by Eric O'Donnell, Managing Director
Many of our clients are new to artificial turf and have little or no knowledge of what goes into the construction processes and components which come together to make a synthetic field. In this article, therefore, we thought it would be a good idea to go back to basics and explain what the role of each facet of the construction process or materials that go into the building of a field.
The design starts from the ground up
A fundamental expectation is that the playing surface will be stable, flat and will drain. The design of any field must take into account the prevailing ground conditions so that a solid foundation can be established not only to meet the expectation that it will perform to requirements but continues to do so well into its life cycle. Future proofing a field is part of the deal. So, let’s talk about what’s goes into the construction of a field and the layer works required to provide a solid foundation that a high performing playing surface needs. Building a base is not the same as creating a parking lot. Make sure you select an experienced contractor for your project, one who has constructed bases before.
Drainage is a fundamental requirement
There is a requirement that an all-weather field should drain and be playable in all sorts of weather. So as part of the infrastructure works which go into the construction of an artificial field, a drainage network is installed under the pitch or within the underlayment system to de-water the field during periods of inclement weather. The design of the drainage system comes down to the design of the field. A vertically draining field, where rainfall percolates down through the structure in a vertical plane, will typically have a piped drainage system which sits in the subsoils. A field which clears the surface with a fall to the side and a drainage layer within the underlayment relies on rainfall collecting in the upper layers of the field within the underlayment and moving to the drains at the sides.
The foundation of the field is called the base
The foundation of the field is critical to the performance of a field. The term 'a solid foundation' is often used but never more appropriate than during the building of a sports field. The base of a field is usually constructed using a crushed stone layering system referred to as sub-base. This material comprises of quarried crushed stone and is installed and compacted to form a thick blanket of stiff material over the soils. This layer is the foundation of the field and should provide a stable, flat, free-draining and durable platform for the playing surface.
In sports such as field hockey, it is not unusual to incorporate an asphalt layer over the sub-base layers. There are some significant benefits to installing asphalt layers:
Asphalt increases the structural integrity of the base, adding strength and stiffness.
The overall flatness of the base is brought to a very high tolerance which is vital for some sports such as field hockey and tennis.
Asphalt bases have been known to retain their favourable properties for 25 years or more when built correctly.
Shock pad or underlayment
Shock Pads are designed to absorb impacts. Artificial turf infill can harden over time because the infill will compact and the turf system wears, falls over and breaks down. A well-designed cushioning layer can help reduce infill compaction to some degree and provide long-term protection against injuries. It is proven through many player studies that fields with shock pads are preferred over fields which do not have them.
Shock pads are made of a variety of different materials. Rubber in the form of sheets or granulate bound by glue have been extensively used in the past and are still popular today. These shock pad layers are known as elayers (elastic layers) and some contractors favour them. Foam systems (there are many) have been increasingly popular as they are cost-effective and may allow turf over pad systems to comply with governing body standards. There are others such as expanded polypropylene panels which are designed to provide unique properties of shock attenuation while offering higher stiffness for a playing performance. The bottom line is that shock pads are an insurance policy against loss of shock absorption, and for this reason, they are highly recommended in all sports fields apart from facilities for tennis..
Artificial turf components
Artificial turf includes a number of components: the most popular turf (variations described later), include a sand layer, and performance infill (which can be a variety of materials but is commonly recycled tire ground to form small pellets). These occupy the interface between the turf and the player. Other turf systems may have only a sand layer (or alternate inert infill) or are non filled.
Sand layer - The majority of long pile artificial turf systems are designed with a sand layer. The sand layer is primarily incorporated in the turf system to provide ballast which reduces the ability of the turf to become dimensionally unstable. The sand provides a medium to keep the filaments erect and acts as part of the shock attenuation system in combination with a shock pad and performance infill.
Performance infill - The performance infill is designed to provide the sports technical function of the playing surface. For the player, this means stability, traction and shock absorption. For the ball surface interaction in sports where this is important, it should provide a natural ball bounce and roll.
Yarn filaments - The plastic filaments are designed to simulate grass blades and are a high-quality polymer made from polyethylene plastics. The filaments can be sophisticated shapes, which make them durable and resistant to wear. The filaments affect ball surface interaction the most. The speed of ball roll and ball rebound are also influenced by the density of the pile incorporated into the turf. Some fibers are less abrasive than others, and typically slit films are less abrasive than monofilaments.
Turf backing is mainly a polypropylene woven textile with plastic filaments tufted through to make the turf look like real grass. The backing is reinforced by the application of latex which is lacquered onto the back of the textile to hold the filaments and stabilise the turf. At the end of the manufacturing process, drainage holes are made in the backing to facilitate drainage. It’s important than any perforations in the backing are well formed and uniform.
The artificial turf system
What is arguably the most critical part of a field is the playing surface – all the foregoing construction works and layers are ultimately brought together to provide a first-class high performing surface for sports. There are thousands of artificial turf products available on the market with a vast range of qualities; hence it is very confusing for the purchaser. However, within this array of products, there is a way to make sense of it. There are sports specific products which suit soccer, football, field hockey, and tennis, plus multi-sport applications. These can be broadly categorised into the following types; Long pile turf systems, short pile turf systems, and multi-use turf systems. Many turf systems are filled with a performance infill but a few are not and are sports specific such as for field hockey and tennis. All artificial turf systems should be laid over a shock pad; it’s an insurance policy against the wear and tear that occurs on turf and provides shock absorption long after the turf doesn’t. The only exception is tennis surfaces.
It’s probably worth defining what is by far the most popular type of artificial turf, that is the type commonly referred to as 3G turf. The term 3G is an abbreviation of Third Generation, broadly referring to the third iteration of the evolution of turf systems which are available -- the first being a basic non-filled short pile artificial turf and the second a sand-filled short pile system. The following ready reckoner should help you work out the suitability of a particular turf system for a specific sport.
Building an artificial turf field is complex. It is important that when you decide to embark on this journey that you select a qualified and experienced designer who has designed at least half a dozen fields before for your project. By doing so, you will avoid some of the pitfalls which can beset what after all is a complex mix of civil engineering and sports field construction.