Objective With the rapid development of urban rail transit, metro tunnel construction faces higher requirements for quality and efficiency. In metro construction using double-shield TBM (tunnel boring machine) method, the void between the tunnel segments and the surrounding rock is typically backfilled by the method of grouting after blowing pea gravel. However, issues such as poor pea gravel backfilling effect and lagging grouting often lead to severe segment dislocation, damage, and seepage. Therefore, it is necessary to improve the technical method for backfilling behind segment wall.

Method Using a section of the Qingdao Metro as the test object, a new type fine aggregate concrete for segment backfilling is developed through onsite concrete mix ratio experiments. Combing the shield tail type and the characteristics of TBM construction method, a new wear-resistant and sealing grout-stop plate is designed to be installed on the TBM shield tail. Based on the application of this grout-stop plate and the developed fine aggregate concrete, a new construction process for synchronous backfilling with fine aggregate concrete is proposed. The feasibility of this new process is ultimately validated through field tests.

Result ＆ Conclusion The fine aggregate concrete with a mix proportion of Shandong University grouting material: water: gravel =5:2:5 exhibits appropriate fluidity and certain consistency, ensuring full backfilling behind the segment wall with little risk of leakage. The backfilling concrete at tunnel bottom tends to generate the pumping pressure, negatively affecting the sealing effect of the grout-stop plate. However, when at above the 3:00 or 9:00 point, the backfilling can achieve the effect of full filling without grout leakage. The total station measurement results show that the method of synchronous concrete backfilling method can effectively control segments vertical displacement, benefiting the stability of the tunnel structure.