Treatment Technology for Grout Eruption during Large Diameter Slurry Shield Tunneling Machine Crossing the Water-Rich Sand Layer at the River Bottom

[Objective] The shield tunneling method has gradually become the preferred construction technology in China′s metro tunnel construction. The slurry-shield tunneling method, featuring high underwater stability, riverbed settlement reduction, and high construction safety, is widely applied in tunnels crossing rivers and seas. Therefore, it is necessary to study the treatment technology for grout eruption when a large diameter slurry-shield tunneling machine crosses the water-rich sand layer at the river bottom. [Method] Taking the project of large diameter slurry-shield tunnel machine crossing the Minjiang River tunnel in Fuzhou Metro as an example, the abnormal situations that occurred during the project construction in the full-section water-rich sand layer are studied, including sudden grout eruption on the river surface under high-pressure water conditions, sudden increase in the thrust, torque, and chamber pressure of the shield machine, and the cutterhead getting stuck and unable to rotate. Main problems encountered in the collapse treatment at the river-crossing section are analyzed, and the treatment plan and relevant treatment measures are introduced. The effectiveness of the proposed treatment plan and relevant treatment measures is verified by monitoring the surrounding bridges. [Result & Conclusion] Through comprehensive treatment methods such as performing water-based operations on the river surface, drilling and grouting to reinforce the soil above, in front of, and on both sides of the shield, adjusting the mud ratio, injecting tail-seal grease, bypassing pipelines, circularly reverse-washing the slurry chamber and air-cushion chamber, and adjusting the tunneling parameters in the reinforcement section, the shield machine is successfully extricated from trouble and smoothly passes through the grout-eruption section. The monitoring results of the adjacent bridge piles show that the maximum settlement value of the piles is 0.6 mm, within the safe control range.