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Recently, forest operations are facing unfavorable climatic conditions more frequently. In Central Europe, machine trafficability and induced soil disturbances are negatively affected by periods of high precipitation and less intensive frost during ground-based harvesting operations. Winch-assist technology is assumed to reduce soil disturbance by forest machines in steep terrain. Still, the potential positive effects of winches to assist traction of forest machines in flat terrain have rarely been surveyed. In this study, a field trial was conducted in flat terrain (slope < 5%). There, a forwarder with an integrated traction-assist was monitored during six consecutive machine passes on a permanent machine operating trail. The first section of the machine operating trail was passed without traction-assist, the remaining section with traction-assist, resulting in two treatment groups. To assess soil impacts, three test plots were positioned per treatment group. Within these plots, pre- and post-operational soil bulk density, soil displacement and rutting were determined. Additionally, wheel slippage and cable tensile force were examined, using incremental rotary encoders and a flexible tensile force measurement kit, respectively. It was observed, that wheel slippage responded inversely with tensile force. Traction-assist technology reduced wheel slippage from 5.3 ± 11.9% to 0.37 ± 10.19% along the section of the machine operating trail, as compared to results from the unassisted section. Although wheel slippage was significantly reduced, no mitigating effect by the usage of traction-assist technology on soil disturbance could be observed, probably due to the low volumetric water content of 27%. [ABSTRACT FROM AUTHOR]

Ground based forest harvesting machines are being used on steeper slopes with the aid of tethers to help maintain traction and stability. It is common to position a base machine containing the tether winch above the forest harvesting machine. This configuration is termed a live tether. The live tethers may be run around rub trees to reduce the time required to reposition the tether. This study developed a new model that includes both friction and cutting forces to estimate cable tension on either side of the rub tree. A dataset collected in the field was used to estimate the parameters in the model. The model appears to be promising; however, further work is required on the interaction of the cable cutting surfaces and the surface toughness of the wood. In general, it was found that the difference in the tension on either side of the rub tree increased with increasing change in angle, that the cable on average cut 3 mm deeper with each 10 m of the cable travel, and that the difference in tension was not correlated with the depth cut into the wood. • This study develops a new model that includes friction and cutting forces to estimate cable tension around a rub tree. • Data was collected and used to estimate the friction coefficient and cutting deformation coefficient in the new model. • The change in tension is independent of the depth the cable cut into the tree. • Interaction between the surface toughness of the wood and the frictional surfaces of the cable requires further study. [ABSTRACT FROM AUTHOR]

In conventional cable-supported forest operations, trees and their stumps are normally employed as anchoring elements to withstand high lateral forces. These loads, even if applied near the stem base where cross-section is larger, are characterised by higher magnitude and dynamic amplification effects. Consequently, failures of anchors due to overturning or stem breakage are possible. To evaluate the load-carrying capacity of anchors processes similar to the techniques used for tree stability assessment were used for tree pulling tests, performed up to failure, on sound Norway spruce with medium-large diameter at breast height grown on mineral soil. To this aim, high-strength pulling equipment was designed and exploited to reproduce the loading conditions for trees used as anchors, while monitoring their movement using low-cost precision sensors. The obtained mechanical response of the tested trees was compared with the predictive statistical and analytical models available in the literature. The main results confirmed the difficulty of giving a direct, sufficiently accurate and non-site-specific prediction on their load carrying capacity. Therefore, a method of normalisation of some of the easily measurable parameters that can be obtained through a non-destructive pulling test was used. A procedure, aimed at providing a more accurate assessment of the stability of anchors to help to reduce the number of accidents in cable-supported harvesting operations, is proposed and discussed. • Development of a method to assess safety of trees as anchors in forest operations. • Low-cost sensors are used to monitor root-plate rotation during tree pulling tests. • Rotation at peak load appears to be less site-specific than peak resisting force. • Normalization of moment vs. displacement curve is fundamental. • The proposed method can be potentially applied in cable-supported forest operations. [ABSTRACT FROM AUTHOR]

The objective of this case study was to develop and test a specific survey protocol for monitoring tensile forces for winch-assisted harvesters and forwarders with a mounted or integrated constant-pull capstan winch technology. Based on the designed survey protocol, the interactions between work phases, machine inclination, and tensile forces in typical work conditions were analysed. The established workflow, including equipment and the developed analysis routines, worked appropriately and smoothly. The working load on the cable during the study did not exceed 50% of the maximum breaking strength. A maximum tensile force peak at 56 kN was observed during delays for the forwarder, and a peak of 75.5 kN was observed for the harvester, both of which are still within the safe working load when considering a safety factor of two. [ABSTRACT FROM AUTHOR]

Cable tensile forces in winch-assist harvesting have been investigated in order to assess the safety concerns of the technology. However, the literature is lacking, particularly in regards to the impact of winch design. In this study, a Summit Winch Assist tethering a feller-director on ground slopes up to 77% was monitored for four days. The cable tensile forces were simultaneously recorded at the harvesting and anchor machine at a frequency of 100 Hz. Cameras and GNSS devices enabled a time study of the operations and the recording of machine positions. Winch functionality and design were disclosed by the manufacturer and used for the interpretation of the results. The cable tensile forces reached 296 kN at the harvesting machine and 260 kN at the anchor machine. The slow negotiation of obstacles while moving downhill recorded the highest peaks, mainly due to threshold settings of the winch in the brake system activation. Lower but significant peaks were also recorded during stationary work tasks. The peaks, however, were limited to a few events and never exceeded the endurance limit of the cable. Overall, the study confirmed recent findings in cable tensile force analysis of active winch-assist operations and provided evidence of the underlaying mechanisms that contribute to cable tensile forces. [ABSTRACT FROM AUTHOR]