循环加载高应力对大理岩Kaiser效应影响的试验研究

Experimental study on the effect of high stress cyclic loading on Kaiser effect in marble

声发射法(AE)广泛用于地应力测量。当单次加载Kaiser效应不明显时,可采用循环加载方式。通常各循环峰值加载应力大于岩石在地壳中所受最大应力?m,将大于?m的加载应力称为高应力。为研究高应力对岩石Kaiser效应的影响,对取自铜绿山矿的垂直钻孔岩芯进行循环加载试验,根据声发射特征曲线变化趋势及变形率分析法(DRA)地应力测量结果,对比水压致裂法所测地应力量值,确定不同加载阶段Kaiser效应点位置。研究结果表明:当循环加载峰值应力大于?m时,高应力将削弱与?m对应声发射事件的能量,使后续加载循环Kaiser效应不明显,同时会改变岩石之前记忆的应力值,使AE法地应力测量结果产生偏差;多次循环加载可导致岩石内部微结构面的破坏,其产生的大量声发射事件会混淆Kaiser效应点的辨识;因岩石差异性,高应力可能会取代岩石之前所受最大应力,成为岩石记忆的新应力。鉴于此,采用循环加载方式时,首次加载峰值应力A?应不超过?m,同时应使岩石跨过压密阶段进入线弹性阶段。铜绿山矿所取岩样循环加载试验结果表明,A?较合适的取值范围为岩石单轴抗压强度的6%~28%。此外,还给出声发射法和DRA法联合用于地应力测量的合理加载方式。

Acoustic emission method（AE） is widely used in in-situ stress measurement. The cyclic loading method can be employed when the Kaiser effect is less pronounced in one cycle uniaxial compression test with AE monitoring. Usually,the peak stress of each cyclic loading is greater than the maximum stress δm that the rock ever experienced in the earth＇s crust. To study the effect of the high stress on Kaiser effect of rock,cyclic loading test on marble specimens from the vertical drilling hole of Tonglushan mine was carried out. The take-off points in different loading cycles were determined according to the characteristics of AE curve and the results of in-situ stress measured with the methods of deformation rate analysis（DRA） and hydraulic fracturing. The results show that the high stress reduces the energy of AE events corresponding to δm,diminishes the Kaiser effect in subsequent loading cycles and changes the magnitude of memorized stress in the rock at the same time. The repeated cyclic loading leads the destruction of rock＇s internal microstructure,and the resulted AE obscures the take-off points. Besides,the high stress may replace δm and becomes the new stress memorized in the rock due to the differences of rock. In view of this,the peak loading stress of first cycle should not exceed δm,and must make the specimen to enter the linear elastic stage. The reasonable range of the peak loading stress of first cycle is 6% to 28% of rock＇s ultimate strength. In addition,the reasonable loading mode when AE and DRA method combined to measure geostress was given in the paper.