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To support the sustainable development of Hong Kong, the Government has been adopting a multi-pronged approach to enhance land supply, including proactively exploring cavern development. This time, I have invited a colleague from the Development Bureau (DEVB) to talk about some projects currently underway for relocating/accommodating government facilities into caverns. A colleague from the Civil Engineering and Development Department (CEDD) will tell us the constraints and challenges for accommodating facilities in caverns and how to adopt innovative technology to overcome the construction difficulties.

Assistant Secretary (Works Policies) of the DEVB, Mr FUNG Yiu-cheung, Dennis, says that the hilly and hard rock terrain of Hong Kong makes it highly suitable for developing caverns, particularly on the urban fringes. At present, there are various government facilities accommodated inside caverns in Hong Kong, including Stanley Sewage Treatment Works, Island West Transfer Station, Kau Shat Wan Government Explosives Depot on Lantau Island and Western Salt Water Service Reservoir.

Cavern development projects underway

The Government is proactively taking forward a number of projects for relocating/accommodating suitable government facilities into caverns to better utilise land resources and improve the urban layout and environment as well as enhance the service quality of these facilities. One example is the relocation of the Sha Tin Sewage Treatment Works to caverns by the Drainage Services Department, which is the largest ongoing cavern development project in Hong Kong. Under which, excavations and construction of a cavern complex at Nui Po Shan in Sha Tin are currently underway. Once the relocation is completed, the surrounding environment of the site of the existing sewage treatment works will be improved and about 28 hectares of land will be released mainly for innovation and technology development.

The Water Supplies Department has commenced the construction works of relocating the Diamond Hill Fresh Water and Salt Water Service Reservoirs to caverns. Once the service reservoirs are relocated to the mountain body at the south of Lion Rock, about four-hectare of valuable land at the existing site in Wong Tai Sin District will be released for the construction of housing and community facilities.

The CEDD will construct caverns inside the mountain body at the Anderson Road Quarry Development site for the relocation of the Public Works Central Laboratory in Kowloon Bay and building of a new Government Records Service’s archives centre. With relatively stable temperature and humidity, caverns can enhance the energy efficiency of the facilities. Currently, funding approval is being sought for the project.

The projects of relocating Tsuen Wan No. 2 Fresh Water Service Reservoir and Yau Tong Group Fresh Water and Salt Water Service Reservoirs to caverns are still in the investigation and design stage. Each of the two projects can release the existing sites together with the adjacent land of about six hectares in total for the construction of housing and community facilities.

Exploring the development of cavern data centres

Furthermore, the DEVB and the Innovation, Technology and Industry Bureau are exploring the development of cavern data centres, using the safe and stable environment of the caverns, to support the sustainable development of data centres. In this connection, we held a Stakeholder Forum on Developing Data Centres in Caverns last September to facilitate sharing and interchange with trade practitioners.

Technological constraints and considerations in cavern development

Although cavern development can bring a number of benefits, there are also many technical constraints and considerations, and not every mountain body is suitable for cavern development. Senior Geotechnical Engineer of the CEDD, Mr TSANG Wai-hon, says that from the geotechnical engineering perspective, the rock cover of a location for cavern development should be thick enough for cavern formation. If there are other facilities above or next to a cavern site, including the foundations of buildings or underground tunnels, the cavern development potential at this location will be limited. Besides, a cavern development is composed of a number of cavern halls and access tunnels with partitioning rock pillars to support the entire cavern complex, therefore large facilitates that cannot be subdivided may not be suitable for accommodation in caverns. Finally, in view of the relatively high costs and relatively long implementation time for cavern development, the Government must carefully assess the costs, environmental and social impacts and cost effectiveness of various development proposals.

Innovative cavern engineering technology

Hong Kong is equipped with rich experience in cavern development and there are various facilities accommodated inside caverns. However, cavern construction still faces some technical challenges, such as how to conduct a blasting operation in a complex geological environment. In this connection, we proactively adopt innovative technologies, including the use of drilling jumbos with the Measurement-While-Drilling system in cavern excavation to enable instant rock data transmission to operators for analysis when drilling blast holes at rock faces for placing explosives, with a view to optimising the blasting design and enhancing works quality and efficiency.

We are now also using an innovative technology of mixed-reality HoloLens at construction sites to project the design blast holes images on the rock faces to help the checking of the accuracy of hundreds of blast holes so as to improve the inspection procedure and reduce processing time.

In future, we will continue to cooperate with the relevant policy bureaux and departments to evaluate whether their government facilities are suitable for cavern development, based on the safety, operational, environmental, technical and financial aspects after taking into account the nature of the facilities, with a view to better utilising cavern resources in Hong Kong.