Study On The Vibration Law Of Rock Joint Under The Vertical Incidence Of Stress Wave

Rock mass and soil mass are natural carriers of various structures.It can be used as the foundation of the above-ground buildings,as well as the surrounding rock of the underground structures and the excavation object of the mining engineering,and with the depth of the stratum,the rock mass becomes the main object of the engineering design and construction.Different from general artificial materials,rock mass is a complex geological body formed in a long geological history.The structural plane is one of the essential reasons for the anisotropy,non-linear elasticity,discontinuity and non-uniformity of rock mass.Therefore,it is the key to study the mechanical properties of rock mass.In engineering practice,rock mass will be disturbed by dynamic loads(such as earthquake load,blasting vibration,etc.).When the rock mass is subjected to dynamic load,the stress wave will propagate in the rock mass.Natural rock mass usually contains one or more groups of parallel joints.Therefore,the study of stress wave attenuation through multiple parallel joints has guiding significance for the stability analysis and failure mechanism research of rock mass in dynamic mechanical state(such as earthquake,blasting,etc.).In this paper,the influence of joint distribution on wave attenuation is studied by means of super detection technique.The control variables are joint number and joint spacing.In order to focus on the influence of joint distribution on wave attenuation,this experiment studies the influence of multiple parallel dry joints on wave attenuation when the wave is incident vertically.The main work and achievements are as follows:(1)In order to study the influence of joint distribution(joint number and joint spacing)on wave attenuation,the ultrasonic model experiment of wave propagation in multi-parallel joint rock mass is designed and the joint sample of cement paste is made for ultrasonic detection.The oscillogram of ultrasonic transmission wave can be obtained by ultrasonic measurement of prefabricated cement paste joint sample.Through the analysis of wave form,it can be seen that the attenuation effect of joint on wave amplitude is obvious,and the total attenuation amplitude increases with the increase of joint number,but the relative attenuation amplitude decreases.That is,with the increase of the number of joints,the attenuation amplitude of the wave is not uniform.According to the comparison of the average propagation velocity of the ultrasonic wave calculated by the distance between the samples and the arrival time of the first wave,it can be seen that the dry joint without filling has no attenuation effect on the propagation velocity of the wave.By comparing the first wave amplitude of different joint spacing samples with the same joint number,it can be seen that in the time domain,the first wave amplitude of the sample with joint spacing of 40 mm is smaller than that of the sample with joint spacing of 20 mm.(2)The frequency spectrum of the experimental data obtained from the ultrasonic experiment is carried out to obtain the frequency spectrum amplitude of each sample so as to analyze the problem of wave propagation in the joint sample in the frequency domain.The influence of joint number on wave attenuation and the influence law of joint spacing on wave attenuation are summarized.After the frequency domain analysis,the relationship between the frequency spectrum amplitude and the dominant frequency rate shows that with the increase of the number of joints,not only the frequency spectrum amplitude of the transmitted wave will decrease,but also the dominant frequency rate will decrease.In the frequency domain,the spectrum amplitude of the sample with joint spacing of40 mm is smaller than that of the sample with joint spacing of 20 mm.The transmission coefficient decreases with the increase of the number of joints.The transmission coefficients in frequency domain and time domain show the same change rule,but the values are not exactly.