The utility model provides a superficial layer is played in dry dock dock bottom that is used for immersed tube tunnel tube section to rise to float, characterized by, the basis in dry dock pipe prefabrication district is traded and is filled out into the medium coarse sand loaded filter, lay the concrete cushion on the medium coarse sand loaded filter, arrange check stalk sleeper beam on the concrete cushion, fill graded gravel layer between the check stalk sleeper beam, the vertical water filtering groove who has three equipartitions is opened on every block of plain concrete board to the plain concrete board of graded gravel layer top for building, and it has horizontal water filtering groove to open on the plain concrete board, and the water filtering groove intussuseption is filled with mi shi. The utility model discloses the dock bottom trade fill out the basis on, rise to float metalling between the stalk roof beam of layer with the pipeline section basement to move about freely and quickly on the plain concrete slabs of the superiors to setting up water filtering groove, pack with rice stone, both can satisfy and float layer roughness requirement, can satisfy the pipeline section again and play to float the waterborne requirement, rise the stage of floating at the pipeline section, the back of pouring water in the dry dock, water filtering groove can become into water route, and water can get into the pipeline section bottom rapidly through pipeline section bottom water filtering groove, makes the pipeline section rise to float smoothly.