On the basis of numerical processing technology of image grayscale and binarization, the concepts of crack rate and calculation method on expansive rock are presented. The dry-wet cycle tests were carried out in situ at Luwangfen test section of South-to-North Water Transfer Project Central Route, the tests focused on the observations of development changes in cracks and soil moisture changes. According to the results in the tests, the variation law of crack width on expansive rock slope and its relationship with moisture content during the dry  wet cycle test were quantitatively analyzed, also the variation law of crack ratio was investigated. The development of crack on expansion rock is closely related to changes in the weather, and with the development of wet and dry cycles, the width of cracks and crack ratio will gradually increase. By using the Mat lab digital image processing method, the crack ratio can be used to effectively describe the growth and development of cracks on expansive rock.

为了解土体干缩裂隙演化规律, 基于MATLAB软件开发了裂隙图像分析系统, 通过对裂隙图像进行二值化、桥接去杂、骨架提取等操作, 进而提取出裂隙率、裂隙长度、平均宽度、隙宽分布率、分维等裂隙形态参数, 实现了平面裂隙图像的无损、连续、动态识别和形态参数定量分析。该裂隙网络图像分析程序为土体干缩裂隙的动态演化分析提供了依据, 可用于边坡稳定性分析、环境污染控制等众多领域。

In order to find out the evolvement regularity of surface cracks in soil due to drying shrinkage, an analysis system of crack’s parameters was developed by using MATLAB. Through binarization, crack restoration, noise reduction and skeleton extraction, the morphological parameters of cracks, such as crack rate, length, width, width grading and fractal dimension, were computed by further recognition methods. Through this system, the non-destructive, continuous and dynamic recognition of cracks, as well as the rapid and accurate quantitative analysis of morphological parameters were achieved. Moreover, this system offered a reliable basis for the analysis of dynamic evolvement of cracks. It can be used in slope stability analysis, environmental pollution-control and many other areas.

裂隙是影响膨胀土力学特性的重要因素之一。以河南南阳地区高速公路路用膨胀土为研究对象,通过制备不同初始含水率和压实度的大尺寸压实膨胀土土样,观察压实膨胀土在脱湿过程中的表面裂隙发育,并拍摄数码图像,然后利用基于MatLab自编程序的改进裂隙图像特征参数提取方法对图像进行定量化分析,获得裂隙的各种特征参数,进而探讨膨胀土表面裂隙发育的相关规律。研究结果表明:压实膨胀土脱湿开裂过程可分为细小裂隙发育、主裂隙发育及裂隙回稳3个阶段;初始含水率越高,膨胀土表面裂隙发育速率越快,发育程度越高,持续时间越长;初始压实度越大,膨胀土表面裂隙率和裂隙总长越小,但宽度较大。上述裂隙发育规律可用表面蒸发和土体内部水分传输机理进行解释。

Crack is a crucial factor that affects the mechanical properties of expansive soil. Expansive soils taken from Nanyang Expressway (Henan Province, China) were compacted to big-size samples with various original water content and compactness, and then the samples were desiccated gradually in a closed greenhouse where a camera was used to record the propagation of cracks on the surfaces of samples. The captured images were analyzed quantitatively using self-compiled program of MatLab to obtain the characteristics of surface cracks which were further used to explore the laws of crack propagation. The results suggest that the course of crack propagation in compacted expansive soil samples can be divided into three stages: in the first stage minor cracks aroused and developed quickly; then main cracks emerged and cracks reached peak in the second stage; at last the cracks withdrew and remained stable in the third stage. The higher the original water content was, the faster the cracks on the surfaces of expansive soil samples developed, the higher the extent of crack development was, and the longer the crack development lasted; the higher the original compactness, the smaller the surface crack ratio and total length of expansive soil samples were, but the larger the crack width was. The above results can be explained by the mechanism of superficial evaporation and water transformation in the soil.