Field loading tests on large-diameter and super-long bored piles of Shanghai Center Tower

Large-diameter and super-long bored piles with a diameter of 1000 mm and a length of 88 m are adopted for Shanghai Center Tower, which is the highest building (632 m) under construction in China. This pile type is different from that adopted in the adjacent Jinmao Tower (420 m) and Shanghai World Financial Center (492 m). As test piles are loaded to failure and measured by distributed optical fiber, the test results are valuable to study the bearing capacity and load transfer mechanism of large-diameter and super-long bored piles in Shanghai soft soils. The results show that the load-movement curves of the piles are almost linear before achieving plunging failure. Distribution and characters of pile shaft friction of shaft and toe post-grouted piles are different from those of only toe post-grouted piles. The ultimate pile-soil relative movements are less than 5 mm and 10 mm to bring pile shaft resistances into full play in clay and sand, respectively. After that, the pile shaft friction in the shallow clay is degraded. The pile shaft friction is lower in the shallow soils and more than 2 times in the deep soils than the empirical value in the local specifications. Since the toe resistance takes a small part of the ultimate load, the piles behave as friction piles. The compression of the piles accounts for about 95% of the pile head movements under the ultimate load. The pile tests provid guidance and technical support for bored piles used for 600 m high-rise buildings in Shanghai soft soils.