锦屏一级水电站左岸浅表大理岩的卸荷微裂隙特征

CHARACTERISTICS OF UNLOADING MICRO CRACKS IN SHALLOW ROCK MASS AT LEFT BANK OF JINPINGⅠHYDROPOWER STATION DAM

在高山峡谷区,浅层岩体的表生改造相当发育。在锦屏一级水电站坝区陡峭的岸坡浅表大理岩岩体中采集定向标本,制作定向薄片,利用偏光显微镜统计和分析了微破碎带及带中微裂隙的方向分布情况。结果表明,(1)垂直于最小主应力σ_3的薄片中微破碎带在整体上未见明显定向性,垂直于最大主应力σ_1或中间主应力σ_2的薄片中微破碎带在整体上存在明显定向性,基本与岸坡平行;(2)微裂隙往往沿低指数晶面(包括解理面)发生,故晶内裂隙表现出直线式或台阶状样式,这符合最小能量原理;(3)卸荷应力场诱导控制微观卸荷裂隙的方向并使之具有强定向性。

In the mountain valley area,epigenetic deformation of the shallow rock mass is common. Directional samples are taken at left bank of Jinping Ⅰ hydropower station dam. Thin sections are made. Direction distribution of micro fracture zones and micro cracks are analyzed by polarization microscope. Three conclusions are drawn.Firstly,micro fracture zone in thin section which is perpendicular to σ_3 has no obvious directionality,but micro fracture zone in thin section which is perpendicular to σ_2 or σ_1 is parallel to bank surface. Secondly,micro cracks tend to occur along low index plane including cleavage plane,which accords with least energy principle. So intracrystalline cracks in calcite crystal show linear or step style. Thirdly,unloading stress induces and controls the direction of micro cracks,so micro cracks have obvious directionality.