The cyclic triaxial test is performed to examine the strength of soil deformation properties. It is carried out under cyclic loading conditions. In many of the geotechnical engineering projects, the soil deposits undergo dynamic cyclic loadings during the lifetime of the project. Environmental factors like earthquakes, ocean storms, or various human activities like vibrations from the machines, passing vehicles, etc. can cause such loadings.With the help of cyclic triaxial testing system, dynamic properties of soil are obtained by two load application methods that are constant load method and constant displacement method.
This test involves placing the soil sample into a cell that can be pressurized. In the process of this test, firstly the soil is prepared and kept in the triaxial cell for application of confining pressure to it. Then there isthe application of deviator stress. Deviator stress is an additional axial stress.Therefore, the procedure includes preparation of soil sample, saturation, consolidation, and shearing. Thecyclic triaxial test is performed with the help of a dynamic triaxial apparatus which is an advanced version of a statictriaxial system.This apparatus containsthe following components:
- Frame: Also called the load frame is a one in which the important interface of the computer is installed. These interfaces are of mechanical and electronic nature. It does not let the sample to deform due to the total load application.
- Dynamic actuator: With the help of a dynamic actuator, the load frame can apply cyclic load to the sample of soil. It varies in capacities and loads. According to the soil sample which is being used for testing and user’s requirement, its capacity, and load is selected.
- Triaxial cell: Sample is kept in this cell along with the cell fluid.A dynamic triaxial cyclic test is performed by using the triaxial cell that is a modified version.
- Pressure controllers: There are automatic pressure controllers for increasing or decreasing the cell pressure according to the amount of stress.
- Back pressure: It evaluates the pore pressure or back pressure on the soil sample and identifies the change in its volume.
- Load cell: These cells compute the axial pressure that is applied to the soil sample. They also help in preventing the friction between the ram and the cell.
- Displacement sensors: These sensors calculate the height and deformation of the sample.
- Pore water pressure measuring sensors: As the name suggests, these sensors evaluate the change in pressure of pore water within the sample.
- Data Acquisition System: It converts the data to digital form. It should be capable of recording data promptly.
There are different ways to perform cyclic triaxial tests, but the user should select the most accurate one according to the soil of their field.There are three different types of the triaxial test-unconsolidated undrained, consolidated undrained, and consolidated drained. The most commonly used method is consolidated drained. The cyclic triaxial testing machine or system must have proper components for accurate and desired results and the procedure should be followed rightly for accurate result.