膨胀土裂隙三维空间分布特征试验研究

Experimental Research on Three-dimensional Space Distribution Characteristics of the Expansive Soil Cracks

膨胀土裂隙性研究多集中在土体表面裂隙,然而实际工程中裂隙是沿三维空间上扩展,土体内部裂隙较土体表面裂隙要复杂得多,针对这一情况采用高精度工业三维CT技术对南阳膨胀土原状样进行扫描;采用医用CT对膨胀土试样裂隙发育过程进行CT扫描实验,研究膨胀土裂隙的三维空间分布扩展规律;采用Poremaster33高压孔隙结构仪进行压汞实验研究土体内部裂隙发育微观机理。从宏观三种尺度进行研究,结果表明:膨胀土原状样三维空间裂隙发育极为复杂,样品中存在几条交错的主裂隙,并延伸出细小裂隙裂隙将整个土样分割得极为破碎;重塑膨胀土样裂隙总是首先出现在土体表层,土样裂隙发育最剧烈的部位是与土体表面有一定距离处,与现场情况相吻合;初始含水率越高试样收缩越明显,脱湿后整体性越强;初始含水率降低土体内裂隙增多,土体被裂隙分割得愈破碎;原状土试样脱湿前后微观结构变化较剧烈,总孔隙体积急剧减小,但大孔隙所占相对比例急剧增加;重塑土样脱湿前后变化明显,脱湿后不同孔隙孔径分布曲线相对于脱湿前的最大区别在于曲线中的波峰被降低削減,波峰向大孔径方向移动。

The research of expansive soil fractures are mostly concentrated in the soil surface cracks, however, the cracks are expanded along the three-dimensional space in actual engineering, soil internal cracks are more complex than the soil surface cracks.According to the situation, the high precision industrial 3D CT technology was used to test the cracks of Nanyang undisturbed expansive soil and the medical CT was carried out on the fracture development of remodeling expansive soil for studying the 3D spatial distribution of expansive soil cracks.The Poremaster33 was used to testing the pore structure of expansive soil.The 3D CT results of undisturbed expansive soil showed that： a large crack distributed in Nanyang undisturbed expansive soil, cracks split the entire soil sample extremely broken.The CT results of remodeling expansive soil showed that： the sample＇s fragmentation was increasing when the degree of compaction was reducing;The higher initial water content of the sample, the greater the shrinkage and the better the integrity after dehumidifying;soil cracks in vivo and vertical cracks also increased with the decreasing of the water content.The results of expansive soil microstructure before and after dewetting showed that： the microstructure of undisturbed expansive soil samples dramatically changed after desorption, the total pore volume decreased sharply and the relative percentage of large pores increased sharply;the remodeling samples curve of internal pore changed from single peak to multimodal peak, from low value to high value;the greatest impact on pore diameter of specimens by dehumidifying were pores whose diameter greater than 10 μm, large pores turned into small pores and small pores as well as ultrafine pores increased after dehumidifying.