Experimental study on roughness characteristics and genesis analysis of granitefracture surface under unloading condition
[Objective]In order to explore the changes and causes of fracture morphology of engineering rock mass during loading and unloading under high stress.[Methods]The roughness is used as an important parameter to describe the geometric character-istics of the morphology,and the morphology change is quantitatively characterized.The tensile-shear ratio is used as an impor-tant parameter to describe the fracture characteristics,and the fracture mode changes are quantitatively characterized.This paper selects two types of granite to carry out loading and unloading mechanical tests,and analyzes the roughness and causes of the fracture surface by digital image technology.[Results]According to the result,Under the condition of high stress unloading,ini-tial confining pressure,unloading confining pressure rate and mineral particle size have a negative correlation effect on the rough-ness of granite fracture surface.The result of microscopic observation of ultra-depth of field show that the lower the roughness of granite,the higher the proportion of shear fracture in the fracture.In the process of confining pressure unloading failure,30 MPa confining pressure unloading,rock fracture surface is mainly intergranular tensile fracture,40 MPa confining pressure unloading,mainly intergranular and transgranular tensile shear composite fracture,50 MPa confining pressure unloading,mainly transgranu-lar shear fracture.With the increase of mineral particle size and unloading confining pressure rate,the proportion of shear fracture increases.Under high confining pressure unloading,the higher the proportion of tensile fracture is,the rougher the frac-ture surface is.[Conclusion]On the contrary,the higher the proportion of shear is,the lower the roughness of the fracture surface is.
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