Centrifuge model tests on deformation of ultra-deep foundation pits in soft ground

The main performance of ultra-deep foundation pits,such as deformation of retaining structure,change of soil pressure and surface settlement of perimeter ground,is studied through centrifugal model tests.Two parallel excavation test cases are designed in the research:one is an exclusive foundation pit and the other is that with adjacent high rise buildings,both of which are 38 m-deep multi-strutted soft ground foundation pits of a restoration work of metro line No.4 in Shanghai.The main performance of the two foundation pits is summarized and discussed,and comparison between the tests and field monitoring data is conducted.The results show similar performance in the two foundation pits,in which the deformation of retaining structure accretes with the progress of excavation at the early stages and the maximum lateral displacement of the wall along the depth remains in a certain value at the later stages,while the location where the maximum displacement occurs goes down and falls roughly around the excavation surface.The change of earth pressure accords with the deformation of retaining structure and the profile of ground settlement is observed to be in trough-shape,where the bottom of the trough goes deeper and farther away from the wall in the process.The results of the centrifugal tests conform well to the field measurement.