Behavior and assessment of mobile anchors in cable yarding systems

Abstract

Cable yarding systems transport logs hoisted off the ground by a system of cables and a carriage that moves along the cable. Ground anchors are used at the end points to maintain sufficient tension between the two ends points of the cable and keep it in the air during operation. Traditional anchoring methods employ tree stumps, but as shorter stand rotations result in younger weaker stumps and because of the inability to visually inspect root structures to calculate a stump’s anchoring capacity, alternative methods of anchoring are being used more frequently. In this paper, the capacity of an alternative anchoring method, known as equipment anchoring or mobile anchoring, is assessed for guyline and skyline applications. Some critical components that are observed to influence anchor capacity are equipment weight, slope, blade embedment, angle of cable pull, and soil type. An analytical design solution for mobile anchor capacity is compared with the results of over two dozen field tests to determine the effectiveness of predicting anchor capacity. In addition to estimating the capacity of mobile anchors, a relationship between skyline and guyline loading recorded on harvest operations is analyzed.