土的水力性质（本构）及渗流 合集二

分析了土壤表面积水入渗过程中压缩气体对土体结构的影响理论，并通过二维土柱入渗试验对其进行了分析及验证。在积水深度为2.8cm的条件下，对2个初始含水量、3个孔隙率下的土柱进行了试验，测量出其在试验过程中的气体压力和入渗量，并同时观察土体结构的变化。理论和试验结果表明，气体出现突破之前，土壤内气体压缩产生的气压对湿润区土体的顶托作用会破坏土体的平衡，从而在湿润锋处产生水平裂缝，破坏入渗土体的连续性。试验还发现，入渗过程中土体结构变化大小受土壤初始结构和含水率的影响，初始结构越牢固、含水量越大，结构和气压变化越小，根据结构变化不同，可以划分出两种不同的试验过程。同时入渗土体内出现裂缝时，气压的减渗作用尤为显著，甚至会导致试验过程的停止。

总结了非饱和土渗透系数的各种测量方法和预测模型。在此基础上，提出一种直接测量瞬态渗透系数的方法和预测模型。这一测量方法采用多步溢出法测量土水特征曲线，同时实时测量渗透流量和土样的含水率。在试验过程中，把气压强增量分为两个部分：一部分克服渗透阻力，驱赶水分运动，另一部分平衡静水平衡条件下的表面张力，转化为基质势，从而根据达西定律公式求出瞬态渗透系数。另一方面，利用孔隙水的平衡微分方程，引进雷诺层流理论来解释土体渗透产生的土骨架和孔隙水之间的相互作用力，推导出了非饱和土渗透系数的理论公式，该公式只有一个参数，可以通过讨论不同孔隙率、饱和渗透系数与土水作用力系数之间的关系拟合得到，从而预测出非饱和土渗透系数。通过与试验结果的对比，证实了所提出的测量方法和预测模型的正确性。

测量了在宽广吸力范围内原状样和压实样的脱湿持水曲线，对比分析了单双峰结构持水性能的差异；并利用压汞试验测试两种土样在脱湿过程的孔隙分布，分析了两者的差异并探讨了脱湿过程孔隙的演化规律；在考虑收缩变形的基础上，基于孔隙分布曲线确定了土−水特征曲线的基本参数。试验结果表明：原状样在宽广吸力范围内基本上呈单峰孔隙结构；饱和压实样具有单峰孔隙结构，随着吸力的增加，双峰结构越来越明显，当吸力达到很大时，演化成完全双峰孔隙结构。

原状样的持水曲线为经典的 S 形，而压实样的持水曲线在过渡段出现了水平台阶状；低吸力段，压实样的持水曲线低于原状样，而高吸力段，两者的持水曲线基本重合。基于孔隙分布曲线确定了控制持水曲线进气值和残余值的孔径，并计算出对应的吸力值，其值更符合实际物理意义。

Natural soils usually experience multiple drying and wetting cycles in geotechnical engineering. In this paper, the influences of history of drying and wetting upon the desorption and adsorption soil–water retention curve (SWRC) of silicon micro-powder (SMP) and Guangxi Guiping clay (GGC) are examined and discussed. The experimental results presented are obtained by using an improved pressure-plate instrument. The results show that the size of the hysteresis loops

decreases with increasing drying–wetting cycles, and these are almost identical after 4 drying–wetting cycles. In addition, the all drying–wetting curves are best fitted by VGM model, and the estimated drying air-entry value reduces with the drying number and remains almost unchanged in the fourth and fifth drying. On the contrary, the wetting estimated airentry value increases with the wetting number and tends to a stable value.

A series of experiments were performed to explore the difference in the soil water retention curves (SWRCs) and the pore size distributions (PSD) between undisturbed and compacted clays over a wide range of suction. It is showed that the SWRCs of undisturbed and compacted specimens are only significantly different in the transition zone. The SWRC of undisturbed specimens has a typical shape of ‘S’, but the compacted specimens have a ‘horizontal stage’ in transition zone. The data of mercury intrusion porosimetry show that the undisturbed soil has the unimodal pore structure, while the compacted soil with 38 MPa has the bimodal pore structure, which can account for the difference of water retention behaviour. The maximum effective pore diameter of the undisturbed specimens which control air entry value (AEV) is lower than the compacted specimens, which further confirmed that the AEV of the undisturbed soils is relatively higher than the compacted soils. As the suction increases, the undisturbed soil always has a unimodal pore structure, whereas the pore structure of the compacted soil is variable significantly. In addition, the AEV and residual water content can be confirmed from the PSD curve accurately and reliably.