To meet the demands of large-diameter shield tunneling in the Chengdu Plain,this paper introduced the experience of selecting the shield for the previously constructed Zirui Tunnel and Jinxiu Tunnel,as well as the performance of shield in the construction of Shu'an Tunnel in Shanghai-Chongqing-Chengdu High-speed Railway(Chongqing-Chengdu Section)under construction,and discussed how to select large-diameter shield,and offer guidance on the adaptable configuration of shield machines.Key conclusions are as follows:(1)Both Earth Pressure Balance(EPB)and Slurry Pressure Balance(SPB)shield technologies are viable for the construction of large-diameter shield tunnels in the Chengdu Plain.(2)When the predominant geology consists of mudstone,EPB shields should be prioritized.For sections with high groundwater pressures or highly permeable strata,a strategy involving surface dewatering coupled with grouting reinforcement,followed by excavation using an upper chamber mud injection with EPB mode under pressure,is recommended.Where mudstone and sandy gravel strata are of comparable length,SPB shields or dual-mode EPB-SPB shields are favored.In cases where sandy gravel formations predominate,SPB shields are the preferred option.(3)In urban areas where large-diameter shield tunneling necessitates stringent control over ground settlement,shield machines should be provisioned with capabilities for synchronous injection of cement-sodium silicate grouts and application of Clayshock and other inert slurries to the exterior of the shield body.
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