Find water flow through weep hole in retaining wall

Question

Hi all, 
 
 I need to provide the diameter, length and distance of the weep hole in the retaining wall. For that reason I used flow analysis by providing a retaining wall and drain but water flow around the retaining wall not through the drain, Can anyone tell how to model to get the flow through the drain so that I will get the quantity of water flow through drain and from there will provide the dimensions of the weep hole. 
 
 Thanks.

Dennis Waterman · Answer

Dear Nitharshan, 
 A drain element is only a boundary condition, it does not have flow. If you want to model the flow, you would have to define a thin area with a higher permeability in your wall. Alternatively you could do it with an interface (instead of the drain you use now) and specify a longitudinal permeability in the interface. However, if you're also planning to do a deformation analysis, an interface may be hard to control in terms of deformation and the thin zone with the same stiffness/strength as the wall, but with high permeability would work better. 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Nitharshan, 
 Something considerably higher than the soil permeability. The discharge will be largely determined by the permeability of the soil, not by that of the pipe. Note that if in reality it's a single pipe, a 2D analysis will not be very good as it will calculate it as an infinitely long gap instead of a single hole. This means the flow pattern will be different, so simply using the 2D discharge per meter length and multiply it by the pipe diameter will not be very accurate. For a single pipe it would require a 3D flow analysis. 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Nitharshan, 
 Because the water is flowing in the direction of the negative x-axis .... 
 With kind regards, 
 Dennis Waterman