Development of compound EPB shield model test system for studying the water inrushes in karst regions

Abstract The shield tunnel, when running through urban karst areas, may induce engineering hazards, such as water inrush, ground collapse, and shield drooping. To reveal the water inrush mechanism triggered by confined karst caves during shield excavation, we developed a model test system for studying the evolution of water inrushes, which could be used to simulate the shield excavation process. The compound EPB shield machine allows the adjustment of parameters, including the cutter rotation speed, torque, excavation speed, supporting force, tunneling footage and excavation height. At a 1780 mm excavation distance, the deflection of the front end can reach the millimeter level. A special cutter with an automatic protection mechanism was designed to avoid low rotation speeds and high jacking forces, thereby effectively protecting the cutter. Moreover, several new and advanced test techniques were developed, including the soluble 3D printing of an irregular karst cave model and ground settling reconstruction using laser measurements. Based on these test devices and advanced techniques, a model test of the water inrush in the Jinan metro was conducted using the EPB shield machine, in which the variations of displacement, stress, and seepage pressure were analyzed. The results showed that the apparatus performed stably and reliably.