Join one of our upcoming courses taking place around the world! Explore now
 

Search Results

08 - Highway Cut with Ru Water Pressure

1.0 Introduction

In this tutorial, a section of a highway with near vertical rock cuts on both sides and jointing will be analyzed under both Dry and Undrained conditions. The effects of Water Pressure can drastically impact slope stability by lowering the normal forces along the sliding joints of blocks, thereby lowering the shear resistance and factor of safety.

Finished Product

The finished product of this tutorial can be found in the Highway Cut - ru water pressure.rocslope_model file. All tutorial files installed with RocSlope can be accessed by selecting File > Recent Folders > Tutorials Folder from the RocSlope main menu.

2.0 Opening the Starting File

  1. Select File > Recent > Tutorials Folder.
  2. Go to the Highway Cut with Ru Water Pressure folder and open the file Highway Cut - dry.rocslope_model.

This model already has the following defined and provides a good starting point to start computing blocks:

  • Units
  • External geometry
  • Material Properties
  • Synthetic Joints
  • Joint Properties

In the starting model, the external is defined by a section of a highway with steep, near-vertical rock slopes straddling both sides of the road.

starting file 3d view
3D View showing the section of a highway with steep, near-vertical rock slopes straddling both sides of the road

2.1 Project Settings

Review the Project Settings.

  1. Select Analysis > Project Settings project settings icon
  2. Select the Units tab. Units are Metric, stress as MPa.
    project settings dialog units tab
    Units tab in Project Settings dialog
  3. Select the Analysis tab.
    1. Design Factor of Safety = 1.5.
    2. Successive Failure is ON.
    project settings analysis tab
    Analysis tab in Project Settings dialog
  4. Click Cancel to exit the dialog.

2.2 Material Properties

Review the Material Properties.

  1. Select Materials > Define Materials define materials icon
  2. One (1) material property is defined in the Define Materials dialog. The Rock material property has:
    • Unit Weight = 0.026 MN/m3.
    • No Water Surface applied.
    materials properties dialog
    Define Materials dialog
  3. Click Cancel to exit the dialog.

2.3 External Geometry

The External is of a highway section with vertical slope cuts on either side and composed of a single volume assigned with the Rock material property.

2.4 Joint Properties

Review the Joint Properties.

  1. Select Joints > Define Joint Properties define joint properties icon
  2. One (1) joint property is defined in the Define Joint Properties dialog. The Shear joint property has:
    • Strength Type = Barton-Bandis
    • JRC = 10
    • JCS = 30 MPa
    • Phir = 25 degrees
    • Waviness = 0 degrees
      define joint properties strength tab
      Shear Joint Property Strength tab in Define Joint Properties dialog

    • Water Pressure Method = Dry
      define joint properties water pressure tab
      Shear Joint Property Water Parameters tab in Define Joint Properties dialog
  3. Click Cancel to exit the dialog.

2.5 Synthetic Joints

Review the Synthetic Joint Properties.

  1. Select Joints > Define Synthetic Joints define synthetic joints icon. Two (2) synthetic joint properties are defined.
  2. The Set 1 synthetic joint property has:
    • Joint Property = Shear
    • Joint Orientation Definition Method = Dip/Dip Direction
    • Mean Dip = 60 degrees
    • Mean Dip Direction = 85 degrees
    • Mean Radius = 12 m
    • Mean Spacing = 1.7 m
    • Spacing Option = True Spacing.
      set1 synthetic joint properties
      Set 1 Synthetic Joint Property in Define Synthetic Joint Properties dialog
  3. The Set 2 synthetic joint property has:
    • Joint Property = Shear
    • Joint Orientation Definition Method = Dip/Dip Direction
    • Mean Dip = 45 degrees
    • Mean Dip Direction = 170 degrees
    • Mean Radius = 12 m
    • Mean Spacing = 2.4 m
    • Spacing Option = True Spacing.
      set2 synthetic joint properties
      Set 2 Synthetic Joint Property in Define Synthetic Joint Properties dialog
All parameters have no statistics assigned which means that the joints across the joint set will be parallel and constant in size and spacing.

Both Synthetic Joint Sets traverse (data collected over a scanline) from:

  • X = 13, Y = 15, Z = 1012 to
  • X = -8, Y = -6, Z = 1012

First, we will compute assuming no water pressure effects (i.e., dry).

    3.0 Compute (Dry)

    RocSlope has a two-part compute process.

    3.1 Compute Blocks

    The first step is to compute the blocks which may potentially be formed by the intersection of joints with other joints and the intersection of joints with the free surface.

    To compute the blocks:

    1. Navigate to the Compute workflow tab compute workflow
    2. Select Analysis > Compute Blocks compute blocks icon

    As compute is run, the progress bar reports the compute status. Once compute is finished, the Results node is added to the Visibility Tree and All Valid Blocks are blocks are shown in the viewport. The Results node consists of the collection of valid blocks and the socketed slope. The original External and Joint Surface visibility is turned off.

    compute blocks 3d view
    3D View of all Valid Blocks

    Once compute is finished, the blocks are coloured according to the Block Color option (Random Colors) set in the Results node's Property pane.

