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Rock cavern development is one of the Government’s multi-pronged strategies to increase land supply, which is of great importance to Hong Kong’s long-term development. To promote sustainable development, after undertaking researches and consultations, in 2014, the Drainage Services Department (DSD) moved forward with relocating the aging Sha Tin Sewage Treatment Works (STW) into caverns. The project is expected to be completed by 2031. Upon completion, not only will 28 hectares of land be released for other beneficial uses, the current issues relating to landscape, odour and aging facilities arising from the existing sewage treatment works will also be resolved.

The relocation project is taken forward in three stages. Stage 1 works mainly include site formation works at the cavern portal area and main access tunnel construction; Stage 2 works cover the main caverns construction and upstream sewerage works; and the remaining works comprise mainly the construction of sewage treatment facilities in the new caverns, and demolition of the existing Sha Tin STW. The Stage 1 works were completed in April 2022, and the Stage 2 works are underway.

The “Relocation of Sha Tin Sewage Treatment Works to Caverns” is the largest cavern sewage treatment works project in Asia. Construction of the caverns involves complicated underground works in a confined space that poses challenges in applying innovations and technologies to the project. The DSD makes use of innovations and technologies and advanced construction methods for improving the progress and quality of work as well as reducing material wastage.

Main caverns construction and upstream sewerage works

The main caverns construction and upstream sewerage works are in progress. The project scope includes:

a) main caverns construction
i. construction of a main caverns complex at Nui Po Shan of about 14 hectares in area and about 2.3 million cubic metres in total volume for accommodating the sewage treatment facilities in the remaining stage of the project;
ii. construction of about 260 metres long secondary access tunnel to connect the main caverns complex and Mui Tsz Lam Road;
iii. construction of a ventilation shaft of about 70 metres deep, and a ventilation adit of about 660 metres long to connect the ventilation shaft and the main caverns complex;
iv. construction of two effluent discharge pipes of about 2.2 metres in diameter and about 320 metres long to connect the relocated STSTW in caverns (the relocated sewage treatment works to be named “Sha Tin Cavern Sewage Treatment Works” and hereinafter referred to as “the cavern STSTW”) to the existing effluent discharge tunnel; and
v. site formation works at the secondary access tunnel portal areas, including natural terrain hazard mitigation measures and construction of the relevant retaining structures;

b) upstream sewerage works
i. construction of a new intermediate sewage pumping station (ISPS) at the south-western edge of the existing STSTW;
ii. construction of rising mains of about 4.6 kilometres in total length with diameters ranging from 0.8 metres to 1.2 metres connecting the existing Sha Tin Main Sewage Pumping Station (STMSPS), the new ISPS and the main access tunnel portal area; and
iii. modification of six sewage pumping stations (SPS) currently serving the Sha Tin and Ma On Shan areas, including STMSPS, A Kung Kok SPS, Ma On Shan SPS, Kau To Area 56A SPS, Chinese University SPS, Pak Shek Kok No. 3 SPS, and other related upstream sewerage facilities;

c) other related works ; and

d) implementation of environmental mitigation measures and related environmental monitoring and audit (EM&A) programme for the works mentioned above.

Buildings, cavern ventilation system and associated works

Buildings, cavern ventilation system and associated works (Stage 3 Works) will be started upon obtaining funding approval from the Finance Committee for anticipated substantial completion in around six and a half years.

The proposed works under the part of the Stage 3 Works, comprise:

a) construction of an administration cum ventilation building and an electric substation at the main access tunnel portal of the Sha Tin Cavern Sewage Treatment Works; and a ventilation building, an electric substation and a sludge skip storage building at the secondary access tunnel portal;

b) construction and installation of the cavern ventilation system for the cavern and tunnel interior space of about 600,000 cubic metres in volume and associated electrical system;

c) construction of an emergency bypass of about 2.5 metres diameter and about 1,150 metres long; and

d) other related works.

Application of innovative technologies

Site Specific 5G Network

In order to break through the restriction of confined space environment in tunnel works to implement innovative technologies, the construction team brought in a site-specific 5G base station. With the advantages from 5G network of low latency, high-speed transmission, and high device capacity, together with the development and implementation of various innovative technologies, they can improve the efficiency of project management, construction safety and site progress monitoring. They can also accumulate large amount of valuable data for the future development of cavern projects in Hong Kong.

