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DEM Analysis on Soil Arching Effect of Unloading Structure of High-Filled Open Cut Tunnels
(1 National and Provincial Joint Engineering Laboratory of Road & Bridge Disaster Prevention and Control, Lanzhou Jiaotong University, Lanzhou 730070; 2 Key Laboratory of Road and Traffic Engineering of the Ministry of Education, Tongji University,Shanghai 201804; 3 School of Civil Engineering, Tianshui Normal University, Tianshui 741000)
Abstract The concentration of soil pressure on the tunnel roof caused by the stiffness difference between the highfilled open cut tunnel and the soil masses will often lead to the longitudinal cracking of the roof, which will lead to the occurrence of engineering accidents. This paper establishes a numerical model for the unloading structure of open cut tunnels through the Mesoscopic Particle Flow Code in 2D (PFC2D) software, and studies the effects of different load reduction measures on soil arching effect at the mesoscopic level of vertical soil pressure, vertical particle displacement, inter-particle contact force chain, and porosity, etc. At the same time, taking the working condition Y7 (EPS plate + geogrid + concrete column) as the benchmark, this paper also takes into consideration the EPS plates of different densities and thicknesses for parametric analysis. The research results show that the load reduction measures above the tunnel roof can effectively reduce the soil pressure on the roof, and the load reduction effects of different load reduction measures are arranged from strong to weak as follows: EPS plate + geogrid + concrete column > EPS plate + geogrid > EPS plate > low compacted soil + geogrid + concrete column > low compacted soil + geogrid > low compacted soil. Among them, setting concrete columns on the side slopes of the original open cut tunnel can strengthen both the soil arching effect and the tensile membrane effect, so that most of the filling soil load can be transferred to the concrete columns and thus reduce the soil pressure on the top and side of the open cut tunnel. The development of soil arching effect is related to the change of porosity of the soil at the top of the tunnel.The porosity increases before decreasing with the increase of the density and thickness of the EPS plates, and it reaches the maximum value when the density of the EPS plate ρ=15 kg/m3 and thickness T=15 cm, while the soil arching effect is the strongest and the load distribution at the top of the open cut tunnel is the least.
Abstract：
The concentration of soil pressure on the tunnel roof caused by the stiffness difference between the highfilled open cut tunnel and the soil masses will often lead to the longitudinal cracking of the roof, which will lead to the occurrence of engineering accidents. This paper establishes a numerical model for the unloading structure of open cut tunnels through the Mesoscopic Particle Flow Code in 2D (PFC2D) software, and studies the effects of different load reduction measures on soil arching effect at the mesoscopic level of vertical soil pressure, vertical particle displacement, inter-particle contact force chain, and porosity, etc. At the same time, taking the working condition Y7 (EPS plate + geogrid + concrete column) as the benchmark, this paper also takes into consideration the EPS plates of different densities and thicknesses for parametric analysis. The research results show that the load reduction measures above the tunnel roof can effectively reduce the soil pressure on the roof, and the load reduction effects of different load reduction measures are arranged from strong to weak as follows: EPS plate + geogrid + concrete column > EPS plate + geogrid > EPS plate > low compacted soil + geogrid + concrete column > low compacted soil + geogrid > low compacted soil. Among them, setting concrete columns on the side slopes of the original open cut tunnel can strengthen both the soil arching effect and the tensile membrane effect, so that most of the filling soil load can be transferred to the concrete columns and thus reduce the soil pressure on the top and side of the open cut tunnel. The development of soil arching effect is related to the change of porosity of the soil at the top of the tunnel.The porosity increases before decreasing with the increase of the density and thickness of the EPS plates, and it reaches the maximum value when the density of the EPS plate ρ=15 kg/m3 and thickness T=15 cm, while the soil arching effect is the strongest and the load distribution at the top of the open cut tunnel is the least.
YAO Yuxiang1 LI Sheng1 MA Li1 WANG Changdan2 ZUO Di3
.DEM Analysis on Soil Arching Effect of Unloading Structure of High-Filled Open Cut Tunnels[J] MODERN TUNNELLING TECHNOLOGY, 2021,V58(3): 84-93
2021, Vol. 58 