Conception and Evaluation of a Novel Type of Support in Loess Tunnels

The limited efficiency of current supports has led to serious support system problems in loess tunnel construction, which are mainly noted in arch distortion, shotcrete cracking, surface subsidence, and even total structural failure. A novel type of support, called the steel-concrete composite support system (SCCS), is proposed in the present study via an in-depth analysis of support failure cases in China’s loess tunnels. Additionally, it places emphasis on the enhancement of the primary lining, which consists of three bearing layers: (1) the arch layer, (2) the reinforcing skeleton layer, and (3) the concrete packed layer. The new type of support can provide greater supporting capacity by closing the excavated space immediately after the new arch has been installed, and it can then be strengthened by grouting and the installation of molded concrete. The hyperstatic reaction method (HRM) model and three-dimensional numerical model were established using ANSYS software, and the results demonstrate that the SCCS outperformed the conventional support system in terms of both structural safety and load-bearing capacity. It was also found to achieve superior practical worthiness with flexibility and efficiency during the tunneling process, which indicates that the new support system is much more reliable for bearing more variable loads and dealing with severe deformation in loess tunnel construction.