What is the standard L/D ratio for a cylindrical rock specimen for a UCS test?

The length to diameter (L/D) ratio should be between 2.0 and 2.5 (Clause 5.1).

What is the tolerance for the flatness of specimen ends?

The end surfaces shall be flat to a tolerance of 0.02 mm (Clause 5.1).

What is the minimum recommended diameter for a rock core specimen?

The diameter should not be less than 38 mm and also not less than ten times the largest grain size in the rock (Clause 5.1).

How is a specimen for a Brazilian (indirect tensile) test prepared?

It's a circular disc with a thickness-to-diameter ratio of approximately 0.5, prepared according to the general principles for cylindrical cores (Clause 5.4).

IS 9179

: 1979

Method for the preparation of rock specimens for laboratory testing

CurrentSpecializedTesting MethodGeotechnical · Rock Mechanics

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This standard specifies the methods for preparing rock specimens for various laboratory tests like compressive strength, tensile strength, and shear strength. It details the procedures for sampling, cutting, coring, grinding, and finishing specimens to required dimensional and geometric tolerances to ensure test results are accurate and repeatable.

Method for the preparation of rock specimens for laboratory testing

Quick Reference Values

Standard Length-to-Diameter (L/D) Ratio for Cylindrical Specimens2.0 to 2.5

End Flatness Tolerance for Cylindrical Specimens0.02 mm

End Perpendicularity Tolerance to Specimen Axis0.001 radian

Minimum Specimen Diameter vs Grain SizeNot less than 10 times the diameter of the largest grain

Standard Minimum Diameter for Cylindrical Specimens38 mm

Practical Notes

Achieving the specified end-face flatness and parallelism is the most critical and challenging part of the preparation, directly impacting compressive strength results.

The choice of coolant (usually water) during cutting and grinding is crucial; for water-sensitive rocks like shale, alternative coolants (e.g., oil) or dry preparation methods must be used to prevent sample degradation.

The orientation of the specimen with respect to the rock's natural bedding planes or foliation must be carefully recorded as it significantly influences the measured mechanical properties.