Tunnels

Question 1

Key aspects of tunnels

Answer 1

Geology and Site Investigation
2. Tunnel Design :

3. Construction Methods
4. Materials and Linings :

Question 2

construction methods for tunnels

Answer 2

1. Drilling and Blasting (D&B) :
   - Uses explosives to break rock, followed by mechanical removal.
   - Suitable for hard rock; slow and generates vibrations.
2. Tunnel Boring Machines (TBMs) :
   - Mechanical excavation with rotating cutting wheels.
   - Fast and efficient but expensive and less flexible.
3. Cut-and-Cover :
   - Excavation from the surface, then covered.
   - Suitable for shallow tunnels; disruptive to surface activities.
4. Immersed Tubes :
   - Pre-fabricated sections sunk into place.
   - Ideal for underwater tunnels or minimal surface disruption.
5. Hand Mining :
   - Labour-intensive with hand tools and small machinery.
   - Suitable for small-scale or limited access tunnels.
6. Mechanized Cut-and-Cover :
   - Combines mechanical excavation with cut-and-cover.
   - Faster but still surface-disruptive.
7. Pipe Jacking :
   - Hydraulic rams push pre-fabricated pipes through soil.
   - Used for small-diameter tunnels like utility pipes.
8. Box Jacking :
   - Similar to pipe jacking but with larger, box-shaped sections.
   - Suitable for larger tunnels like subway stations.

Question 3

design considerations for tunnels

Answer 3

1. Geology :
   - Rock type and strength. - Soil composition and density
   - Groundwater levels and flow - Fault lines and seismic activity
2. Tunnel Purpose and Use :
   - Transportation (highway, railway, pedestrian)
   - Utility (water, sewage, gas, electricity)
   - Mining or excavation. - Military or defense
3. Tunnel Alignment and Profile :
   - Horizontal and vertical curves
   - Gradient and slope. - Tunnel length and depth
4. Tunnel Size and Shape :
   - Diameter or width. - Height or clearance
   - Cross-sectional shape (circular, rectangular, etc.)
5. Materials and Linings :
   - Concrete, steel, or composite materials
   - Shotcrete, cast-in-place, or precast segments
   - Waterproofing and drainage systems
6. Hydrology and Water Management :
7. Ventilation and Air Quality :
   - Fresh air supply and exhaust systems
   - Air quality monitoring and control
   - Emergency ventilation and evacuation plans
8. Lighting and Electrical Systems :
   - Lighting design and installation
   - Power supply and distribution
   - Communication
9. Safety and Emergency Response :
10. Environmental Impact and Sustainability
    - Minimizing environmental disruption
    - Sustainable materials and practices
    - Long-term maintenance and rehabilitation plans
11. Cost and Budget :

Question 4

support systems for tunnels

Answer 4

Support Systems:
- Rock bolts : Steel bolts anchored into the rock to prevent rockfall and stabilise the tunnel.
- Steel ribs : Curved or straight steel beams providing additional support.
- Shotcrete : Sprayed concrete layer to stabilise rock and prevent erosion.
- Steel mesh : Grid of steel wires reinforcing shotcrete and preventing rockfall.

Question 5

linings

Answer 5

• Cast-in-place concrete : Concrete poured directly into the tunnel for a smooth, durable lining.
• Precast concrete segments : Pre-fabricated concrete sections assembled in the tunnel.
• Steel linings : Thin steel plates or sheets used to line the tunnel, often combined with concrete.
• Composite linings : Combination of materials like steel and concrete for optimal strength and durability.
• Membrane linings : Waterproof membranes to prevent water ingress and protect the tunnel.

Question 6

other types of support systems and linings for tunnels

Answer 6

• Grouting : Filling gaps and voids with grout to prevent water ingress and stabilize the rock.
• Anchors : Post-tensioned anchors securing the tunnel lining to the surrounding rock.
• Nailing : Installing nails or pins to secure the rock and prevent rockfall.
• Mesh drapes : Hanging mesh screens to catch loose rock and debris.
• Sprayed concrete arches : Building arches with sprayed concrete for additional support.