The paper describes the results of hard rock samples testing (Khibiny massif, Kola Peninsula) under uniaxial compression. We have established the main failure modes of the samples with height-to-diameter ratios 2:1 and 1:1. The influence of the structure features and texture on the uniaxial compression strength limit values has been analyzed. The comparison of the values with the failure modes of the hard rock has been carried out. On the basis of the studies we have established the specificity of failure processes in the samples under uniaxial compression.

1 Introduction

One of the main parameters of rock properties is uniaxial compressive strength (UCS). It is used when solving the geomechanical problems connected with substantiating mining workings strength, choosing and calculating the support parameters, forecasting the forms of dynamic rock pressure occurrence. To determine the UCS values the special developed methods are used such as GOST (GOST 1984), ISRM (ISRM 2007), and ASTM (ASTM 2010). On the basis of the methods numerous studies of the rock samples behavior under uniaxial compression are conducted (Baron et al. 1962, Hoek & Bieniawski 1965, Turchaninov et al. 1967 and Jaeger et al. 2007 etc.). The results of studies have shown that one of the main difficulties is connected with investigating hard rock which UCS values change within the range from 50 to 300 MPa (Turchaninov et al. 1967). This is related to the fact that to obtain reliable data we have to use test equipment with high rigidness and loading capacity.

Recently the method based on establishing of rock samples' failure modes is obtaining wide growth. The modes depend on the loading device rigidness, structural discontinuities, cleavage and size of the crystal. In the studies of Li et al. (2011), Maji (2011) and Basu et al. (2013) there is an attempt to relate the UCS values of rocks with their failure modes. However according to Esamaldeen et al. (2014) less attention is given to the investigation of structural discontinuities influence. In addition there is no clear evidence whether the rock samples with height-to-diameter ratios 2:1 and 1:1 would have the same failure modes.

On the basis of foregoing it is important to study the relation between failure modes of heterogeneous hard rock samples with their UCS values.

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