Study on the long-term performance of cement-sodium silicate grout and its impact on segment lining structure in synchronous backfill grouting of shield tunnels

Abstract

Synchronous backfill grouting is an important procedure in the construction of shield tunneling. The effect of grouting directly influences the settlement of the stratum and the stress state of the segments structure. During the construction of shield tunnels in rock mass, problems such as cutterhead deadlocking, segments floating and crack, surface subsidence, etc. would occur due to the buoyancy from synchronous backfill grouting. The cement-sodium silicate grouting can solve the above mentioned problems effectively, but meanwhile, its durability cannot be guaranteed, thus so far it has hardly been adopted in synchronous backfill grouting of shield tunnels. In the present paper, the long-term performance of cement-sodium silicate grout and its impact on segment structure in the backfill synchronous grouting during shield tunneling are systematically studied through theoretical analysis, laboratory tests, micro-analysis and numerical calculation. An evaluation method for long-term performance of cement-sodium silicate grout based on the meso-structure is proposed. Distribution form of reaction products of cement and sodium silicate grout and its change rule with the dosage of sodium silicate in cement-sodium silicate grout is revealed through the observation of meso-structure. The reduction factor of mechanical properties of cement-sodium silicate grout after degradation of the reaction products of cement and sodium silicate solution is derived with the help of stochastic finite element numerical calculation. The results reveal that when the proportion of cement and sodium silicate solution is within a certain range, the amplifications of both the internal force and deformation of segment structure are very small, even if grouting layer loses effectiveness completely. The maximum crushing stresses on the grouting layer after degradation is less than the minimum residual compressive strength, which can meet the practical engineering needs and guarantee the safety of the tunnel. Therefore, cement-sodium silicate grout is suitable for synchronous grouting in shield tunneling.