Ensayo

GUIDE TO TRENCH EXCAVATIONS
(SHORING SUPPORT AND DRAINAGE MEASURES)

Utilities Technical Liaison Committee
HIGHWAYS DEPARTMENT
and
Geotechnical Engineering Office
CIVIL ENGINEERING DEPARTMENT
THE GOVERNMENT OF THE HONG KONG
SPECIAL ADMINISTRATIVE REGION
February 2003

GUIDE TO TRENCH EXCAVATIONS
(SHORING SUPPORT AND DRAINAGE MEASURES)

Utilities Technical Liaison CommitteeHIGHWAYS DEPARTMENT
and
Geotechnical Engineering Office
CIVIL ENGINEERING DEPARTMENT
THE GOVERNMENT OF THE HONG KONG
SPECIAL ADMINISTRATIVE REGION
February 2003

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FOREWORD
Trench excavations are carried out principally to allow installation or repair of
public utilities, drains and sewers to serve populated areas. The Geotechnical
Engineering Office (GEO) of the Civil EngineeringDepartment (CED) recently
undertook a study on failures of trench excavations in Hong Kong. The study found
that between 1986 and 2000, there were at least 10 deaths and 4 injuries caused by the
failures of trench excavations. The study also found that a number of landslides
resulting in significant social disruption in recent years were related to trench
excavations adjacent to slopes. Therefore,the study concluded that the risk from trench
excavations is not low and some improvement measures should be done to enhance the
safety standards of trench excavations in Hong Kong.
The findings of the study with recommendations on enhancement of the safety
of trench excavations were presented to the Standing Committee on Slope Safety
(SCOSS) of Environment, Transport & Works Bureau (ETWB). Itwas decided by the
SCOSS that a Working Group should be formed under the Utilities Technical Liaison
Committee (UTLC) of Highways Department to take the recommendations forward,
including the preparation of a technical guide to trench excavations, and GEO/CED
should provide technical assistance to the UTLC to prepare the guide.
The Working Group, composed of the major utility undertakings,representatives
from Hong Kong Construction Association, the Association of Consulting Engineers of
Hong Kong, Highways Department, Water Supplies Department, Drainage Services
Department and Labour Department, in conjunction with GEO/CED prepared this
Guide on good practice of shoring support and drainage measures for trench excavations.
As part of the Government’s continuing effort topromote a safe and healthy working
environment, it is the intention of this Guide that the safety of the personnel involved in
the works and also the general public who may be affected by trench collapses or
failures can be enhanced.

(C. K. WONG)
Chairman
Utilities Technical Liaison Committee
Highways Department
February 2003

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CONTENTS
Page
No.

Title Page
FOREWORD

2CONTENTS
1.0

1

3

INTRODUCTION

5

2.0 OBJECTIVE AND SCOPE

6

3.0 PLANNING STAGE

7

3.1

Desk Study

7

3.2

Timing and Location

7

3.3

Statutory Requirements

8

4.0 DESIGN STAGE

9

4.1

Temporary Support Design

4.2

Design Considerations

10

4.2.1

Loading

10

4.2.2

Drainage

10

4.2.3

Groundwater Control

11

4.2.4Existing Man-Made Slope Features

11

5.0 CONSTRUCTION STAGE

9

12

5.1

Installation of Support

12

5.2

Special Drainage Provisions in the Wet Season

12

5.3

Backfilling of Trench and Reinstatement

13

5.4

Precaution in Use of Machinery

13

5.5

Other Considerations

14

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6.0

SITE SUPERVISION AND SITE SAFETY INSPECTION

15

6.1

SiteSupervision

15

6.2

Site Safety Inspection

16

6.3

Safety Checklist for Supervisors

16

6.3.1

17

Drainage Provisions

7.0 REFERENCES

19

APPENDIX A : TYPICAL ARRANGEMENT OF SHORING
DETAILS

21

APPENDIX B: RECOMMENDED DRAINAGE MEASURES

34

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1.0

INTRODUCTION

The Geotechnical Engineering Office (GEO) of the Civil Engineering Department
(CED)...