Effect of fractal dimension of blocks on the shear strength of blocky pyroclastic rocks

Abstract

In this study, the relationships between shear strength of a blocky rock mass consisting of pyroclastic deposits and the fractal dimension of the blocks within the rock mass were investigated. Within the scope, triaxial shear tests were performed on specimens extracted from a blocky pyroclastic rock mass that defined as “bimrock” in terms of jeo-mechanical description. Thereby, cohesion (c) and internal friction angle (?) values of the rock mass were determined. Fragmentation fractal dimension (DF ) and roughness fractal dimension (DR ) values of the blocks within in the rock mass were calculated through the fractal dimension solutions and digital image processing analysis. In addition, uniaxial compressive strength of the rock and the matrix component of this rock mass were determined. The results revealed that there are positive and negative linear relationships between DR and c, ? and between DF and c, ? pairs. It is determined that, while the values of both DR and DF increase, the values of ? increase and vice versa for cohesion. The increase of ? with the increase of DR is an indication that the friction also increases by applied shear stresses due to the increase in the roughness of the block surfaces. Finally, the increasing of DR yielded an increase in the sum of the surface areas of the contacts between the matrix and blocks. Thus, the cohesion decreases due to the probable increase of weakness zones that loosen the rock mass. © 2021, TMMOB Chamber of Geological Engineers. All rights reserved.