    Compute Blocks only determines the geometry of the blocks. In order to obtain other information such as the factor of safety, Compute Kinematics needs to be run.

    3.2 Compute Kinematics

    The second and final compute step is to compute the removability, forces, and factor of safety for each of the valid blocks.

    To compute the block kinematics:

    1. Ensure that the Compute workflow tab compute workflow is the active workflow.
    2. Select Analysis > Compute Kinematics compute kinematics icon

    As compute is run, the progress bar reports the compute status. By default, after Compute Kinematics is run, only Removable Blocks are shown.

    compute kinematics 3d view
    3D View of Removable Blocks only

    4.0 Interpreting Results

    Once both blocks and kinematics are computed, check to see if any blocks have failed (i.e., Factor of Safety < Design Factor of Safety = 1.5).

    1. Navigate to the Results workflow tab results workflow
    2. Select Interpret > Block Information block info icon
    3. Select the Results node from the Visibility Tree.
    4. In the Results node Properties pane, set the Results Set = Failed Blocks (FS < Design FS).

    Visualizing blocks can be difficult when the slope extents are large compared to the block extents.

    To zoom into all blocks:

    • Select Interpret > Zoom To All Blocks zoom all blocks icon

    No blocks have failed.

    3d view of no blocks with failed results
    3D View showing no Blocks for Failed Blocks Results Set

    5.0 Ru Water Pressure

    Now, let's consider the effects of water pressure in the joints. For this example, the Ru Coefficient Groundwater Method will be used which computes water pressure as a fraction (i.e., Ru Coefficient) of the vertical earth pressure.

    To apply Ru coefficient for modeling groundwater:

    1. Select Materials > Define Materials define material properties icon
    2. In the Define Materials dialog, for the Rock material property:
      1. Set Groundwater Method = Ru Coefficient
      2. Set the Ru Value = 0.4
        rock material property
        Rock Material Property with Ru Coefficient Groundwater Method set in Define Materials dialog
      3. Click OK to save the material property and exit the dialog.

    Next, we have to set the applied Joint Property to use the Groundwater conditions set by the Material Property:

    1. Select Joints > Define Joint Properties define joint properties icon
    2. In the Define Joint Properties dialog, for Shear joint property:
      1. Navigate to the Water Parameters tab.
      2. Set Water Pressure Method = Material Dependent. Any joints with this applied joint property will have water pressure dictated by the Groundwater Method in any portion of the material it passes.
        shear joint property
        Shear Joint Property with Material Dependent Water Pressure method set in Define Joint Properties dialog
      3. Click OK to close the dialog.

    6.0 Compute (Ru Water Pressure)

    Recompute blocks and kinematics.

    1. Ensure that the Compute workflow tab compute icon is the active workflow.
    2. Select Analysis > Compute Blocks compute blocks icon. Computation of blocks are unaffected by water.
    3. Select Analysis > Compute Kinematics compute kinematics icon

    7.0 Interpreting Results

    Once both blocks and kinematics are computed, check to see if any blocks have failed (i.e., Factor of Safety < Design Factor of Safety = 1.5).

    1. Navigate to the Results workflow tab results icon
    2. Select Interpret > Block Information block info icon
    3. Select the Results node from the Visibility Tree.
    4. In the Results node Properties pane, set the Results Set = Failed Blocks (FS < Design FS).

    Visualizing blocks can be difficult when the slope extents are large compared to the block extents.

    To zoom into all blocks:

    • Select Interpret > Zoom To All Blocks.

      All blocks have failed. Failure Modes for all blocks is Sliding since the water pressure has caused the reduction of effective normal stresses acting along sliding joints. When this happens, shear resistance is reduced and the Factors of Safety are also reduced.

      3d view of all blocks failed
      3D View showing Blocks for Failed Blocks Results Set

      This concludes Tutorial 08.

      Portal Account Log Out Home Shopping Cart icon Click here to search our site Click here to close Learning Tech Support Documentation Info Chevron Delete Back to Top View More" PDF File Calendar Location Language Fees Video Click here to visit Rocscience's LinkedIn page Click here to visit Rocscience's YouTube page Click here to visit Rocscience's Twitter page Click here to visit Rocscience's Facebook page Click here to visit Rocscience's Instagram page Bookmark Network Scroll down for more Checkmark Download Print Back to top Single User Multiple Users RSLog RocFall3 CPillar Dips EX3 RocFall RocPlane RocSupport RocSupport RocTopple RS2 RS3 RSData RSPile Settle3 Slide2 Slide3 SWedge UnWedge Commercial License Education License Trial License Shop safe & secure Money-back guarantee