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Bored Pile Capacity

1.0 Introduction

This tutorial demonstrates how to analyze a single bored pile in multiple soil layers under various conditions in RSPile.

Topics Covered in this Tutorial:

  • Multi-layer model
  • Soil types for bored piles
  • Pile properties
  • Export data to Excel
  • Report generator

Finished Product:

The finished product of this tutorial can be found in the Tutorial 8 – Bored Pile Capacity.rspile2 data file. All tutorial files installed with RSPile can be accessed by selecting File > Recent Folders > Tutorials Folder from the RSPile main menu.

2.0 Model

When the RSPile program is started, a new blank document is already opened, allowing you begin creating a model immediately.

Note on sign convention: In RSPile, the default ground surface is at depth = 0, depth is positive downwards, and compressive stress is positive.

2.1 PROJECT SETTINGS

The Project Settings is where you can change the analysis type, tolerance, number of iterations allowed, and the number of pile segments to be used in the analysis.

To open the Project Settings:

  1. Select Analysis > Project Settings (CTRL + J) or click on the Project Settings icon Project Settings icon in the toolbar.
  2. Project Settings Dialog

  3. Set the Pile Analysis Type to Carrying Capacity > Bored.
  4. Click on Advanced Analysis Settings and change Pile Depth Increment (m) to 1.
  5. Click OK to close the dialog.

Tip: The default units for RSPile are metric. To change this setting, select Analysis > Units.

2.2 GROUNDWATER TABLE

  1. Select Analysis > Groundwater or click on the Set Groundwater Icon Set Groundwater icon in the toolbar.

Groundwater Settings Dialog

  1. Check the Enable Groundwater box.
  2. Specify a Ground Water Elevation (m) of -2.
  3. Click OK to close the dialog.

2.3 SOIL PROPERTIES

  1. Select Soils > Define Soil Properties (CTRL + 8) or click on the Define Soil Properties Dialog Define Soil Properties icon in the toolbar.
  2. In this dialog you can define the properties related to the Q-z, t-z, and p-y curves. There is a tab for each analysis type (Axial, Lateral, Driven, Bored) as well as for datum dependency. The Datum Dependency tab allows users to control linearly varying properties. While you can click through all tabs, you will only be able to edit material information that is relevant to the Pile Analysis Type selected in the Project Settings.

  3. Define the material properties as shown below:
  4. Soil Property 1:

    Soil properties - sand

    • Name = Sand
    • Unit Weight = 16 kN/m3
    • Sat. Unit Weight = 16 kN/m3
    • Soil Type = Cohesionless
    • Internal Friction Angle = Use SPT “N” Values
  5. Click on SPT Table.
  6. Enter the following data:
  7. #

    Depth (m)

    SPT N

    1

    0

    25

    2

    1

    25

    3

    2

    25

    4

    3

    25

    5

    4

    25

    6

    5

    25

  8. Click OK to close the dialog.
  9. Soil Property 2:

    Soil Property 2

    • Name = Rock
    • Unit Weight = 20 kN/m3
    • Sat. Unit Weight = 20 kN/m3
    • Soil Type = Weak Rock
    • Unconfined Compressive Strength = 2,000 MPa
    • Skin Friction Limit = 10,000 kPa
    • End Bearing Limit = 100,000 kPa
    • Skin Resistance
      • Method = William and Pells
      • Average RQD = 40%
    • Tip Resistance
      • Tomlinson and Woodward
      • Internal Friction angle = 27 degrees
  10. Click OK to close the dialog.

Note:

  • The end bearing limit for rock was set to 100,000kPa because rocks naturally have higher end bearing capacities. To obtain the actual end bearing capacity and not the capacity limited by the concrete cylinder strength, the limited was raised.
  • Unit weight and saturated unit weight are specified in the Soil Properties Dialogue here for both the sand and rock layer, but it will not affect the ultimate capacity calculations of the bored pile.
  • To consider skin resistance or end bearing losses, the reduction factors option can be turned on by checking the Reduction Factors box and specifying the associated Skin Resistance Loss (%) and/or End Bearing Loss (%).

2.4 SOIL LAYERS

RSPile supports multiple boreholes and non-horizontal soil strata. When multiple boreholes are defined, the program will automatically interpolate between the boreholes. In this tutorial, we will model horizontal soil strata with a single borehole. To begin:

  • Select Soils > Borehole Editor or click on Edit all Boreholes icon

    Edit All Boreholes icon in the toolbar.

  • The default soil column has a single layer and is located at (0, 0). To change the location, enter coordinates for X and Y. We will keep it (0,0) here.

  • Click on Insert Layer Below to add another layer below the first. The name column will fill in by soil property sequence.
  • Layers are defined by thickness by default, but may be defined by top and bottom elevation. This may be changed by toggling Define Layers by Thickness.

