On Design and Construction of Pile Group Foundation of Taipei 101

The evenly distributed cast-in-place reinforced concrete group piles with socketed length into soft bedrock of 15 to 33 m were designed as the foundation for Taipei 101. The high-rise building is extremely sensitive to the foundation settlement. Besides, the bearing behavior of a cast-in-place bored pile is largely determined by the way it was installed. Accordingly, the design of pile group foundation for Taipei 101 was based on a series of full scale pile trial installation as well as comprehensive instrumented pile load tests with compressive and pull-out load up to 40 MN and 22 MN respectively. The characteristic t-z curve for each subsurface stratum was evaluated and used to predict the pile load-settlement behavior for the specific soil stratification of each pile located, thus each pile length was determined according to the anticipated loads during service. Besides, the pile group effects, including bearing capacity reduction and settlement increase, were considered in the foundation design. The creep behaviors for piles embedded into bedrock were also analyzed by using the measured results of pile load tests. The superstructures, basement, mat, piles and retaining diaphragm walls were modeled into one integral system for the structural design of foundation, thus the estimation of foundation behavior under various load combinations were conducted using the above mentioned model with the sub-grade reaction under foundation mat. Based on the investigation of trial installations, the construction specification was proposed for the installation of reverse circulation piles. For piles under the main tower, the measures of bottom cleaning and post-grouting were employed to improve the pile bottom sediments and increase end bearing capacity. Both the conventional static and STATNAMIC dynamic loading tests were employed to verify the bearing capacities and behaviors of production piles. Results of the proof load tests met the design requirements well as compared with the simulation using pile ultimate load test results.