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# Define Hydraulic (Transient)

If the Groundwater Method = Transient (Finite Element Analysis) then the Define Hydraulic Properties option allows you to define the permeability characteristics of materials for transient groundwater seepage analysis. Material permeability is required by the finite element analysis in order to solve the seepage problem (i.e. determine the flow and pore pressure distribution throughout the model).

The hydraulic material parameters for transient analysis are identical to those described for steady-state seepage analysis, with the following additional input parameters:

• WC saturated: The saturated water content which is equivalent to porosity.
• WC residual: The residual volumetric water content represents the volumetric water content of a soil where a further increase in negative pore-water pressure does not produce significant changes in water content.
• mv: The coefficient of volume compressibility. At the beginning of consolidation, the pore water pressure increases and the pore water takes all the additional load applied to the soil. However, after time elapses, the pore pressure slowly dissipates (effective stress increases) and this leads to reduction of void ratio (e) in the soil. The change in void ratio and the change in pore pressure (u) are related to each other using the coefficient of compressibility (av):

• âˆ‚e = av âˆ‚(âˆ†ÏƒÊ¹) = av âˆ‚u

here e, is the void ratio and u is the excess pore water pressure. Mv is also related to av, by:

mv = coefficient of volume compressibility = av/(1+e0).

and e0 is the initial void ratio in the soil. Please note the above equations are derived for a 1D consolidation.

• Water Content / Matric Suction function

Please note, in RS3, when the transient analysis is used, the user has two options; coupled analysis or uncoupled analysis.

If the analysis is Coupled, RS3 will not ask for the mv, since it uses the bulk modulus of solid and fluid which accounts for the deformation of soil and its effect on the soil volume change.

If the analysis is Uncoupled, RS3 will ask the user to input the value of mv, since it ignores the effect of solid on fluid flow.

For details on all other hydraulic material parameters see the Define Hydraulic (Steady State) topic.