Draft:Cavern Development in Hong Kong

The research and policy implementation of Hong Kong Cavern Development is overseen by the Civil Engineering and Development Department (CEDD), specifically the Geotechnical Engineering Office, and the Planning Department. Caverns are large man-made spaces excavated within mountain rock. Hong Kong, with its many steep mountains and solid rock, has geology particularly suitable for cavern development, especially at the edges of urban areas. The Hong Kong Government has been actively researching and successfully implementing cavern projects, such as the Stanley Sewage Treatment Works and the Island West Transfer Station. In 2011, the CEDD developed a territory-wide cavern suitability map, indicating that about two-thirds of Hong Kong's area is suitable for cavern development. The benefits of developing caverns include providing new land resources and relocating appropriate government facilities into caverns, not only freeing up the current land but also releasing the development potential of nearby land for housing or other functions, which are extremely precious to society. Placing facilities such as Sewage Treatment Works and Waste Transfer Stations inside caverns can effectively block and handle odors produced during operations, greatly reducing the negative impact on surrounding communities. Utilizing the unique characteristics of cavern spaces, where temperature and humidity are relatively stable, for functions such as data centers or warehouses, can also enhance operational efficiency.

Research and Development History
The Civil Engineering and Development Department has been conducting a series of research since the early 1980s to explore the technical feasibility and details of cavern development, including:


 * 1982 Underground Oil Storage Study


 * 1991 Cavern and Associated Project Research (CAPRO)


 * 1994 Cavern Siting Study (CAS)


 * 2012 Long-term Strategy for Cavern Development


 * 2017 Technical Study on Underground Quarrying in Hong Kong – Investigation


 * 2019 Strategic Cavern Area Development Planning and Engineering Pilot Study


 * 2022 Updating the Guide to Fire Safety Design for Caverns – Feasibility Study

Cavern Master Plan
In 2017, the CEDD and Planning Department compiled the "Cavern Master Plan" to provide a comprehensive strategic planning framework to guide and promote the development of caverns throughout Hong Kong and to provide important information for project proponents to identify suitable sites for cavern development.

“Cavern Master Plan” identified 48 strategic cavern areas across Hong Kong that can meet the existing or future needs of nearby areas. A strategic cavern area refers to a region that is easily accessible, capable of accommodating multiple facilities for development needs, and is spacious and located at the edges of urban areas with infrastructure network support. The sizes of these strategic cavern areas range from about 30 hectares to 200 hectares. However, the size of a strategic cavern area does not represent the actual developable cavern space, as space must be reserved for other purposes, such as buffer zones for separating facilities, supporting rock pillars for caverns, and tunnels connecting entrances and other pathways.

Cavern Master Plan received international recognition, winning the Innovative Underground Space Concept of the Year in the ITA Tunnelling Awards 2017 on November 15, 2017, awarded by the International Tunnelling and Underground Space Association (ITA). It was also awarded a Certificate of Merit by the Hong Kong Institute of Planners in 2016, recognizing its role in unlocking Hong Kong's hidden land resources.

The Ongoing Cavern Development Projects

 * Relocation of Public Works Central Laboratory to caverns - The Civil Engineering and Development Department is working on relocating its Public Works Central Laboratory to the mountain body of Tai Sheung Tok at the Anderson Road Quarry Development site, freeing up coastal land for housing purposes.


 * Construction of Government Records Service's Archives Centre - The Civil Engineering and Development Department assists the Government Records Service in building the Archives Center in the mountain body of Tai Sheung Tok at the Anderson Road Quarry Development site. Constructing the Government Records Service’s Archives Center in the cavern provides permanent storage space for historical records, addressing the shortage of storage space and the increasing need for historical document storage, while also making more efficient use of land resources.


 * Relocation of Sha Tin Sewage Treatment Works - The Drainage Services Department is undertaking a project to relocate the Sha Tin Sewage Treatment Works from its current location at the mouth of Shing Mun River to a cavern at Nui Po Shan in A Kung Kok, freeing up the current site for innovation and technology development and improving the living environment in the area.


 * Relocation of Diamond Hill Freshwater and Salt Water Service Reservoirs - The Water Supplies Department is conducting a feasibility study to free up approximately 4 hectares of the current site for housing construction and other beneficial public uses, with mountain to the north of Chuk Yuen North Estate as the preliminary relocation site.

Hong Kong

 * Stanley Sewage Treatment Works began operation in 1995, marking the birth of Hong Kong's first sewage treatment facility located inside a cavern. This secondary sewage treatment plant is capable of treating 11,600 cubic meters of sewage per day. The plant adopted the most advanced cavern construction technology of the time, with structures spread across three caverns approximately 120 meters long, 15 meters wide, and 17 meters high, interconnected by over 450 meters of passageways, ventilation tunnels, and shafts.


 * Kau Shat Wan Government Explosives Depot- Established in 1997, mainly for the storage of commercial explosives, the facility includes 10 explosive magazines hidden in caverns, each 20 meters long, 13 meters wide, and 6.8 meters high, providing a safe and reliable storage environment. The depot, hidden within the mountain, minimizes landscape impact and preserves the surrounding natural environment.


 * Western Salt Water Service Reservoirs - In 2007, the Water Supplies Department and the University of Hong Kong reached an agreement to relocate the Western freshwater and salt water Service Reservoirs to free up land for the construction of the Centennial Campus. The project began by moving the salt water service reservoir into a cavern, followed by re-establishing the freshwater service reservoir at the original location of the salt water service reservoir. The salt water service reservoir in the cavern can store up to 12,000 cubic meters of salt water. The project freed up ground space for the construction of the University of Hong Kong Centennial Campus.

Overseas

 * Gjøvik Olympic Mountain Hall, Norway - The Nordic regions of Norway, Finland, and Sweden have gained extensive experience and remarkable achievements in cavern construction. Constructed in 1993, the Gjøvik Olympic Mountain Hall in Norway is the world's largest cavern building, measuring 61 meters in width, 25 meters in height, and 91 meters in length, accommodating up to 5500 people. It served as a venue for ice hockey during the 1994 Winter Olympics. The hall has now been transformed into a concert hall and is used for large-scale exhibition events.


 * Cavern Sewage Treatment Works, Norway - With the increasing demand for sewage treatment and strict marine discharge standards, Norway began establishing large-scale sewage treatment facilities in caverns from the 1970s. The first such facility, the VEAS Sewage Treatment Works in Oslo, commenced operations in 1982, designed to treat sewage from a population equivalent of 565,000, including residential, commercial and industrial discharges.


 * Schollberg Underground Quarry, Switzerland - This private quarry, located in a scenic mountainous area, has been operated since 1985. Operating all year round, unaffected by adverse weather, it preserves the original terrain, significantly reducing environmental and landscape impact. The excavated underground space can also be used for other beneficial purposes.


 * Itäkeskus Swimming Hall, Finland - The facility includes a 50-meter swimming pool, a learner's pool, a children's pool, a massage pool, water slides, diving towers, saunas and a gymnasium, accommodating up to 1000 people at a time, with annual attendance reaching 400,000.

Relevant Departments

 * Civil Engineering and Development Department
 * Drainage Services Department