Permeability evolution of broken coal under triaxial stress

The deep broken coal and rock mass are often in the state of triaxial stress,due to the crustal stress and min- ing disturbance,and its permeability is one of the important factors that affect the prevention of mine water inrush dis- aster and gas drainage. This research aims to carry out the seepage test of broken coal under the triaxial stress,using the self-developed triaxial permeability test system for broken rocks,and the evolution law of the permeability charac- teristics of the broken coal with the confining pressure and the porosity are obtained. The results are as follows ① the maximum Reynolds number in fluid flow through broken coal under triaxial stress is 47. 58,and the seepage velocity and pore pressure gradient are fitted by the Forchheimer relationship. ② Under triaxial stress,there is a negative corre- lation between the porosity and confining pressure of broken coal,and both agree with the logarithmic function relation- ship. ③ The theory of broken coal porosity values are close to the experimental results,and the porosity decreases with the increase of the effective stress. Thus it shows that the calculation method of porosity is feasible. ④ Under the axial displacement at all levels,the permeability of broken coal decreases with the increase of confining pressure,and the e- volution law of permeability of broken coal with different diameter sizes with confining pressure can be expressed by formula k = menσ3 . The larger the particle size,the more sensitive the permeability of the broken coal changes with the confining pressure. ⑤ The permeability of broken coal is affected by particle size and pore arrangement. With the de- crease of porosity,the permeability of the broken coal in different diameter sizes are on the downward trend,and non- Darcy flow β factor increases,integrally. The order of the permeability is 10-14 -10-10 m2 ;the order of non-Darcy flow β factor is 107 -1011 m-1 . The results will be helpful to the understanding of permeability evolution of broken coal and rock mass.