Study on the Law of Grout Pressure Dissipation in Simultaneous Backfill Grouting during Shield Tunneling in Soft Soils

The consolidation and pressure dissipation of the generally adopted cement based grout injected into the tail void during simultaneous backfill grouting in shield tunneling are influenced by many factors, such as grout characteristics, ground permeability, pore water pressure (PWP), dimension of the initial grout pressure, and various loads acted on the lining. Based on the typical simultaneous backfill grouting parameters in soft soils in Shanghai, and excluding the influence of grout hardening, using the theory of fluid mechanics and elastic mechanics, the principle of grout consolidation in tail void is firstly analyzed in this paper, and the changes of grout cake's thickness (GCT) and grout pressure (GP) with time are clarified. Then, as for grout pressure dissipation (GPD), the influences from ground osmotic resistance, PWP and dimension of the initial GP are discussed. The following conclusions are drawn: the ground osmotic resistance can obviously delay grout consolidation, but not the final consolidation state; the increment of soil shear modulus can accelerate the grout pressure dissipation speed (GPDS); consolidation process can be obviously restrained by the increment of PWP; and there is a positive relationship between the initial GPDS and the dimension of GP.