GEO caps 40 years of work on slope safety with anniversary summit

By Angela TAM

The Civil Engineering & Development Department's (CEDD) Geotechnical Engineering Office (GEO) has a special anniversary to celebrate recently, having been established over 40 years ago in response to a series of catastrophic landslides in various parts of Hong Kong in the 1970s.

Many would remember the Po Shan Road landslide in Mid-Levels in 1972 as well as the Sau Mau Ping landslides, which occurred in 1972 and again in 1976, directly driving the establishment of a dedicated office to address landslide risks. Over the past 40 years, GEO has not only launched extensive landslip prevention works all over the city; it has also built up enviable geotechnical engineering expertise that has attracted the attention of officials from countries all over the world anxious to tackle the same challenge. According to GEO, the office receives on average eight overseas delegations per year with more than 100 overseas practitioners visiting every year. These delegations come from the Mainland, Asian cities such as Seoul, Taiwan, Singapore, Malaysia and Indonesia and as far afield as the US, UK, New Zealand and Canada.

To celebrate its 40th anniversary, GEO organised the Slope Safety Summit in December 2017, providing an opportunity for department officials, industry professionals and academics to exchange knowledge on the latest landslide risk management, slope assessment and stakeholder engagement techniques as well as to discuss the impact of climate change. More than 240 experts and stakeholders in the field of slope engineering and landslide risk management attended the Summit.

Holistic landslide risk management
Among the first speakers at the Summit was Prof Norbert R Morgenstern of the University of Alberta, Canada, who was involved with the establishment of the Independent Review Panel on Fill Slopes following the Sau Mau Ping landslide of 1976. The report was instrumental to the establishment of GEO, "to provide continuity throughout the whole process of investigation, design, construction, monitoring and maintenance of slopes in Hong Kong".

As GEO grew into its role in the subsequent years, Hong Kong received another shock in 1994, when the Kwun Lung Lau landslide occurred, resulting in five fatalities and the evacuation of more than 3,900 people. The slope involved had not been considered of marginal stability. Prof Morgenstern was invited back to Hong Kong as a result, both to report on the causes of the landslides and the adequacy of geotechnical practice in Hong Kong.

The outcome of this review was the adoption of a risk management approach to minimise the consequences of landslide hazards. Thus Hong Kong entered an era of holistic landslide risk management, which encompasses land use planning, regulatory control and slope retrofitting works, early warning and public education.

While the landslide risk in Hong Kong has been reduced to an "as low as reasonably practicable" level, Ir W K Pun, current head of GEO, said at the Summit that the landslide risk would never be zero. The key is to anticipate future challenges, which include climate change and rising public expectation of safe slopes, along with low tolerability to disastrous landslides. Landslide risk management in Hong Kong has to continue to evolve to meet the challenges. Constant vigilance is called for, which means GEO has to be prepared for possible extreme landslide scenarios and related emergencies.

Innovative slope assessment and risk management
According to Dr Suzanne Lacasse, technical director of the Norwegian Geotechnical Institute (NGI) and chair of the Slope Safety Technical Review Board (SSTRB) in Hong Kong, the latest technologies are now used to assess and manage slope safety risk. Remote sensing, which has been in use for some time, is now aided by the adoption of internet of things and big data technologies, which enable data from satellites as well as a variety of sensors to be collected and analysed.

At the same time, Dr Lacasse noted a shift in focus from quantitative risk assessment to stress testing and from designing a system, such as sensors at specific locations; to observing a response as rendered through data from diverse sources. Drawing on an example from Norway, Dr Lacasse said that data from retail sales of skiing equipment as well as information from social media is also gathered as indicators of the likely level of participation in skiing activities.

A smartphone app developed by NGI, Bratt, enables skiers and others to check the steepness of slopes, download offline maps of the area surrounding the slopes and find safe routes to and from the slopes.

Dr Lacasse believes that big data and machine learning will transform GEO's work in the future. "There is a paradigm shift to large distributed systems from dedicated, high quality, small-scale monitoring systems," she said. As an example of the strength of machine learning, she referred to Alphago, the computer that beat the world Go champion recently. While the human champion has a rating of 3,681, the machine achieved a rating of 3,739 after learning the game for just three days. Such computing power can help the geotechnical community manage black swan (low frequency, high consequence) events by identifying the weakest links in a system so that the system can be made more robust at these links.

