Huber Christoph, MSc.

Forest road networks are exposed to damage by traffic, climate, timber harvesting and vegetation. To maintain their functionality, they must be maintained regularly. Periodical maintenance is required when the forest road surface layer is deteriorated and eroded. Well-graded material is required for replacing the forest road surface and often has to be sourced from gravel storage areas, which is costly and requires a large number of truck trips. Therefore, converting non-graded aggregate available on site into well-graded aggregate with a mobile stone crusher is considered a viable alternative.

The present study was carried out during a periodical maintenance treatment at the Bavarian State Forest Enterprise and the effect of employing a mobile stone crusher was evaluated with regard to (1) forest road load bearing capacity development during a one-year period post-treatment, (2) particle size distribution of the surface layer material before and after crushing, and (3) its cost compared to other alternatives. Samples were collected pre- and post-operation for particle size distribution analysis, load bearing capacity was measured repeatedly with a light falling weight deflectometer and compared to an untreated reference section and cost of the treatment was compared to two alternatives.

The mobile stone crusher was capable of reducing the non-graded to well-graded/close-to-well-graded material and particle size distributions aligned well with the recommendations for lime-water bonded surfaces. Load bearing capacity exceeded the threshold of 40 MN m-2 (Evd, elastic modulus dynamic) for primary forest roads at all times. It increased significantly after the treatment and remained on a significantly higher level throughout the following year. Absolute and relative increases were higher than on the untreated reference section. The treatment variant involving a mobile stone crusher and material available on site was substantially cheaper (5.31 € m-1) than to supply non-graded (16.29 € m-1) or well-graded (19.82 € m-1) material by truck. Material and transport costs represented 67% and 82% of the total costs in the latter two cases. It can be concluded that mobile stone crushers are capable of producing at least close-to-well-graded forest road surface aggregate and that forest road load bearing capacity can be significantly and lastingly increased at only a part of the costs of the alternatives. A maximum of cost and resource efficiency and environmental soundness can be attained when enough surface aggregate is available on site. If this is not the case, sourcing non-graded material as local as possible is the next best alternative.

Rope end connectors are a cricital component for attaching logs and trees to winches in ground-based harvesting operations. Knowing their strength not only in theory, but also under real working conditions, is crucial for selecting and dimensioning suitable end connectors in order to ensure compliance with the respective safety factors. Currently, there are limited published testing data on the strength and failure types of various end connectors. Furthermore, no information is available how end connectors perform if they are used in combination with rope sliders. Thus, different end connectors suitable for 12 mm steel wire ropes were developed and break-tested under conditions close to reality to determine their suitability for logging operations, considering different load type combinations by including rope sliders. The aim of the study was to give an overview of the suitablity of end connectors and different rope slider – end connector combinations for ground-based harvesting operations and to become aware of where and at which forces failures occure first. The results show that if the load is only attached directly to the end connector, turn-back eyes and wedge sockets provided consistent performance in breaking strengths. Attaching loads only to rope sliders led to siginifcant reductions of the end connectors performance in general. A comparatively high loss of performance was assessed if turn-back eyes were used in combination with rope sliders. This raises the question of their suitability as an appropriate end connector in ground-based logging. The most common cause of failure was found to be rope breakage, which mainly occurs due to the strong deflection angles of the rope during pulling.