The effect of clay structure formed during deposition on the ground deformation induced by shield tunneling

Abstract

Natural clays possess structures with a higher void ratio than reconstituted clays under the same effective stress. Numerical analyses were performed to investigate the effect of clay structure formed during deposition on the ground deformation induced by shield tunneling. The numerical simulation results showed that with the same yield surface size, the ground surface settlement and the lateral displacement around a tunnel increased with an increase in the initial amount of bonding (additional void ratio) due to the strain softening behavior of structured clay. When the initial amount of bonding increased from 0 to 4, the maximum ground surface settlement increased from 18.2 mm to 19.5 mm, and the maximum lateral displacement increased from 19.8 mm to 20.9 mm. The maximum ground surface settlement and lateral displacement increased with increasing absolute and relative destructuration rates. For the same clay structure, the maximum ground surface settlement and lateral displacement generally increased with decreasing face pressure, decreasing grout pressure or increasing volume loss. For the same face pressure, grout pressure or volume loss, the larger the additional void ratio was, the larger the maximum ground surface settlement and lateral displacement. Therefore, the clay structure and its destructuration should be considered for accurate prediction of the ground deformation induced by shield tunneling.