A CPTU-based earth pressure model for deep excavations under complex environment and its practical application

The determination of earth pressure is a key element for the design of retaining structures of deep excavations. However, the existing earth pressure models can not reasonably consider the change of soil properties induced by excavation activities. The piezocone penetration test (CPTU) is capable of effectively avoiding the sampling disturbance and quickly providing the continuous in-situ testing parameters of soils (cone resistance, sleeve friction, pore water pressure). Combining the CPTU tests and the displacement-based earth pressure model, the change of soil properties induced by excavations, surrounding buried structures (confined soil), soil arching effects, soil strength parameters and friction angle of the soil-structure interface are comprehensively taken into account to develop a unified earth pressure model (from active- to passive-state) under the Coulomb's earth pressure framework. The comparisons of earth pressures obtained between 1g-/ng- model tests and the developed model are made for the validation. Subsequently, the developed model is employed in a deep excavation adjacent to a metro station in soft soils deposited in the Taihu Lake. The CPTU tests are then performed in the soils around both sides of retaining structures, of which the earth pressure and lateral deformation are also measured. The interpretation of in-situ testing results indicates that state parameters of soils significantly change due to excavations, but the effective friction angle almost remains unchanged. The further comparisons of earth pressures obtained between the measurement and the developed model indicate that the CPTU-based earth pressure model works well for a deep excavation under a complex environment, thus successfully reaching a practical application.