Macro and micro connections for slip zone soils of landslide under wetting–drying cycles in the Three Gorges Reservoir area

Temporal variability in the macro-mechanics and microstructure induced by periodic water fluctuations during reservoir operation is widespread but adverse for slip zone soils. Herein, taking the slip zone soils of Huangtupo No. 1 landslide in the Three Gorges Reservoir area as a research case, the consolidation undrained (CU) triaxial tests coupled with wetting–drying cycles are organized to address macroscopic temporal variability of shear strength parameters. Then, quantitative microscopic characterizations are performed based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with mercury compression test (MIT). Eventually, the macro and micro connections are identified via gray rational analysis (GRA) and dynamic time warping (DTW) to be thus mathematized. Moreover, the weakened constitutive model is constructed. The test results show that the temporal variability of macroscopic shear strength parameters can be quantified as negative exponential decay. The wetting–drying cycles prominently contribute to the generation of intra-agglomerate pores (0.9–35 μm). Besides, the inter-granular pores (0.007–0.9 μm) and porosity are the connections to bridge microstructural parameters and macroscopic shear strength parameters. Furthermore, empirical equations for macro and micro connections are tentatively derived; the temporal variability of slip zone soils is invited to appropriately model the weakening laws of stress–strain. This study is expected to provide ingenious perspectives and promising references in stability evaluation and even disaster prevention of reservoir landslides.