基于花岗岩卸荷试验的损伤变形特征及其强度准则

 对取自大渡河大岗山水电站的花岗岩开展高应力下2种卸荷方案的力学特性试验，并与同围压下的常规三轴压缩试验结果进行对比分析，研究岩石卸荷过程中的破坏机制、力学强度参数损伤劣化效应及其卸荷破坏的强度特性。研究结果表明：(1) 岩石卸荷过程中向卸荷方向回弹变形强烈、扩容显著，脆性破坏特征明显。(2) 卸荷试验中，开始卸荷点处的变形模量较常规三轴压缩试验已发生一定的损伤劣化，其损伤因子与初始围压近似成线性关系，而该点处的泊松比所表现出的损伤劣化效应却不明显。(3) 卸荷过程中，泊松比随着围压的不断卸除，呈现指数关系增长；变形模量变化平缓，但在岩样卸荷屈服破坏点处陡降。(4) 在高应力卸荷条件下，Mogi-Coulomb强度准则能很好地反映其破坏强度特性。(5) 相比较于常规三轴压缩试验，卸荷时的抗剪强度参数c值减小而j 值增大，其变化量与卸荷方式有关。这些结论揭示高应力条件下花岗岩的卸荷力学特性，为西部水利水电工程的开挖、支护设计及其稳定性分析提供了理论参考。

DAMAGE DEFORMATION CHARACTERISTICS AND ITS STRENGTH CRITERION BASED ON UNLOADING EXPERIMENTS OF GRANITES

Two different unloading tests of granites from the Dagangshan Hydropower Station at Dadu River have been carried out. In order to analyze rock failure mechanism，the damage laws of mechanics and strength parameters，the failure strength criterion during the process of unloading，the conventional triaxial compression tests of granites have been also performed. The results show that：(1) The characteristics of intense rebound deformation，distinct dilatancy and brittleness failure of rock have been observed in two different unloading tests. (2) Compared with the deformation modulus in conventional triaxial compression tests，the deformation modulus at the beginning point of unloading has been degenerated；the relationship between damage factor and initial confining pressure is approximately linear，but little damage is found in the Poisson¢s ratio. (3) During unloading stage，the Poisson¢s ratio rises up continually，and the variation law with the confining pressure can be well described by exponent relation；deformation modulus varies hardly，but at the failure point，it decreases rapidly. (4) In the two different unloading tests under high geostress，the Mogi-Coulomb envelope can match stress circle very well. (5) In the two unloading tests，shear strength parameters have been evaluated by Coulomb laws，and it is founded that the cohesion c decreases，but the inner friction angle increases during unloading；and the variation is dependent of the unloading style. These conclusions have revealed the unloading mechanical properties of granites under high geostress and provided reliable theoretical reference for the numerical simulation about excavation and design for the stability analysis of large-scale hydropower projects in West China.