Quantifying compaction under rollers using marker tracing image analysis

A new laboratory-scale simulator was developed to investigate the compaction of a clay loam soil during repeated passes of a 600 mm diameter × 500 mm wide smooth steel wheeled roller in alternate directions with a mass increasing sequentially from 260 to 1250 kg m−1. Soil displacement in the vertical plane parallel to rolling was quantified using automated image analysis of videos of a 5 × 5 array of 5 mm diameter markers inserted at depths between 15 and 135 mm in the soil. Mean applied stress increased with roller mass but decreased as soil water content increased due to reduced soil bearing capacity which increased roller-soil contact area. Mean profile soil dry bulk density increased as roller mass increased and as soil water content increased. Analysis of marker displacement determined that soil displacement and therefore density change decreased with depth. Analysing the movement of markers in a vertical cross-section throughout a complete pass of the roller, allowed investigation of the vertical recovery of the soil after loading, and the complex fore-and-aft displacement of the marker as the roller passes. An un-replicated investigation of the same clay loam soil with an established perennial ryegrass sward indicated that plant roots reinforce soil and reduce horizontal soil displacement. Optimum water content for rolling in this clay loam soil is above the Proctor optimum water content for compaction due to the additional effect of horizontal soil displacement. The methodology and results not only have implications for the compaction of soils in this specific amenity context of cricket, but also in wider applications to the compaction of soils in agricultural systems.