tutorial 30 analyzing pile resistance for slope stabilization using

Tutorial 30 Analyzing Pile Resistance for Slope

Stabilization using RSPile

• Complex pile models imported from RSPile

• Axial and lateral pile resistance functions

• Multiple material slope with weak layer

• Non-circular slip surface

Slide v.7.0 Tutorial Manual Tutorial 30: Analyzing Pile Resistance with RSPile

30 - 2

Introduction

This tutorial will demonstrate how to install a pile support into Slide, define the pile model in RSPile and compute the pile resistance functions against sliding to be used for slope stability analysis.

The finished product of this tutorial can be found in the Tutorial 30 Analyzing Pile Resistance using RSPile.slim data file. All tutorial files installed with Slide 7.0 can be accessed by selecting File > Recent Folders > Tutorials Folder from the Slide main menu.

Pile Resistance for Slope Stability Analysis

For slope stability analysis using limit equilibrium methods, the soil displacement moving along a slip surface against the pile can be used to compute the axial and lateral resistance against sliding through the principles of superposition. An assumed soil displacement is applied against the pile from the ground to the slip surface. The direction of the applied soil displacement is tangent to the slip surface at the intersection of the pile. The axial and lateral components of the applied displacement are used to compute the axial and lateral resistances separately. The resultant pile resistance force at the slip surface intersection is used to satisfy force equilibrium for the selected limit equilibrium method.

The pile internal axial force at the sliding depth in response to the applied axial soil displacement is the axial resistance against sliding for that particular slip surface. Similarly, the internal shear force at the sliding depth in response to the applied lateral soil displacement is the lateral resistance for that particular slip surface.

𝛿𝑠𝑜𝑖𝑙

𝛿𝑠𝑜𝑖𝑙,𝑎𝑥𝑖𝑎𝑙

𝛿𝑠𝑜𝑖𝑙,𝑙𝑎𝑡𝑒𝑟𝑎𝑙

𝛿𝑠𝑜𝑖𝑙,𝑙𝑎𝑡𝑒𝑟𝑎𝑙 𝛿𝑠𝑜𝑖𝑙,𝑎𝑥𝑖𝑎𝑙


30 - 3

The pile resistance is dependent on the depth and angle of the slip surface since this will affect the pile response from the applied displacement. As such, the pile resistance must be computed at a number of points along the pile varying the depth and angle of applied displacement at each point. Linear interpolation is used to obtain resistance values of intermediate sliding depths. The user may specify the maximum allowable soil displacement moving along any slip surface based on design tolerances to obtain the pile resistances. Alternatively, an ultimate pile resistance can be obtained by increasing the assumed soil displacement independently in the axial and lateral directions until the maximum resistances are reached.

The figure above illustrates a typical axial force and shear diagram along the pile depth for an applied displacement from the ground to the sliding depth of 10 m. The axial force and shear at a sliding depth of 10 m are the axial and lateral resistances respectively for one tested sliding configuration.

𝑉𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙,𝑝𝑖𝑙𝑒 𝑃𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙,𝑝𝑖𝑙𝑒

𝛿𝑠𝑜𝑖𝑙,𝑙𝑎𝑡𝑒𝑟𝑎𝑙 𝛿𝑠𝑜𝑖𝑙,𝑎𝑥𝑖𝑎𝑙 𝛿𝑠𝑜𝑖𝑙

𝐹𝑅𝑒𝑠𝑢𝑙𝑡𝑎𝑛𝑡,𝑝𝑖𝑙𝑒

Sliding Depth of 10 m


30 - 4

RSPile

To compute the pile resistances using the methodology outlined above, the support properties for installed pile supports in Slide are defined using the dedicated pile analysis software RSPile. The software is capable of modelling complex pile models using the load transfer curve method or better known as the p-y method for laterally loaded piles and the t-z method for axially loaded piles.

The soil load transfer curves capture the non-linear soil-pile behavior by relating the soil reaction forces to the soil displacement at each depth. Various recommended load transfer curves are available in RSPile and are presented in the RSPile theory manual. For axially loaded piles, the load transfer curves are known as t-z curves for soil skin friction and q-z curves for soil end bearing resistance. For laterally loaded piles, the load transfer curves are known as p-y curves for soil lateral resistance.

