Reconsideration of the settlement behavior of peat from view point of hydraulic conductivity

Abstract

This paper deals with the settlement of peat from the view point of hydraulic conductivity (k). The validity of using the oedometer tests, including the calculation method, for measuring k is carefully examined by numerical analysis as well as a test combined with an oedometer and a hydraulic conductivity test. It is found from these studies that the conventional oedometer test (JIS A 1217, 2009) can be evaluated to measure k for peat with the same accuracy as that for usual clays, provided that the incremental load ratio is unity. The significant difference in the characteristics of k for peat and usual clayey soils is their relation between the compression index (Cc) and the hydraulic conductivity change index (Ck). As a result, rather than remaining constant during consolidation, the coefficient of consolidation (cv) of peat decreases considerably with increasing consolidation pressure (p), while the cv coefficient for usual clayey soil is almost constant at the normally consolidated stage. The influence of cv dependent on p is studied by a numerical analysis for the one dimensional consolidation problem as well as for the ground improved by vertical drain. It is found that if the incremental consolidation pressure (Δp/p) is large, careful judgment is required when adopting conventional consolidation analyses, especially in case of the vertical drain.