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Franklin To
is a civil and geotechnical engineer with 12 years of professional experience in Hong Kong. His expertise covers planning, feasibility studies, detailed design and site supervision of rock tunnels and caverns. He specialises in permanent rock reinforcement (i.e. RRA using shotcrete and rock bolts), use of explosives, groundwater inflow control, tunnel excavation in rock/mixed/soft ground, contract specifications and quality assurance. He has served as a Resident Geotechnical Engineer (Caverns) for the project Relocation of Sha Tin Sewage Treatment Works to Caverns – Main Caverns Construction), which is the largest rock caverns in Asia using RRA for permanent rock supports. He acted as the GEO/Mines approved Blasting Competent Supervisor (BCS) for underground blasting works (including Mode A Store Entry) and the Category I Supervisor for both Tunnelling Works and Geotechnical Works.
His technical strengths include empirical and analytical analysis, advanced numerical modelling (UDEC, RS2, RS3, PLAXIS 2D/3D), blasting impact assessment, hydrogeological assessment, structural analysis, and geotechnical instrumentation & monitoring.
Design and Construction for the Largest Rock Cavern in Asia – A Case Study on the Relocation of Sha Tin Sewage Treatment Works to Caverns
Design and Construction for the Largest Rock Cavern in Asia – A Case Study on the Relocation of Sha Tin Sewage Treatment Works to Caverns
Franklin K.L. To, Bridges D.C. Guy, Andrew K.W. Seto & Stephen L.C. Tam
AECOM Asia Company Ltd., Hong Kong, China
Michael W.K. Choi & Steve C.H. Leung
Drainage Services Department, the Government of the Hong Kong Special Administrative Region, Hong Kong, China
ABSTRACT
The Drainage Services Department (DSD) commenced the “Relocation of Sha Tin Sewage Treatment Works (STSTW) to Caverns” (STC) project and aims to relocate the aging STSTW in a cost-effective manner, improve the surrounding environment, and release approximately 28 hectares of land for more beneficial uses. The construction of advance works began in 2019. The successive Drill-and-blast excavation of the main caverns complex commenced in January 2022 and was completed in September 2025. The project is currently the largest rock cavern development in Asia, with about 2.3 million m³ of rock excavated.
The caverns complex comprises a grid arrangement of 4 x 7 parallel rock caverns, with individual span and height both reaching maximum of 32m. Permanent cavern support system consists of systematic rock bolts and fiber-reinforced sprayed concrete lining, designed using the Q-system empirical approach and Rock Reinforcement Approach (RRA) with advanced numerical modelling. Adoption of such three-stage rock cavern design procedure in the STC project was proven to be a successful showcase for pragmatic long-term strategic cavern development.
One of the key construction challenges was the planning of blasting sequences and logistics for concurrent top-heading and benches excavation. At peak periods, 7 daily blasts were carried out on 13 active blasting faces. To optimize flexibility and efficiency in explosives’ delivery and blasting operations, a licensed temporary blasting explosives magazine (Mode A store) was established and operated on site.
This paper presents the key geological and geotechnical design considerations, construction challenges, rock handling and performance outcomes of this landmark cavern development project, providing valuable reference for future large-span cavern developments in the community.
KEYWORDS: Rock Caverns, Rock Reinforcement Approach, Reinforced Rock Arch
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