Bored Tunnelling Directly below Buildings in Singapore Downtown Line

Abstract

Other than basement construction of building complexes for parking and other functions, many cities in the world are also embarking on major construction projects to put roads, metro infrastructure, municipal services and utilities, under the ground. One of the specific challenges faced is the construction of bored tunnels directly below buildings. This paper reports the experiences of bored tunnelling directly below several buildings in the recently implemented Downtown Line project. These case studies would include details such as the structural system and foundation details of the buildings, ground condition, geometry and clearance between the building foundation and the tunnelling works, as well as instrumentation monitoring results of ground and building settlement during tunnelling. It is hoped that these cases could be used as references in the design of future bored tunnelling works, to give greater confidence that tunnelling directly below buildings can be carried out without affecting the buildings so long as appropriate tunnelling controls are taken to mitigate ground deformation issues.