Discussion on the Simplified Calculation Method for Diaphragm Wall Deformation of Ultra-Deep Circular Foundation Pit

Circular excavation diaphragm wall structure should be computed in accordance with the spatial structure, such as three-dimensional finite element analysis or certain specifications of the plane vertical elastic foundation beam method, considering the circular arch effect. The calculation is rather complex, with numerous influencing factors. In this paper, the deformation mechanism and influence of the ground connecting wall are analyzed from the aspects of the circumferential stiffness of the ground wall and the thickness of the joint mud skin based on the actual engineering case and the measured results of the foundation pit. The results indicate that: The radial horizontal deformation of the circular ground wall under the circumferential confining pressure is mainly attributed to the compression deformation of mud and concrete. A formula for calculating the radial horizontal displacement of the circular ground wall is established based on the mud compression and concrete compression models. When the confining pressure is low, the annular stiffness of the ground wall is mainly manifested as the mud compression stiffness, which can be nearly disregarded. In the conventional beam method and finite element calculation, the equivalent circumferential stiffness of the wall is applied before the deformation of the ground wall, and the calculation result is too small, leading to an unsafe foundation pit. In this paper, based on the comparison of theoretical analysis and measured results, a simplified calculation method of the beam method for the plane vertical elastic foundation is proposed. In the calculation, it is more rational to consider the toroidal stiffness of the ground connecting wall according to the dynamic joint compression or wall deformation.