Design vacuum consolidation considering energy requirement

In designing a vacuum consolidation project, it is desirable to quantify the energy required. Explicit close form equations were derived for calculating energy consumptions during a vacuum consolidation in terms of extracting sealed-in air (Wair1), seepage consolidation of soils (Wsoil), draining out the water collected by PVDs (Wwater), and air-leaking rate into a vacuum consolidation system under a given level of vacuum. It is shown that for an ideal vacuum consolidation (no air-leaking), the energy required is higher but comparable with the work done by gravity force of the same magnitude of fill material induced consolidation. The results of the analysis using the design guides in China and/or Japan indicate that only a few percentages of the required effective pump energy are consumed on seepage consolidation and draining out of water collected by PVDs, and the other is for extracting the leaked-in air or possibly just wasted. Therefore, having a good sealing system, and setting a target range of vacuum pressure instead of a single value may increase the energy efficiency. Shortening the duration of a project by reducing the spacing between PVDs can also be a possible option for saving energy. Finally, a conceptual design flowchart was proposed.