What type of tunnel support would be best for squeezing ground conditions?

What type of tunnel support would be best for squeezing ground conditions?

• A. invert struts
• B. rock bolts
• C. shotcrete
• D. steel ribs

Answer: (B)

In squeezing ground, the ground mass tends to close around the tunnel as it deforms under high in-situ stress. The best support is one that ties the rock mass together and can tolerate ongoing movement, turning a fractured rock into a more stable, composite mass. Rock bolts do this effectively: they are anchored into stable rock ahead of the face and grout bonds them to the surrounding rock, creating a reinforced lattice that resists block movements and convergence. Because the bolts are tensioned and bonded, they provide a ductile restraint that can accommodate some deformation without sudden failure, helping to arrest progressive instability as the ground squeezes. When used in a suitable pattern (often with mesh or shotcrete for immediate surface stabilization), rock bolts slow or halt closure and keep the tunnel open. Rigid or heavy supports like steel ribs or invert struts, while helpful in other conditions, can struggle in squeezing ground because they don’t accommodate the ongoing convergence well and can be overwhelmed or cause new stress concentrations. Shotcrete alone stabilizes surfaces but doesn’t address the deeper rock mass convergence, so it’s not as effective by itself in squeezing conditions.

In squeezing ground, the ground mass tends to close around the tunnel as it deforms under high in-situ stress. The best support is one that ties the rock mass together and can tolerate ongoing movement, turning a fractured rock into a more stable, composite mass. Rock bolts do this effectively: they are anchored into stable rock ahead of the face and grout bonds them to the surrounding rock, creating a reinforced lattice that resists block movements and convergence. Because the bolts are tensioned and bonded, they provide a ductile restraint that can accommodate some deformation without sudden failure, helping to arrest progressive instability as the ground squeezes. When used in a suitable pattern (often with mesh or shotcrete for immediate surface stabilization), rock bolts slow or halt closure and keep the tunnel open.

Rigid or heavy supports like steel ribs or invert struts, while helpful in other conditions, can struggle in squeezing ground because they don’t accommodate the ongoing convergence well and can be overwhelmed or cause new stress concentrations. Shotcrete alone stabilizes surfaces but doesn’t address the deeper rock mass convergence, so it’s not as effective by itself in squeezing conditions.