Pile Group Tutorial – Example 1: Battered Pile Group in Clay

In this tutorial example, the use of the PileGroup program is demonstrated for analysing a pile group in clay, including battered piles. The example covers the overall workflow - from creating the pile group model to defining soil conditions, applying loads to the pile cap, and reviewing the analysis results.

Objectives:

1. Start a new project

2. Define soil material parameters with nonlinear p-y curves

3. Create the soil stratigraphy

4. Define water table

5. Define pile sections

6. Create piles within the pile group

7. Define loads on the pile cap

8. Define load combinations

9. Define pile group effects

10. Run pile group analysis

11. View pile group analysis results

1.0 Starting a new project

1)    Start PileGroup by double-clicking the icon of the program.

The Quick Start dialog box appears as shown in Figure 1-1, in which you can create a new project or open an existing project.

Figure 1-1 Start-up dialog - PileGroup

2)    Click Start a new project button

A default pile group analysis project with 4 piles will be created as shown in the figure below and the users can start creating the pile group analysis inputs by changing the basic parameters.

Figure 1-2 Main input window

3)    Save the project

Upon creating a new project in Step 2, the program does not automatically generate a project file name. It is advisable for users to save the project using a file name of their own choosing before they continue further.

2.0 Creating soil material parameters

This tutorial example involves a pile group consisting of six numbers of 500 mm diameter driven reinforced concrete piles of 30 m long through the soft clay layers. The ground profile is shown in Table 1-1 together with P-Y models and the detailed strength parameters for different soil layers are shown in Table 1-2. Figure 1-3 shows the ground profile with the pile length and loading conditions for this example.

Figure 1-3 Ground profile with pile length and loading information on XY plane

Note that the cantilever portion of the pile group is modelled with using a layer with “Null” material type in PileGroup program. The water table is shown as a thicker blue line in the ground profile as shown in Figure 1-3.

To create a material set for first clay layer, follow those steps:

• Open the P-Y Curve Material Sets window by clicking the Define Soil Materials with P-Y Curves button  in the top toolbar or clicking the Soil Materials with P-Y Curves submenu under the Define main menu.

• The Material sets window pops up as shown in the figure below. This window contains two existing material inputs by default. You can delete or edit these default inputs as needed.

Figure 1-4 P-y curve material sets window

• Click the New button at the left side of the P-Y Curve Material Sets window.

  
  

  A new material set will be added to the list as shown in the figure below. A default name will be assigned to this material set.

Figure 1-5 Create new material set

• Double-click “New Material 3” from the material set list or single-click it and select Edit to open the P-y Curve Material Input window, as shown below.

  
  

  Note that a default colour will be assigned to this material set. The default material type is “Null” and the default P-Y curve model is “Null Material”. This special material set is usually used to model the ground where no lateral resistance is present.

Figure 1-6 Create null material

• Click the dropdown menu next to Material Type and select “cohesive” option.

• Click the dropdown menu next to P-Y Curve Model and select “3. Matlock Soft Clay” option.

• Enter the proper values in the General Properties, Basic Soil Properties and Advanced Properties for Matlock Soft Clay boxes according to the material properties as shown in Table 1-2.

• Enter “Clay 1” next to Material Name to change the default name of “New Material 3”.

• Click OK in the Material Input window or X icon at the upper right corner of the window to close the p-y curve parameter input.

Figure 1-7 Create “Clay 1” material set

• Single-click “Clay 1” material set from the list and click the Color button at the right side of the P-Y Curve Material Set window to change the color for this material set.

  
  

  The default green color for this material set is changed to yellow color from this step as shown in the Figure 1-8. Note that PileGroup program will generate default color for the new material set and this can be changed if required.

  
  

The remaining soil material sets of “Clay 2”, “Clay 3” and “Null” can be created in the same way as described above. Note that “Null” material set is defined in this example to model the free length portion of piles.

Figure 1-8 Change material set colour

3.0 Creating the soil layers

To create the soil layers of the subsurface foundation, follow the steps below:

• Open the Define Soil Layers window by clicking the Define Soil Layers button  in the top toolbar or clicking the Define Soil Layers submenu under the Define main menu.

