The International Information Center for Geotechnical Engineers

# Seismic Response and Stability Analysis of Landfills

(2) Dynamic Properties of Landfill Waste

As mentioned earlier, landfill seismic analysis is often heavily site-specific. Evaluating the solid waste material properties is critical when designing a landfill for seismic criteria. With landfill solid waste characterization comes uncertainty, variability, and heterogeneity. Thus, the evaluation of waste materials’ properties are performed in conjunction with the parametric and sensitivity studies to compensate for these issues (Kavazanjian et al. 2001).

The intrinsic properties of the landfill required for dynamic analyses include the following (Murali Krishna, 2009):

(i)   unit weight (ɣ)

(ii)  shear wave velocity (Vs)

(iii)   shear strength (τ)

(iv)  strain dependent material damping ratio (ζ)

(v)  strain-dependent normalized shear modulus (G/Gmax)

As mentioned earlier, this paper will use the OII case study to demonstrate examples of results for the properties mentioned above in Figures 1.2 – 1.6 taken from Kavazanjian & Matasovic, 1998. OII will serve as a thematic case study to show real-world application of seismic design of landfills.

Figure 1.2: (i) Unit weight variation with depth

Figure 1.3: (ii) Shear wave velocity versus depth

Figure 1.4: (iii) Shear strength

Figure 1.5: (iv) Shear strain versus damping ratio

Figure 1.6: (v) Shear strain versus normalized shear modulus

Figures 1.2 to 1.6 -

Figure 1.2 shows the unit weights obtained from multiple boreholes obtained from the gravel displacement method. An average unit weight is then calculated.

Figure 1.3 shows the shear wave velocity profiles from Spectral Analysis of Surface Waves (SASW) testing. In general, the shear wave velocity increases with depth. This is natural considering it increases with higher stresses, which exist as greater depths. A greater shear wave velocity is desirable since this means there is less amplification. The solid red line is the calculated mean and the two dotted lines are the standard deviation of one sigma.

Figure 1.4 shows the shear strength. The two dashed plots represent material that passed the 19 mm screen and material that didn’t. The percentages show the amount of refuse, or not-soil material in the sample.

Figure 1.5 and Figure 1.6 show two cyclic shear strain relationships on a log scale. The damping ratio increases while normalized shear modulus decreases with increasing cyclic shear strain. The two graphs agree with the notion that material damping ratio is inversely proportionate to dynamic shear modulus. The shear modulus upper bound and the damping lower bound values were developed from field data and laboratory testing and are commonly used in the industry to this day. The curves were calculated using back-analysis of landfill seismic response (Matasovic & Kavazanjian, 1998).