Binary Medium Model for Rock Sample

Summary

Rock materials exhibit strain softening at low confining pressure. How to accurately describe the strain softening of rock materials is very important for rock engineering. A new model, referred to as Binary Medium Model for rock matrials, is formulated under the theoretical framework of breakage mechanics for geomaterials. In the model, rock materials is conceptualized as binary medium consisting of bonded blocks and weakened bands which are idealized as bonded elements and frictional elements respectively. During the loading process the bonded elements gradually fracture and transform to be the frictional elements. The deformation properties of the bonded elements are described by ideal elastic-brittle materials and those of the frictional elements are described by hardening elasto-plastic materials. Two sets of breakage parameters, i.e., breakage ratios and strain concentration coefficients, describing the influence of rock structure on the process of failure, are introduced. The proposed model has been used to predict the behavior of sandstone sample in triaxial compression test. By making comparisons of predictions with experimental data it is demonstrated that the new model provides satisfactory modeling of many important features of the behavior of rock materials.