ABSTRACT
Grouting of the annular space behind the tunnel lining is a delicate phase of the Earth Pressure Balance excavation process, being related with stress modification and deformation in the surrounding soil. Normally operative parameters such as injection pressure, mechanical properties and hardening rate of the grout are assigned with empirical rules relating them to the soil type, more than on mechanical schematization that analyses their effects. This paper examines the influence of the mechanical characteristics of the annulus grout on the interaction between soil and lining activated by EPB tunneling. To this aim, a three-dimensional numerical model is created reproducing excavation, face pressurization, lining installation and tail void grouting with great accuracy. The computational model is validated against a tunnel built by the Metropolitan Rapid Transit Authority (MRTA) in Bangkok, selected thanks to the availability of experimental investigation and monitoring data. The hydromechanical response of the soil is simulated with a non-linear, irreversible, anisotropic hypoplastic model and the grout with a time dependent increase of stiffness and strength reproducing its hardening process. Final stiffness and hardening rate of the annulus grout are parametrically varied to investigate their role on the interaction between soil and lining and to identify a composition that minimizes the short and long-term effects on the surrounding environment. Results of the analysis are provided in terms of lining stresses, soil deformation and ground subsidence.
