A novel multiphysics modelling approach for grout loss analysis of backfill grouting in highly permeable soils during TBM tunnelling

In order to meet the requirements of refined analysis, a novel hydro-mechanical coupled multi-physical modelling approach is developed to qualitatively evaluate the grout loss in the soils and predict the ground movement induced by tunnelling and backfill grouting. The process of grout transport is described by a group of non-linear transient partial differential equations based on the mechanics of the continuous medium. The blockage of grout in the soil pore space and the resulting changes in the permeability of the soil are considered by introducing the mass exchange term into the mass equilibrium equation. The hydro-mechanical coupling process is further considered by incorporating the momentum balance of the mixture system. Then, through the secondary development of ABAQUS, the governing equations are solved by defining a new plane strain element of 7-degree of freedom, making it possible to analyze engineering-scale initial boundary value problems of grouting. After that, the excavation and grouting process of a typical shield tunnel has been modelled as an example. The results demonstrate that the proposed novel multiphysics modelling approach is able to describe the spatial and temporal changes in grout pressure, ground settlement and the grout penetration range during and after grouting. It is also found that when the permeability coefficient of the soil is greater than 1.0x10(-6) m/s, the grout loss due to grout penetration needs to be considered; meanwhile, the grout blockage in the soil pore space will lead to a reduction in soil porosity and permeability, thus further reducing grout loss, but the ground deformation is barely affected. Therefore, in engineering practice, grout blockage may not be considered in order to analyze the maximum grout loss and ground deformation.