Evaluating the influence of ballast degradation on its shear behaviour

The main goal of this research is to investigate the effect of ballast degradation on its shear strength behaviour. For this purpose, some crushing tests were carried out at different compressive loads to simulate ballast degradation. Large direct shear box tests were conducted on degraded ballast samples at various breakage ratios to investigate their shear strength properties. According to the crushing test results, higher compressive load leads to more degradation and more axial strain, as expected. However, the rate of growth of degradation as well as axial strain decreases with load. In addition, comparison of shear behaviour of fresh ballast and degraded ballast indicates that by increasing the degradation, i.e. the breakage ratio up to 21%, the shear strength is decreased up to 48%. Furthermore, stress–strain responses of specimens indicate that the dilation angle of degraded ballast samples decrease both with an increase in breakage ratio and with increase in normal stress.