Model

If you have not already done so, run the Slide Model program by double-clicking on the Slide

icon in your installation folder. Or from the Start menu, select Programs Rocscience

Slide 7.0 Slide.

If the Slide application window is not already maximized, maximize it now, so that the full screen is available for viewing the model.

Geometry

Start the Slide Model program. Select File > Recent Folders > Tutorials Folder from the Slide main menu, and open the Tutorial 30 Analyzing Pile Resistance using RSPile (initial).slim file.

You should see the following model.


30 - 5

Material Properties

The material properties have already been defined in the model.

Select: Properties Define Materials

The first material is a “Medium Sand” with the following properties:

• Unit Weight = 18 kN/m3

• Strength Type = Mohr-Coulomb

• Cohesion = 5 kPa

• Phi = 38 degrees

The second material is a “Dense Sand” with the following properties:


• Strength Type = Mohr-Coulomb


• Phi = 43 degrees


30 - 6

The third material is “Soft Clay” with the following properties:


• Strength Type = Undrained (Phi =0)



30 - 7

Add Support

We will use the Add Support option to add piles to the slope.

Select: Support Add Support

You will see the Add Support dialog. Select OK.

As you move the mouse, you will notice a small black cross, which follows the cursor around, and snaps to the nearest point on the nearest external boundary segment. To define the support location, all we need to do is enter the start and end points of the support on the external boundary. The points can be entered graphically with the mouse by clicking the left mouse button when the black cross is at the desired location. However, we will use the prompt line to enter the following exact points:


30 - 8

Enter vertex [t=table, esc=cancel]: 65 40


Let’s add a second support. The support installation prompt should still be active, so that you can continue to enter coordinates for more supports. Use the prompt line to enter the following exact points: Enter vertex [t=table, esc=cancel]: 71 44


After you have entered the last coordinate and hit enter, hit the enter key again or hit the esc key to close the support installation prompt. Your model should appear as follows:

Support Properties

You will now define the pile support properties using the RSPile utility.

Select: Properties Define Support

The Define Support Properties dialog should appear. Change the properties to the following.

• Name = RSPile Model 1

• Support Type = RSPile


30 - 9

RSPile

Now you will open the RSPile utility from the Define Support Properties dialog.

Select: Run the RSPile Utiltity

Alternatively, you can run the RSPile Model program by double-clicking on the RSPile icon in

your installation folder. Or from the Start menu, select Programs Rocscience RSPile

1.0 RSPile.

If the RSPile application window is not already maximized, maximize it now, so that the full screen is available for viewing the model.

The finished product of the RSPile model file can be found in the Tutorial 30 Analyzing Pile Resistance using RSPile.rspile data file. All tutorial files installed with Slide 7.0 can be accessed by selecting File > Recent Folders > Tutorials Folder from the Slide main menu.

Model

You will see the RSPile splash screen. Since you are not analyzing the axial capacity for driven piles, you do not need to use the Driven Pile Analysis mode. We will start by defining the properties for a laterally loaded pile.


30 - 10

Select: Laterally Loaded Pile

You should see the following default laterally loaded pile model.

Soil Properties for Laterally Loaded Piles

Now let’s define the material properties for a laterally loaded pile. Many of the pile model properties can be defined on the left table view. You will begin by defining the soil material properties located on the bottom left corner. You do not need to define the layer thickness and soil unit weight because these values will be initialized according to the soil profile of the installed pile support in Slide. As such, we can use one RSPile model file to define the soil and pile properties for multiple piles of various embedment lengths and soil layer configurations. To verify your results later in RSPile, you will define the unit weight as the


30 - 11

same value in RSPile and in Slide. If you are only intending to use the RSPile file as a support property for Slide and will not use RSPile to do a stand-alone pile analysis, it is not necessary to set the unit weight. Change the first layer to the following properties:

• Name = Medium Sand

• Soil Type = Sand

• Unit Weight = 18

• Friction Angle = 38

• Kpy = 16300

The unit weight entered in RSPile is the total unit weight whether the material is saturated or unsaturated and is equal to the unit weight entered in Slide. If a groundwater table exists in the model, the program will automatically calculate effective unit weight if the material is below the groundwater table.

