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IS 9221:1979 is the Indian Standard (BIS) for method for the determination of modulus of elasticity and poisson's ratio of rock materials in uniaxial compression. 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
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
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.
Standard Test Methods for Compressive Strength and Elastic Moduli of Intact Rock Core Specimens under Varying States of Stress and Temperatures
Method D specifically details the determination of elastic moduli in uniaxial compression, aligning directly with the IS code's scope.
ISRM Suggested Methods (2007)International Society for Rock Mechanics (ISRM), International
HighCurrent
Suggested Method for Determining the Uniaxial Compressive Strength and Deformability of Rock Materials
Provides globally recognized guidelines for determining deformability properties (modulus, Poisson's ratio) from uniaxial compression tests.
ASTM D3148-02ASTM International, USA
HighWithdrawn
Standard Test Method for Elastic Moduli of Intact Rock Core Specimens in Uniaxial Compression
As the predecessor to the current ASTM standard, its scope was a direct match, focusing exclusively on elastic moduli from uniaxial tests.
BS EN 1926:2006BSI/CEN, UK/Europe
MediumCurrent
Natural stone test methods - Determination of uniaxial compressive strength
Primarily for compressive strength, but includes determination of the modulus of elasticity as an optional parameter.
Key Differences
≠IS 9221 specifies a time-based loading rate (failure in 5-15 minutes), whereas modern standards like ASTM D7012 and ISRM mandate a more precise stress rate (e.g., 0.5-1.0 MPa/s), improving test repeatability.
≠While IS 9221 suggests measuring strain, modern standards like ASTM D7012 are more prescriptive, requiring a minimum of two axial and two lateral strain gauges to average readings and compensate for any bending effects during loading.
≠The Indian standard is less specific on the exact portion of the stress-strain curve to use for modulus calculation. ASTM D7012 provides more rigorous guidance on selecting the linear portion or using a secant modulus from near-zero to 50% UCS to avoid seating effects.
≠IS 9221 recommends a minimum specimen diameter of 45 mm, while ASTM D7012 and ISRM recommend larger minimum diameters (47 mm and 54 mm, respectively) to reduce scale effects and align with common core sizes (NX).
Key Similarities
≈All standards are based on the same fundamental principle: applying a uniaxial compressive load to a cylindrical specimen and measuring the resulting axial and lateral strains.
≈The required specimen geometry is consistent across all standards, specifying a right-circular cylinder with an L/D ratio typically between 2.0 and 2.5.
≈The formulae used to calculate Young's Modulus (change in axial stress / change in axial strain) and Poisson's Ratio (- change in lateral strain / change in axial strain) are identical.
≈Stringent requirements for specimen end preparation—flatness, parallelism, and perpendicularity to the core axis—are a common critical feature in all the standards to ensure uniform stress distribution.
Parameter Comparison
Parameter
IS Value
International
Source
Specimen L/D Ratio
2.0 to 2.5
2.0 to 2.5
ASTM D7012
Loading Rate
Failure in 5-15 minutes
0.5 - 1.0 MPa/s
ASTM D7012 / ISRM 2007
Min. Specimen Diameter
Preferably not less than 45 mm
Preferably at least 47 mm (NX Core)
ASTM D7012
Specimen End Flatness
Flat to 0.02 mm
Flat to 0.025 mm
ASTM D7012
End Perpendicularity to Axis
Within 0.001 radian (~0.06°)
Within 0.001 radian
ASTM D7012
Modulus Calculation Method
Tangent modulus at 50% UCS or Average modulus over a range.
Tangent modulus at 50% UCS or Secant modulus (e.g., from near zero to 50% UCS).
ASTM D7012
Required Number of Axial Gauges
Not specified (implies one or more)
Minimum of two, diametrically opposed
ASTM D7012
⚠ Verify details from original standards before use
Key Values5
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)
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).