Landslide devastation prompts interest in geohazards

14 August 2019

Dr Louis Wong Ngai Yuen (Croucher Scholarship 2002 and Croucher Fellowship 2007) recalls the devastating landslide and wall collapse near his home in Western district, Hong Kong, that left five people dead and injured three others.

The incident, in July 1994, prompted his determination to understand how geomaterials behave and why they can be so destructive.

At the time, he was a student at King’s College, where he had already been inspired by his teacher’s accounts of the formation of rocks and of plate tectonics to study geography during his senior secondary school years.

“Quite a few landslides occurred in Hong Kong in 1994 and 1995 and these also alerted my attention to landslides and other geohazards,” said Wong, now an associate professor in the Department of Earth Sciences, University of Hong Kong (HKU), and an award-winning engineering geologist.

The landslide that left the greatest impression occurred adjacent to a footpath within the Kwun Lung Lau housing estate. The incident involved the collapse of a masonry wall that was likely to have been intended as a facing to a cut slope. The cutting back of hillsides as humans encroached inland had altered the steepness and stability of slopes, he said.

“This was happening in Western district where I was born and these incidents emphasised the need to understand geology better,” he said. He investigated the undergraduate course at HKU in the recently formed Department of Earth Sciences, signing up after being impressed by the energy and commitment of eminent geologist Professor Chan Lung-sang.

Wong returned to HKU in 2015 after more than a decade in the United States and Singapore. His aim is to improve understanding of the fundamental behaviour of geomaterials, in particular the cracking processes. His research group investigates various aspects of fractures in rocks, which can be broadly divided into four main areas: sampling and characterisation based on photogrammetry and laser scanning techniques; crack evolution under different loading and environmental conditions; rock strength and deformability; and applications in tunnel and cavern engineering.

“If a tunnel or cavern is not properly designed it will collapse. To design it properly, we need empirical measurements of the strength of the rock material and shear strength of the fractures,” Wong explained.

Much of this research has direct implications for civil engineering. Several of his projects have been undertaken in collaboration with the Hong Kong government’s Geotechnical Engineering Office (GEO). However, the impact of this work is not just confined to civil engineering. “It can also offer a better understanding of earthquake mechanisms on a global scale,” he said.

After graduating from HKU, Wong worked for the GEO before completing a PhD in geotechnical and environmental engineering at Massachusetts Institute of Technology. He was assisted by a Croucher Foundation Scholarship and Sir Edward Youde Memorial Fellowship for Overseas Studies.

He later worked as a consulting tunnel engineer at Camp Dresser & McKee Inc. (CDM) in the USA before moving to Singapore in 2009 as assistant professor and assistant chair (academic) in the School of Civil and Environmental Engineering at Nanyang Technological University (NTU).

At NTU, he led several research projects in the field of geomechanics and engineering geology, including Southeast Asia’s first underground hydrocarbons facility opened in 2014.

“In Singapore, I worked on the Jurong Rock Cavern project. This is the first underground hydrocarbon storage facility in Southeast Asia and stores 1.47 million cubic metres of oil and gas at a depth of 130 metres. My team extensively tested the mechanical properties of rock samples using heavy-duty loading machines,” Wong said.

He also updated NTU’s geotechnical engineering laboratory to cater for a variety of rock mechanics tests, involving an investment of around S$2 million.

Since returning to Hong Kong, he has shared his experience and knowledge with the Hong Kong government, which is also seeking to use underground space. Caverns, for example, were identified for the relocation of Sha Tin sewage treatment works.

However, updating equipment at HKU was his first priority, leading to two major laboratory advances: a Phantom V711 high speed camera; and an Acoustic Emission (AE) detection setup. Each cost around HK$0.7 million.

The use of a high-speed camera that captures videos of up to one million frames per second allows researchers to tape and then replay rock fracturing at speeds the human eye and brain can comprehend.

AE detection is another powerful research tool. Wong explained: “Just before rock fractures, minute sounds are emitted by the micro-cracking process. The time interval can be anything between a few micro-seconds to a few minutes from the first micro cracking and eventual abrupt, violent rock failure.” These sounds can be picked up by the AE detection equipment.

Wong recently received a best paper award from the 53rd US Rock Mechanics/Geomechanics Symposium, based on an investigation undertaken with his PhD student Yahui Zhang into the micro-mechanisms of thermal strengthening in rock.

Before the advent of explosives, humans traditionally used fire to weaken rock, leading to the assumption that rock weakened with increased temperature. Over the past 50 years, scientists have tried to replicate field conditions and measure the effect of temperature increases, from room temperature around 25 Celsius to 800 Celsius. Results have consistently shown a near-linear degradation of strength with temperature. However, when Wong and Zhang conducted a detailed literature review, they noticed evidence of subtle rock strengthening in the range from 25 Celsius to 175 Celsius.

“We repeated the experiment in a controlled manner and have come up with the design for a new mathematical model based on data from previous experiments. We have also offered a new hypothesis for this phenomenon, which is related to micro-cracking mechanisms in rock,” Wong said.

The implication is that more cost-effective engineering design can be carried out by letting rock strength do more of the work within those temperature ranges. This would be particularly applicable in the design of nuclear waste disposal sites built within intact rock – when the waste heats up the surrounding rock, it could potentially be strengthening it.

Dr Louis Wong obtained his BSc degree in Earth Sciences from the University of Hong Kong (HKU) in 1999, assisted by a Stephen Kam Chuen Cheung Memorial Scholarship. He subsequently joined the Hong Kong government’s Geotechnical Engineering Office as a graduate engineering geologist. In 2002, he was awarded a Croucher Scholarship to complete his PhD in Geotechnical and Environmental Engineering at Massachusetts Institute of Technology (MIT). He was awarded a Croucher Fellowship in 2007 to pursue further studies as a post-doctoral fellow at MIT. In 2008, he became a consultant geotechnical and tunnel engineer at CDM in the USA. In 2009, he was appointed Assistant Professor and Assistant Chair (Academic) in the School of Civil and Environmental Engineering at Nanyang Technological University (NTU) in Singapore. Wong re-joined the Department of Earth Sciences at HKU as Associate Professor in 2015. He is a member of the Task Force of the Hong Kong Institution of Engineers (HKIE) on Testing of Unconfined Compressive Strength (UCS) of Cement Stabilised Soils in Hong Kong, and is a Technical Assessor for the Hong Kong Accreditation Service.  Dr Louis Wong received a Croucher Scholarship in 2002 and a Croucher Fellowship in 2007.

To view Dr Wong’s Croucher profile, please click here