Unloading confining pressure tests are conducted before different pre-peak confining pressure of gneissic granite obtained at the foundation of Xiaowan hydrodynamic station, the results show that the deformation modulus changes little, but poisson' s ratio increases greatly compared with the loading conditions under the same confining pressure. Samples with different sizes will show different behaviors under the same unloading confining pressure, and the sample with a larger size will show tensile failure; The peak-stress of the sample will increase linearly with the confining pressure increasing, and size effect is obvious, namely, the larger the size of sample, the less the influence of the confining pressure change.%对小湾水电站坝基花岗片麻岩试件进行了室内不同直径、不同峰前围压卸荷试验.结果表明:相同围压下,卸载同加载相比,变形模量变化不大,但泊松比大幅增加,甚至会超过0.5;在相同围压卸荷时,不同尺寸的试样会呈现不同的破坏性状,尺寸越大,越容易产生张破坏;岩块的峰值强度随着围压升高呈线性增加,且尺寸越大受围压变化的影响越小,存在明显的尺寸效应.
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