Development of Experimental Platform for Shield Tail Sealing System
In the process of shield tunnelling, there is a certain gap between the tail shield and the segment. The shield tail grease in the gap cooperates with the tail brush to seal, preventing the water and mortar in the formation from entering the shield machine (Figure 1). The sealing effect plays a very important role in the driving safety and driving quality. The effect of the shield tail seal is mainly affected by the equipment material, the quality of the shield tail sealing grease, and the attitude of the shield. Following are the main forms of shield tail seal failure: the elasticity of the tail brush fails, the steel wire or steel plate falls off; the shield tail grease has poor fluidity, resulting in an empty warehouse, the grease has poor pressure resistance, causing the mortar to enter the grease warehouse.
Figure 1 Shield tail sealing system concept
The importance of the shield tail seal is unquestionable. We can develop a special shield tail sealing experiment platform to diagnose the reasons for the failure of the shield tail seal and the remedial measures after the failure. If the following problems can be solved based on the experimental platform, the further development of shield tail sealing research will be promoted.
1. Method of determining whether the grease is completely filled with the grease tank by using a durable sensor to measure the instantaneous pressure in the grease tank. Compared with ordinary fluids, shield tail grease has high viscosity and poor fluidity, which is very likely to cause insufficient grease injection during the grease injection process and reduce the sealing performance of the grease silo. A pressure sensor is arranged in the grease silo to detect the instantaneous
pressure of the grease, and it can be judged whether the grease build-up pressure is good, whether the grease injection is sufficient, and the leakage of the grease silo. However, due to the influence of grease characteristics, formation sand and slurry invasion, shield tail sealing structure, etc., the sensors arranged in the grease silos are easily damaged and difficult to replace. Therefore, it is very important to find a sensor with high sensitivity and good durability in the grease tank.
2. Detection of the damage degree of the tail brush caused by long-term operation and the retreat of the shield. Damage to the tail brush will seriously affect the performance of the shield tail seal. The existing judging method only includes visual inspection when machine is stop. At this time, water leakage and slurry leakage are often started, and the tail brush has completely failed, which has a certain hysteresis. If the damage degree of the tail brush can be detected in advance, the tail brush can be replaced timely at a small cost, so as to avoid taking measures after the seal fails which causes greater losses.
3. Early detection of the intrusion of water, mortar and other foreign bodies into the grease silo. It takes a certain amount of time for foreign substances to completely penetrate all the shield tail brushes. If they can be detected when they invade the first and second tail brushes, we can take remedial measures in advance, such as increasing the amount of grease injection, Reduce the driving speed to prevent the shield tail seal from being broken down. Losses and risks can also be reduced.
4. Simulation of the plugging measures when the shield tail seal leaks. In addition to verifying the effect of conventional plugging measures, such as increasing the amount of grease injected into the shield tail, blocking the water-stop sponge in the gap between the shield tail and so on. It should also be able to develop new plugging methods on the basis of the experimental platform.
5. Calculation of the pressure loss of grease pipeline. The length of the line from the grease pump to the grease port is often not determined. In order to control the pressure of the grease silo, it is necessary to know the pressure decay law in the grease pipeline, and then control the outlet pressure from the grease pump to control the pressure of the grease silo.
With the development of shield construction in the direction of larger buried depth and higher water pressure, a better performance of shield tail sealing system is required. We hope to develop a special experimental platform to solve the above problems and improve the safety of shield construction. At the same time, we also hope that the users can give us suggestions and advices on the sealing platform to improve the development and design.
Figure 1 Shield tail sealing system concept
The importance of the shield tail seal is unquestionable. We can develop a special shield tail sealing experiment platform to diagnose the reasons for the failure of the shield tail seal and the remedial measures after the failure. If the following problems can be solved based on the experimental platform, the further development of shield tail sealing research will be promoted.
1. Method of determining whether the grease is completely filled with the grease tank by using a durable sensor to measure the instantaneous pressure in the grease tank. Compared with ordinary fluids, shield tail grease has high viscosity and poor fluidity, which is very likely to cause insufficient grease injection during the grease injection process and reduce the sealing performance of the grease silo. A pressure sensor is arranged in the grease silo to detect the instantaneous
pressure of the grease, and it can be judged whether the grease build-up pressure is good, whether the grease injection is sufficient, and the leakage of the grease silo. However, due to the influence of grease characteristics, formation sand and slurry invasion, shield tail sealing structure, etc., the sensors arranged in the grease silos are easily damaged and difficult to replace. Therefore, it is very important to find a sensor with high sensitivity and good durability in the grease tank.
2. Detection of the damage degree of the tail brush caused by long-term operation and the retreat of the shield. Damage to the tail brush will seriously affect the performance of the shield tail seal. The existing judging method only includes visual inspection when machine is stop. At this time, water leakage and slurry leakage are often started, and the tail brush has completely failed, which has a certain hysteresis. If the damage degree of the tail brush can be detected in advance, the tail brush can be replaced timely at a small cost, so as to avoid taking measures after the seal fails which causes greater losses.
3. Early detection of the intrusion of water, mortar and other foreign bodies into the grease silo. It takes a certain amount of time for foreign substances to completely penetrate all the shield tail brushes. If they can be detected when they invade the first and second tail brushes, we can take remedial measures in advance, such as increasing the amount of grease injection, Reduce the driving speed to prevent the shield tail seal from being broken down. Losses and risks can also be reduced.
4. Simulation of the plugging measures when the shield tail seal leaks. In addition to verifying the effect of conventional plugging measures, such as increasing the amount of grease injected into the shield tail, blocking the water-stop sponge in the gap between the shield tail and so on. It should also be able to develop new plugging methods on the basis of the experimental platform.
5. Calculation of the pressure loss of grease pipeline. The length of the line from the grease pump to the grease port is often not determined. In order to control the pressure of the grease silo, it is necessary to know the pressure decay law in the grease pipeline, and then control the outlet pressure from the grease pump to control the pressure of the grease silo.
With the development of shield construction in the direction of larger buried depth and higher water pressure, a better performance of shield tail sealing system is required. We hope to develop a special experimental platform to solve the above problems and improve the safety of shield construction. At the same time, we also hope that the users can give us suggestions and advices on the sealing platform to improve the development and design.