Long-term settlement of Refuse landfills is one of the important design items in the design of protection systems such as caps and leachate collection systems as well as in the technical consideration of feasible redevelopment of a landfill site for building foundations and pavement. Long-term settlement mechanisms cannot be merely dealt with classical Soil Mechanics concepts, since they are considerably dependent upon the biological decomposition of refuse which distinguishes it from typical soil behavior. Nevertheless, a detailed mechanism by which the decomposition causes settlements has not been found. In this dissertation, it is presented a mathematical model that considers the decomposition process of biodegradable refuse from a geotechnical point of view and suggests the overall compressibility behavior of refuse, including the decomposition effect.
Mathematical model that proposed in this dissertation is applied to analyze the measured settlement data of seven landfill sites. A data bank of model parameters was obtained and the trends were analyzed. The long-term settlement behavior of refuse landfills can be fairly well estimated proposed model. The total remaining amount of settlement may be predicted on the basis of the fill age and appropriate two design parameters.
Other several prediction methods are also applied to the measured settlement data of thirteen landfill sites. The effect of biological decomposition on the settlement characteristics is investigated by predicting the long-term settlement of refuse landfill sites in view of the predicted settlement curves and the amount of long-term settlement. Irrespective of the applied prediction methods, false prediction may be performed if the accelerated logarithmic compression due to decomposition of biodegradable refuse is not involved in the settlement characteristics. And it was observed that the predicted long-term settlements considerably decreased with increasing fill age of landfills.
In order to estimate stabilization of settlement of refuse landfill for codisposal refuse and fly ash, large compression test and lysimeter test are performed in this dissertation. Codisposal ratio of fly ash(Fly Ash/MSW) are 0, 8, 15 and 30%, respectively. In large compression test results, compression index(CR) which means mechanical compressibility with variation of applied stress and secondary compression coefficient($C_α$) which means long-term mechanical compressibility in certain stress level considerably decrease with increasing codisposal ratio of fly ash. In second lysimeter test result, $C_α$ value decrease the same.
