Special structures in hill roads

Special structures in hill roads

1. Retaining walls - valley side, to hold fill and to widen the road.
2. Breast walls - hill side, to support cut faces and avoid slips.
3. Revetments and toe walls - protect slopes and river banks from scour.
4. Gabion structures - walls, mattresses and check dams in wire crates; flexible and permeable.
5. Check dams, drop structures, chutes/cascades - gully control and safe disposal of culvert flow.
6. Cross-drainage works - culverts, causeways, Irish bridges and small bridges.
7. Retaining/catch ditches, rock-fall nets and shotcrete for rock slopes.
8. Hairpin bends and passing places (lay-bys) on narrow roads.
9. Parapet/guard walls and crash barriers on the valley edge.
10. Bio-engineering works - grass, shrubs and brush layering.
11. Sub-surface drainage - French drains, horizontal drains, weep holes.
12. Tunnels, snow galleries and avalanche shelters in very difficult or snow-bound areas.

Sketch of the drainage layout in hill road

  hill ~~~~~~~~~~~~~~~~~~~~~~
   catch water drain ===>   (to nala)
         \
          \ cut slope
           \ breast wall
    side drain ---> culvert ---+
    ==== road =================  |
          \ retaining wall      v
           \ fill slope      chute
  valley ~~~~~~~~ stream <------+

Flow path: hillside water is intercepted by the catch drain; road and cut-face water goes to the side drain; both are carried through culverts and chutes to a natural stream. Sub-surface drains (French/horizontal) discharge into the side drain or through weep holes.