Seminar - Ran Chen - The Creep Behaviour of Tunnels in Sydney Basin
Wednesday 10 September 2008, 1.10 - 1.55 pm
Civil Engineering Lecture Theatre 3
Most tunnels built in Sydney penetrate the Hawkesbury sandstone or the shale that lie beneath the city and are supported by a combined rockbolt and shotcrete lining system. New techniques such as the shotcrete mix design, excavation and construction of such tunnels have been successfully employed. Also we have accumulated much experience of the short-term performance of such tunnels, but we still lack understanding and design methods for the long-term creep behaviour of the tunnel support system. A finite element analysis method SAFEA (Semi-analytical FE Analysis) was developed to study the time-dependent behaviour of the rock, shotcrete and the combined tunnel support system.
Time-dependent creep deformation occurs when shotcrete or rock is under an applied load. This property is modelled by representing the bulk modulus K and shear modulus G of material as logarithmic functions in time. A Laplace transform is used in the three-dimensional finite element analysis program to simplify the governing equations and then the Tablot's inversion is used to get the solution in real time.
Tunnels under different ground conditions and with different fibre reinforced shotcrete linings were modelled. The numerical results show the additional creep deflection of tunnel structures and the stress redistribution in the surrounding rock, shotcrete lining and rockbolt support system over time.