含天然节理灰岩加、卸荷力学特性试验研究

EXPERIMENTAL RESEARCH ON MECHANICAL PROPERTIES OF LIMESTONE CONTAINING NATURAL JOINTS UNDER LOADING AND UNLOADING CONDITIONS

为模拟一般地下节理岩体开挖加卸荷效应,进行含天然节理灰岩试样的加轴压、卸围压应力控制试验及常规三轴压缩试验,得到2种试验条件下的全应力-应变曲线。对试验后的岩样破坏特征、强度和变形特性的分析结果表明:无论是常规三轴压缩还是加轴压卸围压试验,其破坏均有沿节理面和穿切节理面2种方式。常规三轴压缩表明,当节理面与最大主应力夹角<40°时,岩样为穿切节理面破坏,当夹角>40°时,岩样为沿节理面破坏。对加、卸荷试验而言,2类破坏看不出与夹角的关系。加、卸荷试验沿节理面破坏试样的峰值强度、残余强度都明显低于穿切节理面破坏试样的峰值强度和残余强度。加、卸荷破坏试验中,沿节理面破坏试样没有明显的屈服阶段,峰值强度后强度迅速降低,没有出现三轴压缩破坏中的屈服和强度提高过程。

For the purpose of jointed rock mass excavation effect simulation, conventional triaxial test and stress control test of increasing axial pressure and unloading confining pressure of limestone containing natural joint have been performed; and the complete stress-strain curves were gained. The analytical results of fracture features of rocks, strength and deformation characteristics show that failure modes of the specimens can be classified into two types; one is shearing failure across the joint plane and the other is sliding failure along the joint plane whether the conventional triaxial test is or the stress control test of increasing axial pressure is. Conventional triaxial test shows that the specimen is shearing failure across the joint plane when the angle between the joint plane and the maximum principal stress is less than 40°; and the specimen is sliding failure along the joint plane when the angle is greater than 40 °. But above two failure modes of loading and unloading test is not interrelated to the angle between the joint plane and the maximum principal stress. The peak strength, strength of sliding failure along the joint plane obviously less than that of shearing failure across the joint plane under loading and unloading condition. The failure specimens of sliding failure along the joint plane have not obvious yield stage; and the strength suddenly decreases after the peak strength; the yield and strength increase process don＇t exist compared to conventional triaxial test.