基于灰度方差统计的冰水堆积体细观建模与力学特性研究

MICROSCOPIC MODELING AND MECHANICAL PROPERTIES OF OUTWASH DEPOSITS BASED ON OTSU STATISTIC OF IMAGE GRAY

提出一种基于数字图像处理技术生成颗粒流模型模拟冰水堆积体力学特性的新方法。该方法以基于比特平面分解的图像消噪技术对数字灰度图像进行预处理,采用最大类间方差算法求解自适应阈值实现图像二值化分割,通过最近像素插值算法建立反映冰水堆积体细观结构的隔层错位模型。将该方法应用于云南古水水电站坝前冰水堆积体工程,通过双轴压缩试验模拟表明:该方法能克服基于像素直接对应建立模型时发生轴向压缩的缺点;由土石混合而成的冰水堆积体在双轴压缩下的应力–应变关系呈硬化特性,岩块的存在增加了弹性模量和峰值强度;土体黏结强度提高对峰值强度有影响,但对初始弹性模量影响不明显;低应力条件下,堆积体近似满足莫尔–库仑强度准则,且与剔除块石影响的"土体"相比,内摩擦角提高了0°～9°,黏结力提高了300 kPa。该方法可为现场冰水堆积体的参数确定提供理论依据。

Based on digital image processing technology, a new method which can generate particle flow model from digital image is proposed to simulate mechanical behavior of outwash deposits. First of all, it implements preprocessing of digital image according to denoising method of images based on their decomposed bit planes. And then, Otsu is used to gain the adaptive threshold to accomplish the binarization of image so that soil and rock can be divided. Finally, it is the two dimensional particle flow code（PFC2t~） compartment dislocation model of the real microstructure that can be built up by the proximate pixel interpolation algorithm. As an example, a outwash deposit ease located at the front of Gushui hydropower station in Yunnan province is used, and the numerical simulation of biaxial compression tests are applied according to above-mentioned method. The results show that this new method overcomes the shortcomings of the axial compression compared with that builds up directly according to the position of pixel. The relationship between the stress and strain of outwash deposits has a feature of hardening under biaxial compression, and it also enhances the elastic modulus and peak strength because of the existing of rock mass. The increasing of bonding strength between soil particles has a greater impact on peak strength of the outwash deposits, while it isn＇t obvious on initial elastic modulus. The outwash deposits meet Mohr-Coulomb strength theory approximately under low stresses. The angle of friction increases from 0 ~ to 90~ and the bonding strength also increases about 300 kPa compared with soil material excluding the impact of rock mass. Anyway, this method provides the basis of theory for the field outwash deposits in determination of parameters.