Importance of surface drainage management to slope performance

Abstract

The vast majority of the landslides in Hong Kong are triggered by rainfall. Surface drainage commonly provided on man-made slopes aims to prevent surface erosion and reduce infiltration. It plays an important role to avert slope instability. However, inadequate management of surface drainage could hamper its efficiency and often results in uncontrolled surface water flow contributory to landsliding. This paper provides insights on the importance of slope surface drainage management under the dense urban settings in Hong Kong from the landslide perspective. Selected landslides involving inadequately managed surface drainage are presented to highlight the key lessons learnt and areas deserving attention on various drainage aspects, including the design and detailing. It is noteworthy that inadequate surface drainage maintenance could exacerbate and lead to sizeable landslides even on engineered slopes. A review of landslide records over the years suggests that some landslides could have been averted had there been proper surface drainage maintenance.

KEYWORDS:

• Surface drainage
• drainage detailing
• maintenance
• slope
• landslide
• washout

Acknowledgements

This paper is published with the permission of the Head of the Geotechnical Engineering Office and the Director of Civil Engineering and Development, the HKSAR Government.

Additional information

Notes on contributors

Ryan W H Lee

Ir Ryan W H Lee graduated from the Hong Kong University of Science and Technology. He worked in Ove Arup & Partners Hong Kong Limited before joining the Geotechnical Engineering Office (GEO) in 2009. He has a wide range of geotechnical experiences, including excavation and lateral support, foundation, tunnelling, site formation and slope, obtained through a number of large-scale infrastructure, railway and building projects. He has worked in the Landslip Investigation Section in the Landslip Preventive Measures Division 1 of the GEO over the past five years. He is responsible for undertaking landslide studies, diagnosing landslide data and managing landslide investigation consultancies.

Rachel H C Law

Ir Rachel H C Law obtained her BEng degree from the University of Hong Kong and her master’s degree from the Massachusetts Institute of Technology (MIT). She is the winner of the 2012 HKIE Fugro Prize. She joined the GEO in 2001 and was responsible for research and development studies on landslides and slope safety for the past few years. Currently, she is a Senior Geotechnical Engineer in the Landslip Preventive Measures Division 1 of the GEO, and leads a team of professional and technical staff in managing a number of landslide investigation consultancies and providing technical direction in undertaking the examination of all reported landslides in the territory and in-depth landslide studies of selected significant landslides. Other areas of her recent work include slope design and geotechnical checking.

Dominic O K Lo

Ir Dr Dominic O K Lo graduated from University College London in 1984 and was awarded the University College London Exchange Postgraduate Scholarship to study at the University of Illinois where he received his M.Sc. and Ph.D. degrees. He was the first recipient of the Ralph B Peck Fellowship awarded by the University of Illinois in 1987. He worked in the New Jersey Office of Golder Associates Incorporated prior to joining the GEO where he conducted landslide investigation, research and development in piling, quantitative risk assessment, design methodology for landslide debris-resistant barriers. He is currently the Chief Geotechnical Engineer of the Landslip Preventive Measures Division 1 of the GEO and leads a team of professional and technical staff in the management of the landslip prevention and mitigation studies and works, and selection and management of consultancies for the Landslip Prevention and Mitigation Programme, and in implementation of the systematic landslide investigation programme.