Stabilising formation and cross slopes

The formation (roadbed) and the cross slopes (cut slope above and fill slope below) of a hill road are unstable because of steep ground, rain and the removal of toe support. The following measures are used (IRC:SP:48, DoR/NRS 2070 guidelines).

1. Drainage measures (most important)

• Catch water drains, side drains, cross-drains, chutes and cascades to keep surface water away.
• Sub-surface drains (French drains, horizontal drains, cut-off drains) and weep holes to reduce pore pressure.

2. Cut slope stabilisation

• Flatten the cut slope to a stable angle (for example 1:4 to 1:1 depending on rock/soil), cut in benches/berms (about 1.5-2 m wide every 6-9 m height) with a drain on each berm.
• Breast walls (stone masonry or gabion), rock bolts, shotcrete and wire-mesh for loose rock; rock-fall nets and catch ditches.

3. Fill slope and formation stabilisation

• Retaining walls (masonry, gabion, reinforced earth) at the toe of high fills; toe walls and buttresses.
• Fill compacted in thin layers on benched ground; use rock-fill or free-draining material; keep fill slope 1:1.5 to 1:2; provide a berm on high fills.
• Avoid dumping spoil on the downhill slope.

4. Bio-engineering and vegetation

Grass planting (vetiver, napier), shrubs and trees, brush layering, live fascines, jute netting, turfing and bamboo planting bind the soil, reduce erosion and are cheap, environment-friendly and recommended in NRS 2070 and the DoR Green Roads approach.

5. Other measures

• Gully control - check dams and drop structures.
• Slope protection - stone pitching, shotcrete, gabion mattress, geotextile.
• Control of landslides by removal of load at the head, loading at the toe, and grouting.
• Regular maintenance and monitoring after the monsoon.