The principle of effective stress and triaxial compression testing of peat

Peat deposits comprise the fragmented remains of dead plant vegetation that have accumulated under waterlogged conditions. Effective stress theories developed for mineral soils are routinely applied in practice for peat, although there are fundamental issues regarding the application of conventional soil mechanics to peat, on account of its extremely high water content, fibrous nature, low shear strength and high compressibility, and also the flexible, permeable and compressible nature of the porous organic solids. This paper presents an experimental study intended to contribute to the ongoing and increasing debate about the degree to which conventional soil mechanics approaches can be applied to peat. A programme of isotropic consolidated-drained triaxial compression tests was performed on saturated fibrous peat under the same effective confining pressure, but developed by applying different cell- and back-pressure combinations. Effects of mini-structure and fibre content on mechanical response were considered by testing undisturbed, reconstituted and refined (blended) peat materials. Similar volumetric strain–time and stress–strain–time responses experienced by identically prepared triaxial specimens were persuasive regarding the applicability of the principle of effective stress to peat, although there is no firm conclusion, since significant challenges occurred in performing these tests and in interpreting the data.