Railway Infrastructure and Tunneling Systems

Railway Infrastructure Overview

Railway Infrastructure Definition: Physical components and systems enabling train operations and movement of goods/passengers.
MRT Station Capacity Design: Station Layout
- Crucial in determining capacity.
Platform Width and Train Length
- Platform width must handle peak-hour passenger flow for efficient boarding/alighting.
- Train length optimized to match platform and passenger demand.
Passenger Flow Analysis:
- Considers peak hour travel, passenger arrival/departure rates, transfer movements, and demand distribution.
Operational Considerations for MRT Station Capacity
- Train Frequency and Headway: Increasing trains and reducing headway increases passenger throughput.
- Train scheduling optimizes operations and capacity.
- Platform Screen Doors (PSDs):
  - Regulate passenger flow.
  - Reduce platform congestion.
  - Enable faster boarding/alighting.
- Passenger Behaviour and Crowd Management:
  - Signage, wayfinding, and crowd control minimize congestion.
  - Continuous monitoring and feedback optimize station capacity.

Evacuation Calculation Example

Scenario: NSEWL Raffles Interchange station evacuation.
- Total passengers: 12,000 (peak hour).
- Number of exits: 8.
- Exit width: 3 meters per exit.
- Passenger flow rate: 1.2 passengers per second per meter of exit width.
- Walking speed: 1.4 m/s.
- Distance to exits: 50 meters.
- Evacuation target time: 7 minutes.
Calculations:
- (a) Total Passenger Flow Rate:
  - Flow rate per exit = $3 \text{ meters} \times 1.2 \frac{\text{passengers}}{\text{s} \cdot \text{m}} = 3.6 \frac{\text{passengers}}{\text{s}}$
  - Total flow rate = $3.6 \frac{\text{passengers}}{\text{s}} \times 8 \text{ exits} = 28.8 \frac{\text{passengers}}{\text{s}}$
- (b) Total Evacuation Time (Flow Rate Limited):
  - Total time = $\frac{12,000 \text{ passengers}}{28.8 \frac{\text{passengers}}{\text{s}}} \approx 416.67 \text{ seconds} \approx 6 \text{ minutes } 57 \text{ seconds}$
- (c) Total Evacuation Time (Walking + Flow):
  - Walking time = $\frac{50 \text{ meters}}{1.4 \frac{\text{m}}{\text{s}}} \approx 35.71 \text{ seconds}$
  - Total evacuation time = $35.71 \text{ s} + 416.67 \text{ s} \approx 452.38 \text{ seconds} \approx 7 \text{ minutes } 32 \text{ seconds}$
- Conclusion: Does not meet 7-minute target.
Multiple Level Underground Station Design Considerations:
- Existing infrastructure.
- Station boundary limitations.
- Train tunnel level relative to underground services.
Purpose of Platform Screen Doors:
- Enhance passenger safety.
- Improve crowd management.
- Provide a barrier between platform and tracks.
- Conserve energy by preventing warm air from tunnels entering air-conditioned stations.

Tunneling Systems and Construction

Tunnel Boring Machine (TBM):
- Specialized heavy construction equipment.
- Excavates tunnels through various geological formations.
Key Features of TBM:
- Cutterhead: Equipped with cutting tools for excavation.
- Shield: Provides stability during excavation.
- Tunnel Lining: Installs tunnel lining segments.
- Conveyor System: Transports excavated material (muck).
- Thrust System: Pushes the TBM forward.
- Control Systems: Monitor and adjust parameters.
Common TBM Types in Singapore:
- Earth Pressure Balance (EPB) Machines.
- Slurry Machines.
Use of Conditioning Agents:
- Reduce friction between soil and cutting wheel.
- Examples: foams, polymers, and anti-clay agents.
Steps for Tunnel Construction:
1. Construction of launch shaft and tunnel eye.
2. Installing cradle and thrust frame.
3. Assembling TBM and supporting systems.
4. Launching TBM.
5. Building segment lining.

TBM Calculation Example 1

Scenario: Slurry TBM excavating a metro tunnel.
- Tunnel Diameter: 6.5 meters.
- Excavation Rate: 12 meters per day.
- Slurry Flow Rate: 900 m³ per hour.
- Muck Volume Expansion Factor: 1.3.
- Operational Time per Day: 20 hours.
- TBM Cutterhead Power: 2.5 MW.
- Torque Applied to Cutterhead: 3.8 MN·m = 3800 kNm.
- Cutterhead Rotation Speed: 2.5 RPM.
The problems associated with the scenario are not solved in the transcript provided.

