昔格达土体涉水填方土压力计算时需查明抗剪参数(如黏聚力与内摩擦角)受干湿循环作用的影响。通过真空饱和增湿及自然风干脱湿模拟干湿循环过程,基于固结慢剪试验得到湿化及干湿循环作用下昔格达土体剪应力-位移曲线,分析峰值剪应力、黏聚力及内摩擦角随干湿循环次数变化规律;采用平行粘结接触模型探讨了宏观与微观参数的联系,揭示了干湿循环作用对微观颗粒间粘结及摩擦特性影响的差异性。试验结果表明:湿化作用降低昔格达土体黏聚力及内摩擦角;随干湿循环次数增加,昔格达土体应力-位移曲线从应变硬化过渡至应变软化,峰值强度、黏聚力及内摩擦角均减小并趋于稳定;黏聚力以前3次循环降幅(55.42%)较大,内摩擦角以第2—第4次循环降幅(11.04%)较大,干湿循环对黏聚力影响显著大于对内摩擦角的影响,对内摩擦角的劣化效应存在滞后性。建议工程中可从微观颗粒间粘结作用的角度削弱干湿循环对昔格达土体力学特性的影响。研究结果可为昔格达土涉水工程安全提供参考。

The influence of cyclic drying and wetting on shear parameters (cohesion and internal friction angle) must be identified in calculating the earth pressure of filling by Xigeda soil involved with water. The shear stress-displacement curve of Xigeda soil was acquired from consolidated drained shear test under cyclic drying and wetting. Soil specimens were humidified by vacuum saturation and dehumidified in natural status to simulate the drying-wetting progress. The variations of peak shear stress, cohesion and internal friction angle with the number of drying-wetting cycles were analyzed. Furthermore, the relationship between macroscopic and microcosmic parameters was discussed by the parallel contact model, and the differences between bond and friction characteristics among micro particles were revealed. Test results showed that the wetting action reduced the cohesion and internal friction angle of the soil. As the number of drying-wetting cycles increased, the stress-displacement curves displayed strain hardening features to strain softening features, and peak strength, cohesion and internal friction angle all decreased and tended to be stable. In the first three cycles, cohesion decreased by 55.42%, while from the second to the forth cycle, internal friction angle decreased by 11.04%. The effect of drying-wetting cycle on cohesion was apparently greater than that on internal friction, and the deterioration effect on internal friction angle delayed. We recommend to weaken the influence of drying-wetting cycles on the mechanical properties of Xigeda soil by means from the aspect of the bonding effect among micro particles.