ABSTRACT
While tunnels in soft ground are more vulnerable to long-term settlement effects, there seems to be lack of research aiming at a particularly soft ground case like that in Shanghai, which is featured as very typical soft ground with a high ground water table, low strength and high compressibility. Factors relating to consolidation properties of soft ground are well understood to be playing an important role in inducing the long-term settlement process. Studies on the relationship between the consolidation of the ground and the long-term tunnel behaviour would contribute to further understanding of such processes, especially when tunnels run through varied ground. This paper concentrates on the influence of varied ground imposed on long-term behaviour through centrifuge modelling. The settlement development is investigated as well as the change with time of earth pressure, porewater pressure and internal forces in the tunnel. By focussing the test initiative, it is expected that a simpler and
1 INTRODUCTION
With the rapid growth of various kinds of tunnels continuing in densely populated urban areas, concerns are growing about the impact of long-term settlement imposed on tunnel structures, which jeopardize both their safety and serviceability. To address these concerns and related problems, it is essential to understand the fundamental behaviour of tunnels over a long time period during the operation. Some early studies on long-term behaviour of tunnels can be traced back to Szechy (1971) and O’Reilly et al. (1991), in which measurement on a shield tunnel in Chicago and the Grimsby tunnel in the UK have been conducted separately for more than 10 years. Earth pressure measured in the Chicago tunnel shows an increase with time, while results from the Grimsby tunnel indicate a long period before the tunnel settlement stabilized. Shin et al. (2002) obtained the same trend of increasing lining load with time in both vertical & horizontal directions by using Finite Element Method (FEM), while assuming the linings to be impermeable. A more detailed examination on ground response induced by tunnelling was conducted by Wongsaroj (2005), based on field data in London. The long-term subsurface settlement mechanism was found to be a combination by swelling of soil above the crown, consolidation of the soil on either side of the tunnel and a rigid
clearer mechanism will eventuate and such results would provide a basis for further studies about other factors, such as lining permeability, soil disturbance and traffic vibrations.
