冻融作用下水分迁移对压实黄土强度影响的宏微观试验研究

在季节性冻土区，冻融作用下土体的水分迁移及其伴生现象会诱发黄土路基发生病害，探明冻融作用下水分迁移对压实黄土强度的影响及其机制，对于黄土地区路基工程冻融病害防治非常必要。采用大尺寸设备对洛川黄土开展单向冻结-双向融化作用下的冻融循环试验，对土体温度场、水分场均加以监测，并在此基础上进行直剪试验和电镜扫描试验。结果表明：土体温度场在每级负温作用下50 h达到稳定，单向冻结完成后冻结深度为46 cm；含水量在冻结区增加，在未冻结区减小，土体融化后水分回迁但回迁量小于冻结时的迁移量；土体剪切强度与含水量分布沿土体轴向呈现出较强的一致性，冻融后土体强度随含水量增加而降低，临界冻结锋面处强度劣化效应最明显；随着冻融循环次数的增大，土体孔隙面积和分形维数均表现为增加，其中微、小孔隙减少，中、大孔隙增加，冻融循环7次后土体微结构基本趋于稳定，土体强度与孔隙面积成反比例关系；土体在冻-融过程中，冻结区水分的显著增加是造成土体强度衰减、孔隙增多的重要原因。

Macro and Micro Experimental Study on the Influence of Moisture Migration on the Strength of Compacted Loess Under Freeze-thaw Cycling

In seasonally frozen soil regions, moisture migration and the accompanying phenomenon of soils under freezing and thawing can cause the failure of loess subgrades. The effect of moisture migration on the strength of compacted loess under freezing and thawing and its mechanism should be investigated as it is necessary to prevent freezing and thawing failure in roadbed engineering in loess areas. First, a piece of large-scale equipment was used to carry out a freeze-thaw cycle test on Luochuan loess under the action of axial freezing and bidirectional thawing, and the temperature and moisture fields of the soil were monitored. Based on this, a direct shear test and a scanning electron microscopy analysis were performed. The results show that the soil temperature field is stable for 50 h at each stage of negative temperature. After axial freezing is completed, the freezing depth is 46 cm; the moisture content increases in the frozen area and decreases in the unfrozen area. The moisture migrates back after thawing, but the migration volume is smaller than that during freezing. The soil shear strength and moisture content distribution show strong uniformity along the soil axis. After freezing and thawing, the strength of the soil decreases with increasing water content. The strength degradation effect at the critical freezing front is the most evident. With an increase in the number of freeze-thaw cycles, the soil pore area and fractal dimension both increase, the number of micro and small pores decreases, and the number of medium and large pores increases. After seven freeze-thaw cycles, the soil microstructure is basically stabilized, and the relationship between soil strength and pore area is inversely proportional. During the freeze-thaw process of soil, a significant increase in the moisture in the frozen area is an important factor that causes the strength of the soil to decrease and the number of pores to increase.