What is a triaxial test?
Why it is significant to know soil property? and which type of property?
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Following are the drainage conditions used for triaxial testing:
In triaxial test shear, strength parameters are cohesion and angle of internal friction which is calculated.
During the process of testing that is the shear process, the soil sample under the experience of axial strain for the volume changes and pore water pressure develops. Magnitude acting on the shear stress is different for different planes of soil sample. When at some plane, the soil fails, that plane is called a failure plane, and the corresponding strength is called shear strength.
Triaxial test is basically used to determine the shear strength of soil.
It has a great importance over direct shear test some important points are as follows
1- Drainage conditions can be controlled for all type of soil .For example ,even while previous soils can be tested under undrained condition.
2- Pore water measurement can be done accurately.
3- Volume change can be measured
4- There is no rotation of the principle stress during the test . The failure plane is not forced
5. The specimen can fail on any weak plane ( but in direct shear test we forced to fail inthe horizontal plane which might not be the weakest plane )
Hope it will help
Triaxial test ;
The triaxial test is one of the most versatile and widely performed tests in the geotechnical laboratory. It allows shear strength and stiffness of soil and rock to be determined for use in geotechnical design.
– Procedure of triaxial test :-
The triaxial test typically involves subjecting a cylindrical specimen of soil, whose diameter ranges from 38mm to 100mm, into a cell that can be pressurized. Most of the specimens have an approximate 2:1 height to dia ratio and are sealed with a rubber membrane. The specimen preparation generally depends upon the type of soil. Cohesive soil samples are prepared directly from saturated compacted samples, either undisturbed or remolded. The specimen for cohesion-less soil is prepared with the help of the mold that maintains the required shape of the specimen.
And then the specimen is vertically covered with a thin rubber membrane and placed between two rigid ends inside a pressure chamber. The upper plate can move vertically and apply vertical stresses to the specimen. The axial stress/strain of the sample is controlled by the movement of this vertical axis. The water pressure surrounding the sample in the pressure chamber controls the confining pressure. Also, the volume change of the sample is controlled by measuring the exact volume of moving water.
There are three primary triaxial test carried out in a laboratory, depending upon the combination of loading and drainage condition ;
Triaxial test is significant to know soil property because it determines the ability of soil to resist shear stress and strain. Different combination of confining and axial stresses can be applied. Drained and undrained test can be carried out. The types of properties of soil which can be known by triaxial test are followed ;
a triaxial test involves confining a cylindrical soil or rock specimen in a pressure shell to stimulate the stress condition and then shearing to failure in order to determine the shear strength properties of the soil sample.
the sample should be saturated then consolidated and finally sheared, most commonly in compression