Macro-micro deformation characteristics of undisturbed loess under different hydraulic paths

Understanding the mechanical behavior of undisturbed loess under different hydraulic paths (wetting followed by loading(W-L) and loading followed by wetting(L-W)) is critical for geotechnical engineering in loess regions. This study investigates the macro-micro deformation characteristics of undisturbed loess using improved triaxial tests, scanning electron microscopy (SEM), Grey Relational Analysis, and Pearson correlation analysis. This combined approach quantitatively links macroscopic mechanical responses with microstructural evolution. Grey Relational Analysis and Pearson correlation analysis were used to quantify the coupling between macroscopic mechanical properties and microscopic pore parameters. The results reveal distinct deformation behaviors: the L-W path induces significantly larger deviatoric strain than the W-L path, with strain increasing notably as deviatoric stress rises. Microstructurally,both paths promote the transformation of large and medium pores into small and micropores with increasing stress, accompanied by enhanced pore orientation and reduced morphological complexity. The L-W path intensifies these effects due to stress-induced particle rearrangement followed by wetting-induced effective stress redistribution. Grey Relational Analysis and Pearson correlation analysis confirms that pore orientation (distribution entropy) is the most sensitive to hydraulic paths, followed by pore roundness and abundance, while pore circumference and length exhibit minimal correlation. These findings highlight the critical role of the loading-wetting sequence and provide a quantitative macro-micro framework for assessing moisture-induced deformation risks in loess-region infrastructure.