Groundwater Seepage Analysis

1.0 Introduction

This tutorial introduces groundwater seepage analysis in RS3. The model used in this tutorial consists of a basic, steady-state groundwater seepage analysis. In the tutorial, we will cover adding groundwater boundary conditions as well as ponded water loading. This tutorial will focus on the results of the analysis; after a groundwater seepage analysis is computed, the results (pore pressures) are compared in Slide3, RS2 and RS3.

2.0 Import Slide3 to RS3 for Pore Water Pressure Analysis

We will be performing a groundwater seepage analysis using RS3. RS3 uses Finite Element Methods to run seepage analysis using groundwater boundary conditions which is different from Slide3. Here we will demonstrate how this can be done with the geometry created from Slide3.

First, we will import Slide3 model to RS3.

1. Select: File > Import > Import Slide3 Project
2. Select Steady state seepage_Slide3.slide3m2 within the Groundwater Seepage analysis tutorial folder. Click Open.
3. De-select Generate Mesh and set Auto Restraints to None.
   
4. Click OK.
5. Go to Project Settings by selecting Analysis > Project Settings
6. Under the Groundwater tab, change the method to Steady State as shown below:
   
7. Under the Shear Strength Reduction tab, when a model is imported from Slide3 the Determine Strength Reduction Factor check box is on automatically. If a SSR analysis is not desired turn the Determine Strength Reduction Factor check box off.
   
   Use the default values for the settings, and then select OK.

3.0 Applying Groundwater Boundary Conditions

3.1 APPLYING GROUNDWATER BOUNDARY CONDITIONS

We will now assign ground water boundary condition to the model.

1. Select the Groundwater workflow tab
2. Select: Groundwater > Define Groundwater Boundary Conditions
3. Add two more layers of groundwater boundary condition by selecting add button in left bottom side of the dialog.
4. For Groundwater BC 1: select Type = Total Head (H), and enter Total Head Value (m) = 31.8 as shown below.
   
5. For Groundwater BC 2: select Type = Total Head (H), and enter Total Head Value (m) = 26 as shown below.
   
6. For Groundwater BC 3: select Type = Unknown (P=0 or Q=0).
   
7. Click OK to save and close the dialog. Now we will assign these boundary conditions to the geometry.
8. Select the top surface and the top portion of the slope of the geometry.
   
9. Then select Groundwater > Add Groundwater Boundary Conditions. Use the dropdown to assign Groundwater BC 3 to those surfaces.
   
10. Click OK. You should see the following groundwater boundary condition as shown below:
    
11. Now, select the back end of the surface (surface on a higher slope)
    
12. Then select Groundwater > Add Groundwater Boundary Condition. Under the drop-down menu for the Boundary Condition, select Groundwater BC1.
    
13. Click OK. The model should look as the following:
    
14. Select three surfaces at the front (lower end) and front surface as shown in the figure below:
    
15. Then select Groundwater > Add Groundwater Boundary Condition. Under the drop-down menu for the boundary condition, select Groundwater BC2.
    
16. Click OK.

The model should look as the following:

3.2 APPLYING LOAD

1. Next, go to the Loads workflow tab . Ponded water needs to be applied as a load to account for the weight of water.
2. Select two surfaces at the front (lower end) as shown in the figure below:
   
3. Then select Loading > Add Loads to Selected.
   
4. Under the drop-down menu for the load type, select Ponded Water Load. Enter Total Head = Constant and 26 (m).
   
5. Click OK.
   

4.0 Applying Boundary Conditions

1. Go to the Restraints workflow tab
2. Select: Restraints > Auto Restrain (Surface)

The model should look like this.

5.0 Mesh

1. Go to the Mesh workflow tab
2. Select: Mesh > Mesh Settings
3. Keep the mesh setting to the pre-defined values.
   
4. Select Mesh . Then click OK. You should see the following:

6.0 Compute for Seepage Analysis

1. Next, we move to Compute workflow tab . From this tab, we can compute the results of our model.
2. First, save your model: File > Save As.
3. Next, you need to save the compute file: File > Save Compute File. You are now ready to compute the results.
4. Select: Compute > Compute

RS3 will run the analysis with SRF. This will allow us to analyze slope stability, as well as groundwater seepage analysis in RS3 for comparison with Slide3.

7.0 Results

1. Go to the Results workflow tab
   
2. Select: Interpret > Show Data on Plane > XZ.
3. Use the default settings.
   
4. Select Add.
5. For comparison with Slide3, RS2 and RS3 results, we will choose Pore Water Pressure. Go to the Legend, and under Solids, select Total Pore Water Pressure.
   
6. Click Contour Options
7. Under the contour range section, select 0 to 144 for the Custom Range as also shown below. Also, select Interval Count = 24.
   
8. Click OK to save and close the dialog.

Using the analysis results from RS3, we will now export the water pressure grid from RS3 to Slide3.

1. Select: File > Export > Export Pore Water Pressure to Slide3
2. Save the file with title of the project (pore water pressure grid slide3.pwp3). We will import this file to Slide3.

We can compare the result from RS2 with same setting. We can see that the two models resemble similarities with the result from pore water pressure analysis in the side section view as shown below. The RS2 model can be found from RS2 Tutorial - Finite Element Groundwater Seepage.