Reference

IS-9143-1979-Method for the determination of unconfined compressive strength of rock materials

Objective

The objective of this test is to determine unconfined compressive strength of rock. This test is primarily done to classify the rock on the basis of strength.

Apparatus used

 Procedure

• Specimen shall be tested at a moisture content close to field condition as possible.
• L/D ratio, preferably be 2 to 3. If L/D < 2, then correction shall be applied.
• Dia of specimen must be greater than 10 times the dia of largest grain size. Preferable dia is 45 mm. But in no case the dia of the core sample should not be less than 35 mm.
• Specimen should be prepared in such a manner that the cylindrical surface shall be smooth and free from abrupt and irregularities.
• Dia of the test specimen shall be measured to the nearest 0.1 mm by averaging two diameters measured at right angles to each other at about the upper height, the mid height and the lower height of the specimen.
• Clean the surfaces of the two bearing discs and the test specimen. Place the specimen on the lower disc.
• Carefully align the axis of specimen with the center of thrust of the spherical seat.
• Apply load continuously at a constant stress rate within the limits of 0.5 MPa/s to 1.0 MPa/s.
• Record the maximum load on the specimen at failure in N within 1% accuracy.
• At least 5 specimens are required to give a representative value.

Calculations

The UCS of the specimen is calculated by dividing the maximum load carried by the specimen during the test, by the average cross sectional area.

Report

The U.C.S. is reported for each specimen in the sample, together with the average result of the sample. The U.C.S. value is expressed to 3 significant figures.