What is the rubber membrane used for in triaxial test?

Question

I am doing exams in college and my soil mechanics exam is soon so i need to know this. Thanks

Answer 1

a thin rubber membrane separates the air and water and ... horizontally and vertically so as to trim the sample to the. required diameter. ...

The following is a basic outline of the triaxial test procedure:

1-The specimen is a cylindrical sample normally 100 mm (4 in.) in diameter by 200 mm (8 in.) high .The sample is generally compacted in the laboratory; however, undisturbed samples are best if available (which is rare).

2-The specimen is enclosed vertically by a thin "rubber" membrane and on both ends by rigid surfaces (platens)

3-The sample is placed in a pressure chamber and a confining pressure is applied (s3)

4-The deviator stress is the axial stress applied by the testing apparatus (s1) minus the confining stress (s3). In other words, the deviator stress is the repeated stress applied to the sample.

5-The resulting strains are calculated over a gauge length, which is designated by "L"

6-Basically, the initial condition of the sample is unloaded (no induced stress). When the deviator stress is applied, the sample deforms, changing in length.This change in sample length is directly proportional to the stiffness.

Answer 2

It is a rubber cylindrical sheeth that stops fluid escaping and impregnating inaccuracies into the test!!