Case studies and examples

1. This link shows a potential rotational failure of the toe of the slope. The failure is provoked by the insufficient shear resistance of the interface between smooth HDPE geo-membrane and geotextile (in saturated condition) in the bottom liner system of the landfill. The shear forces are mobilized in the governing interface as a consequence of the inclination of the waste cell the bottom.
    
2. This link shows a potential composite sliding failure in a temporary ramp, built on the capping system of a landfill. The failure mechanism is activated by the presence of the heavy traffic load. The traffic load was modelled as a dead uniformly distributed load of 800 kPa. The factor of safety for that failure mechanism was equal to 1.2, fully complying with the requirement for temporary road constructions.
    
3. This link shows a potential rotational failure of the foundation of the landfill. The failure surface propagates through the bottom liner and the waste. The foundation, including “polder clay”, is made of saturated soft soil. In color, the map that relates the magnitude of the factors of safety with the corresponding centers of rotation of the failure mechanisms looked at.
    
4. This link shows a steady state seepage analysis of a typical landfill capping. The capping is made of a layer of sand and a layer of re-cultivation soil. At the toe of the slope, the evacuation of the water through a ditch was modelled as a drain. The colors shows the total head and the blue arrows represent the flow lines. Per definition, flow lines and total head contours intersect with a 90° angle.
   It is evident how the sand layer collects the water from the re-cultivation layer, and transports it to the discharging point. On the right low corner, the saturation distribution is visible (red: saturated; blue: not saturated).
    
5. This link shows the stability simulation of the capping system shown in the item just above. The simulation shows the pore water pressure evaluated by seepage analysis. Seepage forces in fact can drastically reduce the factor of safety of a slope. It’s proven that most of the slope failures occur during or a few days after a big rainfall event.
    
6. This link shows the influence of the construction of a landfill in the surroundings of a rail road. Color represents horizontal displacement. The effect on the rail road was a movement of its foundation by 4 cm !
    
7. This link shows a potential failure of the slope of an embankment (Plaxis 3D simulation). The already existing embankment (blue layer on the right), had to be further loaded with new waste material (pink layer). From lab tests, the new waste was found to be weaker and capable of generating excess pore water pressure. The failure mode predicted is a toe rotational failure mode of the new waste.
    
8. This link describes a potential failure mechanism of a landfill (blue layer) built in between two existing landfills. The model was created with Plaxis 3D. Due to the presence of a weak geo-synthetic interface between the new landfill and the slope of the existing ones, a potential failure mechanism develops as materials flow through the sliding interface. This failure modes could not be seen in a 2D analysis due to its “3D morphology”.
    
9. This link shows the differential settlements of the top of the new landfill (blue layer), referring to the case reported just above. The differential settlement is provoked by the different stiffness characteristics of the 2 existing landfills. The landfill on the left is made of municipal solid waste (compressible and subjected to creep); the landfill on the right is made of waste assimilated to biologically inert sandy material. The rate of the deformation of the existing landfill slopes is different, and this generates the differential settlement.