Numerical Simulation for Predicting The Anisotropy of Faryab Cromite Rock Using PFC Software

Summary:

In this research, a series of experimental tests and numerical models, including simulation of Uniaxial Compressive Strength test (UCS), Brazilian Tensile Strength test (BTS), and Triaxial Compressive Strength test (TCS), are performed to investigate the anisotropy of rocks from Faryab Chromite Mine. Based on the results of this study, it was found that the highest anisotropy occurred between the X-direction and other directions (Y and Z). The difference in the strength properties of the X-direction compared to other directions was not so great, and the rock samples of Faryab Chromite Mine have low anisotropy also the lateral pressure on chromite rocks has a great impact on their mechanical properties.

Anisotropy can be considered as one of the main behavioral characteristics of different rock masses and this behavior is mainly due to the non-uniformity and irregular geometry of rock fracture systems. Due to the different mechanical behavior of anisotropic rocks under tension or pressure in different directions, it is necessary to study the anisotropy behavior of rock masses more carefully in the designs to prevent possible accidents. The novelty of the research is that so far not much information is available on the effect of microcracks and anisotropy on the tensile strength of chromite rock samples.

Methodology and Approaches:

After dividing the main block into smaller parts, cores were taken from rock blocks for analysis, then in order to determine the mechanical properties of rock, several laboratory tests were performed on the cores. To evaluate the behavior of the samples in the uniaxial compressive strength test, samples with a diameter of 54 mm and a height of 115 mm are considered. the Brazilian test was also used to evaluate the tensile strength of rock samples which are cores with a diameter of 54 mm and height of 27 mm. Numerical simulation was performed by using PFC and particle size is controlled by using two parameters: minimum particle radius (Rmin=0.45) and maximum particle radius (Rmax=0.675) and has a normal size distribution.

The highest ratio of anisotropic rate is related to the X and Y directions and therefore it can be inferred that the rocks have low anisotropy in the compressive state. Also, it was observed that chromite rock samples in the tensile state showed brittle behavior in all three directions and the tensile cracks were the most common cracks. In this analysis, a lateral pressure of 5 MPa was applied to the samples and it was observed that all three directions showed ductile behavior. In these tests, the expansion of shear cracks had the greatest effect on the failure of rock samples and it was observed that in the enclosed state (triaxial test) the highest anisotropy occurred in the rock samples between the X and Z directions, which is different from the unenclosed state (uniaxial test).