Basic Expererimental Study On Characteristics Of Strength, Deformation And Microseismic Under Compression Of Coal

Adapting MTS815.03 servo-controlled rock mechanical test system, a large number of tests of coal samples under uniaxial compression, triaxial compression, cyclic loading, permeability during the complete stress-strain path are carried out; besides, acoustic emission of coal and rock samples under uniaxial compression rapture process and microseism monitoring on fracturing and destabilizing of overburden strata of coal face are carried out. The characteristics of strength, deformation and microseism of coal are fairly analyzed and studied.Through analysis of scanning electronic microscopy measuring and mechanical test of coal samples, coal obviously has the mechanical characteristics such as discontinuousness, anisotropy and heterogeneousness. The strength and deformation of coal is largely influenced by the original damage variable. The exponential function relationship between the strength and the corresponding P-wave velocity of coal sample has high confidence degree which is regressed from test results of a large number of coal samples. This provides basis for choosing proper coal samples before carrying out comparative experiments such as strength in order to avoid blind experiments.The characteristics of deformation and rapture evolvement can fairly be described by the feature of acoustic emission of coal. Due to the development of primary damage, the micro-porosities and micro-cracks are compacted and closed by confining pressure, the stiffness of coal is increased and the relationship between elastic modulus and confining pressure conforms to quadratic polynomial function. The segmental constitution equation of coal is obtained through fitting method according to the triaxial compression test results and simplified model. The characteristic of triaxial compressive fracture of coal conforms to Coulomb strength criterion, but due to the large quantities of micro defects in coal, along therandom fissures, the possibility of fracture angle departed for θ₀ = 45° + φ/2 is big. Comparing with hardand compact rocks, coal is inclined to fatigue damage under cyclic loading. The value of fatigue damage "threshold" of coal is relative with its micro structures and micro components. The deformation and fatigue damage process of coal is in close accordance with its damage accumulation. The permeability rate-strain and stress-strain curves of coal are on the whole the same but the permeability rate-strain curve is relatively "hysteretic" which indicates that the close relativity between the evolvement of damage and the development of permeability rate and the permeability developing needs a time course. The segmental permeability rate-strain curve equations are obtained through fitting method according to the experimental results.