Experimental Research On Crack Propagation Of Multi Fractured Rock Mass Material

Since the 50 s and 60 s of the last century,many scholars at home and abroad have carried out a series of theoretical and experimental studies on fracture mechanism of fractured rock mass,and have obtained fruitful research results.Many engineering examples at home and abroad show that fracture and failure expansion of rock mass engineering is mainly caused by joint cracks in rock mass,forming new cracks,resulting in large displacement and deformation,causing major engineering accidents.Rock mass is a brittle material,and its strength and deformation characteristics are the key factors that affect the safety of underground engineering.Under various loads,the joint cracks in rock mass cause stress redistribution and local stress concentration.The fracture,expansion and failure evolution process have great influence on the mechanical properties and failure characteristics of joint fractures.In order to fully understand the fracture evolution process of joints and fractures,this paper mainly adopts theoretical analysis and indoor test methods to carry out related research.Based on the similarity theory,the specimens of single,double and three fractured rock masses with different joint dip angle and length of rock bridge were made respectively.The specimens were tested by the uniaxial compression loading test machine,and the fracture damage process of the fractured specimen was analyzed.The main contents and conclusions of the experimental study are as follows:(1)Based on the similarity principle,rock samples with different dip angles,different length of rock bridges and different numbers of cracks are made.In the process of testing,the dynamic data parameters in the single axis compression load process are obtained by using the uniaxial compression servo machine,the ultrasonic testing equipment and the high-definition digital camera.The test results show that the sliding crack theory is applicable to rock samples under uniaxial compression,and can explain the mechanism of crack propagation very well.(2)The failure forms of the fractured specimens with different spatial arrangement in the test process are recorded and arranged respectively.The failure characteristics of the fracture specimens are analyzed as follows: for class I and class II fracture specimens,the secondary coplanar cracks are not produced when the dip angle of the fracture specimen is 30,45 and 60 degrees.However,there are great differences in failure modes for fractured specimens of class III and type IV.When a certain rock bridge length is generated,the failure of rock bridge will occur.In the same way,the failure forms of type V and VI crack specimens are similar to those of single and double fracture specimens,and the crack failure modes are different at a certain angle and the length of the rock bridge.This test proves that the spatial layout of prefabricated cracks,such as the number of cracks,the number of cracks and the distance between rock bridges,will affect the failure mode of fractured specimens.(3)According to the mechanical characteristics of fracture specimens with different slit angle and length of rock bridge,from the angle of prefabricated fissures inclination angle,compared with the same dip angle of different crack bars,it is found that with the change of the prefabricated fissures,the change of the dip angle of the prefabricated fissures will affect the strength of the fracture specimen.With the different length of the rock bridge,the strength of the double fracture and three fracture specimens is different with the length of the rock bridge,and the cracks in the rock bridge and the shear crack are easy to occur.