Change the second layer to the following properties:

• Name = Dense Sand

• Soil Type = User Defined


A user defined material allows the user to enter the p-y curve that relates soil lateral reaction force to the soil displacement.


30 - 12

Select: Enter p-y curve

The P-Y Curve dialog should appear. Enter the following values in the table.

Add a third layer using the Add Layer button in the Soil Layers List. Change the third layer to the following properties:


30 - 13

• Name = Soft Clay

• Soil Type = Soft Clay Soil


• Strain Factor (E50) = 0.007

• Undrained Shear Strength = 57

You model should now appear as follows.


30 - 14

Soil Properties for Axially Loaded Piles

You can toggle between lateral and axial analysis modes using the toggle buttons. To demonstrate this feature, change the analysis type to Axially Loaded Piles using the Axial Mode button. Select: Axial Mode

You should see the following axially loaded pile model.

Notice that some soil properties common to laterally or axially loaded piles remain the same as you toggle between modes. These properties include layer names, thicknesses and colours. Other properties that may be common within one base type, such as friction angle for any sand, are not copied between modes because the material models are different and usually contain unique property values depending on the problem. To return to the laterally loaded pile model, select the Lateral Mode button. Select: Lateral Mode

Alternatively, you can toggle between modes using the Project Settings dialog. Open the Project Settings dialog from the toolbar.

Select: Project Settings General

You should see the following Project Settings dialog. If you haven’t done so already, change the Analysis Type back to Axially Loaded Piles. Select OK.


30 - 15

You should now see the axially loaded pile model.

On the left table view, select Medium Sand from the Soil Layers List. Change the soil properties to the following.

• Soil Type = API Sand



• Coefficient of Lateral Earth Pressure = 0.8

• Bearing Capacity Factor = 35


30 - 16

Select Dense Sand from the Soil Layers List. Change the soil properties to the following.



• Ultimate Unit Skin Friction = 150

• Ultimate Unit End bearing Resistance = 0


30 - 17

Similarly to user defined material in laterally loaded piles, you must define the t-z curve that relates soil skin friction to soil displacement. You do not have to define the Q-z curve for this tutorial since it is assumed that this soil layer has no end bearing strength.

Select: Enter t-z curve

The following T-Z Curve dialog should appear.

Enter the following values into the table as shown above. This is an example of a typical non-linear t-z curve based on empirical data. Select OK.

Select Soft Clay from the Soil Layers List. Change the soil properties to the following.


30 - 18

• Soil Type = API Clay


• Undrained Shear Strength = 57

• Remolded Shear Strength = 57

Pile Properties

You will now define the pile properties. Select Define Pile Properties from the top toolbar.

Select: Define Pile Properties

The Define Pile Properties dialog should appear. Change the properties as follows.

• Name = Steel Pipe

• Pile Type = Pipe

• Pile Outside Diameter = 0.61

• Pipe Wall Thickness = 0.02

• Young’s Modulus = 200,000,000


30 - 19

Select OK. In the table view on the left, you can quickly change the pile configuration in the Pile Properties section by using the drop down menu for the pile name. We do not need to change the embedment length because it will be defined in Slide.

Before you import the RSPile model into Slide, save it as a file called Tutorial 30.rspile. (RSPile model files have a .rspile filename extension).

Select: File Save As

Use the Save As dialog to save the file.

Importing RSPile model into Slide

Navigate back to the Slide modeler. If you have closed Slide, run the Slide Model program by double-clicking on the Slide icon in your installation folder and opening the previously saved

Slide .slim file. Or from the Start menu, select Programs Rocscience Slide 7.0 Slide.

Now you will import the soil and pile properties specifically for the pile model. You can do this from the Define Support Properties dialog. If it is not open, navigate back to the Define


30 - 20

Support Properties dialog.

Select: Properties Define Support

In the RSPile File section, select Choose file to import the RSPile model you have just created.

Locate the RSPile model file Tutorial 30.rspile. Select Open. The following Match Slide and RSPile Materials dialog should appear.

Ensure that each material in Slide is matched with the same material in RSPile. Select OK.

