Influence of shallow loess crack patterns on meso-pore morphology and distribution

Frequent shallow loess disasters pose severe threats to line engineering and public safety. Millimeter-scale cracks serve as key controlling factors in the initial stage of shallow loess disaster development. Such cracks can alter the morphology and distribution of mesoscopic pores within loess to influence permeability and mechanical behavior, consequently reducing the stability of shallow loess masses. Therefore, this study investigates the mesoscale initial damage state of loess specimens containing millimeter-scale cracks with different patterns through laboratory experiments. Uniaxial compression tests coordinated with CT scanning were conducted to record damage state images. Machine learning methods were employed to establish three-dimensional models of the meso-pore structure, allowing systematic quantitative analysis of pore size, arrangement, and morphology. Experimental results indicate that specimens containing cracks reach the initial damage state at lower stresses. Cracks at different depths reduced the initial damage stress by approximately 68%, cracks with different inclinations reduced it by about 72%, and cracks with different combinations reduced it by about 83%. Under the damage state, small pores increased while large pores decreased. Near-horizontal and near-vertical pores suffered severe damage. Spherical pores exhibited more regular morphology, and irregular pores showed more complex morphology. Damage pores primarily distribute in clustered patterns along the extension directions of cracks at different depths, in striped patterns along the inclination directions of different inclined crack tips, and in concentrated patterns between different combined cracks. Under the localized concentration of tensile and shear stresses at crack tips and sides, pore structures collapsed and particles rearranged within the affected soil, leading to the formation of small pores and the disappearance of large pores. Changes in the meso-pore structure initiate and exacerbate internal damage within soil.