Abstract: The physico-mechanical properties and compressibility of marshy-Lacustrine clay, a special regional soft soil, differ from those of other soft soils markedly. We performed oedometer tests to investigate the consolidated compressibility and mechanism of marshy-Lacustrine clay, and analyzed quantitatively and qualitatively the change of microstructure characteristics by extracting the microstructural parameters under different pressures using scanning electron microscopy and computer image processing. Results demonstrated that due to apparent structural strength, the compressibility of undisturbed marshy-Lacustrine clay was significantly smaller than that of reconstituted soil. Such structural strength perished gradually when the consolidation pressure exceeded the structural yield stress. Moreover, the change laws of the microstructural parameters varied and displayed a form of two broken lines when the consolidation pressure was around the structural yield stress, and also at this time the dynamic restructuring of the soil is the fundamental cause of the change of compressibility of marshy-Lacustrine clay. During consolidation compression, the morphological characteristics and directionalities of pores changed markedly, while the morphological characteristics of particles changed slightly but the directionalities of particles changed remarkably. The particles and pores affect the compressibility of soil in different ways.

Key words: marshy-Lacustrine clay, structure of soil, oedometer tests, microstructure, structural parameters