Abstract: With the development of city modernization, deeper and larger foundation excavations are rapidly increasing. The challenge of determining the bearing capacity of such excavated foundation soils is ever becoming urgent. The estimation formula for the deep foundation bearing capacity defined by the current code is a semi-empirical approach which is established based on the Prandtl foundation bearing capacity model and modified by the Reissner approach. However, the current formula ignores the shear strength of soils above the excavated area. This paper starts from the principles of Prandtl foundation bearing capacity model, then deduces theoretically the value of the foundation soil bearing capacity of deep foundations. This paper also presents a case history of the theoretical bearing capacity value in a cut and cover highway tunnel in Guangdong Province. These analytical results are compared with the value derived from the current code. The results show that the proposed theoretical formula is more comprehensive and intuitive, and it also provides a reference in determining the bearing capacity of deep excavation soils.

Key words: Deep Excavation, Limit Equilibrium Theory, Bearing Capacity of Foundation Soils