Effect of Grid Under Sleeper Pad on Shear Resistance at Sleeper

Effect of Grid Under Sleeper Pad on Shear Resistance at Sleeper–Ballast Interface

Mayuranga, H. G. S. / Navaratnarajah, S. K. / Bandara, C. S. / Jayasinghe, J. A. S. C.

The shear resistance at the sleeper–ballast interface of ballasted rail tracks is crucial in maintaining the stability of the track superstructure under repetitive train loading. The application of Under Sleeper Pads (USPs) in ballasted tracks by attaching them underneath the concrete sleepers is popular for the purpose of reducing ballast degradation and improving track performance. Additionally, USPs contribute to improving the shear resistance at the sleeper–ballast interface compared to traditional concrete sleepers. Nevertheless, further improving the shear resistance at the sleeper–ballast interface is imperative when the rail tracks are subjected to larger axle loads under higher frequency due to the presence of faster and heavier trains. Consequently, the novel Grid Under Sleeper Pad (GridUSP) is proposed in this study to further enhance the shear resistance at the sleeper–ballast interface. Compared to traditional USPs, the GridUSP facilitates ballast particles to interlock at the sleeper–ballast interface and thereby improves shear resistance. This paper explores the effectiveness of GridUSPs in improving shear resistance at the sleeper–ballast interface through a series of large-scale direct shear tests and a numerical investigation using the Discrete Element Method (DEM). The direct shear tests were conducted under 60 kPa normal stress, considering different sleeper–ballast interfaces such as Ballast–Ballast, Ballast–Concrete, Ballast–USP, and Ballast–GridUSP. For this purpose, USPs and two types of GridUSPs manufactured using recycled material were employed. Numerical models of each interface were developed to evaluate shear behaviour under different normal stresses. Based on the numerical results, non-linear Mohr–Coulomb failure envelopes were developed for each interface, and apparent peak friction angle values were determined. The results revealed that the GridUSP with 30 ‍mm diameter apertures and a 60 mm staggered pitch provides 34% and 158% improvements in peak shear stress at the sleeper–ballast interface compared to the conventional USP and concrete sleeper, respectively.