Simulation of Consolidated Undrained (CU) Triaxial Test Abaqus

Project Overview

This tutorial focuses on the simulation of a Consolidated Undrained (CU) triaxial test using Abaqus software. The example is based on Example 5.7 from the Sam Helwany book.

The numerical results obtained from Abaqus are compared with the corresponding results presented in the book. The comparison is performed using the deviator stress and excess pore water pressure developed during the triaxial test.

Model Description

The soil specimen is modeled as a cylindrical sample with a diameter of 5 cm and a height of 5 cm.

The consolidated undrained 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.

Confining Pressure

In the first step, a uniform confining pressure of 210 kPa is applied to the soil specimen.

The confining pressure is applied to the top surface and the lateral surface of the soil specimen to establish the required stress state before the shearing stage.

Shearing Step

In the second step, a vertical load is applied to the soil specimen until failure. This step represents the undrained shearing stage of the triaxial test.

The duration of the shearing step is set to 100 seconds. Since the test is performed under undrained conditions, a relatively short loading time is used so that there is insufficient time for water to drain from the soil.

Undrained Conditions

The model is analyzed under undrained conditions. The top and bottom surfaces of the soil specimen are considered impervious, preventing water from draining through these surfaces during the shearing stage.

As a result, excess pore water pressure develops inside the soil specimen during the application of the vertical load.

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 deviator stress versus axial strain curve obtained from Abaqus is compared with the corresponding curve presented in the Sam Helwany book.

Excess Pore Water Pressure

The development of excess pore water pressure during the undrained shearing stage is also investigated.

Because drainage is prevented during the shearing stage, the applied loading results in the generation of excess pore water pressure within the soil specimen.

The relationship between excess pore water pressure and axial strain is obtained from the Abaqus analysis.

Comparison with Sam Helwany Book

The numerical results obtained from Abaqus are compared with the results presented in Example 5.7 of the Sam Helwany book.

The comparison includes both the deviator stress versus axial strain relationship and the excess pore water pressure versus axial strain relationship.

What You Will Learn

• How to model a cylindrical soil specimen in Abaqus.
• How to simulate a Consolidated Undrained (CU) triaxial test.
• How to apply a confining pressure of 210 kPa.
• How to define the consolidation stage.
• How to perform the shearing stage under undrained conditions.
• How to define impervious surfaces for the soil specimen.
• How to select an appropriate loading time for an undrained test.
• How to obtain deviator stress versus axial strain.
• How to investigate excess pore water pressure.
• How to obtain excess pore water pressure versus axial strain.
• How to compare Abaqus results with reference results.

Key Features

• Consolidated Undrained (CU) triaxial test.
• Cylindrical soil specimen.
• 5 cm diameter and 5 cm height.
• 210 kPa confining pressure.
• Two-step analysis.
• 100-second shearing step.
• Undrained loading conditions.
• Impervious top and bottom surfaces.
• Deviator stress versus axial strain.
• Excess pore water pressure versus axial strain.
• Comparison with Sam Helwany Example 5.7.
• Free Abaqus tutorial.