Study On Damage And Failure Mechanism Of Fractured Sandstone Based On Energy Dissipation And Release Principle

In order to study the damage and failure mechanism of the cracked sandstone samples,distortion and failure character of the cracked sandstone,energy distribution and evolution,damage evolution law and damage constitutive equation are studied in this paper based on the results of uniaxial compression test,triaxial compression test,ring loading and unloading test and RFPA numerical test.Based on the principle of energy dissipation and release and the rock damage theory,this paper investigates energy evolution rule and the corresponding failure modes of the sandstone with different crack.The internal relation between damage and failure development and energy evolution of fractured sandstone is studied.Damage evolution equation of the cracked sandstone is deduced by combining energy distribution principle with rock damage mechanics,which is more suitable for describing the behavior of the cracked sandstone damage evolution.Based on the principle of minimum dissipated energy,the damage constitutive equation of fractured sandstone is derived,and the application of the principle of minimum dissipated energy in the process of fracture of fractured sandstone is preliminarily explored.The FLAC3 D software was used to analyze the stability of the fractured sandstone slope,and the program was written with fish language to monitor the energy changes in the deformation process of the slope,and the changes in dissipated energy were used to describe the damage of the slope,and exploring the application of the damage evolution law in the initial analysis of the slope engineering.The main conclusions are as follows:(1)The fracture dip Angle ranges from 0°to 60°,the larger the fracture angle is,the smaller the peak strength of the fractured sandstone is.In the process of damage and failure,crack propagation begins at the tip of the prefabricated crack.The Failure pattern of sandstone samples with 30°crack dip angle are the pressure-shear mixed failure mode,while the sandstone samples with 45° crack dip angle and 60°crack dip angle are the shear failure mode.Under uniaxial compression,the sandstone specimens with fracture inclination of 45°and 60° presented significant brittle failure,and the residual strength was small.(2)In the crack compaction stage,the dissipated energy increases more than the elastic energy,the energy increases slowly,and the rock damage is slight.When the damage development was in its stable stage,the accumulation of elastic energy is greater than dissipated energy,and the dissipated energy increases linearly.In the stage of damage mutation,the increasing extent of dissipated energy increased suddenly,and the development rate of damage changed suddenly.When the development of demage is in its accelerated stage,the dissipated energy increases continuously,the dissipated energy curve become ‘up concavity',and the development rate of damage increases continuously.In the failure stage of fractured sandstone,the elastic energy is released,causing rock failure.The more the elastic energy is released,the more severe the failure degree will be.(3)According to the damage evolution law,under uniaxial compression,the larger the fracture angle is,the shorter the slow growth stage of the damage evolution curve is,and the growth rate of the damage variables become more faster,and the damage degree of the rock become more weaker.With the increase of confining pressure,the increasing range of damage variables is decreasing and the damage evolution rate is slowing down,which indicates that the confining pressure has certain enhancement effect on the mechanical properties of fractured sandstone.The damage process of fractured sandstone conforms to the objective law described by the minimum dissipated energy principle.(4)The existence of cracks will cause stress redistribution of the slope.In the reduction process of the strength coefficient,the elastic energy increases first and then decreases,while the dissipated energy increases continuously,which indicates the slope damage also increases continuously.When the calculation reaches the equilibrium,the elastic energy and the dissipated energy are both constant.In the inside of the slope,the unit of the slope,which is closer to the failure center,has greater dissipated energy and the dissipated energy increases exponentially when the slope is unstable.