JRC分形估测方法的实用性

THE PRACTICABILITY OF FRACTAL METHODS ON ESTIMATING ROCK JOINT ROUGHNESS COEFFICIENT

基于分形几何的码尺法分维数与岩石节理粗糙度系数的物理意义剖析，认为Ｄ－ＪＲＣ之间不存在必然的相关性．分析标准轮廓曲线的分维数，发现其分维数差级微小，难以实行粗糙度系数分级．根据实测资料阐述了岩石节理表面轮廓曲线的“自相似”是统计意义而不是绝对的，它要求ＪＲＣ分形估测应统计求取，而过繁的分维数测量步骤削弱了ＪＲＣ的分形统计估测的可行性．建立在实测资料统计分析基础上的ＪＲＣ尺寸效应分形模型ＪＲＣｎ＝ＪＲＣ０（Ｌｎ／Ｌ０）－Ｄ客观而真实地刻画了粗糙度系数随取样长度增大而降低的规律，其中，ＪＲＣ尺寸效应分维数（Ｄ）具明确的物理意义，它描述了ＪＲＣ随结构面规模增大而降低的衰减速率．最后，运用ＪＲＣ尺寸效应分维数（Ｄ）探讨了岩石节理粗糙度系数尺寸效应的各向异性规律．

The fractal methods to estimate rock joint roughness coefficient ( JRC ) are more and more applied in recent years. Their practicability is discussed in this paper. According to the analysis of the physical meanings of fractal dimension ( D ) and JRC , there is no inexorable coherency between them. After analysing the fractal dimensions of Barton-Bandis's profiles, it is found that the gaps of fractal dimensions are too small to distinguish their JRC . The analysis measurement data also reveal that self-similarity of surface profiles of rock joint is statistical, not absolute, so the fractal measurement of JRC has to be taken on the basis of statistics. This makes the fractal measurement of JRC complicated and infeasible. The fractal model of JRC scale effects: JRC n=JRC 0(L 0/L n) -D is built in the light of analysing practical rock joint roughness coefficients. In this model, the fractal dimension ( D ) reflects the decreasing velocity of JRC with the joint scale increase. The anisotropism of JRC scale effect of rock joints is also discussed in this paper.