- Asked 2/21
- 2080 Baishakh · 2+4 marks
- 2069 Chaitra · 3 marks
Importance and types of tunnel lining
Short answer
Lining reduces friction, provides support, resists internal pressure, prevents leakage and erosion. Types: shotcrete (non‑pressure), plain concrete (20–40 cm, non‑pressure), reinforced concrete (pressure), steel (high‑pressure sections), precast segments (TBM, weak ground), and unlined with bolts in good rock.
Why is lining important in hydropower tunnels? Explain the importance and the different types of lining.
Importance of lining in hydropower tunnels
- Reduces friction loss: a smooth concrete surface has against for rough rock, so a smaller section can carry the same discharge with less head loss.
- Structural support: carries the rock load and prevents falls of rock, slaking and collapse, especially in weak or jointed rock.
- Resists internal water pressure in pressure tunnels: the lining (reinforced concrete or steel) transfers the pressure to the rock and prevents hydraulic fracturing.
- Prevents leakage of water into the rock (loss of water, slope instability, damage to nearby structures) and prevents the entry of groundwater when the tunnel is empty.
- Protects the rock from erosion and from deterioration, and prevents damage by high velocity flow.
- Smooth flow reduces cavitation and vibration, and provides a durable surface for maintenance.
Types of lining
| Type | Features and use |
|---|---|
| Shotcrete (sprayed concrete) lining | Thin layer (5-15 cm), with mesh/fibre; quick, used for primary support and for non-pressure tunnels in good rock |
| Plain (mass) concrete lining | Poured behind steel forms, 20-40 cm thick; used for non-pressure tunnels of medium quality rock |
| Reinforced concrete lining | Used in pressure tunnels where internal pressure is high and rock cover is small, and in weak rock |
| Steel lining | Used for high pressure sections (near the penstock, shafts and under low rock cover); filled with backfill concrete and contact grout |
| Precast concrete segments | Used with a TBM in weak or soil-like ground |
| Unlined (with bolts and shotcrete only) | In very good rock with low velocity; common in Norway; needs a large area |
Grouting (contact and consolidation) is done behind the lining, and drainage holes relieve the external water pressure.
✓ Answer checked by Claude Opus 5.5 (high effort)
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