Effective stress testing of peat

Abstract

Recent peat soil problems, including failures of dykes, foundations and slopes in peat deposits, have focused greater attention on understanding the mechanical behavior of peat. Stability calculations routinely involve effective stress analysis, with pertinent strength and stiffness parameters often determined from standard triaxial testing, without special consideration given to internal tensile reinforcement provided by the fiber content and also the high compressibility of the peat material. This paper investigates consolidated-drained triaxial compression testing applied to peat soils. Significant differences in mini-structure and fiber content between test-specimens of undisturbed, reconstituted and blended peat materials were found not to cause significant differences in shear resistance under drained triaxial compression, with mobilized shear resistance increasing approximately linearly with increasing axial strain. Hence it was concluded that and deduced from drained triaxial compression testing of peat are unlikely to be intrinsic material properties, and rather are largely a function of strain level, with higher values of deduced for higher strain levels. End of primary consolidation should be deduced from pore-water pressure measurements rather than volume change response; although the repeatability of the triaxial consolidation tests was generally found to be poor on account of the natural variability of peat and small size of the test specimens.