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Abstract The splitting of stressed rock in the neighborhood of underground openings is a common phenomenon that is not well explained theoretically up to the present. The stress concentration at nonuniformities is believed to be the crucial one among the factors influencing the tensile failure process under pressure conditions. Based on the model of rock with nonuniformities，three main factors of the splitting fracture of rock，including unloading duration(or deviator strain rate)，scale of nonuniformities and initial geostress，are detailed investigated in order to reveal the mechanism behind the phenomenon of splitting. The results of theoretical analysis show that：(1) The excess tension stress of nonuniformities is affected by deviator strain rate significantly；and it increases nonlinearly as the unloading duration shrinks. (2) There is a nonlinear corresponding relationship between the scale of nonuniformities and the magnitude of deviator strain rate；and higher deviator strain rate tends to excite smaller nonuniformities. (3) If there exist nonuniformities with big scale enough，the maximum excess tension stress is proportional to the initial geostress. Therefore，the possibility of unloading splitting is determined by the relation among the three parameters：initial geostress，stress concentration coefficient and tensile strength. Results of an unloading test，in which the axial stress of hydraulic stressed rock samples is unloaded with different control modes，and data of in-situ core disking observation，are cited to verify the analytical analysis results. The main phenomena and critical stress condition of core disking predicted by the theoretical model coincide well with the results of the cited experiments and in-situ observation data.
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Received: 18 January 2010
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