Influence of wetting–drying cycles on the compression behavior of a compacted loess from microstructure analysis

摘要

This study explores the compression deformation characteristics of compacted loess after different wetting–drying (WD)cycles, by tracking microstructure changes by scanning electron microscope (SEM), laser particle size analyzer, Fourier transforminfrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). Experimental results show that, as the numberof wetting–drying cycles increases, the compression deformation of the compacted loess upon mechanical loading increasesand the yield stress decreases. The first wetting–drying cycle causes the largest change in terms of mechanical response. Aslong as the number of wetting–drying cycles increases, their effect is less significant. Microstructural analyses have beenexploited to interpret the evolution of the mechanical properties at the laboratory scale. With the increase in the number ofwetting–drying cycles, FTIR results showed that the functional group strength gradually decreased, implying a reductionof the cementation strength between the particles of the compacted material. SEM images showed that the contacts amongloess aggregates (composed by particles) varied from “face to face” to “point to point.” NMR results demonstrated that thetotal and inter-aggregate pores volume increased, while the intra-aggregate pores volume decreased upon wetting–dryingcycling. The microstructure investigation allowed understanding the major role played by cementation strength, aggregatecontact type, and pore size distribution on the compression behavior of compacted loess after wetting–drying cycles.