Stress dependence of elastic P-wave velocity and amplitude in coal specimens under varied loading conditions

Experiments allowed finding regular patterns in propagation of elastic P-waves in specimens of black coal exposed to uniaxial compression and triaxial compression by von Karman. It is shown that in case of uniaxial compression, the largest information content is ensured by translucence in perpendicular to bedding and loading axis of coal specimens. Such translucence exhibits four stages of deformation of a specimen. The information content of translucence under triaxial compression reduces with the increase in the constrained pressure that prevents from disintegration of a coal specimen. Four deformation stages are best identified with the constrained pressure of 2.5 MPa, while only stages of specimen consolidation and failure are traced at the pressure of 10 MPa.