循环荷载下层理岩石的弹性和衰减各向异性

ELASTIC AND ATTENUATIVE ANISOTROPY OF BEDDING ROCK UNDER CYCLIC LOADING

对具有层理的砂岩进行单轴循环荷载实验,研究砂岩层理对其弹性模量和泊松比的影响。实验表明,垂直层理方向的弹性模量和泊松比小于平行层理方向的弹性模量和泊松比；衰减正好相反,垂直层理方向的衰减大于平行方向的衰减,而某个倾角层理的弹性模量在垂直层理和平行层理荷载的弹性模量之间,泊松比和衰减也是如此。从弹性系数的坐标变换出发,导出方向性模量和泊松比与岩石垂直层理、平行层理的弹性参数的关系,并用最小二乘法来进行拟合测量数据,以此关系来讨论层理砂岩弹性系数的各向异性程度。这种处理可减少计算得到的各向异性参数的误差,在泊松比计算误差较大的情况下也能得到比较理想的结果。计算表明,本实验砂岩泊松比的各向异性大于弹性模量的各向异性。

Sandstone is a typical sedimentary rock with bedding stratum as a result of weathering, transportation and sedimentation of clastic substances, which possess strong inherent anisotropy in deformation, energy dissipation and wave propagation. The effects of bedding inclination on elastic modulus, Poisson＇s ratio and attenuation of bedding sandstone are investigated by uniaxial cyclic loading tests. The data of 10 specimens in which the bedding inclinations are from 0° to 90° with increment of 10° are gained, and used to compute the anisotropy of the sandstone instead of the data in the directions parallel and perpendicular to the bedding stratum. Experiments demonstrate that the elastic modulus and Poisson＇s ratio of sandstone subjected to cyclic loading parallel to bedding are smaller than those of sandstone subjected to cyclic loading perpendicular to bedding, whereas the attenuation of the sandstone subjected to cyclic loading parallel to bedding is larger than that of sandstone subjected to cyclic loading perpendicular to bedding. Elastic modulus, Poisson＇s ratio and attenuation at any inclination bedding are between those in the directions parallel and perpendicular to bedding. By a transformation of the coordinate system, the equations linking the oriented elastic modulus and Poisson＇s ratio to the elastic parameters in the directions parallel and perpendicular to bedding of sandstone are obtained. The over-determined set of equations is solved by a least-square method to compute the elastic parameters by which the degree of anisotropy of elastic properties is discussed. This treatment can reduce the errors of computed anisotropic parameters, and even with large error of computed Poisson＇s ratio, its degree of anisotropy can also be estimated. The anisotropy of elastic modulus, Poisson＇s ratio and attenuation of Wuhan sandstone are 5.6%, 5.7% and 5.5%, respectively. The anisotropy of Poisson＇s ratio is larger than that of elastic modulus for Wuhan sandstone.anisotropic parameters, and even with large error of computed Poisson＇s ratio, its degree of anisotropy can also be estimated. The anisotropy of elastic modulus, Poisson＇s ratio and attenuation of Wuhan sandstone are 5.6%, 5.7% and 5.5%, respectively. The anisotropy of Poisson＇s ratio is larger than that of elastic modulus for Wuhan sandstone.