Special Rocks:

In last few years, lot of tunneling works are being executed in all over the world. One of the toughest challenge engineers face during design and construction phase is to deal with geology of that area. Presented below a brief note on 4 specific types of rock that need special attention when dealing with it.

There are many special types of rocks which present a difficulty in

  • design of tunnel supports
  • construction of tunnel and
  • inspection & maintenance of tunnels.

1. Weathered Rocks:

Weathering is the process of gradual deterioration of a rock mass. Due to weathering all rock mass starts to disintegrate.

All rocks disintegrate slowly because of mechanical and chemical weathering.

Some weathered rocks show structure and texture as normal rock, but due to weathering, rock material strength is significantly reduced.

Weathered rock

2. Soft Rocks and Hard Soils:

Sedimentary rocks are formed by sediments (soils) through long process of compaction and cementation.

Many times, this process is stopped before the sediments are completely solidified.

The materials then could be highly consolidated but not fully solidified.

Typically, these materials have low strength and high deformability, and when placed in water, they often can be dissolved. But in dry condition, they behave as weak rock.

3. Swelling Rocks:

Some rocks have the characteristics of swelling, when exposed to water.

Rock and soil containing considerable amount of montmorillonite minerals will exhibit swelling and shrinkage characteristics.

Such rocks can cause excessive pressures on the tunnel supports and can lead to their collapse.

In worst case, even after completion of tunnel construction.

4. Crushed Rock:

Characteristics of highly fractured and crushed rocks are quite different from the massive rock mass. When such materials are encountered, they need to be addressed separately.

crushed rock

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