A Synthetic Landmark
Chesterfield County officials had a unique opportunity in creating the county’s first public synthetic-turf field in Stratton Park.
But the idea was even better than that; officials decided to partner with the Richmond Kickers and utilize the multi-purpose fields adjacent to the private soccer group’s existing natural-grass and synthetic-turf fields so that the fields could be jointly programmed for larger events.
The plan was developed through a public process involving the Kickers organization and stakeholder groups representing soccer, football, lacrosse, and field hockey.
Design And Grading
The grading for the two fields was designed as one plane with a minimal slope of .0067, allowing flexibility of use for various sports. The fields are 210 feet x 330 feet with a minimum 15-foot safety zone.
A paved walking/jogging trail around the two fields provides access to spectator areas and a family exercise outlet. The area between the fields is programmed for coaching and players. A welcoming plaza with shade trees accommodates concessions and provides convenient restrooms. Reinforced concrete in the plaza allows access to the fields for both emergency and maintenance vehicles.
Building The System
The new synthetic-turf system’s appearance is amazingly similar to that of natural turf, with grass blades that are three dimensional and multi-color green.
The front-end cost for a synthetic-turf system is a major investment, so it pays to visit several installations to set realistic expectations for the appearance and performance of the system within the project budget.
A performance specification was prepared to allow multiple manufacturers to bid on the project, since each manufacturer had a different system to achieve similar results. Specification and bidding were a collaborative effort between consultant and owner, resulting in several “lessons learned” through the process (see sidebar).
Building a synthetic-turf system utilizing a traditional drainage approach begins with a sub-base layer of stone in a herringbone trench pattern around a system of 4-inch perforated tubing. Above this, a layer of geotextile is placed, overlaid with a dynamic base of dense graded stone and a fine topping layer.
All is compacted to 95-percent Standard Proctor.
Other drainage methods have been developed by the manufacturers. The option selected for Stratton utilizes a pre-molded drainage board of lightweight, injection-molded plastic tiles instead of the traditional under-drain system. The drainage board is made of 100-percent recyclable material, and forms a porous shock pad.
The pad allows for water infiltration and conveyance through hollow drainage channels on the bottom of the pad that slope towards the field perimeter. The pad offers a potential savings by eliminating the under-drain tubing system, decreasing the required depth of the stone base, and minimizing the depth of excavation.
It also allows for virtually level fields, with a minimal slope center to ends of .0067.
There is an additional benefit in using a drainage pad since it provides added resilience for player safety--decreasing the tested G-Max by a minimum of 20. Resilience of the surface is measured as a factor of gravitational pull, and is noted as the G-Max rating of a surface system.
Several factors in the design of the field section impact the G-Max rating, including the drainage system and the sand/rubber ratio of the infill mix. The recommended G-Max rating varies, but a range is between 80 and 110. However, the softer, more resilient surface that results from a lower G-Max rating also results in slower speed of play and ball roll. A balance between safety and speed is the goal.
The fiber height or finished pile height varies from 1.5 to 2.5 inches, but the real test of a system’s performance is the weight. The total turf weight, as well as the face weight of each system, needs to be compared.
The face weight is the weight of the grass or pile fiber without the backing. Comparing the face weight based on the same fiber height will reflect the density of the fibers. Like carpeting, this impacts the appearance of the turf and can also impact the performance and life of the system.
The face weight ranges from 35 to 48 ounces per square yard. The pile tufting also plays a role in the density of the pile fibers. It is generally recommended to have a 3/8- to ½-inch gauge with a stitch rate of approximately 10 stitches per 3 inches (10/3). The total turf weight also includes the backing layers.
Most manufacturers provide a three- or four-layer backing consisting of two layers of woven fabric and one layer of non-woven fabric. The secondary backing is a high grade of polyurethane, and is applied to the entire primary backing. If the backing is not porous, 3/8-inch drainage holes should be perforated through the backing every 2 to 4 inches in both directions.
The best field markings are 4-inch-wide inlaid lines, either factory-installed or seamed into the field after installation. Varied colors of the turf fibers are used to mark a field for multiple sports.
The turf is anchored to the field by fastening it to a wood nailer board inset in a concrete curb that is flush along the field perimeter. The perimeter curb must be set a minimum of 15 feet out from the playing field to allow for the safety zone.
A 4-foot-high chain-link fence at the field perimeter prevents ball roll away from the fields. Although the concrete curb is typically 6 inches wide at Stratton, the curb is widened in order to embed the fence posts in the curb.
Infill must be thoroughly mixed before the synthetic-turf surface is installed. The sand is rounded silica, and the rubber is typically SBR crumb rubber made from recycled tires, usually mixed in a ratio of 30:70, sand to rubber, although with a drainage pad the ratio may be 50:50.
The infill acts as a ballast to help hold the field in place and adds resiliency based on the percentage of rubber used in mix. Infill helps to hold the grass blades in a vertical position and adds to the life of the blade since less of the blade leaf is exposed to wear during play.
The depth of the infill at the time of installation should be about ½ inch below the blade tip so it settles to a maximum of 5/8 inches below the tip.
Maintenance And Warranty
Cost and frequency of maintenance and replacement are part of the selection criteria for a synthetic-pile system. Life expectancy of the synthetic-turf surface is generally 8 to 10 years, while the life expectancy of a pad/drainage board is 16 to 20 years.
The typical warranty length for the turf is 8 years. In considering life-cycle evaluation, be sure to budget for removal of the old system, in addition to the replacement cost. The system warranty should include that the surface system is to maintain the specified G-Max range for the life of the field.
Maintenance of the infill material is critical, particularly in hot spots like corner-kick areas. As the percentage of sand is increased, the frequency of grooming the infill also increases to prevent the compaction of the infill mix.
Require additional sacks of infill, seaming tape, and patch turf as part of the bid package. It is recommended to groom the infill every 3 to 4 weeks. Hot spots should be filled by hand and raked in bi-weekly.
Defibrillation--brushing synthetic turf in the opposite direction of its turf lean--is also a maintenance requirement to bring turf vertical and increase the field life. This is done manually with a push broom or mechanically with a Gator and motorized sweeper.
The Synthetic Turf Council (STC) is a recognized professional association in the synthetic-turf marketplace that offers a third-party certification. This is a voluntary commitment to deliver products and services that meet or exceed the specifications. The specifications should include qualifications and the experience of the installer. An insured third-party warranty also should be required.
Nancy Rodrique is a Landscape Architect with Vanasse Hangen Brustlin, Inc., in Virginia Beach, Va. She can be reached at (757) 490-0132 or email@example.com. For more information on the firm, visit www.vhb.com .
------------------------------------------------------ Sidebar ---------------------------------------------------------------------
• Involvement of stakeholders
• Cost benefit of synthetic turf vs. natural turf
• Selling local officials on the investment
• Public procurement of performance-based specifications
• Obtaining approvals prior to bidding