Closure pressure in the excavation chamber during TRM excavation stoppages

Closure pressure in the excavation chamber during TRM excavation stoppages and interventions
The seal pressure must not only support the tunnel seal during shielded TBM excavation, but also support the seal during excavation stoppage.
during excavation. Typically, a shielded TBM with earth pressure will have the excavation chamber filled with a
burr is filled while the TBM is stopped. The shield pressure is maintained by injecting the appropriate additive (foam). Water and additive
separation of water and additive can cause problems with air in the shear zone of the drilling chamber. Water Shield TBMs
A filter cake or infiltration zone is formed to support the tunnel casing during downtime, and excess hydrostatic pressure in the excavation chamber is used to maintain support pressure.
The support pressure can be maintained through excess water pressure in the excavation chamber, which is much simpler. TBM intervention
(interventions are usually required for maintenance and inspection of the cutterhead.
The mechanisms for end-of-tunnel support vary slightly depending on the type of equipment used. Generally speaking
Shielded TBMs typically use a filtercake for tunnel capping. In tunnel capping, a conventional filter cake
In tunnel capping, a conventional filter cake seals the tunnel face and allows excess pressure to be transferred to the ground. During long interventions
During prolonged interventions, the filter cake dries out/shrinks and needs to be reproduced. As the filter cake
dried, the excess pressure transferred to the ground can be reduced. The difficulty of interventions using compressed air
The difficulty of intervention with compressed air depends on the ground conditions at the end of the tunnel. The
In the main application range of TBMs, intervention can be performed relatively easily due to the high water absorption capacity of the ground.
intervention. However, it is more complicated to intervene in ground conditions such as cobbles. In these cases
You may prefer to intervene within a grouting block. The Jet grouting block prevents excess air
can stabilize the target ground while excess air pressure prevents groundwater flow into the excavation chamber.
C. Alternatively, the excavation chamber can be temporarily filled with slurry to allow compressed air to act.
This creates a slurry filter cake that seals the tunnel casing. Compressed air
interventions, in most countries, require a combination of pressurization and depressurization. Safety and health regulations for permissible working hours
Safety and health regulations should be followed for permissible working hours. If higher compressed air is required to stabilize the tunnel wall
If higher compressed air is required to stabilize the tunnel closure, workers must enter the chamber breathing a special gas mixture.
On the other hand, water shield TBMs have the additional option of deploying saturation divers without lowering the slurry in the excavation chamber.
diver without lowering the slurry inside the drilling chamber. This method is extremely laborious and costly, and should only be used in special cases.
special cases.