Basic Law For The Shear Failure Of Granite Joints Based On Three-dimensional Surface Parameters

This thesis is aimed at studying the shear failure of rock joints, and focuses onestablishing the mechanical model of failure process and deriving the theoreticalformulas of peak shear strength based on three-dimensional surface parameters. In thisthesis, the author took the granite as an example and took the shear failure process ofrock joints as the object of study. The study started from figuring out the shearproperties of closed rock joints by comparing the results of particle flow numericalmodeling and that of direct shear tests, and established the mechanical model of failureprocess. Finally by analyzing the varied characteristics of rock joints’ surfacetopography under shear stress，the theoretical formulas of peak shear strength werederived, further improved and verified. These formulas are totally based onthree-dimensional surface parameters and have to do with the process of shear failure.The main results are as follows:According to the results of particle flow numerical modeling （PFC2D）and thatof direct shear tests, closed rock joints’ shear stress vs shear displacement curves andnormal displacement vs shear displacement curves, under different normal stress androughness, exist distinctive differences. Moreover, through elaborating the shearmechanical behavior of closed granite joints and studying the distribution features ofmicro-cracks and contact force inside samples, some macro phenomenon like theorder of destroy of asperities on the surface, dilatancy effect and the tensile stressconcentration at the bottom of asperities can be explained from the mesoscopic pointof view, which contribute directly to putting forward the reasonable assumption ofrock joints’ shear failure progress.On the basis of analyzing the mechanical behavior of shearing of rock joints,granite joints’ theoretical mechanics model of shear failure process based on Mohr- Coulomb strength criterion was established step by step (from the study of a singleasperity’s damage model to analyze the failure model of a whole joint surface). Thenthe theoretical equations of peak shear strength related to three-dimensional surfaceparameters were derived successfully.Based on establishing mechanical model and theoretical formula of rock jointswith shear failure progress, using3D high precision laser scanning technology andGIS technology, the3D surface topography on rock joints can be measured accuratelyand analyzed visually. There are two major achievements: on one hand,3D surfaceparameters’ physical and mechanical meaning were figured out and the extractionmethods of some significant parameters were found, eventually, rock joints’roughness coefficient can be described by these3D parameters successfully. On theother hand, in accordance with the results of direct shear tests, the contact area withdifferent shear displacement can be measured and through this, the variedcharacteristics of rock joints’ surface topography under shear stress can be studied andthe effect of different normal stress and roughness can be evaluated.Finally, according to the varied characteristics of granite joints’ surfacetopography under shear stress, the author further improved and verified the theoreticalformulas of peak shear strength and set up a complete set of basic law for the shearfailure of granite joints.