Abstract
Large-scale direct shear tests were conducted to assess the performance of geogrid-reinforced ballast-subballast interface followed by triaxial tests to explore the deformation and degradation response of geogrid-reinforced ballast under cyclic loading. While the direct shear testing was performed at applied normal stresses (n) ranging from 20 to 100 kPa and rate of shearing (Sr) from 2.5 to 10.0 mm/min, the cyclic triaxial tests were performed to capture the role of loading frequency (f) ranging from 10 to 40 Hz. Fresh granite ballast and subballast with mean particle size (D50) of 42 and 3.5 mm, and five geogrids having different aperture shapes and sizes (A) were used in this study. The tests results indicated that the behavior of ballast-subballast interface is highly influenced by n and Sr. The friction (φ) and dilation angles (ψ) of unreinforced and geogrid-reinforced ballast-subballast interface is found to reduce from 67.96° to 47.82° and 14.56° to 3.34° with the increase in n and Sr. Marsal’s Breakage (Bg: an index to quantify the breakage of ballast) of unreinforced ballast was found to increase from 2.84 to 6.69 % with the increase in n and Sr. However, the inclusion of geogrids significantly enhanced the friction angle (φ), reduced the extent of dilation angle (ψ), and minimized Bg. The interface efficiency factor () and Bg were found to be a function of A/D50 ratio. Accordingly, a model is developed using multiple linear regression analysis to predict the values of φ, ψ and Bg in terms of the input parameters n, Sr and A/D50 ratio. The results from triaxial tests indicate the deformation and degradation behavior of ballast under cyclic loading conditions to be influenced by the loading frequency (f). The extent of ld and Sv of unreinforced ballast increases from 5.48 to 28.32 mm and 20.13 to 45.40 mm with the increase in f. The value of Bg increased from 4.3 to 11.69 % when the value of f was increased from 10 to 40 Hz. Similarly, the extent of lateral and vertical deformation of ballast was found to be a function of A/D50 ratio.
Highlights
Railways are one of the most economical modes of transportation for moving freight as well as passengers from one place to another
It is seen that the φ of unreinforced ballast-sub-ballast interface reduces from 61.82 to 48.95◦ as σn increases from 20 to 100 kPa
The current study investigated the shear behavior of geogridreinforced ballast-sub-ballast interface and the deformation and degradation behavior of geogrid-reinforced ballast under cyclic loading conditions
Summary
Railways are one of the most economical modes of transportation for moving freight as well as passengers from one place to another. A rail track under operating conditions may be subjected to different shearing rates depending upon the magnitude of cyclic stress and the train speed In this context, a series of large-scale direct shear tests were carried out to study the influence of σn and Sr on ballast-geogridsub-ballast interface followed by large-scale cubical triaxial tests to determine the effect of loading frequency (f ) on ballast with and without geogrids. A cyclic vertical stress of 300 kPa was applied onto the test specimen with the help of vertical dynamic actuator, and a confining pressure of 10 kPa was applied onto the two side walls having five movable plates It is well-known that the tendency of unbound ballast is to move laterally in outward direction (parallel to sleeper) under track operating conditions.
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