Extending the applicability of the Geological Strength Index (GSI) to karstified rock mass based on the numerical tests of the discrete element method

The theoretical scheme of the Hoek–Brown criterion and Geological Strength Index (GSI) has been critical during analyzing engineering problems in karst geological environments. However, it is very difficult to explore the mechanical features of karstified rock mass. In this paper, a new corresponding way was put forward based on the Discrete Element Method (PFC^2D). Firs,a dissolution algorithm inspired by Cellular Automata was proposed to simulate discontinuity of karstified rock mass; then, according to the Hoek–Brown criterion, the relations between the GSI value of the karstified rock mass and GSI value of the jointed rock mass were deduced based on the results of a series of compression tests; finally, the karstified characteristics were incorporated into the GSI scheme. The following conclusions can be drawn: 1) in addition to the karstified rate (k), the karstified uniformity-coefficient (u) proposed in this paper is also an important influencing factor of GSI value, and the influencing degree of k is greater than u by about 3 times; 2) tensile-microcrack expansions reflect the low strength of the karstified rock mass due to the stress concentration at the rock-bridge between the karst cavity-gaps; 3) the GSI value of the karstified rock mass is expressed as a reduction to the GSI value of the jointed rock mass, so the karst features play the role of a karst correction-coefficient λ (0 < λ < 1) to update the GSI from the discontinuity features, and λ decreases linearly with k, and the decreasing degree is also negatively linearly correlated with u.