软硬互层岩体卸荷蠕变力学特性试验研究

 利用岩石全自动三轴蠕变仪对锦屏二级水电站辅助交通洞典型灰白色细晶大理岩与绿片岩软硬互层岩样开展卸荷蠕变试验，得到岩样轴向、侧向典型的蠕变全程曲线。蠕变试验结果表明：围压较高时，试样的轴向与侧向变形随时间的推移变化不大，蠕变现象不明显；随着围压逐渐减小，试样的蠕变变形越来越显著，在最后一级出现了典型的蠕变3个阶段并发生了非线性加速蠕变现象直至试样破坏。软硬互层岩样三轴卸荷蠕变破裂形式主要以剪切破坏为主，局部伴随着一定程度的张拉破坏，主裂纹与水平面大致呈45°角，剪切破裂面较为单一平整，且破坏面基本是沿着强度较低的绿片岩层理内部并平行于层理面产生和扩展贯通而形成的。在加速蠕变阶段之前，其侧向蠕变变形比轴向蠕变变形小，但试样处于加速蠕变阶段时，侧向蠕变变形量与蠕变速率均要高于轴向蠕变；这表明随着时间的增长和围压的降低，岩样的侧向蠕变比轴向蠕变更为灵敏，而且体积扩容效应显著。卸荷条件下，蠕变力学参数表现出较为显著的非定常性规律，当外荷载小于岩样长期强度时，岩石卸荷蠕变力学参数与卸荷量有关，随着卸荷量的增大逐渐弱化；当外荷载大于岩样长期强度时，岩石卸荷蠕变力学参数不仅与卸荷量有关，而且还与蠕变时间有关。

EXPERIMENTAL STUDY OF UNLOADING CREEP MECHANICAL PROPERTIES OF ALTERNATIVELY DISTRIBUTED SOFT AND HARD ROCKMASS

Triaxial unloading creep tests with alternatively distributed soft and hard rock specimen from auxiliary traffic tunnel of Jinping II hydropower station are carried out by the rock servo-controlled rheological testing machine.The creep laws of axial and lateral deformations under unloading confining pressure are obtained.According to creep test results,axial and lateral deformations are both unchangeable under high confining pressure with time;and the creep phenomenon of rock specimen is not obvious.As confining pressure decreases gradually,the specimen creep deformations become more and more prominent,and the typical creep three stages of rock appear;and the specimen creep deformations increase nonlinearly until the specimen damages.The creep rupture form of rock specimen is mainly shear failure and with a certain degree of tension damage;and the angle between failure plane and level is 45°roughly.Shear rapture surface is relatively single and smooth;and the evolution process of failure surface is along green schist bedding with lower strength and parallel to bedding plane.Before the accelerated creep stage,lateral creep deformation of rock specimen is smaller than axial creep deformation,while in the accelerated creep stage,lateral creep deformation and creep rate are both higher than those of axial creep,which suggest that the lateral creep deformation is more sensitive than axial creep deformation,and the specimen volume dilatation effect is remarkable with time and the decreasing confining pressure.In the condition of unloading,when the applied load is less than the long-term strength of rock specimen,the rock unloading creep parameters are related with unloading quantity,they are gradually weakening with the increase of unloading quantity;but when the applied load exceeds the long-term strength of rock specimen,the rock unloading creep parameters are related with both unloading quantity and creep time.