Finite Element Simulation of Tunnel Excavations in Creeping Rock

Abstract

<p>A procedure based on the finite element method was developed for simulating the excavation of underground openings in rock for the actual initial state of stress in the field for various K conditions. This procedure can also incorporate orthotropic behaviour due to rock bedding, and other directional variations in the elastic properties of rock. This excavation simulation was then coupled into the time-dependent analysis of underground openings to study the influence of rock squeezing using the incremental initial strain method. Appropriate stress-strain-time relationships and strain accumulation methods are readily incorporated into this finite element program. (A survey of time-dependent constitutive relationships for rock is given to guide in the selection of appropriate creep laws.) The excavation and creep simulation aspects were then extended to model underground linings and lining placement strategies. This includes the ability to consider the lining and the rock as two different materials with rough or jointed interfaces between them. Further, this simulation allows for creep of the rock before lining installation, and creep of the rock and concrete lining after its construction for appropriate rock and concrete constitutive relationships. The full simulation procedure (excavation, creep and lining) was used to study an actual tunnel constructed in squeezing rock. There is reasonable agreement between the predicted performance and measured performance to date, and this comparison with monitored field information is continuing.</p>