Hydraulic Radius in Fluid Mechanics

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Questions and Answers

What does hydraulic radius specifically measure in a rock structure?

  • The age of the rock formation
  • The point where rock begins to cave under stress (correct)
  • The total mass of the rock
  • The point of erosion on the surface

Which formula correctly represents the concept of hydraulic radius?

  • HR = volume/area
  • HR = area^2/perimeter
  • HR = perimeter/area
  • HR = area/perimeter (correct)

What factors are necessary to determine the hydraulic radius?

  • Area and perimeter (correct)
  • Volume and weight
  • Surface area and temperature
  • Height and density

Which of the following factors does NOT directly affect the hydraulic radius?

<p>The temperature of the environment (D)</p> Signup and view all the answers

In what scenario would understanding hydraulic radius be most critical?

<p>Designing drainage systems for flood zones (C)</p> Signup and view all the answers

Which factor is NOT a consideration when selecting a mining method?

<p>Evaluate mineral variety (D)</p> Signup and view all the answers

Which underground mining method is categorized as unsupported?

<p>Longwall mining (A)</p> Signup and view all the answers

What primarily dictates the economic cut-off grade in mining?

<p>Cost-effectiveness analysis (A)</p> Signup and view all the answers

Which of the following mining methods is considered artificially supported?

<p>Shrinkage mining (B)</p> Signup and view all the answers

In the context of mining, optimizing process plant and recoveries mainly involves...

<p>Maximizing ore extraction rates (B)</p> Signup and view all the answers

What is a significant characteristic of block caving as a mining method?

<p>It involves high tonnage from a massive weak ore body. (A)</p> Signup and view all the answers

Sub-level open stoping mining requires which of the following conditions?

<p>A competent rock mass to reduce dilution. (B)</p> Signup and view all the answers

Which method is suitable for tabular orebodies with a dip less than 30°?

<p>Drift and fill mining. (A)</p> Signup and view all the answers

What role does broken rock play in shrinkage stoping?

<p>It acts as a working platform to support the excavation walls. (A)</p> Signup and view all the answers

What is a necessary condition for successful sub-level caving?

<p>Ample rock stability to keep sub-level drifts open. (B)</p> Signup and view all the answers

Flashcards

Hydraulic Radius

The ratio of the cross-sectional area of a flowing fluid to its wetted perimeter.

Hydraulic Radius Formula

HR = Area / Perimeter

Area (in HR)

Cross-sectional area of the fluid.

Perimeter (in HR)

Wetted perimeter of the flowing fluid

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Hydraulic Radius Application

Useful in fluid mechanics to understand how fluids behave in different pipes, channels and other structures.

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Mining Method Selection

Choosing the best way to extract ore from the ground, considering safety, environmental impact, cost-effectiveness, and orebody conditions.

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Naturally Supported Mining

Mining methods that rely on the strength of the surrounding rock to support the excavation, often used for strong, stable orebodies.

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Artificially Supported Mining

Mining methods that require additional support systems to prevent the excavation from collapsing, used for weaker or more fractured orebodies.

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Unsupported Mining

Mining methods that rely on the weight of the overlying rock to break and extract the ore, often used for large, massive orebodies.

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Factors Affecting Mining Method Choice

Key considerations when selecting a mining method, including safety, environmental impact, cost-effectiveness, orebody conditions, and production requirements.

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Block Caving

A complex underground mining method for extracting massive, weak orebodies. It involves creating a large, controlled collapse of the orebody to access the valuable minerals.

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Sub-Level Caving

A method used for large, steeply dipping orebodies. It involves creating horizontal drifts (sub-levels) below the orebody and carefully removing the ore in sections.

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Sub-level Open Stoping (SLOS)

A safer, more precise mining method than sub-level caving. It requires a stronger rockmass and involves a more controlled removal of the ore.

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Drift and Fill Mining

A method suitable for flat, tabular orebodies. It involves creating drifts (tunnels) and filling the mined-out areas with cemented backfill.

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Shrinkage Stoping

Excavation from the bottom up, leaving crushed rock as a working platform. The rock acts as support and helps to stabilize the excavation.

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Study Notes

Hydraulic Radius Definition

  • Hydraulic radius (HR) is a measure used in hydraulics and related fields.
  • It describes the relationship between the cross-sectional area of flow and the wetted perimeter of a channel or conduit.
  • It is specifically defined as the ratio of the cross-sectional area of flow to the wetted perimeter.

Formula

  • The formula for calculating hydraulic radius is: HR = Area / Perimeter
  • Where:
    • HR is the hydraulic radius
    • Area is the cross-sectional area of the flowing fluid
    • Perimeter is the wetted perimeter of the channel or conduit.

Application in Geotechnical Engineering (Cave-in)

  • The provided text incorrectly implies that hydraulic radius is a point where rock caves in. This interpretation is not accurate.

  • The concept of hydraulic radius, in a geotechnical engineering context of rock stability, is not directly about the point of cave-in. Hydraulic radius calculations are more commonly applied to the analysis of flow in open channels and conduits.

  • Cave-ins are determined by different factors like:

    • Rock type and strength
    • Geometry and orientation of the rock mass.
    • Stress conditions (in situ stress, excavation stress).
    • Support systems (presence and type of shoring).
    • The presence and geometry of any fractures or discontinuities in the rock.
    • The total weight of the overlying material, which puts downward stress on the rock mass.

  • While the relationship between water flow and rock stability can exist, it's not directly described by the hydraulic radius.

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