Influence spatial behavior of surface cracks and prospects for prevention methods in shallow loess tunnels in China

A great concern for the construction surface cracks of large cross-section tunnels, which are being or to be built in the loess strata of China, is attracted. The mechanism of surface crack formation is analyzed from both internal and external perspectives. Loess is a multi-phase porous medium and develops complex stress and strain variation while executing a tunnel project. The surface is highly susceptible to construction surface cracks in shallow sections. A statistical analysis of the constructed loess tunnels in China shows that the main factors affecting surface cracks are settlement deformation, construction scheme, and the surrounding soil environment. To gain an in-depth knowledge of the mechanism of action of factors influencing surface cracks in loess tunnel construction, we relied on the actual project engineering to conduct numerical simulations, which can reproduce the formation mechanism of surface cracks more intuitively. Through numerical simulation, the influence mechanism of tunnel surface cracks under different tunnel diameters, tunnel depths, excavation methods, and surrounding soil grades was obtained. Through the analysis of the factors affecting surface cracks, specific measures to prevent and deal with construction surface cracks are further optimized to provide new ideas for the selection of surface crack control routes in loess tunnels.