Improvement of secondary consolidation characteristics of peaty clay by preconsolidation

Abstract

Special consideration should be given to secondary consolidation settlements during service in the construction of high road embankments in lands underlain by thick layers of soft peaty clay.Usually a preload design will be done to ensure that the peaty clay will remain in an over consolidated state during the operation of the road. Peaty clays are known for high secondary consolidation settlements. As such, possible secondary consolidation settlement during service life is also a major concern. The coefficient of secondary consolidation (C) is expected to reduce with increasing over consolidation ratio (OCR) achieved during preloading. At the stage of surcharge removal, the settlement during operation has to be estimated. In a preload design the practically achievable over-consolidation ratios (OCRs) are in the range of 1.1 to 1.2. Effectiveness of such OCR values in keeping the long term in service secondary consolidation settlements within acceptable limits was studied in this research. Oedometer tests were carried out simulating the process of loading-unloading-reloading on remoulded samples. Effects of prolonged loading on the coefficient of secondary consolidation was also assessed. Further tests were done on undisturbed samples obtained from preloaded peaty clay layers in two different projects. Results illustrate that the level of reduction of C is related to the achieved OCR.