Abstract
This research outlined the field survey on failures of the grout pad connections of the track-on-concrete railway system, along with Finite Element Analysis to understand the stress distribution in the connection and link the site investigation to theoretical findings. The field survey involved visiting eleven sites across South Africa that used the track-on-concrete system. The purpose of the site visits was to identify and document the application, configuration, failures, and systems maintenance to assess their weakness, focusing on the connection. All sites visited showed that the concrete and rails were in good condition. Only the connections were failing. The five sites with direct fixation fastener connections confirmed that the grout pad fails first before the other components. The presence or absence of elastic pads in the connection contributes to grout failure and other factors. A comparison was made with regard to requirements of American Railway Engineering and Maintenance-of-way (AREMA).
For grout pad strength in the connection, majority of this pads had a strength greater than 40 MPa compared to 28 MPa, but in most cases, this grout pads still failed. Properties that can affect the durability of the grout pad are dimensional (thickness), strength, stiffness, and age relative to the loading. These factors were confirmed with a further desktop study using Finite Element Analysis in conjunction with literature and industry standards, and the findings showed that the presence of grout in the connection was used to reduce compressive stresses in the concrete, acting as a transition layer. Therefore, a thicker grout of 40 to 60mm is recommended. When rails are inclined vertically at 1:20, stresses are evenly distributed on both sides of the connection, compared to when the rails have zero inclination to vertical, resulting in eccentric loading leading to the outer bolt and surrounding Concrete and grout experiencing higher stress levels on one side. Grout failures are not due to static loads, but an impact load with a dynamic factor of 4 can cause sudden deterioration and a minimum dynamic factor of 2 results in fatigue failure over time. Quality measures are required to maintain standards of grout construction.
Keywords: ballasted track system, grout, rail, rail pad.