Geostatic stress in oil-sand tailings

Abstract

Horizontal geostatic stress estimated from self-bored pressuremeter (SBP) data using the ‘lift off’ method is uncertain because of even small deficiencies in self-boring, but that uncertainty can be minimised by modelling the complete test. Iterative forward modelling based on large-strain cavity expansion in frictional dilating (non-associated Mohr–Coulomb) soil, with correction for finite SBP geometry, is both easily implemented in a spreadsheet and computes quickly. Such modelling of a campaign of SBP tests in oil-sand tailings shows a baseline geostatic stress ratio K0 = 0.6 for those tailings that are truly normally consolidated. Other geological history factors, including compaction by tracking and wetting–drying cycles, adds about a Δσh ≈ 60 kPa ‘locked-in’ stress to this normally consolidated trend; an alternative view is that these factors produce K0 ≈ 1. The modelling spreadsheet is provided as a downloadable Excel application in the online supplementary material.