Figure 1-9 Define soil layers window

• The Define Soil Layers window pops up as shown in the figure below. This window contains two existing soil layer inputs by default. You can add, delete or edit these default inputs as needed.

• Select the second soil layer (the second row) by clicking any cell at the second row.

• Delete the existing second soil layer by clicking the Delete button on the right side of the input table.

  The current soil layer input window is shown in the figure below.

Figure 1-10 Current define soil layers window after deleting the existing second layer

• Select “Null” material from the dropdown menu under the Material Name column in the first row.

• Enter 0 for the top level of the first soil layer under the Top column. Pressing the Enter key on the keyboard or clicking the Apply button on the right side of the input table to save the input.

• Enter -3.0 for the bottom level of the first soil layer under the Bottom column. Pressing the Enter key on the keyboard or clicking the Apply button on the right side of the input table to save the input.

• Create the second soil layer by clicking the Add button on the right side of the input table. By default, the soil material type for the second soil layer is the same as the first soil layer.

• Select “Clay 1” material from the dropdown menu under the Material Name column in the second row. The top level for this layer will be the same as the bottom level of the layer above and it cannot be changed by the users.

• Enter -5.5 for the bottom level of the second soil layer under the Bottom column. Pressing the Enter key on the keyboard or clicking the Apply button on the right side of the input table to save the input.

• Create the third soil layer by clicking the Add button on the right side of the input table. By default, the soil material type for this soil layer is the same as the soil layer above.

• Select “Clay 2” material from the dropdown menu under the Material Name column in the third row. The top level for this layer will be the same as the bottom level of the layer above and it cannot be changed by the users.

• Enter -27.0 for the bottom level of the third soil layer under the Bottom column.

• Create the fourth soil layer by clicking the Add button on the right side of the input table. By default, the soil material type for this soil layer is the same as the soil layer above.

• Select “Clay 3” material from the dropdown menu under the Material Name column in the third row. The top level for this layer will be the same as the bottom level of the layer above and it cannot be changed by the users.

• Enter -37.0 for the bottom level of the fourth soil layer under the Bottom column.

• Select “Soil-layering Correction for All Layers (Default)” from the dropdown menu for Soil-Layering Correction Option below the soil layer input table.

• Enter 0 for the input field of Depth of water table below pile head (m).

  The soil layer input window with all the inputs above is shown in the figure below.

Figure 1-11 Soil layer inputs

4.0 Creating the pile section

Pile sections must be created before entering detailed inputs like positions and lengths for the pile group. To create a pile section, follow these steps:

• Open the Define Section window by clicking the Define Section button  in the top toolbar while select the pile section from the list box under Pile Section Sub-window on the left side of the main input window or clicking the Edit button on the right side of the Pile Section Sub-window.

  The figure below shows the pile section sub-window on the left side of the main input window. By default, there is one existing pile section with the name of “Pile Section 1”. This existing pile section can be modified by the users.

Figure 1-12 Pile section sub-window

• The Define Section window pops up as shown in the figure below.

• Select “Circular” from the dropdown menu under Section Type.

• Enter 0.5 m for Diameter, D under Section Dimension.

• Enter 35 GPa for Young’s Modulus, E and 0.2 for Poisson’s Ratio, ν under Material Properties.

• Enter “Pile Section 1” under Pile Section Name.

• Click OK button to save the inputs and close the input window.

Figure 1-13 Section parameter input window

5.0 Creating the piles within the pile group

To create the piles within the pile group, follow these steps:

• Open the Pile Group – Layout Table Input window by clicking the Define Pile Length and Layout button  in the top toolbar or clicking the Pile Length and Layout submenu under the Define main menu.

• By default, there are 4 existing piles pre-defined in the group. Those existing piles can be deleted or modified to suit the actual analysis case. Note that the minimum number of piles with the group is 2. This means that the number of piles cannot be reduced to a number less than 2.

• For this tutorial example, there are 6 piles within the group with two battered piles.

• Click Add button at the bottom of the window to add one pile into the group. A new pile (5^th pile) with the default position and length will be added to the group. The total number of piles is 5 after this.

• Click Add button at the bottom of the window to add one pile into the group. A new pile (6^th pile) with the default position and length will be added to the group. The total number of piles is 6 after this.

