Response of the ground and adjacent end-bearing piles due to side-by-side twin tunnelling in compound rock strata

Considering that the subway tunnelling projects in the Chongqing region are located in strata dominated by sandstone and mudstone, the main empirical construction parameters (excavation thrust = 5 880 ∼ 6 860 kN, average pea gravel content (APC) ≥ 85%, and grouting pressure (GP) = 0.3 MPa) were obtained by engineering surveys; these empirical parameters were similar to those optimized under interval tunnel construction conditions. Additionally, a simulation method was developed based on the construction characteristics of a single shield TBM by using the ADINA software to simulate the construction process of subway tunnels undercrossing the pile foundations (end-bearing piles) of an old surface building in the composite strata of the Chongqing Rail Transit Loop Line. A sensitivity analysis was performed on the calculation parameters first because the changes in the stratigraphic and TBM construction parameters greatly influenced the calculation results. Then, we used the modified calculation parameters to study the effects of tunnel construction on the settlements of the ground surface and pile foundations in the composite strata, and these effects were compared to the field monitoring results. The results showed good agreement between the numerical calculations and the monitoring findings. Thus, the methodology and empirical construction parameters adopted in this paper can provide a reference for the construction of other tunnel sections of this project in similar construction conditions.