Abstract: A sinking simulation test of deep and large caisson is designed based on the caisson of Hutong Bridge. The undrained sucking sediment sinking of the caisson in the water is simulated and spatial distribution of the stress at the tread and oblique planes of the foot blade during the sinking process of the caisson. It concludes that the maximum stress occurs in corners of the caisson, the minimum stress occurs in the middle of long side, and the average stress at the short side is larger than that of the long side. Applying the reference stress at the midpoint of the long side, the total cross-section stress coefficient of the foot blade with the aspect ratio of 1.33 is calculated. In addition to be affected by spatial position, the stress on the incline plane of the foot blade is also greatly related with the mud surface height, and it changes contrary to the stresses at the tread. When the mud surface height is determined, the cubic function is used to determine its stress distribution. The influences of inclination, sand-casting and sudden sinking on the stress of the foot blade are also discussed and it is found that both can cause changes in spatial distribution of the stress of blade foot. Stresses at the tread and incline planes hydraulic gradient of the foot blade change significantly before and after the sand-casting and sudden sinking of caisson. They occur earlier than the sand-casting and sudden sinking of caisson and it is of great significance to early warning of sand-casting and sudden sinking.

Key words: caisson sinking, foot blade, spatial stress, caisson inclination, sand-casting and sudden sinking