Protection of a 193.5-m High Concrete Tube-Shaped TV Tower Close to Subway Excavations

Abstract

A 193.5-m high concrete tube-shaped TV tower in the city of Nantong, China, was founded on short piled–raft footing, whose safety was threatened by implementation of four 10.9–26.5-m-deep excavations for an interchange subway station within close proximity. Considering the great damage potential of the TV tower associated with excavation-induced ground movement, a row of barrier piles consisting of bored piles was initially constructed between the excavations and TV tower. Field monitoring data indicated that the TV tower developed limited settlements during excavation of the two farthermost subway zones. However, it suffered notable settlements during excavation of the second farthest subway zone; hence, large-diameter metro-jet-system (MJS) piles along with bislurry piles were constructed between the excavations and TV tower to mitigate the adverse excavation influence. As a result, the tower gradually stabilized as construction continued, but it still exhibited an accelerated rate of differential settlement. Since excessive differential settlements might incur cracking, tilting, or even an overturning failure of the tower, it was determined finally to underpin the TV tower with long end-bearing steel pipe piles before excavation of the closest subway zone. With the aid of the comprehensive underpinning plan, the tower gradually became steady during excavation of the closest subway zone, without suffering structural damages or excessive deformations. The lessons and experience learned from this project as well as the extensive protection plans and measures are practically useful for engineers worldwide to safeguard high-rise superstructures sensitive to ground movement.