2.4 TURF AND PITCH DESIGN
The pitch is the focal point of any stadium, and as such the pitch can be considered as the main stage.
The quality of the pitch is therefore fundamental to the performance, appearance and reputation of the entire stadium.
The choice of turf will depend on the needs and resources of each project, and there are three main types to choose from:
• 100% natural grass
• Hybrid pitches (synthetic fibres are added to the natural grass for the purposes of reinforcement)
• 100% synthetic grass (artificial)
FIFA’s position on 100% synthetic pitches, as an alternative to natural grass, is well established: the FIFA Quality Programme for Football Turf defines what is acceptable, and provides guidance on procurement, installation, testing and maintenance. A summary is provided in Sub-Section 2.4.3, along with references for further information.
The majority of this section therefore focuses on grass and hybrid pitches. Whilst hybrid pitches are becoming increasingly common (and in some cases are a requirement) at elite level, they can also be beneficial if a pitch is intended for intensive use, particularly in a multi-use environment. However, in smaller or less intensively used stadiums, a 100% natural grass pitch would be considered as the norm.
This section firstly addresses the interaction of the pitch with the stadium design, before considering the design of the pitch base and the supporting infrastructure. Further information is then offered on the different types of hybrid pitch options, before the focus switches to the supporting equipment and maintenance required.
The dimensions and requirements of the pitch and its surrounding area are considered in Section 5.3.
„THE PITCH CAN BE CONSIDERED AS THE MAIN STAGE“
A hybrid grass pitch at Spartak Stadium, Moscow
2.4.1 INTERACTION OF STADIUM DESIGN WITH THE PITCH
Irrespective of the stadium’s geographical location, the design (and in particular the roof and positioning of the stands) will create a microclimate within the stadium bowl, and this needs to be carefully evaluated and factored into the pitch design and choice of turf. It is recommended that a sun path survey of the natural light track in the stadium be carried out as part of the design process (see Section 2.2).
Designs that enclose the stadium on all four sides can restrict natural air movement through the stadium bowl and over the pitch. If tall stands are incorporated (especially multi-tier stands), sunlight will be blocked and significant areas of the pitch will be in shadow. Both of these factors are detrimental to the growth of natural grass but can be mitigated by the choice of turf and other design factors, such as the inclusion of translucent panels in the stadium roof. Grow lights can also compensate for a lack of natural sunlight.
Fully enclosed stadiums and retractable roofs and their impact on the pitch require specialist input. Any systems to move the pitch, either in its entirety or in sections, to an outside location need careful consideration and they will have a fundamental impact on the cost as well as the design of the stadium.
2.4.2 PITCH BASE
Pitch design is site-specific, and must be considered on an individual basis, with specifically modelled drainage systems and soil profiles to ensure high-quality playing conditions throughout the season.
A full geotechnical investigation should be carried out to determine the physical and chemical properties of the local geology, its performance and its load-bearing potential, as well as to identify contamination or other factors which could influence the development of the site. The underlying geology will establish the nature of the sub-base, its drainage characteristics and any water-table issues that would need to be addressed as part of the design. The data collected from the site investigation will determine if any specific remediation is required prior to construction.
It is crucial to identify the location of the main drainage outlet for the pitch. This drainage outlet usually needs to be agreed with the local authority, which will confirm the position of the outlet drain. In some cases, as part of the planning conditions, an agreed water discharge rate is set, which must be monitored and adhered to throughout the stadium’s lifetime.
The drainage design and any attenuation required is calculated based on local climate knowledge and predicted extreme rainfall incidents. In order to future-proof the project in relation to climate change (see Section 1.2), it is becoming increasingly common to increase the required drainage capacity by 30%-40%.
Figure 2.4.1
Typical elite pitch profile with irrigation and air system
• Irrigation pipes are to be installed within the gravel raft
• Combined depth of upper rootzone and lower rootzone shall be 300mm
• Pitch drainage to be 600 to 800mm deep
• If lower rootzone and gravel are compatible, no blinding layer is required
• Impermeable geotextile layer to be installed between general fill and gravel carpet
• Undersoil heating pipes to be installed on top of gravel carpet
Figure 2.4.1 provides an illustration of a typical profile for an elite-level pitch where water management is crucial to successful pitch management. The construction layers are carefully selected to sit on top of each other (without migrating into the layers below), and as water moves through the profile, the moisture builds up until the weight of water, under gravity, forces the excess water to drain through to the lower layers and away through the pipe drainage system. Sufficient water is retained in the rootzone for the demands of the plant. All materials must therefore pass through an approved laboratory for analysis in order to meet the design criteria for each project.
The layers beneath the surface comprise the following:
• Drainage aggregate/gravel raft: this allows for the uniform movement of water across the whole profile. It also provides direct access to a drainage point.
• Upper rootzone: this provides the growing environment for the turf, using a mix of the same sand as the lower rootzone, but with added organic matter (soil).
• Lower rootzone sand: this allows the rootzone of the grass plant to extend (typically to 300mm) without the need to use organic matter throughout.
