Study on deformation and permeability properties of raw coal during alternate loading and unloading

Abstract

The deformation and permeability experiments of raw coal in the process of alternating loading and unloading under variable axial pressure loading rate are carried out by using the thermal fluid structure coupling servo experimental system, and the deformation and permeability characteristics of coal containing gas in the process of alternating increasing axial pressure and unloading confining pressure are analyzed. The results show that during the process of loading axial stress and unloading confining pressure, the specimen presents axial compression deformation and radial expansion deformation, and the axial compression deformation and radial expansion deformation gradually increase with the decrease of confining pressure stress level. It is considered that the sample shows axial compression deformation and radial expansion deformation in the process of loading axial stress and unloading confining pressure, and the deformation of axial compression and radial expansion gradually increase with the decrease of confining pressure stress level. The permeability decreases slowly during loading axial stress and increases slowly during unloading confining pressure, which satisfies the quadratic function relationship. The change rate of axial strain, radial strain and permeability under unit stress state are used to analyze the influence characteristics of axial stress and confining pressure on the deformation parameters of the sample. The variation rates of axial strain, radial strain and permeability in unit time are used to analyze the influence of variable axial compression loading rate on the deformation parameters of the sample. With the increase of axial load strength and axial stress loading rate, the absolute value of variation rate of axial strain and radial strain gradually increases, and the absolute value of permeability variation rate first increases and then decreases. On the contrary, with the decrease of axial stress loading rate, the absolute values of axial strain, radial strain and permeability first increase and then decrease. In the process of unloading confining pressure, the absolute values of axial strain and radial strain change rate of the two samples gradually increase, while the change law of permeability change rate is opposite.

Keywords

• alternate loading and unloading
• variable axial pressure loading rate
• raw coal
• deformation properties
• permeability