The Unconfined Compression Test of a soil is an axial compression test in which the test specimen is provide with no lateral support while undergoing vertical compression. The test affords a quick and simple method for measuring the unconfined compressive strength of a cylinder of a cohesive soil and indirectly shear strength which is generally taken to be one half of the unconfined compressive strength. The results of unconfined compression test are widely used for ascertaining the relative consistency of soils and sensitivity of clayey soils, for estimating ultimate bearing capacity of a homogenous deposit of a clay and allowable load on a group of friction piles in clay, design of roads, runways and building construction.

The primary purpose of the Unconfined Compression Test is to quickly determine a measure of the unconfined compressive strength of rocks or fine-grained soils that possess sufficient cohesion to permit testing in the unconfined state. This measure is then used to calculate the unconsolidated undrained shear strength of the clay under unconfined conditions. In general, The UCT can be conducted on rock samples or on undisturbed, reconstituted or compacted cohesive soil sample.

In the unconfined compression test, the sample si placed in the loading machine between the lower and upper plates. Before starting the loading, the upper plate is adjusted to be in contact with the sample and the deformation is set as zero.