Field measurement study of earth pressure on a double-layered diaphragm wall

A super-deep foundation pit project in Nanjing is constructed with a double diaphragm wall of shaped enclosure structure. The soil between the double walls is in a non-limit equilibrium state, and the evolution of soil pressure distribution and the mechanism of wall-soil interaction are not well understood. To investigate the soil pressure variation within the limited soil body between the double walls caused by deep foundation pit excavation, and to examine the influence of the soil arching effect on the soil pressure distribution outside the walls, this study employs a combination of on-site measurement analysis and physical model calculations. Initially, earth pressure monitoring points are established within the soil layers through field testing, aiming to capture the evolution of earth pressure between the walls during the excavation process. Subsequently, a curved conical soil arch model is established, taking into account the layering of the soil body. This model calculates the changes in earth pressure outside the walls due to the development of lateral soil arches. The accuracy of the model's results is then discussed through parameter inversion and error analysis of the experimental data. The findings reveal that the excavation process predominantly impacts the soil between the double walls by causing compressive deformation. The lateral constraints imposed on this limited soil body contribute to further enhancing its shear strength. Among various excavation stages, the soil excavation process significantly disturbs the geological layers. The lateral soil arching effect further increases the earth pressure on the shallow soil retaining wall, while there is almost no development of lateral soil arches in the middle and deep soil layers. When considering the lateral soil arching effect, the calculated soil pressure aligns more closely with field measurements compared to the traditional Coulomb theory method, which separately calculates soil and water pressures. This study can provide insights and suggestions for the design and construction of deep foundation pit projects with special-shaped enclosure structures.