Key Points of Sinking Operation for Pipe of cutter suction dredger

Selection Principle of Immersed Pipe Line

Within the range of blowing distance of the cutter suction dredger in the construction area, the route that the terrain is relatively flat and the average water depth meets the requirements of ensuring the navigable water depth even after the discharge pipe is submerged and discharged.

Excavation or leveling

Cutter suction dredger is used to excavate or leveling the submerged pipeline channel. The purpose of excavation is to ensure sufficient water depth for the submerged pipeline. After the pipeline is sunk, the top standard height of the pipe is lower than the bottom elevation of the channel, and at the same time, there is a certain surplus water depth (0. 5 m surplus water depth) : When leveling, use the minimum amount of excavation to reach the bottom of the immersed tube groove and avoid obstacles, and improve the quality of the underwater drain pipe.

Immersed tube assembly

There are two ways to assemble immersed pipes: the first method is to assemble the submerged pipe on the shore by taking advantage of the open shoreline near the construction site, near the water line, so as to make the immersed pipeline have a higher underwater adaptability. At the same time, in order to facilitate floating and maintenance in the future, it is best to connect one rubber joint with each discharge pipe. If the number of rubber joint is limited, it is best to arrange one rubber joint with two consecutive discharge pipes, and the rubber joint is best to use flange joint. When the discharge pipe is connected with the discharge pipe and the discharge pipe is connected with the rubber joint, bolts are required to be tightened in all screw holes, and the anti-leakage rubber pad should be added between flange and flange. Each bolt must be tightened, the tightening torque is not less than 50KN. M. After the piece-wise assembly is completed, the two ends are sealed with sealing iron plate to prevent water from entering into the immersed pipes, so as to be in semi-submersible state for traction when in place.

The second method is to use the floating buoy to carry out the surface assembly under the buoy. The assembers use the auxiliary equipment such as anchor boats and mechanical boats to carry out the assembly. The assembly method is the same as that of shore assembly, except that there is no need to install an iron plate at both ends of the underwater discharge pipe.

The sink pipe is connected with the land shore pipe and the sink pipe with the floater at the tail section of the cutter suction dredger

Firstly, the sinking pipe is connected with the end of the land bank pipe.In order to better adapt to the changes of water level, water flow and waves, the tension of the fixed bank pipe is reduced, and ensure the sinking quality of the immersed pipe. Two or three groups of floating pipes are installed between the sink pipe and the shore pipe to form a flexible connection, and the first group of floating pipes connected with the sink pipe are anchored with anchor cables on and downstream.
Then the cutter suction dredger and several length floating pipes are moved to the other end of the baseline of the sinking tank. The temporary closure of the channel is carried out when the water surface is relatively calm, the velocity is relatively slow and the passing ships are relatively few.
Use the tug or anchor boat floating towing (or semi-submersible towing) to the other end of the sink pipe to the other end of the baseline of the sunken pipe trough is connected with the floating pipe at the stern of the cutter suction dredger. The first group of floating pipes at the connection end are also anchored by anchor cables upstream and downstream.
Install an exhaust valve on the second section of the sink and float end. At the same time, a vent valve is also installed on the second floating pipe of the tail section of the cutter suction dredger.
The connection end of the immersed pipe and the floating pipe is tied up by more than 18 steel cables, and the other end of the steel cables is connected with the winch of the cutter suction dredger.
Use the anchor boat and motor boat to remove the float box (buoy) one by one to make the whole section of the sink tube in a semi-submersible state.
The steel cable is tightened by the winch on the cutter suction dredger, so that the whole sunken pipe is laid straight on the sinking design line.

Settlement of immersed pipe

The cutter suction dredger starts the machine, lowers the ladderto the water,and sucks the water with the dredge pump at the low speed of the main engine.
The two exhaust valves on the floating pipe work to make the gas in the pipe discharge smoothly.The sinking pipe slowly fills with water and then sinks into the bottom of the sinking pipe trough with its own weight. Because one end of the sinking pipe is connected with the winch of the cutter suction dredger with more than 18 steel cables, the steel cables are in a tension state, and its both ends in advance with anchor cable fixed, and can be kept in the sinking pipe foundation groove after sinking.
Remove the cable from the winch and take it back.
Further tightening and reinforcing the anchor cables fixed in advance at both ends of the immersed pipe.

Check the sinking quality of immersed pipes

Whether the two exhaust valves are effective or not,the setting pressure of the exhaust valves is generally 3.5kg/cm^2-4.Okg/cm^2. When sinking, arrange someone to observe the working condition of the exhaust valve. when the exhaust valve complete exhaust drainage 5 seconds to outward seal as an ideal, if the exhaust valve did not explain to external drainage was blocked in the valve “floating” partial light, then can be to “float” in the body with water or sand to increase its weight, if the exhaust valve is very difficult to block or not block, after drainage “float” is too heavy, then will reduce the “floating” dead weight.
Check whether the immersed pipe leaks or not, and observe whether there is spray on the water surface when the cutter suction dredger sucksif there is, there is leakage; divers should to inspect underwater to seal the leak in time. In addition to checking whether the immersed pipe leaks or not, it is also necessary to check whether there is any distortion at the rubber joint of the immersed pipe.
Increasethe speed of the main engine gradually until the normal construction state, arrange divers to check again.
After the cutter suction dredger carries out normal dredging operation, the third inspection is carried out.If mud sewage appears on the surface of the immersed pipe, the leakage still exists, and the leakage is sealed in time after the inspection is confirmed.
Carry out top elevation measurement and actual strike track line measurement of the sunken tube after sinking and releasing and draw the measurement results.

Leakage treatment of immersed pipe

No matter the leakage and fracture phenomenon detected in the initial sinking or the fault in the use process, the channel needs to be temporarily sealed. For small leakage problems, divers can be arranged to stop the leakage underwater; Otherwise, it will be partially lifted and floated in the pontoon to stop or replace the leakage.

Warning signs shall be set up within 50 meters of the upper and lower reaches after the sinking is completed and the quality is checked to be in good condition. It is forbidden for ships to anchor and fish in the warning area.