The site is located in Ma On Shan, where 3.5GHz spectrum is solely for aircraft satellite channel. However, 3.5GHz is the common spectrum for 5G network. Therefore, they chose 4.9GHz spectrum to create a unique 5G network in Ma On Shan. Thanks to this site specific 5G network, the construction team can use the digitalized systems freely without the restriction of location and network speed, e.g. the DWSS system, Measure-While-Drilling system even 200 metres length inside tunnel, RFID system, electronic document management system and 3D Scanning, etc. It allows site staff to send and receive large amount of real time construction information at different locations, strengthens connection.

The blasting process monitoring apps solely developed by the construction team helps collecting real-time data of the blasting process for comparison and analysis, so as to optimize each process. When combined with the application of BIM, 5G network can help strengthen the performance of BIM, improve the constructability of construction projects, and save time and costs. Engineers can immediately grasp the actual situation in the tunnel, and then adjust the design and planning.

The high efficiency of 5G network also helps to monitor the real-time conditions of the tunnel. For example, immediately after blasting, an automated guided robotic car can go inside the tunnel to instantly transmit a full range of real-time high-definition images, to ensure tunnel safety before workers to enter into it. Furthermore, the real-time air monitoring device and UWB positioning watch are used separately to monitor the air, temperature, luminosity, gas and the health status of workers in the tunnel, as well as the safety of the location. In case of danger, an alarm will be issued immediately. It greatly improves construction efficiency and ensures the safety of workers.

Mixed Reality- HoloLens 2

The project involves large amount of blasting works, a pair of mixed reality smart glasses “HoloLens 2” enables the project team to check location of drill holes or rock bolts anytime during construction, improving efficiency and safety of the entire blasting process.

HoloLens 2 allows design computer models to be precisely visualized in real world and also allows interaction and modification of the design. It provides step-to-step stimulation training to workers on blasting works such as explosive charging. It also helps the project team to identify the locations of existing underground utilities so as to avoid damaging them.

Robotic Monitoring System

The project team developed a robotic monitoring system for unmanned tunnel entry right after the blasting works, which would carry out preliminary assessment and monitoring of the tunnel conditions, so as to identify potential safety risks in the tunnel for necessary mitigation measures.

Engineers can monitor in real time through the system the level of various types of gas in the tunnel, including oxygen, explosive gas, carbon monoxide and hydrogen sulfide, and check the air quality in the tunnel to ensure it is safe for entry. The system is also equipped with laser scanner to analyse the face and crown conditions of excavated tunnel section. High-definition point cloud images and data collected are then transferred to the project team offsite through 5G network, enabling geotechnical engineers to evaluate the geotechnical risk in the tunnel after blasting and implement necessary mitigation measures, thus minimising the safety risk of workers for tunnel entry.

Smart Drilling Jumbo

During tunnel excavation, drilling jumbos (commonly known as Jumbo) are used by the DSD for blast hole drilling at tunnel face to facilitate explosive charging works. In order to further enhance the accuracy and control of the drilling operation, Measure-While-Drilling (MWD) system is adopted to supplement Jumbo in the drilling operation, improving the quality of construction works.

The MWD system is built in the smart drilling jumbo, which monitors the actual position, direction and depth of each blast hole in real time, and enables the operator in the control room to check against the original blasting design instantaneously and make timely corrections when necessary. The monitoring system can not only help improve the accuracy of drilling works but also make it easier for the project team to track the progress of work.

Releasing land for I&T development

Taking the opportunity of relocating the STSTW to caverns, the Government can adopt more advance technologies in the proposed cavern STSTW and have a comprehensive upgrading of the facilities, in order to enhance the operational efficiency and provide better sewage treatment services to the local residents. On the other hand, this cavern development can release the exisitng site of 28 hectares which, together with the land from the Ma Liu Shui reclamation project, will provide a total of 88 hectares of new land mainly for I&T development.

The Innovation, Technology and Industry Bureau has engaged the Hong Kong Science and Technology Parks Corporation to carry out the “Preliminary Planning Study for Land Development and Preliminary Engineering Feasibility Study” in early 2023, covering the study of the site development and supporting infrastructure of the land released by the Ma Liu Shui reclamation project and the relocation of STSTW to caverns. The study is expected to be completed within 2024 and will make recommendations on the required infrastructure at that time.

Source of Information and Picture:
Relocation of Sha Tin Sewage Treatment Works to Caverns Website of Drainage Services Department

Complimentary copies available to members of the following associations:

The Hong Kong Construction Association
Macau Coustruction Association
Hong Kong General Building Contractors Association
Hong Kong Institute of Utility Specialists
China Hongkong Society for Trenchless Technology Association
Hong Kong Construction Materials Association Limited
Contractor's Authorised Signatory Association
Hong Kong Construction Machinery Association