The construction of a gravel base is a critical step in building a stable and durable surface, especially for sports fields like football grounds. The process typically involves three main stages: paving, watering, and rolling. Proper execution at each stage ensures the base is well-compacted and even.
When it comes to paving, controlling the thickness is essential. This means understanding and adjusting the compaction coefficient. For mechanical paving using equipment such as bulldozers or graders, the compaction coefficient is usually set between 1.20 and 1.25. If the work is done manually, the coefficient can be slightly higher, ranging from 1.25 to 1.30. This helps ensure that the material settles properly once compacted.
After the initial paving, any areas where coarse aggregates have clumped together should be broken up and evenly spread out. Similarly, if fine sand has concentrated in certain spots, those areas should be dug up and refilled with a more uniform mix. Once the entire area is covered, water should be evenly sprinkled across the gravel. The goal is to moisten the entire structure without over-saturating it. After letting the water settle for about 1 to 2 hours, the surface can be air-dried before starting the rolling process.
The amount of water used depends on the season and the thickness of the gravel layer. Here’s a reference table showing 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 around 7%.
- The optimal moisture content for graded sand should be between 5% and 9%.
When it comes to grading and rolling, it's best to work on a large enough area—ideally one-third to one-half of a football field. Avoid working on 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. On a football field, begin from the sideline and gradually work your way toward the center. After the first pass, check the elevation and surface flatness. If there are noticeable high or low spots, they need to be corrected. For sloped areas, add more sand and gravel to fill in the depressions. For high spots, dig small pits and then spread the surrounding material to level the area.
If there are areas with concentrated coarse aggregates (like "plums"), remove them and replace them with well-graded gravel. Avoid filling with coarse sand, as this can create weak points. As you continue rolling, always check for signs of soft spots or frost heave. Any problematic areas must be addressed thoroughly to ensure the final base meets the required density and stability standards.
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