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Section D - Pitch Design

In many countries, Rugby is played in winter when grass growth is minimal and weather conditions less than ideal. Poor quality surfaces mean that players are unable to experience a satisfactory standard of play which can influence the outcome of a match, a situation that is unacceptable at the highest levels of the Game. Furthermore pitch maintenance can be a challenge when drainage compromises pitch performance.

However, upgrading a poor quality pitch or constructing a new one does not necessarily solve the drainage and usage problems. Proper drainage design is an essential item of quality pitch design, along with the projected intensity of use. Drainage design must take account of local rainfall statistics and defines what eventualities are being catered for so that these may be incorporated in to the final pitch design process.

Poor construction, ineffective maintenance and overuse will eventually lead to deterioration in pitch performance, poor drainage and unacceptable playing conditions.

Unless the existing ground contours are acceptable, some form of grading may be necessary. The extent of the grading works will be confirmed by the detailed topographical survey. In certain circumstances, this may require the removal of the topsoil with adjustment made in the underlying subsoil.

Rock, running sand and peat will all require specialist treatment but these hazards should have been identified during the feasibility stage. Soils should only be moved when ground and weather conditions are sufficiently dry.

Normally final gradients will depend upon local site conditions but a general rule is to achieve a maximum gradient of 1:80 – 1:100 along the length of the pitch and 1:40 – 1:50 across the field of play. Occasionally pitches may be crowned with a central higher spine running between the goals and a fall to either wing.

Pitch design can take many different forms dependent upon site conditions and the client’s requirements for performance. The more common forms of pitch design are discussed in the following section.

It is recommended that all materials are approved for their specific use before any construction work commences.

1) Undrained pitches

Even with free draining soils, there are few instances where undrained pitches provide satisfactory year round playing conditions. Sandy soils over gravel or chalk may be an exception, but these are rare. On certain sites where the soils are naturally well drained, there may be local issues with a fluctuating water table which can lead to surface wetness and poor playing conditions during the winter months.

2) Pipe drained pitches

This form of construction is popular as a means of upgrading an existing facility. The foundation of a pipe system is a series of pipe drains with permeable backfill to within 150-200mm of the surface at drain spacings of 5-10m centres. On a new construction, a properly designed pipe system would form the cornerstone of the development. The design for a new drainage system should also include a positive outfall into which water collected by the drains can be discharged.

Figure D1: Pipe drained pitch

Drain spacing is dependent upon the infiltration (drainage) potential of the native soil and the drainage design rate. Increasing the drain spacing as a cost saving exercise should be considered with caution as this could compromise the effectiveness of the drainage design.

A pipe system alone still depends upon the infiltration rate of the native soil to function, as its main use is to control the water table. Surface water movement and collection of rainwater is still the rate limiting step of this type of system.

3) Pipe and slit drained pitches

This form of construction is most commonly used on native soils where good drainage rates are required and is usually a cost effective solution. The foundation is a primary pipe drainage system that acts as a means of controlling the height of the underlying water table and to gather water from a secondary slit drainage system.

Secondary slit drains consist of a series of narrow (usually 50-70mm diameter) trenches cut through the porous backfill of the lateral drains. These trenches are filled with grit and topped off with approved sand or a sandy growing medium. The Secondary slit drains can be installed at a spacing of 600-1200mm.

There are a number of variations on the above principle using varying depths, widths, slit spacings and backfill materials. It is important that proper advice is sought regarding the choice of materials, and form of installation so that the drainage system will function as intended. Poor quality materials or workmanship can have a significant impact on drainage performance as can subsequent maintenance.

The main advantage of this approach is that it does not rely on the drainage capacity of the soil and high drainage rates can be achieved on poor quality soils. Nonetheless, for the system to function effectively over a prolonged period, it is essential that:

Figure D2: Pitch profile with pipe and slit drainage

This type of construction is effective but can have its pitfalls, which are as follows:

4) Sand surfaces over soil

The application of sand on a regular and consistent basis can improve the majority of soil based pitches; building up a 25mm depth of suitable sand on the surface of a pipe or pipe and slit drained pitch over a two to three year period can improve performance further.

Therefore the provision of greater depths of sand (75-100mm) over the native soil at the time of construction can create surfaces with high drainage rates. The choice of sand is important and advice should be sought on the suitability of local materials for this type of construction.

Pipe drains are normally installed into the base soil at an appropriate spacing either with or without a secondary drainage system before the sand layer is spread. The sward cover is established in the upper sand profile but roots should be capable of penetrating the underlying soil to reach the nutrient and moisture therein. Whilst this form of construction may appear attractive, there are a number of potential pitfalls that should be avoided. Some factors to consider as part of this form of construction include the following:

Figure D3: Sand surface over native soil

5) Sand soil surfaces

Natural soils depend upon structure for drainage whilst sand/soil mixes depend more upon the relationship of the sand, silt and clay particles in the mix than structure. The success of this approach depends upon the following:

Almost without exception, unless the indigenous topsoil is predominantly sand, this approach will not be successful unless significant quantities of sand are incorporated into the soil.

It is therefore vital that such an approach is only considered after consultation with an experienced consultant. It would be normal practice to formulate a number of design mixes and to have these tested at an accredited laboratory to determine how the mixes are likely to perform in the field.

