The influences of natural structure damage and stress path on mechanical behaviors of soft clay

• Published in: Bulletin of engineering geology and the environment 2023-06, Vol.82 (6), Article 208
• Main Authors: Liang, Zhixin, Sun, Hong, Huang, Zhaoxing, Niu, Fujun
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Foundations; Geoecology/Natural Processes; Geoengineering; Geotechnical Engineering & Applied Earth Sciences; Hydraulics; Nature Conservation; Original Paper
• ISSN: 1435-9529; 1435-9537
• DOI: 10.1007/s10064-023-03237-w

This work aims to investigate the influence of structural damage to natural soft clay on its mechanical behavior. K 0 consolidated triaxial tests with loading and unloading stress paths were conducted, and field emission scanning electron microscopy (FESEM) and mercury intrusion porosimetry (MIP) were utilized for microstructural investigation. Macroscopic properties of soil were analyzed by microstructure evolution and damage theory. A pore size distribution index ( S ) was proposed that collectively accounts for the effect of pore size distribution and pore volume. Damage variables were determined based on the S to evaluate the damage degree of soft clay after K 0 consolidation. The soil structure is obviously damaged when the confining pressure exceeds the preconsolidation pressure (119 kPa), with damage variables reaching 0.5 ~ 0.6 between 150 and 250 kPa. The initial tangent modulus and ultimate deviator stress of soft clay by reduced triaxial compression (RTC) tests are lower than those by conventional triaxial compression (CTC) tests. It is associated with relatively different microstructure failure modes, i.e., a loose uniform failure mode for RTC specimens and a locally dense non-uniform failure mode for CTC ones. However, the natural structure is slightly damaged after consolidation, and marginal macro and micro differences were observed between CTC and RTC test results when the confining pressure is less than the preconsolidation pressure. Therefore, the mechanical behavior of soft clay is strongly affected by stress paths and damage to the natural structure during consolidation and shearing processes on the macroscopic and microscopic views.