岩石节理粗糙度新指标及新的JRC确定方法

为使二维粗糙度指标能够反映岩石节理形貌的方向特征,同时可以克服采样间距取值对粗糙度指标大小的影响。将岩石节理面划分为一系列连续的长方体微凸体,提出一种确定长方体微凸体计算长度的计算模型。通过平均同一剪切方向上长方体微凸体的计算高度提出了一个新的描述形貌面粗糙度的指标c。指标c是由长方体微凸体2种破坏模式结合一种确定长方体计算长度的模型得到,可以将节理几何特征与剪切强度结合起来,进而将节理粗糙度与节理剪切强度结合起来,这就为考虑剪切方向性的岩石节理剪切强度公式的提出提供可能。粗糙度指标c可以将形貌面客观定量表示,同时具有方向性,即剪切方向不同时对应的c不同。以标准JRC曲线为例,基于图像分割技术提取了标准JRC曲线坐标信息,阐述了粗糙度指标c的计算过程。在某一测量间距下获取的粗糙度指标不足之处是比该测量间距较小的粗糙度将被掩盖,而小尺度的粗糙对于抵抗剪切的贡献不应被忽略。通过计算不同采样间距的粗糙度指标c,发现指标c随着采样间距增大而呈幂函数形式减小,显示具有分形特征。基于分形思想,提出可同时反映节理形貌面各向异性并且不受测量尺度影响的粗糙度评价系统。分析了粗糙度描述系统指标与JRC之间的关系,证明该描述系统指标可与节理剪切强度建立良好的关系。

A new method for determining the JRC with new roughness parameters

To make the two dimensional roughness parameters fully reflect the directional features of rock joints,and overcome the influence of sampling interval on the roughness parameter,the joint surface is divided into a series of rectangular shaped asperities,and a computational model for determining the deduced height of a rectangular shaped asperity is proposed.A new parameter c for describing surface roughness is proposed by calculating the average value of the deduced height of rectangular shaped asperities in the same shear direction.Index c is obtained by combining the two failure modes of rectangular shaped asperity to determine the deduced height.It can combine the geometric characteristics of joints with the shear strength,and then combine the roughness of joints with the shear strength.This provides a possibility for the peak shear strength model of rock joints considering the shear direction.The parameter c is able to objectively reflect the roughness and show the directional characteristics of the shear strength of rock joints.Taking the standard JRC profile as an example,the calculation process of the roughness parameter c is expounded.The obtained parameter c under a certain measurement interval has the drawback that the roughness with smaller measurement interval will be concealed,and the contribution of small scale roughness to shear resistance should not be neglected.The parameter c with different sampling interval is obtained,and the result shows that the parameter c decreases with the increase of sampling interval and shows a fractal feature.Based on the fractal theory,the roughness of joints can be described by two fractal parameters,and these two parameters are independent of measurement scale.The relationship between the roughness parameters and JRC is proposed.It is proved that the new method can establish a good relationship with the shear strength of rock joints.