Hidden soil caves pose a serious threat to the stability and safety of subgrades. In this study, using the two-dimensional particle flow discrete element code, a total of eight subgrade models with circular soil caves of different dimensions, depths, and locations were established. Under self-weight and superimposed loading, the deformation characteristics of fill subgrade models, such as the evolution of displacement field and crack development process, were analyzed. The results show that under the self-weight, after the fill subgrade model of soil caves with diameters of 2 m, 4 m, 6 m, and 8 m is stable, the overlying soil layer of the soil cave corresponds to the transformation of slag falling, block falling, collapse and rapid collapse, respectively. The larger the dimension of the soil cave, the larger the number of cracks and damage areas, and the more prone the fill subgrade is to collapse. The superimposed load makes the fill subgrade compress from shallow to deep, significantly increasing the overall subgrade deformation, the number of cracks, and the development range. The evolution of the displacement field and crack propagation of the fill subgrade are also controlled by the buried depth and location of the soil cave. Whether the fill subgrade collapses is comprehensively controlled by the dimension and buried depth of the soil cave, the mechanical parameters of the soil layer, the load, and its scope of action. Thus, a comprehensive criterion of cylindrical collapse of the soil layer above the soil cave is constructed.

As a new mechanism to cause karst collapse, the positive pressure effect causes geological disasters that seriously affect the safety of people's lives and properties in karst areas. If we can understand the characteristics and rules of karst soil cavities in different evolutionary stages from the kinetic point of view, it can play an important role in saving the funds for engineering investigation, reducing the cost of soil cavity treatment and reducing the risk of engineering disasters. Therefore, in this paper, based on the analysis of the damage mechanism of karst soil cavern under the effect of positive pressure, based on the ASCII text provided by FLAC itself, the orthorectified simulation calculation program is prepared and finite element analysis is realized in FLAC3D, focusing on the uneven change of soil displacement, stress redistribution and plastic damage of karst soil cavern in different evolutionary stages under the effect of positive pressure, and summarizing the the stress, strain and damage characteristics and rules of plastic zone in karst soil caverns at different evolutionary stages are summarized. It is hoped that the research results will be of scientific value to deepen the research on the theory of cave-in prevention and control of covered karst soil caverns.