In EPB tunnelling, the TBM soil conditioning agents have to be selected according to the geological conditions. The correct choice and use of well-adapted soil conditioners makes a considerable difference in the success of a tunnelling project - both in highly permeable soils and in sticky clay conditions.
Ground conditions originally judged to be ‘difficult’ can be transformed to be (more) manageable, drastically reducing the time for cleaning the TBM working chamber and cutterhead, thus avoiding unnecessary and/or frequent chamber interventions.
Soil conditioners allow TBM cutterhead torque to be reduced and decrease the cutterhead tool and screw wear, enabling the TBM to work in pressurised closed mode even under difficult mixed face conditions or in soils with high clay content. The different types of soil conditioner are used a follows
- Standard and polymerised soil conditioners are normally used for silty to gravelly sands. Different foam types may be used depending on the nature of the soil and its humidity or the groundwater pressure.
- Anti-clogging agents are used for clay and clayey soils that significantly reduce clogging and re-agglomeration effects. Due to the complex nature of clay and clayey soils, different clay formations also require different anti-clay agents.
- Polymers are generally used when tunnelling through water-bearing grounds, where the excavated soil becomes very liquid and difficult for the screw conveyor and conveyor belt to handle
Eco-friendly Water Binding Polymer