Effects of twin stacked tunnel excavation with lagging distance on adjacent structure

In the dense urban area, twin stacked tunnels may inevitably be constructed near the existing pile foundations. Since rapid construction is required, the twin tunnels are constructed with short the lagging distance between twin stacked tunnel faces. However, the effect of lagging distance on the behavior of the adjacent piles has not been considered in past studies. In this study, a series of three-dimensional finite element analyses of twin stacked tunneling with different lagging distances of 0𝐿𝑆 , 1𝐿𝑆 , 3𝐿𝑆 , 5𝐿𝑆 and 8𝐿𝑆 (𝐿𝑆 is the length of shield) adjacent to existing piles of a building. The research used soil parameters and calibrated tunnel simulation methods from the MRT blue line. The results of the analysis indicate that the lagging distance between twin stacked tunnel faces significantly affects soil deformation and the behavior of existing piles.