January 20, 2022
Hong Kong – University of Hong Kong student Cheng Fei didn’t know that a huge saltwater service reservoir lay hidden in a mountain next to the Centennial Campus garden, even though he had studied at the institution for a year.
Cheng was amazed by the “invisible” facility, which became operational in 2009. “There were no noises, strange smells or any other indication that it was there,” he said.
In the early 2000s, the university, also known as HKU, drew up plans to become a world-class research institution, but the much-needed extra space to achieve this goal was a real headache.
It was almost mission impossible, as there is an acute local land shortage, land costs are high, and Hong Kong Island, where the university is located, is one of the most densely populated areas of the city.
Finally, the university submitted an innovative proposal to the Hong Kong Special Administrative Region government.
The plan involved digging caverns in nearby mountains to house the old Western Saltwater Service Reservoir and then relocating the Western Freshwater Service Reservoir to the area vacated by the saltwater facility.
One cavern, which is 50 meters long, 17.6 m wide and 17 m high, can store a maximum of 12,000 sq m of saltwater. It also helped release land for construction of HKU’s Centennial Campus.
Quentin Yue Zhongqi, professor in the university’s department of civil engineering, said, “This was a great way to achieve two goals with a single attempt.
“An advanced concept at that time, the saltwater reservoir near the university is the city’s first service reservoir built in rock caverns.”
In addition to the reservoir in the caverns, which has been in use for more than a decade, the city is relocating more public facilities to caverns as a solution to provide more space.
A project underway to relocate the sewage treatment plant in Sha Tin to caverns forms part of this program.
Proposed by the Hong Kong government in 2013 to solve the city’s land shortage problem, this plan will see the 28-hectare sewage treatment plant in Ma Liu Shui, Sha Tin, moved to caverns in nearby Nui Po Shan.
After it is relocated, the 14-hectare plant in the caverns is expected to be the largest project of its type in Asia. It is scheduled to start operating in 2029.
The old site will be converted into housing and put to other uses to improve people’s lives.
Site preparation and work to construct the tunnel for phase one of this project began in February 2019. This phase is targeted for completion this year, while work on the main cavern for phase two started in July.
After the open-air plant is relocated, each cavern will serve as a natural barrier, fully enclosing the facility.
Work on the main cavern calls for engineering teams to excavate 11 caverns for the sewage treatment facility, and the entire underground complex will cover 2.3 million cu m. The caverns will be excavated by drilling and blasting.
Li Yifeng, senior site manager at China State Construction Engineering (Hong Kong), which is responsible for the project, said, “We are exploring high-technology solutions to address difficult problems, and we aim to promote the use of smart construction sites and create demonstration projects for technological innovation.”
The construction site is the first in Hong Kong equipped with 5G technology. Numerous industrial sensors and internet of things, or IoT, equipment have been installed to help surveying and engineering teams－reducing safety risks for workers in a hazardous environment.
This equipment monitors the impact of construction, including groundwater levels, blasting vibrations, other noise, and tunnel air quality in real time, as well as construction activity data, including drilling, use of electricity and worker location.
The engineering team developed its own robotic monitoring system to ensure workers’ safety.
Li said teams at the site also installed noise barriers, blasting doors, and used the IoT monitoring systems to minimize the impact of construction on nearby residents.
Tony Leung Ka-chung, chief engineer (cavern projects) at the city’s Drainage Services Department, said the relocation project will benefit residents and have a positive effect on Sha Tin and the surrounding area.
Hong Kong resident Tsang Chuen-ming, who lives about 900 meters from the existing Sha Tin Sewage Treatment Plant, said he supports the relocation project, as he believes it will improve the environment.
“Sometimes, I can detect the odors coming from the sewage treatment plant at home. I hope this problem will be addressed after the new one is put into use,” Tsang said.
He added that when he heard that the construction project would involve blasting, he was worried about safety and excessive noise. “But now I have no such concerns, as I haven’t heard any noise at all,” he said.
The construction team also used the self-developed robotic monitoring system for blasting work in the tunnel and caverns.
An automatically-driven vehicle with 3D cameras and sensors enters the tunnel or caverns and sends back real-time information about chemical composition of the air and images of rock surfaces.
Zhu Juling, an engineer who took part in the sewage facility relocation project, said this technology can help ensure construction workers’ safety and largely reduce such risks.
The plant currently serves a population of 650,000 in Sha Tin and Ma On Shan districts, which produce a total of 260,000 cu m of sewage a day.
The Sha Tin sewage treatment facility is just one of the projects in the Hong Kong government’s master plan for cavern development, which was released in late 2017.
The plan lists 48 potential underground and hillside sites for new caverns, eliminating the need for companies to find their own. It could free as much as 1,000 hectares of land.
Caverns will be mainly used to house sewage treatment facilities and as depots to store explosives.
Before the project to relocate the Sha Tin sewage facility to caverns was proposed, the city already had a small pilot cavern sewage treatment facility program in Stanley on Hong Kong Island. Put into use in 1995, this program serves a population of more than 27,000.
Hong Kong is not the only place to venture deep into the mountains to free up much-needed space. In Norway, the National Archives and Olympic Sports Center have been built in caverns; in France, wine and food storage facilities have been built within hills; while in Finland, caverns are used to house swimming pools and parking lots.
On the Chinese mainland, internet giant Tencent is building a data center in rock caverns in Guizhou province.
According to Yue, the HKU professor, various factors, such as geological environments, climate, topography and local needs have a significant impact on the roles caverns can play.
Countries in northern Europe have opted to build entertainment facilities in caverns due to harsh winter weather, as the interior temperature tends to be constant throughout the year, Yue said.
“However, in Hong Kong, there’s no need to develop caverns in this way, as the city’s average winter temperature is higher than 10 C,” he added.
Yue said it is not clear whether Hong Kong’s Northern Metropolis Development Strategy, an ambitious plan by the local government to develop land near the boundary with the mainland, will influence the overall aim to develop caverns. But he stressed that developing underground space is still important for the city’s further development and expansion, adding that there is great potential to develop underground space in the Guangdong-Hong Kong-Macao Greater Bay Area.
Developing underground infrastructure can help Hong Kong withstand threats from disasters such as floods and earthquakes, and is also an indicator of the city’s development progress, Yue said.
According to the Hong Kong Highways Department, utility services have installed, on average, about 50 kilometers of underground pipes and cables per km of public roads.
Chen Xiangsheng, an academician at the Chinese Academy of Engineering and dean of the College of Civil and Transportation Engineering at Shenzhen University, Guangdong province, highlighted the significance of developing underground space to enhance a city’s resilience and safety.
In the Greater Bay Area, the 11-city cluster is exploring its own underground space, as it faces population growth and limited room above ground. “We must look under the ground to find solutions,” Chen said.
Shenzhen, Hong Kong’s neighbor, is poised to develop underground areas in 45 locations across the city in an attempt to optimize urban space and improve the ability to withstand disasters.
Several large underground projects centered on metro stations have been developed in Shenzhen, linking stations, underground shopping malls and parking lots.
Since August, districts in the city have introduced their own measures to exploit and develop underground space to address public concerns over safety issues.
Chen said that staying below ground is sometimes safer in the event of natural or man-made threats, such as earthquakes and terrorist attacks.
However, he added that it is still not time to allow people to live underground, as relevant research and experience is lacking worldwide.
Chen said the best way to boost development in Hong Kong is to synergize the smart city and underground city development concepts and make full use of technology to explore possibilities below ground.
Applying advanced technology, such as big data and cloud computing services, to building a smart city could help monitor and manage safety under the ground 24 hours a day, Chen added.