Numerical study on backfilling the tail void using a two-component grout

In shielded mechanized tunneling, the annular gap caused due to the Tunnel boring machine (TBM) driving must be backfilled instantaneously using a suitable grout. A two-component grout which is composed of a chemically retarded cement slurry and an accel-erator is pumped into the annular gap behind the TBM shield where it gels and attains sufficient mechanical stiffness in a very short time. This property of the grout helps restrict the immediate ground movements adjacent to the TBM tail shield and reduce volume loss. In this research, the hardened two-component mix is tested using a confined oedometric condition and a complete time-dependent hardening stiffness evolution is developed. More-over, the freshly prepared grout is tested in terms of its performance suitability (storage & transportation) and serviceability owing to permeability and dewatering. The obtained pa-rameters from the oedometer tests are incorporated into a numerical simulation of an Earth pressure balance (EPB) excavation focusing on modelling of the backfilling procedure using FDM (Finite-difference method) software FLAC 3D (Fast lagrangian analysis of continua in three dimensions). The research also focuses on distinguishing between two commonly used backfilling techniques implemented in numerical analysis. The numerical model consists of testing a regular tunnel section using a newly introduced Hardening soil (HS) constitutive model with the soil parameters obtained from Torino metro case. Another set of synthetic softer soil parameters are chosen to highlight the soil properties in the model response. The two-component grout satisfies all the prerequisites for a good backfilling material in its fresh and hardened state. The grout attains sufficient mechanical strength in a very short time, remains impermeable and achieves a stiffness of 43 MPa in 28 days. The results obtained from the the oedometer tests enable with the development of a complete time-dependent stiffness evolution of the grout. The implementation of hardening behavior of the two-component grout is evident in terms of ground settlements when compared to the conventional backfilling simulation technique.