Cyclic Triaxial Testing and The Reasons Why It Is Conducted

Different cyclic loading conditions like earthquakes, sea waves, vehicles and trains, winds etc. are the reasons why cyclic triaxial testing is performed on soils. This testing is necessary to assess the strength and deformation properties of soil. This article is an attempt to explain what is cyclic triaxial testing and why it is conducted.

What is cyclic triaxial testing?

In cyclic triaxial testing, the strength and the deformation properties of soil are determined, which gets affected by dynamic loading conditions. The dynamic conditions which affect the soil are the earthquakes, sea waves, vibrating machines etc. The dynamic properties of soil are measured using a variety of dynamic triaxial tests in the laboratories.

Why the dynamic cyclic triaxial test is conducted?

In various engineering projects, the soil deposits undergo dynamic cyclic loading. These loadings occur because of many reasons. It can be due to the environmental factors like ocean storms, earthquakes and seismic activities, or it can be due to human activities like traffic passing and machines vibrating on site.

Conducting dynamic triaxial tests are more complicated than conducting static tests because, in the cyclic triaxial testthe dynamic behaviour of soil in response to a different frequency of load is investigated in the laboratory as well as in the field. The dynamic triaxial testing is one of the most convenient and versatile methods in which soil behaviour in respect to dynamic loading is assessed in the laboratory.

 Frequency of dynamic load

The frequency of the dynamic load depends on the source of loading. The waveform of loading can be relatively uniform and have a single frequency like in the case of vibrating machines, or it can be random and has a range of frequencies like in case of earthquakes. In order to determine the effect on soil, it requires modern test system in the laboratories.

Scope of cyclic triaxial testing 

In the dynamic triaxial test, we determine the shear modulus and damping ratio of soils by using load and displacement system of cyclic triaxial. This test can be applied to both the fine-grained and the coarse-grained soil. This test is also applicable to study the liquefaction analysis of sandy and salty soil.

In order to perform a dynamic triaxial test, the same process as in case of a static triaxial test is followed, considering the significant differences in the sheering stage and during an analysis of the soil response. When preparing for the dynamic cyclic test, some additional suggestions can also be followed like prepare for the extension loading, select the most appropriate control parameter, ensure accuracy in the deformation measurement and consider the frequency effect of loading etc.

Cyclic triaxial test of dynamic soil is easier in handling for the practising engineer. It is one of the most reliable and rational ways to measure the dynamic properties of the soil. This article provides deep insight into the concept of cyclic testing, reasons why it is conducted, the frequency of the dynamic load and its scope.

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