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

• Published in: Tunnelling and underground space technology 2020-07, Vol.101, p.103404, Article 103404
• Main Authors: Li, Liping, Sun, Shangqu, Wang, Jing, Song, Shuguang, Fang, Zhongdong, Zhang, Mingguang
• Format: Article
• Language: English
• Subjects: Caves; Computer simulation; EPB shield machine; Excavation; Geomechanical model test; Karst; Model testing; Precursory information; Rotation; Seepage; Surrounding rock stability; Three dimensional imaging; Three dimensional printing; Tunneling shields; Tunnels; Underground construction; Water; Water inrush
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2020.103404

•Compound EPB shield machine was developed to simulate the tunnel excavation.•Soluble 3D printing of an irregular cave solve the problem of model prefabrication.•Ground settlement model can be constructed by laser scanning technology.•Mechanical force provided by the machine are related to precursory information. 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.