Drainage: pipe drainage carries any excess water that drains through the pitch. A good drainage system needs to be supported by a good irrigation system (see Sub-Section 2.4.4). The irrigation system is normally installed at the same time as the gravel.
Vacuum and ventilation systems: vacuum and ventilation systems can be installed in the sub-base, alongside the drainage system, and perform the dual function of providing air to the rootzone, and they can also be used to quickly remove surface water, thus ensuring that games can take place despite heavy rainfall. The ventilation function is also beneficial for enhancing any heating/cooling elements within the profile.
These systems are relatively expensive but can be beneficial at elite level, where the potential consequences of postponing or abandoning a match are significant. They also require a plant room to accommodate the accompanying technical installations.
Undersoil heating/cooling: in colder climates, there may be a requirement for a subsurface heating system. Most modern systems are installed at the interface between the gravel and the lower rootzone sand – 300mm from the surface. This is close enough to the surface to have a positive effect and is reasonably economic, but deep enough to allow the profile to be managed. Most modern systems are installed using hot-water pipes, or in extreme cold climates, the water is replaced with glycol to prevent freezing. In hotter climates, such systems could be developed for cooling.
Figure 2.4.2
Pitch types and their usage
2.4.3 TYPES OF PITCH SURFACE
There are three main types of pitch surfaces:100% natural grass, hybrid pitches, which use some synthetic fibres to reinforce the natural grass, and 100% synthetic (artificial) fibres.
There are several types of hybrid pitches. Figure 2.4.2 features the three varieties of hybrid pitches most commonly used:
Natural grass: these are 100% plant-based on a sand- or soil-based rootzone. This surface is best suited to an open environment where there is free circulation of natural air and no significant shadowing from surrounding stands or other objects. The advantage of a natural grass pitch is that it is cheaper to install compared to other pitch types. The disadvantage is that it is dependent on (micro) climatic conditions for growth and performance. This is increasingly challenging in those cases where the pitch can spend significant periods in shadow. Natural grass pitches are also less robust in terms of intensity of use when compared to hybrid pitches. This can manifest itself both in terms of grass coverage and consistency of the surface (which can affect the players’ footing and the bounce of the ball). For these reasons, natural grass pitches have become less common at elite level compared to hybrid pitches.
Reinforced rootzone (hybrid): these pitches can either feature synthetic fibres or other forms of support to reinforce the upper section of the rootzone. These pitches tend to be favoured in multi-use stadiums.
Carpet-type (hybrid): these pitches are grown on a synthetic mat which contains some synthetic fibres. The mat or carpet is then infilled with rootzone and planted with natural grass seed. These types of pitches tend to be used by stadiums where the pitch is renewed regularly, for example, because of intensive multi-use or a challenging growing environment.
Stitched fibre (hybrid): these pitches achieve long-term reinforcement as synthetic fibres are stitched into the rootzone. This is done by using large sewing machines which install a line of fibres approximately every 20mm. It is recommended that seeding take place prior to stitching but it can also be done afterwards. This technology is well established and is considered by many to produce the best performing pitch type.
Figure 2.4.3
Stitched fibre
Grass types
There are different natural grass types (species) available, and the choice should be based on its suitability to local climatic conditions and the growing environment within the stadium.
There are two main groups of grasses, which vary considerably in their basic biology and climate adaption: cool-season grasses and warm-season grasses. There are different types of grass within these groups, for example, perennial ryegrass or Kentucky bluegrass suit cooler climate regions, whilst Bermuda or Zoysia species suit tropical regions. Increasingly, grasses can also be selected for their resistance to certain diseases and this should also be considered in relation to the local conditions.
2.4.4 PITCH MAINTENANCE AND SUPPORT EQUIPMENT
Grass and hybrid pitches require comprehensive maintenance programmes, which, at elite level, will often require specialist support equipment.
Sub-Section 2.4.2 noted that an irrigation system is often installed in the pitch base, and this system is now regarded as essential in terms of pitch maintenance.
Other support equipment, such as grow lights and pitchside fans, is, to some extent, movable and can be added after the pitch base has been laid. Any power connectivity, storage spaces and access requirements should be considered as part of the stadium design process.
Irrigation systems
Most grass pitches are grown on bases containing high volumes of sand, which facilitates efficient drainage but also means that regular watering (irrigation) is required to:
• maintain the condition and appearance of the grass;
• dilute rootzone nutrients to be taken up by the plant root system;
• bind the pitch base and provide a stable platform for the players; and
• facilitate the slick movement of the ball.
Therefore, it is now common for the pitch to be watered both before the game and at half-time, although this can be subject to individual competition regulations.
Water sprinklers and staff tending to the pitch
Pitch maintenance
Irrespective of the choice of turf, every pitch requires a detailed maintenance plan. The plan should cover all key operations required to ensure that the pitch is maintained to a high standard. The plan should include, but not be limited to, mowing, aeration, fertilising and line-marking.
In addition, an annual maintenance programme featuring a more thorough renovation is recommended. This is normally planned outside of the main football season.
