Import Slide2 File
The Import Slide2 File option allows you to import a Slide2 model into RS2.
Slide2 is a 2D limit equilibrium slope stability program available from Rocscience, see the Rocscience website for information. The Slide2 program interface and modeling procedures are very similar to RS2. The two programs can be used as complementary methods of analyzing the same slope stability problem.
After importing a Slide2 model, you can run a finite element stress analysis in RS2, and with the finite element slope stability feature of RS2 using the Shear Strength Reduction method, you can compare limit equilibrium and finite element results for the same slope model.
To import a Slide2 model into RS2:
- In the RS2 Model program, select Import Slide from the Import sub-menu of the File menu.
- You will see an Open File dialog. Select the Slide2 file that you wish to import, and select Open. Slide2 files have a .sli, . slim, or .slmd filename extension. Note that when importing a multi-scenario Slide2 file, you must select which scenarios you want to import; each scenario will be imported as a separate document.
- You will see the Slide Import Options dialog. This allows you to choose various options related to the import of the Slide2 file. Use the checkboxes to select the following:
- Turn on Strength Reduction
- Import Groundwater Mesh
- Automatically Generate Mesh
- Automatically Generate Boundary Conditions
- Run Geometry Cleanup
- Select [OK] in the Slide Import Options dialog, and the Slide2 file will be imported into RS2, according to the selections you have made in the dialog. Notice that the Slide filename is preserved, but the filename extension (in RS2) is .FEZ. When you Save the imported file it will be saved as a RS2 file.
- For details about how the various Slide2 modeling options are imported or converted into RS2 modeling options, see the section below - How Slide Modeling Options are Imported into RS2.
- If you select Compute, the RS2 stress analysis will be carried out. If the first check box was selected in the dialog in Step 3, then the finite element slope stability analysis will be computed as well. See the Shear Strength Reduction topic for more information.
Import a Slide File with the Open File Option
A Slide file can also be imported into RS2 with the Open file option in the File menu.
- Select File > Open in the RS2 Model program.
- In the Open File dialog, set Files of Type = Slide File Format (*.slim, *.sli, or *.slmd).
- Open a Slide2 file and follow the steps described above.
How Slide Modeling Options are Imported into RS2
Note that after importing, a warning dialog might appear. This is because not all functionality in Slide2 is supported by RS2. The warning dialog will appear if the Slide model contains unsupported functionality. In this case, it may be necessary to make alterations to the model.
The following is a listing of Slide2 features which are imported into RS2 and those features which are not currently imported into RS2.
Files written with a version of Slide prior to 5.0 are not supported but may read correctly depending on what you are trying to model.
Please note that RSPile support elements from Slide2 files are not supported in RS2.
SLIDE PROJECT SETTINGS
RS2 supports Metric and Imperial English units and will properly read Slide2 files with either metric or imperial units (pounds and feet). Other project settings such as failure direction, method, tolerances etc. have no meaning in RS2 and are not read. The groundwater setting is read. Sensitivity and probability settings are not read.
GROUNDWATER
RS2 supports the definition of pore pressures using piezometric lines, Ru, water pressure grids, and finite element groundwater seepage analysis. The properties and settings for all these techniques are properly read from the Slide2 file during import.
SENSITIVITY AND PROBABILISTIC ANALYSES
Sensitivity and probabilistic analysis settings from Slide are currently NOT imported into RS2. RS2 does offer the point estimate and Monte Carlo methods for probabilistic analysis, and applicable parameters (e.g. material property standard deviations) can be copied manually.
BOUNDARIES
The Slide2 external boundary and material boundaries are all read into RS2. The water table is read into RS2 but since RS2 does not support a specific water table entity, it is converted to a piezometric line with id equal to 1. Piezometric lines are read directly into RS2. Water pressure grids are read into RS2. Tension crack polylines are NOT read into RS2.
TENSION CRACKS
The explicit modeling of a tension crack region is not directly supported in RS2 since no facilities exist in the finite-element method for a zero strength material with possible hydrostatic forces applied to the surface of a tension crack. Consequently, how one models a tension crack zone using a finite-element analysis is open to debate.
One method that has been used successfully (see Verification#27 in the RS2 Slope Stability Verification manual), is to represent the soil in the tension crack region as a distributed load applied to the soil underlying the tension crack zone. This works well for dry tension cracks but water filled tension cracks is another issue.
DISTRIBUTED AND LINE LOADS
Distributed loads (uniform and triangular) and line loads are imported into RS2.
PSEUDO-STATIC SEISMIC LOADS
RS2 supports the import of pseudo-static seismic load coefficients from Slide2.
