Effect of excavation on adjacent tunnel and performance of grouting-based active protective method in spatially variable soil

The soil is a key medium for transmitting the effects of excavation to the tunnel structures. However, the spatial variability of soil has not yet been considered when analyzing the response and control method of existing tunnels to adjacent excavation. Therefore, the coupling effects of soil spatial variability and excavation on the tunnel structural response were investigated via the random finite difference method. Moreover, the control performances of capsuled grouting and tube-a-manchette (TAM) grouting on tunnel deformation in spatially variable soil were compared. It is found that the tunnel deformation may be underestimated without reliability-based design. As for the soil with high variability, the probability of tunnel displacement exceeding the allowable value can reach up to 35.2 %. The variation of tunnel response depends on the relative relationship among the fluctuation scale of soil, tunnel diameter, diaphragm wall length and the wall-tunnel distance. Furthermore, the control reliability of the innovative capsuled grouting can be twice that of the TAM grouting in spatially variable soil. The control reliability of capsuled grouting increases with increasing length of the capsule, but is not affected by the distance between the grouting area and tunnel.