In-situ testing methods for dynamic properties of MSW landfills

Cost-effective techniques have been developed for measuring P and S-wave velocities and in-situ shear strength for landfill waste materials. These techniques include both surface profiling and downhole measurements to capture the typical velocity inversion which accompanies a compacted soil cover. The measurement scheme is basically a simplified tomography survey which characterizes the material within a large cone around the borehole. A computer code is being developed to fit the data to a statistical model for each cone. Using a least-squares fit the code will automatically iterate to mean values and quantify the local variability (on a scale of 5 to 20 m). Variability across the landfill is assessed by repeating the measurements at several locations. Static shear strength of landfill materials is also being measured with a large-scale (1.22m × 1.22m) in-situ direct shear box. Because it is common practice to use a percentage of the static strength as the seismic strength in obtaining yield accelerations, these static strengths are useful for earthquake analyses. Attempts will be made to correlate these in-situ shear strengths with wave velocities and moduli at the same locations when more in-situ strength data are available.