A study on surface settlement of diversion tunnel in the sandy loam composite stratum constructed by shield tunneling

Abstract

Shield tunneling is used more frequently in water diversion projects. The prediction and control of surface settlement are particularly important when shield tunneling through the composite stratum. The numerical simulation method can be used to effectively predict the surface settlement caused by shield construction. A two-dimensional finite element model is established based on a shield construction diversion tunnel project passing through a sandy loam composite stratum. The orthogonal test with the surface settlement as the index is designed. The sensitivity analysis of internal friction angle, elastic modulus, density, and elastic modulus of the lining of the sandy soil layer is carried out. The results show that the surface settlement is the most sensitive to the change in the friction angle in the sand layer. Then, taking the monitored value of surface settlement as the target value, the improved genetic algorithm is used to inverse the elastic modulus of the sandy soil layer, internal friction angle, and the elastic modulus of the lining. The inversion results are substituted into the finite element model. The results show that the calculated results are in good agreement with the measured values. On this basis, the surface settlement of shield construction under different burial depths and different loam thicknesses is calculated. The results show that when the shield depth increases, the surface settlement will decrease, and the width of the “settlement tank” will increase. When the thickness of the loam layer increases, the surface settlement will increase, and the width of the “settlement tank” will decrease.