Retaining and slope protection structures

Hill roads need structures to hold the soil and to protect slopes from erosion and failure (IRC:SP:48; Nepal DoR hill-road guidelines).

A. Retaining structures

1. Retaining walls - on the valley side, to support the fill and the road. Types:
   • Stone masonry gravity wall (most common; dry or in cement mortar, height up to 6-8 m);
   • Gabion wall (wire crates filled with stone; flexible, permeable, cheap and good on settling ground);
   • Concrete/RCC cantilever or counterfort wall for greater heights;
   • Reinforced earth / geosynthetic wall.
2. Breast walls - on the hill side, supporting the cut face and preventing slips and rock fall.
3. Toe walls and buttresses - stabilise the base of the slope.
4. Crib walls (timber/concrete) - interlocking members filled with soil.

All walls must have weep holes and a filter backfill, be founded on firm ground, and be designed against sliding, overturning and bearing failure.

B. Slope protection structures

1. Stone pitching/turfing on embankment and cut slopes.
2. Shotcrete/guniting and wire-mesh on rocky cut slopes.
3. Gabion mattresses and river training works (spurs, revetments) along rivers.
4. Rock-fall protection - rock-fall nets, catch ditches and fences.
5. Bio-engineering - grass, shrubs, tree planting, brush layering, fascines.
6. Check dams, drop structures and chutes for gully control.
7. Drainage works - catch drains, side drains, French drains.

 hill ->  |breast wall|  road  |retaining wall| <- valley
          cut slope             fill slope

Selection depends on the height, soil/rock type, availability of stone, water and cost; gabion and masonry walls are the most commonly used in Nepal.