Structural characterization of natural loess and remolded loess under triaxial tests

• The structural evolution of loess upon loading are characterized.
• Compare the structural evolution of loess along different stress paths.
• Compare the structural evolution of natural loess and that of remolded loess.
• Reveal the effects of structural characteristics on the mechanical behavior.

This paper characterizes the microstructural evolution of saturated natural loess from a site in Jingyang, China, during triaxial test along two stress paths. For comparison, the same soil in remolded state is also characterized. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM) were used for the microstructure investigation. Results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained (CU) triaxial tests including conventional triaxial compression (CTC) test and reduced triaxial compression (RTC) test. On the contrary, their microstructures are different after the tests. Deeper examination shows that loading led to a significant change of inter-aggregate pores, without modifying the intra-aggregate pores. In addition, the volume of inter-aggregate pores after the RTC test is greater than that after the CTC test under the same consolidation stress. The microstructure features of natural and remolded loess after the tests are further used to analyze the macro-mechanical behavior for better understanding the relationship between them. The results show that it is the cementation bonds, of which breakage is influenced by stress path and confining pressure, that play important roles in the strength and deformation behavior.