The key to protecting assets during tunnelling
Most tunnels today are constructed using tunnel boring machines (TBMs) which are highly specialized pieces of equipment which can excavate tunnels through various ground conditions from soft soils to hard rock.
At the very front of the TBM is a rotating cutterhead equipped with tools such scrapers or picks when boring through for soil or soft ground.
The excavated material is collected behind the cutterhead in a chamber and moved away from the front using conveyor belts, this keeps the cutterhead clear so excavation can continue. The final part of the TBM places the tunnel lining, which is usually pre-cast concrete ring sections.
Most tunnels today are constructed using tunnel boring machines (TBMs) which are highly specialized pieces of equipment which can excavate tunnels through various ground conditions from soft soils to hard rock. At the very front of the TBM is a rotating cutterhead equipped with tools such scrapers or picks when boring through for soil or soft ground. The excavated material is collected behind the cutterhead in a chamber and moved away from the front using conveyor belts, this keeps the cutterhead clear so excavation can continue. The final part of the TBM places the tunnel lining, which is usually pre-cast concrete ring sections.
During excavation the face of the cut has to be supported by the TBM to prevent ground from collapsing. This is very difficult to achieve without any face losses, which leads to surface subsidence. The magnitude of surface subsidence is essentially a function of how well the TBM balances the earth pressures during excavation and the depth of the tunnel.
The surface subsidence takes the form of a trough moving in front of the TBM as it advances. The shape of the trough takes a bell or Gaussian-shaped curve, with the maximum settlement directly above the tunnel centre line. The width of influence depends on tunnel depth and soil type, with deeper tunnels forming wider but shallower settlement profiles. The magnitude of settlement varies from <10 mm in well-controlled urban tunnelling, but can exceed 50 mm if poorly managed. In extreme cases, TBMs have been known to create sinkholes, where a catastrophic failure has occurred due a total loss of face support in loose soil at shallow depth.
This issue impacts all types of infrastructure
Tunnels
Total loss of face support can compromise the structural integrity of the tunnel itself, requiring extensive and costly re-lining or repairs.
Sinkholes
Sinkholes can be formed through poorly controlled tunneling, leading to catastrophic damage to buildings, roads and services.
Roads
Subsidence caused by tunnelling can create depressions and cracks in the road surface, leading to closures and safety risks.
Buildings
Nearby buildings and facilities can suffer from differential settlement which cracks foundations and walls, creates uneven floors, and other structural damage.
Utilities
Buried pipelines, power lines, and other critical utilities are highly susceptible to damage from differential settlement, leading to service interruptions.
How does Geobear approach the issue?
Geobear's Ground improvement solution is a highly effective, non-disruptive solution for controlling ground displacement. We combine our geopolymer injection with our proprietary Geobear RT (real-time) monitoring system. The process involves:
Real-time monitoring
Our highly accurate sensors are placed on the surface to monitor ground movement as the TBM advances.
Precision injection
A fluid geopolymer is injected into the ground in front of the TBM. The injection process is controlled in real-time by the monitoring system, ensuring the exact volume of material needed is delivered to compensate for the ground loss wave (settlement trough) which advances in front of the TBM.
Rapid reaction
Our solution can be deployed quickly and react instantly to ground movement, preventing damage before it becomes a major problem.
Versatility
The geopolymer can be used to densify ground to reduce future settlement or lift and relevel subsided structures, providing a new, stable foundation.
Contact us to learn how we can help
