基于压汞法的冻融循环对土体孔隙特征影响的试验研究

冻融循环会改变土的微观结构, 孔隙特征的变化是其结构性发生改变的重要体现. 以青藏铁路沿线粉质黏土为研究对象, 借助压汞技术对不同冻融次数下重塑土样的孔隙特征进行了研究. 结果表明:土体孔隙特征分布曲线表现出明显的双峰特征, 据此可将土样的孔隙分为大孔和小孔两大类; 冻融循环次数对小孔隙的影响较小, 小孔隙直径和体积基本保持不变; 冻融循环次数对大孔隙的影响较大, 特别是孔径为20～40 μm的孔隙, 其直径和体积均随冻融次数的增加而增大. 试样的孔隙率随冻融次数的增加并无明显规律, 但总体的变化趋势是先增大后减小. 由孔隙分形维数计算结果可知, 冻融循环在改变土体孔隙结构的同时, 使孔隙内壁的粗糙程度及孔隙结构的复杂程度降低.

Experimental study of the effect of freezing-thawing cycles on porosity characters of silty clay by using mercury intrusion porosimetry

Freezing-thawing is a kind of weathering process, which considerably changes structures of soil. Change in soil pore structures has given expression to change in structure characteristics. In order to study the influence of freezing-thawing cycles on pore structures, specimens of silty clay from the Tibetan Plateau were prepared for tests under freezing-thawing cycles, 50 at most. Mercury intrusion porosimetry (MIP) is used to obtain pore size distribution and pore fractal dimension. A bimodal pattern is found the log-differential curves, which indicates that two different mechanisms are involved in forming the pores within the material. Freezing-thawing cycles have less impact on pores of small size, because of the pore size and pore volume almost remaining unchanged. However, pores of large size (especially the pore size at 20-40 μm) are influenced greatly by freezing-thawing cycles for the pore size and pore volume greatly increased. There is no obvious relation between soil porosity and freezing-thawing cycles. However, the overall changing trend of the soil porosity is first increasing and then decreasing. According to a pore fractal dimension calculation, freezing-thawing cycles change the pore structures, resulting in decrease in pore wall roughness and pore structure complexity.