西部弱胶结砂岩循环载荷作用下塑性应变能变化规律

The variation law of plastic strain energy of western weak cemented sandstone during cyclic loading experiment

通过不同应力路径下的三轴循环加卸载实验,对中国西部矿区中不同粒径弱胶结砂岩的塑性应变能和塑性变形变化规律进行了研究。实验结果表明,加载路径对砂岩的塑性应变能及塑性变形特征有显著影响;在加载过程中,粗砂,中砂,细砂储存的塑性应变能以及累计速度依次递减,并且塑性应变能随应力增大按指数规律变化;各加卸载周期内储存的塑性应变能随加卸载次数及应力的增大呈"U"字形变化,即初始阶段由于孔隙裂隙压密,会储存较多塑性应变能;弹性阶段变形源于晶格弹性压缩,卸载时可以恢复,储存的塑性应变能较少;屈服阶段由于破裂面滑移也会储存较多塑性应变能;轴向和径向残余应变随应力增大呈指数形式增长,并且径向残余应变增长速度大于轴向;残余应变与塑性应变能变化规律不同,塑性应变能更能真实反映岩石在受载过程中的状态变化。

The variations of plastic strain energy and plastic deformation of weak cemented sandstone in different particle sizes were analyzed in triaxial cyclic loading experiments. The sandstone was taken from a coal mine in Western China. The results show that the cyclic loading paths have a notable effect on the deformation properties and plastic strain energy. The plastic strain energy and its growth rate of sandstone decrease with the decrease of sandstone particle sizes,moreover,the plastic strain energy increases exponentially with the increase of loading. The plastic strain energy stored in each loading and unloading cycles changes in the form of 'U'with the increase of number of cycles and stress,namely,at the initial stage,the void and cracks are consolidated,so the plastic strain energy is stored,and during the elastic stage,the deformation stemmed from lattice elastic compression can recover when the loading is released,so the plastic strain energy is less,and during the yield stage,the plastic strain energy stemmed from fractureslipping grows rapidly. Furthermore,during the cyclic loading,the axial residual deformation and lateral residual deformation increase exponentially with the increase of loading,and the lateral residual deformation grows faster than the axial residual deformation. The plastic strain energy is more reliable than the residual deformation in reflecting the change of state in the process of loading.