A modular terrain model for daily variations in machine-specific forest soil trafficability

Abstract

A modular approach is presented to assess terrain-specific soil trafficability in terms of soil resistance to penetration and machine-specific rut depths. These modules address: (1) soil resistance to cone penetration (cone index, or CI) as affected by soil moisture, texture and pore space (Module 1), (2) machine-induced rut depths (single-pass and multi-cycles) as affected by wheel loads, tire specifications and CI (accounting for depth of compactable soil, Module 2), (3) temporal variations in hydrothermal conditions, CI, and potential rut depths due to daily soil moisture and temperature variations (Module 3), and (4) spatial variations in CI and rut depth across terrain due to corresponding changes in soil moisture, depth of compactable soil, bulk density, texture, frost depth, organic matter and coarse fragments (Module 4). The approach is applied to off-road wood-forwarding operations. Modules 1 and 2 were calibrated to apply to a wide range of soil conditions. Modules 3 and 4 were initialized for a wood-forwarding case study at CFB Gagetown, New Brunswick, Canada. Model results should be most applicable for flat to near-flat terrain, with insignificant wheel obstructions, and no organic matter accumulations on top of the mineral soil. Key words: Forest harvesting, soil penetration resistance, cone index, soil rut depth, soil disturbance, soil trafficability, soil compaction, terrain modelling