土壤大孔隙分形网络空间结构及对坡地产汇流影响机理研究

The project's purpose is to study on the influence of soil macropore on slope runoff. The research contents are as follows. Firstly, the fractal network space structure of soil macropore is established through fractal diffusion-limited aggregation model. In order to achieve this, undisturbed soil columns are scanned by computerized tomography（CT）.Wavelet transform and projection on convex sets are utilized to extract high-resolution image, and adaptive particle swarm optimization (PSO) is employed to obtain the optimal threshold for binary image processing. The left-turn technology and nine direction judgment method are adopted to identify the network spatial structure of soil macropore. The step-by- step analysis method and the upward and downward track method are used to determine the soil pore space network parameters. The three-dimensional space structure of soil macropore is built, and the self-similar correlation length and anisotropy characteristics of soil macropore are analyzed. Secondly, soil macropore fractal network structure is regarded as flow channel and then the infiltrating model considering soil macropore is established. The lattice boltzmann method is used to simulate the movement of water. The infiltration model is evaluated and corrected through carrying out rainfall infiltration experiment on undisturbed soil column. Finally, the quantitative analysis of the effect of soil macropore on slope runoff is studied through flow experiment on field and the infiltration model. The project will help to further recognize the influence mechanism of soil macropore on slope runoff. It can lay a foundation for revealing the movement mechanism of macropore flow.

本项目针对土壤大孔隙对坡地产汇流的影响机理，开展原状土柱CT扫描实验，采用凸集投影超分辨率算法结合小波变换算法提高CT图像分辨率，通过自适应粒子群优化算法对CT图像进行二值化处理，利用左拐弯和九方向判断法识别土壤大孔隙网络结构，利用逐层分析法和向上、向下追踪法确定土壤大孔隙空间网络参数，构建土壤大孔隙三维空间结构，分析土壤大孔隙自相似相关长度和各向异性特性，最后通过分形凝聚模型模拟土壤大孔隙结构动态演化过程，建立土壤大孔隙分形网络空间结构；以土壤大孔隙分形网络空间结构作为土壤大孔隙水流通道，建立水分在大孔隙土壤中的运移模型，运用Lattice Boltzmann方法模拟水分在大孔隙土壤中的运移，开展原状土柱水流实验进行模型评价和修正；开展坡面水流实验，结合所建运移模型，研究土壤大孔隙对坡地产汇流的影响。该项目对于揭示大孔隙流运动规律，进一步明确土壤大孔隙对径流影响机理有重要的科学意义。

土壤大孔隙是土壤中的一种普遍存在的现象，而不是一种例外。土壤大孔隙体积虽然仅占土壤体积的0.1%~5%，但却很大程度上影响着水分在土壤中的运移，进而影响了坡地产汇流规律。本项目针对土壤大孔隙对坡地产汇流影响机理展开了研究。首先开展了原状土柱CT扫描实验，通过自适应粒子群优化算法对CT图像进行了二值化处理，运用左拐弯和九方向判断法识别了土壤大孔隙网络结构，利用逐层分析法和向上、向下追踪法确定了土壤大孔隙空间网络参数，构建了土壤大孔隙三维空间结构。在此研究基础上，将土壤分成了基质域、贯穿大孔隙域和内集水域，基于基质域水流为达西水流、通过贯穿大孔隙域的水流由运动波方程模拟、大孔隙域的水可以从大孔隙壁水平入渗到土壤基质域中、内集水域水流为一端封闭大孔隙中的水流的假设，构建了水分在大孔隙土壤中的运移模型；通过对时间进行多重尺度化处理，以多尺度分析为手段运用待定系数法确定了平衡态分布函数，以宏观上边界条件作为限制条件，用平衡态分布函数代替上边界结点上的分布函数，通过分布函数外推格式确定了下边界结点上的分布函数，运用Lattice Boltzmann方法求解了坡面流的运动波方程，利用实验槽尺度的水流实验进行了模型评价，研究结果表明在整个地面径流出流期间，各场次地面径流量计算值的平均相对误差小于12.96%，降雨刚开始和降雨结束后，相对误差较大，从降雨中后期到降雨结束期间，各场次地面径流量计算值的平均相对误差小于7.59%。最后研究了土壤大孔隙对地面径流、地下径流、土壤容积含水量、坡面流流速等的影响，研究表明大孔隙的存在使土槽下渗容量变大，地下径流量增加，地面径流量减少；有大孔隙的实验槽，土壤水力传导度偏大，地下径流出现时间提前；孔隙度的增加，加快了土壤含水量变化响应速度，影响了导水率在实验槽深度方向上的分布形式。该项目的研究成果对于明确土壤大孔隙与水分运移之间的关系、揭示土壤大孔隙对径流影响机理、阐述大孔隙流运动规律提供了一定的理论基础。