Engineering significance of joints

A joint is a fracture or crack in a rock along which there has been no (or negligible) displacement of the two sides.

• Joints reduce the strength and bearing capacity of the rock mass; blocks bounded by joints can slide or fall.
• They control slope stability (plane, wedge and toppling failures) in cuts and dam abutments.
• They give paths for seepage, so reservoirs leak and tunnels get water inflow.
• Weathering is faster along joints.
• In tunnels they cause overbreak and roof falls; the tunnel axis should be at a high angle to the main joint set.
• They help in quarrying blocks, but closely spaced joints give only small blocks.
• Grouting, rock bolts and shotcrete are used for treatment.