The unconsolidated undrained (UU) Triaxial Test is a quick method of estimating the shear strength of a soil. The soil which undergoes the test is sheared to failure without prior consolidation meaning this test is perfect for soil samples which are undisturbed however this is never the case. This means that results have to be interpreted with care so the undrained shear strength of the soil is not underestimated. For the purpose of this test I used the results posted by Dr.Brian Mc Cabe on blackboard as some of the equipment used in the practical was faulty. 1. Water content and the bulk density of your test specimen
2. Results of UU test on datasheet
3. Deviator stress and excess pore pressure vs. axial strain
Above we can see the plots of both excess pore pressure and deviator stress against axial strain. These results are typical of a consolidated undrained test for normally consolidated clays. The maximum deviator stress that occurred was 76.21kPa which results in a strain of 0.18. The excess pore pressure increases linearly with axial strain which can be seen clearly on the graph above. 4. Mohr’s circles of total and effective stress at failure for your test
5. Progression of the test (Deviator Stress Against Mean Effective Stress)
The above graph shows the progression of the test with relation to the deviator stress and mean effective stress over a given time. It is clear over the timeframe the deviator stress increase which the mean effective stress decreases. 6. Compare UU tests and CU tests. Comment on where the results are beneficial to geotechnical engineers.
The unconsolidated undrained test is does not measure the pore pressures where the consolidated undrained test does. It is also cheaper in cost and can be used for clays, silt clays and silts where the consolidated undrained test is mainly used for clays. The test can be beneficial to geotechnical engineers where construction is quick. As it is...