CP Systems

Hailang Dam

Rebuilding the gate grooves of a diversion tunnel at the 444 MW Vishnugad Pipalkoti project, with the river still running through it.

Client
THDCIL
Location
Helang, Chamoli
Capacity
444 MW
Flow during work
50–60 cumec
Scroll to the work

Two gates, one tunnel, no shutdown

Two gates sit in the 10.5 × 10.5 m box section of the diversion tunnel, about 16 m from the portal and 50 m from the intake. Their grooves, pier and side walls were badly damaged.

CPS repaired them one side at a time across two lean seasons: the right gate in 2024, the left in 2025. The tunnel kept carrying 50–60 cumec the whole time.

Damage inside the diversion tunnel, before repair The repaired gate groove, phase 1
The repaired gate groove, phase 1

How the repair was done

Twelve steps, the same on each side, from cutting a way in through the tunnel roof to closing it again with a steel plate.

  1. Debris removed from the top slab of the DT
  2. DT top slab cut open with a diamond wire saw
  3. Coffer dam of boulder-filled MS boxes in 50–60 cumec of flow
  4. MS boxes lowered into the flowing river by crane
  5. Loose concrete scaled off with breakers
  6. New reinforcement drilled, anchored and fixed
  7. Micro concrete poured above and under water
  8. Cracks and honeycombing sealed with epoxy putty
  9. Concrete surfaces repaired with epoxy mortar
  10. Three-component epoxy grout in the groove and T guide plate
  11. Boulder-filled MS boxes removed
  12. MS cover plate fabricated and fixed over the cut
Diamond wire saw cutting inside the diversion tunnel
Lowering MS boxes into 50-60 cumec of water
Crane positioned over the slab opening

Phase 1: right bay and gate groove

Jan – Mar 2024Lean season

The right gate came first: open the slab, push the water to one side of the tunnel, and rebuild the pier and walls in the dry half.

  • DT slab cut for access
  • Temporary diversion made inside the tunnel
  • Pier and side walls rebuilt
  • Concrete placed through hopper and pipe
Reinforcement over the opening into the tunnel
Rope-access crew preparing the damaged pier

Phase 1, photographed

  • Removing debris from the DT
  • Marking the DT slab for cutting
  • Opening made by cutting the DT slab
  • Damage inside the diversion tunnel
  • Temporary diversion for the right bay
  • Reinforcement and concreting through the hopper
  • Pier reinforcement
  • Concreting through hopper and pipe
  • Completed: the repaired gate groove

Phase 2: left bay and gate groove

Dec 2024 – Mar 2025The next lean season

A year later the same sequence on the left: a new cut in the slab, the water moved the other way, and the left wall rebuilt and closed.

  • Left side DT slab cut for an approach
  • Temporary diversion inside the tunnel
  • Rebaring of the damaged left wall
  • Micro concrete poured under water
  • MS slab cover fabricated and placed
Cutting the left side DT slab for access
Fixing new reinforcement in the left wall
Concreting through the hopper and chute
Looking down the cut opening into the tunnel

Phase 2, photographed

  • Cutting the left side DT slab
  • Making an approach to the damage
  • THDC inspection and temporary diversion
  • Temporary diversion inside the tunnel
  • Rebaring the damaged left wall
  • Pouring underwater micro concrete
  • Fabricating the MS slab cover
  • Placing the cover over the cut

More of the work

Every CPS site has its own window, river and rock. Pick the next one.

Discuss a project