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Questions and Answers
Which parameter is NOT considered a basic data type for tunnel design?
Which parameter is NOT considered a basic data type for tunnel design?
What is the purpose of rock mass classification schemes in tunnel engineering?
What is the purpose of rock mass classification schemes in tunnel engineering?
Which parameter would primarily deal with the physical condition of rock joints?
Which parameter would primarily deal with the physical condition of rock joints?
At what stages can rock mass classification schemes be beneficial?
At what stages can rock mass classification schemes be beneficial?
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Which of the following is associated with the structural integrity of a tunnel?
Which of the following is associated with the structural integrity of a tunnel?
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What aspect does the parameter 'Joint Persistence' primarily refer to?
What aspect does the parameter 'Joint Persistence' primarily refer to?
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In terms of tunnel design, what does 'Fracture Density' measure?
In terms of tunnel design, what does 'Fracture Density' measure?
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Why is field stress measurement important in tunnel engineering?
Why is field stress measurement important in tunnel engineering?
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What is the value of $Q$ calculated using the given parameters?
What is the value of $Q$ calculated using the given parameters?
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Which parameter indicates the degree of alteration along the weakest joint?
Which parameter indicates the degree of alteration along the weakest joint?
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How is the Excavation Support Ratio (ESR) defined?
How is the Excavation Support Ratio (ESR) defined?
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What does the parameter $De$ represent in the context of the Q-system?
What does the parameter $De$ represent in the context of the Q-system?
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What does the stress reduction factor (SRF) of 27.5 indicate?
What does the stress reduction factor (SRF) of 27.5 indicate?
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What does the joint roughness number (JR) specifically measure in rock mass classification?
What does the joint roughness number (JR) specifically measure in rock mass classification?
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What characteristic of the rock does the rock quality designation (RQD) quantify?
What characteristic of the rock does the rock quality designation (RQD) quantify?
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In the context of the Q-System, what information does the Stress Reduction Factor (SRF) provide?
In the context of the Q-System, what information does the Stress Reduction Factor (SRF) provide?
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How does the presence of water affect joint stability in rock masses?
How does the presence of water affect joint stability in rock masses?
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Which parameter is NOT a part of the Q-System equation for rock mass classification?
Which parameter is NOT a part of the Q-System equation for rock mass classification?
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What condition of the critical joint walls indicated in the Q-System example enhances rock quality?
What condition of the critical joint walls indicated in the Q-System example enhances rock quality?
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What factor does the joint water reduction factor (Jw) measure?
What factor does the joint water reduction factor (Jw) measure?
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What does the term 'squeezing loads' refer to in relation to the SRF?
What does the term 'squeezing loads' refer to in relation to the SRF?
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What is the typical length range for reinforcement rock bolts?
What is the typical length range for reinforcement rock bolts?
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Which of the following types of support is generally considered to be greater than 5 meters long?
Which of the following types of support is generally considered to be greater than 5 meters long?
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What is the formula used to estimate the length of rock bolts?
What is the formula used to estimate the length of rock bolts?
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Which failure mechanism of shotcrete occurs if adhesion fails?
Which failure mechanism of shotcrete occurs if adhesion fails?
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What is a critical requirement for efficient tunneling using shotcrete?
What is a critical requirement for efficient tunneling using shotcrete?
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Which of the following is typically NOT associated with failure mechanisms in thin shotcrete?
Which of the following is typically NOT associated with failure mechanisms in thin shotcrete?
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What reinforces shotcrete to improve its performance?
What reinforces shotcrete to improve its performance?
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In the context of shotcrete, which failure mechanism is uncommon?
In the context of shotcrete, which failure mechanism is uncommon?
