The construction of a gravel base is a critical step in preparing surfaces such as football fields, playgrounds, or roadways. The process typically involves three main stages: paving, watering, and rolling. Proper execution of each stage ensures the stability and longevity of the base layer.
Paving is the first and most crucial step. It's essential to control the virtual thickness of the gravel layer, which refers to the compaction coefficient. For mechanical paving using equipment like bulldozers and graders, the compaction coefficient is usually set between 1.20 and 1.25. If the paving is done manually, the coefficient can be slightly higher, ranging from 1.25 to 1.30. This helps ensure that the base is dense enough to support the layers above.
After the initial paving, any areas where coarse aggregates have clumped together should be manually broken apart and evenly distributed. Similarly, regions with an excess of fine sand need to be excavated and refilled with appropriate materials. Once the surface is even, water should be sprinkled evenly across the entire area. The sprinkling must penetrate through the entire structure to help achieve proper moisture content.
Once the water has been absorbed and the surface has dried slightly (usually after 1–2 hours), rolling can begin. The amount of water used during this phase varies depending on the season and the thickness of the base. Here’s a reference table for the recommended sprinkler scale:
| 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 |
**Note:**
1. The natural moisture content of graded sand is around 7%.
2. The optimal moisture content for graded sand is between 5% and 9%.
When compacting the gravel, it's best to work over a large, continuous area—ideally one-third to one-half of the football field. Avoid working in small, scattered sections, as this can lead to uneven compaction. 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 distribution. On a football field, this means starting from the sidelines and moving inward toward the center. After the initial rolling, check the elevation and surface flatness. If any irregularities are found, they should be corrected immediately. For low spots, add more gravel; for high spots, dig out small pits and spread surrounding material to level the area.
If coarse aggregates form "plum-like" clusters, they should be removed and replaced with well-graded sand. Avoid filling with coarse sand, as it can compromise the base's integrity. Throughout the rolling process, maintain the optimal moisture content and continue rolling until the required density is achieved.
During the entire process, carefully inspect the surface for signs of soft spots or frost heave. Any problematic areas must be thoroughly treated to prevent future issues. By following these steps, you ensure a strong, stable, and long-lasting gravel base.
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