Maintenance best practice and recent research

This paper sets out to capture the recent discussions on maintenance best practice for artificial turf surfaces, from a SportSURF workshop in 2009, supplemented with a case study from Loughborough University. This is enhanced with recent research findings from two studies investigating damage to artificial carpet fibres caused by power brushing, and the usefulness of simple portable tools in monitoring pitch degradation and the alleviating effects of maintenance interventions. The outcomes of the maintenance seminar showed good consensus for frequency and type of maintenance practice, with a useful rule of thumb of one hour of maintenance for every 10 hours of use of the surface system. Maintenance costs of artificial turf should be expected to be similar to natural turf however, but expressed as ‘per hour of use’ are much lower. Damage caused by power brushing, from a laboratory study, was found to be minimal in terms of fibre splits or breaks, for three different standard brush systems and three different carpet systems. Portable monitoring tools, such as the Clegg hammer and rotational traction devices may be suited to monitoring two important pitch properties over time. These relatively low cost tools are potentially useful to manage aspects regarding infill depth and mobility, frozen ground and advice on intervention maintenance

LWD best practice guide

This Best Practice Guide has emerged from a working group (Pavement Foundations Group) to address the need for consistency in the implementation of LWD’s into UK practice. However, the guide does reflect best practice for a range of applications. It describes the industry best practice for using Lightweight Deflectometers to verify the construction quality of road foundations. The guide is seen as a statement of current knowledge, and includes recommendations for site operations. It is expected that this guidance will be updated periodically

A performance approach to the design and specification of foundations for industrial ground bearing slabs and pavements

The foundations for industrial flooring and pavements are normally designed based on measurements, or prediction, of the California Bearing Ratio (CBR) of the subgrade, and from this the design thickness of the foundation is chosen utilising long established empirical relationships. The modulus of subgrade reaction (k) measured by static plate bearing tests may also be used, and is correlated to CBR. The thickness design charts are the same as those used for the design of highway foundations and are based primarily on observed performance. The foundations are then constructed to a recipe specification whereby specific (tightly graded) materials are placed and compacted upon the subgrade with specified plant. The soil CBR can only be regarded as an index property and does not directly or explicitly assess the primary functional performance parameters, of stiffness or strength. If CBR were replaced with direct measurement of these parameters, then the current empirical approach could be replaced with more powerful analytical design. Performance of the as-built foundation could then be better assured by compliance testing (end product) on site during construction. By moving to a performance-based specification approach, requiring some analytical foundation design, it is anticipated that more appropriate and efficient use of plant and materials can be made. This should enable better quality construction to be achieved, more efficient use of recycled materials or stabilisation of weak subgrades, hence leading to more sustainable construction. Recent research at Loughborough University has developed such a performance-based specification approach for the design of (major) highway foundations, and has assessed those devices suitable to measure the performance parameters for both design and compliance testing. In this paper the transfer of this technology to industrial flooring and paving is suggested. The benefits of a performance-based approach to foundation design and specification are explained. The loading and function of a foundation is described and the performance parameters required to perform these functions are detailed. Suitable methods currently available to measure these performance parameters are described in brief. Finally, the implications and benefits of a move to a performance-based specification approach are discussed

Artificial turf research at Loughborough University

Research into artificial turf surfaces can be divided into the categories infrastructure, user safety and play performance. This paper discusses these three categories, presents current knowledge and appraises some remaining questions. A simple diagrammatic framework is proposed for describing and relating the fundamental components of sport surface related research. Infrastructure includes the design, construction, operation, and whole life costs associated with a facility. A key area for future research is to better understand maintenance and the benefits of various strategies / techniques. User safety, or injury risk, is a key concern for many stakeholders. Injury risk is a complex interaction of many factors related to the user, sport, equipment and environment. Whilst the introduction of an injury consensus in the late 1990s permitted much greater impact of studies in soccer and rugby, these have contributed little to understanding injury mechanisms. Furthermore, previous research is hampered with regard to the effect of the surface by utilizing simple mechanical tests that appear inappropriate to user activity, e.g. traction. Advancement of knowledge within this category demands better integration with play performance related measurements and research methods that support a more mechanistic approach. Play performance has been the focus of much recent research. For example, mechanical evaluation of surface systems in the laboratory / field, player testing with regard to player and surface response and perception of surface performance. There exists a real need to develop a ‘consensus’ in establishing suitable boundary conditions for both mechanical and player testing. This would help to identify the fundamental research questions related to play performance and allow improved comparison between research studies

Mechanical characterization and numerical modelling of rubber shockpads in 3G artificial turf

Third generation (3G) artificial turf systems use in sporting applications is increasingly prolific. These multi-component systems are comprised of a range of polymeric and elastomeric materials that exhibit non-linear and strain rate dependent behaviours under the complex loads applied from players and equipment. To further study and better understand the behaviours of these systems, the development of a numerical model to accurately predict individual layers’ behaviour as well as the overall system response under different loading conditions is necessary. The purpose of this study was to characterise and model the mechanical behaviour of a rubber shockpad found in 3G artificial surfaces for vertical shock absorption using finite element analysis. A series of uniaxial compression tests were performed to characterise the mechanical behaviour of the shockpad. Compression loading was performed at 0.9 Hz to match human walking speeds. A Microfoam material model was selected from the PolyUMod library and optimised using MCalibration software before being imported into ABAQUS for analysis. A finite element model was created for the shockpad using ABAQUS and a compressive load applied to match that of the experimental data. Friction coefficients were altered to view the effect on the loading response. The accuracy of the model was compared using a series of comparative measures including the energy loss and root mean square error

