张开穿透型单裂隙岩体三轴卸荷蠕变特性试验

Triaxial unloading creep tests on rock mass with an open and penetrating flaw

高应力条件下较多岩体工程在开挖卸荷过程中表现出显著的时效变形特征。为研究裂隙岩体在卸荷状态下的蠕变特征,以锦屏I级水电站大理岩为原样制备模型试样,开展了恒轴压分级卸围压三轴卸荷蠕变试验。试验结果表明:试件在破坏时对应应力差最小的是倾角为30°裂隙试样,其次为倾角为60°裂隙试样,倾角为90°裂隙试样最大。从破坏形式来看,完整试件与倾角为90°裂隙试件均呈整体剪切破坏模式,倾角为30°和60°裂隙试件均从裂纹尖端扩展至破坏。变形特征方面,均可采用Burgers模型对各裂隙试样不含加速蠕变阶段的蠕变曲线进行拟合,试样在不同裂隙类型和应力水平下的变形特点则通过参数数值加以区分。该结论与Lemaitre应变等效原理和Sidoroff能量等价原理中有关损伤材料和无损材料间相关关系的基本观点一致。基于此,提出了裂隙岩体损伤蠕变模型,该模型建立了完整岩石与裂隙岩体间的相关关系,对裂隙岩体时效变形特征的进一步研究具有较好的参考价值。

Time-dependent deformation of rock mass is obviously found under high stress condition during excavation unloading process. To investigate the unloading creep characteristics of fractured rock, specimens were prepared by marbles from Jinping I hydropower station. Then unloading creep experiments were performed in the laboratory under constant axial pressure and stepwise unloading lateral stress. The results showed that when the specimens fail, the corresponding smallest stress difference is found on the specimen with the angle of 30°, the middle one is specimen with the angle of 60 °, and the largest one is the specimen with the angle of 90°. Overall, shear failure occurs in the intact specimen and the specimen with the angle of 90°, while the cracks initiate from internal tips of pre-existing flaw of specimens with angles of 30° and 60°. The Burgers model is also employed to describe deformation characteristics of all intact rock and fractured rock without the accelerated creep stage. The values of parameters are used to distinguish the deformation characteristics of specimens with different fissures and under different stress Conditions. The obtained results are consistent with the views of Lemaitre equivalent strain and Sidoroff energy equivalent principle on the correlations between damaged materials and undamaged materials. According to above results, damage creep constitutive models are put forward for the fractured rock mass. Moreover, the relationship between the intact rock and fractured rock masses is estabfished using the proposed models. Therefore, this study can provide references for further study on time-dependent deformation characteristics of fractured rock mass.