Forest Investment Account (FIA) - Forest Science Program
FIA Project M085197

    Extending the logging season in Mountain Pine Beetle damaged stands by using ground wood to surface in-block roads
Project lead: Lyons, C. Kevin (University of British Columbia)
Contributing Authors: Lyons, C. Kevin; Day, Ken
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
INTRODUCTION: Warmer winters and the need to harvest Mountain Pine Beetle killed timber has resulted in the need to extend the operating season into periods when the ground is not frozen. In regions where the Mountain Pine Beetle is active, inexpensive gravel is commonly unavailable for surfacing in-block roads. Thus, temporary in-block roads are constructed of the local soil which can have a high silt and clay content, and these roads perform very poorly if hauled on during rainy periods (Arola et al. 1991). This project will assess whether mulching windrows of slash can produce an all weather road surface for in-block roads. Using mulched wood for the road surface will reduce the environmental impact since it does not produce fine sediments, the permeability of mulched wood is much higher than for most gravels and sand, and it poses less of a barrier for reforestation (Karksy 1993). Construction costs of all weather temporary roads will be reduced since it will not be necessary to haul gravel long distances for surfacing (Arola et al. 1990). In addition, the efficiency of logging operations will be increased by increasing the length of the operating season, which will reduce scheduling conflicts and the need to stockpile large amounts of timber, and by allowing a higher in-block road density without increasing the site degradation due to roads (Tice 1998). In unpaved roads the term base course refers to the material used to cap the subgrade to provide a running surface for traffic. Load spread refers to the phenomenon where a load applied to the top surface of the base course radiates laterally as well as vertically through the material, this results in the magnitude of the stress field at the bottom of the base course being less than the stress field applied to the top surface (Lyons and Fannin 2006, Lyons and Lansdowne 2006). This is an important attribute of the base course particularly when the road is built over weak subgrades such as fine grained and organic soils. Load spread is a function of the depth of the material and possibly the material type. Mulched wood has been used as the base course for unpaved roads (Tice 1998, Karksy 1993); however, the load spread ability of mulched wood has not been documented. Thus, it is important to consider the amount of mulched material that can be generated by mulching the right of way slash, and its ability to spread wheel loads over weak subgrades. Note this project has lost one of its partners with the result that detailed mechanical analysis of the mulched slash is not possible. Given the urgency of the MPB problem and the need for practical solutions this project will concentrate on conducting a field trial where the most important question is the amount of mulched material that can be generated from right of way logging. A field trial will be conducted to determine if a sufficient amount of slash can be generated by right of way logging in-block roads so that mulching this material will produce a viable road surface. The field trial will be conducted in Mountain Pine Beetle killed stands in the UBC Alex Fraser research forest, located near Williams Lake. In the field trial a road section that normally will not support large axle loads during periods with precipitation if it is not frozen will have slash from right of way logging forwarded to it. A mobile mulcher will be used to grind the slash forwarded to the road and a cat will be used to shape the road surface. The data collected from the field trial will include; the volume of mulched wood per hectare of right of way logging, depth of mulched wood in the finished road, and rut depth given the number of standard axle passes. This project will consider two main questions; 1) does windrowing right of way slash on a temporary road location and then mulching this material produce a sufficient volume of mulched material to surface the temporary road, and 2) does slash mulched with a mobile grinder produce material that is suitable for the running surface of a temporary road when considering rut formation with the number of truck passes and damage to the trucks.
FIELD TRIAL DESCRIPTION: The road used in the field trial will be located in the Gavin Lake Block of the UBC Alex Fraser Research Forest. The field trial the road will access a stand consisting of 70-80 year old Douglas-fir (Pseudotsuga menziesii) (60%) and lodgepole pine (Pinus contorta) (40%). Most of the pine has been killed in the last 4-6 years. The soil is a fine textured brunisol (silt-loam) and the topography is gently undulating. One of the objectives of this study is to determine if sufficient mulched material can be generated from right of way logging slash. The standard right of way width is 10m either side of centerline; however, this may not produce sufficient slash to surface the road and so a wide right of way of 20m either side of centerline will also be considered. The right of way will be harvested using a feller processor and the slash will be deposited on the road centerline. A mobile mulcher such as a Fecon Bull Hog Mulcher on tracks will be used to mulch the slash decked at centerline and the mulched material will be spread with a bulldozer to produce the road surface. The second objective of this study is to determine if the mulched wood improves the performance of the road during wet periods when the ground is not frozen. It will be difficult to schedule logging and hauling phases to coincide with the desired weather conditions, and even if this was possible using loaded log trucks to explore the serviceability limit of the roads is not advisable. Therefore, a gravel truck will be loaded to produce drive axle loads similar to a log truck and this will be used in the cyclic loading of the test road. Using a gravel truck dedicated to loading the test road will allow rapid application of multiple axle loads and can easily be scheduled for periods of rain. Additionally if the gravel truck becomes stuck it is less likely to be damaged when winching it out and since log hauling is not in progress operational downtime will not be experienced by the logging contractor (Arola et al. 1991). Two response variables will be collected in this study; the amount of mulched wood produced and rut depth. The amount of mulched wood produced will be measured both as the mass of mulched wood and as the volume of mulched wood in a test section, and this will be related to the area of right of way logging used to produce the slash for the mulcher. The profile of the road surface will be re-measured periodically as the axle loads are applied. Refer to the methods section for a detailed description of the sampling and analysis procedures.


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Updated August 16, 2010 

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