ABSTRACT
The centrifuge tests were conducted in a geotechnical beam centrifuge at the Hong Kong University of Science and Technology (Ng et al. 2001). This centrifuge has a maximum capacity of 400 g-ton, with arm radius of 4.2 m. The acceleration of the
1 INTRODUCTION
When a basement excavation in an urban area has to be carried out close to, or directly above, existing tunnels, the influence of basement excavation on tunnel response is a key issue of concern for designers. This problem was recognized as early as 1959, when the basement excavation of the Shell Building on the South Bank in London caused significant upward movement of the underlying tunnels (Burford 1988). Other cases, such as basement excavation of the Phase III of the York Mills Centre in Toronto (Lo & Ramsay 1991) and Shanghai Square excavation (Kuang et al. 2000), also revealed that basement excavation caused serious damage to the existing tunnels if no protection measure was implemented.
