We have a simple question regarding groundwater flow analysis using drains.
We are using Plaxis-2D flow only steady state, with drains (similar to a trench drain) about 1m high to analyze and control groundwater flow below around a structure . We want to confirm the flow interpretation from the analysis. When we look at the drains and flow we see what we expected, however, when we go to look at the details of the drain discharge we see each drain has 5 nodes and each node has the same flow. If we are looking for the total flow, do we add these values or is this the total flow for the drain? Any assistance would be greatly appreciated.
Dear Geoffrey,
There are two possibilities to model drains in PLAXIS: by using the drain element or by using an interface with a hydraulic conductivity.
The drain element is just an internal boundary condition where the groundwater head is fixed to a user-defined value. In this case it is not possible to get the discharge in the drain. The drain consists of 1 single row of nodes and water flows from all sides to that node....which leaves a very low flow in the nodes itself. If you want to determine the approximate discharge for a drain element, the best option would be to draw cross sections on either side of the drain (very close to the drain) and check the discharge through those cross sections. Since that is the discharge flowing towards the drain, the discharges of the both cross sections give an idea of the expected discharge of the drain.
The alternative is to use an interface element. In the (soil) parameter set of the interface it's possible to specify the hydraulic conductivity of the drain. When doing so, one can double click on the drain in the output program and check the discharge in the interface (Q).
With kind regards,
Dennis Waterman