Study on the Initial Setting Time of Simultaneous Slurry Based on Shield Tunnel Segment Floatation Control

Currently, there is a little research on the impact of simultaneous slurry initial setting time on the buoyancy of tunnel lining during shield tunneling construction. This makes it difficult to provide reasonable recommendations for slurry initial setting time under various construction conditions. Therefore, a quantitative longitudinal analytical model considering the influence of tunnel depth on shield tunnel construction buoyancy has been established. Based on the relationship between simultaneous slurry initial setting time and the length of the section where the shield tunnel lining is affected by buoyancy, the proper selection of initial setting time for simultaneous slurry during the construction period in moderately weathered clayey formations was systematically studied. The results show that the initial setting time of the slurry has a significant impact on the final cumulative longitudinal behavior of the shield tunnel during the construction period. A longer initial setting time leads to greater cumulative uplift load, longitudinal bending moment, and longitudinal shear caused by buoyancy. Moreover, with an equidistant increase in the initial setting time, the magnitudes of these behavior indicators also increase to a certain extent. From the perspective of controlling buoyancy in shield tunnel construction, there should be a matching relationship between the simultaneous slurry initial setting time and the average excavation speed of the shield. Specifically, as the average excavation speed increases, the reasonable initial setting time should be shorter. By adjusting the simultaneous slurry initial setting time to approximately 5 hours through mix design, a significant improvement in the buoyancy problem during construction has been achieved.