Analysis of Settlement Caused by TBM Construction in Sand Formations in Beijing

Based on data collected in tunnel boring machine (TBM) construction in Beijing subway, soil settlement prediction models for sand formations are analyzed and verified. Through the analysis of Peck's formula, the paper points out that the precondition is to determine the coefficient of settlement groove width (i), while i is further controlled by the maximum settlement of single tunnel (δ_1max). By using the settlement equation of Takeyama Takashi, δ_1max can be calculated directly, but the elastic modulus (E) should be an equivalent value that represents all the soils involved. In the calculation of the coefficient of settlement groove width (i) by using O'Reilly-New method, the results is largely affected by the formation parameters. In order to find an ideal model to predict the settlement in TBM construction in Beijing sandy formation, modified calculation methods of E and i are recommended. The results show that the maximum settlement in the ground surface, the total width of settlement groove and the settlement curve in the cross section match monitored data very well. For double parallel tunnels, the settlement at any point can be calculated by adding individual settlement generated by each tunnel construction, and each of which can be calculated by using the formulas of Peck and Takeyama Takashi. But the settlements at the centerline of each tunnel are different. The amount of settlement is affected by construction sequence of the two tunnels. The earlier the tunnel is constructed, the larger the eventually settlement is.