Simplified analysis method of pillar uplift in deep excavation of subway station in thick soft clays

Unloading in deep excavation in thick soft soil usually leads to large pillar uplift which may endanger the safety of the retaining system. In the pillar uplift analysis, complex interactions among soil, pillar (pillar pile) and struts are involved, and the soil heave behavior during undrained excavation shall be understood well, but there is no simplified calculation method available at present. Firstly, the interactions among soil, pillar (pillar pile) and strut are simplified, and a theoretical analysis model for pillar uplift estimation in practical design is proposed, in which the key point is the determination of the heave of the soil around the pillar. Based on the numerical analysis results, a normalized soil heave curve was proposed, and the soil heave could be estimated in terms of the maximum lateral displacement of the retaining wall. Finally, with the deep excavation of a subway station in Shanghai taken as an example, the design procedures with this new method were elaborated, and the rationality of the method was verified; the stress and deformation characteristics of the pillar and the design principles of uplift control of the pillar were also discussed in depth based on the calculation results. © 2023 Editorial Office of China Civil Engineering Journal. All rights reserved.