One of the important problems for structure calculation of a tunnel is to estimate the stability of rock mass surrounding the tunnel.
A safety factor of rock mass surrounding the tunnel can be determined by strength reduction method (SRM). Here, the most important is to solve the criterion of critical state.
Recently, several researchers have conducted studies to apply SRM, which has already been in use for estimation of slope stability, in order to estimate the stability of rock mass surrounding the tunnel. Many researchers have compared the various criteria of the critical state of a slope, which is the most important in the estimation of slope stability by SRM. Although various criteria were developed, there were mainly 3 methods: penetration of equivalent plastic strain, non-convergence of numerical calculation and sudden change of horizontal displacement at a specific point.
Jong Tok Yong, a section head at the Faculty of Earth Science and Technology, has proposed a new method for determination of a safety factor by sudden change of equivalent plastic strain in the relationship between a reduction coefficient of strength parameter and equivalent plastic strain.
This method is based on elasto-plastic FEM and SRM by ABAQUS and Mohr-Coulomb yield criterion.
Simulations in circular and square tunnels showed how a safety factor varies with geometries, friction angles and cohesions and how it varies with quality change of rock mass, pore water pressure and tunnel depth.
If further information is needed, please refer to “Determination of safety factor for rock mass surrounding tunnel by sudden change of equivalent plastic strain in strength reduction method” published in the EI Journal “Geotechnology and Geological Engineering”.
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