膨胀土湿干胀缩裂隙演化及其定量分析

Quantitative analysis of fracture evolution of expansive soils under wetting-drying cycles

膨胀土是一种分布广泛且具有明显胀缩性的裂隙土,其裂纹萌生及裂隙扩展会受到诸多因素的影响。此试验利用基于MATLAB开发的图像处理与裂隙定量分析程序,研究了膨胀土裂隙开展的尺寸和温度效应。制备25个不同初始状态的膨胀土泥浆试样,利用拍照台对其失水收缩过程中试样表面裂隙演化过程以及对应含水率进行记录。运用裂隙定量分析程序,分别对两类效应单独作用、耦合作用下的膨胀土裂隙度Df、长径比C、裂隙平均宽度w、分形维数值等指标进行定量化分析发现:膨胀土裂隙的分形维数值具有较好的稳定性,其指标仅受试样厚度轻微影响,分形维数与含水率ω的关系呈近似对数曲线;在失水收缩过程中膨胀土最终裂隙指标主要受到试样厚度的影响,表面尺寸对裂隙长径比、宽度最终值也有一定影响,温度影响主要体现在促使裂隙更早、更快的发育并稳定,对最终指标影响相对不明显,影响显著性顺序为:厚度>表面尺寸>温度;此外还对膨胀土失水收缩开裂过程机制进行分析,进一步研究膨胀土的裂隙发育以及两类效应对其裂隙扩展的影响规律。

Expansive soil is a widely distributed soil with obvious dilatancy,shrinkage and crack-rich properties.Its crack initiation and propagation are affected by many factors.In this study,the image processing and crack quantitative analysis program developed by MATLAB were used to explore the size and temperature effects of the crack evolution of expansive soil samples.Firstly,twenty-five expansive soil mud samples with different initial states were prepared.Then,the evolution of cracks on the surface and the corresponding water content of the samples during the shrinkage due to water loss were recorded using a designed camera system.Finally,using crack quantitative analysis program,some indexes including fracture degree,aspect ratio,average crack width and fractal dimension,were quantitatively analyzed under the size effect or temperature effect,and the size-temperature combined action,respectively.It is shown that the fractal dimension value of the crack remains stable,and is only slightly affected by the thickness of the samples.But there exists an approximate logarithmic relationship between the fractal dimension and the moisture content.In the process of water loss and shrinkage,the final fracture index of the expansive soil was mainly affected by the thickness of the sample,and the surface size also had a certain impact on the final value of the fracture length to diameter ratio and width.Temperature accelerates fracture development and stability.However,the impact of average width value and temperature on the final index was not obvious.The thickness was the most significant factor,followed by the surface size,and finally temperature.Additionally,the microcosmic mechanism of shrinkage and cracking process of expansive soil were also analyzed according to this experiment.