The construction of a gravel base is a critical step in building a stable and durable surface, such as for a football field. The process typically involves three main stages: paving, watering, and rolling. Proper execution of each stage ensures the structural integrity and long-term performance of the base layer.
When it comes to paving, controlling the thickness is essential. This means maintaining the correct compaction coefficient. For mechanical paving using equipment like bulldozers or graders, the compaction factor is usually set between 1.20 and 1.25. If the work is done manually, the compaction coefficient can be slightly higher, ranging from 1.25 to 1.30. Ensuring accurate compaction helps prevent future settling and uneven surfaces.
After the initial paving, any areas where coarse aggregates have clumped together should be broken up and evenly distributed. Similarly, if fine sand has gathered in certain spots, those areas need to be dug out and refilled with the right mix. Once the entire area is covered, water should be sprinkled evenly across the surface. The goal is to moisten the entire structure so that the gravel can settle properly. After about 1–2 hours of air drying, the rolling process can begin.
The amount of water used depends on the season and the thickness of the gravel layer. Here's a reference table for the recommended sprinkling rates:
| Thickness (cm) | Spring and Autumn (kg/m²) | Summer (kg/m²) |
|---|---|---|
| 10 | 6–8 | 8–12 |
| 15 | 9–12 | 12–16 |
| 20 | 12–16 | 16–20 |
| 25 | 15–20 | 20–28 |
Notes:
- The natural moisture content of graded sand is approximately 7%.
- The ideal moisture content for graded sand is between 5% and 9%.
For grading and rolling, it's best to work on a large, continuous area—ideally one-third to half the size of a football field. Avoid working in small, scattered sections, as this can lead to inconsistent results. The maximum thickness of the gravel layer should not exceed 30 cm.
Rolling should start from the lowest point and move toward the highest, ensuring even pressure. On a football field, the process should begin from the sidelines and gradually move toward the center. After the first pass, check the elevation and flatness of the surface. If there are significant irregularities, adjust them immediately by adding or removing material. In sloped areas, distribute more sand and gravel, while in raised areas, dig small pits and level them out with surrounding material.
If coarse aggregates form "plum-like" clusters, remove them and replace them with well-graded gravel. Avoid filling with coarse sand, as it can compromise the stability of the base. Throughout the rolling process, maintain the optimal moisture level and continue compacting until the required density is achieved. Always inspect the surface for soft spots or frozen areas, and address any issues promptly to ensure a solid foundation.
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