Design and construction problems of hill roads

Hill roads are built in steep, unstable and rain-fed terrain, so they face many more problems than roads in the plains. The main problems are:

Design problems

1. Alignment and geometry: steep gradients (ruling about 6%, limiting 7 to 8%), many sharp bends (hairpin bends) with small radius and extra widening and superelevation, and short sight distances.
2. Gradient compensation on curves, and the need to limit the maximum gradient to reduce vehicle operating costs.
3. Cross-section: limited width, partial cut and fill with retaining structures, and a difficult choice of formation width.
4. Drainage design: heavy runoff and many streams and gullies, so many culverts and catch drains are needed.
5. Slope stability and the design of retaining and breast walls, with limited site data.
6. Choice of cut-fill balance and disposal of spoil.

Construction problems

1. Difficult access: materials, equipment and labour must be transported to remote, steep sites, so costs are high.
2. Rock and boulder excavation: blasting needs care to avoid shattering the hill.
3. Landslides, rockfalls and slope failure, especially in the monsoon in weak geology (Siwalik and Himalayan fold belt), and earthquakes.
4. Heavy rain and a short working season, flooding and erosion.
5. Spoil disposal and the environmental damage to slopes and rivers.
6. Shortage of suitable material, labour and skills; quality control is hard.
7. Maintenance: frequent landslide clearing, drain cleaning and repairs; high recurrent cost.
8. Environmental and social issues: deforestation, impact on water sources and villages.

Good practice follows NRS 2070, DoR's Environmental and Social Manual and the principles of "green roads": simple, low-cost construction, bio-engineering, and proper drainage.