JNTU
JNTU B.Tech III ROCK MECHANICS Previous Question Paper (February - 2022 - R18)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
Explain the Geo-mechanical rock mass classification.
Answer
The Geo-mechanical rock mass classification, commonly known as the Rock Mass Rating (RMR) system, is a widely used empirical method for assessing the stability of rock masses. It integrates six primary parameters to provide a quantitative rating for the rock mass quality:
- Uniaxial Compressive Strength (UCS): The strength of the intact rock material.
- Rock Quality Designation (RQD): A measure of the degree of jointing or fracturing based on core recovery.
- Spacing of Discontinuities: The average distance between parallel joints or fractures.
- Condition of Discontinuities: Assessment of joint persistence, aperture, roughness, infilling, and weathering.
- Groundwater Conditions: The presence of water, ranging from completely dry to flowing conditions.
- Orientation of Discontinuities: The adjustment factor based on the relative strike and dip of joints with respect to the excavation axis.
The sum of these ratings results in a total RMR value ranging from 0 to 100, which classifies the rock mass into five classes: Very Poor, Poor, Fair, Good, or Very Good. This classification is essential for estimating rock mass strength, deformation modulus, and determining support requirements for tunnels, slopes, and foundations.
A dry rock sample of Diameter 50 mm and length 100 mm weighs 300g, after saturating in brine solution at specific gravity 1.05, its weight increased to 330g. Calculate the porosity of the rock sample in percentage.
Answer
To calculate the porosity, we first determine the volume of the voids using the weight of the brine absorbed. Given: Diameter (d) = 50 mm = 5 cm, Length (l) = 100 mm = 10 cm, Dry weight (Wd) = 300 g, Saturated weight (Ws) = 330 g, Specific gravity of brine (Gs_brine) = 1.05.
1. Calculate the total volume of the rock sample (V):
2. Calculate the volume of the voids (Vv):
3. Calculate porosity (n):
The porosity of the rock sample is 14.55%.
Explain the Rock Structure Rating (RSR).
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Explain about Rock Mass Rating (RMR).
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Explain the method of determining tensile strength of rocks as per ISRM standards. How do you report the test results?
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Explain the factors affecting the compressive strength of rocks.
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Discuss the method of determining the triaxial strength of rocks.
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Explain the method determining slake durability index of rocks.
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Define dynamic elastic constants and state how they are related to dynamic wave velocities.
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Explain the strength criteria for isotropic intact rocks.
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Discuss the “Toppling failure” with neat sketch.
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Draw the diagram of a pit slope undergoing circular failure and mention the equilibrium equation and define the parameters used.
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Distinguish between factor of safety of a dry slope and a wet slope underground planar Failure.
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Distinguish between a planar failure and wedge failure and state the conditions under which each type of failure occur.
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Describe the drilling and blasting operation in drifting.
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Find out the toe burden of a vertical hole located in a 15 m bench having a face slope angle of 20° and possessing a crest burden of 2.0 m?
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