黏土触变过程中强度恢复的微观机理

触变性是复杂的流变特性之一,它是指外力扰动导致土体强度衰减,静止后随时间增长逐渐强度恢复的现象。为了探寻黏土触变过程中强度恢复机理,开展了在长达500 d的龄期内,观测湛江黏土扰动后不同静置龄期下的无侧限抗压强度与贯入阻力,分析触变强度的恢复时间与过程,利用触变强度比率评价湛江粘土的触变性。利用扫描电镜与压汞试验,分析不同静置龄期下的结构演变规律。结果表明,湛江粘土具有明显的触变性,扰动后静置500 d后土体持有强度是其扰动后的2.58倍,但触变恢复强度仅占扰动损失强度的21.2%~23.5%。对于高灵敏性、强结构性的地基土,因施工扰动带来的强度损失引发的工程灾害不容忽视。黏土触变过程中的强度恢复主要是颗粒间引力与斥力的相互作用的力场变化使结构有分散趋向絮凝发展所导致,这一过程中结构产生自适应调整,孔隙分布均匀化发展,微观结构向亚稳定结构转变,在一定时期内表现出触变现象。

Microscopic mechanism of strength increase of clay during thixotropic process

The thixotropy is one of rheological properties, and it is the phenomenon that the strength decreases owing to external force and then gradually increases with time after stopping disturbance. In order to explore the microscopic mechanism of strength increase of clay during thixotropic process, the unconfined compressive strength and penetration resistance of Zhanjiang clay after disturbance of 500 d are tested, the thixotropic strength evolution process is analyzed, and the thixotropic rules are determined according to the thixotropic strength ratio. Furthermore, microstructural change at different standing time is studied using the scanning electron microscope and mercury injection experiment. The results show that the thixotropic characteristics of Zhanjiang clay are significant, and the strength after 500 d is 2.58 times that after the disturbance, but the thixotropic increase strength only accounts for 21.2%~23.5% of the disturbance strength loss. Therefore, for the soils with high sensitivity and strong structure engineering disasters can not be ignored because of strength loss caused by construction disturbance. The thixotropic strength recovery is the result of the structural evolution from dispersion to flocculation through attraction and repulsion between particles owing to change of force field. In this process, the microstructure is self-adapted and pore distribution uniformly develops, and in a certain period of time the thixotropic phenomenon occurs.