土壤表层结皮失水裂缝形态发育规律研究

Formation of Crusts and Initiation and Development of Cracks in Them Following Soil Wetting and Drying

【目的】明确坡耕地条件下土壤物理结皮失水裂缝开裂规律。【方法】采用室外人工模拟降雨试验,结合MATLAB图像处理功能,对结构结皮、沉积结皮和过渡带结皮物理性质及裂缝网络发育进行了定量分析,并探讨了裂缝形态特征随土壤含水率的变化情况。【结果】不同类型结皮土壤物理性质差异显著,其中结皮体积质量及黏粒质量分数均表现为沉积结皮(DC)最高,其次为过渡带结皮(TZ)、结构结皮(SC);而砂粒质量分数则表现为结构结皮高于过渡带结皮和沉积结皮。垄沟区域不同部位土壤结皮干缩裂缝形态特征存在显著差异,其中裂缝面积率(RC)、裂缝长度密度(LC)和裂缝平均宽度(Wi)均表现为沉积结皮(DC)<过渡带结皮(TZ)<结构结皮(SC),各区域间的连通性指数(K)差异不显著。裂缝形态差异主要受土壤物理性质、含水率下降速率和初始含水率影响,同时结构结皮裂缝形态特征还与其特有的弧状结构有关。裂缝发育过程中,结构结皮、沉积结皮的裂缝面积率、长度密度和平均宽度随含水率降低而增大,裂缝发育完成时,结构结皮的土壤含水率为11.88%,沉积结皮的土壤含水率为20.57%,同时沉积结皮裂缝的发育历时最长为357 h。【结论】结皮类型对裂缝发育产生了重要影响,结构结皮裂缝开裂最为明显,沉积结皮裂缝形态复杂多样且发育历时最长。

【Objective】Crust is a thin soil layer formed on soil surface when water on the soil surface recedes;continuing soil drying after that could result in cracks to develop.Crusts and cracks could significantly affect water infiltration and soil water evaporation,and the purpose of this paper is to experimentally study how crusts form and cracks subsequently develop following a rainfall on a slope.【Method】The experiment was conducted on a slope watered by artificial rainfall.After the rainfall stopped,we measured physical properties of the crusts,imaged the initiation and development of cracks in them at different locations on the slop.These images were processed using MATLAB to quantify their morphological characteristics as well as their relationship with soil water content【.Result】Based on where the crusts were formed,they can be classified into structural crusts,depositional crusts and transitional crusts,with different physical properties.The depositional crusts have the highest volumetric weight and clay content.In contrast,the structural crusts have the greatest sand particle content.The morphology of cracks developed in the crusts at different locations in the gully differed from each other significantly.For crusts where the cracks developed,their impacts on crack area ratio(RC),length density of the cracks(LC),and the average width of the crack(Wi)were ranked in the order of depositional crusts<transitional zone crusts<structural crusts.The connectivity index of cracks developed in different crusts was not significantly different.The formation of cracks was mainly affected by physical properties of the crusts,decreasing rate of the soil moisture,and the initial soil moisture content.The cracks developed in the structural crusts were in arch-shape.Relevant analysis showed that RC,LC,and Wi of the structural and depositional crusts increased as the soil moisture decreased.After crack development was completed,the soil moisture content of the structural and depositional crusts was 11.88%and 20.57%respectively.The maximum duration for cracks in the depositional crusts to develop was 357 hours.【Conclusion】Crack development depends on the physical properties of the crusts there they initiated.The cracks in structural crusts are most visually visible,while the cracks in the depositional crusts were morphologically complex and took more time to develop.