Overconsolidation in Agricultural Soils: I. Compression and Consolidation Behavior of Remolded and Structured Soils

Abstract

The identification of meaningful physical indicators of soil quality is an important part of characterizing the present state of our soil resources. A study was undertaken with the main objective of examining the compressive behavior of remolded (saturated only) and structurally intact (variable degrees of saturation including saturated) solum horizons sampled from an agricultural region in south western Ontario, Canada. The measured compression lines for the majority of soils showed significant convergence as Cc, the slope of the virgin compression line (VCL), increased with initial void ratio (e0) and preconsolidation stress (ρc). The deegree of saturation affected Cc mostly through its influence on ρc. Strength gain with progressive desorption was most apparent in nonplastic soils with more than a minimum contnet of structure stabilizing substances (transient strengthening) and in plastic soils with higher e0 values. The widely adopted compaction paradigm derived from compression of sieved aggregates (i.e., constant Cc and VCL displacement to higher void ratios for a given stress with progressive desorption) was found to hold only for soils with relatively uniform e0 and weaker grades of structure. Samples identified as highly overconsolidated (mostly subsoils) had their measured VCL displaced below the normal compression line (NCL) at ρc, which occurred when the void ratio difference between the NCL at unit stress and e0 exceeded ≈0.36. Factors contributing to subsoil overconsolidation were believed to be mostly natural, including secondary compression and soil dessication. A pedotransfer function based on VCL reconstruction and ρc estimation is proposed for assessing the degree of overconsolidation in agricultural soils located in this part of Ontario.