Analysis of Mechanism of Sand Gushing and Sudden Sinking of Ultra-large Deep-water Open Caisson in sand via Field and Model Tests

In view of the sinking of the largest and deepest open caisson in sand, detailed statistical analyses of sand gushing (29 times) and sudden sinking (18 times) are conducted for the first time. Through on-site monitoring tests and sinking simulation tests of sand gushing and sudden sinking, the relevant laws are investigated. Statistics show that an ultra-large deep-water open caisson is prone to sand gushing and sudden sinking when the burial depth is more than 50m. Sand gushing is the inducement of sudden sinking, and there is a progressive failure mode. Field and model tests indicated that the probability of sand gushing and sudden sinking is positively correlated with the penetration near the blade foot and negatively correlated with the blade foot resistance and lateral pressure. In addition, the development laws of sand gushing, sudden sinking and inclination after changing the force balance of caisson are put forward and verified. Spatial effects of stress distribution and inclination result in local stress concentration, which accumulates potential energy for sudden sinking. Thus, based on the assumption of limit equilibrium in elastic semi-infinite space and instantaneous failure of core soil column, a judgment model for sand gushing is proposed and a calculation method for engineering application is established, which is used to validate the sand gushing case in Section 3.2.