An Urban Tunnelling Challenge – A Case Study for a Tunnel under an Ancient Tree Wall in Hong Kong

Abstract

Achieving the balance of civilisation versus heritage preservation is becoming a significant consideration for civil engineering and tunnelling projects worldwide. This is especially the case in the highly urbanised city of Hong Kong, whereby much of the new infrastructure conflicts with and impinges upon the concentrated areas of historical and heritage features that are treasured by the community. This paper considers one recent case study, relating to the upgrading railway network projects of West Island Line (WIL) in Hong Kong, which is at a particular location facing the challenge of constructing a 12 m span railway tunnel underneath a ‘valuable ancient tree wall’ with only 10 m ground cover. Such challenge is a serious issue for tunnel works in Hong Kong since no disturbance to such community assets can be allowed. Hence, this section of the project involves tunnelling through shallow mixed ground conditions whilst simultaneously preserving the tree wall. This made the engineering design one of the most challenging aspects of the whole project. A combined tunnelling design considerations and monitoring strategy is developed, in conjunction with local tree experts, as described in the paper herein.