排水剪切下湿地湖泊相黏土结构性宏微观试验研究

为了探讨排水剪切条件下结构性对湿地湖泊相黏土力学特性的影响,对湿地湖泊相黏土原状样和重塑样进行三轴排水剪切试验,将试验后的原状样进行微观定性和定量分析,研究不同围压下结构性对土体剪切强度和变形特性的影响。结果表明:在土体结构屈服破坏前,结构性会提高原状土抗剪强度,减小剪切变形;当土体结构屈服破坏后,结构性会降低原状土抗剪强度,增大剪切变形。原状土的峰值结构强度随围压增大近似呈线性增加,而峰值结构体积应变随围压增大呈指数型趋势减小。在围压小于结构屈服应力时,剪切阶段由胶结联结和结构骨架承担荷载,孔隙压缩较小,颗粒和孔隙的形状和排列变化较小;当围压超过结构屈服应力后,在剪切阶段胶结联结和结构骨架逐渐破坏,孔隙受到压缩,颗粒和孔隙的形状趋向圆形,并向荷载优势方向调整排列。研究成果对于揭示湿地湖泊相黏土的结构破损机理及指导湖泊湿地地区的工程建设具有重要意义。

Macroscopic and Microscopic Experimental Study on Structural Characteristics of Marshy and Lacustrine Clays under Drained Shearing

Triaxial drainage shear tests are conducted on undisturbed and remolded samples of marshy and lacustrine clay to explore the mechanism of structure affecting shear strength and deformation. The undisturbed soil samples after the triaxial drainage shear test are photographed by scanning electron microscope (SEM) and the SEM photos are qualitatively and quantitatively analyzed by IPP program. In addition, the effects of soil structure on shear strength and deformation and the change of microstructure of marshy and lacustrine clay are examined under different consolidation pressures. Results demonstrate that before the yield failure of soil structure, the soil structure of the undisturbed soil could enhance shear strength and reduce shear deformation, while after the yield failure of soil structure, the soil structure of undisturbed soil reduces shear strength and instigates shear deformation which is similar to the remolded soil. Moreover, the peak structural strength of undisturbed soil increases linearly and the peak structural volumetric strain decreases exponentially with the growth of confining pressure. When consolidation pressure is smaller than structural yield stress, the soil structure damages slightly in consolidation stage, and the shear load is bore by the bonding and fabric of the undisturbed soil in shearing stage. Meanwhile, the pores are almost uncompressed and the shape and arrangement of particles and pores have changed slightly. However, when consolidation pressure exceeds the structural yield stress, the soil structure damages significantly in consolidation stage and the bonding and fabric gradually degrades in shearing stage. As a result, the pores are compressed, the shape of particles and pores gradually becomes circular, and the arrangement orientation of particles and pores adjust with the direction of load.