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Using Remotely Operated Jacks to Fall Dangerous Trees*
RS2007-DG03
Final Report Date: October 2008
| Principal Investigator: | Kevin Lyons (UBC) |
For more information about this project, please contact Dr. Kevin Lyons.
*In partnership with the Workers’ Compensation Board of Nova Scotia
Issue
Manual tree falling, which is required when mechanical harvesting is not possible, is extremely dangerous. A key hazard is the risk of being struck by falling trees and flying debris while the tree is being displaced from the stump. If remote-operated, lightweight hydraulic jacks could be used to fall trees that would normally require hand falling, the hazards posed by falling trees and debris would be reduced. This project conducted a preliminary analysis of the feasibility of using remote jacks for this purpose.
Key findings
- A holding wood design procedure (which determines how much wood to leave between the initial cuts at the base of the tree before setting the jack) was tested using a mathematical model. The holding wood must be strong enough to keep the tree stationary until the faller exits the area, but be weak enough to allow the remote jack to fall the tree.
- Results showed that small remotely operated hydraulic jacks are a possible method of tree falling. However, for some trees, a relatively small initial lean of the tree could compromise the ability of the holding wood to keep the tree stationary while the jack is being set.
- Field testing is planned to determine if a more effective holding wood design procedure for use with remote jacks can be developed.
Objectives
- To determine if it is possible to use light weight remotely operated jacks to hand fall dangerous trees, to reduce the risk of injury to hand fallers
- To determine if a proposed new holding wood design procedure would be strong enough to allow trees to remain stationary while the jack is being set, but be weak enough to allow a lightweight jack to initiate falling after the faller has exited the area
Methods
A mathematical modeling procedure called the finite element method was used to analyze whether the holding wood procedure would be strong enough to keep the tree stable while setting the jack, but weak enough for the jack to remotely initiate displacement of the top of the tree from the stump. The model included a design stress value of 33 Mega Pascals (MPa) to predict the point at which a tree will commit to falling under its own weight. This value is suggested by existing data and was further confirmed by analyzing the maximum compression in the holding wood for a small number of test trees.
Analyses were conducted for different combinations of tree heights and diameters, and for straight trees as well as trees with an initial lean (with the assumption that the tree would be felled in the direction of the lean).
Results
- When designing the holding wood so that it is weak enough to permit a lightweight jack to initiate falling of the tree, this project found the acceptable width of the holding wood depended on the diameter of the tree at the stump height; however, the acceptable width of the holding wood did not depend on the total height of the tree.
- When designing the holding wood so that it is strong enough to ensure the tree does not begin to fall while the initial cuts are being made, this project found the acceptable width of the holding wood depended on the total height of the tree; however, the acceptable width of the holding wood did not depend on the diameter at the stump height.
- For some combinations of diameter at breast height and total tree height, a relatively small initial lean could compromise the ability of the holding wood to keep the tree stable while the jack is being set.
Conclusions
The results indicate that small remotely operated hydraulic jacks are a possible method of initiating tree falling. However, field testing is required to understand how the complicated mechanics of the holding wood will affect the reliability of this method.
Future directions
Field testing is planned to determine how much holding wood is needed to resist naturally occurring destabilizing forces before the jack is engaged, yet still make the tree weak enough for a small jack to initiate displacement of the tree stem from the stump. The field testing is being funded by a WorkSafeBC research grant.
Publications and Presentations
C. Kevin Lyons. 2009. Remote-operated jacks: A safer way to fall trees manually. Link, 10(4), 18-19.