TBM Calculation Example 2

Scenario: Slurry TBM excavating an underground road tunnel.
- Tunnel Diameter (D): 8 meters.
- Excavation Rate: 15 m/ day.
- Muck Volume Expansion Factor: 1.4.
- Operational Time per Day: 22 hours.
- Cutterhead Power: 3 MW.
- Torque Applied to Cutterhead: 4.5 MN·m (4,500 kN·m).
- Cutterhead Rotation Speed: 3 RPM.
- Bentonite Slurry Cost per Cubic Meter: $30.
- Electricity Cost per kWh: $0.08.
The problems associated with the scenario are not completely solved in the transcript provided. However, this is the solution from items e) and f):
- f) The total power output of the TBM in MW, based on torque and rotation speed.
  - Formula to find mechanical power from torque and RPM:
    $P = \frac{2π \times T \times N}{60}$
    where:
    $T = \text{Torque in Newton-meters} = 4.5 \times 10^6 \text{ Nm}$
    $N = \text{Rotation Speed} = 3 \text{ RPM}$
    Substitute:
    $P : = \frac{2π \times 4.5 \times 10^6 \times 3}{60} = \frac{2π \times 13.5 \times 10^6}{60} = \frac{84.823 \times 10^6}{60} = 1.4137 \times 10^6 \text{ W} = 1.41 \text{ MW}$
    Answer: ≈ 1.41 MW
- e) Total electricity cost for TBM operation per day
  - First, convert GJ to kWh:
    $1 \text{ GJ} = 277.78 \text{ kWh}$
    $237.6 \text{ GJ} \times 277.78 = 66,000 \text{ kWh}$
  - Electricity cost:
    $66,000 \text{ kWh} \times 0.08 = 5,280 \text{ USD/day}$
    Answer: $5,280/day

Tunnel Ventilation Systems (TVS)

Air Quality Improvement:
- Removes pollutants from the tunnel air.
- Maintains acceptable air quality.
- Minimizes health risks.
Temperature Control:
- Tunnels experience extreme temperatures.
- Normal operation maintains bulk air temperature below 40ºC.
Airflow Distribution:
- Ensures fresh air reaches all areas.
- Prevents pollutant accumulation.
Smoke Management and Control:
- Extracts and removes smoke.
- Maintains visibility.
- Provides safe evacuation paths.
Sub-systems of TVS:
- Tunnel Ventilation Fan (TVF) System: Allows air exchange.
- Tunnel Booster Fan (TBF) System: Assists airflow in specific sections.
- Underplatform Exhaust (UPE) System: Extracts heat from trains at stations.
Mode Operations in TVS:
- Normal.
- Congestion.
- Emergency.
Critical Velocity:
- Minimum airspeed to remove smoke and pollutants during emergencies.
- Maintains safe conditions in tunnels.

TVS Calculation Example

Scenario: Road tunnel ventilation.
- Tunnel Length: 500 meters.
- Tunnel Width: 7 meters.
- Tunnel Height: 5 meters.
- Traffic: 1200 vehicles per hour.
- CO Emission: 1.5 g/s per vehicle.
- Max Allowable CO: 50 ppm.
- Fresh Air CO: Negligible.
- Air Density: 1.2 kg/m³.
- CO Conversion: 1 ppm CO = 1.145 mg/m³.
- Mixing: Perfect.
- Frictional Pressure Loss: 1.5 Pa per meter.
- Fan Efficiency: 70% (0.70).
The problems associated with the scenario are not completely solved in the transcript provided. However, this is the solution from item b):
- (b) Required fan power
  - Use the equation for power:
    $P = \frac{ΔP \times Q}{η}$
    Where:
    $ΔP = \text{Pressure loss} = 750 \text{ Pa}$
    $Q = \text{airflow} = 31,428.57 \text{ m³/s}$
    $n = \text{fan efficiency} = 0.70$
    $P = \frac{750 \times 31428.57}{0.70} = \frac{23,571,429}{0.70} = 33,673, 470 \text{ W} = 33, 673 \text{ kW}$
    Answer (b): 33,673 kW
9. Find the critical velocity $V_c$ needed for preventing back-layering of smoke during a tunnel fire scenario given the following:
- Area of tunnel = $127.3m^2$
- Front surface area of train = $9.8m^2$
- Fire heat release rate, Q = $10MW$
- Smoke fume temperature $T_f = 135\text{degC}$
- For the air, take density = $1.15kg/m^3$ , $C_p = 1003J/kgK$ , and Ambient temperature = $37\text{degC}$
- $Q<em>c = V</em>c \times \text{Annular Tunnel Area}$
- $\dot{m} = 𝜌Q_c$
- $Q = \dot{m} C_p ΔT$