岩体强度各向异性及其转化的应力条件

ANISOTROPY OF ROCKMASS STRENGTH AND ITS TRANSFORMATION CRITICAL CONFINING STRESS

不连续面的存在导致岩体强度具有强烈的各向异性,然而随着围压的增大,岩体不连续性逐渐弱化,岩体强度的各向异性特征逐渐转化为各向同性特征。基于岩体硬性结构面的摩擦准则及岩体的Hoek-Brown强度准则,推导含坚硬结构面岩体强度各向异性转化为各向同性的临界围压σc≥σ(mσmσ54)/27,其中,σc为岩块单轴抗压强度,m为Hoek-Brown准则参数。利用前人开展的含结构面岩体试样的三轴试验,建立FLAC3D数值模型,对文中所采用的准则及所求得的临界围压进行验证。结果发现:数值模拟所得岩体强度与试验资料吻合较好;含单组硬性结构面岩体强度在围压低于临界围压时呈现各向异性,高于临界围压则呈现各向同性;含2组结构面(其中一组为贯通型结构面)的岩体,强度由各向异性转化为各向同性的临界围压符合所求得的临界围压;含3组非贯通型结构面岩体试样,因为锁固原因,试验所得的临界围压稍小于理论求得的转化围压。

As the confining stress is higher,rock mass strength is less anisotropic. On the basis of the friction criterion of rigid discontinuities in the rock mass and the Hoek-Brown strength criterion of rock mass,the critical confining pressure 23 c ( 54 )/27m mσ σ + +≥ is deduced. When the confining pressure is larger than the critical value,the strength of the rock mass with rigid discontinuities would change from anisotropy to isotropy. The derivation results show that the critical confining pressure is mainly related to parameter m in Hoek-Brown strength criterion and the uniaxial compressive strength. Based on the existing tests,rock mass with continuities are modeled with FLAC3D. Then,the Hoek-Brown criterion and the critical confining pressure mentioned above are verified. The results show that the strength of rock mass with one group or two groups of rigid discontinuities is anisotropic when the confining stress is lower than the critical confining stress,but isotropic when the confining stress is higher than the critical confining stress. For the rock mass with three group of cracks,the real critical confining stress is smaller than expected due to the locking effect.