Project Overview
This tutorial focuses on the simulation of a Consolidated Drained (CD) triaxial test using the Abaqus software.
The model is based on Example 5.6 from the Sam Helwany book. A cylindrical soil specimen is subjected to a confining pressure and then sheared under drained conditions.
The Abaqus analysis is used to obtain the deviator stress–axial strain and volumetric strain–axial strain relationships. The numerical results are then compared with the corresponding results presented in the reference example.
Model Description
The soil specimen is modeled using a two-dimensional axisymmetric finite element model. The specimen has a diameter of 5 cm and a height of 5 cm.
The soil is modeled using a pore fluid/stress axisymmetric element, which allows both soil deformation and pore water pressure to be considered in the analysis.
The clay specimen is assumed to be normally consolidated and is modeled using the Extended Cam-Clay model. The initial void ratio is 0.889 and the permeability is 0.025 m/s.
The CD triaxial test is performed in two main steps. In the first step, the soil specimen is subjected to a uniform confining pressure. In the second step, a vertical load is applied to the specimen until failure.
Analysis Steps
The analysis is performed in two steps to simulate the consolidated drained triaxial test.
Step 1: Consolidation
In the first step, a uniform confining pressure of 210 kPa is applied to the top and lateral surfaces of the soil specimen.
The top surface is permeable, allowing water to drain during the consolidation stage. The Geostatic option is also used to establish equilibrium within the specimen and ensure that the initial stress state is consistent with the initial yield surface of the Extended Cam-Clay model.
Step 2: Shearing
In the second step, a downward displacement of 8 mm is applied to the top of the specimen to simulate axial shearing.
The displacement is applied at a very low rate over a period of 109 seconds. This very slow loading rate is used to maintain drained conditions and keep the excess pore water pressure approximately zero.
The duration of the shearing step is set to 109 seconds. A very long analysis time is considered because the test is performed under drained conditions and the loading rate must be sufficiently low.
Drainage Conditions
The analysis is performed under drainage conditions. The top and bottom surfaces of the soil specimen are considered permeable, allowing water to drain through these surfaces during the analysis.
These drainage conditions allow the pore water pressure generated during loading to dissipate and reproduce the conditions of a consolidated drained triaxial test.
Deviator Stress vs. Axial Strain
One of the main objectives of this simulation is to obtain the relationship between deviator stress and axial strain.
The curve obtained from Abaqus is compared with the corresponding deviator stress versus axial strain curve from the Sam Helwany book.
Volumetric Strain vs. Axial Strain
The volumetric strain is also investigated during the shearing stage. The volumetric strain is calculated from the normal strains in the three principal directions:
εv = εx + εy + εz
The relationship between volumetric strain and axial strain is obtained from the Abaqus results and compared with the corresponding consolidated drained triaxial test results given in Example 5.6 of the Sam Helwany book.
Comparison with Sam Helwany Book
The numerical results obtained from Abaqus are compared with the results presented in Example 5.6 of the Sam Helwany book.
The comparison includes both the deviator stress versus axial strain relationship and the volumetric strain versus axial strain relationship.
What You Will Learn
- How to model a cylindrical soil specimen in Abaqus.
- How to simulate a Consolidated Drained (CD) triaxial test.
- How to apply a confining pressure of 210 kPa.
- How to define the consolidation stage.
- How to perform the shearing stage under drained conditions.
- How to define permeable surfaces for drainage.
- Why a very long analysis time is required for drained loading.
- How to obtain deviator stress versus axial strain.
- How to calculate volumetric strain from the three normal strains.
- How to compare Abaqus results with reference results.
Key Features
- Consolidated Drained (CD) triaxial test.
- Cylindrical soil specimen.
- 5 cm diameter and 5 cm height.
- 210 kPa confining pressure.
- Two-step analysis.
- Long-duration shearing step.
- Drained loading conditions.
- Permeable top and bottom surfaces.
- Deviator stress versus axial strain.
- Volumetric strain versus axial strain.
- Comparison with Sam Helwany Example 5.6.
- Free Abaqus tutorial.
Project Information
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