Fig 1.
Location map of the study area and typical loess–mudstone landslides:
(a) Loess Plateau; (b) loess–mudstone landslides and sampling points; (c) sampling point. (Note: The digital elevation model used in Fig 1a is derived from the ASTER GDEM (URL: https://terra.nasa.gov/data/aster-data). The boundary of loess pleatue used in Fig 1a is are available at https://doi.org/10.5281/zenodo.17948985).
Table 1.
Basic physical and mechanical indexes of loess and mudstone.
Fig 2.
Analysis of particle size gradation of loess and mudstone for test.
Fig 3.
(a) Effective shear area diagram of the upper and lower shear boxes after dislocation (the gray part is the actual shear area after dislocation); (b) force diagram of the soil sample in the upper shear box after shear dislocation.
Table 2.
Design of direct shear test conditions.
Fig 4.
Direct shear specimens with different interface morphologies.
(a) smooth interface; (b) stepped interface; (c) shallow serrated interface; (d) deep serrated interface.
Fig 5.
Relationship between shear strength and normal stress for loess and the smooth interface under different moisture content conditions: loess at (a) 10%, (b) 13%, (c) 16%, and (d) 19% moisture contents.
Fig 6.
Microstructural scanning images of contact surface under different moisture contents of upper loess: (a) w = 10%, (b) w = 13%, (c) w = 16%, (d) w = 19%.
Fig 7.
Relationship between shear strength and normal stress for loess and the smooth interface under different dry density conditions: loess with dry densities of (a) 1.4 g/cm3, (b) 1.45 g/cm3, (c) 1.5 g/cm3, and (d) 1.55 g/cm3.
Fig 8.
Microstructural scanning images of the contact interface under different dry densities of the upper loess: (a) ρd = 1.4 g/cm3, (b) ρd = 1.45 g/cm3, (c) ρd = 1.5 g/cm3, (d) ρd = 1.55 g/cm3.
Fig 9.
The relationship between shear strength and normal stress under different interface morphology.
Fig 10.
Microstructural scanning images of shear sections with different contact surface morphologies: (a) stepped, (b) shallow serrated, and (c) deep serrated.
Fig 11.
Shear strength parameters of loess and smooth interface under different water content and dry density conditions: (a) Cohesion under different moisture content conditions.
(b) Internal friction angle under different moisture content conditions. (c) Cohesion under different dry density conditions. (d) Internal friction angle under different dry density conditions.
Fig 12.
The variation law of microstructure parameters of contact interface under different water content and dry density conditions: (a) Moisture content; (b) Dry density.
Fig 13.
The microstructure diagram of the sample under different water content and dry density conditions: (a) Moisture content; (b) Dry density.
Fig 14.
The change of shear strength parameters under different contact interface morphology.
Fig 15.
The change of microstructure parameters under different contact interface morphology.
Fig 16.
Macroscopic shear failure surface characteristics and shear failure modes of specimens with different contact interface morphologies.
(a) Macroscopic shear failure surface characteristics of samples with different contact interface; (b) Roughness and shear failure mode of macroscopic shear failure surface with different contact interface morphology.
Fig 17.
Principle diagram of disaster effect of loess-mudstone landslide: (a) Schematic diagram of loess-mudstone slope; (b) The change of dry density of overlying loess before and after unloading; (c) Different sedimentary environments form different interface morphology; (d) Interface roughness decreases after shearing process.