Tunnel Engineering and Rock Mechanics Quiz
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Questions and Answers

What is the primary purpose of rock mechanics in tunnel engineering?

  • To study rock mass behavior under stress (correct)
  • To measure drill core quality
  • To evaluate joint spacing
  • To assess groundwater impact on excavation

    • Which factor is NOT part of the Q-System formula used for rock quality assessment?

  • Groundwater impact factor (G) (correct)
  • Joint water reduction factor (Jw)
  • Stress Reduction Factor (SRF)
  • Rock Quality Designation (RQD)

    • What does the term 'joint spacing' refer to in tunnel engineering?

  • The width of the joints in rock
  • The distance between fractures in the rock (correct)
  • The angle at which fractures occur
  • The length of the fractures in the rock

    • What is the main advantage of using Fiber-Reinforced Shotcrete (FRS) over standard shotcrete?

    <p>Reduced cracking and increased flexibility</p> Signup and view all the answers

    In the context of tunnel support systems, what is a primary function of rock bolts?

    <p>To prevent rock movement by anchoring it</p> Signup and view all the answers

    Which support system is typically used for immediate stabilization of tunnel walls?

    <p>Shotcrete</p> Signup and view all the answers

    What does an Excavation Support Ratio (ESR) indicate about a tunnel project?

    <p>The level of support required based on usage</p> Signup and view all the answers

    Which of the following factors is NOT influenced by groundwater in tunnel engineering?

    <p>Intact rock strength</p> Signup and view all the answers

    What is the significance of measuring intact rock strength in tunnel engineering?

    <p>It provides resistance measurements for excavation</p> Signup and view all the answers

    What common failure mechanism occurs when shotcrete separates from the rock?

    <p>Adhesion Failure</p> Signup and view all the answers

    What is the role of 'Joint Orientation' in tunnel engineering?

    <p>Describes the fracture direction relative to the tunnel.</p> Signup and view all the answers

    How does the Excavation Support Ratio (ESR) influence tunnel design?

    <p>Reflects the required stability based on tunnel usage.</p> Signup and view all the answers

    What does a low Q value indicate regarding rock mass quality?

    <p>Poor quality, necessitating robust support systems.</p> Signup and view all the answers

    What is the primary function of Cable Bolts in tunnel support systems?

    <p>To anchor and stabilize rock at deeper levels.</p> Signup and view all the answers

    Which factor does NOT influence the effectiveness of Joint Water Reduction in the Q-System?

    <p>Fracture density in drill core samples.</p> Signup and view all the answers

    What characterizes Fiber-Reinforced Shotcrete over standard shotcrete?

    <p>Reduced cracking and enhanced flexibility.</p> Signup and view all the answers

    What does the formula for the Q-System aim to evaluate?

    <p>Quality and behavior of rock mass.</p> Signup and view all the answers

    What is the main purpose of measuring Joint Persistence in rock mechanics?

    <p>To determine the length of fractures.</p> Signup and view all the answers

    What is the significance of the Rock Quality Designation (RQD) in rock mass classification?

    <p>It indicates the percentage of intact rock in core samples.</p> Signup and view all the answers

    What type of failure does shear failure refer to in the context of shotcrete?

    <p>The layer slides or shifts under applied pressure.</p> Signup and view all the answers

    Which factor primarily affects the stability and excavation process of a tunnel?

    <p>Intact Rock Strength</p> Signup and view all the answers

    What does the variable 'Jn' in the Q-System formula represent?

    <p>Number of Joint Sets</p> Signup and view all the answers

    Which method is used for immediate stabilization of tunnel walls?

    <p>Shotcrete</p> Signup and view all the answers

    What does a higher Excavation Support Ratio (ESR) generally imply for tunnel stability?

    <p>Less support needed</p> Signup and view all the answers

    Which characteristic of a joint is quantified by the term 'joint aperture'?

    <p>Width of the fracture</p> Signup and view all the answers

    What is the outcome of a poor quality rock mass, indicated by a low Q value?

    <p>Need for enhanced support systems</p> Signup and view all the answers

    Which of these materials is reinforced with fibers to improve its properties?

    <p>Shotcrete</p> Signup and view all the answers

    What does the Q value depend on regarding joint characteristics?

    <p>Joint Water Reduction Factor</p> Signup and view all the answers

    What is the main purpose of the Rock Quality Designation (RQD) measure?

    <p>To determine intact rock percentage</p> Signup and view all the answers

    Which failure type is characterized by the layer sliding under pressure in shotcrete?

    <p>Shear Failure</p> Signup and view all the answers

    What does the variable 'Ja' represent in the Q-System formula?

    <p>Joint alteration</p> Signup and view all the answers

    Which material is typically used to distribute forces during tunnel support?

    <p>Steel mesh</p> Signup and view all the answers

    In the context of tunnel engineering, what does a low Excavation Support Ratio (ESR) suggest?