6) Stone carpet

A stone carpet system would be chosen where:

A permeable stone layer is usually laid to a depth of at least 100-150mm over a consolidated sub-base. A pipe drainage system is installed in the sub-base, normally at a spacing of 5-10m. A geotextile may be included but only to help stabilise the sub-base and preserve the integrity of the stone carpet. The choice of stone is important, being durable, resistant to weathering and properly sized to accept the materials placed above without these washing into the stone. On this basis, a one or two layer system may be required, dependent upon the availability of local materials.

The choice of material to place above the stone carpet will depend upon a number of factors and design requirements. Options include, soil, a formulated rootzone or pure sand.

Very high drainage rates can be achieved with either pure sand or rootzone materials placed over a stone carpet and this form of construction is usually the preferred method for multi-use international stadia.

On an intensively used pitch, the grass cover can thin where growth rates are insufficient to promote recovery between matches and, when combined with a very sandy rootzone, the surface may become unstable particularly if the grass cover is lost altogether. In such circumstances, the inclusion of some form of reinforcement may be required to help maintain surface stability and playability.

1) Soil over gravel carpet

In certain instances it might be desirable to replace the preserved topsoil over the gravel carpet. This offers the benefit of the moisture and nutrient retentive properties of the soil to support healthy grass growth. Drainage rates are maximised by ameliorating sand into the surface immediately prior to seeding as well as through the installation of an appropriately designed secondary drainage system either during construction or once the sward cover is established.

Water movement through the topsoil is dependent upon soil structure but if this structure happens to be damaged then it should be possible to use mechanical aeration equipment to connect the pitch surface with the gravel layer below. Every effort should be taken to avoid working soils in wet weather to minimise the risk to the natural soil structure, essential for good drainage.

2) Rootzone over gravel carpet

A formulated rootzone with sand as the primary constituent can confer particularly good and uniform drainage characteristics when placed over a gravel carpet. It is normal practice to place a 250 – 300mm depth of carefully selected rootzone over the gravel layer. As well as sand dominating the material, other amendments may be incorporated primarily to aid maintenance; these could include a small proportion of sandy soil, peat, compost or a mineral supplement. The intensity of use will determine the need for rootzone reinforcement in this form of construction.

Rootzone formulation and selection is based upon sound scientific principles and should only be completed by competent personnel who have experience in such matters and furthermore are able to interpret the laboratory test results from a technical point of view. It is essential that a full set of performance tests are conducted in an accredited laboratory to determine which mix will perform best under local climatic conditions. Tests are usually conducted to determine:

3) Sand over gravel carpet

The option to use only sand for the rootzone also exists but similar principles apply as regards identifying a suitable sand and performance testing.

A sand only profile will prove much more challenging to maintain, particularly during the first year of establishment. It is highly likely that some form of reinforcement would be considered as part of this profile. In addition a skilled grounds maintenance manager is essential if this approach is to be successful. There will be a much greater demand for nutrient and supplementary irrigation until the sward is adequately established.

Figure D4: Reinforced rootzone over gravel carpet

7) Reinforcement materials

On very sandy rootzones, the surface is very likely to become more unstable as the grass cover thins and stability is eventually lost altogether. The aim of the maintenance programme is to retain a grass cover and prevent this from occurring. However, various reinforcement options are available to provide added stability.

1) Reinforcements incorporated in to the rootzone

This includes the incorporation of polypropylene fibres mixed with the sand or rootzone, e.g. Fibresand or Fibrelastic to provide added stability. The fibres are typically incorporated into the rootzone at a fibre content of 0.3% weight/weight to provide the enhanced performance.

Figure D5: Fibresand concentrate

2) Hybrid systems

The most common reinforced hybrid system is Desso GrassMaster. This is a 100% natural grass pitch stitched with Desso synthetic grass fibres. The fibres are stitched 200mm deep in to the rootzone and make up 3% of the final sward cover. The purpose of the fibres is to anchor the turf to provide a stable pitch. Desso GrassMaster has been installed at many venues including Forsyth Barr Stadium, New Zealand, Newlands Rugby Stadium, SA and Doncaster RLC, UK.

Motz Stabilised Turf is a patented system of natural turf grown in a stabilising synthetic mat. The system comprises a dual-component backing of biodegradable fabric and tough plastic mesh to provide the stability for the rootzone material and grass sward grown in the material. The concept involves allowing the natural turf to grow above the tops of the synthetic tufts whilst the grass roots become entwined in the synthetic matrix and grow through the backing in to the rootzone below.

The choice and selection of the rootzone infill is important to ensure compatibility with the site or construction profile. The turf is normally prepared and grown in a nursery prior to being used.

The advantages of this system are added stability and sod strength following turfing on very sandy rootzones.

All reinforced pitches require a different approach to management and will periodically require the surface to be removed as the fibres may become buried under top dressings or as organic matter accumulates.

Figure D6: Motz stabilised turf

8) Modular systems

Modular pitch systems such as the ITM™ system from GreenTech or the StrathAyr system are used in stadia where a combination of turf and hard surface events may be held. The movable turf system enables the turf, grown in high density polyethylene or galvanised steel trays, to be removed from the stadium environment if desired.

The turf trays usually have dimensions from 1.15m x 1.15m up to 2.44m x 2.44 m with each tray potentially covering an area of 6m². The pitch profile contained within each tray is generally 200mm deep and comprises a gravel drainage layer and purpose specified rootzone. The rootzone may be reinforced as in the StrathAyr system.

One of the potential benefits of this type of system is the ability to remove and replace damaged or worn turf.

Figure D7: ITM™ Modular system
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