Validation of a laboratory method for evaluating dynamic properties of reconstructed equine racetrack surfaces.

BackgroundRacetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior.ObjectiveTo develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties.MethodsTrack-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression.ResultsMost dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces.ConclusionsLaboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD).Potential relevanceDynamic impact properties of race surfaces can be evaluated in a laboratory setting, allowing for further study of factors affecting surface behavior under controlled conditions

Correction: Validation of a Laboratory Method for Evaluating Dynamic Properties of Reconstructed Equine Racetrack Surfaces.

[This corrects the article DOI: 10.1371/journal.pone.0050534.]

Correction: Validation of a Laboratory Method for Evaluating Dynamic Properties of Reconstructed Equine Racetrack Surfaces.

[This corrects the article DOI: 10.1371/journal.pone.0050534.]

Validation of a laboratory method for evaluating dynamic properties of reconstructed equine racetrack surfaces.

BackgroundRacetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior.ObjectiveTo develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties.MethodsTrack-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression.ResultsMost dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces.ConclusionsLaboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD).Potential relevanceDynamic impact properties of race surfaces can be evaluated in a laboratory setting, allowing for further study of factors affecting surface behavior under controlled conditions

Racetrack and laboratory surface material moisture contents (%, percent) and temperatures (°, degree) [mean (standard deviation)] at 4 depths (cm, centimeter) measured from the top of the surface material.

<p>Laboratory surface temperature was approximately 21.5°C.</p

TTD shown on portable frame (left) and laboratory frame (right).

<p>The portable frame was leveled and fixed to the ground using 3 adjustable legs. The Z-axis (center) is parallel to the linear shafts (positive up), the X-axis is forward-backward (positive into page), and the Y-axis is lateral (positive left).</p

Racetrack and laboratory cohesion (c, N/m², newton per square meter), angle of internal friction (φ, °, degree), and R² from the linear fit of shear vane data, and shear failure stress at a normal stress of 400 kN/m² (τ₄₀₀, kN/m², kilonewton per square meter) calculated using the Mohr-Coulomb equation.

<p>Racetrack and laboratory cohesion (c, N/m², newton per square meter), angle of internal friction (φ, °, degree), and R² from the linear fit of shear vane data, and shear failure stress at a normal stress of 400 kN/m² (τ₄₀₀, kN/m², kilonewton per square meter) calculated using the Mohr-Coulomb equation.</p

Adjusted least squares means of the laboratory-racetrack difference in TTD dynamic surface properties for each main effect surface, impact velocity [m/s, meter per second], impact angle [°, degree]) averaged over all other factors, and reported as a percentage of the overall racetrack average for that variable.

<p>For each main effect, a P<0.05 means the magnitude of the laboratory-racetrack difference changed significantly when the level of that main effect changed.</p

Custom compaction device.

<p>Conical spikes (92) were 1.9 cm wide, 2.5 cm high, and spaced 3.5 cm apart.</p

Laboratory TTD dynamic surface properties [adjusted least squares means (standard error)] for each main effect (surface, impact velocity [m/s, meter per second], impact angle [°, degree]) averaged over all other factors.

<p>Dynamic surface properties within a variable row and within each main effect with different superscripts are significantly (P<0.05) different. Main effects were significant unless values are underlined.</p