Question

what are some failure types of unconfined compression test? how do sample disturbance and soil remolding change the results of the unconfined compression test? and does the moisture content affect the unconfined compression strength and shear strength of clay?

Answer 1

The soil specimen may undergo either plastic failure or brittle failure .When a brittle failure of the soil specimen occurs, the proving ring dial gauge indicates a peak load, which decreases rapidly with a further increase of strain. In brittle failure, a distinct failure plane in the form of a crack will occur across the specimen.

In plastic failure, no definite peak load is indicated and the soil specimen bulges laterally. In such a case, the load corresponding to 20% axial strain is taken as the failure load. There will be no distinct failure plan and a number of small and fine cracks occur, distributed throughout the specimen.

Due to sample disturbance and soil remolding loss of strength of clay soils is primarily caused by the destruction of the clay particle structure that was developed during the original process of sedimentation.whatever strength you are supposed to get with the undisturbed sample you will be getting rather lesser value.

The shear strength and unconfined compression strength of soil goes on decreasing with increase in moisture content.