Debakanta Mishra

The challenge of maintaining ride quality and serviceability in flexible pavements built over expansive soil deposits remains a critical concern for transportation agencies. These expansive subgrades exhibit swell-shrink behavior in response to moisture fluctuations, leading to differential heaving and subsequent costly maintenance. This paper explores the effectiveness of a Hybrid Geosynthetic Reinforcement System (HGRS)—a composite of geocell and geogrid—as a targeted mitigation strategy for differential heaving induced by expansive soils. A large-scale box test was designed to simulate a flexible pavement section, consisting solely of a base course layer and the underlying expansive subgrade. Four test conditions were investigated: an unreinforced control, a geocell-reinforced section, a geogrid-reinforced section, and an HGRS-reinforced section. Vertical displacements on the surface of the base course layer were longitudinally monitored and compared against the control. The results reveal that the use of geosynthetic reinforcements, and HGRS in particular, significantly mitigates both maximum surficial heave and differential swelling. Among the systems tested, flexible pavements featuring HGRS demonstrated the most effective performance in alleviating the challenges posed by expansive soil deposits.

This manuscript presents findings from an ongoing research study at Oklahoma State University studying different factors that affect vertical tie reaction forces in ballasted railroad tracks. A combined approach involving field instrumentation and numerical modeling has been adopted for this purpose. Measurements of tie reactions can indicate the load distribution patterns and quality of vertical support along a track. Locations where tie support conditions are not adequate can develop geometry defects, ultimately leading to component failure. Three different approaches are adopted in this study to measure the forces being transmitted through the rail-tie interface; this is equal to the tie reaction force. The field instrumentation effort validates an alternative method to measure forces at the rail-tie interface using rail-mounted strain gauges. Results from this approach are compared to two other conventional methods of force measurement, i.e. through the use of load cells (LC), and an instrumented tie plate (ITP). A validated 3-dimensional Finite Element (FE) model is used to support the field-observed trends, and explain any observed discrepancy. Parametric analyses using the FE model identify different factors that can contribute to the rail-tie interaction force, thus affecting the instrumentation results. The strain gauge-based approach, using the concept of differential shear strain measurement, has been established as a suitable method for tie reaction force measurement. Exact measurement of the tie reaction force can be ensured through proper installation of the strain gauges, away from possible boundary effects.