含卸荷裂隙北山花岗岩蠕变特征试验研究

Experimental Study on Creep Behavior of Unloading-Cracked Beishan Granite

为研究开挖卸荷后围岩的长期力学行为特征,以完整岩石卸荷试验获得的含裂隙花岗岩为研究对象,基于裂隙试样三轴压缩试验获得的强度参数,开展了干燥和饱和2种状态下的蠕变特性试验研究。试验过程中采用三维声发射定位系统对试样的应力应变全过程进行实时监测。结果表明:裂隙花岗岩的横向蠕变变形及稳态蠕变速率均比轴向上更加显著;饱和条件下的蠕变应变占总应变的比例及稳态蠕变率比干燥条件下的更低;损伤加速发展的临界应力值约为抗压强度的90%,声发射累积振铃计数的变化趋势与横向应变的变化趋势一致;建议在地下工程围岩稳定性分析中,根据工程实际状况考虑含水状态对围岩变形和强度弱化效应的影响。

In order to investigate the long-term behavior of host rock after excavation unloading,the creep tests under dry and saturated conditions were carried out on unloading-cracked granite,based on the mechanical parameters obtained from triaxial compression tests on unloading-cracked granite.The unloading-cracked granite were produced from triaxial unloading tests on intact rock.The full processes of stress and strain were monitored in real time by the three-dimensional acoustic emission monitoring system.The test results indicate that the creep deformation and steady state creep strain rate in lateral direction were found to be greater than in axial direction.Meanwhile,the ratio of creep strain to total strain and steady state creep strain rate were shown to be degraded by the saturation.The critical stress value corresponding to the accelerated development of damage was about 90%of the compressive strength of unloading-cracked specimen.What's more,the acoustic emission ringing counts during the last step of creep test had the same trendline of change with lateral strain.It is suggested that the degeneracy effects of saturation on the deformation and strength of host rock should be considered in the stability analysis of underground engineering.