A gravel road is built up from a cleared subgrade through a base course of large stones 15-20 cm thick, a surface course of smaller gravel 10-15 cm thick, and an optional wearing course of fine gravel 3-5 cm thick, and it is 3 m wide for one-way traffic with passing places or 4-5 m for two-way. A kilometre 4 m wide needs 1,120-1,600 m³ of stone, so haul distance rather than digging sets the pace; a crew of 10 builds 50-100 m a day. It lasts only if it is crowned and drained.
Part of Road Construction Basics
A layered gravel surface that carries carts, wagons and foot traffic in all weather, built by hand.
Gravel Roads Work Because The Layers Shed Water And Spread The Load
The parent article calls the gravel road the workhorse of pre-industrial transport. The stone layers lift traffic off wet ground and spread each wheel load across a wider area. They only work if water drains away: see Road Crown & Camber and Side Ditches. A longer treatment of the principle is in Gravel Roads, which gives the two layers a total of 175-275 mm, thinner than the parent’s. The parent’s thicknesses are used here; the disagreement is noted below.
What You Need
- Large stone for the base: pieces of 10-20 cm.
- Smaller gravel of 2-5 cm for the surface course.
- Fine gravel or stone dust for the optional wearing course.
- Hand tools — see Essential Tools.
- Carts or barrows to haul material.
- A compaction method — see Compaction Methods.
Method: Build The Layers
Step 1: Prepare the subgrade Clear and shape the natural ground. Remove topsoil and organic material, because it holds water and rots.
Step 2: Lay the base course Place stones of 10-20 cm in a layer 15-20 cm thick. This is the foundation.
Step 3: Add the surface course Pack smaller gravel of 2-5 cm over the base, 10-15 cm thick.
Step 4: Add a wearing course if you can Fine gravel or crushed stone dust, 3-5 cm thick, fills gaps between larger stones and gives a smooth surface.
Step 5: Set the width Make it 3 m for one-way traffic with passing places, or 4-5 m for two-way. At passing places, every 200-300 m on narrow roads, widen to 5-6 m.
Step 6: Crown and compact Shape the crown and compact before opening to loaded carts.
Worked Example: Stone For One Kilometre
Inputs: 1,000 m long, 4 m wide, which is 4,000 m²; the parent’s layer thicknesses (compacted, in place); loose-gravel density of 1,400-1,800 kg/m³ from Common Material Weights; cart capacity of 600-1,200 kg from Carts and Wagons.
| Layer | Thickness | Volume of 4,000 m² |
|---|---|---|
| Base | 15-20 cm | 600-800 m³ |
| Surface | 10-15 cm | 400-600 m³ |
| Wearing | 3-5 cm | 120-200 m³ |
| Total | 1,120-1,600 m³ |
- Mass at the lowest volume and lowest density: 1,120 × 1,400 = 1,568,000 kg, about 1,570 tonnes. At the highest: 1,600 × 1,800 = 2,880,000 kg, about 2,880 tonnes. Compacted stone is denser than loose gravel, so these are lower bounds.
- Cart loads: 1,568,000 / 1,200 = 1,307 loads at best and 2,880,000 / 600 = 4,800 loads at worst. That is roughly 1,300 to 4,800 loads.
- The parent gives 50-100 m a day for a crew of 10, so 1,000 m takes 1,000 / 100 = 10 to 1,000 / 50 = 20 days. Spread over those 10-20 days, that is 65-130 cart loads a day at the best end and 240-480 at the worst. This is why the parent says the rate depends on material distance.
Common Mistakes
- Leaving topsoil in place — it holds water and rots, and the road sinks.
- Skipping the crown — water pools and softens the base. Maintain the crown with every grading.
- A single thin layer — it mixes with the soil beneath. Use both courses.
- Following one thickness blindly — the parent gives 25-35 cm in two courses (plus 3-5 cm wearing) while Gravel Roads gives 175-275 mm in total. The two disagree; use the thicker where the subgrade is soft.
Safety
Heavy stone and loaded carts
Stones of 10-20 cm can weigh several kilograms each, and a loaded cart on a slope is hard to stop. Lift with the legs, keep feet clear of rolling stones, and keep animals and workers out of the path of a cart being tipped.
What’s Next
- Learn next: Compaction Methods — firming each layer
- Combine with: Side Ditches — draining the road