干湿循环作用下膨胀土表观胀缩变形特性

Swelling-Shrinking characteristics and irreversible deformation of expansive soil during wetting-drying cycles

为揭示不同上覆压力及含水率幅值条件下膨胀土胀缩特性及表观不可逆变形,开展了干湿循环作用下膨胀土表现胀缩变形特性试验研究.从微观的角度分析了膨胀土吸水膨胀、失水收缩的特性及产生裂隙的原因;探讨了不同压力及含水率循环幅值条件下,膨胀土试样高度、相对膨胀率、相对线缩率、随含水率及循环次数的变化关系以及试样表观相对不可逆变形量与累计不可逆变形量随循环次数的变化关系.研究结果表明:膨胀土吸水膨胀失水收缩是土颗粒间水体变化叠加的直观反应,也是土体内部产生裂隙的主要诱因;膨胀土失水收缩过程中,基质吸力以最大程度限制含水率减小的方式逐渐增大;不同压力作用下,试件高度随含水率呈线性变化关系,而无压力作用下的变化关系波动较大;随着循环次数的增加,膨胀土相对膨胀率逐渐减小,而相对线缩率先增大后减小,且上覆压力越大,相对膨胀率越低;不同含水率幅值范围内的相对膨胀率与相对线缩率随着循环次数的增加具有逐渐减小的趋势;不同压力作用下,含水率为15%时,膨胀土的累计不可逆变形随着循环次数的增加逐渐增大,而在含水率为25%时其反而逐渐减小.

To investigate the Swelling-Shrinking characteristics and irreversible deformation of expansive soil under different pressures and moisture contents, a series of tests under wetting-drying cycles were carried out, and the Swelling-Shrinking characteristics and reasons for fissuring were analyzed from the microcosmic point of view. Based on the above studies, the relationship among heights, relative expansion ratios, relative linear shrinking rates and cycle index under different pressures and moisture contents were explored. Meanwhile, the variation curves of the relative irreversible deformation and accumulative irreversible deformation with increasing cycle index were obtained. The results indicate that the swelling and shrinking are visualized response of the variation of water between soil particles, and also the incentive of fissuring. During the shrinking process, the matric suction increases by the way of maximum limit to prevent moisture content decreasing. There is a linear correlation between the height of test specimen and moisture content under different pressures. The relative expansion ratios will decrease if the cycle index rises, and the same happens with higher pressure. The relative linear shrinking rates will rises firstly and then decreases with the increasing of cycle index. It is shown that the relative expansion ratios and relative linear shrinking rates under different amplitudes of moisture content have a decreasing trend along with the increase of cycle index. The accumulative irreversible deformations increase gradually on the condition that the moisture content is 15% with different pressures, and there will be opposite results with the moisture content of 25%.