动力夯实法处理湿陷性黄土的微观机理

Micro-Mechanism of Dynamic Compaction on Collapsible Loess

利用取自山西的湿陷性黄土,模拟动力夯实现场试验,设计不同夯击次数的模型试验,得到随着夯击次数的增加,土样的密度、强度参数逐渐提高,湿陷性系数逐渐降低的变化规律,但当夯击次数大于8次时,土样竖向变形、密度、内摩擦角和粘聚力均趋于稳定,且湿陷性系数小于0.015。另外,对不同夯击次数下的土样进行SEM(扫描电镜)微观试验,编制SEM图像分析程序,经定性分析得到:随着夯击次数的增加,中小孔隙含量越来越大;夯击前土样等效孔径16μm以下的孔隙占92.6%,大于16μm的大孔隙占7.4%,小于4μm的小孔隙占66.9%。10次夯击后,土体中几乎不存在等效孔径大于16μm的大孔隙,而等效孔径小于4μm的小孔隙占81.8%。经定量分析建立了夯击次数与平面孔隙率、平均等效孔径之间的量化关系。从而建立了湿陷性系数与平面孔隙率和平均等效孔径的量化关系。

Collapsible loess was collected from a suburban district of Shanxi, China. Dynamic model experiments of different hammer blows were designed to simulate the in-situ test on collapsible loess. The model experiments results showed that the density and shear strength parameters of the soil specimens increased with the increase of blows while the collapsible coefficient of the loess decreased with the increase of blows. However, after eight blows, the vertical displacement, the density, the internal friction angle and the cohesion of the loess were tend to be constant, and the collapsible coefficient was less than 0. 015 that means the loess is stable. Furthermore, scanning electron microscope was used and SEM image analysis program was established to study the micro-structure of the specimens. The analysis of results showed that small pores in the soil increased with the increase of the blows; before compaction the content of pores with an equivalent pore diameter under 16 μm was 92.6%, the content of pores with an equivalent pore diameter larger than 16 μm was 7.4% and the content of pores with an equivalent pore diameter less than 4 lμm was 66.9%. After ten blows, there were nearly no pores with an equivalent pore diameter larger than 16 μm, while the content of the pores with an equivalent pore diameter less than 4 μm was 81.8%. According to quantitative analysis, the relations between the blows and the plane void ratio, and the equivalent pore diameter were established. Meanwhile, the relations between the collapsible coefficient and the plane void ratio, the equivalent pore diameter were established.