So often, those of us in the sports construction business assume that "all" of our customers understand how synthetic turf fields are built. Regardless, we at MWSTS believe that educating/clarifying the process is important since we want our customers to be well informed and to understand potential issues that can come up. Accordingly, the following information is intended to help with that process. While this information can be used as a general guideline, various locations, site conditions and local and state regulations can affect the overall process.
Let's get started:
Before any construction commences, topographical surveys, geotechnical reports about the soil conditions, as well as storm water management and erosion control reports/permits should be obtained. Without them, costs for the construction can only be estimated. The above reports are critical in determining such things as: how much soil will need to be excavated to get to "subgrade"; potential stability and/or contamination issues with the soil; specifics associated with perimeter trenches and associated drainage pipes; and, the size and amount of stone above sub-grade that will be required for structural stability and storm water management.
"Typical Base Construction"
Assuming nothing out of the ordinary, a "typical" base construction is as follows:
1. Excavate approximately 8"-12" of top soil to reach sub-grade (this could be less, or considerably more depending on above referenced reports); 2. Proof roll sub-grade -- we don't want to see more than approx. 1/4" of deflection as heavy trucks loaded with stone roll over the sub-grade; 3. Excavate approx. 3' x 3' trenches around entire inside perimeter of the field; 4. Construct 6" wide (sometimes 12") by 12" deep (sometimes more) concrete curbs around entire outside perimeter of field; 5. Attach pressure treated or composite 2" x 4" boards (called "nailer boards" -- this is where the turf is attached) approx. 1 1/2" to 2" below the top of the concrete curbs, on the side facing the inside of the field; 6. Laser grade the sub-grade toward approx. .05% slope from the center longitudinal axis of the field to the side perimeters of the field; 7. Apply a geotextile filter fabric (typical a 4 ounce fabric) in the trenches and over the entire field; 8. Position perimeter drain pipes (approx. 12" in diameter) into all trenches and connect them all. Then connect one corner to another drainage pipe that will connect tan existing drainage source; 9. Position 1" x 12" flat panel drains in a "hearing bone" pattern where a first end of the drains start near the center longitudinal axis of the field and the second distal end extends and drops into the trenches along the longitudinal sides. These flat panel drains are spaced between 20' and 25' on center. 10. Roll, compact and laser grade approximately 4" - 4 1/2" of 3/4" - 1" clean free draining stone; and 11. Roll, compact and grade approx. 1.5" - 2" of 3/8" finish stone or manufactured sand to final grade - maintaining the .05% slope from the center of the field to the top of the "nailer board. 12. Check entire base to ensure substantial planarity.
The base is now ready for turf. A subsequent post on how the synthetic turf field is constructed will be forthcoming.
Please note that the above description should only be used to provide a general understanding of base construction and should not be relied on. As stated, different projects have different requirements and conditions. Obtaining the previously referenced engineering reports and permits is the only way to know exactly how each particular base needs to be built.
One final note: Proper base construction for synthetic turf fields is significantly more complex than it is for things like a parking lot, or a natural grass field. MWSTS cannot over emphasize the importance of engaging a highly experienced "synthetic turf" base contractor. Proper base construction is absolutely critical to obtaining a flat/planar surface that will stay that way over the entire field, as well as for ensuring proper long term drainage.
We hope you find this explanation helpful. Please reach out to us if you have any questions about the above, or, about issues unique to your situation.