Skyline tensile force monitoring of mobile tower yarders operating in the Italian Alps

This study analysed the skyline tensile forces in 502 complete work cycles during ordinary cable logging operations on 12 different cable lines in the Italian Alps. The objectives of the research were to quantify the frequency of exceeding the recommended safe working limits and to determine the skyline peak tensile forces and dynamic amplifications, as well as their explanatory variables. Data collection was based on skyline tensile force monitoring synchronized with the video recording of the logging operations and the monitoring of the carriage positions. The load volumes were measured at the landing, and the total loads were estimated for each cycle. The results showed 55% of the work cycles exceeding the safe working load. The highest peak tensile forces were often recorded while starting the load moving during lateral skid. High-peak tensile forces were also recorded during inhaul, where the tensile forces were amplified by the cyclic load behaviour. It appears that some operators underestimate the effects of pretension, payload, and cable line geometry on the magnitude of the skyline tensile force. The complexity in identifying reliable theoretical models inclusive of dynamic amplifications and the inefficacy of the load limiters installed on the machines highlighted the need to improve the best practices within the operators, and to adopt technical solutions for the continuous skyline tensile force monitoring during ordinary cable logging operations.