Introduction Of Compression Testing Machine

By Author: sudarshan singh
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Compression testing is a good way to measure the condition of the rings, cylinders, and valves. You will need a helper to do this test. It can be done alone, but is more difficult, and you cannot see how the cylinder pumps up.

The unconfined compression test is still used as a means of rapidly evaluating the shear strength of cohesive soils although it is gradually losing favour. The unconfined compressive strength is the maximum load attained per unit area or the load at 15% axial strain, whichever occurs first on a cylindrical sample tested in compression. The shear strength is taken as equal to 1/2 the unconfined compressive strength.

In this laboratory, strain control will be used and the compression machines will be adjusted to a rate of loading which will provide 15% axial strain on the sample in approximately 10 minutes. Sensitivity of a cohesive soil is defined as the undisturbed strength of the soil divided by the remolded strength. The sensitivity cannot be less than 1. For most local clays, the sensitivity is between 1 and 3. For some highly sensitive clays it can exceed 10 and,

In practice ...
... strain controlled loading is now almost universally used for this test.

In practice the test specimens are usually obtained by extruding thin-wall tube samples.The length to diameter ratio of the specimen should be between 2 and 3. Two types of loading devices are permitted, either strain controlled or stress controlled.

In the strain controlled test the rate of loading is controlled so as to produce a uniform axial strain.

in some cases, be so high that it cannot even be accurately measured. The most accurate method of determining sensitivity involves use of the laboratoryvane shear apparatus. Two devices used to check the unconfined strength or shear strength in the field are the Torvane and the Pocket Penetrometrer.

In the stress controlled test the rate of loading is controlled so as to produce a uniform increase in axial load.

You will use both and compare the results with that obtained from the unconfined test. The results of this lab will also be compared to the results of a triaxial compression test performed in a later lab. It is therefore necessary to retain a copy of all the results from this lab.

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