    <p>Less stability is required for the tunnel</p> Signup and view all the answers

    What does 'RQD' stand for in rock mass classification?

    <p>Rock Quality Designation</p> Signup and view all the answers

    Which aspect of rock behavior is assessed by studying joint persistence?

    <p>Length of fractures within the rock</p> Signup and view all the answers

    What factor influences the stability of shotcrete in tunnel construction?

    <p>Adhesion failure</p> Signup and view all the answers

    Which support system is specifically designed for deeper tunnel applications?

    <p>Cable bolts</p> Signup and view all the answers

    What is the purpose of measuring groundwater in tunnel engineering?

    <p>To evaluate rock stability</p> Signup and view all the answers

    Which of the following describes the joint shape in rock mechanics?

    <p>Joint contour</p> Signup and view all the answers

    What does the term 'stress reduction factor (SRF)' refer to in the Q-System?

    <p>Net rock stress divided by excavation impact</p> Signup and view all the answers

    Study Notes

    Tunnel Engineering and Rock Mechanics

    • Tunnel engineering focuses on building underground passages for transportation, utilities, or mining.
    • Rock mechanics studies how rocks behave under pressure, essential for safe tunnel design.

    Key Data Types

    • Intact Rock Strength: Measured in a lab, it's the resistance a rock piece offers to force.
    • Field Stresses: Pre-existing stresses within the rock before tunnel construction.
    • Groundwater: Affects tunnel stability; it can cause the rock mass to collapse.
    • Drill Core Quality (Fracture Density): Shows how much the rock is fractured; high fractures mean less stable rock.
    • Joint Spacing: Distance between fractures in the rock mass, a critical stability factor.
    • Joint Persistence: Length of a fracture; longer fractures can lead to greater structural weakness.
    • Joint Orientation: Fracture direction relative to the tunnel; alignment affects stability.
    • Joint Contour (Shape): Smooth or rough joint surfaces. Smooth surfaces cause less disruption to the rock mass.
    • Joint Aperture and Surface Condition: Joint width and condition influence the tunnel's stability greatly.

    Rock Mass Classification

    • Purpose: To assess the quality and behavior of the rock mass.
    • Applications: Helps determine tunnel project feasibility, the appropriate tunnel support system, and initial estimations of rock strength and deformation.
    • Q-System (Rock Quality Assessment): Formula to rate rock mass quality.

    Q-System Formula

    • Q = [RQD / Jn] * [Jr / Ja] * [Jw / SRF]

    • RQD (Rock Quality Designation): Percentage of intact rock in core samples. High RQD indicates better rock conditions.

    • Jn: Number of joint sets; higher numbers signify more problematic joints (more likely to cause failure).

    • Jr: Roughness of the most unfavorable joint; smoother joints mean more stability for the tunneling process.

    • Ja: Joint alteration (weakness or filling); poor alteration values indicate more rock issues.

    • Jw: Joint water reduction factor; presence of water reduces stability.

    • SRF (Stress Reduction Factor): Evaluates the impact of stresses on the rock mass; greater stress means less certainty about the rock's behavior.

    Support Systems for Tunnels

    • Reinforcement: Steel bars and cables embedded in the rock to improve stability
      • Rock Bolts: Short steel bars anchored into the rock.
      • Cable Bolts: Longer, flexible steel cables for greater depths.
    • Surface Support: Methods to prevent rock movement along the tunnel walls
      • Plates & Straps: Distribute forces, prevent movement.
      • Mesh: Steel mesh to contain loose rock.
      • Shotcrete: Sprayed concrete for immediate stabilization (a type of surface support).

    Excavation Support Ratio (ESR)

    • Definition: Measures support level for a tunnel, based on safety needs.
    • Values: Lower ESR values (e.g., nuclear facilities) require more extensive support to ensure stability. Higher ESR (e.g., temporary mine tunnels) need less support.

    Bolt Length and Design

    • Bolt length (L) calculation: L = 2 + 0.15 * Span. This ensures proper anchorage for stability.

    Shotcrete and Fiber-Reinforced Shotcrete (FRS)

    • Shotcrete: Spray-applied concrete improving tunnel wall stability.
    • Fiber-Reinforced Shotcrete (FRS): Improves shotcrete's resilience and resistance to cracking.

    Failure Mechanisms

    • Adhesion Failure: Shotcrete separates from rock.
    • Shear Failure: Layers of rock slide under pressure.
    • Compression/Tension Failure: (rare, in thin shotcrete).

    Applications of Tunnel Engineering

    • Transportation: Rail, road tunnels.
    • Utilities: Water, sewage, power transmission.
    • Mining: Underground ore extraction.

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    Description

    Test your knowledge on tunnel engineering and rock mechanics through this quiz. Explore critical data types like joint spacing, rock strength, and the effects of groundwater on tunnel stability. Perfect for students and professionals in the field of civil engineering.

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