Relationship between required power and drainage area


Some important considerations can be made on the power required by the suction units of the wellpoint systems in relation to the drained surface in the various types of soil. The energy absorbed by a suction group of a wellpoint system is linked to the hydraulic capacity (hydraulic flow that must come out from the ground) and to the vacuum capacity, ex. the degree of vacuum that the suction group must maintain in the wellpoint system to make it functional. With the same vacuum capacity in soils with high permeability (sands and gravels) there are large hydraulic flows to be extracted and therefore proportionally high powers are required.
In low permeability soils (silts, clays, silty sands), the hydraulic flow to be extracted is low and therefore the possibility of using low energy consumption groups has been studied.
It is therefore possible to highlight the relationship existing in the two groups of soils analyzed, between the power required for the operation of the wellpoint systems and the size of the drainage area and, therefore, the size of the system itself. The diagram highlights the existence of a band within which the extension of the drained surface (and therefore the size of the system) does not affect the power required by the wellpoint system.

Sandy soils
The power required is an exclusive function of the hydraulic flow to be emitted from the ground and, with the same water table lowering to be obtained, the same number of wellpoints must be used to drain excavations of different sizes.


Soils with loamy-clayey layers
The diagram highlights how in these soils the band within which the required power doesn’t increase with the variation of the extension of the drained surface is much more extensive than in sandy soils. With the same lowering of the groundwater, it has been noticed how the required powers are considerably lower than for sandy soils and compared to those required in the recent past (dashed lines of the diagram) when evidently, to keep the wellpoint system in depression, the suction units had higher dimensions and, therefore, absorbed higher powers.