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Timestamp: 2019-04-22 19:04:49+00:00

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maintaining a suitable factor of safety.
By plotting the slope angle versus the factor of safety. Slope Angle Optimization 30-2 Problem An open pit mine is excavated through weak rock. you will see the following dialog.sli) from the drop down menu. This can be done in Phase2 by constructing a series of models with different slope angles and observing the factors of safety.8.rocscience. TIP: You can also import a Slide file by simply choosing Open from the File menu.0 Tutorial Manual . At the bottom of the Open dialog. The specification of the mine design states that the factor of safety must be greater than 1.sli found in the Tutorials folder. we can obtain the optimum slope angle for the mine. You do not need to have Slide installed to import this model. Phase2 v.asp for more information on Slide). which is a subfolder of the Examples folder in the Phase2 installation directory. select Slide File Format (*. Go to File → Import → Import Slide. Open the Slide file Tutorial 30 Slope Angle. Model Start the Phase2 Model program. for Files of type. The goal is to create as steep a slope as possible (to minimize costs) while maintaining a factor of safety greater than 1.25. Once you have opened the Slide file.25.com/products/Slide. In this tutorial we will start by importing a model created in the slope stability program Slide (see http://www.
Now move the mouse to the right to draw a horizontal line. click OK to run the Geometry Cleanup process. Click OK to accept the defaults.8. Click the mouse button to finish drawing the angle and you should see that the overall slope is approximately 41°. We also want Phase2 to automatically generate a finite element mesh and appropriate boundary conditions so leave these options on as well (Slide analyses do not require a finite element mesh so the mesh must be generated by Phase2). You will see a model that looks like this: This is a model of an open pit mine in which there is a layer of sediments and a layer of weak weathered rock on top of the bedrock. Slope Angle Optimization 30-3 This allows you to set various options for the finite element analysis. We want to perform a shear strength reduction (SSR) analysis to determine the factor of safety for slope stability so leave this option on. Click on the crest of the slope (near 122. go to Tools → Add Tool → Dimension Angle. Phase2 v. If a “Geometry Cleanup” dialog appears. This is recommended when importing Slide and DXF files to ensure good mesh quality. 120) and then click on the toe (at 30. 40).0 Tutorial Manual . To determine the overall angle of the slope.
the finite element analysis performed by Phase2 requires some additional properties. Change the peak Tensile Strength to 5.0 Tutorial Manual . However. For the Surficial sediments. Slide does not require Young’s modulus. Slope Angle Optimization 30-4 Material properties The material properties used by Slide are imported along with the model.8. Be sure you are looking at the properties for Surficial sediments. Phase2 v. Poisson’s ratio or Tensile strength to perform a slope stability analysis. so default values are assigned to all materials in Phase2. change the Young’s Modulus to 10000 kPa and the peak and residual Tensile Strength to 0 as shown: Now click on the tab for the Weathered Rock. Go to the Properties menu and select Define Materials.
change the Young’s Modulus to 200000. Slope Angle Optimization 30-5 Now for the Rock material. The model definition is now complete. Click OK to close the dialog. the Poisson’s Ratio to 0. Save the model using the Save As option in the File menu.0 Tutorial Manual .3 and the Tensile Strength to 40 kPa.8. Phase2 v.
select the Interpret option in the Analysis menu to view the results. We will now proceed to modify the slope angle to produce a higher factor of safety. A value of 0. Once the model has finished computing (Compute dialog closes).99 is clearly unacceptable. You will now see the maximum shear strain contours for the critical strength reduction factor of 0. Because it is performing a Shear Strength Reduction analysis. If you click the tab for SRF: 1 you get a better picture of the critical failure surface as shown. Interpret The Interpret program starts and reads the results of the analysis. the model will take several minutes to run. Slope Angle Optimization 30-6 Compute Run the model using the Compute option in the Analysis menu.8. The critical SRF is equal to the factor of safety.0 Tutorial Manual . Phase2 v.99.
