Impact of Soil Layer Distribution on the Morphology Characteristics of Underground Cavities

Abstract

Urban road collapse disasters pose a serious threat to public safety and national economic development. The underground cavities formed by drainage pipe exfiltration are the primary cause of road collapse disasters in Beijing, with soil layer distributions playing a crucial role in their formation and development. In this study, a physical model test system for road collapse induced by drainage pipe exfiltration was developed, which comprised a drainage control unit, pressure regulation unit, experiment platform, multiple information monitoring unit, and water circulation unit. Internal and external imaging, coupled with waterproof laser rangefinders, were employed to study the formation, development, and collapse morphologies of the underground cavity influenced by clay, sand–clay, and clay–sand distributions. The results indicated that the underground cavity formed in four phases: soil–water mixture adhesion, seepage-induced runoff generation, irregular void development, and arched cavity formation. Furthermore, the physical and mechanical properties of the soil in proximity to the drainage pipe exerted the most significant influence on cavity development. The vertical cross section of the underground cavity was mushroom cloud-shaped, characterized by an upper bearing structure zone, middle saturated rheology zone, and lower stacking repose zone. The findings provide theoretical support to reveal the mechanisms of road collapse. The primary cause of urban road collapse disasters is the formation of soil cavities beneath the road, with drainage pipe exfiltration being a significant contributing factor to their formation. We developed a physical model test system for road collapse that enables real-time monitoring of soil cavity development. The progression of soil cavity development and the patterns of road collapse under clay, sand–clay, and clay–sand distributions were analyzed based on the physical model test system. Our findings reveal that the presence of sandy soil with weak physical and mechanical properties around the pipeline can sharply increase the collapse diameter of the soil cavity. The insights presented in this study can enhance our comprehensive understanding of road collapse mechanisms and provide guidance for mitigating road collapse hazards during the construction of new drainage pipes. For instance, it is advisable to use materials with low permeability and erosion resistance around drainage pipes to retard the expansion of soil cavities.