For every infrastructural project, no matter it is site formation, tunneling or other construction works, comprehensive, professional assessment is essential prior to the commencement of the works. Our colleagues in the Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department (CEDD), who are responsible for a wide range of geotechnical-related activities to ensure safe and economic development and use of land in Hong Kong, are those unsung heroes who play an important role in promoting growth of this city. The Hong Kong Geological Survey Section, under the GEO, was established in 1982 to undertake detailed geological survey, compile geological maps of Hong Kong and offer authoritative geological advices to the Government, the engineering sector and the general public. Now I would like to introduce the work of this important unit.

The work of the CEDD is closely related to town planning and land and infrastructure development, which require geological survey and site investigation. Besides offering geological advices on various works departments at different stages of development projects, our colleagues in GEO also provide professional support on natural terrain hazard studies as well as developing of caverns and tunnel excavation works. The series of geological maps of Hong Kong, which provide useful information for town planning, exploring of geological resources, and prevention and control of geological hazards, are the achievement of years of their hard work.

A supervolcano in Hong Kong?

Do you know there was once a supervolcano in Hong Kong? The discovery of the ancient High Island Supervolcano in southeastern Hong Kong in 2012 was an example showcasing the high-quality research being conducted by the Hong Kong Geological Survey over the years. The supervolcano has long been extinct since it last erupted 140 million years ago. Due to weathering and erosion, most of the volcanic rocks have been removed and only a remnant remains and forms the fascinating landscape of hexagonal rock columns now expose in the Hong Kong UNESCO Global Geopark in Sai Kung. The discovery is the result of years of geological studies by the CEDD and has involved detailed radiometric age-dating of rocks, geochemical and geophysical analyses, as well as geological mapping. Such geological research has enriched our understanding of local geology and also laid out a foundation for assessing engineering geological conditions and slope stability, etc. There are about 50 supervolcanoes on record in the world and the High Island Supervolcano is one of them.

Geological conditions critical to construction projects

There are many uncertainties in every construction project, and geological conditions of the site may be one of those. The Hong Kong Geological Survey has played an important role in many construction projects. Dr Denise TANG, a senior geotechnical engineer of the CEDD, who has worked in the field of geology for many years, said some government consultants responsible for public works will seek geological information of the proposed site (such as underlying rock types and geological structures) for tunneling and foundation projects, in order to learn if the geological conditions are suitable for excavation and piling. Government departments will also seek professional geological advice from the CEDD on study reports conducted by their consultants to ensure that the works can be proceeded smoothly.

Apart from geological surveying, the Hong Kong Geological Survey is also responsible for collecting and archiving geological information. I learnt that our colleagues would take every chance to visit remote places to collect rock specimens, offshore areas in particular. Recently, Denise and her colleagues visited the drilling site at the third runway system project at the airport to collect core samples. She said, compared with samples from the surface, it is more difficult to retrieve rock samples in offshore areas, so they would take every chance to get the samples. After collecting the rocks, they would classify and describe the rock samples, analyze the composition or even carry out laboratory testing. The rocks they collected have become an important source of information for future geological study of that area.

Developing rock caverns to provide usable space

Hong Kong’s comprehensive study on geology, meanwhile, contributes to locating suitable lands for development. The Government has been striving to release land resources through a number of options, including rock cavern development (RCD). Last year, the CEDD completed Cavern Master Plans. After considering the geology and other factors, the CEDD have identified 48 Strategic Cavern Areas (SCVAs). I agreed with Denise that Hong Kong is extremely suitable for developing rock caverns because Hong Kong is underlain by relatively strong and stable granite and volcanic rocks. Moreover, in light of the increasing urban development close to hillsides with comprehensive ancillary facilities, the use of rock caverns can be one of the innovative measures to expand Hong Kong’s land resources.

In fact, the CEDD and the Planning Department have long commenced the pilot study on cavern development, including relocating the sewage treatment plants in Shatin, Sai Kung and Sham Tseng as well as Diamond Hill Fresh Water and Salt Water Service Reservoirs into cavern. The above rock cavern projects could release a total of about dozens hectors of land for development. However, cavern development requires a relatively long time and includes comprehensive assessment and consultation during the process to ensure that it would pose no significant impact on nearby ecological environment and local residents' daily living.

Besides, underground space is a hidden land resource. If we can use it systematically, it can bring new opportunities to meet various needs of social and commercial facilities as well as to address various issues including traffic, environmental, etc. We are now studying on the potential for underground space developments, but it involves many considerations including geotechnical and structural constraints, and interfaces with existing underground uses such as basements, fire safety, and the possible uses for the potential underground spaces, etc. All of them need to be duly assessed by our professional colleagues.

In face of land shortage, I hope the public and various shareholders will continue to offer valuable suggestions on land development, whether they are short-, medium- or long-term development. We will communicate and listen patiently to other’s ideas and be open minded with a view to removing blind spots. Our departments are willing to offer professional advice to you so as to draw on collective wisdom in making Hong Kong a livable city.