[GTS NX] 3D Slope Stability Check

0. Contents 

1. Overview

1-1 Learning Purpose

Recent advancements have enabled numerical slope stability analysis to replicate destroyed shapes with a realism that closely mirrors reality and accurately reflects site conditions. However, a significant limitation remains in analyzing 3D slope behavior using 2D analysis, which only accounts for the cross-section of a slope. The key disparity between 2D and 3D analyses lies in their ability to incorporate factors that influence slope behavior, such as the shape of the slip surface, distribution of ground materials, and rigidity of the slip surface.

While 2D analysis overlooks these critical components, 3D analysis can integrate them, resulting in more reliable outcomes. Put simply, 3D slope stability analysis allows for the consideration of the slope's slip range, identification of areas where slope activity is concentrated, and the formulation of solution plans based on these findings.

Analysis Model Overview

In this tutorial, we will cover the following main concepts :

1. Generating surface and bedding planes using grid face

2. Generating meshes

3. Conducting slope stability analysis

4. Interpreting analysis results, including safety factor and maximum shearing strain

5. Checking results on specific cross-sections using the 'Clipping plane' functionality

1-2 Modeling and Analysis Summary

This 3D model comprises weathering soil and bedrock layers. Through an evaluation of slope stability during both dry and rainy seasons, we aim to identify vulnerable areas prone to potential failure.

Cross-Section

2. Analysis Setting

2-1 Analysis Setting

Configure the model type, gravity direction, initial parameters, and unit system for the analysis. The unit system is flexible and can be adjusted at any point during the modeling process or after conducting the analysis. Input parameters will be automatically converted based on the selected unit system.

This tutorial employs a 3D model with gravity acting in the Z direction and utilizes the SI unit system.

Analysis Setting Window

3. Material and Property

3-1 Definition of Ground and Structural Materials

Define the soil model type as 'Mohr-Coulomb'. The ground materials are defined as follows:

Ground Material

Parameters for General Porous Non-linear

3-2 Define Properties

Properties represent physical attributes of the meshes and will be assigned to mesh sets during mesh generation. Define the ground properties by assigning the materials to be used in each ground layer.

Ground Property

4. Modeling

4-1 Geometry Modeling

The primary objective of this tutorial is to generate 3D bedding planes from grid face, conduct slope stability analysis using the SRM method, and analyze the results. You can begin the tutorial by opening the start file, where basic materials and properties have already been predefined.

[ : Geometry → Surface & Solid → Make Face]

To generate a face with coordinate data containing strata and ground geometry information, follow these steps :

① Go to the [Grid Face] tab.

② Enter '50' for both 'M (No. In X)' and 'N (No. In Y)'.

③ Input '-10' for both the origin X and Y coordinates.

④ Input '270' for both the LX and LY coordinates.

⑤ Click on [Elevation], then select [Load…] to import the geometry data from '3d_slope_terrain.txt'.

⑥ Click [OK], then press the [Apply] button.

⑦ Similarly, generate the strata by importing '3d_slope_strata.txt' using the same procedure.

Make Face

[ : Geometry → Surface & Solid → Box]

To generate a box solid representing the ground, follow these steps :

① Enter the Origin point as (0, 0, 0).

② Input '250' for the length, width, and height.

③ Name the geometry set as 'ground'.

④ Click [OK].

[ : Geometry → Divide → Solid]

To divide the ground solid with the surface and bedding plane created using the grid face :

① Select the ground solid as the target object.

② Change the selection filter to 'Face(A)'.

③ Choose the ground surface and bedding plane generated in the previous step as the tool surface.

④ Select the geometry set as 'Ground'.

⑤ Click [OK].

⑥ Press the [Delete] key to remove any unnecessary solid above the ground surface.

Divide Solid

4-2 Generate Mesh

[  : Mesh → Generate → 3D]

To generate meshes for the upper solid in the [Auto-Solid] tab :

① Input a size of '10'.

② Select 'Hybrid Mesher'.

③ Check the box for [Match Adjacent Faces].

④ Choose '2: Weathering soil' as the property and name the mesh set as 'Weathering soil'.

⑤ Click the button. In the Advanced options, check [Higher-Order Element] and click [OK].

⑥ Generate weathering soil meshes by clicking [Apply].

⑦ Repeat the same process to generate meshes for 'Bed rock'.

Mesh Generation

5. Analysis

5-1 Setting Boundary Conditions

[ : Static/Slope Analysis → Boundary → Constraint]

To set boundary conditions against internal deformation or rotation based on the GCS :

① Go to the [Auto] tab.

② Type in the name and boundary set name.

③ Click [OK].

[ : Static/Slope Analysis → Water Level]

To set a boundary to simulate the saturated status of the ground surface :

① In the Work Tree > Geometry, right-click and select [Show].

② In the [Face] tab, choose the ground surface as the target object.

③ Enter an interval of '5'.

④ Name it 'Water level' and click [OK].

5-2 Setting Analysis Case

[ : Static/Slope Analysis → Analysis Case → General]

To set the analysis method and model data for the analysis :

① Input the name as 'Dry period'.

② Select the solution type as 'Slope Stability (SRM)'.

③ In Analysis Control > Slope Stability (SRM) tab, select [Advanced Nonlinear Parameter]. Check [Use Arc-Length Method] and input the value as shown in the following image.

④ Move all mesh sets, boundary conditions, and load sets to [Active set].

⑤ In [Output Control], check 'Strain' at the [Output type] tab.

⑥ Click [Apply].

⑦ Similarly, create an analysis case for the 'Rainy period'.

⑧ For the rainy period, check [Define water level] in Analysis Control > General. Input '1', and select 'Water Level'.

Nonlinear Analysis Option

Output Control (Check Strain)                            Analysis (Define Water Level)

5-3 Perform Analysis

[ : Analysis → Analysis → Perform]

① Perform the analysis

6. Results

6-1 Safety Factor and Destroyed Shape

After the analysis, you can verify displacement and stress in the Result Tree. All results can be visualized as contour plots, tables, and graphs. In this tutorial, the main result items that need to be checked are :

• Safety factor/Destroyed shape

• Reviewing through 'Clipping plane'

To verify the minimum safety factor and the destroyed shape in the Result Tree when performing the strength reduction method :

② Select the last stage to verify the results (the stage which shows the minimum safety factor).

③ Navigate to Solid Strains > E-MAX SHEAR in the Work Tree under Results > Dry period > Slope stability analysis.

Maximum Shear Strain (Dry and Rain Period)

6-2 Verify with Clipping Plane

① To view the result at any cross-section in GTS NX using the "clipping plane" tool :

② Select the stage to verify the result (the stage which shows the minimum safety factor).

③ Navigate to Solid Strains > E-MAX SHEAR in the Work Tree under Results > Dry period > Slope stability analysis.

④ Select the Clipping plane icon ( ) in the 'Advanced View Toolbar'.

⑤ In the [Define Plane] settings, set the plane direction to 'X' and the distance to '125(m)'.

⑥ Click [Add] to create 'plane1'.

• Uncheck the [Display Capped Part] option.

• In Result > General > Contour, set the contour type to 'Fringe'.

Break Down Plane (Dry and Rain Period)

• In the 'Clip & Slice Plane' section, click the button(). You can observe the destroyed shape in specific locations by defining several planes.

Multi Break Down Plane (Dry and Rain Period)