A laboratory method to measure deformation of baseball infield soil surfaces using cleated footwear

Abstract

Baseball and softball are played primarily on the infield skin. An ideal infield surface allows players’ cleats to penetrate the soil and provide adequate traction yet impart minimal surface disruption. This ideal state has been termed the “cleat-in/cleat-out effect.” As an infield soil dries, it transitions from the cleat-in/cleat-out state to a brittle condition in which the soil readily fractures into chips or clods. . Surface irregularities formed in the brittle condition may deflect batted balls and induce a fielding error or injury. The objective of this research was to develop a laboratory test for identifying the critical water content ${\theta }_{\mathrm{critical}}$ corresponding to the cleat-in/cleat-out behavioral threshold for any soil. A pneumatically driven apparatus was fabricated to emulate an athlete’s footstrike by applying normal, shearing, and torsional stresses using baseball cleats removed from a commercially available shoe. The test produced several cleat indentations on a cylindrical soil sample. A 3D scanning technique quantified surface disruption via Dirichlet Normal Energy. Volumetric water content was measured using a combination of 3D scanning and gravimetric methods. A given soil sample was tested at several water contents. ${\theta }_{\mathrm{critical}}$ was determined by plotting Dirichlet Normal Energy against θ and fitting a curve to solve for the local minimum. The method successfully detected differences in ${\theta }_{\mathrm{critical}}$ between infield soils containing identical clay mineralogy but differing sand content (60% and 75%; p < 0.001). Reasonable correspondence was achieved across test replicates, with a coefficient of variation of 8.5%. It is envisaged that the method will find utility in future investigations of infield mix design.