Experimental Research On Mechanical Properties And Acoustic Emission Characteristics Of Red Sandstone After Impact Damage

The reserved rock masses of rock engineering such as mining,tunnels,underground chamber and slopes will be under the combined action of blasting impact,periodic static load and water for a long time,and its instability failure evolution mechanism is more complicated than when single factors such as dynamic load,static load and water act.At present,there are few researches on the mechanical properties and acoustic emission characteristics of the rock deformation and failure process under the action of water and rock after impact damage.This paper takes red sandstone as the research object,through the combination of laboratory test and theoretical analysis,discuss the influence of water on the static and acoustic emission characteristics of red sandstone after impact damage.The main research contents and conclusions are as follows:(1)In order to explore the static mechanical properties of red sandstone after impact damage,the SHPB test device is used to carry out cyclic impact damage tests on the rock samples at a constant impact velocity to prepare rock samples with different initial damage degrees.In the impact damage test,with the increase in the number of cyclic impacts,the red sandstone pore size and number were increasing.The T₂ spectrum distribution curve changed from single-peak to double-peak and triple-peak,and the porosity was inferior to the T₂spectrum distribution curve.The peak"passivation"phenomenon is more pronounced.(2)A modified rock damage model is constructed based on P waves.The modified model can better reflect the damage evolution characteristics of the rock under cyclic impact loading.Under the action of cyclic impact load,the critical damage of the rock is related to the amount of energy absorbed per unit volume.If the absorbed energy per unit volume is higher than the critical damage absorbed energy,the rock will damage.(3)The red sandstone after impact damage was dried and saturated with water.On this basis,uniaxial compression tests and uniaxial graded cyclic loading and unloading acoustic emission tests were carried out.The changes of rock peak stress,peak strain,elastic modulus and failure mode were studied.Under uniaxial compression,with the increase of impact damage,the peak stress,peak strain and elastic modulus of red sandstone in the dry and saturated state show a gradual decreasing trend;under uniaxial hierarchical cyclic loading and unloading conditions,with the increase of impact damage,the peak stress and peak strain of red sandstone in dry and saturated state change little.The loading modulus and unloading modulus generally increase first and then decrease.Rock failure mode is closely related to damage degree,water and loading mode.(4)According to the active level of acoustic emission signal,the rock fracture process under cyclic loading and unloading conditions is divided into three stages.The number of acoustic emission events,ringing count,and energy rate response characteristics at different stages are closely related to impact damage and water content.The RA and AF values can be used to judge the changes in the microstructure and the evolution of cracks in the rock fracture process,and to predict the macroscopic failure mode of the rock.(5)Based on the theory of loading and unloading response ratio,the calculated elastic modulus response ratio showed a trend of first decreasing and then increasing;the acoustic emission response ratio showed a decreasing trend as a whole,and the value gradually tended to 2.At the initial stage of loading,the acoustic emission response ratio of the dry red sandstone after impact damage is much greater than that of the saturated state,and there is no significant change in the acoustic emission response ratio of the red sandstone without impact damage in the dry and saturated state.(6)The FR value of dry and saturated red sandstone after impact damage is different,and the specific manifestations are as follows:The FR value of the red sandstone in the dry state increases first and then decreases.The FR value of saturated red sandstone shows a continuous decreasing trend.