What specimen shape and size are required?

A cylindrical core with a length-to-diameter (L/D) ratio between 2.0 and 2.5. The minimum diameter should preferably be NX size (approx 54 mm). (Clause 4).

How is the Modulus of Elasticity (E) determined?

It's determined from the slope of the axial stress vs. axial strain curve, typically as the Tangent Modulus at 50% of the ultimate compressive strength. (Clause 7.1).

What is the specified loading rate?

The axial stress should be applied continuously at a constant rate between 0.5 to 1.0 MPa/s. (Clause 6.3).

How is Poisson's Ratio (ν) determined?

It is calculated as the negative ratio of the change in lateral (diametral) strain to the change in axial strain, taken from the same portion of the curve used for E. (Clause 7.2).

IS 9221

: 1979

Method for the determination of modulus of elasticity and Poisson's ratio of rock materials in uniaxial compression

CurrentSpecializedTesting MethodBIMGeotechnical · Rock Mechanics

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This standard specifies the laboratory method for determining the static Modulus of Elasticity and Poisson's ratio of intact rock core specimens. It details the requirements for specimen preparation, testing apparatus, procedure, and calculation of results from a uniaxial compression test.

Method for the determination of modulus of elasticity and Poisson's ratio of rock materials in uniaxial compression

Quick Reference Values

Specimen Length to Diameter (L/D) Ratio2.0 to 2.5

Minimum Specimen DiameterNX size (54 mm approx.)

Rate of Axial Stress Application0.5 to 1.0 MPa/s

Specimen End Flatness Tolerance0.02 mm

Perpendicularity of Ends to Specimen Axiswithin 0.001 radian

Key Formulas

Modulus of Elasticity (E) = Δσa / Δεa (Ratio of axial stress change to axial strain change)

Poisson's Ratio (ν) = - (Δεd / Δεa) (Negative ratio of diametral strain change to axial strain change)

Practical Notes

Specimen preparation is the most critical part of this test; non-parallel, rough, or non-perpendicular ends will lead to significant errors and premature failure.

Ensure strain gauges are properly bonded and positioned at the mid-height of the specimen to avoid end effects and capture representative strain.

The standard describes calculating Tangent Modulus at 50% ultimate strength or Secant Modulus between two stress levels; the choice depends on project requirements.