FILL PROCESS FOR ENCLOSED CAISSON

PURPOSE:To improve the charge rate of fill sand by providing a drain port larger than the diameter of a return pipe and a flared portion having the diameter larger than the return pipe on the end thereof to connect the flared side end to the drain port. CONSTITUTION:A caisson body 1 is provided on a top plate 2 with a pouring port 3 and a drain port 11 having the sectional area of about 5 times the pouring port. Then, a return pipe 7 is provided on the end with a flared part 12 having the lower end opening diameter equal to the drain port diameter so that the end is connected to the drain port 11. The sectional area of each opening of the drain port 11 is made 5 times that of the pouring port 3, the number of the drain port two times that of the pouring port and the flow rate 1/10 so that the sinking speed of fill sand is slowed down in still water. Thus, the charging rate in a partitioned chamber 8 having the drain port can be improved.