Abstract:

A shield bored tunnel of line 3 of Nanjing Metro crosses underneath a box culvert and its pile foundations are in fluidplastic strata. In this paper, four pile foundation treatment plans are compared and analyzed: Plan A: removing the piles from the ground surface, reinforcing the box culvert, and proceeding with shield tunneling; Plan B: removing the piles from the ground surface, underpinning the pile foundations, restoring the box culvert and proceeding with shield tunneling; Plan C: cutting off the piles intervening into the mined tunnel scope, underpinning the pile foundations by using the mined tunnel structure, and the shield machine passing through the mined tunnel; and Plan D: underpinning the box culvert, removing the piles from inside the mined tunnel, backfilling the mined tunnel and proceeding with shield tunneling. Plan D is adopted in the end. The key technologies for mining tunneling and shield tunneling in fluidplastic strata are presented. Based on the data collected from the site, it is established that the key measures taken, such as underpinning the box culvert after the foundation is reinforced, incorporating the CRD excavation method in the mining tunneling after the ground is reinforced by splitting grouting technology, removing the piles from inside the mined tunnel and shield tunneling through the mined tunnel, are important technologies in ensuring the safe passing of the shield machine through the pile foundations.

Key words: shieldbored tunnel, mined tunnel, soft fluidplastic strata, pile foundation underpinning, tunnel backfilling, shield passing through Metro station