MATERIAL PROPERTIES
The following Slide2 material models are supported: 1) Mohr-Coulomb, 2) Undrained (Constant), 3) Undrained F(datum), 4) Infinite Strength, 5) Shear-Normal Function, 6) Hoek-Brown, 7) Generalized Hoek-Brown, 8) Power Curve, 9) Barton-Bandis, 10) Vertical Stress Ratio, 11) Hyperbolic, 12) Shansep, 13) Generalized Anisotropic, 14) Discrete Function,
The following Slide2 material models are not supported: 1) Undrained F(depth), 2) Anisotropic Strength, 3) Drained-Undrained.
The Anisotropic Strength and Anisotropic Function set the material type to Mohr-Coulomb and set the strength as being the minimum of the different directions.
NOTE: RS2 does not support any Generalized Hoek-Brown parameters varying with depth. RS2 only supports variation from a fixed datum or variation that is radial; it does not support depth from the slope surface or from the top of the layer.
SUPPORT AND SUPPORT PROPERTIES
RS2 will read Slide2 support elements. All support elements in a Slide2 file are read in as RS2 bolt elements EXCEPT for geotextiles. Geotextiles are read in as structural interface elements. Structural interfaces have two components: 1) A structural beam element to model the tensile behavior of the geotextile, 2) Two interface elements on either side of the geotextile to model slip between the geotextile and the soil.
Active and passive force application methods for Slide2 support models have no meaning in a RS2 finite-element analysis, and are therefore ignored. An equivalent behavior can be defined by setting a Pre-Tensioning force in the RS2 bolts.
Slide2 support models that are imported into RS2 are: 1) End Anchored, 2) Geotextiles, 3) Grouted Tieback, 4) Soil Nail.
Support models which are NOT imported: 1) Grouted Tieback (with friction), 2) Micro-Pile.
End anchored or deadman anchors are read in as RS2 end-anchored bolts. Peak capacity of the RS2 bolt is set to the Slide2 anchor capacity, the residual capacity is set to zero. The bolt spacing is read from the Slide2 file.
Geotextiles will convert to structural interfaces with RS2 liner elements being defined as geotextiles with a default tensile modulus and a peak tensile capacity. The peak tensile capacity is read from the Slide2 geotextile support properties. The residual tensile strength is set to zero. The tensile modulus is given a default value equal to 100 times the tensile strength. The user should define the appropriate tensile modulus for the geogrid/geotextile they are using. See the online help for a description of this parameter. If the Slide2 Shear Strength Model for the geotextile-soil interface is linear, the RS2 joint interface properties for the structural interface are given a Mohr-Coulomb slip criterion with cohesion and friction angle equal to the adhesion and friction angle defined for the Slide geotextile. If the Slide2 Shear Strength Model for the geotextile-soil interface is hyperbolic, the RS2 joint interface properties for the structural interface are given a Geosynthetic Hyperbolic slip criterion with adhesion and friction angle equal to the adhesion and friction angle defined for the Slide2 geotextile. Interface normal and shear stiffnesses between the geotextile and the soil are also required. Default values of Kn=100000KPa/m and Ks=10000KPa/m are used. These are based on a number of published values and can be changed in the Joint Properties dialog. Material dependent geotextile properties are not read from the Slide file but can be manually defined in RS2. Slide anchorage methods are supported through the different finite-element mesh end conditions of the structural interface. See the online help for more information on these parameters. Strip coverage is not supported for values other than 100%. You will have to factor the interface and tensile strength properties to account for strip coverage.
Slide2 Grouted Tiebacks and Soil Nails are both converted to RS2 tieback bolts. The only difference between the two is the grouted length. Soil Nails have 100% grouted length. The RS2 tieback peak tensile capacity is taken as the minimum of the Slide2 plate capacity and tensile capacity. The residual capacity is set to zero. The bolt spacing is read from the support spacing in the Slide2 file. In the case of tiebacks, the grouted length is properly read. For both Slide2 soil nails and grouted tiebacks, the bond strength is properly read.
Slide2 Grouted Tiebacks with friction are not properly read into RS2. They are read as RS2 tieback bolts but no bond capacity is defined. The user must either define an equivalent bond capacity to the frictional characteristics, thus accounting for the depth of the anchor, or use structural interface elements instead. In the case of structural interface elements, the debonded length of the bolt should be given different material properties than the bonded length. In particular, the debonded length should be given joint stiffness properties (normal and shear) equal to zero. You will require a vertex on the structural interface to separate the bonded from the debonded length.
Micro-piles are not supported in RS2. Piles should be modeled using structural interfaces or liner elements.
User-defined support properties in Slide2 are not supported in RS2.
