How tunnel boring machines maintain pressure?
How tunnel boring machines maintain pressure? Tunnel boring machines (TBMs) mainly maintain pressure through the following methods:
I、 Sealing system
1. Sealing between the cutterhead and the shield
-The cutterhead of TBM excavates rocks or soil in front, and the shield follows closely behind to provide protection for operators and equipment. Multiple sealing devices such as rubber seals, grease seals, etc. are usually used between the cutterhead and the shield. These seals can effectively prevent external soil pressure and groundwater from entering the interior of the TBM, while also maintaining stable internal pressure.
-Rubber seals have good elasticity and wear resistance, can adapt to the rotation and vibration of the cutterhead, and can also withstand certain pressure. Oil sealing is achieved by continuously injecting grease to form a layer of grease film between the seals, thereby providing sealing and lubrication.
2. Shield tail seal
-The shield tail is the connecting part between TBM and the already built tunnel segments, and it is also a place where pressure leakage is prone to occur. To maintain pressure, shield tails typically use multiple wire brush seals and grease injection systems.
-The wire brush seal is composed of multiple wire brushes, which can effectively prevent groundwater and mud from entering the interior of the shield tail. The grease injection system continuously injects grease to form a grease film between the wire brushes, thereby providing sealing and lubrication.
II、 Pressure control device
1. Earth Pressure Balance (EPB) system
-For earth pressure balanced TBM, pressure balance is maintained by controlling the earth pressure in front of the cutterhead. The soil pressure balance system mainly consists of a screw conveyor, soil silo, pressure sensor, etc.
-During the excavation process, the soil cut by the cutterhead enters the soil bin and is discharged through a screw conveyor. The pressure sensor monitors the soil pressure inside the soil silo in real time and feeds back the signal to the control system. The control system adjusts the speed and output of the screw conveyor based on changes in soil pressure, in order to maintain a balance between the soil pressure inside the silo and the external soil pressure.
2. Sludge Pressure Balance (SPB) system
-The slurry balanced TBM maintains pressure balance by controlling the slurry pressure. The mud water balance system mainly consists of mud water storage tanks, mud water pipelines, pressure sensors, etc.
-During the excavation process, the soil cut by the cutterhead mixes with mud and water to form a slurry, which enters the mud and water tank. The mud and water pipeline transports the mud to the ground for treatment. The pressure sensor monitors the real-time pressure of the mud and water in the mud and water tank, and feeds back the signal to the control system. The control system adjusts the flow rate and pressure of the mud and water according to changes in mud and water pressure, in order to maintain a balance between the mud and water pressure inside the mud and water tank and the external soil pressure and water pressure.
III、 Operation control
1. Reasonable excavation parameter settings
-TBM operators set excavation parameters reasonably based on geological conditions, tunnel design requirements, and other factors, such as cutterhead speed, advance speed, and excavation volume. By optimizing excavation parameters, disturbance to the surrounding soil can be reduced and the risk of pressure fluctuations can be minimized.
-For example, in weak formations, the pushing speed and cutterhead speed should be reduced to decrease the amount of excavation and maintain the stability of soil pressure.
2. Real time monitoring and adjustment
-TBM is equipped with various monitoring devices, such as pressure sensors, displacement sensors, gyroscopes, etc., which can monitor the real-time operation status of TBM and changes in the surrounding soil. Operators adjust excavation parameters and pressure control devices in a timely manner based on monitoring data to ensure that the TBM always operates at a safe and stable pressure state.
In summary, tunnel boring machines maintain pressure through various methods such as sealing systems, pressure control devices, and reasonable operational controls to ensure the safety and smooth progress of tunnel excavation.