岩石试样的强度准则及内摩擦系数

STRENGTH CRITERION AND INTERNAL FRICTION COEFFICIENT OF ROCK SPECIMEN

岩石是一种非均质材料并含有各种缺陷 ,利用岩样的应力应变全程曲线可以确定理想强度 ,在排除岩样缺陷后讨论峰值强度与围压的关系 ,即强度准则。通过岩样剪切破坏后保持轴向变形恒定降低围压试验 ,可以确定岩样由摩擦力维持的承载能力随围压的变化关系。比较峰值强度和残余强度随围压变化关系的异同 ,可以研究岩样屈服过程中内摩擦系数的变化情况 ,以及内摩擦力对岩样变形特性的影响。粉砂岩试样在峰值应力时内摩擦系数已经达到最大值 ,峰后只是粘结力或者说是材料强度的降低过程 ,围压对变形没有明显影响。大理岩试样屈服过程中内摩擦系数不断增加 ,而内摩擦力的增加量与围压有关 ,高围压时只有材料强度完全丧失之后 ,由内摩擦力达到岩样的承载极限。内摩擦力系数随屈服过程增大 ,是岩石由脆性转变为延性的根本原因。

Rock is heterogeneous material with various flaws. The ideal strength of rock specimen can be determined from its complete stress strain curve. After specimen is failed the experiment,reducing confi ning pressure and keeping the constant axial deformation, was carried out. According to the experiment the relationship of loading capacity of specimen,which is sustained by the internal friction, with confining pressure is given. To compare the relations of residual strength and peak strength with confining pressure, the internal friction coefficient in the yielding process is studied. The effect of internal friction coefficient on deformation and strength of various rock specimens is discussed. For siltsand, the internal friction coefficient reaches the maximum at the peak strength, and then the cohesion or material strength decreases only, so the confining pressure does not influence the specimen's deformation beyond the peak stress. For marble, the internal friction coefficient increases in the whole yielding, and the increasing of internal friction is various with the normal stress on the shear surface or confining pressure. At high confining pressure, the maximum axial stress is realized by internal friction when material strength of the specimen has wholly lost. The increasing of internal friction coefficient results in the transformation of brittle to ductile.