Her views are supported by those of another speaker, GEO's chief geotechnical engineer Ir Dr Julian Kwan. Expanding on the use of remote sensing techniques, Ir Dr Kwan said the advent of drones has made it possible to obtain ground data from a large area much more quickly than in years past while machine learning can provide quick interpretation of geological data. The use of big data also means landslide susceptibility maps can be drawn up based on geological attributes and correlated with rainfall. Advances in numerical modelling for assessing landslide risk are now supported by the latest mobile technologies, which enhance the effectiveness of GEO's landslide warning system by obtaining rainfall data from rain gauges that is relayed every minute.

According to Ir Dr Kwan, GEO is now piloting the use of smart barriers - physical debris-resisting barriers fitted with impact sensors that will send signals back to the office when impact is detected. GEO is also introducing the use of virtual reality to educate the public about landslide risk.

The GEO's work in landslide risk assessment and management is supported by the research of academics such as the studies being conducted by Ir Prof Charles Ng of the Hong Kong University of Science & Technology. Ir Prof Ng has set up large-scale flumes in both Hong Kong and Chengdu on the Mainland to study debris flow mechanisms, to facilitate landslide risk mitigation.

The flume in Tai Po in Hong Kong is 28 m long and has an adjustable flume angle. The flume in Chengdu is much bigger, being 172 m long and 6 m wide, and is used to model the interaction between debris flow and barriers.

During the discussion that followed the presentations on landslide risk assessment and management, Ir Prof C F Lee of the University of Hong Kong's Department of Civil Engineering said that there were two levels of achievements in this area. The first is the mitigation of landslide hazards to the extent of eliminating fatalities, which in Hong Kong has witnessed much progress since GEO's establishment. The next level concerns the accurate prediction of future landslides through artificial intelligence and various research efforts, which remains a challenge not just for Hong Kong but for the whole world.

Impact of climate change
This challenge has become more critical as a result of climate change. According to Prof Dave Petley of the University of Sheffield and member of the SSTRB, who spoke in the afternoon session of the Summit, climate change affects slope stability primarily through its impact on landslide hydrogeology. Heavier or more frequent rainfall can increase pore water pressures within a slope while higher temperature and increased airflow can lead to higher levels of evapotranspiration.

The effect of precipitation on slope stability means GEO now works closely with the Hong Kong Observatory, whose data is critical to predictions of landslide risk events.

According to S M Lee of the Hong Kong Observatory, the projected annual maximum daily rainfall and annual maximum three-day rainfall in Hong Kong by the end of this century could exceed 270 mm and 520 mm respectively under the 'business-as-usual' scenario for greenhouse gas emissions. The increased rainfall is expected to increase the risk of flooding and landslides.

GEO's Ir Dr H W Sun noted that the impact of the rainstorm that struck Hong Kong in June 2008 and how it highlighted the impact of extreme rainfall on the community and its effect on slope safety. On 7 June 2008, 145.5 mm of rain fell in one hour, the highest on record. More than 400 mm of rain fell on Tung Chung on that day, causing severe flooding and landslides. CEDD estimated at the time that it was a 'once in 1,100 years' event. In view of the more likely occurrence of such extreme weather events due to climate change, GEO has strove to improve the resilience of the Hong Kong Slope Safety System. Measures include:

- enhancement made to the landslip warning system
- identifying the nature and scale of extreme landslide events
- assessing the severity of landslide consequences
- assessing the need to change the risk profile of slopes
- evaluating the capacity of emergency management
- improving crisis preparedness

GEO has also recognised the need for cross-departmental cooperation in tackling the challenge as different types of hazards could occur at the same time and now works with other government departments to review the Government's emergency preparedness and develop an overall adaptation strategy.

Stakeholder engagement
Promoting slope safety requires not only technical expertise but also public education. Stakeholder engagement therefore is an important component of GEO's efforts. Speaking at the Summit, Ir Jenny Yeung highlighted the office's work in promoting public awareness of slope safety through an extensive year-round publicity campaign targeted at the general public, to ensure they stay away from dangerous slopes, especially under adverse weather conditions; and building owners with responsibility for maintaining private slopes.

According to Ir Yeung, the effort of all stakeholders over the past 40 years has led to a substantial reduction of the overall landslide risk in Hong Kong, to an 'as low as reasonably practicable' level, in line with international best practice in risk management. However, Ir Yeung stressed that constant vigilance is necessary as we move forward due to great uncertainties in landslide risk due to climate change, increasing population and slope deterioration. In the long run, risk reduction through the engineering approach has to be complemented by widespread public education.

It is therefore important for us to step up public education to enhance community resilience while maintaining the Government's effort and resources, so as to meet the future challenges in landslide risk management. Six of the eight heads of GEO attended the Summit, to show their support and share their knowledge. The knowledge sharing is both a celebration of GEO's work and a demonstration of its commitment to continuous improvement. It is knowledge that is sure to benefit not just Hong Kong, but the world.