Analysis and application of longitudinal uplift characteristics of segments of shield tunnels affected by synchronous grouting during construction period

The synchronous grouting is a key procedure during the construction of shield tunnels, and the uplift pressure generated by the grout is an important factor leading to the uplift of segments. Within the length of unconsolidated zone, the uplift pressure decreases and the foundation coefficient of the overlying soil increases gradually. Aiming at this kind of complex mechanical problem, a method for predicting the uplift of segments of shield tunnels during the construction period is proposed based on the theory of the matrix transfer method for elastic foundation beams. The influences of the time-varying property of grout viscosity, the variety of the foundation coefficient and the superimposed effect of construction load step are considered. The proposed model is well verified by the comparison between the theoretical results and the field test data. The results show that the maximum uplift of segments caused by the synchronous grouting is generally 6~7 rings away from the shield tail, and the influences are small beyond 40 rings. The time-varying property of grout viscosity affects the longitudinal distribution of unconsolidated zone and the uplift pressure. The grout viscosity increasing with time will decrease the grout fluidity and the permeability of surrounding soil. Therefore, it leads to the decrease of grout pressure which causes a larger uplift pressure and a longer length of unconsolidated zone. The coupling calculation of two kinds of elastic foundation beams under the complex variable foundation coefficient and the fine prediction for uplift of segments under the influences of multiple factors are solved. The research results can provide a reference for the subsequent control for the uplift of segments of the similar shield tunnels.