You can always reassign the materials by selecting Match materials in the Define Support Properties dialog.

In the Define Support Properties, you can also change which components of pile resistances are considered in the analysis by changing the Resistance Type. Your analysis can consider


30 - 21

only axial resistance, only lateral resistance or both by changing the Resistance Type to Axial, Lateral or Axial and Lateral respectively. For this tutorial, you will consider both axial and lateral resistance.

Note that under the Soil Displacement section we have a choice between Maximum and Ultimate modes. The Maximum mode assumes that a maximum allowable soil displacement of 25 mm in the direction tangent to the tested slip surface is used to compute the axial and lateral resistance against sliding. The Ultimate mode increases the applied soil displacement in the axial and lateral direction until a maximum resistance is reached. In Slide, a uniform soil displacement is applied from the ground surface to each of the tested slip surface intersections to the pile. The magnitude of the applied displacement is constant with depth. When using RSPile for a stand-alone pile analysis, the user may define more complex soil displacement profiles to apply to the model. However, due to the variability of slip surfaces that could intersect a pile in Slide, more complex soil displacement profiles cannot be defined for a Slide analysis of imported RSPile files. We will use the default Maximum Soil Displacement settings. Select OK.

Compute

Before you analyze your model, save it as a file called Tutorial 30.slim. (Slide model files have a .slim filename extension).


Use the Save As dialog to save the file. You are now ready to run the analysis.

Select: Analysis Compute

The Slide Compute engine will proceed in running the analysis. When completed, you are ready to view the results in Interpret.


30 - 22

Interpret

To view the results of the analysis:

Select: Analysis Interpret

This will start the Slide Interpret program. You should see the following figure.

Pile Resistance

To view the pile resistance force, select Show Slices from the Query menu.

Select: Query Show Slices

The pile resistance is indicated by the blue arrow with its origin located at the intersection


30 - 23

of the pile and slip surface. Notice that the direction of pile resistance is always opposite to the direction of sliding although it may not always be tangent to the slip surface. Each slip surface will have a different pile resistance depending on the depth and angle of intersection.

This part of the tutorial is now complete.

Please continue if you would like to compare the results from Slide to an analysis done completely in RSPile. Otherwise, you can exit either program by selecting the following.

Select: File Exit

Verifying Pile Resistance using RSPile

You can verify the pile resistance results from Slide by using the same pile length and soil layer configuration for the RSPile model. For this tutorial, we will be verifying the pile resistance of the downslope, shorter pile.

The finished product of the RSPile model file for verification can be found in the Tutorial 30 Analyzing Pile Resistance using RSPile (Verification).rspile data file. All tutorial files installed with Slide 7.0 can be accessed by selecting File > Recent Folders > Tutorials Folder from the Slide main menu.

Return to the RSPile Model program and open the Tutorial 30.rspile file if it is not already open.

Soil Properties for Laterally Loaded Piles

Make sure you are in lateral mode to begin.

Select: Lateral Mode

In the table view, change the soil layer thicknesses to the following.


30 - 24

A warning should appear notifying you that since the pile length is longer than the sum of all soil layer thicknesses, the pile embedment length will be shortened to this value. Select OK. The pile embedment length should be automatically changed to 13 m, the total sum of all layer thicknesses.

You will now duplicate materials to create the fourth and fifth layer to match the soil profile of the pile in Slide. Add a fourth layer using the Add Layer button in the Soil Layers List. Change the fourth layer to the following properties.


• Thickness of layer = 2




30 - 25

Again, enter the p-y curve that relates soil lateral reaction force to the soil displacement.

Select: Enter p-y curve

The P-Y Curve dialog should appear. Enter the following values in the table.

Add a fifth layer using the Add Layer button in the Soil Layers List. Change the fifth layer to the following properties:



• Soil Type = Sand



• Kpy = 16300


30 - 26

You can also match the colours of duplicate layers to indicate their relation to each other.

Soil Properties for Axially Loaded Piles

Change to axial mode to define the newly added layers for an axially loaded pile. Select: Axial Mode

Change the fourth layer to the following properties.




• Effective Unit Weight = 20

• Ultimate Unit Skin Friction = 150

• Ultimate Unit End bearing Resistance = 0


30 - 27

Again, you must define the t-z curve that relates soil skin friction to soil displacement.

