Key Technologies of Large-diameter Shield Tunneling in Sand and Gravel Strata

[Objective] Key construction technologies for large-diameter shield tunneling in sand and gravel strata are summarized and analyzed, including shield machine model selection, shield launching and receiving, and shield excavation posture control. Specific construction control parameters and measures are proposed to reduce cutterhead tool wear, decrease stratum losses, and minimize land subsidence and deformation. [Method] Considering the engineering structural characteristics, such as the loose structure, non-cemented or weakly cemented particles, large particle size, and strong permeability of sand and gravel strata, theoretical analysis and on-site monitoring methods are employed to deeply analyze the key construction technologies for large-diameter shield tunneling in sand and gravel strata, from aspects of shield machine model selection, shield originating and receiving, shield excavation posture control, as well as shield cutterhead tool detection-maintenance. [Result & Conclusion] The cutterhead opening rate, cutterhead tool models, and spoil improvement scheme of large-diameter shield should be specially designed according to the stratigraphical structure characteristics, facilitating efficient shield spoil discharge and advance cutting. Comprehensive reinforcement measures, such as stratum grouting consolidation, large pipe shed support, and construction dewatering, should be adopted at shield tunnel shaft end to ensure strata stability during large-diameter shield launching or receiving. In large-diameter shield tunneling, the control of parameters such as cutterhead rotational speed, spoil discharge rate, and spoil discharge temperature should be emphasized, along with appropriate increases in grouting volume to improve spoil modification effects and avoid excessive over-excavation, keeping stratum losses within a reasonable range. By implementing the aforementioned construction parameters and measures, the risk of shield excavation can be controlled, while significantly enhancing construction quality and efficiency, and substantially reducing construction costs.