PRESCRIPTIVE MEASURES FOR MAN-MADE SLOPES AND …

[Pages:80]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

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? 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.

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

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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. 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 W.M. Cheung, Ms Becky L.S. Lui and Mr Lawrence K.W. Shum, under the supervision initially of Mr W.K. Pun and later Mr Ken K.S. Ho.

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.

R.K.S. Chan

Head, Geotechnical Engineering Office

August 2009

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CONTENTS

Page No.

TITLE PAGE

1

FOREWORD

3

CONTENTS

4

LIST OF TABLES

7

LIST OF FIGURES

9

1. INTRODUCTION

11

1.1 PURPOSE AND SCOPE

11

2. APPLICATIONS

12

2.1 GENERAL

12

2.2 DEVELOPMENT OF PRESCRIPTIVE MEASURES

12

2.3 AREAS OF APPLICATION

14

2.4 MERITS AND LIMITATIONS OF PRESCRIPTIVE MEASURES

14

2.5 TYPES OF PRESCRIPTIVE MEASURES

15

2.6 SELECTION OF PRESCRIPTIVE MEASURES

16

2.7 RECOMMENDED PROCEDURES FOR APPLICATION

18

2.8 QUALIFICATION REQUIREMENTS OF PERSONNEL

20

2.9 STATUS OF SLOPE FEATURES IMPROVED BY

23

PRESCRIPTIVE MEASURES

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Page No.

3. TYPE 1 PRESCRIPTIVE MEASURES

24

3.1 GENERAL

24

3.2 TYPE 1 PRESCRIPTIVE MEASURES

24

3.2.1 Surface Protection

24

3.2.2 Surface Drainage

27

3.2.3 Local Stability

29

4. TYPE 2 PRESCRIPTIVE MEASURES

31

4.1 GENERAL

31

4.2 TYPE 2 PRESCRIPTIVE MEASURES

31

4.2.1 Subsurface Drainage

31

5. TYPE 3 PRESCRIPTIVE MEASURES

41

5.1 GENERAL

41

5.2 PRESCRIPTIVE SOIL NAILS FOR SOIL CUT SLOPES

41

5.2.1 Qualifying Criteria

41

5.2.2 Soil Nail Layout

43

5.2.3 Soil Nail Head and Facing

46

5.2.4 Corrosion Protection

47

5.3 PRESCRIPTIVE SOIL NAILS FOR SOIL CUT SLOPES WITH

48

TOE WALLS

5.3.1 Qualifying Criteria

48

5.3.2 Soil Nail Layout

52

5.3.3 Soil Nail Head and Facing

54

5.3.4 Corrosion Protection

54

5.4 PRESCRIPTIVE SOIL NAILS FOR CONCRETE OR MASONRY

54

RETAINING WALLS

5.4.1 Qualifying Criteria

54

5.4.2 Soil Nail Layout

57

5.4.3 Soil Nail Head and Facing

60

5.4.4 Corrosion Protection

62

5.5 PRESCRIPTIVE SKIN WALLS FOR MASONRY RETAINING

62

WALLS

5.5.1 Qualifying Criteria

62

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Page No.

5.5.2 Skin Wall Design

63

5.6 PRESCRIPTIVE CONCRETE BUTTRESSES FOR ROCK CUT

64

SLOPES

5.7 PRESCRIPTIVE ROCK DOWELS FOR ROCK CUT SLOPES

64

5.7.1 Collection and Assessment of Discontinuity Data

64

5.7.2 Prescriptive Rock Dowels

65

6. OTHER CONSIDERATIONS

67

6.1 GENERAL

67

6.2 SLOPE APPEARANCE AND LANDSCAPING

67

6.3 TREE PRESERVATION

67

6.4 BUILDABILITY

68

6.5 WORKS IN THE VICINITY OF SENSITIVE STRUCTURES

68

6.6 CONSTRUCTION SUPERVISION AND CONTROL

68

6.7 CONSTRUCTION REVIEW

68

6.8 MAINTENANCE

69

REFERENCES

70

GLOSSARY OF SYMBOLS

74

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LIST OF TABLES

Table

Page

No.

No.

2.1

Common Applications of Different Types of Prescriptive

16

Measures

3.1

Items of Type 1 Prescriptive Measures

24

3.2

Prescriptive Use of Vegetation Cover for Soil Slopes

25

4.1

Items of Type 2 Prescriptive Measures

31

5.1

Items of Type 3 Prescriptive Measures

41

5.2

Qualifying Criteria for Application of Prescriptive Soil

42

Nails to Soil Cut Slopes

5.3

Stability Enhancement for Application of Prescriptive Soil

44

Nails to Soil Cut Slopes

5.4

Standard Prescriptive Soil Nail Layouts for Soil Cut

45

Slopes

5.5

Sizing of Prescriptive Soil Nail Heads

47

5.6

Additional Qualifying Criteria for Application of

48

Prescriptive Soil Nails to Soil Cut Slopes with Toe Walls

as Upgrading Works

5.7

Classification of Condition of Masonry Retaining Walls

49

5.8

Guidelines for Evaluation of the State of Masonry

49

Retaining Wall Deformation

5.9

Qualifying Criteria for Application of Prescriptive Soil

54

Nails to Concrete or Masonry Retaining Walls as

Upgrading Works

5.10

Standard Prescriptive Soil Nail Layouts for Concrete or

59

Masonry Retaining Walls

5.11

Qualifying Criteria for Application of Prescriptive Skin

62

Walls to Masonry Retaining Walls as Upgrading Works

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