应力-基质吸力耦合作用下粉土的孔隙比演化过程

Void Ratio Evolution Process of Silt under Stress-matrix Suction Coupling Effect

外部荷载和含水量的变动都会引起土体体积的变化,但大多研究都仅从固结压缩或增减湿胀缩角度进行研究,而把荷载、基质吸力和孔隙联合起来考虑的较少。为了探究应力-基质吸力耦合作用下粉土的孔隙比演化过程,采用了能考虑固结应力作用的土水特征曲线试验仪,获得了荷载、基质吸力和孔隙的变化规律。分析了压实粉土固结稳定后(即荷载全部由有效应力承担),有/无荷载继续作用下脱湿引起的体变差异性,并提出了荷载、基质吸力与孔隙相互作用的概念模型;从粉土孔隙和颗粒分布等微观角度,阐释了负荷作用加剧孔隙比减少的主要原因。研究结果表明:负荷条件下脱湿引起的体变量大于无荷条件下的体变量,说明脱湿过程中荷载对其孔隙变化继续起到助推作用。造成负荷作用加剧孔隙比减少的原因是由于荷载-基质吸力发生"一步一趋"的耦合作用,使得土体初始脱湿阶段总处于准饱和状态,没有形成有效的非饱和强度。

The volume of soil could change with external load and moisture variation. Most scholars merely pay attention to research on consolidated compression or swelling-shrinkage due to moisture variation, and less work has been done which considers loading-suction-pore distribution as a whole. To explore the void ratio evolution process of silt under the coupling effect of stress-matrix suction, the characteristic curve for silt and water interaction that considers the action of consolidation stress is used to obtain the variation behavior of load, matrix suction, and pore distribution. The changes in volume caused by dehydration under loading and unloading conditions after consolidation and stabilization of compacted silt (for all loading conditions assumed by effective stress) are analyzed. Further, a conceptual model for the interaction among loading, matrix suction, and pore structure is put forward. The main reasons for the decrease of void ratio aggravated by load action are explained from the microscopic aspects of silt pore and size distribution. The result shows that the volume changes caused by dehydration process due to loading is larger than that under unloading condition, indicating that the loading played a major role in enhancing the pore change during dehydration process. Consequently, the aggravation of the decrease in pore ratio under load is attributed to the " step-by-step'' coupling of load-matrix suction, which resulted in the initial dehumidification stage of soil to be in a quasisaturated state, hence, no effective unsaturated strength is formed.