MESH GENERATION
The complete finite-element mesh is automatically created during the import of the Slide2 file. No user intervention is required. The mesh, by default, will contain approximately 3000 uniformly distributed 6 noded triangular elements.
BOUNDARY CONDITIONS
The import facility automatically determines the top, bottom and sides of the external boundary used in the Slide2 model. The boundary conditions applied to these surfaces are: 1) the top boundary (ground surface) is free to move in the x and y directions, 2) the sides are fixed in the x and y directions (pinned), 3) the bottom surface is fixed in the x and y directions (pinned). The following image shows a typical mesh and boundary conditions after import of a Slide2 model.
INITIAL STRESS AND BODY FORCE
By default, each finite-element is given both an initial stress and a body force (self weight). The initial vertical stress is estimated from the weight of the material above the element. RS2 automatically determines the ground surface above the element and automatically determines the stress due to the material above the element. The horizontal initial stress is set equal to the vertical stress (hydrostatic stress state). The body force is equal to the unit weight defined for the material in Slide2. Since RS2 allows for only one unit weight, when reading a Slide2 file, the greater of the moist or saturated unit weight is taken.
This system of element loading (the combination of initial stress and body force) is defined in the material properties dialog by defining the Initial Element Loading as being Field Stress & Body Force. Initial Element Loading is one of the more complicated concepts in RS2 and it is highly recommended for people who do not understand it, to review the online help on the subject.
Since the initial stress and body force does not define an equilibrium state for a slope (or any non-horizontal ground surface), the material within the slope will deform under the influence of its own self weight and initial stress. In general, the material will deform horizontally away from the slope surface since the initial horizontal stresses are not in equilibrium. The final vertical stress distribution within the slope will be a gravitational stress distribution while the horizontal stress will be due to some unloading and redistribution of stress due to the Poisson effect. When you import a Slide2 file, all imported materials are given a Poisson’s ratio of 0.4. If you know your material Poisson’s ratio, you may change the default value inside the RS2 material properties dialog.
Horizontal stress plays a very important role in the stability analysis. In general, little is known about the horizontal stress distribution within a soil or rock mass. So assuming that the material has an initial hydrostatic stress state is not unreasonable. This is the assumption made in a large number of the slope stability verification examples. Results from these examples show good agreement with the Slide2 results. If knowledge of the initial vertical and horizontal stress state is known, it should be used in defining the initial stress state for the model.
PONDED WATER
In RS2, ponded water is replaced by an equivalent distributed load (pressure) normal to the submerged portion of the external boundary. The distributed load, which varies according to the submerged topology, is defined using a series of “Ponded Water” loads which are oriented normal to the external boundary. When importing a Slide2 file with ponded water, RS2 will automatically replace the ponded water by these ponded water distributed loads.
GROUNDWATER FINITE-ELEMENT ANALYSIS
Both Slide2 and RS2 have integrated finite element steady-state or transient unsaturated groundwater modeling capabilities. Thus RS2 will read the hydraulic properties (i.e. permeability, unsaturated hydraulic parameters), boundary conditions, and finite-element mesh from the Slide2 data file. By default, if a Slide2 model contains a groundwater mesh, RS2 will use this mesh for both stress and groundwater analysis and will not generate a new mesh on import of the Slide2 file. The only exception to this rule is if a distributed load exists in the Slide2 file as well. In this case, the mesh must be created during import but the boundary conditions of the groundwater mesh are preserved.
ELASTIC PARAMETERS
RS2 requires a material modulus and poisson ratio, both of which are not defined in Slide2. By default, the modulus is set to 50000 kPa for metric Slide2 files and 1000000 psf for imperial files. The poisson ratio is set to 0.4. It’s important to note that this is a typical modulus for a sandy soil. If the model you are converting is a rock slope, it is recommended to use the appropriate rock mass modulus. Rock mass modulus can be computed using the program RSData. The following table is a quick guide to typical values:
Young’s Modulus (E)
- Clay soil: 10-200 MPa (soft to stiff)
- Sandy soil: 10-50 MPa (loose to compact)
- Gravel soil: 70-170 MPa (loose to compact)
- Soft clay: 1-3 MPa
- Hard clay: 6-14 MPa
- Loose sand: 10-28 MPa
- Dense sand: 35-69 MPa
- Granite: 10-70 GPa
- Sandstone: 1-20 GPa
- Shale: 1-70 GPa
- Limestone: 15-55 GPa
- Marble: 50-70 GPa
Poisson’s ratio
- Sandy Soil: 0.25-0.4
- Gravel Soil: 0.15-0.35
- Granite: 0.1-0.3
- Sandstone: 0.21-0.38
- Shale: 0.2-0.4
- Limestone: 0.18-0.33
- Chalk: 0.35
- Marble: 0.06-0.22