Design and development of a novel natural turf shear stability tester

The stability of natural Rugby Union pitches continues to be a recurring problem at all levels of the game. The effects of poor stability are seen when the pitch surface shears under player loading, creating unsightly divots and an uneven and potentially injurious surface. This observed instability is a real concern for many stakeholders, from the groundsmen to the revenue-generating television companies, and is arguably increasing caused by greater popularity of sports, more intensive use of natural turf pitches and advances in player physical conditioning. However, perhaps surprisingly, no objective quantitative mechanical test method currently exists for assessing the shear stability of the natural turf prior to games being played. This paper presents the findings from a (ongoing) research study into the design and development of a prototype turf stability apparatus (‘Turf Tester’). The key aim was to measure the shearing stability of natural and hybrid turf in order to assess a recurring failure problem. In order to be relatable to sporting performance, this failure imitates conditions to simulate player(s) interaction. The prototype and test method was developed with properties suggested from published papers discussing rugby and agronomists’ experience. It was theorized that there was a potential zone susceptible to failure within the top 100 mm of the sports turf. The position of this zone was variable and depended on pitch construction. The prototype was built to explore this variable failure zone using a 50 mm and 100 mm pin that sheared through the soil when a known load was applied to it. Both the Clegg Impact Hammer (CIH) and the rotational traction (RTD) were suggested to be relatable to penetration and shear stability; however, their relatability to the failure zone was an unknown. This paper details the background behind the study, the prototype design and principle, the observed failure mechanisms of sports turf, and presents the results of the prototype apparatus trailed on a range of turf constructions at venues used for the 2015 Rugby World Cup. Data was collected at each venue using Labosport’s Scoreplay system detailing full agronomic classifications and a suite of industry standard player performance tests. The combined data from 13 of the venues provided a powerful data set to evaluate and refine the prototype apparatus, providing validity of its conceptual design. The findings show that the shear tester assessed the upper level of ability of pitches with a 50 mm depth pin and the lower ability with the 100 mm pin. There was some evidence of a relationship to the CIH and RTD, albeit weak, and it was concluded the shear tester was assessing a characteristic of the sport turf not currently measured by standard industry tests currently utilized. The shear tester differentiated between the high stability of the hybrid pitch constructions and the weaker natural pitches. The shear tester rankings for pitch quality also approximated well the ranking from the Scoreplay pitch quality system. Incorporation of the shear tester into routine pitch evaluations could benefit a scoring system approach