Predictions of settlement in peat soils

Abstract

Abstract:Laboratory predictions of the compression behaviour of peat are compared with field data through use of a database of laboratory tests from 14 sites and information from full scale field loading at 5 sites. Data presented confirms the complexity of the deposits.Nonetheless from the point of view of normal engineering works, calculations based on laboratory test data are likely to give reasonable predictions of the magnitude of immediate and primary compression.Standard (20 mm thickness) samples may give misleading data on time for primary consolidation.Thicker samples, e.g. 50 mm, should be used. Sampling by conventional samplers, as used for mineral soils, can cause densification of the peat resulting in non-conservative design parameters. It was found that the data presented follow the C α /C c law of compressibility. There is also is some evidence to suggestthat the H 2 scaling law may be applicable. Good correlations were found between vertical yield stress (p vy ') and compression index (C c ) and index parameters such as water content (w i ) and void ratio (e 0 ).Conventional staged construction with surcharge loading may be successfully applied to peat soils as long as adequate drainage exists to permit consolidation over reasonable time intervals.

Empirical correlations for the compression index of Irish soft soils

“…Interestingly, Long and Boylan (2013), reporting values of C c and C c /1 + e 0 for peats in three countries including Ireland, have also found that C c relationships with w n exhibit less scatter than the C c /1 + e 0 relationships with w n . (b) The Mesri and Ajlouni (2007) relationship represents the data quite well for w n values in excess of 60% (Figure 4(a)).…”

Thermally induced pore pressure response in peat beneath a railway embankment

“…However, this gaseous nature of peat is rarely considered within the geotechnical literature. During laboratory tests, peat is often considered as fully saturated or saturated with very high backpressure (Mesri and Ajlouni 2007;Hendry et al 2012;Long and Boylan 2013).…”

“…The four peat specimens used in this testing were cut from a Shelby tube. Shelby tube samples have been used to study the drained and undrained compression behavior of peat (Hendry, Sharma, Martin and Barbour 2012;Long and Boylan 2013). These Shelby tube samples were extruded and trimmed into specimens with diameters of were sealed and stored in a moisture-controlled room with a constant temperature of 1.5°C until they were tested.…”

“…Peat's organic composition, variability in properties, low modulus, and potential for large volumetric strains have posed challenges for the construction of structures upon it (Stanek and Worley 1983;Landva 2007;Long and Boylan 2013). The settlement and failure of railway and road embankments constructed on peat subgrade have been the subject of several studies.…”

Editorial

“…Authors are encouraged to follow established themes and give due recognition of earlier relevant publications in the journal, whether or not these contribute to computed Impact Factors. The breadth of the subject area encapsulated by engineering geology is captured by papers in the journal, with examples as disparate as stiffness of residual dolomite (Jacobsz 2013), soil abrasion for tunnel boring machines (Barzegari et al 2013), desert engineering geology and geomorphology (Fookes et al 2013), settlement in peats (Long & Boylan 2013), landslide monitoring (Gunn et al 2013), the properties of specific deposits (e.g. the engineering geology of chalk; Bowden 2013) and advances in theory and analysis (e.g.…”