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Geoenvironmental Engineering Fall 2017
 Seismic Response and Stability Analysis of Landfills
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Seismic Response and Stability Analysis of Landfills
 Seismic Response and Stability Analysis of Landfills
 Landfill Performance
 Case Study of OII
 Seismic Analysis of Landfill
 (1) Site Specific Geological Evaluation
 (2) Dynamic Properties Landfill Waste
 (6) Slope Stability Analysis
 Computer Program Application
 Seismic Analysis of a Geosynthetic Liner System
 Seismic Response of a Composite Cover (Case study)
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(6) Slope Stability Analysis
The two conventional approaches to evaluate the stability of landfill structural systems consist of the pseudostatic method of analysis and the Newmark SlidingBlock analysis.
Pseudostatic analysis –
The pseudostatic method yields the limit state equilibrium expressed in terms of factor of safety of slopes during seismic loading. A minimum FS of 1 is desired and essentially means that the driving force is equal to the resisting force since,
FS = 1 = resisting force / driving force
thus, resisting force = driving force if FS = 1
FS = ( ( W * cos(α) – k * W * sin(α) * tan(φ) ) / ( W * sin(α) + k * W * cos(α) )
where k = a_{h} / g
Where,
a_{h} = pseudostatic acceleration in horizontal direction
k = coefficient for the horizontal direction
W = weight of failure mass
g = Earth’s gravitational constant
φ = Friction angle of soil
α = Angle of toe up to failure surface of sliding mass. See Figure 1.8
Selecting the k coefficients is based on very subjective criteria and descriptions. This can significantly affect the accuracy of this method.
Also, the seismic accelerations exist in the horizontal and vertical directions, however, the horizontal component is the only one considered in design since the vertical forces average out to 0 and are typically not insync with horizontal motion (Kramer,1996).
Figure 1.8: Force diagram depicting a sliding mass on an inclined plan. Force diagram of a landslide mass sitting on an inclined planar slip surface (Terzaghi, 1950).
As per the diagram,
W = weight / unit length of landslide mass
k = seismic coefficient
s = shear resistance along slip surface
α = angle of slip surface inclination
Note in this scenario, the whole landslide mass is considered as a whole, from the toe of the slope to the surface above.
Newmark analysis –
The slidingblock analysis was introduced by Nathan Newmark in 1965. The Newmark analysis yields the cumulative, permanent displacement of the slopes during seismic loading. The method utilizes the basic physics scenario of the rigid block on an inclined plane, as shown in Figure 1.9 (Kramer, 1996). Just as there is a certain amount of friction that a wooden block on an inclined surface will need to overcome to slide likewise, the yield acceleration is the acceleration required for the landslide mass to initiate motion, or sliding. The yield acceleration is a_{y} = k_{y}g. When the a_{y} is exceeded, permanent deformation occurs. This method is used to compare between the displacement of the slopes and allowable displacement of the landfill components in the event of a major earthquake. This method is more refined than the pseudostatic method and as it provides an indicative estimate of amount of displacement when the material slides.
Figure 1.9: Forces acting on a block on an inclined plane in dynamic conditions. (Kramer, 1996)
Figure 1.10: Illustrated the integration of the accelertion above the yield acceleration to render the velocity which is integrated again to obtain the displacement (Krishna, 2009).