Compressibility and shear strength of a tropical fibrous peat

Abstract

This study examines the compressibility and shear strength of an Indonesian fibrous peat through oedometric and consolidated undrained (CU) triaxial tests. The influence of fibres is considered by preparing two series of specimens – undisturbed and reconstituted. For the latter, the coarse fibres larger than 80 μm were removed by wet sieving. Oedometric test results show that, as the coarse fibres are removed, (a) the secondary consolidation (log t, ε1) curves change from concave-down to linear and (b) the compression index of the oedometric (log σv, e) curves becomes smaller. These observations agree well with previous results on peats from polar and temperate zones. In CU triaxial tests, the undisturbed specimens fail to show strain hardening behaviour in the (ε1, q) diagram. Their effective friction angle (37·5°) is smaller than the typical values for other fibrous peats (40–60°). By comparing the shear strengths reached at different void ratios for both undisturbed and reconstituted specimens, it was found that the presence of structure adds additional shear strength in undisturbed specimens. With a smaller density, the undisturbed specimens reach the same peak deviator stress (e.g. 100 kPa) as the much denser reconstituted specimens.