反复冻融作用下粉质黏土的微观分形特征研究

Study on the Microcosmic Fractal Characteristics of Silty Clay Subject to Repeated Freezing and Thawing

粉质黏土作为一种常用的路基填料,受冻融循环作用的影响后其微观结构的变化直接导致路基强度的改变。为研究多次冻融后土体力学强度与微观结构的关系,以东北地区粉质黏土为研究对象,进行不同冻融循环次数下土体的扫描电镜(SEM)、压汞(MIP)及无侧限抗压强度试验。基于分形理论,分别计算土体颗粒、孔隙三维分形维数,并据此建立分形维数与力学强度的关系公式。研究结果表明:随冻融次数的增加,土体颗粒重新排列,整体性受到破坏,孔隙体积呈波动上升的趋势;试样含水量升高后,5~20μm孔径的孔隙含量逐渐减小,而0.3~5μm孔径孔隙含量增加;分形维数很好地反映了冻融循环过程中土体微观结构的变化特点,由分形维数与无侧限抗压强度构建的回归方程得知,分形维数越大,土体强度越大。

Silty clay is often used in roadbed stuffing.The influence of freezing-thawing cycles on the microstructure leads directly to the change of subgrade strength.For the silty clay in north-eastern regions,the scanning electron microscope（SEM）,mercury intrusion porosimetry（MIP） and unconfined compressive strength tests after freeze-thaw cycling are conducted.Based on fractal theory,threedimensional fractal dimensions of soil particle and pore are calculated,and the relation formula between fractal dimensions and mechanical strength is created.The results indicate that with the increase of freezing and thawing cycles,soil is rearranged and its integrity is destroyed.Meanwhile,the pore volume tends to fluctuate and increase.With the increase of the water content,the pore content of pore size in 5~20 μm gradually decreases,while,that of pore size in 0.3~5 μm increases.In the progress of freezethaw cycling,the changing characteristics of soil microstructure are well reflected by fractal dimension.The egression equations constructed by fractal dimension and unconfined compressive strength show that the bigger the fractal dimension,the higher the strength.