Experimental investigation of construction of a 56 m deep constant thickness cement-soil wall using trench cutting re-mixing deep wall (TRD) method in deep aquifers

The excavation area of Shanghai International Financial Center, whose surrounding environment is complex, is 48 860 m(2). The depth of the excavation ranges from 26.5 to 27.9 m. In order to minimize pumping effects of confined water on the surrounding environment, a 700 mm thick and 56 m deep constant thickness cement-soil wall has constructed as a watertight screen along the periphery of the excavation. As the first time to construct such a deep TRD wall in Shanghai, a series of tests had carried out on the site. The monitoring results show that the strength of the cement-soil wall has ranged from 0.84 MPa to 1.38 MPa in the deep aquifer. Laboratory permeability test results show that the permeability of the wall is increased from 10 - 3 cm/s to 10 - 7 cm/s. Both strength and permeability of the wall satisfied the design requirements for a watertight screen. During construction of the wall, the maximum surface settlement is about 8 mm and the main influence zone is approximately 5m away from the wall. It is also observed that lateral soil displacements mainly took place within 5 m from the wall. Therefore, the influence of the wall construction on the surrounding environment is negligible. The test results provide references for subsequent construction of the TRD walls and serve as a case study for similar projects in Shanghai as well.