Pattern and Mechanism of Response of Loess Shear Strength to Acid Pollution in Seasonal Frozen Areas

In seasonally frozen areas polluted by acid solution, loess is prone to uneven settlement, collapse, and other disasters, posing a severe threat to human life and property. This study subjected remolded loess samples to different levels of pollution by hydrochloric acid solution and several freeze–thaw cycles. Then, direct shear tests, scanning electron microscopy (SEM) observations, and X-ray diffraction (XRD) analysis were carried out. As the acid concentration and freeze–thaw cycles increased, the mineral composition of loess in the seasonally frozen area underwent a series of chemical reactions, with a sharp decrease in peak strength, significant decrease in cohesion, and limited decrease in the internal friction angle. The soil particles underwent fragmentation, a large amount of intergranular cementitious material dissolved, and the number and size of pores increased. Moreover, many agglomerated particles were generated. These results provide a useful reference for investigating the engineering properties of loess in seasonally frozen areas after acid pollution.