Study On The Reflection Law Of Rock Joints With Oblique Incident Stress Wave

Natural rock mass contains many discontinuous structural surfaces such as joints,faults,and layers.These discontinuous structural surfaces make the mechanical properties of the rock mass different from those of the rock.Research results show that the mechanical properties of joints have a vital influence on the strength and stability of rock mass.In the past decades,researchers in rock mechanics,geophysics and seismic engineering have done a lot of theoretical and experimental research on various cases of stress wave propagating across joints.Most of the studies are limited to the case of the stress wave incident vertically,which is one-dimensional case,while the case of oblique incident in nature is more common.When stress waves oblique incident on a rock joint,the shear deformation characteristics need to be considered.Besides,complex reflections between joints need to be considered when stress wave incident a set of joints.These contents are of great value but also bring great difficulties to relevant laboratory experiment design.Considering the above factors,the purpose of this laboratory experiment is to study the effects of the number of joints and the spacing of joints on the stress amplitude attenuation and the velocity attenuation.Meanwhile,the effect of different incident angles under high strain rate will be studied by designing samples with different joint undulation.The stability assessment of rock mass structure is based on critical values such as stress,displacement,velocity,and acceleration.The joint deformation of rock joints is in an elastic state with ultrasonic wave.Meanwhile,due to the high frequency of ultrasonic wave,the ratio of joint spacing to wavelength is large,therefore the ultrasonic experiment mainly focuses on the attenuation of stress amplitude and wave velocity.while the failure strength of joints in the nonlinear deformation state with high strain rate is the key point.When ultrasonic wave incident into a set of joints,the time domain results have higher accuracy,but it can be influenced by coupling effect within sample and measuring instrument,the actual measured data in time domain is a result of complex superposition.With spectrum analysis,initial wave can be stripping in frequency domain without superposition.This article will calculate amplitude attenuation in both time domain and frequency domain.Joint deformation keeps elastic state under ultrasonic wave,but in high strain rate dynamic problem as the earthquake,explosion,impact load function,rock mass damage occurs,the test results of ultrasonic model is not valid.The author designed samples with different joint undulation to study the strength of joint rock mass under the shock load.The basic data of interpolation method is accumulated by measuring the failure strength of multiple groups of samples.Test result s will be applied to stress wave oblique incidence of joints in common engineering practice.The results of this ultrasonic experiment are in good agreement with the theoretical solution of effective medium theory and virtual wave source method,which proves the feasibility of theoretical solution in study stress wave incident in a set of parallel joints.This experiment also reveals a conclusion of practical significance to predict the joint distribution of a particular rock mass based on the duration of the initial wave.The innovative research on joint undulation can give some inspiration to other researchers.