为研究干湿循环作用下弱膨胀土的干湿循环直剪强度特征,采用南京胥河边坡弱膨胀土进行2种干密度下的干湿循环试验,对干湿循环后土体的剪应力、凝聚力及内摩擦角进行了分析,探究了膨胀土土样干湿循环后的直剪强度变化规律。试验结果表明膨胀土干湿循环后的裂缝扩展随着干湿循环次数的增加而增多、增宽,并呈现明显的不可逆性;土体的凝聚力随着干湿循环次数的增加而逐渐减小,且不同干密度土体干湿循环稳定后的凝聚力趋近于相同的稳定值;内摩擦角随干湿循环次数的增加变化规律不明显;直剪试验时的上覆压力对于土体抗剪强度测定的剪应力衰减影响明显,上覆压力越大,剪应力的衰减越小。在进行膨胀性土的边坡稳定性分析时,应采用低应力下的直剪强度参数作为分析参数,研究结论可为工程设计提供参考。

Direct shear test was conducted on weak expansive soil specimens of two different dry densities under dry-wet cycles. The test soils were collected from the bank slope of Xuhe River in Nanjing. The shear stress, cohesion and internal friction angle of soil after dry-wet cycles were analyzed, and the variation rules of direct shear strength were investigated. Test results indicated that cracks of expansive soil expanded and widened irreversibility with the increase of dry-wet cycles; cohesion of soil of different densities decreased with the increasing of dry-wet cycles, and tended to be uniform; internal friction angle showed no obvious change. Moreover, overburden pressure during the direct shear had an apparent influence on shear stress decay. Larger overburden pressure resulted in smaller decay. In conclusion, shear strength parameters under low stress is recommended for stability analysis of expansive soil slope.