Compressibility and Shear Characteristics of Radforth Peats

Radforth peat is a term introduced here to describe peats with a negligible content of mineral matter. The Sphagnum peat discussed in this paper consists mostly of fibrous particles such as stems, leaves, fiber hairs, etc.

Outstanding characteristics of Radforth peats are their extremely high compressibility and high rate of creep. The variability of peat is often almost unpredictable, even within an apparently uniform deposit. Predictions of magnitude and rate of settlement are therefore difficult. Frequent disturbed sampling and classification combined with empirical relationships may give better results than infrequent undisturbed sampling, consolidation testing, and theoretical relationships.

Peat fibers affect the geotechnical behavior of peat by providing an internal lateral resistance to shear deformations in the triaxial mode of shear. Since pore pressures reduce this resistance, loading under drained conditions will provide better stability through higher lateral resistance.

The shear strength of peat in ring shear would be virtually unaffected by fiber reinforcement. The behavior of the Escuminac peat in ring shear was surprisingly consistent and gave parameters of c = 2.4 kPa and φ = 27 to 32 deg within a load range of 3 to 50 kPa. These values would be directly applicable in the case of retaining structures on peat, for which triaxial φ-values of 40 to 50 deg, as consistently reported in the literature, could in fact be misleading.