Coupled mechanical creep and bio-compression and residual settlement in a multi-stage municipal solid waste landfill, Korea

Based on a field monitored dataset measured at landfill #1 over 21 years, the characteristics of settlement coupling mechanical creep and biodegradation and the residual settlement were analyzed. Since landfill #1 is a multi-stage municipal solid waste (MSW) landfill where dykes are constructed after landfilling for subsequent waste fills, the waste decomposition between the lower and upper lifts was quite different and it is difficult to discern between the mechanical creep and bio-compression on the settlement curves. The compression ratio coupled with mechanical creep and bio-compression and the residual compression ratio were determined as 0.233 and 0.068, respectively. This implies that biodegradation was gradually and significantly reduced in the MSW settlement behavior after the residual settlement began. The starting date of residual settlement was distributed between 3821 and 5402 days from the initial date of landfilling. The settlement coupling mechanical creep and biodegradation (S(MB)) was 2.9 times larger than the residual settlement (S(RS)), and the duration of S(MB) is determined to be 0.3 times that of S(RS). In addition, the remnant methane gas content existed in the landfill gas, and low-level biodegradation was still generated in the waste buried for more than 10 years after the residual settlement began.