Multiphysics modelling of backfill grouting in sandy soils during TBM tunnelling

During the tunnel boring machine-based tunnelling, the grout loss caused by the grout penetration and filtration in sandy soils is a complicated multiphysics process. In this study, a novel coupled hydro-mechanical modelling approach based on mixture theory is developed and implemented into a finite element code, which can qualitatively simulate the transport of grout in the soils around the tail void of the TBM tunnel, as well as predict the ground deformation induced by tunnelling and backfill grouting. Using the proposed approach, the time-dependent grout penetration area, grout loss, variation of soil porosity due to grout filtration and the ground deformation are identified. The effects of five key variables including grout pressure, duration, rheological property, filtration in soil mass and hydraulic conductivity of the soil are simulated. The results reveal that to reduce the ground disturbance and grout loss of TBM tunnelling in highly permeable soil, the grout pressure should be increased and the grout time reduced. In addition, grout materials with large permeability, dehydration and hardening rate are recommended.