Question 4 of 12: Compacted Density

Question 4: Compacted Density (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Compacted (in-place) density is important because it directly sets the airspace consumed per tonne of waste placed, and airspace is the landfill's single non-renewable resource: a higher achievable compacted density means more waste can be placed within a given permitted footprint and final grade, extending the site's remaining operating life for the same disposal capacity. It also governs collection-vehicle payload optimization (compactor trucks are volume-limited before they are weight-limited if waste is poorly compacted), the required daily/intermediate cover-soil volume per tonne of refuse, and the equipment (compactor type, number of passes, lift thickness) selected for the working face.

4.1 Calculation. In-place compacted density is calculated as the mass of waste placed divided by the in-place volume it occupies, $\rho_{compacted} = W/V$, where $W$ is obtained from the facility's weigh-scale tonnage records for a given lift or time period and $V$ is obtained from a topographic (survey or laser/photogrammetric) volume-difference calculation between successive surveys of the working face. Where direct weigh-scale/survey data are unavailable, it may instead be expressed via a compaction ratio $CR = V_{loose}/V_{compacted} = \rho_{compacted}/\rho_{loose}$, with $\rho_{loose}$ taken from truck-load records before compaction and $CR$ estimated from the number of compactor passes and lift thickness used at the working face.