Tunnel Engineering and Rock Mechanics
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Questions and Answers

What is the primary purpose of rock mass classification in tunnel engineering?

  • To determine the tunnel's route
  • To evaluate rock mass quality and behavior (correct)
  • To assess groundwater presence
  • To measure intact rock strength

    • Which of the following factors is NOT included in the Q-system formula?

  • Groundwater pressure (Jw) (correct)
  • Joint alteration (Ja)
  • Rock Quality Designation (RQD)
  • Joint roughness (Jr)

    • What does a high Rock Quality Designation (RQD) indicate?

  • Poor rock quality
  • High percentage of intact rock (correct)
  • High percentage of fractured rock
  • Low joint spacing

    • How does groundwater presence impact tunnel design?

    <p>It increases the risk of collapse</p> Signup and view all the answers

    What can joint spacing tell engineers about a rock mass?

    <p>The density of natural fractures</p> Signup and view all the answers

    What is the primary purpose of cable bolts in tunnel construction?

    <p>To provide deeper stabilization</p> Signup and view all the answers

    Which support method is typically used for immediate stabilization in tunnels?

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

    What type of support may be utilized if rock classification suggests poor rock quality?

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

    Which of the following would be an example of field stresses in the context of tunnel engineering?

    <p>The weight of the overlying soil</p> Signup and view all the answers

    How is the bolt length calculated for adequate anchorage in a tunnel?

    <p>$L = 2 + 0.15 imes Span$</p> Signup and view all the answers

    What type of shotcrete contains fibers to improve strength and reduce cracking?

    <p>Fiber-reinforced shotcrete</p> Signup and view all the answers

    What does the term 'joint orientation' refer to in rock mechanics?

    <p>The angle at which joints are positioned relative to the tunnel</p> Signup and view all the answers

    Which failure mechanism involves the shotcrete detaching from the rock surface?

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

    In the calculation of the Q-value, what does a higher Stress Reduction Factor (SRF) imply?

    <p>Improved rock mass stability</p> Signup and view all the answers

    What does the drill core quality (fracture density) indicate about the rock?

    <p>How broken or intact the rock is</p> Signup and view all the answers

    What does a low Excavation Support Ratio (ESR) indicate for tunnel stability requirements?

    <p>Requires high stability for safety</p> Signup and view all the answers

    In what situation would fiber-reinforced shotcrete be particularly beneficial?

    <p>High-pressure tunnels</p> Signup and view all the answers

    Which type of tunnel typically requires high stability due to its purpose?

    <p>Nuclear facility tunnels</p> Signup and view all the answers

    What is the main function of surface support plates and straps in tunnel construction?

    <p>To distribute forces and prevent movement</p> Signup and view all the answers

    In tunnel engineering, what is the critical factor that varies based on rock type and tunnel purpose?

    <p>Support systems</p> Signup and view all the answers

    What is the main advantage of using fiber-reinforced shotcrete in tunnel construction?

    <p>It increases flexibility and reduces cracking.</p> Signup and view all the answers

    How is the bolt length for tunnel support determined?

    <p>It is calculated using the formula: $L = 2 + 0.15 \times Span$.</p> Signup and view all the answers

    Which scenario would require a low Excavation Support Ratio (ESR)?

    <p>Temporary mine tunnels.</p> Signup and view all the answers

    What failure mechanism is characterized by the shotcrete sliding off under pressure?

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

    In what type of tunnel application is shotcrete especially crucial for immediate stabilization?

    <p>Tunnels in soft or fractured rock.</p> Signup and view all the answers

    What does the term 'intact rock strength' refer to in tunnel engineering?

    <p>The resistance of a rock sample to deformation when measured in a laboratory</p> Signup and view all the answers

    How does joint aperture affect tunnel stability according to rock mechanics?

    <p>Wider joints can lead to increased instability</p> Signup and view all the answers

    Which factor is NOT part of the Q-system formula for assessing rock mass quality?

    <p>ER (Excavation rate)</p> Signup and view all the answers

    In which scenario would engineers most likely choose rock bolts as a support system for a tunnel?

    <p>In areas showing signs of potential rock failures</p> Signup and view all the answers

    What is the role of stress reduction factor (SRF) in the Q-system formula?

    <p>To account for the natural rock stresses during excavation</p> Signup and view all the answers

    What does a rock mass classified as 'Fair' in the Q-system typically indicate?

    <p>Needs robust support systems for safety</p> Signup and view all the answers

    Which of the following describes the purpose of joint orientation in rock mechanics?

    <p>To determine the alignment of fractures relative to the tunnel</p> Signup and view all the answers

    What type of rocks would likely require detailed joint analysis when designing a tunnel under mountains?

    <p>Highly fractured rocks with diverse joint characteristics</p> Signup and view all the answers

    What is the primary function of reinforced earth walls in structural engineering?

    <p>To retain soil and prevent collapse</p> Signup and view all the answers

    Which method is primarily used for temporary stabilization of excavations?

    <p>Excavation shoring systems</p> Signup and view all the answers

    What characteristic of composite beams offers structural efficiency?

    <p>Combination of steel and concrete</p> Signup and view all the answers

    In bridge design, which type is characterized by direct cable connections to towers?

    <p>Cable-Stayed Bridges</p> Signup and view all the answers

    What does the Fire Resistance Period (FRP) indicate in structural design?

