Abstract

This paper used PFC2D to simulate bimrock mechanical behaviors under uniaxial compressive tests and presents the means and variances of uniaxial compressive strength (UCS), Young’s modulus (E), and Poisson’s ratios (?) for various volume fractions and strain gauge lengths. The results show that UCS, E, and ? increase as Vf increases, and simulated E and ? were consistent with the differential scheme and Hashin-Shtrikman bounds. In quantifying the uncertainty of Young’s modulus and Poisson’s ratio measurements using a strain gauge, the measurement uncertainties initially increase and then decrease with increasing Vf; when Vf =0.3~0.4 (0 or 1), Young’s modulus and Poisson’s ratio reach a maximum (minimum) value. In addition, crack propagation was also observed and discussed in this paper.

1. INTRODUCTION

Rock strength and its elastic modulus are important geotechnical engineering parameters. However, it is difficult to obtain completely mechanical behaviors if rocks belong to highly heterogeneous media, i.e., mélange and fault breccia, which are considered as a type of bimrock, and defined as "a mixture of rocks, composed of geotechnically significant blocks within a bonded matrix of finer texture" [1]. Because bimrock has chaotic block dispersion, it is difficult to sample the representative specimen. In addition, its engineering characteristics and mechanical behaviors are more complicated than other geomaterials. Volume fraction (Vf) plays an important role in bimrock mechanical behaviors [2-6].

Bimrock spatial variability could cause uncertainties in physical and mechanical measurements. Medley [7] manufactured physical synthetic bimrocks to investigate the uncertainty of Vf estimation using the scanline method. Tien et al. [8-10] proposed analytical and numerical solutions for quantifying the uncertainty of Vf measurements using the scanline method and a sampling window. Kahraman and Alber [3, 11-12] tested various sizes of fault breccia with a uniaxial compressive test; the results show that the variability of fault breccia strength decreases with increasing size.

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