Size effect on triaxial strength of randomly fractured rock mass with discrete fracture network

The finite element method is limited in that it cannot represent a large number of discontinuities of a completely randomized distribution. The discrete element method, however, is ideal to study the behavior of jointed rock mass and assess the changes in mechanical properties caused by fractures and size effect. In this research, it is used in combination with discrete fracture networks so as to effectively capture the complexity of fractured rock mass and the influence of size effects on the peak mechanical properties. Starting off by generating a random discrete fracture network on a large-scale numerical specimen of 20 x 40 m that corresponds to the scale of the rock mass surrounding typical structures in rocks - such as tunnels, adits, caverns, exploration works - this prototype is subsequently used for the generation of a series of simulated in situ fractured rock mass specimens of smaller but steadily larger-than-laboratory standard sizes, i.e., 10 x 20 m, 5 x 10 m, 2.5 x 5.0 m, 1.25 x 2.50 m. These specimens are then used to perform numerical triaxial tests and to measure the compressive strength of the fractured rock mass. Behavior patterns emerge and the size of the specimen in combination to random fracturing is deemed to have a measurable effect on the rock mass strength. Indices are proposed to represent the degree of fragmentation with respect to the specimen volume and their correlation to the rock mass strength. Comparison to existing research yields satisfactory results. Therefore, this methodology may be used to initially predict the rock mass strength for geotechnical projects.