Post peak behavior of rocks and its numerical simulation considering softening

The post peak behavior of rocks has a significant influence on its strength and deformational characteristics and is crucial in many applications like underground coal mining. A clear understanding of post peak behavior of coal is necessary for economical and safe underground coal extraction. In this study, laboratory experiments and corresponding numerical modeling is done to understand the post peak behavior of a coal and coal pillar. A series of laboratory tests are conducted using coal samples and also artificially prepared gypsum samples with varying material strength. A numerical model is developed in FLAC3D and simulations are run with strain softening model to capture the post peak responses of the material. This model allows to attain the peak strength following the Mohr-Coulomb behavior and once it attains the peak, the strength parameters are softened with respect to plastic strain that the material experienced using a piecewise linear functions. The softening parameters are selected in such a way that a realistic behavior could be achieved. With the validated model, several parametric studies such as influence of dilation, confinement, and friction angle are performed. Understanding the influence of the post peak parameters gave a full extent of the usage of material performance in the numerical model for better design of underground excavations. The numerical model is subsequently extended to design coal pillar for a underground mines is briefly discussed.