Relationships between rut depth and soil mechanical properties in a calcareous soil with unstable structure

Abstract

For proper management of soil-machinery interactions, it is essential to know the mechanical strength (i.e. pre-compaction stress, σ pc ) of agricultural soils. However, there is little information linked directly to soil sinkage in the field to σ pc . This research was conducted to explore the relationships of rut depth ( d R ) with σ pc , penetration resistance (CI) and dynamic drop-cone resistance (DCI) in a calcareous clay loam soil with unstable structure. The σ pc , CI, DCI, and d R were determined before and after single or multiple wheelings with two tractors under different soil conditions. Average ground pressure ( σ g ) applied by the tractors was also determined. The σ pc was determined using large undisturbed soil samples which were taken from the 0–15 cm layer in the wheel track. The CI, DCI and d R were measured simultaneously along the tyre centreline. When σ pc values before each wheeling were compared with d R values after wheeling, it was found that σ pc was approximately a threshold value between reversible and irreversible deformations. The results indicated that when the σ pc / σ g is well above 1 (e.g. 1.6), soil sinkage is essentially negligible. However, for the ratios d R and CI or DCI. As soil trafficability criteria, soil properties such as CI and DCI, which are easily and quickly measurable, might be used for practical purposes.