ANALYSIS OF SIZE EFFECT OF STRUCTURAL SURFACE ROUGHNESS BASED ON IMPROVED PROJECTIVE COVERING METHOD

The surface roughness is one of the important factors in the mechanical properties. And,more significantly,the surface roughness has size effect characteristics. So,investigation of size effect characteristics of surface roughness is of great significance for further understanding of mechanical properties of structural surface. In view of this,firstly,we improve the Projective Covering Method by a new calculation that the random number is applied to the triangular element division. Secondly,to investigate the size effect of surface roughness of rock joints,we select six sampling windows,respectively,from the central and four corners part of structural planes(2 m×2 m). The sampling windows range from 62.5 mm×62.5 mm to 2000 mm×2000 mm. And then,we calculate fractal parameters of the different size surfaces using the improved projective covering method at the same resolution. Thirdly,we discuss the method of determining the reasonable structural surface by the parameter ΔD_max^SD. This parameter is the difference of the maximum fractal dimensions of the same size structural surfaces in different regions. The results show that:(1) The size effect of structure surface is different with different morphological surface. Generally,as the size increases,the roughness of structure surface increases and then decreases. There is positive size effect in small scale and negative size effect in large scale. (2) For a certain structural surface,when the same size surfaces are selected from different locations of the structural planes,and the size effect characteristics are also different. (3) As the size of the structure surface increases,the parameter ΔD_max^SD gradually decreases and tends to almost constant. The result of this study is a useful supplement to the comprehensive understanding of the size effect of structural surface roughness.