Numerical Simulation On Failure Mechanism Of Rocks Containing Holes Under Dynamic Loads

Rock is a naturally heterogeneous anisotropic material with many cracks and void defects.Defects such as cracks or holes can cause cracks to gestate,sprout,expand,and intersect,resulting in the destruction of rock materials.In geotechnical engineering,it will cause disasters such as rock bursts,landslides,and collapse.The main cause of rock material damage is the interaction of defects and irregular crack propagation.Defects are not only sharp cracks,but also other weak media such as holes.However,existing research on crack propagation problems is usually caused by stress concentration at crack tips,and is not suitable for crack propagation in heterogeneous brittle materials.Therefore,it is necessary to study the failure mechanism of rock samples containing holes,and it has certain engineering significance.In this paper,the 3D numerical test analysis system of RFPA(Realistic Failure Process Analysis)is used to systematically study the failure behavior of rock ring specimens,single-hole rock specimens and rock specimens containing porous caves under dynamic loading.The following questions were analyzed:(1)The effect of the ratio of the inner and outer diameter of the rock ring specimen and the loading rate of the impact load on the failure mode of the specimen.The results show that there are three failure modes for rock ring specimens under dynamic loading.In general,it is a symmetrical four-sector ring failure mode.When the loading rate is large,the failure mode is similar to the static load splitting test.Only the vertical crack divides the sample into left and right parts.When the ratio of the inner and outer diameters of the ring is large,the number of vertical and horizontal cracks increases,the overall shape of the crack is in the shape of “#”.(2)The results of rock ring specimens under dynamic and static loading were compared and analyzed.The results show that different internal and external diameter ratio samples have different failure modes in the case of static loading.When the ratio of inner and outer diameters is less than 0.3,the fracture crack morphology of the specimen is similar to the disc splitting test under static loading.When the ratio of the inner and outer diameters is larger than 0.3,the overall shape of the crack is divided into four pieces similarly to the damage under dynamic load.(3)The effect of the radius of the hole on the failure of a rock sample containing a single hole was investigated.The results show that with the decrease of the radius of the hole,the angle of the two shear cracks initiated by the hole increases gradually.When the diameter of the hole decreases to a certain value,the non-uniformity of the rock will be the dominant factor affecting the crack propagation mode of the rock with holes.(4)The effects of impact load loading rate and peak value on the failure of rock samples containing single holes were studied.The results show that with the increase of the peak value of the impact load,the initial crack shape around the hole gradually changes from the “-” type to the “Y” type and the “X” type.When the loading rate of the impact load is large,the spallation is concentrated on the right side of the sample.As the loading rate decreases,the number of spallation cracks decreases and shifts to the left side of the sample.When the loading rate is less than a certain value,cracks only appear around the holes.In addition,the larger the peak of the impact load,the more the cumulative energy of the acoustic emission;the greater the loading rate of the impact load,the less the cumulative energy of the final acoustic emission.(5)The effects of different pore arrangements on the failure of rock specimens with porous caves were investigated.The results show that when the distance between the centers of adjacent circular holes is constant,the failure modes of the samples can be divided into three types with different inclination: the adjacent circular holes only communicate through the Atype cracks;the adjacent circular holes were connected by the A and B-type cracks;the cracks around the holes do not overlap each other.When α = 90°,the influence of the hole spacing “L” on the damage of the sample is mainly realized as with “L” increases,the interaction between the holes is weakened.