Click on the point at the top of the slope (close to 122 . 120). you are presented with the Change Slope dialog. Go to Boundaries → Edit → Change Slope Angle. Crest Toe After clicking on the top point.8.0 Tutorial Manual . You are now asked to pick the vertex at the crest of the slope. You will be asked if you wish to reset the mesh. Click on the point at 30 . You are now prompted to pick the starting vertex at the toe of the slope. Click OK and the current mesh will be deleted. First delete the Dimension Angle drawing tool by right clicking on it and selecting Delete Tool. This is what we want since we have flat benches in our slope and we do not want them to be rotated (try clicking on the option for rotate and see what happens). Phase2 v. The default action is to Project Horizontally. 40. The default value of 5° is suitable for a first guess. We want to make the slope shallower so choose clockwise for the rotation. Slope Angle Optimization 30-7 Changing slope angle Go back to the Phase2 Model program.
8. You will now see that the overall slope angle is shallower. Phase2 v.0 Tutorial Manual . Slope Angle Optimization 30-8 Click OK to close the dialog.
8. The model will look like this: Boundary conditions You can see that the boundary conditions on the slope face have reverted to the default (fixed in x and y direction). Compute Run the model using the Compute option in the Analysis menu. the model will take several minutes to run. Choose Free from the Displacements menu. Hit Enter to finish selecting segments.0 Tutorial Manual . Slope Angle Optimization 30-9 Mesh Remesh the model by selecting Discretize and Mesh from the Mesh menu. Click on all of the segments of the slope face. The model should now look like this: Save the model using the Save As option in the File menu (give it a different name from the previous model). Because it is performing a Shear Strength Reduction analysis. Phase2 v. We must free these boundaries.
NOTE: in general. This is still less than the desired factor of safety (1. We can then interpolate to get the desired slope angle. Slope optimization We now want to determine what slope angle will give a factor of safety of 1. This fourth model will have a slope that has been rotated 15° from the original. Then repeat again rotating by another 5°.25. If you start with a shallow slope and make it steeper. Phase2 v. it is better to start with the maximum slope angle. Go back to the Phase2 Model program. The best way to do this is to run a few more examples and then plot a graph of factor of safety versus slope angle. Slope Angle Optimization 30-10 Once the model has finished computing (Compute dialog closes). Repeat the above analysis and rotate the slope by another 5° clockwise. and use the Change Slope Angle option to decrease the slope angle. however the results may not be as you intended. Interpret You will see the maximum shear strain contours for the critical strength reduction factor of 1. If you do this. Phase2 will simply crop any material boundaries at the new slope face.0 Tutorial Manual . select the Interpret option in the Analysis menu to view the results. and you may have to perform additional editing to achieve the correct boundaries.08.8. so we will continue to decrease the slope angle.25). Phase2 will automatically extend any material boundaries which intersect the slope.
after you have created your models.8. After you have finished running the models. For example. and select All Programs → Rocscience → Phase2 → Utilities → Compute). Slope Angle Optimization 30-11 TIP: you can create multiple Phase2 models and then run them all in batch mode. open them in the Interpret program to determine the factors of safety.g. go the windows Start menu. The plot should look like this: Phase2 v. In the Compute dialog. The program will then compute them all sequentially. you can open multiple files and then hit Compute. Use a spreadsheet program (e. Microsoft Excel) to plot Factor of Safety versus Change in Slope Angle.0 Tutorial Manual .
9 0 5 10 15 20 Change in Slope Angle You can now interpolate to estimate the change in slope angle that will produce a factor of safety of 1. You should see a factor of safety of 1.3 Factor of Safety 1. toe and a third point to the right of the toe).8.4 1. You will see that the overall angle is now 28°. Run Compute and view the results in Interpret. Measure the overall angle of the slope as you did for the first model (go to Tools → Add Tool → Dimension Angle and click on the crest. Slope Angle Optimization 30-12 1.0 Tutorial Manual .25 (shown with dashed lines in the above plot). Final pit design In the Phase2 Model program.1 1 0. Phase2 v. open the original model and rotate the slope by 13° clockwise following the steps outlined above.25 as expected.2 1. It appears that a value of 13° should produce the desired results.
Phase2 v.8. you may now exit the Phase2 Interpret and Phase2 Model programs.0 Tutorial Manual . Slope Angle Optimization 30-13 This concludes the tutorial.

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