Dynamic Rock

Dynamic rock

Dynamic Rock

Introduction

A variety of techniques are used to extract minerals around the world, including drilling, blasting, excavating, crushing and cutting. The success of these operations often requires knowledge of the relationships between rock properties such as porosity, unit volume weight and Schmidt hardness, and rock dynamic mechanical properties such as compressive strength and elastic modulus. However, in the past, relatively little work has been done to investigate the dynamic mechanical behavior of rock materials. Rock mass properties are of great importance concerning drilling, excavation, and blasting, sawing and crushing performance. There are many publications in the rock mechanics literature about selection of equipment by considering geotechnical parameters of the rock mass, and various empirical approaches have been proposed in these publications. One of the parameters that are widely used in those empirical approaches is the quasi-static uni-axial compressive strength of the rock material. Nevertheless, civil engineering structures, designed for either civilian or military use, could be subjected to dynamic loads that they were not originally designed to resist. Such dynamic loads can arise from natural phenomenon (e.g. earthquakes) or from accidental explosions caused by deflagration of natural gas or rapid chemical reaction (e.g. detonation of high explosives).

Discussion

A considerable number of studies have been conducted in recent years to study cutting, excavating and drilling efficiency in rocks. Most of these studies establish relations between the quasi-static mechanical properties of rocks and the cutting and drilling speed or wear ratio of bead or socket parameters for rocks. Those relations were used to derive the equations that predict the cutting or drilling rates from the quasi-static compressive strength properties of the rock samples. However, dynamic failure of rocks is a commonly observed phenomenon in rock bursts, earthquakes, and mining operations such as drilling, cutting and excavation.

The quasi-static compressive strength of rock materials has been used as an important parameter for almost all empirical approaches in the previous studies that predict the efficiency of rock operations and develop the operational parameters such as cutting and drilling rates, wear ratio and blade life. However, as mentioned in the previous paragraphs, dynamic loading conditions are encountered in rock operations, and the mechanical behavior of the rock materials, as other engineering materials, could be significantly different under dynamic loading conditions. Therefore, inclusion of the dynamic compressive strength, rather than the quasi-static compressive strength, into the empirical approaches and the operational parameters might give better results regarding the performance of the rock operations. To accomplish this, it is first necessary to determine the dynamic compressive mechanical properties of the rock materials and their relations with the physical properties such as porosity, unit volume weight and Schmidt hardness.

The split Hopkinson pressure bar (SHPB), originally developed in 1950s by Kolsky to test metallic materials under compression at high strain rates, has received considerable attention for characterizing the dynamic response of a variety of engineering materials. The materials studied with the SHPB were mostly metals in the past, the plastic behavior and rate dependence of which have been ...