This standard outlines the laboratory procedure for determining the dynamic elastic properties of rock core specimens, such as Young's modulus, shear modulus, and Poisson's ratio. The method is based on measuring the transit time of high-frequency ultrasonic pulses through a prepared cylindrical sample.
Method for laboratory determination of dynamic modulus of rock core specimens
Quick Reference Values
Specimen Length to Diameter (L/D) Ratio2.0 to 2.5
Minimum Specimen Diameter45 mm (preferably NX size 54.7 mm)
Specimen End Flatness Tolerance0.02 mm
Specimen End Perpendicularity to Axiswithin 0.001 radian (approx 0.06 degrees)
Frequency Range of Transducers20 kHz to 1 MHz
Key Formulas
Ed = ρ * Vp² * [(1+νd)(1-2νd) / (1-νd)] — Dynamic Young's Modulus
Gd = ρ * Vs² — Dynamic Shear Modulus
νd = ( (Vp/Vs)² - 2 ) / ( 2 * ( (Vp/Vs)² - 1 ) ) — Dynamic Poisson's Ratio
Practical Notes
Meticulous specimen preparation is paramount; ends must be perfectly flat, parallel, and perpendicular to the core axis to ensure accurate velocity measurements.
A good acoustic coupling agent (e.g., grease, petroleum jelly) is essential between the transducers and the rock specimen to ensure efficient energy transmission.
The determined modulus represents the property of the intact rock core and does not reflect the influence of discontinuities (joints, fractures) present in the in-situ rock mass.