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In this paper, the shear strength of biodried and then subsequently mechanically treated (BMT) municipal solid waste (MSW) is presented. For the purposes of the presented research, the BMT waste samples, with maximum particle size of 25 mm, were obtained from the Croatian Regional Waste Management Centre, Marišćina. Biodrying is an aerobic process, the main purpose of which is to bring the biodegradation of organic waste to an extent sufficient to produce biologically induced heat to dry the waste via evaporation. During the life-time of the bioreactor landfill, the landfill operator disposes BMT waste in its dry state. Once the landfill is closed, the landfill operator will initiate the recirculation of leachate through the landfill body in order to induce intensive gas production and energy recovery. For the design purposes of bioreactor landfill, three dry BMT samples were tested a large direct shear box and in a triaxial testing device as well. The initial dry density of the installed samples in both devices was 380 kg/m3. The initial density of the installed samples is close to the density values achieved on the Marišćina landfill, as was reported by the landfill operator. The design height of landfill Mariscina after closure is 21 metres. Based on the closure height and initial waste unit weight of about 3.9 kN/m2, the vertical stress at the landfill bottom should be close to 80 kPa. Therefore, the selected normal stress levels for direct shear tests were 75, 100 and 125 kPa. The cell pressures in the triaxial tests were 50, 100 and 200 kPa. The obtained results show that BMT waste materials aimed for disposal in bioreactor landfill have a shear friction angle significantly lower than the similar waste materials, e.g., biostabilised MBT waste. Therefore, special care has to be taken in the design process of the bioreactor landfill. |
