Effect Of Joints On The Attenuation Of Elastic Wave Propagation

Natural rock mass is made up of intact rock and joints,fractures and other geologic body,due to the joint often have different characteristics,security and stability as well as related engineering elastic wave testing technique has brought some challenges,It is necessary to study the influence of joints with different characteristics on the attenuation rule of elastic wave propagation,thus effectively guiding the engineering practice.Therefore,this paper takes granite and sandstone as the research objects and,on the basis of theory,carries out two studies on elastic wave velocity tests and numerical simulation of complete specimens and joints with different characteristics respectively.The main contents and research results are as follows:（1）In view of the granite intact specimen and the joint specimen with different joint number,the P-wave velocity test under different joint angles was carried out by changing the test angle to explore the influence of joint angles on the attenuation rule of elastic P-wave propagation under different joint number.The results show that the existence of joints has a certain attenuation effect on the velocity of elastic p-wave regardless of the dip angle of joints.The wave velocity decreases with the increase of the number of joints,and the attenuation decreases gradually.When the number of joints was from 1 to 5,the single joints with joint angle of 0°had almost no attenuation to the wave velocity,while the five joints with joint angle of 90°had the greatest attenuation to the wave velocity,with the attenuation rate reaching 55%,and the wave velocity attenuation trend was almost the same at each dip angle.（2）For two groups of intact rock samples with almost the same wave velocity and joint samples with different consistence and roughness（expressed by JRC value）after processing,the P-wave velocity test is carried out to explore the influence of different joint consistence and roughness on the attenuation law of elastic P-wave propagation.The results show that the P-wave velocity increases slowly with the increase of joint coincidence degree.The P-wave velocity decreases with the increase of joint roughness,but the magnitude of the decrease is decreasing.When the roughness coefficient JRC value ranges from 10～12 to14～16,P-wave velocity attenuation rate is the smallest,only 1.4%.（3）The PFC^2D software was used to simulate the propagation of wave in rock mass.The influence of joint number,joint roughness and joint normal stiffness on the attenuation of wave propagation is studied when the joint angle is 90°.The results show that the numerical calculation velocity of wave propagation in intact rock mass is close to the theoretical wave velocity and the experimental wave velocity,which shows that the software has high reliability in simulating wave propagation.When the wave is incident to the jointed rock mass at a 90°angle,the wave velocity and amplitude decrease with the increase of the number of joints,but the decreasing amplitude is decreasing.The joint roughness（JRC）has an obvious effect on the velocity and amplitude of P-wave,when other conditions are not changed,the transmissivity of wave gradually decreases with the increase of joint roughness,and the attenuation rate of wave gradually increases with the increase of joint roughness.The normal stiffness of joint is also an important factor affecting the attenuation of wave propagation.When joint roughness and other conditions are not changed,the attenuation rate of wave decreases with the increase of joint normal phase stiffness,which can be predicted when the normal stiffness increases to a certain value,the influence of joint roughness on wave propagation attenuation can be ignored.