Select: Enter t-z curve

The following T-Z Curve dialog should appear.

Enter the following values into the table as shown above. Select OK.


30 - 28

Change the fifth layer to the following properties.



• Soil Type = API Sand

• Effective Unit Weight = 18


• Coefficient of Lateral Earth Pressure = 0.8

• Bearing Capacity Factor = 35

Pile Properties

On the left table view under Pile Properties, change the Pile Length to 21 m.

Pile Resistance

The maximum soil displacement entered into Slide to calculate pile resistance is 25 mm.


30 - 29

Since the critical slip surface intersects the pile at approximately 1.65 degrees to the horizontal, the components of soil displacement for the axial and lateral direction are 0.72 mm and 24.99 mm respectively.

In RSPile, you must compute the axial and lateral resistances separately in each mode and the resultant pile resistance is the force shown in Slide.

Ensure that you are still in Axial Mode.

Select: Axial Mode

In the table view under Axial Soil Loading, select Show Axial Resistance Graph and change the Max Allowable Axial Displacement to 0.72 mm.

The Number of Intervals defines the number of sliding depths that will be tested along the pile length. By default, the Number of Intervals is 20. Since the pile has an embedment length of 21 m, the pile will be loaded with the Max Allowable Axial Displacement of 0.70 mm from the ground surface to each sliding depth. The tested sliding depths begin at 0 m and increase to 21 m by an increment of 1.05 m (21 m/20 intervals = 1.05 m). The following Axial Resistance plot should appear.

1.65 degrees

0.72 mm

24.99 mm 25 mm


30 - 30

The above plot is the axial resistance at each sliding depth along the pile. Since the slip surface in the Slide model intersects the pile at approximately 12.42 m, you need to linearly interpolate the resistance from the sliding depths of 11.55 m and 12.6 m. You can either hover over these points in the plot to view the resistance values or export the data into Excel. Allow a few seconds for the data to be fully exported to excel.

Select: Export to Excel

In the Axial Res vs. Sliding Depth tab, the resistance values corresponding to a sliding depth of 11.55 m and 12.6 m are 363 kN and 367 kN respectively. The Interpolated axial resistance at a sliding depth of 12.42 m is 366 kN. You now need to compute the lateral resistance to find the resultant pile resistance. Change to Lateral Mode.

Select: Laterally Loaded Pile

In the table view under Lateral Soil Loading, select Show Lateral Resistance Graph and change the Max Allowable Lateral Displacement to 24.99 mm.

The following Lateral Resistance plot should appear.


30 - 31

Select: Export to Excel

In the Lateral Res vs Sliding Depth tab, the resistance values corresponding to a sliding depth of 11.55 m and 12.6 m are 396 kN and 480 kN respectively. The Interpolated lateral resistance at a sliding depth of 12.42 m is 465 kN. The resultant pile resistance from the axial and lateral resistance of 366 kN and 465 kN is 592 kN. Slide shows a value of 591 kN as shown below.


30 - 32

The discrepancies are due primarily to linear interpolation of the resistance at two locations. In Slide, the resistance functions are constructed for the number of sliding depths as set in RSPile and the soil displacement is varied at each sliding depth to account for the unknown slip surface angle of intersection. First, linear interpolation must be done to compute the resistance function for the exact component of soil displacement produced by the slip surface based on the closest tested soil displacements. Secondly, linear interpolation is done to compute the resistance for the exact sliding depth since the tested sliding depths are unlikely to align exactly with the actual slip surface intersection with the pile. In RSPile, you have more control on the exact soil displacement and sliding depth since you are verifying one known slip surface. However, repeating this resistance computation for every slip surface would be rather tedious hence the necessity for an automated process in Slide. Even with a relatively low Number of Intervals, the resultant pile resistance computed in RSPile is within 1% of the value from Slide which is well within typically accepted tolerances. Before you exit RSPile, save this file as Tutorial 30 (verification).rspile.


Use the Save As dialog to save the file.

That concludes this tutorial. To exit either program:

Select: File Exit

tutorial 30 analyzing pile resistance for slope stabilization using

Documents