Numerical study on mechanical properties of sandstone under varied unloading rates of confining pressure
Existing researches on the mechanical properties of rock specimens under unloading confining pressure suffers the inability of completely remove the impacts on testing results due to specimen differ-ences and stress paths changes during loading process.This study carried out numerical tests with discrete element method by deploying homogeneous specimens suffering constant axial pressure and four unloa-ding rates of confining pressure,and the macro-micro mechanic and energy evolution laws are compared and analyzed.The results showed that the ultimate bearing capacity of the specimens increased continu-ously with the decrease of the unloading rate,and the unloading processes of the confining pressure ex-pressed obvious falls and bounces of the axial pressure and confining pressure.It indicated a multi-stage sudden and progressive failure process,consecutive accumulation of localized cracking contributed to the instability of the specimen.For the unloading process,the growth rate of tensile cracking was greater than that of shear cracking,and tension-induced failure predominated.Under the four unloading rate con-ditions,with the increase of acoustic emission events accompanying each cracking,overall fluctuation range of the seismic magnitude gradually decreased,but overall seismic magnitude increased step by step.With the decrease of unloading rate,energy density expressed apparent staged arising characteristic,and the extent of sudden cracking of the specimen increased gradually at the unloading process.Compared with the high-speed unloading that facilitated rapid changes of energy density of the specimen with an approximate linear manner,relative low-speed unloading allowed for enough time for the specimen to change the energy density with a staged increasing manner.This research could provide theoretical and engineering reference for the analysis of rock failure instability and mechanism under un-loading confining pressure environment.
numerical experimentconfining pressure unloading ratemechanical propertiessandstonediscrete element method
万方数据
维普
