Podcast
Questions and Answers
What is a primary reason the connection between surface elements and rock bolts is considered the weakest link in the support system?
What is a primary reason the connection between surface elements and rock bolts is considered the weakest link in the support system?
- It is far from the failure zone.
- The surrounding rock is highly stable.
- It is close to areas of unsupported rocks. (correct)
- Rock bolts are usually too short.
What external factor can affect the integrity of rock bolts apart from the rock joint visibility?
What external factor can affect the integrity of rock bolts apart from the rock joint visibility?
- The temperature variations in the rock.
- The type of bolt used.
- The length of the rock bolt.
- Corrosion from ground water. (correct)
What is the effect of high dry shrinkage in shotcrete on construction practices?
What is the effect of high dry shrinkage in shotcrete on construction practices?
- It eliminates the need for joint spacings.
- It requires closer control-joint spacings. (correct)
- It allows for wider joint spacings.
- It improves the hardness of the shotcrete.
Why does shrinkage occur in hardened concrete?
Why does shrinkage occur in hardened concrete?
Which of the following methods can help mitigate tensile stresses in shotcrete?
Which of the following methods can help mitigate tensile stresses in shotcrete?
What defines creep in shotcrete under load?
What defines creep in shotcrete under load?
What is a consequence of tensile stresses caused by shrinkage in shotcrete?
What is a consequence of tensile stresses caused by shrinkage in shotcrete?
Which factor does NOT contribute to the weakening of rock bolts in corrosive environments?
Which factor does NOT contribute to the weakening of rock bolts in corrosive environments?
What role does the aggregate type play in the shrinkage of shotcrete?
What role does the aggregate type play in the shrinkage of shotcrete?
What condition in shotcrete can cause greater loads on the ground support system?
What condition in shotcrete can cause greater loads on the ground support system?
Flashcards
Weakest link in tunnel support system
Weakest link in tunnel support system
The connection between surface elements (e.g., rock bolts/cables) and the surrounding rock is often the most vulnerable point, frequently situated near the tunnel's surface where rocks have become unsupported.
Failure zone (tunnel)
Failure zone (tunnel)
Region near the tunnel's face where rocks have lost support due to tunneling
Rock bolt anchoring
Rock bolt anchoring
The process of anchoring rock bolts or cables to stable rock beyond the failure zone to stabilize the unsupported surface.
Corrosion (rock bolts)
Corrosion (rock bolts)
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Shotcrete shrinkage
Shotcrete shrinkage
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Shotcrete control joints
Shotcrete control joints
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Shotcrete fibers
Shotcrete fibers
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Creep (material)
Creep (material)
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Low water-cement ratio (shotcrete)
Low water-cement ratio (shotcrete)
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Tensile stress (shotcrete)
Tensile stress (shotcrete)
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Study Notes
Question 1-1
- Connection between surface elements and rock/cable bolts is weakest point in support system.
- Tunneling exposes rock in failure zone, making it unstable.
- Rock outside failure zone is stable.
- Bolts and cables must extend to stable rock to anchor unstable rock.
- Locating support structure depth is challenging cause features inside the rock are usually unseen.
- Corrosion weakens rock support systems.
- Galvanizing and corrosion reducing treatments are needed.
- Exposure to aggressive water can lead to pitting, erosion, corrosion fatigue, and fretting.
Question 1-2
- Shotcrete shrinkage varies based on water content and aggregate type.
- High dry shrinkage requires closer control joints.
- Shrinkage causes contraction and tensile stress in hardened concrete.
- Cracks form at joints and cause external deflection.
- Adding fibers reduces tensile stress.
- Creep is time-dependent deformation under load.
- Low water-cement ratio reduces creep.
- High water-cement ratio increases creep and deflection, leading to collapse risk.
- Forces from deflection and rock wall pressure can cause collapse.
Question 2
- Rock bolts have two main functions:
- Increase beam depth.
- Reinforce lamination to reduce interlayer slip.
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Description
Explore the critical aspects of tunneling and support systems in geological conditions. This quiz addresses the challenges posed by surface elements, rock stability, support structure depth, and the effects of corrosion and shrinkage in concrete. Test your knowledge on the connections and materials that play a crucial role in maintaining rock stability and integrity in tunnel construction.
