Design and Research of Circular Diaphragm Wall for Deep Excavation of Shanghai Tower

Shanghai Tower, the tallest skyscraper in China with 632m building height is under construction. For such height of building, time for construction completion of the tower is the most critical issue in planning the project. It would be the best beneficial to the whole project if the excavation of basements could be commenced as early as possible and the period of construction could be as short as possible. A best solution came up after numerous discussion and comparison - conventional open excavation for basements in tower area and top-down method in podium area. Moreover, a cylinder-shaped diaphragm with outer diameter 123.4m, 1.2m thick and 50m in height was adopted as a lateral retaining structure for basement excavation in tower area with 31.1m excavation depth. This scheme provides a faster program by means of no extra lateral supporting strut installation and demolition during excavation and basement construction. Although the design scheme of cylinder-shaped diaphragm without lateral supporting strut has been applied in some projects domestically and oversea, in view of the project scale (excavation depth and excavation area), design difficulty (excavation in soft clay in extensive depth and diameter), it would be the first project in China mainland. This paper serves to summarize the discussion and design calculation, analysis and control measure on deep and large diameter cylinder-shaped diaphragm wall in conventional open excavation, and also intends to provide as a reference for future similar projects.