Analysis and Countermeasures of Key and Difficult Points in the Investigation of a Super Large Diameter Shield Project

With the continuous development of urban municipal construction to ultra deep underground space, super large diameter tunnel construction technology is gradually adopted. At present, the technology of super large diameter shield tunnel is developing in the direction of large depth, large section and long distance. Due to the large cross-section size, large fluctuation of buried depth, complex engineering geological and hydrogeological conditions, complex geotechnical engineering problems will be encountered. Based on the reconstruction tunnel project of Beijing East Sixth Ring Road, the characteristics of the large-diameter shield project, such as high survey level, complex engineering geology and hydrogeology, and great difficulty in ultra deep foundation pit support and groundwater control were summarized. Standard penetration in situ test and indoor physical and mechanical tests such as particle analysis, static lateral pressure coefficient and subgrade bed coefficient have been carried out. A special hydrogeological survey such as layered observation of groundwater level, pore water pressure test of cohesive soil layer, pumping test and water injection test was carried out to provide hydrogeological parameters. All these provided a basis for the selection of super large diameter shield machine, cutter head and cutter configuration, the matching of various construction parameters in the process of super large shield tunneling, the support design of shield shaft and the design of groundwater control scheme. It also provides reference for similar projects.