不同含水率砂岩无损检测参数的尺度效应研究

Research on nondestructive testing parameters' scale effect of sandstone of different moisture contents

利用螺旋CT机和智能超声波测速仪对5种尺寸的砂岩试样进行干燥及不同饱和条件下的无损检测试验。试验结果表明,当试件直径一定时(D=50 mm),真空饱和法吸水率比自然浸水法略大,饱和吸水率与试件高度几乎成线性相关,试件两个方向的尺寸比值为2.0附近时其吸水能力较强,高径比最大的h/D=3.5时其吸水能力最差;由于岩石天然缺陷造成的各向异性,试件尺寸选取越小其各向异性指数越高,尺寸足够大其宏观均匀性才明显;砂岩的宏观力学参数和细观特征都存在尺度效应,当试件高径比h/D<2.0时岩样的弹性模量波动比较大,当高径比h/D≥2.0时试件计算弹性模量随着高度的增加而缓慢增加。得到了不同含水率砂岩无损检测参数的尺度效应方程,公式表明砂岩的吸水效果与试件的纵波波速的平方和CT数反比例相关,对于研究水岩相互作用时考虑试件的尺度效应有一定的指导意义。

Spiral CT(Computerized Tomography)and intelligent ultrasonic velocimeter were used in the non-destructive testing of five sandstone samples of different scales under the condition of drying and of different degrees of saturation. The test results show that water absorption of vacuum saturation method is a bit bigger than that of natural immersion method(D = 50 mm); saturated water absorption and the height of specimen are almost linearly related; the water absorbing ability of the specimen is weakest when the height to diameter ratio(h/D) is maximum and its value is 3.5, while it is relatively strong when the size ratio in the two directions is near two; duo to the anisotropy of rock caused by its natural defects, the smaller specimen size is, the higher anisotropy index will be, and the macro-uniformity of the specimen will be obvious when the size of it is large enough; both of the macro mechanical parameters and micro mechanical parameters of sandstone are of scale effect, The variation of the elastic modulus of the rock specimen is huge when its height to diameter ratio is less than two(h/D<2.0) and the calculation elastic modulus of the rock specimen increases slowly with the increase of height when its height to diameter ratio is greater than or equal to two(h/D≥2.0). Nondestructive testing parameters' scale effect equation of sandstone of different moisture contents is obtained in this article; the formula shows that squares of the test specimen's longitudinal wave velocity and numbers have inverse correlation to the water absorption effect of sandstone; the result is of certain guiding significance for the research of water rock interaction when considering the scale effect of the specimens.