Tunnels
Cavity and void filling
After a crown collapse or overbreak, the void above the support keeps loosening and carries water. We fill it from below with high-foaming polyurethane, which expands into the space, binds the loose material and adds little weight to the support.
When to call us
The signs
- A void above the crown after a collapse or overbreak.
- Hollow-sounding lining, or voids found by GPR behind it.
- Voids under slabs, foundations and track beds.
- Ground still running into an opening.
- 1Note 1: A void above the crown, left by a collapse or by overbreak.
- 2Note 2: Loose material that keeps running if it is disturbed.
- 3Note 3: Steel ribs and shotcrete holding the opening.
- 4Note 4: Pipes or self-drilling anchors drilled through the support into the void.
- 5Note 5: High-foaming PU fills the void from the bottom up and binds the loose material.
- 6Note 6: Cured foam is light, so it adds little load to the support below it.
- 7Note 7: Check holes and pressure readings confirm the void is full before the next advance.
How we do it
Method, step by step
Locate and size
From the collapse records, probing, GPR or drilling.
Secure the opening
Ribs, shotcrete and, where needed, a first consolidation of the loose material.
Drill
Pipes or self-drilling anchors through the support into the void, with vents at the high points.
Fill from the bottom up
High-foaming resin in lifts, each lift setting before the next, with pressure on the support kept low.
Consolidate
The loose ground around the void grouted so that it stops running.
Check
Check holes and pressure readings confirm the void is full before the face moves on.
What we use
Made at our plant in Alwar
PuTeRA (aqueonglobal.com, opens in a new tab)
Water stopping, void filling, ground reinforcement, slab and track lifting.
DrucHyd 2C (aqueonglobal.com, opens in a new tab)
Curtain grouting against active inflow; waterproofing and consolidation under water pressure.
DrucPietra (aqueonglobal.com, opens in a new tab)
Low-foaming resin for deep curtain grouting and rock consolidation.
Quality
Checks and proof
- Fill volume compared with the estimated void.
- Pressure on the support monitored during every lift.
- Check holes at the high points before the void is signed off.
On record
Where we have done it
T-49B escape tunnel, Arpinchala, USBRL
Cavities in a Himalayan escape tunnel treated with low-foaming and water-reactive PU resins: one of the two largest chemical grouting jobs we have held.
Tunnel T-77D, USBRL, Banihal
A collapse at the crown left an 8 to 10 m cavity in fractured, water-bearing rock, and the ground above began to settle.
Questions
What clients ask
Why not fill the void with concrete or cement grout?
A void above a crown is hard to reach and may still be taking water. Cementitious grout is heavy, can wash out, and loads a support that is already working hard. High-foaming PU expands to fill the space, reacts with the water present and cures light.
Can the work continue while the tunnel advances?
Usually, yes. The filling is done from inside the tunnel, in lifts, and planned around the excavation cycle.
Related services
Often used together
Pre- and post-excavation grouting
Water cut off and weak ground consolidated ahead of the face; voids closed behind it.
Tunnel water ingress control
Leaks and inflow stopped in tunnels, shafts and underground structures.
Tunnel rehabilitation
Old and operating tunnels: seepage stopped, ground consolidated and lining repaired, under traffic.
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