Reanalysis of the Kettleman Hills Landfill Slope Stability Failure

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other words, the slippage in the 3D model occurred at firstalong the back part of waste layer (FS values from 1.05 to0.99) - just like in 2D analysis results. Afterwards, whenshear strain zone is increasing to the top of the waste layer,the value of the factor of safety is falling to FS = 0.99. At thepoint of instability occurred the shear strain zone, whichincluded all cross-sectional thickness of waste layer. Usinglow-strength parameters for the interface, for which the factorof safety is lower than unity, one is able to determine theprogress of the slip surface. For the value of friction angleϕ = 6.0˚ the failure continued to develop by crossing againthe entire waste layer up to the upper corner, which connectsthe waste layer with interface (FS=0.9). Continued damageprogress (for ϕ = 4.3˚) caused the sliding surface at the backside of interface. The shape obtained for FS = 0.76 recalls acharacteristic wedge figure.Further comparison between 2D and 3D analysis resultsindicates that for the same value of friction angle ϕ= 9.0˚ wereceived a different value for the factor of safety - FS = 1.31for 2D, FS = 1.05 for 3D (figure 9). The lower value of theFS for 3D analysis is caused by the possibility of reproducingthe real geometry conditions of the object.The next indicator for the coming landslide is a largeincrease of displacement velocities. Table 3 comparesdisplacement velocity for different factor of safety values. Itcan be seen that when the FS value is falls, the movement ofthe velocity vector becomes much more orderly.TABLE IIIVELOCITY DISPLACEMENTS – 2D ANALYSISFSVelocity (m/s)1,31 8,376e-50,99 2,354e-4Source: Own studyThe abnormal displacement increase is related to the valuesof the velocity and it is also the indicator for impendinglandslide. Figure 10 shows increasing displacement obtainedin 2D analysis which are connected with decreasing values offactor of safety.As in the case of the velocity displacement vector, there isa direct connection between the falling value of factor ofsafety and spreading displacements.Fig. 10. Abnormal displacements – 2D analysis.Source: Own study.Landslide development can be seen also in plasticity indexdistribution. Figure 11 presents the failure zone spreading asthe result of shearing, which is due to the reduction of themechanical property values. This destruction process starts inthe lower part of the waste layer, afterwards cuts the layer andfinally reaches the entire cross section of the layer and passesto the damage zone due to tensile stress.The progressive failure effects were more significant ininterface plasticity analysis. Figure 11 shows the relationbetween slip surface development and decreasing factor ofsafety values. For the factor of safety is FS = 1.05, the slopeis stable because the interface is not yet fully plasticized. Thefigure shows the place in the basin of the landfill, on theinterface surface, which has not yet reached the peak shearstrength. The same location was received by Filz et.al. (2001)in the analysis of landfill slope stability (the analysis wascarried out using the finite element method).Fig. 9. Comparison between 2D and 3D analysis results.Source: Own study.Fig. 11. Plasticity index distribution - 2D analysis.Source: Own study.23
Figure 12 shows a progressive slip surface plastificationand its relation to a decreasing factor of safety value. For thefriction angle ϕ = 9.0˚, the slip surface area is not yet fullyplasticized. It can be seen that in the middle of the basin thereis a place, which has not reached the peak shear strengthvalue. The location of this place is in agreement with thatreceived by Filz et. al. (2001).IV. CONCLUSIONSThe stability of the Kettleman Hills slope failure wasreanalyzed using 2D and 3D models implementedin FLAC v. 5.0 and FLAC 3D v. 4.0, respectively. Thecalculations relied on the Finite Difference Method Theanalysis was conducted using the Shear Strength ReductionTechnique. In the present study, the parameter value whichdecreased was that of the friction angle.The 3D model successfully reflected the landslidegeometry. The trend of damage in the 3D model was locatedin the same places as real cracks which were observed afterfailure occurred.The slip surface was located in a geosynthetic layer whichwas characterized by relatively poor strength values incomparison with the waste layer and subgrade parameters.It was found that the failure occurred when the value of thefriction angle amounts to 4.3 (for 2D analysis) and 8.0 (for3D analysis). Similar results for the stability analysis werereceived by Chang.The analysis also made it possible to obtain informationabout the progress of the landslide, including its direction,range and slip surface shape.The considerations above lead to the followingconclusions:1. The key point for the Kettleman Hills landfill slopestability failure was insufficient strength of thegeosynthetic layer (complete interface plasticity wasequivalent to the slide surface occurrence).2. Comparison of the results of the planar and the spatialanalysis shows that there are notable differencesbetween the values of the friction angle for which thelandfill slope instability occurred.3. The reason that the spatial analysis registers instabilityfor greater values of the friction angle is connectedwith the ability to reproduce real conditions of thelandfill geometry as well as to perform propagation ofthe shear strain deformations.4. Three-dimensional stability analysis confirms themajor benefits of using spatial analysis. Thecontinuation of this type of calculation allows one todetermine the appropriate size of the strengthparameters for materials used for protective andisolate barriers in compacted liner systems used inlandfill construction.ACKNOWLEDGMENTFinancial support for this work was given by organisationsnamed below:Fig. 12. Plasticity distibution on the interface - 3D analysis.Source: Own study.Part-financed by the European Union (European Regional DevelopmentFund and European Neighbourhood and Partnership Instrument)Scientific work financed from science funds in 2011-2013 allocated for cofinancingimplement international project24
Page 2 and 3: Based on the geometry defined in fi
Page 6: REFERENCES1. Cała M., Flisiak J.,

Reanalysis of the Kettleman Hills Landfill Slope Stability Failure

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