Study on Stability of Loess Tunnel Based on Three-dimensional Numerical Simulation in Different Excavation Length of Invert

The 3D finite element simulation was adopted to study the globality stability of tunnel caused by the different excavation length of invert. Kelan-Linxian highway loess tunnels were taken as an example. The research results are shown as follows: The vertical displacement and horizontal convergence increased by the increasing of the excavation length of the invert. But the latter increase range is larger than the fonner. The horizontal convergence in sidewall is convergence value is greater than the level of the arch and the corner, the horizontal displacement primarily occurred in the side wall position. The surrounding rock's maximum plastic strain occurred in side wall and corner wall in 4 working conditions. The plastic zone occurred around from arch corner to wall side. In Tab. 4, the maximum plastic strain is increased by the excavation length of invert's increasing.