• Enter the proper values in the layout input table for each pile. Those values include X and Z coordinates, lengths and batter values for all the piles.

  The pile length and layout input window with all the inputs above is shown in the figure below.

Figure 1-14 Pie length and layout input window

• Click OK button to save the inputs and close the input window.

• A three-dimensional view for the whole pile group is updated in the Model Input window as shown in the figure below.

Figure 1-15 Three-dimensional view of pile group

6.0 Creating the loads on the pile cap

To create the loads on the pile cap, follow these steps:

• Click the Load button in the tabbed window panel located under the top toolbar on the left side of the main input window to open the Load tab.

  By default, the first load case will be automatically selected

• Click the Edit button on the right side of the tab window to open the Pile Cap Loads window.

  The Pile Cap Loads window pops up and is shown in the figure below.

Figure 1-16 Pile cap load input window

• Alternatively, open the Pile Cap Loads window by clicking the Define Pile Cap Loads button  in the top toolbar or clicking the Pile Cap Loads submenu under the Define main menu. This will open the Pile Cap Loads window corresponding to the selected load case from the Load tab window.

• Enter -200 for Axial Load, Fy (kN).

• Enter 1000 for Shear Load, Fx (kN).

• Enter 500 for Shear Load, Fz (kN).

• Keep the default Pile Cap Load Name as “Load Case 1”.

• Enter 0 for the other input fields.

• Pressing the Enter key on the keyboard or clicking the Apply button on the bottom of the input window to save the input.

• Click OK button to save the inputs and close the input window.

  The pile cap load input window with all the inputs above is shown in the figure below.

Figure 1-17 Pile cap load input

7.0 Creating the load combinations

All the analyses in the PileGroup program are carried out using the load combinations which are based on the input pile cap loads. To create the load combinations on the pile cap, follow these steps:

• Open the Load Combination window by clicking the Define Load Combination button  in the top toolbar or clicking the Load Combination submenu under the Define main menu.

  The Load Combination window pops up and is shown in the figure below.

Figure 1-18 Load combination input window

• Enter “Load Combination 1” under the column of Name for the first row.

• Enter 1 under the column of Cyclic Load Number for the first row.

• Enter 1.0 under the column of “Load Case 1” for the first row.

• Click OK button to save the inputs and close the input window.

8.0 Define pile group effect

To define pile group effect, follow these steps:

• Open the Pile Group Effects window by clicking the Define Pile Group Effects button  in the top toolbar or clicking the Pile Group Effects submenu under the Define main menu.

Figure 1-19 Pile group effects input window

• Select the option of “Automatically generated P-Multipliers for pile group effect (Reese & Van Impe, 2001)”.

• Click OK button to save the inputs and close the input window.

9.0 Run the pile group analysis

To run the pile group analysis, follow these steps:

• Open the Run Analysis window by clicking the Run Analysis button  in the top toolbar or clicking the Run Analysis submenu under the Analyze main menu.

Figure 1-20 PileGroup solver window

• Click OK button to close the PileGroup Solver window and open the PileGroup Output window to view the analysis results.

Figure 1-21 PileGroup output window

10.0 View the pile group analysis results

In the PileGroup Output window as shown in the figure above, the deformations and forces for all the piles within the group can be viewed. The calculated results are also available in tabular form. To check the deformations and forces, follow these steps:

• Select all the piles from the Piles list window on the left upper side of the output window.

• Select “Load Combination 1” from the Load Combo list window on the left bottom side of the output window.

• Click Global Displacement, Ux sub-menu under the Deformations main menu of the output program to view the global displacement in the X direction. Note that all the deformations within the PileGroup program are reported in both global and local coordination.

Figure 1-22 Global displacement Ux results

• Click Axial Force, F2 sub-menu under the Forces main menu of the output program to view the axial forces along the piles in the local axis 2 direction. Note that all the forces within the PileGroup program are reported in the local coordination for the structure.

Figure 1-23 Axial force F2 results

• Click Bending Moment, M3 sub-menu under the Forces main menu of the output program to view the bending moments along the piles in the local axis 3 direction. Note that all the forces within the PileGroup program are reported in the local coordination for the structure.

Figure 1-24 Bending moment M3 results