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Piled Raft Foundation

1.0 Introduction

This tutorial demonstrates some of the support systems available in RS3. This tutorial models a square shaped piled raft foundation.

All tutorial files installed with RS3 can be accessed by selecting File > Recent > Tutorials Folder from the RS3 main menu. The starting file can be found in Piled Raft Foundation - starting file.rs3v3. The finished product of this tutorial can be found in the Piled Raft Foundation.rs3v3.

2.0 Starting the Model

  1. Select File > Recent > Tutorials Folder from the RS3 main menu.
  2. Open the starting file Piled Raft Foundation - starting file.rs3v3.

The model should have initial project settings already defined for the user.

  1. Select: Analysis > Project Setting Project Settings icon
  2. Check the following inputs:
    • In the [Stages] tab:
      • Number of Stages = 2
        • Stage 1 Name = Initial
        • Stage 2 Name = Piled raft foundation

    Project Settings dialog in the Stages Tab

    • In the [Groundwater] tab:
      • Method = Phreatic Surfaces,
      • Pore Fluid Unit Weight = 9.81 kN/m3

    Project Settings dialog Groundwater Tab

  3. Click OK to close the dialog.

3.0 Defining the Materials

  1. Ensure the current workflow tab is set to Geology geology workflow tab

The model should have the Clay layer already defined for the user.

  1. Select: Materials > Define Materials Define Materials icon
  2. Check that you have the following inputs:
    • In the [Initial Conditions] tab:
      • Initial Element Loading = Field Stress & Body Force
      • Unit Weight = 18 kN/m3

    Define Materials dialog

    • In the [Strength] tab:
      • Material Type = Plastic,
      • Peak Cohesion = 4 kPa,
      • Peak Friction Angle = 30°
      • Peak Tensile Strength = 0 kPa,
      • Residual Cohesion = 4 kPa,
      • Residual Friction Angle = 30°
      • Residual Tensile Strength = 0 kPa,
      • Dilation Angle =

    Define Materials dialog: Strength Tab for Clay

    • In the [Stiffness] tab:
      • Type = Linear Isotropic,
      • Use Unloading Condition = No,
      • Poisson's Ratio = 0.35,
      • Young's Modulus = 5000 kPa,
      • Use Residual Young's Modulus = No

    Define Materials dialog: Stiffness Tab for Clay

  3. Click OK to close the dialog.

4.0 Creating Geometry

  1. Select: Geometry > Create External Box.
  2. A Create External dialog will open. Enter the following:
    • First Corner (x, y, z) = (0, -160, 0),
    • Second Corner (x, y, z) = (160, 10, -40)

    Create External Box dialog

  3. Click OK.
  4. Select: Geometry > 3D Primitive Geometry > Box
  5. Enter the following:
    • Defined By = 2 Corners,
    • Role = Geology,
    • First Corner (x, y, z) = (72, -88, 0),
    • Second Corner (x, y, z) = (88, -72, -3)

    Create Primitive 3D Box dialog

  6. Click OK.
  7. Select: Geometry > 3D Boolean > Divide All Geometry Divide all geometry icon
  8. We will be using all default values.
    Divide All Parameters dialog
  9. Click OK.

5.0 Adding Supports

5.1 Adding Liners

  1. Select the Support workflow tab support workflow tab at the top of the screen.

Before adding the liner, we must select the faces that we want the liner to be assigned to.