  • Specify the following layer thicknesses:
  • #

    Name

    Thickness

    Top Elevation

    Bottom Elevation

    1

    Sand

    5

    0

    -5

    2

    Rock

    20

    -5

    -25

  • Click OK to save your input and exit the dialog.
  • 2.5 OPTIONAL CAPACITY CONSIDERATIONS

    1. Select Analysis > Optional Capacity Consideration
    2. In the Optional Capacity Consideration dialog, you can define additional parameters that will affect the Ultimate Capacity Analysis.

      Optional Capacity Considerations - Soft Soil

      • Under the Design Type of Soft Compressible Soil, you can specify a Depth of Soft Compressible Soil at the top of the soil profile. The skin resistance for the layer will be neglected for ultimate capacity calculations.
      • The Consider Soil Resistance as Negative option will treat the skin resistance obtained for the layer as negative and is subtracted from the the total skin friction for ultimate capacity computations.
    3. Change the Design Type to Scourable Soil
    4. Optional Capacity Considerations - Scourable

      The design option of Scourable Soil allows for the consideration of short-term and/or long-term scour.

      • For short-term scour, the shear stress (skin friction) is reduced to zero until the scour consideration depth. Since no end bearing can be placed above this level, the end bearing is also reduced to zero.
      • For long-term scour, the effective overburden stress is reduced to zero until the scour consideration depth. This would imply that skin friction and end bearing are also reduced to zero.
      • If both short-term and long-term scour are being considered, RSPile will stack the effects of both scour types, with the long-term scour being considered first, followed by short-term scour considerations below in term of depth.
    5. We will keep the inputs for Optional Capacity Considerations as default. Click OK to close the dialog.
      1. 2.6 PILE PROPERTIES

        1. Select Piles > Pile Properties or click on the Define Pile Properties icon in the toolbar.
        2. Select Pile 1 (by default, the Bored tab will be selected) and enter the properties displayed below:
        3. Define Pile Properties Dialog

            • Pile Cross Section = Circular
            • Diameter of Pile (m) = 1.2
            • Concrete Cylinder Strength (kPa) = 40,000
        4. Click OK to close the dialog.

        2.7 ADDING A PILE

        The Add Single Pile dialog is where the pile elevation (depth of top of pile) and length are defined. To add a pile:

        1. Select Piles > Add Pile or click on the Add single pile Add Single Pile icon in the toolbar.
        2. Add Pile

        3. Click on the edit icon for the Pile Type and enter the Length (m) = 25 for Pile Type 1. Click OK to return to the Add Pile Dialog.
        4. Edit pile type dialog

        5. Under the Location field, deselect the Mouse selection button Mouse Selection icon to enter the (x,y) coordinates of the new single pile. We will keep the default location of (0,0).
        6. Keep the rest of the properties as default.
        7. Click OK to close the dialog.

        Notice that the soil column has now updated to reflect the strata.

        Borehole image

        3.0 Results

        Save and compute the file by clicking on the Calculator icon Compute icon in the toolbar.

        3.1 RESULT VISUALIZATION

        RSPile allows for the 3D visualization of results along the length of the pile. Use the Data Type dropdown to control what results are shown.

        Data type drop down

        Pile Results may be toggled on or off using the View Controls in the sidebar.

        View Controls

        3.2 CHARTS

        In the Plan View, right-click on the pile and select Graph Piles Graph Pile. The RSPile results section presents several default graphs and a table of results. You should see the following:

        Graphed piles

        Bored pile analysis generates three graphs:

        • Skin Friction Capacity vs. Depth
        • End Bearing Capacity vs. Depth
        • Ultimate Capacity vs. Depth

        3.3 EXPORT TO EXCEL

        From the Results tab you can export your data to Excel. To do so, click on the Export to Excel Export Data to Excel icon in the toolbar.

        Each data type is exported to its own Sheet in the Excel file.

        4.0 Report Generator

        The Report Generator presents a formatted summary of input data and analysis results. Go back to the model view and click on the Report Generator Report Generator icon in the toolbar. The Report Generator contains a summary of the model input data:

        • Project Summary
        • Soil Layers
        • Soil Properties
        • Pile Section Properties
        • Pile Types
        • Pile Settings

        The tool bar contains the Report Generator Controls, which allow you to select what information is displayed, and customize the appearance.

        Report Generator

        The data can be exported in a variety of ways: it may be manually copied, viewed in a browser, printed, or the information may be saved as a .pdf file. Prior to printing the file, results may be formatted to your specifications.

        Close the Report Generator window to return to the model view.

        5.0 Further Analysis

        From the computed results, it can be seen that there is a huge difference between the skin friction and end bearing capacities that of the sand and rock layers. Therefore, the ultimate capacities of the sand layer can be neglected.

        To do this, change the values of the Skin Friction Limit (kPa) and End Bearing Limit (kPa) of the sand layer in the Soil Properties dialogue to zero and recompute the results.

        You should get the following results:

        This concludes the Bored Pile Analysis Tutorial. You may now exit the RSPile program.

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