SEDL / STP / STP883-EB / STP36349S

The Use of the Point Load Index in Weak Carbonate Rocks

Abbs, AF
Senior engineer, Dames and Moore, London, SWIA

Pages: 9    Published: Jan 1985

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Abstract

There has been increasing use of the point load index as a measure of rock strength since its introduction in 1972. The test results have been correlated to in the uniaxial compressive strength σ^f of the rock. The correlations between the rates of point load index Is and the uniaxial strength σ^f for conventional strong rocks are σf/Is = 16 to 24. The small size of the equipment and the simplicity of the test have led to its use on site on many offshore projects.

Recent experience with weak porous carbonate rocks from offshore areas of the Middle East have proven that the relationship for these materials is much closer to σf/Is = 3.7 with actual field correlations varying from 2.7 to 8.8. Moreover, statistical studies of a large number of point load test data show that this test is poorly suited to weak carbonate rocks.