Continuum approach and representative elementary volume
In modeling the groundwater flow and transport processes in an aquifer, it is not possible to consider the microscopic level phenomenon happening at the pore level. Rather we consider a hypothetical average value of the properties to model the phenomenon. For example, in modeling groundwater flow, average linear flow path is considered in place of the actual flow path (Fig. 2.3). In order to apply the averaging concept, we consider the porous medium as continuum. Continuum theory explains that the variation in the properties is gradual without abrupt changes or discontinuity. |
Fig. 2.3 Actual and liner flow paths |
Representative elementary volume In order to apply the averaging concept discussed above, a representative elementary volume (REV) is required to be considered. Now what should be the size of a REV? Suppose, the inner smallest rectangular is an elementary volume (Fig. 2.4). In this case, the porosity for the elementary volume will be equal to 1 as the volume is in the void portion of the soil. Similarly, if we change the location of the volume, the porosity may be zero also, if it is placed over a soil particle. As such this small elementary volume cannot represent the properties of the whole soil matrix. |
Fig. 2.4 Representative elementary volume |
Fig. 2.5 Representative elementary volume
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Now, if we increase the size of the elementary volume as shown in the Fig. 2.4, the porosity value will change (Fig. 2.5) and finally will reach a nearly constant value. The volume at which the property of the soil matrix is nearly constant is the representative elementary volume.
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