Experimental Study on Fresh State Properties of Single-Liquid Semi-Inert Synchronous Grouting for Shield Tunnels in Water-Rich Sand Strata

Synchronous grouting has a very important effect on shield tunnel, which directly affects the stability of excavation face and the safety of segment structure. Testing the setting time and early strength of mortar is conducive to timely control the surface settlement and prevent the segment from floating. The flow table test can ensure that synchronous grouting can fill the excavation gap of shield machine to the greatest extent. Oedometer test can obtain physical and mechanical indexes such as elastic modulus, Poisson's ratio, compression and drainage of slurry at different ages. The test results showed that the use of well-graded, small-sized machine-made gravel (0-5 mm) and natural sand (0-2 mm) with high-efficiency additives promoted the formation of early strength in grout and reduced the probability of plugging in the grouting pipe at the tail shield. The oedometer test results indicated that the quantity of water drained from a grout mixed for more than 2 h was stable and the grout deformation within 1 h of compression accounted for 80% of the total deformation. The Young's modulus of the grout reached 10 MPa when the grouting pressure was > 0.2 MPa, meeting the requirements for field injection. In this study, an efficient synchronous grouting mixture proportion suitable for calcareous sand layer is proposed, and the performance of slurry in fresh state is obtained through a variety of tests, which can be widely used in shield tunnels in similar strata.

Automated summary

Synchronous grouting plays a significant role in shield tunnels, impacting the stability of the excavation face and segment structure. Testing mortar setting time and early strength, as well as conducting flow table and oedometer tests, can ensure optimal grouting performance and structural safety. Using well-graded materials and high-efficiency additives can enhance early strength formation in grout and reduce the likelihood of pipe plugging.