High-Temporal-Resolution Measurement of Subsurface Pressure Response and Vertical Soil Displacement during Field Traffic

Agricultural soils are often subject to compaction by plastic soil deformation leading to alterations of their functionality. Soil pressure transformation and soil displacement under typical dynamic wheeling loads in real farm settings is rarely analysed. This study aims to present an innovative method for synchronically measuring soil pressure and vertical soil displacement in high temporal resolution with a multi-channel measuring system. The displacement measurement probes are composed of a hydrostatic tube-in-tube system with difference pressure sensors. The displacement at the lower end of the hydrostatic water column is indicative of the vertical displacement of the soil. Twenty wheeling campaigns with multi-axle vehicles were conducted under real farm conditions using typical agricultural machinery on a silt loam soil. Bolling-probe pressure and soil displacement were measured at 20, 35 and 50 cm depths underneath the soil surface. The method offers detailed insights into the pressure–displacement response of individual wheels. On average the first wheel of a vehicle leads to the greatest displacement, while the subsequent wheels have further but significantly less influence. The averaged displacement for the second wheel was 34% of the first-wheel displacement, while the third and fourth wheel passes resulted in displacements of 20–26% relative to the first-wheel displacement. The new measuring system yielded detailed, largely reliable data for pressure-displacement relationships for multi-axle vehicles, with a high temporal and spatial resolution. The method offers new insights into the dynamic soil load-displacement relations.