To examine the long-term settlement of peaty soft ground improved using the vacuum consolidation method, a test construction was conducted for an expressway construction project near Sapporo. The results from the test construction have revealed that the operation period of vacuum pump in which the excess pore water pressure decreases to hydrostatic pressure is suitable way to reduce the long-term settlement of peat and organic clay. The negative pressure, which was applied during pump operation, was unloaded after the stopping of pumps and caused overconsolidation of the ground as an effect of surcharge. The coefficient of secondary consolidation decreased with an increase in the overconsolidation ratio (OCR) at this time, and the coefficient became approximately 50 to 70% when OCR = 1.2 to 1.3.
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