Experimental and simplified model study of the development of ground settlement under hazards induced by loss of groundwater and sand

Most catastrophic failure in underground engineering is caused by soil and water loss. However, few studies have focused on the evolution of ground deformation during such a process. In this study, model tests were conducted to investigate the flow channel boundary (the interface between the flowing and stationary ground) and ground settlement profile during the flow process of sandy soil and water, and a simplified model was proposed based on the experiment results. The model was validated against measurements from laboratory model tests with fine and medium sand, and the tendency of the simplified model to predict the subsurface ground movement boundary was verified with case records of tunneling, which can also lead to similar soil loss. Finally, parameter analysis was performed according to the simplified model. The study showed that the flow channel boundary could be described by an ellipse for a planar problem (i.e., loosening ellipse). Furthermore, the flow channel boundary was related to the soil loss volume, buried depth of soil extraction location, and eccentricity of the loosening ellipse. The eccentricity of the loosening ellipse decreased with increasing average particle diameter. Peck’s curve could be used to describe the profile of the settlement trough when the mass loss ratio was not >20 %. The ground surface settlement profile changed to the shape of an “inverted triangle” with increased soil loss. The goodness of fit of Peck’s curve to subsurface settlement increased with depth before the deep ground flowed out from the opening. The effect of groundwater flow was considered in the model tests and simplified model to analyze the disaster mechanism, which can provide a reference for the further research.