The 1987 edition of IS 11315 Part 7 establishes a uniform approach for quantitatively describing filled discontinuities within rock masses. It emphasizes analyzing the characteristics of filling materials—such as clays, silts, and fault gouges—and evaluates parameters including mineral composition, particle size distribution, shear strength, permeability, and swelling behavior. This standard is indispensable for professionals assessing stability in rock engineering projects involving filled joints and discontinuities.
Overview
The 1987 edition of IS 11315 Part 7 establishes a uniform approach for quantitatively describing filled discontinuities within rock masses. It emphasizes analyzing the characteristics of filling materials—such as clays, silts, and fault gouges—and evaluates parameters including mineral composition, particle size distribution, shear strength, permeability, and swelling behavior. This standard is indispensable for professionals assessing stability in rock engineering projects involving filled joints and discontinuities.
Audience
Contents
Structure
This section outlines the objectives of characterizing and documenting filled discontinuities in rock masses, highlighting their role in evaluating structural stability. It specifies key parameters such as discontinuity width, wall roughness, filling type (including mineralogy, particle dimensions, weathering status, soil indices, and swelling capacity), filling strength indices, and seepage characteristics like water content ratings and permeability.
This part consolidates essential reference tables, including the manual index test classification (Grades S1 to S6) for cohesive soil fillings, detailing field identification methods and approximate uniaxial compressive strengths. It differentiates between soil and rock discontinuity grading and provides guidance for presenting measurement results.
Defines terms as per IS 11358-1986, ensuring consistent use of nomenclature related to filled discontinuities. It reviews the parameters required for describing discontinuities, including dimension measurements, filling material properties, and seepage characteristics, supported by manual index strength grading.
Details procedural steps for measuring discontinuity widths and wall roughness, classifying filling materials by mineralogy and particle size, performing manual field strength tests, assessing over-consolidation and shear displacement, and evaluating water content and permeability. It also discusses proper presentation formats including field sketches and data tabulation.
Provides guidance on accurately measuring minimum, maximum, and modal widths of simple and complex filled discontinuities with an accuracy of ±10%. It includes methods for assessing wall roughness amplitude and preparing field sketches that document wall rock conditions.
Explains classification of filling substances using manual penetration tests, estimating the proportion of clay, silt, sand, and rock fragments, and integrating these observations into comprehensive reports.
Focuses on analyzing the finest fractions of fillings for mineralogical composition, particularly identifying swelling clays. Particle size classification follows IS 1498-1970, supported by manual index testing to estimate uniaxial compressive strength.
Describes laboratory procedures for evaluating filling materials, emphasizing manual index tests to estimate strength and the importance of reporting water content, permeability, and swelling potential.
Details the manual penetration test grades (S1-S6), their field identification, and corresponding strength ranges. It also notes the use of penetrometers as alternatives and the significance of these tests in engineering assessments.
Discusses criteria for identifying prior shear displacement in fillings, the role of over-consolidation ratio (OCR) in determining peak or residual shear strength, and considerations for time-dependent strength degradation due to swelling or unloading.
Outlines the water content rating system (W1 to W6), describing moisture and flow conditions within filled discontinuities. It highlights the anisotropic nature of seepage and the influence of filling properties on permeability.
Specifies the format and content for reporting filled discontinuity data, including dimensional measurements, wall roughness, field sketches, filling characteristics, strength indices, and seepage parameters, ensuring clarity and project relevance.
Provides sample sketches and diagrams for effectively documenting filled discontinuities, illustrating principal dimensions, wall conditions, filling types, strength classifications, and seepage characteristics.
Frequently Asked
IS 11315 Part 7 (1987) covers the assessment of filling materials such as clays, silts, and fault gouges found within rock discontinuities. These materials are classified based on mineralogy, particle size, and physical properties to aid in stability evaluation. Although not explicitly listing materials like sand or fly ash, the standard focuses on natural fine-grained deposits that affect rock mass behavior.
The standard recommends assessing shear strength by examining evidence of prior shear displacement—such as slickensides or displaced joints—and evaluating the over-consolidation ratio (OCR) of the filling material. If prior displacement is confirmed, residual shear strength governs behavior, making OCR less significant. Conversely, if no displacement exists, peak drained shear strength influenced by OCR is critical. Considerations for time-dependent strength loss from swelling and softening are also emphasized.
For accurate soil mechanics testing, IS 11315 Part 7 recommends collecting undisturbed samples of filling materials using tube samplers to preserve natural structure and moisture content. The finest fractions are targeted for detailed grading and mineralogical analyses, which are essential for evaluating shear strength and swelling potential.
It classifies water content and permeability into six ratings (W1 to W6), ranging from dry, heavily consolidated fillings with negligible flow to completely washed-out zones with high-pressure water flow. The system accounts for anisotropic flow patterns and encourages quantitative estimation of seepage where necessary to inform engineering decisions.
The OCR is vital because it influences the shear strength characteristics of clay fillings. A high OCR indicates over-consolidated clays with higher peak strength, but potential for strength reduction over time due to swelling and softening. It helps distinguish whether the discontinuity strength reflects peak or residual conditions, which is crucial for stability analyses.
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