This standard outlines the prescribed procedure for assessing the modulus of elasticity (Young's modulus) and Poisson's ratio of rock specimens subjected to uniaxial compressive stress using cylindrical samples. It serves as a crucial reference for geotechnical professionals and researchers focused on accurately evaluating the elastic characteristics of rock materials for engineering and mining applications.
Overview
This standard outlines the prescribed procedure for assessing the modulus of elasticity (Young's modulus) and Poisson's ratio of rock specimens subjected to uniaxial compressive stress using cylindrical samples. It serves as a crucial reference for geotechnical professionals and researchers focused on accurately evaluating the elastic characteristics of rock materials for engineering and mining applications.
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Contents
Structure
This section delineates the scope covering standardized testing and assessment of mechanical properties focusing on stress-strain behavior. It specifies uniform specimen dimensions ensuring consistency across tests and outlines necessary report components such as stress-strain plots, computed elastic modulus, Poisson's ratio, determination techniques, and applied stress levels. Numeric results must adhere to rounding guidelines per IS 2-1960.
Details mandatory elements for test reports including specimen count, failure modes, rock lithology, orientation relative to anisotropic features, sample provenance, storage history, test conditions, and physical properties. It also references associated Indian Standards critical for comprehensive rock property evaluation. Adherence to rounding and specimen dimension stipulations is emphasized.
Describes preferred specimen geometry as right circular cylinders, preparation procedures per related standards, dimension measurement methods with tolerance limits, and strain gauge placement requirements. Emphasizes measurement accuracy and precision standards, gauge positioning away from specimen ends, and minimum gauge length relative to grain size.
Outlines the step-by-step process for specimen dimension verification, strain gauge installation, loading application with controlled rates, and data acquisition. Includes formula for average diameter calculation and diagrams for strain gauge positioning to guarantee balanced strain monitoring around the specimen circumference.
Presents formulas for determining modulus of elasticity from stress-strain curves using various moduli (initial tangent, secant, tangent at mid-stress). Defines Poisson's ratio as the ratio of lateral to axial strain measured at specified stress levels, typically at 50% of ultimate stress. Includes tabulated summaries and schematic representations for conceptual clarity.
Specifies comprehensive requirements for test reporting including graphical stress-strain data, calculated elastic parameters, specimen details, environmental conditions, and testing variables. Highlights the necessity for averaging multiple strain measurements and rounding results according to prescribed standards.
Defines strict accuracy criteria for strain measurement (±2% of reading) and precision (±0.2% full scale), mandates a minimum number of axial and circumferential gauges symmetrically placed, and sets tolerances for specimen end flatness and parallelism. Visual diagrams illustrate the recommended gauge layout ensuring data reliability.
Details dimensional requirements including minimum diameters relative to grain size, preferred specimen size, measurement techniques at multiple heights with perpendicular diameters, and length-to-diameter ratio guidelines. Tolerances are defined with references to related specimen preparation standards, ensuring geometric conformity.
Describes recommended instrumentation such as electrical resistance strain gauges, compressometers, and optical devices. Emphasizes equal circumferential spacing of gauges near mid-height, avoidance of specimen ends proximity, measurement lengths in relation to grain size, and data accuracy. Includes formulas for axial and diametric strain calculations and flow charts representing measurement workflows.
Specifies apparatus requirements including strain measurement devices, loading machines with controlled rates, and calibration protocols. Details strain gauge placement and accuracy standards, along with essential test report documentation items to ensure standardized testing and reliable data collection.
Provides guidance on interpreting test results with emphasis on reporting specimen characteristics, failure modes, test conditions, and physical properties. Includes rounding off procedures and references to relevant strength calculation formulae from related standards. Flow diagrams illustrate the data recording and reporting process.
While the standard does not explicitly detail safety procedures, it underscores careful specimen handling to prevent damage, adherence to dimension tolerances, and use of personal protective equipment during testing. It also references related standards for detailed handling and preparation protocols, ensuring test integrity and operator safety.
Summarizes key reporting parameters such as specimen dimensions, failure modes, rock descriptions, and test conditions. Lists related Indian Standards for cross-reference and provides diagrams illustrating specimen measurement, testing, data recording, and reporting sequences to promote comprehensive understanding and compliance.
Frequently Asked
The standard mandates that rock specimens should ideally be right circular cylinders with a diameter at least ten times the largest mineral grain size, preferably 45 mm, but no less than 30 mm with relaxed tolerances. The length-to-diameter ratio typically ranges between 2 and 3. Steel end discs must have a diameter matching the specimen, minimum thickness of 15 mm, hardness not less than HRC 30, and flatness within 0.025 mm. Other regular shapes are permitted if prepared as per related standards. All specimen dimensions and any deviations must be clearly indicated in test reports.
Poisson's ratio is computed as the ratio of lateral (diametric) strain to axial strain measured simultaneously on a cylindrical rock sample under compressive load. It is typically evaluated at 50% of the ultimate stress. Both strains are recorded using appropriately positioned gauges, and the ratio is calculated by dividing the measured diametric strain by the axial strain, reflecting the material's lateral contraction relative to axial deformation.
The standard recommends using electrical resistance strain gauges, compressometers, optical devices, or comparable instruments to measure strains. At least two axial and two circumferential strain measurements should be obtained per load increment. Gauges must be evenly spaced around the specimen's circumference near mid-height, avoiding placement within half the specimen diameter from the ends. Measurement lengths should be no less than five times the largest grain size, with accuracy of ±2% of reading and precision within ±0.2% full scale.
Modulus of elasticity can be determined using various approaches such as the initial tangent modulus (slope at curve origin), secant modulus (slope between origin and a defined stress), or tangent modulus at specific stress points like 50% of ultimate stress. The chosen method and the stress or strain range must be clearly stated in reports. Typical stress-strain curve stages including crack closure, linear elasticity, and crack initiation should be considered during analysis.
Specimens must have ends flat within 0.05 mm and parallelism within 0.002 times the diameter. Prior to testing, surfaces of both the specimen and steel bearing discs should be cleaned. During setup, the specimen is placed on the lower bearing disc and aligned precisely with the spherical seat's center of thrust. The movable spherical seat is adjusted to achieve uniform seating as load is applied. These measures reduce eccentric loading and improve reliability of test results.
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