In order to solve the problem of cracking of tunnel construction joints and the frequently-appearing handover acceptance problem, various construction units have paid a great price to solve this problem. If there is a way to effectively effect the newly poured second lining end during the construction process Protection not only saves a lot of cost, but also improves the quality of the secondary lining to a large extent. Today we introduce in detail a flexible joint device to protect the concrete at the end of the second lining, the soft lap technology of the tunnel lining trolley.
The damage of traditional rigid joint to the end of the second liner
In the secondary lining formwork trolley processing of the tunnel, limited by the factory production conditions and processing accuracy, the contour accuracy of the panels at both ends is not high and cannot be exactly the same, resulting in the slippage of the formwork trolley, due to the forming of the front panel of the formwork trolley There is a difference in shape between the concrete structure surface and the rear-end trolley panel, which cannot be completely coupled. In addition, the concrete pouring process cannot be consistent with the theoretical model. As the number of uses increases, irregular deformations of the formwork trolley panels will be difficult to correct, which will make the coupling problem more serious.
Therefore, during the construction overlap of the front and rear linings, there is a direct topping of the concrete at the overlap due to fear of leakage and tightening of the poured concrete surface, or invisible cracks in the concrete on the early pouring side of the construction joint that cannot be recognized by the naked eye. , During operation, it will fall under the action of the piston pressure difference formed by the high-speed train, jeopardizing driving safety. Moreover, due to the different causes and locations of the arch, the arch has the characteristics of “concealment, suddenness, complexity, and repeatability”. It is a relatively large source of danger for operating tunnels and must be completely eradicated. This problem is currently an important item of lining defects.
Introduction to the soft overlap technology of tunnel lining trolley
A compressible rubber gasket is set at the overlapping part of the lining trolley and the upper concrete slab, the compression amount is 50%, the socket type connection, the rubber needs to be customized by the factory, and it is completely elastic and close to contact, so that it will not be crushed. The concrete will not leak, and at the same time effectively prevent misalignment.
In order to prevent the concrete leakage and dislocation at the overlap between the secondary lining trolley and the low side wall of the tunnel, the formwork of the bottom of the lining trolley is anchored with a compressible elastic rubber gasket with a thickness of 5-10mm, which changes the previous hard connection between the trolley and the concrete. For elastic contact, it ensures that the concrete does not leak when vibrating, and eliminates common problems such as misalignment, sandification, and honeycomb pockmark.
As the number of times of use of the tunnel lining trolley increases, the panel will deform to a certain extent. The maximum difference between the front and rear panel contours of the deformed backstage car can reach 2～3cm. With the increase of the number of times of use, the deformation will continue to increase. The soft lap rubber The actual thickness of the strip should be increased during design.
Key points of soft overlap operation of tunnel lining trolley
Lining trolley transformation
The soft overlap pallet of the trolley is processed in advance, and the pallet is welded to the end template of the second lining trolley with bolts, and the trolley panel is 2cm higher than the pallet.
Install the rubber gasket
Install the rubber gasket into the groove of the tray before the trolley is in place. The thickness of the gasket is 4cm (according to the pressure test of the rubber gasket on the hydraulic cylinder of the trolley), and the adjacent circumferential rubber gaskets are connected by socket .
Trolley transformation and positioning
The second liner trolley is in place, the pallet is positioned at the construction joint, and the trolley panel is pushed up to a concrete surface by controlling the hydraulic oil cylinder.
After the rubber gasket contacts the concrete surface, continue to pressurize with the oil cylinder. Observed from the side, when the rubber gasket is compressed to 2cm, the pressure stops. At this time, the trolley panel can be compressed by the compressible rubber gasket to ensure the second liner trolley. The panel is closely attached to the secondary lining concrete surface of the upper one.
The main solution to the problem of soft overlap of tunnel lining trolley
This process mainly solves the serious problems of tunnel lining during construction. Due to the incomplete coupling of the front and rear panels of the tunnel lining trolley, there are serious problems such as grout leakage, honeycomb pockmarked surface, concrete cracking, and invisible cracks at the circumferential construction joints of each lining concrete. At the same time, due to the construction joints on the basis of the above problems, there are the following two problems:
(1) The ends of the steel-wood combination are easy to cause slurry leakage and under-vibration;
(2) The problem that the construction joint is far away from the feed window and cannot be vibrated. The superimposition of these problems will lead to greater operational safety problems.
Evaluation on the application effect of the soft overlap of tunnel lining trolley and suggestions for improvement
Through the actual construction effect in the tunnel construction, the use of soft lap technology has solved the common quality problems that have existed in the tunnel construction period for a long time, and eliminated the block drop caused by the rigid lap in the operation period.
Of course, the following factors should also be considered in actual use to determine the parameters of the rubber strip:
(1) There are big differences between single-track railway, double-track, and third-track, and construction parameters need to be determined carefully;
(2) The nature of concrete entering the warehouse is different, the lateral pressure is different, the deformation of the trolley and the degree of fatigue resistance are different, and the construction parameters need to be carefully selected;
(3) The rubber strip and the tray should be bonded with welding-free glue;
(4) When opening the rubber strip, the deformation of the trolley should be considered, and the processing size of the rubber strip should be adjusted rationally and flexibly, so as to facilitate the on-site adjustment of measures to local conditions and flexible improvement.