Experimental Research on Double-O-Tube Shield Tunneling-Induced Adjacent Pile-Soil Displacement

Due to the complexities of the cross-sectional form of double-O-tube (DOT) shield tunnels larger than circular shield tunnels, the resulting displacement characteristics of the adjacent soils and piles are relatively complex. This paper designs and develops a DOT shield tunnel transparent soil model test device. The displacement characteristics of horizontal and vertical soil layers above the tunnel, soil displacement contour maps around the tunnel, pile and soil displacement patterns around the piles are carried out to systematically investigate pile-soil displacement response caused by the DOT shield tunneling under different buried depths. The results show that: with the depth of the DOT shield tunnel increases, the maximum horizontal displacement of the surface increases and then decreases, the maximum surface settlement gradually decreases and the settlement at the top of the tunnel gradually increases. In addition, settlement curves gradually transform from the surface to the top of the DOT tunnel in a "U-V-W" shape. Horizontal displacements of the surface and settlements above the longitudinal section of the DOT tunnel peck and plateau after the shield tail passes the monitoring face (at the pile axis) at 0.7D and 0.6D (D is the diameter of the tunnel excavation), respectively. With the increase of the soil depth, horizontal displacements of vertical soil layers decrease, then increase and finally decrease, maximum horizontal displacements are located at the horizontal axis of the DOT tunnel, while settlements decrease slowly first and fast afterward. The adjacent pile limits soil displacements beside the pile, and the pile occurs overall settlement and deflection. The pile-soil displacements for a tunnel buried depth of 1.5D are obviously larger than those for tunnel buried depths of 1.0D and 2.0D.