Numerical simulation of the creation and performance of extruded concrete linings in microtunnelling

Microtunnelling traditionally utilises pipe-jacked or segmental lining systems, however when employed over long, continuous distances, which may include changes in depth and direction, both lining systems have associated limitations that would reduce the drive rate of the TBM and increase the costs of the project. The use of an extruded lining system could circumvent a number of these limitations and make such an undertaking economically viable. A numerical model has been developed to simulate the extrusion of a tunnel lining from a microtunnelling TBM. The model was created in Plaxis (3-D Tunnel), a commercially available finite element modelling package. A methodology was developed and tested to approximate the movement of a TBM and the curing of the extruded lining, both of which are time-based phenomena. The extruded materials were subsequently investigated, using published strength-curing time for a normal strength concrete and a polymer concrete, for two drive rates. The outcome of the modelling suggests that the relationship between the developing stiffness and time in the early phases of curing is critical if an extruded lining system is to be deployed behind a TBM without slowing its drive rate.