Grow lights
Good quality artificial light solutions can help to compensate for the shadowing caused by modern stadium designs or simply boost growth in the darkest months of the year.
Traditional bulb technologies have been based on high-pressure sodium (HPS), but light-emitting diode (LED) lighting is also becoming increasingly common. LED lighting is more cost-effective in terms of the whole lifecycle cost of the bulbs and energy consumption. The initial disadvantage of LED lighting was that it did not provide an additional heat element when compared to HPS. However, some recent LED rigs have also incorporated infrared bulbs to provide the heat element if required (although this will increase energy consumption). This heat element is not required in warmer climates.
The additional costs in using these lights (and their environmental impact) require careful consideration.
Grow lights at the Puskás Aréna, Budapest
Pitchside fans
Large pitchside fans can be used to compensate for the lack of natural airflow in a stadium as they help to dry and cool the grass.
Further information on pitch maintenance is available in the FIFA Pitch Operations Handbook.
2.4.5 ARTIFICIAL TURF
Artificial pitches are composed of 100% synthetic fibres. These should not be confused with hybrid pitches, which contain a large element of natural grass supported by synthetic fibres. The advantages of artificial pitches are that they can sustain more intensive use than natural grass-based pitches and are not dependent on (micro) climatic conditions for plant growth.
FIFA has an established Quality Programme for Football Turf, and only products that are compliant with this programme should be considered as suitable football turf.
This programme covers licensed manufacturers whose products are specifically designed to ensure that they deliver in terms of playing performance, safety, durability and quality assurance. The programme then requires a specific on-site performance test to ensure each installation is of the correct standard.
There are three levels to the programme:
• FIFA BASIC, an entry-level standard that fulfils basic performance and safety criteria whilst ensuring affordability.
• FIFA QUALITY PRO, which is designed for professional football with a typical usage of up to 20 hours per week.
• FIFA QUALITY, designed for municipal, recreational and community football with a typical usage of 40-60 hours per week.
For further details, please see:
FIFA QUALITY PROGRAMME FOR FOOTBALL TURF
Artificial turf at the Stade de Suisse, Bern, Switzerland.
Artificial pitch base
The requirements for an artificial turf base are the same as those specified in Sub-Section 2.4.2 for natural grass and hybrid pitches. A geotechnical study of the land to determine the physical and chemical properties of the local geology, as well as the load-bearing potential for the site, is critical. Of equal importance is the availability of an approved drainage outlet for the removal of water from the pitch.
There are many patented systems available on the market that can be used for pitch profile construction, but the fundamental requirements for an artificial pitch base, from the ground up, are as follows:
• Formation layer – the platform on which the pitch is to be constructed must be stable, and the design contours for the field of play will be mirrored in this formation layer
• Pipe drainage – to collect and remove water moving through the pitch profile
• Sub-base – approved, permeable (unbound) aggregate provides a stable base layer for the field of play, which will also act as a collection medium for drainage water. A geotextile membrane divides the sub-base and formation layer
• Levelling layer – two basic options exist for the levelling layer:
• One or more layers of porous bituminous macadam (Bitmac) or asphalt, creating an engineered or bound base
• Graded aggregate material, which can be levelled, to create an unbound base
Figure 2.4.4
Artificial pitch profile
Some turf systems use a shock-absorbing pad which is installed as a patented system to provide the playing characteristics determined for an individual pitch.
For more details on the use of artificial turf in the various categories of stadium, refer to Section 7.1.
From an environmental perspective, there are three key aspects that need to be considered in terms of artificial turf:
• Although a good maintenance programme is essential, this should be less intense in terms of natural resources when compared to natural pitches. For example, the use of water should be significantly lower when compared to the irrigation of natural grass. However, it should be noted that some irrigation might be needed to cool artificial pitches due to heat absorption and it can also benefit the cleaning programme and pitch presentation.
• The choice of infill material used on artificial pitches will also affect its environmental impact. Elastomeric products, both virgin polymers and recycled materials, are classed as micro-plastics which have a negative environmental impact if they are lost and ultimately find their way into rivers and oceans. More recent technologies are moving away from the need for infill to be applied in response to these environmental challenges.
• The whole life cycle of the artificial pitch, including its ultimate removal and disposal.
Just like grass-based pitches, artificial turf requires a comprehensive maintenance programme to ensure that its playing condition, appearance and lifespan are maximised. For artificial turf, the key maintenance requirements are:
• Regular brushing – using a tractor-pulled brush is recommended. Appropriate access for the tractor to the pitch area is required. See the FIFA Quality Programme for Football Turf for further details.
• Removing any debris from the surface, including leaves, bird droppings, litter, etc.
• A drag mat and ball-roll ramp should also be used as maintenance equipment.
There will also be a requirement to disinfect the surface to reduce the potential spread of harmful bacteria that might be retained and transmitted via the synthetic fibres.
Artificial pitches also benefit from irrigation systems to help with cleaning and pitch presentation, and in warmer climates they can be used to cool the carpet ahead of play.