膨胀土强度干湿循环试验研究

Experimental studies of strength of expansive soil in drying and wetting cycle

通过南宁地区原状膨胀土干湿循环试验,探讨了膨胀土抗剪强度与含水率、循环次数、循环幅度等循环控制参数的关系。研究结果表明:膨胀土抗剪强度随干湿循环次数增加而衰减,最终趋于稳定,强度稳定值与稳定时所需循环次数均随含水率变化幅度的增加而减小。在此基础上,利用压汞试验测定了膨胀土干湿循环过程中的孔径分布,发现干湿循环对土的粒间联结产生不可逆的削弱,使得土体形成更大的孔隙空间,在高含水率时主要表现为集聚体间孔体积增加,在低含水率时集聚体内孔体积增加,从而降低土的抗剪强度。

Experimental studies were undertaken on an expansive soil from Nanning area in order to establish relationship between shear strength indices and cyclic drying and wetting parameters. It is shown that the shear strength of expansive soil decreases with increasing number of cycles and finally reaches to a constant state. The value and cyclic number of the constant state reduce with increase of amplitude of variation of water content. Furthermore, the mercury intrusion porosimetry （MIP） test was applied to determine the pore size distribution curve of expansive soil during wetting-drying cycle. The MIP test results show that the bond of soil is irreversibly damaged by cyclic drying and wetting, which leads to increase the volume of pore. In high water content, volume of outer-aggregate pores increase with number of cycles; while in low water content, volume of intra-aggregate pores will increase. As a result of degradation of microstructure, the shear strength of expansive soil quickly decreases.