Abstract:

A number of studies have been conducted to investigate the relationships between point loading strength (PLS) and uniaxial compressive strength (UCS). The method is widely used in on-site tests because it is convenient and the requirement for the sample in PLS is not very strict. However, it's difficult to get an accurate relationship between UCS and PLS in laboratory due to strong heterogeneity of rocks. Discrete element method (DEM) has been proved to be a great tool to simulate and analyze the behavior of rock material. In DEM, the particle properties (such as particle contact modulus) can be set to ensure the rock materials to possess the same properties. So we can get the correct correspondence between PLS and UCS. In this paper 23 sets of data are simulated which from the laboratory test, and it is found that there are good correspondences. Through further analysis, the authors also discuss the influence of experimental conditions on the PLS by DEM, which includes indenter radius, aspect ratio and particle size. By the simulations, we reached three conclusions: 1) the simulated result is higher than that of laboratory test in PLS because of homogeneity; 2) the larger indenter radius, the higher PLS will be; 3) PLS is nearly a constant when the aspect ratio of samples is between 0.3 and1. Besides, if the aspect ratio is lower than 0.3, the PLS will increase rapidly.

Introduction

In rock mechanics, how to describe the mechanical properties of rock accurately has been one of the key issues. So far, some methods can be applied to measure the mechanics properties of rock, such as point loading test, uniaxial compression test, conventional tri-axial compression test, Brazilian disc test, and fracture toughness test. The detailed standard specifications for these experiments are all published (Franklin, 1985; Hatheway, 2009). As one of the main properties, uniaxial compressive strength (UCS) can be measured commonly through uniaxial compression test.

However, uniaxial compression test itself has some disadvantages. First of all, it is time-consuming and expensive to make a high precision sample. The flatness of specimen ends must be machined to 0.001 mm. The side must be smooth and straight and the smoothness of all side must reach 0.3 mm (Hatheway, 2009). And then, some of the rocks are difficult to be processed into standard specimens, such as coal, which is featured by cleats. On the other hand, point loading test is convenient and simple to measure the strength of rock, because it is not strict with the shape of the specimen, and we can get results with any size. Moreover, the point loading test instrument is easy to carry. Point loading test has been widely used in the field of engineering because of these advantages.

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