Size Effect of a Rock Fracture's Shear Property Estimated by Using a Fractal Model

为了合理地估计岩石裂隙的表面粗糙度，我们提出了一种利用JRC图估计岩石裂隙剪切特性尺寸效应的方法。为了验证JRC评价方法的有效性，设计并搭建了由精密注射泵、液压活塞室、刚架和剪切箱组成的简易剪切试验装置，并利用该装置进行了剪切试验。剪切试验的试件是通过以下方法人工制备的。首先，用Brown方法建立了断裂面的数值地形数据。‘其次，利用数控成型机在造型蜡上雕刻断口，制成硅橡胶基质。最后，通过造型制作了人体骨折标本。通过这种方法，我们成功地设置了任意试件的联锁粗糙度、表面粗糙度和材料强度。制备了3种互锁粗糙度尺寸分别为2 mm、4 mm和6 mm，尺寸分别为30 mm×30 mm、60 mm×60 mm和90 mm×90 mm的试件。通过对这些试件的剪切试验，证实了峰值抗剪强度随联锁粗糙度的增大而降低的趋势。利用JRC图和Barton等人提出的方法对每个试件的JRC进行了评估，并与根据实验结果估计的JRC进行了比较。结果表明，JRC图比Barton方法给出的JRC更准确。此外，砂岩和花岗岩试件的剪切试验结果证明，只要正确评价连锁粗糙度大小，JRC图可以给出正确的JRC。

We have proposed a method to estimate the size effect on shear properties of rock fracture using JRC-diagram newly developed by us to estimate the surface roughness of a rock fracture rationally based on a fractal model. In order to confirm the validity of this our method for the JRC evaluation, simple shear testing equipment which consisted of precise syringe pump, hydraulic piston cell, rigid frame and shear box was newly designed and was set up, and shear test was carried out by using it. The specimens for the shear test were prepared artificially by the following way. First, numerical topography data of a fracture surface were created using Brown's method. ' Second, a fracture surface was carved on a modeling wax using a NC modeling machine and a matrix of silicon rubber was made. Finally, fracture specimen of mortal was made by molding. By this way, we succeeded in setting the interlocking asperity size, surface roughness, and material strength at will to any specimen. Three types of the specimen whose interlocking asperity size is 2mm, 4mm, and 6mm and whose size is 30mmx30mm, 60mmx60mm, and 90mmx90mm respectively were prepared. As a result of the shear tests for these specimens, the tendency in which the peak shear strength lowered with the increase in the interlocking asperity size was confirmed. For each specimen, JRC was evaluated by using JRC-diagram and the method presented by Barton et al., and they were compared to the JRC estimated from the experimental results. As the result, it was proven that JRC-diagram gives more correct JRC than Barton's. method. In addition, it was proven from the result of shear test for the specimens of sandstone and granite that JRC-diagram could give correct JRC, if the interlocking asperity size is correctly evaluated.