Abstract:

The shield launching section of Nanjing Weisanlu rivercrossing tunnel has such features as shallow overburden, small spacing between the left tunnel tube and the right tunnel tube, large gradient, curved launching and small launching shaft. Cement mixing piles and freezing are adopted to reinforce the shield launching section. Because the shield cannot make a turn during launching, secant launching technology is adopted. Proper selection of launching soft eye seal structure and high seal structure installation accuracy provide excellent sealing for the shield launching. A new launching soft eye seal structure is introduced in this paper. The negative steel ring is designed in the form of normal segments and is assembled by the erector, because the longitudinal space of the launching shaft is not big enough to lift the negative ring. Besides, techniques for slurry pressure establishment, which are determined on basis of full consideration of the geology conditions, are systematically presented. By adopting the key technologies presented above, the slurry shield for Weisanlu rivercrossing tunnel in Nanjing has bored through the launching section successfully, with the tunneling position of the slurry shield matching well with the design position, the reaction frame being solid and reliable, the steel negative rings having been positioned precisely and the sealing of the launching soft eye being in good condition.

Key words: Weisanlu rivercrossing tunnel in Nanjing, superlarge diameter shield, shallow overburden, slurry shield, launching soft eye sealing, launching, negative steel ring, slurry pressure establishment