Scheduled Element State (SES) and Scheduled Head Boundary (SHB) Ditch Example
Description
A simple 3D cross section model of a ditch demonstrates the use of Scheduled Element State (SES) and Scheduled Head Boundary (SHB) modules. Using SES, the excavation and backfilling of a ditch is simulated by automatically inactivating (excavation) and activating (backfilling) elements. Using SHB to simulated dewatering the ditch, keep it dry for a while, and then allow it to flood after dewatering stops: four different SHB boundary condition (BC) node definition methods are combined with standard FEFLOW Dirichlet (fixed head) BCs. Some background SHB and FEFLOW BC definitions are unrelated to the ditch specifically, but demonstrate the modules use with features that FFTools does not control.
The model has 20 horizontal layers, each 2.5m thick. There are 50 nodes per slice and 64 elements per layer. Every element has the same dimensions. There is an upper unconfined aquifer (layers 1-16, 10m - 50m elevation), a leaky confining layer (layers 17-18, 5m - 10m elevation), and a lower semi-confined aquifer (layers 19-20, 0m - 5m elevation). Initial heads in the upper aquifer are set to 50m. Initial heads in the lower aquifer are set to 75m. There is no model recharge. Hydraulic conductivities ranges from 0.1 m/d in the confining layer to 20 m/d in the upper unconfined aquifer.
- 3D cross-section on model showing K distribution, mesh, and BCs.
In the model, five sets of Dirichlet (fixed-head) BC nodes are used:
- The "FEFLOW Fixed-Head" nodes, specified using FEFLOW and not SHB, are FH nodes are set at upper west side of the model, with FH set at 50m for the duration of the model run.
- The "SHB SURF_NODE" nodes define the excavated ditch in the center of the model (NOTE: elements are not inactivated but could be by using SES). The ditch is excavated from a depth of 44m to 20m over the first 50 days of the model run. The ditch is kept dry for the next 50 days, and then the SHB-controlled BC's are turned off
- The "SHB GROUP (V)" nodes are defined on the east side of the model using SHB's option "V" input. BC heads drop from 41m to 36m over 150 days.
- The "SHB BY_NODE" nodes control FH's at the west end of the confined aquifer (under the purple confining bed). FH's increase from 75m to 100m over 150 days.
- The "SHB GROUP (XML)" nodes FH's at the east end of the confined aquifer, decreasing linearly from 75m to 50m over 150 days.
Inactivating the SES elements follows a schedule similar to the SHB schedule. As material is excavated, which is represented by inactivation of elements (red elements in the figure below), the water level is held (fixed) at the active bottom of the excavation.
- 3D cross-section of the example model showing elements which will be inactivated by SES (red elements) during the model run:
Example Input Files
SES setup input (examples/import+export/ex.ditch.ses):
SES
GROUP
#1,1,0,0 XML,[ModelIEPath]DitchElements.xml
0.0,50.0,44,19.999
#2,1,1,0,0.00,3,1.00
XML,[ModelIEPath]DitchElements.xml
100.0,102.0,19.999,44.0
SHB setup input (examples/import+export/ex.ditch.shb):
SHB
BY_NODE,F,0.00
901,0,150,75,100,0,0
935,0,150,75,100,0,0
951,0,150,75,100,0,0
985,0,150,75,100,0,0
1001,0,150,75,100,0,0
1035,0,150,75,100,0,0
SURF,F,0.00
3,0,50,44,20,T,1,0
14,0,50,44,20,T,1,0
15,0,50,44,20,T,1,0
32,0,50,44,20,T,1,0
33,0,50,44,20,T,1,0
34,0,50,44,20,T,1,0
49,0,50,44,20,T,1,0
50,0,50,44,20,T,1,0
3,50,100,20,20,T,1,0
14,50,100,20,20,T,1,0
15,50,100,20,20,T,1,0
32,50,100,20,20,T,1,0
33,50,100,20,20,T,1,0
34,50,100,20,20,T,1,0
49,50,100,20,20,T,1,0
50,50,100,20,20,T,1,0
GROUP
#1,0,0.0,T,0.99,0,0
V,202,221,302,321
0,150,41,36
150,1500,36,36
#2,0,0.0,F,0.0,0,0
XML,[ModelIEPath]\ex4.ConfinedBCNodes.xml
0,150,75,50
Example FEM File
- examples/femdata/ex.ditch.fem
Results
Results at several times are shown below (elements inactivated by SES highlighed):
- Hydraulic-head equipotentials (black contours) and the zero-pressure contour (white, water table) at 20 days (note that equipotentials do not cross into elements inactivated by SES)
- Head and water table at 49 days
- Head and water table at 100.3 days
- Head and water table at 150 days (note that the elements representing the ditch have been re-activated by SES to simulate its backfilled condition)
See also: Tailing Impoundment and Mine Pit example