EVALUATION OF DYNAMIC PROPERTIES OF MUNICIPAL SOLID WASTE SITES BY GEOPHYSICAL TESTS

摘要

Landfill design needs to consider dynamic properties for safety not only under static conditions, but also under dynamic loading conditions. In recent years, geophysical surveys are becoming popular mainly to understand the profiles within the landfills and estimate its dynamic propertieslike shear wave velocity, shear modulus and Poisson's ratio. Shear wave and P-wave velocity (Vs, Vp) are very well related to the dynamic properties of soil at lower strains. Geophysical tests provide a direct measurement of Vs and hence widely accepted for the seismic site characterizationpurpose. In this study, seismic survey was performed using Multi channel Analyzer of Surface Waves (MASW) technique at Mavallipura landfill site, Bangalore. MASW test involves three steps: data acquisition, construction of a dispersion curve (showing the variation of phase velocity among variousfrequencies), and inversion of the dispersion curve to get shear wave (Vs) profile from the calculated dispersion curve. The typical MASW test setup used for the present study consists of 24-channel geode seismograph and 24 geophones of 4.5 Hz capacity. Seismic data were recorded using geodeseismograph with sledge hammer source on one side of the landfill and geophones on the other side with 1m spacing of geophones. The landfill was surveyed up to a length of about 25m from the top level. The deposit consisted of uncompacted waste up to a depth 6m with Shear wave velocity of74 to 130m/s. Series of 1-D MASW tests have been carried out to map the entire solid waste site and the results will be presented in the paper. Overall, the results from the study showed that seismic surveys have the potential to capture the changes in dynamic properties like shear wave velocityand Poisson's ratio with respect to depth of MSW landfill to infer the extent of degradation and provide dynamic properties needed for seismic stability evaluations.