Transmittivity in-plane permeability

It is a necessary property in drainage applications. In fact, drainage refers to an in-plane flow of water. In this regard, drainage is different from filtration, which refers to the flow of water in the cross-plane direction. 

Flow rate and transmissivity can be evaluated under constant hydraulic load according to the previous equations. 

Transmissivity test results have shown that flow rate and transmissivity depend on the hydraulic gradient apphed and vertical stress (Figs. 8.11 and 8.12). Therefore it is necessary to evaluate the transmissivity allowable value starting from the test results obtained with the vertical stress and the hydrauUc gradient characteristic specific to the project. 

An example of test apparatus used to measure the in-plane permeability is shown in Fig. 8.13. 

Compressive creep test results have also shown that the variation in thickness in time owing to compressive creep of the material produces a variation of porosity and, as a consequence, also transmissivity during the structure s service life (Fig. 8.14). 

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