Unconfined Compression Test
Definition - What does Unconfined Compression Test mean?
The unconfined compression test is used to measure the shear strength of the soil. It is the most popular, cheapest, and quickest method to measure shear strength.
The test can be performed on intact, remolded, or reconstituted soil specimens using the strain-controlled application of axial load. The test method is only applicable to cohesive soils such as clays or cemented soils that will not expel water when loaded and will retain intrinsic strength once confining pressure is removed.
ASTM D2166/ D2166M-16 lays out the standard test method for determining the unconfined compressive strength of cohesive soil.
Trenchlesspedia explains Unconfined Compression Test
The apparatus required for an unconfined compression test includes a loading frame with two metal plates, a sampling tube, a split mold, a load measuring device, a calibrated proving ring or an electronic load cell, and a dial gauge.
For the test procedure, the sampling tube is pushed into the soil sample and then removed along with the soil.
The soil sample is then saturated and the specimen is extruded to the greased split mold and the ends are trimmed. The soil sample and the mold are then weighed.
The soil sample is now removed from the mold by splitting it. The length and diameter of the specimen are noted and placed at the bottom plate of the loading frame. The bottom plate is then raised so that the specimen contacts the top plate.
The proving ring and strain dial gauge are adjusted to read zero. The compression load is applied by raising the bottom plate to produce axial strain at the rate of 1/2 to 2% per minute.
The readings of the proving ring and strain dial gauges are recorded every 30 seconds. The compression is continued till the specimen fails or the specimen vertically deforms by 20%, whichever is earlier.