Numerical analysis of time-dependent of creep behaviour tunnel support systems

Most tunnels built in Sydney encounter similar ground situations; they penetrate either the Hawkesbury Sandstone or the shales that lie beneath the city. Tunnels in these materials are generally supported by rock bolts in combination with a shotcrete lining. A method of analysis is presented to improve our understanding of the long term behaviour of fiber reinforced shotcrete (FRS) materials and the tunnel support systems. A finite element method SAFEA (Semi-analytical FE Analysis) is developed to model the combined creep behaviour of a shotcrete lining and the Hawkesbury Sandstone. To model the time-dependent creep behaviour, the bulk modulus and shear modulus of the materials are represented by logarithmic functions in time. A Laplace transform is then applied to these functions of time and the solution of the problem found from a finite element analysis. Tablot's method is then used to invert the transformed values and find the solution in real time. The time dependent creep deflection of the numerical tunnel models reflects the interaction of the shotcrete lining and rock which have different creep parameters.