOPES , soil cut SLOPES with toe walls, rock SLOPES , concrete retaining walls, masonry retaining walls and fill SLOPES .