A closer look at synthetic pitches
(Turf Business, March/April 2008)
In the British climate the multi-use of grassed sports pitches has become virtually impossible in view of the persistent wet conditions and dominance of clay topsoil.
Many schools require outdoor playing areas throughout the year in all weather conditions. The hours of use prevent grass cover being satisfactory maintained and soil conditions deteriorate with continual wetness and compaction.
In the last 20 years artificial grass surfaces have developed considerably with the emergency of sand infill surfaces and the third generation surface filled with rubber crumb and sand. With this true and firm surface it has become the accepted finish for hockey.
There are however a number of factors that need to be considered before installing a pitch.
The soil survey
The initial soil survey is vital since once the foundations are laid any further attention to the sub-grade becomes a very expensive undertaking. It is essential to establish the load bearing potential of the sub-soil as well as its drainage characteristics and the depth of top soil. Californian Bearing Ratio tests (CPR) are carried out to assess the load bearing potential. This is a plate test that simply measures the load the sub-soil is able to withstand. In addition, the tests are vital in designing the floodlight foundations. Once construction is complete loading will be restricted to players and light specialised maintenance equipment.
The highly permeable artificial grass surface should permit water infiltration at the rate of at least 150mm/hr and hence the maintenance of the drainage system is very important. With an even grade and relatively short pile, rain water enters the drainage system after limited attenuation in the surface sand and aggregates within the drainage system. In view of the fact that surface water is removed far quicker than from grass pitches, peak water flow should be expected at the time of flash storms. The drainage system must be able to cope with this high intensity flow until the storm subsides.
It is advisable that the base construction is tested for compaction, porosity and even grade. This necessitates the engagement of an independent testing house. Furthermore, samples of the shockpad and carpet should be tested to conform to FIH standards. On completion the surface should again the tested for evenness of grade with no deviation being greater than 6mm over a 3m straight edge. Seams should be assessed together with the evenness of sand infill. Undertaking these tests involves extra cost but it is worth having an independent appraisal when the installation is to perform satisfactorily over a period of at least 10 years or longer – and no disturbance can be considered within that time.
Day to day maintenance
Unlike grassed pitches that can be deeply tined and aerated, the foundation to a synthetic path cannot be disturbed. Maintenance needs sound planning. Weekly brushing sand infill is an essential duty. It is vital that the sand is evenly spread so that it supports the upright ‘pile’ of the artificial grass fibres. Once fibres are allowed to curl down with insufficient sand covering, they do not retain the desired surface and can never be brushed back into the upright position that is essential for a true and resilient surface.
Contaminants in many forms need to be removed or washed out and there is a constant need to remove debris. Dust is inevitable and with time the sand can become contaminated. Within about four years of the installation, the sand may need to be removed wholly or partially with specialised equipment and replaced with approved sand. The accumulation of moss must be prevented and this can normally be achieved with regular brushing. Fencing and flood lights require constant checking. Electricity costs alone can amount to in the region of £2000 in the year.
Access to all weather facilities can easily be overlooked. There is much greater use of the facility when compared with a grassed facility. Besides parking provisions, pathways must be adequate to cope with the foot traffic and the equipment used in the maintenance of the synthetic grass. Provisions should be made available too for the stockpiling of sand infill material and temporary storage of equipment to be used. Furthermore, there is a need for local lock-up facilities for sports equipment including goal posts, basketball posts, flags and small tools. Line marking should be permanent provided lines are inlaid prior to installation. Otherwise periodic marking would be necessary.
Contrary to expectations total annual maintenance costs of all-weather surfaces are similar to those of grassed pitches. They can be in the region of £10000 with the main costs incorporating the regular brushing of the sand fill, daily attention to debris, periodic sand cleaning, attention to fencing and floodlight cost.
April 29 2008