Assessing physical quality of plastic soils of differing mineralogy and pre-stress history using mechanical parameters. I. Saturated compression tests

Abstract

The comparison of selected soil mechanical parameters measured on plastic soils under remoulded and structurally intact conditions may provide an opportunity to assess soil structural quality on a regional or even broader scale. This study was conducted to determine: (i) if existing pedotransfer functions developed for southwestern Ontario soils could be used outside this physiographic region, and (ii) if key mechanical parameters were sensitive to a range of land use conditions that are likely to influence soil structural quality. Soil profiles were sampled in natural (forested or grassland), agricultural and pipeline workspace areas (land use variable) located in southwestern Ontario, eastern Ontario, Alberta and Texas (mineralogy variable). Slurry consolidation and uniaxial compression tests were conducted on remoulded and structurally intact samples, the resulting void ratio-log stress [e(logσ')]data were fitted to linear or nonlinear model equations, respectively, and several key mechanical parameters were derived. The effective stresses at the liquid and plastic limits could not be adequately estimated for soils with smectitic mineralogy using existing pedotransfer functions because of the absence of a significant relationship with organic carbon content. The difference between void ratio intercepts for remoulded and structurally intact soils (e*1kPa–e0) was found to be a suitable indicator of physical soil quality because of the convergence of remoulded and structured compression lines in e(logσ') co-ordinates. Severely overconsolidated soils were identified when the (e*1kPa–e0) variable exceeded 0.40. This threshold also corresponded to soil conditions that could limit plant growth. Key words: Compression, consolidation, pedotransfer function, soil quality, Atterberg limits, remoulded, structured, pipeline, woodland