The artificial grass base is the layer between the subsoil and the artificial grass. One of the most important elements of constructing a synthetic grass facility is sub-base preparation. For a football field, A properly constructed sub-base can extend the lifespan of football grass and ensure the performance of the football field surface. It is a large and very important aspect of your football field construction and football artificial grass installation. It must be constructed correctly.
Depending on the size of the facility, it is important to consult with professionals in the civil- and geoengineering fields for their professional advice and support. Although expensive, geotechnical tests are recommended for all proposed large football field facilities.
Basic Principles of Sub-base Preparation
Basic principles of sub-base preparation for football fields(and other sports fields) as follows:
- Stable
- Flat & even
- Good drainage performance
- Frost free
The sub-base should consist of a combination of materials, resulting in an overall stable construction that will, therefore, withstand the local climatological conditions, such as periods of heavy rains, frost, etc. The upper surface of the sub-base should not contain any sharp objects that could damage the shock pad or the backing of the artificial grass carpet.
There are three main factors for the failure of any artificial grass base constructions:
- Inadequate backfill materials,
- Not compaction
- Insufficient drainage.
Football Field Slope and Drainage
Drainage considerations for a football field are very important. Generally, in the case of a non-water permeable football pitch, the surface water, and the water that drains through the perforated backing of the artificial grass will follow the slope to the lowest areas of the base. This water needs to be let into an outlet and carried away from the pitch area.
Drainage requirements for a water-permeable base need additional subsurface drains to collect the water that seeps through to the sub-base. The base is usually leveled with a slope between 0.8 – 1%. The location and surroundings of the proposed site and the water outlet locations are important factors in the design of a drainage system. There exists a close relationship between soil permeability, spacing, and depth of drains. The capacity of water that drainage pipes can carry depends on the pipe’s inside diameter, the slope at which it will be installed and the material the pipes are made of. The installation method is just as important for a successful system. Therefore, we strongly recommend including consultations with drainage professionals in the design phase of the proposed football pitch.
Types of Base for Artificial Grass Football Field:
Artificial grass may be installed on a well-engineered asphalt base, unbounded base (compacted aggregates) or concrete.
Asphalt base: A compacted aggregate foundation is finished off with asphalt which results in the most durable and stable base to date. The synthetic grass is then installed over the asphalt wearing course. Some sports regulations require the installation of shock pads to provide shock absorbency. The shock pad will be installed over the asphalt wearing course followed by the installation of the synthetic turf. Most asphalt bases are non-water permeable.
Unbounded, free-draining base: The base foundation consists of a compacted course and fine aggregates. A shock pad, if required, is then installed over the compacted base. If a shock pad is not required, we recommend the installation of a geosynthetic material between the base aggregates and artificial turf. The benefit of an unbounded base is that it is water permeable, less costly than an asphalt base but it is not as durable than asphalt and might need replacement or repairs within a few years.
Reinforcement Cement: Smaller size sports pitches can be constructed by means of reinforced concrete slabs minimum 150mm thickness. The synthetic grass is then installed on top of the concrete surface.
Recommended further reading:
Guidelines for Synthetic Turf Base Systems – By&Copyright belongs to Synthetic Turf Council
Preparation of a Sub-base for a Football Turf System – By&Copyright belongs to FIFA