Short note: construction procedure of gravel road

Gravel road has a wearing course of naturally occurring gravel or an aggregate-soil mix compacted on the subgrade; it is the common low-cost road in rural Nepal (Nepal Rural Road Standards / DoLIDAR, IRC:SP:20).

Materials: well-graded gravel with 50-70 percent gravel, 20-40 percent sand and 8-15 percent fines (plasticity index 4-12 percent, liquid limit below 35 percent), maximum size 40 mm (CBR above 30 percent for base, above 15 percent for sub-base).

Construction procedure

1. Clear the site and set out the centre line and width; construct the subgrade to grade and camber (4-5 percent), compacting the top 150 mm to 95-97 percent of Proctor density; construct side drains and cross drains.
2. Haul gravel from the borrow pit or quarry and spread it by grader or manually to the required depth, usually 100-150 mm loose, in one or two layers.
3. Mix with water to near the optimum moisture content, adding fines or sand if the gravel is deficient in binder.
4. Shape with a grader to the camber and compact with an 8-10 t roller (or vibratory roller); repeat for the second layer.
5. Finish to the cross-fall, check the thickness and shoulders, and complete the drainage structures.
6. Open to traffic once compaction is complete. Maintain the surface by regular grading, and regravel (about 75-100 mm) every 3 to 5 years, because the gravel wears away at roughly 20-25 mm a year.