OVERCONSOLIDATION IN AGRICULTURAL SOILS .1. COMPRESSION AND CONSOLIDATION BEHAVIOR OF REMOLDED AND STRUCTURED SOILS

The identification of meaningful physical indicators of soil quality i s an important part of characterizing the present state of our soil re sources, A study was undertaken with the main objective of examining t he compressive behavior of remolded (saturated only) and structurally intact (variable degrees of saturation including saturated) solum hori zons sampled from an agricultural region in southwestern Ontario, Cana da. The measured compression lines for the majority of soils showed si gnificant convergence as C-c, the slope of the virgin compression line (VCL), increased with initial void ratio (e(0)) and preconsolidation stress (sigma(c)), The degree of saturation affected C-c mostly throug h its influence on sigma(c). Strength gain with progressive desorption was most apparent in nonplastic soils with more than a minimum conten t of structure stabilizing substances (transient strengthening) and in plastic soils with higher e(0) values. The widely adopted compaction paradigm derived from compression of sieved aggregates (i,e., constant C-c and VCL displacement to higher void ratios for a given stress wit h progressive desorption) was found to hold only for soils with relati vely uniform eo and weaker grades of structure. Samples identified as highly overconsolidated (mostly subsoils) had their measured VCL displ aced below the normal compression line (NCL) at sigma(c), which occurr ed when the void ratio difference between the NCL at unit stress and e (0) exceeded approximate to 0.36, Factors contributing to subsoil over consolidation were believed to be mostly natural, including secondary compression and soil dessication. A pedotransfer function based on VCL reconstruction and sigma(c) estimation is proposed for assessing the degree of overconsolidation in agricultural soils located in this part of Ontario.