The development of a translational traction rig to investigate the mechanisms of traction in 3G turf

During football specific movements a high translational traction is desired at the shoe-surface interface to facilitate player movement. Translational traction is commonly assessed through bespoke mechanical test devices which provide a more repeatable tool for characterising the shoe-surface interaction compared to player testing. Following development, application of the rig is demonstrated through an initial investigation into the effect of the number of studs and stud orientation on translational traction. The translational rig consists of a tray attached to two trails, with surface samples of varying specification placed in the tray. A number of stud configurations were chosen and tested on a 3G artificial turf sample. The initial stiffness response of the surface as well as larger displacements were considered to help inform the mechanisms of traction. The study showed the increasing force as the number of studs increased and how the positions of the studs also relate to the forces produced in the infill and the effect on the mechanism of traction

Advanced measurement of sports surface system behaviour under player loading

Artificial turf sport surface systems are comprised of a number of different materials. Improving the understanding of the sports surface system's response to actual player loading is important for developing enhanced products and system designs for improving play performance and durability. Previous research has tested and compared the mechanical properties of artificial turf systems with relatively simple mechanical tests intended to simulate loading from the player or ball. However, these test methods have known shortcomings in representing real in-service loading and it is often assumed a peak value of force or peak deformation is sufficient to describe the surface behaviour. Little literature exists that describes the force-deflection or stress- strain behaviour of artificial turf system under mechanical or player loading. This paper outlines methodologies developed for surface response measurement under real-time player movements including: the advanced measurement systems and data analysis methods for determining surface deflection/strain under player foot strike during a ground contact, and further evaluating the force-deflection and stress-strain relationships of the synthetic carpet-shockpad composite surface systems. The results show the ability of the surface system to accommodate the player applied loads by deforming to large strains with strong non-linearity and rate-dependent energy loss (hysteresis) in the load-unload phases. The contrast between the surface systems’ response to player loading using different shockpads is also presented and discussed. By combining these findings from the development of measurement techniques and the data analysis methods a new surface system evaluation regime is proposed for future studies into mechanical behaviour and cushioning response of artificial turf systems under player loading

Mechanical characterisation and modelling of elastomeric shockpads

Third generation artificial turf systems are comprised of a range of polymeric and elastomeric materials that exhibit non-linear and strain rate dependent behaviours under the complex loads applied from players and equipment. An elastomeric shockpad is often included beneath the carpet layer to aid in the absorption of impact forces. The purpose of this study was to characterise the behaviour of two elastomeric shockpads and find a suitable material model to represent them in finite element simulations. To characterise the behaviour of the shockpads an Advanced Artificial Athlete test device was used to gather stress-strain data from different drop heights (15, 35 and 55 mm). The experimental results from both shockpads showed a hyperelastic material response with viscoelasticity. Microfoam material models were found to describe the material behaviour of the shockpads and were calibrated using the 55 mm drop height experimental data. The material model for each shockpad was verified through finite element simulations of the Advanced Artificial Athlete impact from different drop heights (35 and 15 mm). Finite element model accuracy was assessed through the comparison of a series of key variables including shock absorption, energy restitution, vertical deformation and contact time. Both shockpad models produced results with a mean error of less than 10% compared to experimental data

The player surface interaction of rugby players with 3G artificial turf during rugby specific movements

A number of high profile rugby teams in the UK have installed ATS for both training and competition. However, little is known about how the player interacts with ATS during rugby specific tasks. To date the pitches are tested using mechanical testing devices with little understanding as to how these relate to the player interaction with the surface. The aim of this pilot study was to determine the viability of using 3D motion capture system to quantify the player surface interaction and surface performance characteristics during rugby specific movements. Two tasks were selected, kicking and simulated scrummaging, for players to perform on a sample ATS within a biomechanics laboratory. Using a 3D motion capture system synchronised with a force plate the movement of the players on the ATS was analysed. This analysis showed that using a 3D motion capture system with players on an ATS was a viable method to investigate and understand the interaction between the player and the surface. Baseline data for comparison between player loading and the mechanical testing devices was also obtained

Advanced measurement of sports surface system behaviour under player loading

Artificial turf sport surface systems are comprised of a number of different materials. Improving the understanding of the sports surface system's response to actual player loading is important for developing enhanced products and system designs for improving play performance and durability. Previous research has tested and compared the mechanical properties of artificial turf systems with relatively simple mechanical tests intended to simulate loading from the player or ball. However, these test methods have known shortcomings in representing real in-service loading and it is often assumed a peak value of force or peak deformation is sufficient to describe the surface behaviour. Little literature exists that describes the force-deflection or stress- strain behaviour of artificial turf system under mechanical or player loading. This paper outlines methodologies developed for surface response measurement under real-time player movements including: the advanced measurement systems and data analysis methods for determining surface deflection/strain under player foot strike during a ground contact, and further evaluating the force-deflection and stress-strain relationships of the synthetic carpet-shockpad composite surface systems. The results show the ability of the surface system to accommodate the player applied loads by deforming to large strains with strong non-linearity and rate-dependent energy loss (hysteresis) in the load-unload phases. The contrast between the surface systems’ response to player loading using different shockpads is also presented and discussed. By combining these findings from the development of measurement techniques and the data analysis methods a new surface system evaluation regime is proposed for future studies into mechanical behaviour and cushioning response of artificial turf systems under player loading