Experimental Research On Stress Wave Propagation Characteristics Of Red Sandstone Under Axial Static Load

This paper selects the red sandstone of Anyuan Ganzhou as the test material,the material has good integrity and homogeneity.The test is completed in the laboratory of the static and dynamic load test system of Jiangxi University of Science and Technology.The test is done on the sandstone with large diameter,which purpose of the study is to investigate the stress wave propagation characteristics in sandstone.The attenuation law of stress wave velocity and amplitude in time and distance are studied in this paper.The main conclusions are as follows;?1?Based on the stress wave theory,assuming that the incident wave is the harmonic wave,the amplitude of stress in time and distance is introduced,and results show that the amplitude is exponential decay in time and distance.The impact test was carried out under 13 levels of axial load and unload by means of static and dynamic combined loading device.?2?With the increase of the axial static stress,the longitudinal wave velocity of the red sandstone presents a trend of "sharp increase,smooth development and rapid decrease".The analysis shows that this is caused by the different axial static stress caused by the closure and expansion of micro cracks in the rock.The stress value and the uniaxial compressive strength ratio of the ?s/?sp is less than 30%,the porosity decreases with increasing stress.When the value of ?s/?sp is between 30% and 55%,the porosity changes little,analyzed that the closed part of the pore and another part of crack initiation and propagation phase offset.When the value of ?s/?sp is greater than 55%,the porosity of rock?or damage?increase rapidly with the increase of the static stress and longitudinal wave velocity V and ? approximate quadratic function fitting loading.When unloading,the longitudinal wave velocity has experienced "slow reduction?A₂-B₂?","steady development?B₂-C₂?","slow reduction(C₂-D₂₁)" and "rapid reduction(D₂₁-D₂₂)" in four stages.The fitting relation is similar to the first order exponential function relation between V and ?.Research results show that,the path is reduced by comparing the unloading wave velocity with the loading.Obviously,different loading path has great influence on the variation of longitudinal wave velocity in red sandstone?3?The research shows that the amplitude of the loading and unloading process is exponential decay in time and distance,however,the effect of axial stress on amplitude attenuation is different in different loading paths.In the loading conditions,? and axial compression were a first-order exponential function relationship.There are different levels of? due to different loading paths of sandstone in different degree of closure.For attenuation coefficient ? including ?t and ?x,the amplitude in time and distance attenuation is quadratic function relationship between ?t and ? under the loading conditions,but,the amplitude in time and distance attenuation is the three function relationship between ?x and ? under the unloading conditions.?4?According to the process of loading and unloading test,the variation relationship of?A and ? is explored,the results show that the variation trend of attenuation ?A with axial compression ? has three functions relation,which can be expressed as ?A=B₁e³+B₂e²+B₃e+B₀.The change trend of ?A and ? is not nearly the same in different loading paths.The results of the study can provide reference value for the analysis of rock mass stability and stress wave propagation and attenuation in the complex rock mass,which is helpful to the blasting and excavation of underground engineering rock mass.