1.overview
The undersea tunnel of the hong kong-zhuhai-macao bridge consists of 33 sunk pipe joints and a final joint, which is connected underwater. Using floating crane hoisting in place, will eventually joint embedded hydraulic jack system startup, pusher trabecular structure to the ontology of direction, away from the final joint drive M water-stop tensioning, moved to a certain distance, pusher trabecular end of Gina water stop arrived in neighboring union steel cap, Gina water stop after compaction, namely realize union internal and external isolation, finally, the internal drainage pipe joint, forming a space of welds, the welding of steel joint is conducted in the space, the relevant structural relationships refer to figure 1. The steel joint consists of an inner ring connected to the steel plate, an outer ring connected to the steel plate, a small stiffener, and a baffle system. The connected steel plates are made in pieces in the factory and shipped to the tunnel installation site. After the completion of the steel joint welding, a permanent closed interior is formed, which is filled with highly mobile concrete to complete the connection of the tunnel and achieve the final breakthrough. There are a large number of invert welding operations in the welding of connecting steel plates, and the working space is limited. There is no experience for reference at home and abroad, and there are the following difficulties:
(1) poor construction environment and limited welding space. The welding of steel joints is carried out under Gina’s temporary water stop condition, and combined with the moist internal environment of the cavity and no natural ventilation condition, the net operating space between the joint and steel cap is only 1 meter.
(2) the welding work of steel joint is large, and the welding quality requirements are high. The butt weld must be fully welded and 100% passed UT/MT inspection.
(3) the welding construction period of steel joints shall be as short as possible. Before the completion of welding of steel joints, the risk of sealing off seawater in the joint cavity is too high because the GINA water-stop belt only depends on the top push of the oil cylinder. Therefore, it is an effective guarantee for the safe penetration of the submerged pipe project to complete the welding of the steel joint connecting the steel plate in the cavity as soon as possible.
(4) heavy workload, high labor intensity and high safety risk of transporting components to the combined chamber. We adjust the steel joint plate from the following aspects to effectively reduce the difficulty of on-site welding.
(1) optimize the division of steel joint connection plate, reduce the field welding length, and effectively reduce the difficulty of field welding.
(2) connect the section steel joints of steel suspension to the end connectors on the structure of () in the factory, in order to reduce the construction site connection plate carrying capacity, greatly reduce the labor intensity, reduce the safety risk.
(3) make local improvements to the steel joint structure to enhance the stability and safety of the entire structure in the process of steel joint welding.
2.Optimization of steel joint connecting plate block scheme
Steel joint panel on inner and outer block is more, in the preliminary design of steel to the top of the head wall section area as an example, on the length of 2.2 meters (two clapboard interval), inside and outside the circle connecting plate block diagrams of parts as shown in figure 2. There are 6 steel plates in the outer ring of the steel joint, which are connected by on-site welding of the t-rib. In the longitudinal direction of the tunnel, they are welded to the steel caps of adjacent pipe joints and to the steel structures of the final joints. The inner ring of the steel joint also has 6 pieces of steel plate, which are connected on the spot through the L rib. In the length direction of the tunnel, they are welded to the steel cap of the adjacent pipe joints and the steel structure of the final joint. According to the statistics, the length of the weld reached about 25 meters in the 2.2 meter long range, and the total length of the weld of the steel joint reached 4200 meters by calculation.
After preliminary assessment, we guarantee the steel structure of the whole structure under the premise of performance does not decline, take the following method of steel joint to the connection plate block to reduce the welding work, at the same time guarantee the quality of welding is more manageable.
(1) the connecting steel plate of the steel joint, the key geometric positioning dimension of the partition plate and the plate thickness and material shall remain unchanged;
(2) the key geometric positioning dimensions of steel joints in the cross-section of the tunnel, including connecting steel plates and partitions, remain unchanged;
(3) reduce the inner ring of the steel joint, and the outer ring is connected with the steel plate into pieces, and the T rib and L rib are all replaced by flat steel.
3.steel joints connected to steel plate suspension
After the adjustment of the steel joint connecting plate, the steel joint connecting plate within a 2.2-meter long range of the steel joint mentioned above is also taken as an example. The block breaking is shown in the part below figure 2.
There are two steel plates in the outer ring of the steel joint, which are connected by butt welding. In the longitudinal direction of the tunnel, they are welded to the steel caps of adjacent pipe joints and to the steel structures of the final joints.
There is only one steel plate in the inner ring of the steel joint. In the longitudinal direction of the tunnel, it is welded to the steel cap of the adjacent pipe joints and the steel structure of the final joint. After measuring, within 2.2 meters long, the weld length of about 12 meters long (also did not consider clapboard welding), compared with the connecting plate block before the adjustment, the weld length is reduced by more than 50%, the whole project to reduce the weld length to 2000 meters.
Steel joint is connected with steel plate suspension
In the factory, part of the connected steel plate assembly is suspended to the final joint structure, so as to reduce the on-site steel joint steel plate handling, installation work.
Weld the lug plate on the inclined surface of the final joint steel structure, connect the lug plate assembly that is also welded together on the steel plate assembly, and connect the lug plate and lug plate assembly with the pin shaft. Steel joint inner ring connection steel plate and outer ring connection steel plate are also treated, the difference is only that the lifting lug welding position is different. By this method, the connecting plate assemblies of the top wall and side wall are processed
25% of the total amount of steel plate is connected, which greatly reduces the handling and installation of steel plate on site.
4.Partial baffle modification of steel joint
The temporary support tube of the push beam is removed before the steel joint is welded to the steel plate. Demolition of the temporary support at the same time, pushing trabecular by outside force will change, this can lead to pushing trabecular uncontrolled displacement occurs, rubber water stop could be destroyed, it is the aftermath of the combination of water stop in validation of cavity, this for the whole immersed tube tunnel, was disastrous. In order to ensure that this will not happen, we strengthen the structure before removing the steel pipe of the push beam. In a small space, if the structure is reinforced, it will increase the difficulty of welding and make the welding quality more difficult to control. The most reliable plan is to transform the existing structures.
Steel joint structure is formed by connecting plate and baffle plate, the modification of part of the diaphragm structure, the baffle structure of pure “work” word (removal of the original small stiffening plate), the steel plate for outer ring on the flange connections, the web for clapboard, bottom flange plate as the inner ring connector plates, and add on top of the top flange plate.
For the whole circle of steel joint, we transform the clapboard on to wall area, around two side wall area, seven bottom wall area, modified diaphragm structure in temporary bracing tube removed or partly dismantled before welding, reinforce the pusher trabecular, as to avoid the situation of combined water stop in validation of cavity.
5.conclusion
Through the optimization of steel joints connecting plate blocking, connecting plate of the suspension and the renovation of the diaphragm structure, reduce the workload and difficulty of construction site welding, improving the security of the site structure, for subsequent tunnel concrete pouring and eventually pave the way for all of the channel.
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