The 1987 edition of IS 11358 offers an extensive glossary detailing the terminology and symbols prevalent in rock mechanics. This compilation is vital for professionals interpreting rock characteristics, mechanical behavior, and engineering practices involved with rock masses, tunnels, and subterranean works.
Overview
The 1987 edition of IS 11358 offers an extensive glossary detailing the terminology and symbols prevalent in rock mechanics. This compilation is vital for professionals interpreting rock characteristics, mechanical behavior, and engineering practices involved with rock masses, tunnels, and subterranean works.
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Contents
Structure
IS 11358 delineates the standardized vocabulary and symbolic representations used in rock mechanics, promoting consistent communication across engineering disciplines. It encompasses terminology related to rock characteristics, testing methods, and behavior, along with the symbols employed in calculations pertinent to rock engineering. This standard functions primarily as a reference glossary without including direct formulas or tabular data and supports other related IS standards in rock mechanics.
This section provides standardized definitions and symbols crucial for rock mechanics practice. Key parameters such as stress (c3), strain (b5), modulus of elasticity (E), cohesion (c), internal friction angle (c6), and unit weight (b3) are precisely defined. It includes terms describing rock mass features, discontinuities, joint sets, strength, deformability, and failure criteria, ensuring clarity and uniformity in technical communications.
IS 11358 emphasizes a Basic Geotechnical Description (BGD) of rock masses using five principal parameters: the geological rock name, layer thickness, fracture intercept spacing, uniaxial compressive strength (UCS), and friction angle of fractures. Additionally, hydraulic conductivity characterizes the permeability of rock masses, which is vital for seepage and drainage evaluations. The standard also categorizes UCS to assist in classifying rock strength.
While IS 11358 focuses on terminology, it outlines fundamental parameters influencing rock mass behavior under stress, including geological description, layer thickness, fracture intercept frequency, UCS, and friction angle. Empirical relationships like the Hoek & Brown deformation modulus estimation and failure criteria are referenced to interpret rock mass deformation and strength characteristics.
This part defines ten essential parameters describing rock discontinuities, such as orientation, spacing, persistence, roughness, wall strength, aperture, filling material, seepage presence, number of joint sets, and block size. These factors influence shear strength, rock mass anisotropy, and stability, and are fundamental for rock mass classification and design considerations.
IS 11358 clarifies terms related to blasting operations including blastability (rock resistance to blasting), bench blasting (stepwise excavation with parallel drilled holes), smooth blasting (reduced damage technique), and controlled blasting methods. Typical parameters like burden, spacing, bench height, and powder factor are presented with fundamental formulas guiding explosive charge calculations.
Key definitions include long-term rock pressure affecting underground supports and both horizontal and vertical rock pressures acting on tunnel linings. Formulas for vertical pressure as a function of rock unit weight and depth, and horizontal pressure via lateral earth pressure coefficients, are provided. Typical coefficient ranges based on rock conditions assist in design computations.
Although IS 11358 mainly offers glossary entries, it identifies fundamental failure modes such as shear failure, tensile failure, compressive failure, sliding along discontinuities, and toppling. It references the Mohr-Coulomb failure criterion for shear strength and emphasizes factor of safety calculations in rock stability analysis, while detailed design procedures are found in other standards.
The standard lists definitions for hydraulic testing terms—permeability, porosity, pore pressure, hydraulic conductivity—and mechanical testing terms including uniaxial compressive strength, tensile strength, modulus of elasticity, and Poisson’s ratio. It highlights common formulas for these parameters, aiding understanding of rock testing results, with detailed testing protocols referenced in companion standards.
IS 11358 describes support classifications such as stiff supports (rigid, minimal deformation), flexible supports (allowing controlled deformation), and yielding supports (accommodating significant strain). It defines unsupported span and its impact on stand-up time, providing guidance on selecting support types based on rock behavior and deformation characteristics for underground excavations.
This section explains the conceptual models of strain and stress ellipsoids, which visually represent principal strains and stresses by deforming a unit sphere. It defines Young’s modulus as the ratio of axial stress to strain and presents the diagonalization of stress and strain tensors into principal components, facilitating comprehensive stress-strain analysis.
IS 11358 acts as a comprehensive glossary standardizing terminology related to rock properties, stresses, discontinuities, and mechanical behavior. It provides succinct definitions for commonly used terms like uniaxial compressive strength, modulus of elasticity, Poisson’s ratio, and discontinuity, ensuring consistent usage throughout rock mechanics documentation and design.
Frequently Asked
IS 11358 specifies essential rock properties through the Basic Geotechnical Description (BGD), which includes five primary parameters: the rock's geological name, thickness of the rock layer, fracture intercept spacing, uniaxial compressive strength (UCS) indicating compressive resistance, and the angle of friction along fractures representing shear resistance. These are commonly noted as, for example, Quartz - L2, F4, S3, A2, facilitating consistent rock mass characterization.
The standard categorizes rock deformation by classifying rock masses based on seam and structural attributes: Massive (intact rock with negligible seams and minimal deformation), Sheets (layers 1–3 m thick with thin horizontal seams), Laminated (thin layers 30–100 cm with horizontal seams and minimal gouge), Seamy (numerous open seams indicating moderate deformation), and Blocky (extensive open seams filled with gouge, representing significant fracturing). This classification aids in understanding rock stability and deformation behavior.
Key blasting and excavation terms include Bench Blasting, describing stepwise excavations with blast holes parallel to the free face; Smooth Blasting, a technique minimizing rock damage via light charges and close hole spacing; Controlled Blasting, encompassing methods to preserve rock integrity such as presplitting; and Blastability, an index measuring rock resistance to blasting. These terms guide efficient and safe excavation planning.
IS 11358 addresses rock mass behavior under stress by defining terms such as shear strength—the maximum resistance of rock mass including joints to shearing stresses—and the Stress Reduction Factor (SRF), which accounts for stress changes from excavation, including loosening pressure, strength ratios, and swelling or squeezing pressures. These definitions provide a framework for evaluating rock stability and response to loading.
The standard adopts the Greek letters c3 for stress, measured in Pascals or Megapascals, representing internal forces per unit area, and b5 for strain, a dimensionless ratio of deformation per unit length. Principal stresses and strains are denoted as c31, c32, c33 and b51, b52, b53 respectively, with shear stress and strain represented by c4 and b3, standardizing notation for clarity in analysis and communication.
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