THE DESIGN AND CONSTRUCTION OF LARGE DIAMETER PIPELINES IN A SHAFT AND TUNNEL SYSTEM - HONG KONG EXPERIENCE

The Water Supplies Department of the Hong Kong Special Administrative Region (HKSAR) commissioned Black & Veatch Hong Kong Limited to design and supervise the construction of a service reservoir with an ultimate capacity of 200,000 cubic meters. Provided the pipeworks for the service reservoir were arranged in a conventional approach, five large diameter pipelines: 2 nos. DN 2000 inlet mains, 2 nos. DN 2000 outlet mains and 1 no. DN 1200 outlet main would have to be laid on steep slopes supporting the service reservoir. Potential leakage from these pipelines would undoubtedly pose a risk on slope stability threatening the structural integrity of the service reservoir. To alleviate this potential hazard, an innovative design has been implemented in which all inlet and outlet mains, and their associated valves are accommodated in a shaft and tunnel system. As added merits, this design significantly reduces traffic disruption and aesthetically unpleasing, as well as facilitates ease of future inspection and maintenance. This paper describes the key issues involved in this innovative design and discusses the challenges encountered in installation of large diameter pipelines in a shaft and tunnel system.