Abstract

Rock masses contain cracks and discontinuities which have an influence on their elastic properties and on velocity of seismic waves. Seismic waves velocity can vary depending on the direction of propagation. This effect is called seismic anisotropy. This paper presents results of the research which concern directional changes of dynamic elastic moduli. They were calculated on a base of P- and S-wave velocity obtained from laboratory and field measurements for Triassic carbonate rocks. In the same quarry the geometry and orientation of main crack systems were measured. On the base of these data obtained the information about main crack systems. The application of direct, laboratory and seismic methods allowed to obtain a lot of information about fractured rock mass. They are useful tool to study the degree of fracturing and rock massifs quality assessment for engineering purposes.

1 Introduction

The crack systems which exist in rocks decide about their physical properties. Especially, they have an essential influence on velocity of seismic waves propagating through the fractured rock mass. It is well known that oriented cracks produce velocity anisotropy. The velocity of the P-wave is maximum for a wave propagating parallel to the crack strike and is minimum for the wave propagating perpendicular to it. This problem has been studied by many researchers (Bamford & Nunn 1979, Crampin 1980, Crampin 1993, Vilhelm et al. 2010, Stan-Kleczek & Mendecki 2014). If two or more systems of parallel cracks exist in rocks, the minimum value of velocity is observed for the wave propagating diagonally to crack systems. This dependence allowed to develop a method of seismic anisotropy measurements to study seismic wave velocity in a rock mass. Velocity of P- and S- waves can be also used to assign dynamic elastic moduli of rock mass (Stan-Kłeczek & Idziak 2008, Živor et al. 2011). Dynamic modulus can be calculated using P – and S- wave seismic velocity measured by refraction method directly in the quarry or determined on samples using ultrasonic equipment.

The aim of research was to establish directional changes of dynamic elastic moduli for Triassic dolomite and compare them with results obtained for samples of this rock.

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