Coupled Effect of Expanded Polystyrene and Geogrid on Load Reduction for High-Filled Cut-and-Cover Tunnels Using the Discrete-Element Method

Abstract

High-filled cut-and-cover tunnels (HFCCTs) can be used to reclaim usable land due to the unique landforms in western China. The load reduction methods used to reduce the earth pressure on such cut-and-cover tunnels (CCTs) can significantly affect the safety of CCTs. This paper describes a study of three load reduction measures: expanded polystyrene (EPS); a combination of EPS and geogrid; and a combination of EPS, geogrid, and concrete wedges. PFC2D, a computer program based on the discrete-element method (DEM), was employed to analyze and examine the evolution of the load reduction mechanisms. Parametric studies were conducted to investigate six influential factors: the density, thickness, width of the EPS, the location (or level) where the EPS is placed in the structure, the tensile strength of the geogrid, and the number of layers of the geogrid. The analysis results are based on the observed changes in average vertical earth pressure (VEP), relative vertical displacement of the soil, relative vertical deformation of the geogrid, and the contact force among soil particles. This study found that these influential factors have significant effects on the soil arching effect and the tensioned member effect on load reduction mechanisms. In order to optimize the load reduction of the earth pressure on the top of HFCCTs, the optimal values for the influential factors are derived.