冻融作用下不同级配土的粉质化程度研究

Freeze-thaw actions cause soil particle split and reunion, which in turn result in enrichment of silty particles. When such enrichment reaches a certain extent, the silty phenomenon occurs. The silty process involves the changes of the structure of the soil and as a results its properties, which incurs a series of ecological and engineering problems. The start to understand and tackle these problems is to identify and evaluate the degree of silt enrichment. As soil gradation is an important factor that affecting the vulnerability of the silt enrichment under free-thaw actions, this paper presents a study of laboratory freeze-thaw experiments performed under controlled conditions on different graded soils of Qinghai-Tibetan Plateau region. The granular composition, microstructure and physical properties of the soil samples before and after experiments were compared and studied. The relationship between soil gradation and silt enrichment was investigated and the impact of silt enrichment on the physical properties was explored. Based on the experimental results, criteria to identity the vulnerability and degree of silt enrichment of the soil under freeze-thaw actions were proposed.

冻融作用可以使土中颗粒发生分裂和团聚，从而引起土的粉粒级富集，当富集到一定程度时会出现粉质化现象，粉质化过程是土的结构以及性质的变化过程，随之又会带来一系列的生态环境和工程问题。了解这些问题的规律和解决这些问题的首要任务是对粉质化程度的研究、判别和评价。由于土的级配是决定其粉质化程度的重要内部因素，因此本项目选择青藏高原地区的不同级配土作为研究对象，并进行特定条件下的室内冻融实验研究。通过对其冻融前后的粒度成分、细观结构物理性质的测试，分析冻融作用下土颗粒的分裂和团聚规律，说明土的级配与粉粒富集程度的关系，并探讨粉粒的富集对土的物理性质的影响。最终力争全面、深入的分析冻融作用下不同级配土的粉质化过程和程度，在此基础上建立冻融作用下土粉质化程度的判定标准及评价体系。

冻融循环作用可以引起土的粉质化现象, 尤其是在0.01-0.05mm粒级发生富集。粉质化可能会影响到一系列的生态环境与工程问题。本项目选取青藏高原地区不同级配土样作为研究对象进行冻融试验，从土颗粒分裂与团聚规律入手，揭示了土的级配对粉质化程度的影响，并分析了粉质化过程中土的组构和性质的变化规律，对冻融作用下不同级配土的粉质化程度进行了全面的剖析，并在此基础上建立了冻融作用下土的粉质化程度的判定方法。研究主要获得了以下主要结果： 1）通过理论计算验证了颗粒间大应力的存在，在理论上支持了冻融作用下土颗粒分裂和团聚的理论；2）冻融作用下土壤粉质化的强烈程度与土壤的级配有着必然的联系，粉质化程度：粘性土>砂性土>粉质土；3）发现并验证了“界限粒级”的存在，“界限粒级”与矿物颗粒的裂隙尺寸有关；4）粉质化程度对土的组构和性质有直接的影响，粉质化程度越大土的组构和性质变化越大；5）验证了粉粒级（0.01-0.05mm）在冻融循环作用下的稳定性，并在此基础上利用粉质化程度系数（ψ）对粉质化程度进行判定。