  1. Select: Edit > Selection Mode > Faces Selection Faces Selection icon
  2. Select the top face of the smaller box either using the XY-plane modeler view or the 3D modeler view. When selected the 3D modeler view should look similar to the following:
    3D model view of the top face selected
  3. Select: Support > Liners > Add Lining Add Lining icon
  4. Press the pencil iconPencil icon beside Lining 1 to open the Liner Composition dialog.
    Lining Composition dialog
  5. Navigate to the last column (Edit) and select the pencil iconPencil icon to open the Liner Properties dialog.
  6. Enter the following values and leave all else default:
  7. Name

    Young's Modulus (kPa)

    Poisson's ratio

    Thickness (m)

    Include Weight in Analysis

    Unit Weight (kN/m3)

    Liner 1

    Raft Foundation






    Liner Properties dialog

  8. Click OK to save and exit the liner properties dialog, then click OK to exit the lining composition dialog.
  9. In the Add Lining dialog, set Install at stage = Piled raft foundation.
    Add Lining dialog
  10. Click OK.

5.2 Adding Piles

In RS3, a pile is simulated as a beam. Therefore, beam properties are used when defining pile properties, such as Young’s Modulus, Poisson’s ratio and the pile dimensions. Material properties distinct for a pile, such as the soil-pile interaction, are found in the Pile Properties dialog.
  1. Select: Support > Beams > Define Beams.
  2. Enter the following values for the beam parameters:
  3. Name

    Young's Modulus (kPa)

    Poisson's ratio

    Area (m2)

    I-min (m4)

    I-max (m4)

    Include Weight in Analysis

    Unit Weight (kN/m3)

    Beam 1

    Beam 1








  4. Leave all other values as default.
  5. Beam Properties dialog

  6. Click OK to save and close the Beam Properties dialog.
  7. Now we must select the face that we want the piles to be assigned to.

  8. Select: Edit > Selection Mode > Faces Selection Face selection
  9. Select the top face of the foundation.
  10. Select: Support > Piles or Forepoles > Add Piles or Forepoles Add Piles or Forepoles icon
  11. Select the pencil icon Pencil icon located next to Pile 1 to open the Pile/Forepole Properties dialog.
  12. Enter the following parameter inputs:
    • Set Connection Type = Rigid,
    • Lining Connection Type = All Liners,
    • Shear Stiffness = 5000 kPa/m,
    • Normal Stiffness = 50000 kPa/m,
    • Base Normal Stiffness = 50000 kN/m,
    • Base Force Resistance = 100 kN,
    • Skin Resistance = C and phi,
    • Perimeter = 1.1 m,
    • Cohesion = 3.2 kN/m,
    • Residual Cohesion = 3.2 kN/m,
    • Friction Angle = 24.79°,
    • Residual Friction Angle = 24.79°,
  13. Leave all other values as default. Click OK.
    Pile/Forepole Properties dialog
  14. Now that we’ve returned to the Add Piles/Forepoles dialog, enter the following:
    • Flip Direction = Active,
    • Length = 20 m,
    • Install at stage = Piled Raft Foundation,
    • Application = Pile Pattern,
    • Primary Spacing = 4,
    • Secondary Spacing = 4,
    • Primary Offset = 2,
    • Secondary Offset = 2
  15. Make sure the Secondary Path (Optional) is enabled.
    Add Pile/Forepoles dialog
  16. Do not select Done. We still need to define the Start and End points of our pile pattern paths.
  17. You must keep the Add Piles/Forepoles dialog open while you use any selection tools to define the Start and End points of a path.
  18. In the XY plane viewport select the top-left vertex of the selected face, followed by the top-right vertex. At this point we have defined the Primary Path. Subsequently, we can set the Secondary Path by selecting the top-left vertex again, followed by the bottom-left vertex.
  19. The order of vertices selected does not matter in this tutorial as the foundation is square. You can choose any vertices to start, but the following sequence should be the same.

    You will see the coordinates are now being displayed for the Primary Path and Secondary Path.

    Add Pile/Forepoles dialog after pile pattern paths entered

    Alternatively, we could have entered the coordinates manually instead of using the vertices selection tool.

  20. Select Preview Pattern to ensure everything was entered correctly. The model should look like the following:
    3D model view of piles
  21. If everything looks correct, select Add to add the piles to the model. Click Done to close the dialog.
If you do not see the piles after selecting Done make sure you are in the Piled Raft Foundation stage.

