露天煤矿冻岩边坡饱和砂岩冻融损伤试验与劣化模型研究

Damage test and degradation model of saturated sandstone due to cyclic freezing and thawing of rock slopes of open-pit coal mine

高海拔多年冻土区露天煤矿岩质边坡常年处于冻融交替环境中,边坡浅部病害显著。为了分析边坡上岩石在冻融环境中的劣化规律,利用采集于木里地区露天矿边坡钻孔中的砂岩试样进行了室内饱和冻融循环试验,并建立了饱和岩石冻融劣化的理论模型。岩样冻融循环试验结果显示随着冻融循环次数的增大,饱和砂岩的微裂隙率逐渐增大,单轴和三轴抗压强度以及表示岩石质量的常见物理参数逐渐降低。基于岩石在冻融循环过程中的微裂隙变化,提出并推导了微裂隙扩展因子,理论建立了岩石强度随冻融循环变化的劣化模型和本构关系,利用劣化理论模型所计算的岩石强度与试验结果吻合较好。分析岩石微裂隙的变化规律,可以获得饱和砂岩在冻融循环环境中的劣化是由于岩石内部的微裂隙在水成冰相变过程中产生的巨大复合应力超过了岩石微裂隙开裂强度,而导致微裂隙逐渐失稳扩展,岩石整体性被削弱等结论。

The slopes of open-pit mine are always in freezing- thawing environment in permafrost region, and the surface rock of slopes is weathering during the freezing- thawing cycles. The cyclic freezing-thawing tests on the saturated sandstone from the mining area in Muli were completed in laboratory in order to understand the physical and mechanical characteristics of saturated rock in freezing-thawing cycles. The degradation model for the saturated rock was studied. The micro-fracture rate increases gradually with increasing the freezing-thawing cycles, but the uniaxial and triaxial compression strengthes and other physical parameters decreases with the number of the freezing-thawing cycles. The micro-fracture propagation factor was suggested according to the micro-fracture change in the freezing-thawing cycles. The theoretical damage model and constitutive relations of rock strength were established using the micro-fracture propagation factor. The proposed model explained quantitatively the damage of the saturated rock due to freezing-thawing. The theoretical strength calculated with the damage model matched well with the test results. The composite stress generated due to water transformation to ice exceeded the strength of rock and drove the micro- fracture to expand.