Experimental study on side friction distribution of caissons during sinking in water

A sinking simulation experiment on a deep and large caisson is carried out based on the main caisson of Shanghai-Nomtong Bridge. Through the analysis of the whole dynamic sinking, it is determined that the effective stress on the sidewall is affected by various factors such as sinking rate, pressure relaxation, inclination, sand-casting and sudden sinking. After stopping sand suction, the effective stress of the sidewall changes from a dynamic distribution to a quasi-static one, the overall trend is decreasing and shows the reduction of extreme points and recovery of pressure relaxation zone. The arrangement of the step can reduce the total side friction of the caisson, and the reduction mainly comes from the vertical section of the caisson. It is found that the sidewall of stepped caisson can be divided into linear zone, step zone, excess zone and pressure relaxation zone. A model for calculating the side friction of the caisson in vertical state is established based on the influences of the step and verified by the on-site monitoring tests on No. 29 caisson of Shanghai-Nantong Bridge. The inclination the of caisson causes a change in the effective stress distribution of the sidewall, and the increased earth pressure generated by the compaction is 3~4 times the active earth pressure of the corresponding side.