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Study Notes
Tunnel Engineering Rock Mechanics
- Course code: CIVL3811
- Course name: Engineering Design and Construction
- Institution: The University of Sydney
- School: School of Civil Engineering
- Faculty: Faculty of Engineering
Basic Data Types
- Nine basic data types for tunnel design
- Intact Rock Strength: measured in a laboratory
- Field Stresses
- Ground Water
- Drill Core Quality (Fracture Density)
- Joint Spacing
- Joint Persistence (length)
- Joint Orientation
- Joint Contour (Shape)
- Joint Aperture and Surface Condition
Main Characteristics
- Measured by the International Society of Rock Mechanics (ISRM)
- Orientation
- Spacing
- Persistence
- Roughness
- Wall strength
- Aperture
- Filling
- Seepage
- Number of sets
- Block size
Jointed Rock
- Discrete large rock blocks falling or sliding
- Unraveling and progressive collapse of small blocks
- Crushing and spalling under high stress
- Tensile cracking, crushing, sliding, and dilation
Core Logging
- Exploration boreholes drilled for ore reserve data
- Standard geological exploration logs may provide geotechnical information such as faults
- Re-logging the core is often necessary for geotechnical purposes
Exposure Mapping → Outcrop & Spot Mapping
- A preliminary assessment mechanism
- Only important discontinuities (in terms of persistence) are considered
Exposure Mapping → Window Mapping
- Far more time consuming than scanline mapping
- The amount of data collected is far greater
- Geometric bias may be reduced in certain cases
Laboratory Testing
- Uniaxial compression
- Triaxial compression
- Tensile strength (Direct, Indirect)
- Direct shear
- Water content and density
In-situ Stresses
- Vertical stress, σv
- Maximum horizontal stress, σHmax
- Minimum horizontal stress, σhmin
Importance of Groundwater in Geomechanics
- High moisture content increases the density of geomaterials, increasing transport costs and reducing value
- Accelerated weathering with reduced stability of shales and mudstones
- Freezing of groundwater:
- Wedging in water-filled fissures - volume changes from water to ice (mechanical weathering)
- Drainage blockage leading to increased water pressure and reduced stability
Rock Mass Classification
- Classification schemes are beneficial for feasibility studies and preliminary design stages
- Schemes act as a checklist to ensure all relevant information is considered
- Classification can help build a picture of rock mass composition and characteristics, providing initial estimates of support requirements, and/or strength & deformation properties for support estimates
- Classification schemes cannot replace engineering analysis and design procedures
Q-System
- Rock Quality Designation: RQD
- Joint set number: Jn
- Joint roughness number: Jr
- Joint alteration number: Ja
- Joint water reduction factor: Jw
- Stress reduction factor: SRF
How Q-System Works
- Rating number is calculated using the following equation: Q = (RQD / Jn) × (Jr / Ja) × Jw / SRF
- RQD roughly represents block size
- Jr describes the frictional characteristics
- Jw represents active stress situation
RQD (Rock Quality Designation)
- RQD values and corresponding classifications
- Very poor, Poor, Fair, Good, Excellent
Jn (Joint Set Number)
- Jn values and their corresponding descriptions
- Massive, One joint set, Two joint sets, Two joint sets with random joints, etc.
- Notes on usage for tunnel intersections and portals
Jr (Joint Roughness Number)
- Values and descriptions
- Planar, undulating and discontinuous
Ja (Joint Alteration Number)
- Values, descriptions, and conditions
Jw (Joint Water Reduction Factor)
- Values and descriptions, relevant conditions
Jw/SRF
- The quotient consists of two stress parameters, SRF and Jw
- SRF measures loosening loads in excavations through shear zones and clay-bearing rock
- Jw measures water pressure, which affect normal stress on joints
Q-System-Rock Classes
- Classification chart based on Q values and their descriptions. (Exceptionally poor, Extremely poor, Very poor, Poor, Fair, Good, Very Good, Extremely Good, Exceptionally Good)
Q-System - Example 1
- Description of a strong competent jointed rock sequence with 70% RQD, 200 MPa UCS and little water.
- 3 major joint sets, smooth & wavy critical joint walls.
Solution
- Example using the Q-System to find the rock class and needed support
- Given values for RQD,Jn, Jr, Ja, Jw,SRF
Q-System - Application - Design Support and Reinforcement
- Tabulated version by Barton
- Summary graph of recommendations by Grimstad.
- Graph for permanent support in civil tunnels, shafts, and caverns.
Rock Mass Quality and Rock Support-Diagram
- Chart for support type, rock class and other factors
Excavation Support Ratio (ESR)
- Table of ESR values by excavation category
- Temporary mine openings (3-5)
- Permanent mine openings, water tunnels, drifts & headings (1.6)
- Storage rooms, water treatment plants, minor roads, railway tunnels (1.3)
- Power stations, major roads & railway tunnels, civil defence chambers (1.0)
- Portal intersections, etc
Equivalent Dimension - De
- Equation: De = span, diameter or height (m) / Excavation Support Ratio (ESR)
Plates
- Typical plates used for ground support: flat, dome, or combination plate
Straps
- Strap support with reinforcing elements
Mesh Reinforcement
- Methods to reinforce with mesh
Shotcrete
- A key for rapid tunneling excavation and fast cycle times
- Rapid early strength development is critical for short cycle times and to ensure efficient rates of progress in tunneling
- Failure mechanisms of thin shotcrete design (Adhesion, Flexural Failure, Punching Shear Failure, Direct Shear Failure, Compression/Tension)
Shotcrete with Fiber-reinforced
- Shotcrete application with wire mesh reinforcement
- Fibre-reinforced shotcrete application
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