Experimental Study On Cyclic Loading And Unloading Of Microstructure Damage Of Mixed Rock

As the main surrounding rock of the Anshan Iron and Steel Co.Ltd.Dagushan open-pit iron mine slope,its cyclic loading and unloading mechanics and meso-damage characteristics are important to the stability of the slope.This article aims to reveal the failure of the mixed rock through cyclic loading and unloading tests& mesoscopic damage laws to guide engineering practice.In this paper,a single cycle loading and unloading test of mixed rocks under different confining pressures(?3)and different peak stress ratios(p)was carried out through the SAM-2000 rock triaxial test system.The evolution of meso-damage of mixed rocks was monitored by acoustic emission and nuclear magnetic resonance(NMR).The effects of ?3 and p on the damage characteristics and the accumulation of meso-damage were compared and analyzed.The following research results have been achieved:The mixed rock samples were subjected to cyclic loading and unloading tests under five kinds of confining pressures,and the corresponding relationships between their failure characteristics,stress-strain curves,and the change law of acoustic emission parameters,It is concluded that when p <pmax,the rock samples are in the elastic stage and accompanied by a small amount of residual deformation.When p =pmax,the entire load is loaded,During the process,the rock samples went through the compaction phase,the elastic phase,the elastoplastic phase,and the failure phase.There was almost no acoustic emission signal in the early stage of loading.Only when the rock sample was near the failure phase,the acoustic emission signal increased sharply.The damage variables were defined by the number of impacts in the acoustic emission parameters,and the damage curve(axial stress-time-damage variable)of the rock under the action of five confining pressures was analyzed it is almost zero,After a long period of time,the damage is basically unchanged,When the rock sample is near the damage,the damage curve shows a steep increase.After each cycle of loading and unloading tests,NMR analysis was performed on the rock samples,and the stress ratio-porosity relationship curve,pore size distribution,pore throat distribution,T2 spectrum curve,and total peak area curve were analyzed,At the same time,combining the damage variables defined by porosity,it is concluded that When p=pmax,the above variables increase steeply.