    <p>The duration structural elements can withstand fire</p> Signup and view all the answers

    What role do shear connectors play in composite structures?

    <p>They ensure composite action between materials</p> Signup and view all the answers

    What is a key consideration for long-span bridge designs?

    <p>Load distribution and structural stability</p> Signup and view all the answers

    Which factor primarily affects the natural frequencies of structures?

    <p>Material properties and structural stiffness</p> Signup and view all the answers

    What feature is crucial for the functionality of gabion walls?

    <p>Rock-filled cages for erosion control</p> Signup and view all the answers

    What is the significance of overlapping rebars in reinforced concrete detailing?

    <p>To ensure proper stress transfer</p> Signup and view all the answers

    What is the purpose of hydraulic braces in excavations?

    <p>To prevent soil collapse during construction</p> Signup and view all the answers

    Which type of piling system is used specifically for deep foundations?

    <p>Driven piles</p> Signup and view all the answers

    What are the benefits of prestressing in concrete applications?

    <p>It increases tensile strength and reduces cracking</p> Signup and view all the answers

    In what scenarios are rock bolts typically used?

    <p>To stabilize tunnel sidewalls</p> Signup and view all the answers

    What is the purpose of utilizing composite beams in construction?

    <p>To combine strengths of different materials</p> Signup and view all the answers

    Which of the following describes shotcrete?

    <p>A method of applying concrete underpressure</p> Signup and view all the answers

    What role do retaining walls serve in construction?

    <p>To manage drainage and prevent soil erosion</p> Signup and view all the answers

    Which structural feature is critical for the effectiveness of prestressed concrete?

    <p>Pre-applied tension</p> Signup and view all the answers

    What is the main function of overlaps in reinforcement?

    <p>To ensure effective stress transfer</p> Signup and view all the answers

    Where would prestressed concrete be most beneficially utilized?

    <p>In bridges and long-span buildings</p> Signup and view all the answers

    Study Notes

    Tunnel Engineering and Rock Mechanics

    • Tunnel engineering involves constructing underground passages for transport, utilities, or mining. Rock mechanics studies rock mass behavior under stress for safe tunnel design.

    Key Data Types for Design

    • Intact Rock Strength: Lab-measured resistance to force.
    • Field Stresses: Pre-tunnel natural stresses in the rock.
    • Groundwater: Impacts stability and excavation.
    • Drill Core Quality (Fracture Density): Indicates rock intactness.
    • Joint Spacing: Distance between fractures.
    • Joint Persistence: Length of fractures.
    • Joint Orientation: Fracture direction relative to the tunnel.
    • Joint Contour (Shape): Smooth or rough joint surfaces for stability.
    • Joint Aperture and Surface Condition: Joint width and condition.

    Rock Mass Classification

    • Purpose: Evaluate rock mass quality and behavior.
    • Applications:
      • Tunnel project feasibility.
      • Determining tunnel support systems.
      • Initial estimates of rock strength and deformation.

    Q-System (Rock Quality Assessment)

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

    • RQD: Rock Quality Designation (intact rock percentage in core samples).

    • Jn: Number of joint sets.

    • Jr: Roughness of the most unfavorable joint.

    • Ja: Joint alteration (weakness or filling).

    • Jw: Joint water reduction factor.

    • SRF: Stress Reduction Factor (rock stress/excavation impact).

    • Example Calculation (Fair Rock Mass Quality): RQD = 70%, Jn = 9, Jr = 2, Ja = 1, Jw = 1, SRF = 27.5, Q = 0.57 → Poor quality, needing robust support.

    Support Systems for Tunnels

    • Reinforcement:
      • Rock Bolts: Short steel bars anchored for stability.
      • Cable Bolts: Longer, flexible steel cables for greater depth.
    • Surface Support:
      • Plates & Straps: Distribute forces, prevent rock movement.
      • Mesh: Steel mesh to contain loose rock.
      • Shotcrete: Sprayed concrete for immediate stabilization.

    Excavation Support Ratio (ESR)

    • Definition: Support level based on tunnel usage and safety.
    • Values: Lower ESR (e.g., nuclear facilities) = High stability needed. Higher ESR (e.g., temporary mine tunnels) = Less stability needed.

    Bolt Length and Design

    • Bolt length (L) calculation: L = 2 + 0.15 * Span
    • Ensures adequate anchorage for stability.

    Shotcrete and Fiber-Reinforced Shotcrete

    • Shotcrete: Sprayed concrete for immediate tunnel wall stability.
    • Fiber-Reinforced Shotcrete (FRS): Strengthened with fibers, reducing cracking and increasing flexibility.
    • Failure Mechanisms:
      • Adhesion Failure: Shotcrete separates from rock.
      • Shear Failure: Layer slides under pressure.
      • Compression/Tension Failure: (rare, in thin shotcrete).

    Applications of Tunnel Engineering

    • Transportation: Rail, road tunnels (under mountains/cities).
    • Utilities: Water supply, sewage, power transmission tunnels.
    • Mining: Underground ore extraction.

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    Description

    This quiz covers the essential concepts of tunnel engineering and rock mechanics, focusing on key data types for design and rock mass classification. Understand the various factors that influence underground construction, including rock strength, field stresses, and joint characteristics.

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