Design parameter analysis of the bogie track surface pressure in peatland forest operations

Abstract

This thesis studies the effect of different design parameters on surface pressure under a wheeled forestry machine equipped with bogie tracks. The chosen design parameters were bogie dimensions, especially the distance between wheel hubs, an additional auxiliary wheel between the bogie wheels, bogie balancing and peat soil moisture content. The thesis introduces several variables to be considered if constructing a realistic simulation model for peatland forestry operations. A wide introduction to soft terrain logging gives the base to further studies. Rut formation is based on complex terramechanical theories and the machine dynamics. The mechanisms of rut formation and the effect of heavy machinery on forest soil were also included. Widely used equations for surface pressure don’t take the effect of soil type nor compaction into account. Most of the equation are constructed for silt or clay soil, and it seems, that they are not necessarily applicable for peat soil. The resulting surface pressure values are not fully comparable, and they should only be used as a reference, when comparing different forest machines to each other. The lowest value is about 9 times smaller than the largest one. Most of the surface pressure values exceed the widely used limit of 50 kPa for peatland operations. The resulting exact values for surface pressure should thus be used carefully. Forming a valid surface pressure equation for peat soil has proven to be extremely challenging. Field testing seems to be an adequate way to study the machine properties before suitable simulation models are available.