RESEARCH ON THE RELATIONSHIP BETWEEN JOINT ROUGHNESS COEFFICIENT AND SAMPLING PRECISION OF STRUCTURAL PLANE

The roughness of rock structure plane affects its shear strength. The joint roughness coefficient(JRC)has been widely used as a roughness parameter. However, there are sampling precision problems existing in the acquisition of JRC values. In order to obtain reasonable JRC values, this paper conducts a study on the precision of JRC profile sampling. 10 structure planes of sandstone, diorite and granite with a size of 10 cm ·10 cm are selected as study objects, respectively. A hand-held 3D laser scanner is used to scan the structure plane surface to obtain its geometric features. Digital processing is carried out with the help of 3D morphological image post-processing software. On the basis of this, fractal theory is selected to calculate JRC values under different sampling point spacing conditions. Then sampling point interval effects on JRC value is analyzed and its influencing factors are studied. Results show that:JRC values are affected mainly by the sample point interval on profile line. However, when the sampling interval is less than a certain critical value, the JRC basically remains unchanged. The critical interval of sampling point is related to the roughness of structural plane and has a negative exponential relation with the JRC values. In addition, the negative exponential relation is influenced by rock type. The smaller the rock particles are, the better the imitative effect is. When the three types of rock are considered comprehensively, a negative exponential function y=1.8314e^-0.067x is obtained between the critical interval of sampling point and JRC value. So, to remove the interval effects on the JRC evaluation, the critical interval of sampling points can be quantified according to the function. This study can provide a scientific method for the collection of roughness information of structural plane. And the precision and efficiency of structural plane information collection can be ensured by selecting a reasonable number of sampling points.