📋 Case Study
Tunnel Ventilation Shaft Closure at Gotthard Base Tunnel (Switzerland)
Vertical shaft closure in karst terrain with unknown fracture flow paths and groundwater interaction
🏗️ Project Overview
Alpine rail tunnel – decommissioned ventilation shaft near Sedrun
🎯 Challenge
Vertical shaft closure in karst terrain with unknown fracture flow paths and groundwater interaction
🔧 Design Approach
Multi-stage engineered plug: lower grouted concrete seal (10 m), middle bentonite-sand capillary barrier (3 m), upper vegetated evapotranspirative cover (1.5 m) with piezometer network
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Bentonite Swell Pressure
σ_swell = C × log(ω/ω₀)
Result: 125 kPa
Ensures self-healing of fractures at interface
Shaft Plug Hydraulic Gradient
Δh / L
Result: <0.05
Prevents preferential flow along shaft-concrete interface
📊 Results
No measurable leakage after 4 years; pore pressure stabilized below phreatic level; surface vegetation fully established💡 Lessons Learned
- •Shaft roughness must be mapped via LiDAR prior to sealing
- •Bentonite placement requires controlled moisture content (14–16%)
- •Long-term monitoring must include strain gauges in concrete plug
✅ Key Takeaways
- 1Shaft roughness must be mapped via LiDAR prior to sealing
- 2Bentonite placement requires controlled moisture content (14–16%)
- 3Long-term monitoring must include strain gauges in concrete plug