Improvement of engineering properties of peat by preconsolidation

摘要

Peats that are formed by the disintegration of plant and organic matter are of very high void ratios and very large water contents. The material forming the peats are porous and of low specific gravity and also subjected to biodegradation with time. As such peats are of very high compressibility and very low shear strength and presence of thick peat layers in the subsoil poses major construction difficulties. Peats are characterised by very high primary and secondary consolidation settlements. Compressibility and strength characteristics of a peat can be improved by preconsolidation. Preloading with a surcharge is one method of preconsolidating a peat. The process of preloading in the field was simulated in the laboratory by carrying out loading -unloading and reloading tests in a conventional consolidation setup. Test results indicated that the primary consolidation settlement characteristics as given by compression index c_c, or the coefficient of volume compressibility m_ⅴ, and the secondary consolidation settlement characteristics as given by the coefficient of secondary consolidation c_α are improved considerably by preloading. The improvement of the coefficient of secondary consolidation ca could be related to the overconsolidation ratio achieved through preloading. The shear strength gain through consolidation was examined by undrained shearing of peat samples that were isotropically consolidated under different cell pressures.