Variation Law of Excavation Depth and Surrounding Rock Displacement of Loess Cavern

The elastoplastic finite element analysis of a loess cavern was carried out by two-dimensional, three-dimensional step-by-step excavation and three-dimensional one-shot excavation using PLAXIS 2D/3D finite element analysis software. The variation law in displacement of surrounding rock of cavern under different working conditions is analyzed, and the spatial effect of the tunnel face is analyzed. The analysis results show that the final displacement of the two-dimensional and three-dimensional step-by-step calculations is basically the same. Therefore, the two-dimensional calculation results can be used to estimate the final displacement of the cavern excavation. The analysis of three-dimensional step-by-step excavation shows that the displacement development of underground caverns with different depths is basically the same. When L/B≤1 (L is the tunneling depth and B is the tunnel span), the displacement ratio increases linearly. When L/B>1, the displacement ratio increases nonlinearly. When L/B>3, the maximum displacement is close to the final displacement. The spatial effect analysis of the tunnel face shows that the displacement at the tunnel face is about 1/3 of the final displacement. The displacement at a distance of 0.5 times span from the tunnel face is about 2/3 of the final displacement. The displacement at 2.5 times span from tunnel face is basically the final displacement.