Abstract: The sinking process of the traditional open caisson construction is uncontrollable and is greatly influenced by the soil stratigraphy and the excavation method. The active control of the sinking state by the lifting and sinking of the open caisson can effectively solve a series of problems, such as, sudden sinking and over sinking in the sinking process in the traditional soft soils. However, during the lifting and lowering process, the lock ring beam outside the well needs to resist the upper lifting reaction force, and its mechanical behavior is not clear. This paper presents a case history of an underground intelligent parking garage project of Kunshan Forest Park. A mechanical model of lifting and locking forces is established according to the characteristics of the open caisson lifting and sinking construction. By using the threedimensional finite element simulation, the deformation and stress changes of the lock ring beam during the lifting and lowering of the open caisson are evaluated. The results show that there are differences in the convergence deformation of the lock structure during the lifting and sinking process. It expands upward and contracts outward along the downward direction, and transits from circular to oblong shape along the radial direction; During the sinking process, the settlement at the outer edge of the lock ring beam is the largest. With the sinking of the open caisson, the influence range of surface settlement decreases to both sides along the lifting system, and the influence range is 0.6~1.1 times of the sinking depth; Before sinking, due to the reinforcement of the local soil at the lower part of the caisson lock, the stress concentration occurs at the contact corner edge with the lock mouth beam, the structure should be strengthened at this location in the design.

Key words: Open Caisson, Suspension Force, Numerical Simulation, Deformation, Stress