Can the EM38 Probe Detect Spatial Patterns of Subsoil Compaction?

Abstract

So far, an easy way of locating regions of subsoil compaction on the field scale has not been achieved using common soil physical methods. Our potential solution to this problem is to approximate the mechanical strength of the soil using K 0 (a stress-at-rest coefficient) and relate it to the apparent electrical conductivity (ECa). Firstly, we prove the validity of the underlying assumption that the horizontal stress component characterises the compaction state of the soil. This consists of assigning penetration resistance (PR) values to the principal stress (σ x) as a function of depth, normalised by a relation involving the PR value at the greatest accessible depth (0.8 m). Secondly, we evaluate how well non-destructive ECa measurements (made with an electromagnetic induction meter) localise compacted areas. Results from two experimental sites located in the loess belt of northern Germany showed a strong correlation between penetration resistance and an electromagnetic induction meter, especially in areas with high PR values. We conclude that the geophysically based electromagnetic induction technique can be used to map spatial patterns of subsoil compaction in loess-derived soils.