Characteristics of stress-strain and strain-permeability of coal-bearing sedimentary rocks

The characteristics of permeability of the sandstone of coal seam 3 roof and red bed threatening the mining activities were analyzed by spot sampling and laboratory experiments on rock samples of No.3 Jining coal mine. The test results indicated that permeability of medium-coarse sandstone is the biggest, but that of mudstone is the smallest; Stress has great influence on the permeability in different ways which include closure in the normal direction and dilatancy effect of joints, stress dilatancy changes the permeability of rock significantly; strain-permeability curve of rocks displays lag of permeability peak value. The rock permeability changes acutely and unpredictably at phase of elastic-plasticity, however, there is a good agreement between permeability and volumetric strain. By summarizing and analyzing the experimentation results, permeability variation can be divided into 5 stages:stage of consolidation and closure of microfissures, stage of random expansion of microfissures, stage of propagation and cutthrough of fissures, stage of diastrophsm and sufficient development of fissures, and stage of secondary closure of fissures.