Ballast direct shear testing

This paper summarizes the appropriate equipment and test procedure for ballast shear strength testing using the direct shear method (ASTM D3080 and D5321) and presents some typical results. To accomplish this ballast testing, a full-scale direct shear box was developed that can accommodate an approximately 1 m (3 feet) wide and 0.6 m (2 feet) deep specimen, which is much larger than current shear boxes used for ballast testing. This larger specimen size resulted in significant differences in measured shear behavior and shear strength parameters. The shear strength properties of the ballast under typical as-placed conditions are determined herein using the new shear box and normal stresses applied through dead weight loading that are representative of railroad track conditions. Effects of direct shear specimen size and confining normal stress are demonstrated using a typical angular granite ballast and the results are compared to published ballast shear strength data.