6.0 Groundwater Conditions

  1. Select the Groundwater workflow tab groundwater workflow tab at the top of the screen.
  2. Select: Groundwater > Add Water by Location Add water by location icon
  3. In the Water by Location dialog, enter the four points (X, Y, Elevation):
    1. (-10, -170, -3)
    2. (170, -170, -3)
    3. (170, 20, -3)
    4. (-10, 20, -3)
  4. Click OK.
  5. Water By location dialog

    In the visibility pane you will notice that Water Surface 1 has a red “X” symbol. This is because the water condition in the material is undefined.
  6. Select: Materials > Define Materials Materials icon
  7. Navigate to the Clay's [Hydraulics] tab and change the Default Water Condition = Water Surface 1 and leave all other settings as default.
  8. Click OK. The red "X" symbol should now be gone, indicating that the water condition has been defined.

7.0 Adding Stress Loading

7.1 Adding Field Stress

  1. Select the Loads workflow tab Loads workflow tab
  2. Select: Loading > Field Stress Field Stress icon
  3. Make sure that the Field Stress Type is set to Gravity.
    Field Stress dialog
  4. Click OK to close.

7.2 Loading the Raft Foundation

Now we will place a surface load on the top face of the foundation.

  1. Select the face as we did in Section 5.1.
  2. Select: Loading > Add Loads to Selected
    Apply Load to Selected dialog
  3. Enter the following:
    • Load Type = Uniform Load,
    • Magnitude = 30 kN/m2, and
    • Install at stage = Piled raft foundation
  4. All other settings should be left as default. Click OK to save and close the dialog.

8.0 Setting Boundary Conditions

  1. Move to the Restraints workflow tab Restraints workflow tab to assign restraints to the external boundary of the model.
  2. RS3 has a built-in “Auto Restrain” tool for use on underground models.
  3. Select: Restraints > Auto Restrain (Surface) Auto Restrain (Surface) icon

3D model view showing restraints

This completes the construction of the model's geometry.

9.0 Meshing

  1. Next, we move to the Mesh workflow tab Mesh workflow tab
  2. Select: Mesh > Mesh

Your model should look like the following:

3D model view with mesh

10.0 Computing Results

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

Compute dialog

11.0 Interpreting Results

  1. Next we move to Results workflow tab Results tab
  2. First, refresh the results. Select Interpret > Refresh All Results Refresh All Results icon
  3. By default the Element is set to Solids and Data Type = Sigma 1 Effective.

Let’s turn on the exterior contours so we can see results:

  1. Select: Interpret > Show Exterior Contour.

We will also include a contour plane in the center of the model.

  1. Select: Interpret > Show data on plane > XZ Plane XZ Plane icon
  2. Under Plane Definition, set the Origin (x,y,z) = (80, -80, -20) and leave the plane orientation normal vector as default.
    Contour Plane dialog
  3. Select Add and then Close.
  4. In the Legend bar on the right, change Data Type = Total Displacement.
To see the contour on the XZ Plane, click the "eye" icon next to Exterior Contour in the visibility pane to turn off the 3D Contour.

Total Displacement Exterior Contour Plane (Stage 2)

3D model view of exterior contour showing total displacement
Legend bar showing total displacement

Total Displacement Contour Plane (Stage 2)

Contour Plane showing Total Displacement (Stage 2)

The highest displacement, as expected, is in the center of the loaded foundation.

  1. Next we will change Element = Liners and Data Type = Moment Y

The internal moment (about the Y direction) of the liner is shown below:

Moment Y in Liner

  1. Lastly, we will change Element = Beams & Piles and change the Data Type = Axial Force.

The axial force in the piles (at Stage 2) is shown below:

Axial Force in Piles (Stage 2)

The axial force, as expected, decreases with depth into the pile.

Other results are available to view as well. This concludes the tutorial.

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