Rigorous experiments have established the regular relationships between the longitudinal and transverse strain under the stress limit and under the ambient pressure. Characteristic points on the plots were utilised to define the pressure involved in transition from brittle cracking to ductile flow and the pressure involve in the rock becoming fully ductile.

Experiments have revealed that when the ambient pressure exceeds the crack locking pressure or the pressure leading to lasting deformation, the inclination angle of the curve expressing the dependence between the yield strength and the ambient pressure will be increased.

Rock strength properties and rock deformability are given a synoptic description basing on the research data collected by the authors.

The dependence is revealed between the pressure of sorbed carbon dioxide and the transition pressure and coal ductility.

It is revealed that rock properties will change when subjected to hydrostatic squeezing under sufficiently high pressures.

During the sorption swelling of coal and rock after imposing the constant dimensions of samples initially loaded with a constant force, two opposite processes are observed: stress increase due to swelling and stress relaxation.

Experiments have revealed a dependence between the pore structure in rocks and the influence of the pore pressure on the stress limit and strain at the stress limit of rocks under the triaxial state of stress.

Research was undertaken to investigate the effects of water sorption or carbon dioxide under pressure on rock properties under the triaxial state of stress: stress limit, strength limit, elastic constants. The behaviour of rocks and coal was studied during the water absorption or carbon dioxide.

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