Lubna landfill

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4.4 Permeability testsThe permeability coefficients were determined by laboratory and field tests for wastes, aquitardlayers and bentonite material. The waste permeability in the field was established by the Maggmethod. The waste permeability coefficient was determined in the laboratory in the triaxial cell andby the modified constant gradient. The modification was based on permeability measurementsunder stress modelling conditions, at different depths of the landfill. On the basis of these testswithout loading, the coefficient of permeability for fresh wastes was approximately k 10 =5x10 -4 m/s,while for the old wastes - k 10 =1x10 -4 m/s. The coefficient values for fresh wastes under loading of25 and 50 kPa resulted in: k 10 =1x10 -5 m/s and k 10 =8x10 -6 m/s, while these of the old wastes:k 10 =8x10 -6 m/s and k 10 =4x10 -6 m/s, respectively.The permeability coefficients of soils creating aquitard layers were performed by the BAT system.The average permeability coefficient for these layers was k=10 -8 m/s.The permeability of the bentonite vertical barrier was tested in the laboratory using triaxial cell(Fig. 7) and falling head methods (Fig. 8), while in the field, the permeability was tested by theBAT system (Fig. 9). All permeability coefficients were lower than k
FIG. 9 Field permeability tests of the aquitard layer by the BAT system4.5 Settlement and lateral movement measurementsLandfill settlement consists of load-, decomposition- and time-dependant compression. Thedetermination of compressibility parameters of wastes needs long-term field and/or laboratorytests. Permanent surveys of settlement and horizontal slope movements of the landfill body havebeen carried out since 1996. The bench-marks were installed on the slopes (for settlement andlateral displacement measurements) and along the main access road (for settlementmeasurement). The total number of installed bench-marks was approximately 50 points.Displacement measurements using geodesy techniques are taken every 3 months. The testresults serve to forecasting settlement of the access roads on further sections, designing the solidshape and assessing the capacity of the landfill. The landfill map with measured lateralmovements and settlements values is presented in Fig. 10.4.6 Back-analysisBack stability analyses by Bishop’s, Swedish and FEM (Z-SOIL numerical program) methods forthe landslide that took place in 1995 on the Lubna landfill were applied for verification of the shearstrength parameters. The calculated minimum factor of safety, F min =0.994 (cross-section, on thenorthern slope of the landfill), was reached for the following shear strength parameters: ϕ’=21°and c’=15 kPa (Table 2). These parameters were accepted for the use of fresh wastes for designpurposes.Table 2. Geotechnical parameters of solid municipal wastes and the mineral capping layerCategory of wastes ρ [t/m 3 ] σ [kPa] φ [°] c [kPa] Testing methodsFresh municipal wastes 1.1 125 21 15Back-analysis of landslide,WST, failure testsOld municipal wastes 1.4 65 25 18Back-analysis of landslide,CPT and WST soundingsClay mineral cappingsystem2.1 40 15 12 Back-analysis, CPT sounding9
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Lubna landfill

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