Abstract
Peat deposits are complex natural formations encountered in many geographical areas. Peat itself is considered as a challenging geomaterial, with many aspects of its behaviour seemingly remaining enigmas. This state-of-the-art review paper provides an extensive summary of current knowledge on the strength and shear behaviour of fibrous peats. Critical assessments and interpretations of the undrained strength, effective-stress strength and at-rest earth pressure coefficient parameter values determined for fibrous peat materials using standard and advanced laboratory apparatus are presented, focusing particularly on the consolidated undrained triaxial compression and direct simple shear approaches. Based on documented case histories of embankments, dikes and natural peat slopes, guidance is given for operational shear strength assessments in peat, aimed at bearing capacity and slope stability calculations, considering both the normalised undrained strength ratio and limit equilibrium effective-stress strength approaches. In particular, the botanical origin, structural anisotropy, humification level, likely initial overconsolidated state, tensile resistance associated with the peat fibres and possible scale effect related to the test-specimen size are discussed in the context of the strength mobilised for different testing apparatus. The test methodologies and interpretations of experimental results presented for fibrous peat in this paper should be transferable to other fibrous soil and soil-like materials.
Highlights
Peat and other highly organic soil deposits are encountered in many geographical areas, covering large areas of the world’s land mass, and they are considered challenging materials in geotechnical engineering practice, with many aspects of their behaviours seemingly remaining enigmas
The deduced fD0 SS value is in close agreement with the 28° typically associated with standard DSS testing of normally consolidated (NC) fibrous peat materials, possibly suggesting that compared with TC testing, the scale effect may not be as significant for DSS testing, since the shear deformation mainly occurs in the direction of the predominantly horizontally aligned fibres
For TC testing, with the CK0UC approach preferred over the consolidated undrained compression (CIUC) one, fibre tensioning produces very high M and fT0 C values and low K0 and n 0 values, with axial tensile failure occurring for larger test specimens at ea = 15–30%
Summary
Peat and other highly organic soil deposits are encountered in many geographical areas, covering large areas of the world’s land mass, and they are considered challenging materials in geotechnical engineering practice, with many aspects of their behaviours seemingly remaining enigmas. The sr0 1⁄4 0 condition that develops during CU TC testing of some fibrous peats has been explained in terms of the internal lateral resistance against shear deformation provided by the predominantly horizontally-orientated plant fibre remnants present in the peat material (Cola and Cortellazzo, 2005; Landva, 2007; Landva and La Rochelle, 1983) This so-called fibre tensioning occurs during expansive (tensile) strain on the horizontal plane, giving the material its low drained Poisson’s ratio, n0, and strong anisotropy in strength (see Den Haan and Kruse (2007)). 0·47 0·53a CK0UC: 0·62b CIUC: 0·61b CIUC: 0·59 (n, 23; s, 0·13)b,c CK0UC: 0·54 (n, 8; s, 13)b,c
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