|
Abstract Based on the briquette specimens of the outburst coal seam of typical coal and gas outburst mine of Datong in Songzao，the experimental study of unloading confining pressure of briquette specimen is performed by means of mechanical testing machine MTS815. The results are shown as follows：(1) unloading confining pressure with displacement control leads to the dilatancy and damage of briquette specimens，unloading confining pressure with load control leads to the failure of briquette specimens；(2) if the confining pressure is unloaded by means of displacement control，within a certain range of initial confining pressure，the axial stress of briquette specimens drops with decreasing confining pressure，and the velocity of axial stress drop rises，the nonlinearity of curve of unloading confining pressure is more significant when unloading confining pressure in yield phase than that in elastic phase；the nonlinearity is more and more obvious with the increase in initial confining pressure；(3) if the confining pressure is unloaded by means of load control，within a certain range of initial confining pressure，the axial strain of briquette specimens rises with decreasing confining pressure，the velocity of axial strain rise increases，the increase in axial strain is more significant when unloading confining pressure in yield phase than that in elastic phase. The increasing failure is more and more obvious in yield phase with the increase in initial confining pressure；the work of testing machine done in the process of unloading confining pressure can be calculated and analyzed according to axial strain. Based on the test results，combining with the test results of permeability of briquette specimens in the complete stress-strain process，the permeability curve of briquette specimens in the process of unloading confining pressure is deduced. Based on these results，using damage theory and Mohr-Coulomb theory，the formula for calculating the damage of briquette specimens containing gas in the process of unloading confining pressure is derived. The study results have a reference value for predicting gas emission and failure in the process of unloading confining pressure.
|
|
Received: 13 March 2010
|
|
|
|
