Consolidation settlements of tropical peat domes by plantation development

Settlement of tropical peat domes after cultivation for agriculture is the result of oxidation and compaction components above the ground water table, and consolidation below the ground water table. This report studies the consolidation component, making use of an advanced geotechnical compression model. An example case of plantation development on a peat dome in SE Asia is constructed, and geotechnical parameters are deduced from laboratory tests on tropical peat in SE Asia. The model calculations reveal that during the initial development phase in which the ground water table is lowered to more than 1.5 metres below the peat surface, over 1 metre subsidence by consolidation can occur in a matter of months assuming a peat thickness of 10 metres. As ground water table depths decrease, first mainly as a result of the subsidence itself and at a later stage maybe also due to water management efforts, consolidation of the peat below the ground water table comes to a complete standstill. This is explained in geotechnical terms by the relatively large degree of unloading following the rise in ground water level, and leads to the conclusion that after the first year of drainage, further subsidence stems wholly from processes above the water table, i.e. oxidation and compaction.