Unit Weight Determination of Landfill Waste Using Sonic Drilling Methods

The total unit weight of waste in a 40.5 ha landfill, up to 34 m thick, was estimated based on tube samples taken from borings made using sonic drilling technology. The wasteʹs unit weight was needed for input into slope stability calculations, which were part of the landfillʹs closure design. The sonic drill was capable of penetrating and obtaining samples of all types of materials in the landfill. No significant correlation of waste unit weight, with depth, was found. Instead, the waste samplesʹ constituents were observed to have the greatest effect on their unit weights. The site also offered the unique opportunity to back-calculate the wasteʹs overall unit weight using a numerical model, and knowledge of the in situ stresses in the underlying clay as determined by oedometer testing. These calculations indicated that samples taken, using sonic drilling, gave a good a approximation of the wasteʹs overall unit weight at each boring location.