Abstract: The Karnaphuli River-crossing Tunnel project in Bangladesh has the characteristics of nearby sea area, spring tide difference, large slope, large diameter and crossing through water-rich sandy stratum. The risk of water and sand gushing is very high. Hence, to solve the water and sand gushing problem during shield launching, the large-diameter air cushion type slurry pressure balanced shield is adopted. The reinforcement technology of triple-pipe jet grouting pile, dewatering technology and large-diameter steel sleeve launching technology are put forward from the aspects of strengthening the soft stratum, cutting off the source of groundwater and reducing the consequence of water and sand gushing. The large-diameter steel sleeve launching technology includes large-diameter steel sleeve and support system design and installation technology, large steel sleeve and reaction frame deformation monitoring technology and technology of establishing slurry chamber in steel sleeve. The conventional curtain rubber hole sealing device is replaced by steel sleeve seal, and the partial seal is changed into the whole seal, which greatly reduces the risk of water and sand gushing in the hole in water-rich sandy stratum and improves the safety of shield launching.

Key words: river-crossing tunnel, large-diameter slurry shield, steel sleeve, shield launching, monitoring