基于Matlab和IPP的黄土孔隙微观结构研究

黄土的孔隙结构是区别于其他土类的重要特点之一,黄土的湿陷、震陷等宏观力学表现与其孔隙结构密切相关。本文开发了利用Matlab和IPP(Image-Pro Plus)软件相结合的方法对黄土微结构图像进行处理,提出了一种基于灰度计算土的三维孔隙率方法,并对青海西宁、甘肃永登、甘肃兰州、宁夏西吉和山西芮城五处场地的原状黄土微观结构进行了定性与定量分析。结果表明:不同地区的Q3黄土微结构往往与地域、深度以及气候条件密切相关。在定性方面,六盘山附近及以东的地区降雨量较为丰富,颗粒以集粒和凝块为主;而六盘山以西的地区气候较为干旱,颗粒之间接触面较小,易形成架空孔隙。在定量方面,在空间上自西北向东南,黄土大孔隙含量增加;在深度上自上至下,黄土颗粒相互靠拢,粒间距离减小,大孔隙含量减小;随着深度的增加,地应力逐渐增大,黄土颗粒和孔隙受到挤压发生转动和变形,中孔隙和大孔隙的椭圆率变小,其中大孔隙变化显著;土体发生重塑,孔隙排列变得有序,孔隙大小以及孔隙面积在各个区域分布相对均匀,分维数和概率熵减小,玫瑰图曲线变得圆滑。

Study of the Microscopic Pores of Structured Loess Basedon Matlab and IPP

The pore structure is an important characteristic of loess that helps distinguish it from other soil types. The macroscopic mechanical behaviors of loess, such as its collapsibility and seismic subsidence, are closely related to its pore structure. In this paper, we develop a method combining Matlab and Image-Pro Plus (IPP) software to pre-process images of the loess microstructure. Qualitative and quantitative analyses of intact loess samples taken from Xining in Qinghai, Yongdeng, and Lanzhou in Gansu, Xiji in Ningxia, and Ruicheng in Shanxi are also performed at the microscopic level. Microstructural image processing is introduced, and a new method to determine three-dimensional porosity based on gray scale calculation is proposed. Results indicate that the microstructure of the Q₃ loess in different regions is closely related to the regional, depth, and climatic conditions. In qualitative analytical tests, loess particles in the area near and esat of Liupan Mountain were given priority to with grains and grume because of its rich rainwater. The climate in the western region of Liupan Mountain significantly differs from that in the east; specifically, the western region is more arid and shows a smaller contact area between particles and tendency to form trellis pores. In the test of quantitative analysis, the large pore content increases gradually from northwest to southeast in the space. Particles move closer to each other, and the distance between grains decreases with increasing depth from top to bottom; thus, the large pore content is gradually reduced. In-situ stress gradually increases, and loess particles and pores appear to rotate and deform because of squeezing with increasing of stratum depth. The elliptical ratio of medium and large pores decreases, and macropores change significantly. The soil is remodeled, and an orderly pore arrangement is achieved. Pore size and area are relatively uniform in each region, fractal dimensions and probability entropies decrease, and the rose curve is gradually smoothened.