黄土湿陷过程中临界浸润面的形成机理及深度数值模型

Water infiltrating into loess is the process that filtrating surface moves forward. Water infiltrates into the collapse loess and collapse occurs under certain pressure. When it happens, the structure of loess is broken, the gap reduces and permeability decreases, resulting in decline of water infiltrating capability.The air in aeration zone, which is below saturated zone, is leaked out hardly and compressed, so the air pressure increases and thereby the water infiltration is further impeded. Therefore, under a certain depth, water infiltrating capability and infiltrating resistance can reach a balance, the depth of infiltrating surface has a threshold limit value. Under this value, moisture content does't increases obviously and collapse does't occur any more.By applying seepage mechanics, loess mechanics and other intersecting sciences as well as utilizing outside and inside experimental methods, this research studies the change of physical property in seepage and collapse processes, analyzes permeability and change of infiltrating surface, as well as discussing laws in its occurance and development, and calculating critical depth of infiltrating surface.This research is significant for depth selection in the process of dealing with thick collapse loess foundations and soil infiltration in agriculture and hydro engineering.

水浸入湿陷性黄土，在一定压力下发生湿陷，黄土结构被破坏，孔隙减小、渗透性减弱，使水的入渗能力衰减，已发生湿陷的土层起到了隔水层的作用；同时孔隙的减小使土中孔隙间液桥力增大，使得水的入渗进一步受阻，故在一定深度内水的渗透能力与渗透阻力会达到平衡，浸润面停止向深部推进，即浸润面深度存在一临界值，在该深度以下，土的含水率不会明显增大，不会发生湿陷。本项目运用黄土力学与渗流力学等多学科交叉方法，通过野外及室内试验手段，从机理上揭示湿陷过程中的入渗及浸润面发展规律与形面机理，通过室内试验及数值计算方法确定浸润面临界深度。这一研究对大厚度湿陷性黄土的地基处理深度选择，对农业、水利工程中的土壤入渗等均有积极意义。

对于大厚度自重湿陷性黄土，由于其地基处理深度较大，工程造价高，技术上也较困难，所以其地基处理深度的确定一直是黄土力学与工程方面的热点问题，本项目为了通过黄土湿陷过程中临界浸润面的形面形成机理及其深度数值模型的研究，确定大厚度自重湿陷性黄土的地基处理深度，以便工程中能节约造价、缩短工期。通过CT、核磁共振、扫描电镜、压汞试验、比表面积测试、接触角测定、粒度分析等，对黄土的颗粒排队列关系、孔隙大小与分布有了较全面的了解。研究发现黄土中连通性孔隙的数量明显大于非连通性孔隙。对黄土的孔喉半经与水膜厚度进行了测试，确定了重力水及毛细水不能运移的孔径。研制了黄土吸附力试验系统，进行了黄土颗粒的吸附力测试；进行了湿陷性黄土的渗透性试验，进行了不同水头下、以及湿陷前后渗透速度对比、向上向下渗透等的试验，研究发现自重湿陷后的黄土其渗透速度大于天然黄土；进行了毛细水上升试验，进行了黄土现场试坑浸水试验，进一步掌握和认识了黄土的渗透特点，发现了Jurin准则存在的问题，提出了Jurin准则的适用条件，通过毛细水上升试验及黄土结构性试验对该准则进行了改进，通过试验研究及理论分析，对临界浸润面存在的机理进行了阐述，提出了临界浸润面深度的计算方法。自重湿陷量的计算是大厚度湿陷性黄土研究方面的重要课题，本文提出通过变形模量进行黄土的自重湿陷量计算，经与试坑浸水试验结果对比，变形模量法与实测值接近。

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