Mesoscopic Damage Of Rock By Cyclic Impact Based On Energy Time Density

The rock mass will produce cumulative damage under the repeated action of explosion stress waves,and the internal damage is often difficult to be detected by naked eyes.With the increase of the number of influence,the initial microscopic defects continue to expand,thus affecting the stability of rock mass and construction safety.In addition,it is difficult to accurately describe the damage process by conventional test methods and analysis methods due to the short time of impact load in the process of simulating the damage of rock caused by explosion stress wave in laboratory test.To solve this problem,SHPB test system and nuclear magnetic resonance apparatus were used in this paper to study the dynamic mechanical properties,energy consumption characteristics and mesoscopic damage evolution law of red sandstone,basalt and granite under cyclic impact load,and the damage degree of rock was predicted by IA-BP algorithm.The main research contents and conclusions are as follows:（1）The dynamic mechanical properties of three kinds of rocks under cyclic impact load are studied,and the effects of confining pressure and impact pressure on average strain rate,peak stress and peak strain are also discussed.The difference of dynamic compressive strength of three kinds of rocks with the change of confining pressure is compared and analyzed.It is concluded that the increase of confining pressure strengthens the ability of rock to resist impact,but the sensitivity of different rocks to confining pressure is different,red sandstone is the strongest,granite is the second,basalt is the weakest.（2）The variation rules of porosity and T₂spectrum curves of three kinds of rocks under cyclic impact load are analyzed,and the impact of impact pressure on the compaction of specimens is studied.In addition,different types of rocks lead to great differences in the compaction.Cyclic impact improves the pore structure of inner rocks.The contribution of pores of different scales to porosity growth of different rocks under cyclic impact is compared and analyzed.（3）The energy time density theory is applied to the cyclic impact test to study the variation law of energy time density with the number of impact and the influence of confining pressure on the variation of energy-hour density,and explain the reason of the variation law from the Angle of damage and energy consumption.At the same time,it is found that there are great differences in the energy absorption capacity of the three rocks in unit time,among which,the energy absorption level of red sandstone is the highest,basalt is the second,and granite is the weakest.（4）A new damage degree calculation method is proposed based on porosity fitting,and the damage degree of rock after cyclic impact is predicted based on the improved IA-BP intelligent algorithm.The experimental data such as energy density and mechanical properties are used as training samples,and 12 groups of predicted values are compared with the measured values.The results show that the error is small,which is an effective method for predicting and calculating the damage degree.