Improving Understanding of Low Adhesion Transience in the Rail-Wheel Contact through Experiment and Modelling

Low adhesion caused by leaves creates safety and reliability issues across the UK. However, the reasons for the transience in adhesion levels are not well understood. This project aimed to improve the understanding through field and laboratory testing as well as using industrial data sets.
A literature review assessed the current knowledge base in leaf low adhesion and highlighted the gaps in knowledge around the transience of low adhesion. These gaps included: the effect of axle passes on layer characteristics; the role of moisture in leaf low adhesion; and the limited data on leaf layers in changing environmental conditions.
A novel method for creating low adhesion leaf layers was created for a linear full scale rig. Layer characteristics and adhesion levels at a one wheel pass resolution were tracked. Leaf layer formation was also observed in the field. The chemistry of the layers was assessed using in situ FTIR. Heritage railways were also used to created and track layers. Collating all of this data allowed for relationships between the number of wheel passes and layer characteristics to be qualified.
Climate chamber testing highlighted the role of moisture in creating dangerous adhesion conditions. Testing showed that raised moisture greatly increases the chances of low adhesion in leaf layers regardless of environmental conditions. Testing in the field demonstrated a linear relationship between humidity and layer moisture. Field testing in a cutting revealed that in certain locations weather moisture and traction relationships are more complex.
A risk prediction model for low adhesion was adapted from remote use and used to assess a line with leaf fall issues, both spatially and temporally. The model was able to reflect environmental changes around the line and compared against low adhesion observations. The impact of vegetation management and remediation actions on the line were also assessed.