Phosphogypsum is a kind of solid waste that occupies land resources and harms the environment. It can be used as a solidified material, but the utilization of phosphogypsum is limited by its impurities and weak strength performance. This study aimed to use microbial-induced carbonate precipitation (MICP) to improve the water stability, permeability, and hydraulic erosion resistance of phosphogypsum and evaluate its impact on the environment. In this paper, the phosphogypsum samples and artificial slopes were prepared and solidified by spraying various concentrations of bacteria solution and cementation solution to achieve microbial modification. The water stability and permeability test were used to calculate the mass of spalling under water shaking and the permeability coefficient. A rainfall scouring test was carried out to estimate the erosion resistance. The erosion degree was quantitatively calculated using 3D laser scanning technology. The results show that the microorganism treatment can improve water stability and reduce the permeability coefficient, while the differences between the content of CaCO₃ in the outermost layer and in the inner layer gradually increase with the increase in bacterial concentration, and the permeability coefficient was reduced uniformly. The sediment loss of the slope after MICP treatment was much less than that of the untreated slope, and the connection force between the particles was strengthened. By observing the morphology of the scoured samples, we found that the treated particles were aggregated and flocculated with more macropores, which led to the formation of erosion pits under scouring. The pH of the outflow of the modified slope was neutral, and the heavy metal elements were fixed by microbial action and carbonate, which is not harmful to the environment.

Construction operations in cold regions may encounter frozen geomaterials. In construction, it is important to understand the processes by which geomaterials fail under common loading conditions to avoid accidents and work efficiently. In this work, an artificial frozen soil–rock mixture was used for uniaxial compression and indirect tension loading analysis to investigate macroscopic failure patterns and soil–rock interface crack evolution mechanisms. To further understand and compare the meso-mechanical failure mechanisms of the soil–rock interface, we used two types of rock block particles with different surface roughness for fabricating frozen artificial soil–rock mixtures. Acoustic emission (AE), ultrasonic plus velocity (UPV), and digital microscopy were utilized here to obtain the sample deformation response and analyze the morphology of the soil–rock interface. The results were as follows. From the perspective of macroscopic observation, bulging deformations and short tension cracks represent the main failure pattern under compression, and a tortuous tension crack in the center of the disk is the main failure pattern under indirect tension. From the perspective of microscopic observation, the soil–rock interface will evolve into a soil–rock contact band for the sample containing a rough rock block. The strength of the soil–rock contact band is obviously larger than that of the soil–rock interface. Three main failure patterns of the soil–rock interface were observed: a crack path through the accurate soil–rock interface, a crack path through the envelope of the rough rock block, and a crack path passing through the rough rock block. The experimental results could provide a reference for foundation engineering, especially in pile foundation engineering in cold regions.