Subterranean Hydro Tunnel Survival & Rescue Profile Explorer

Air Pocket Volume

1,662.5 m³

Hydrostatic Head: 1.34 atm

Atmospheric PaO2 / PCO2

17.4 / 2.8 kPa

Viable Air Pocket Maintained

Acoustic Geophone Array

+14.8 dB

Voices Confirmed by Listening Array

Rotary Borehole Time

38.9 hrs

Depth: 280 m Metamorphic Rock

Subterranean Tunnel Elevation Cutaway (1,850 m Headrace Bore)

Metamorphic Overburden

Debris Plug (Silt Slurry)

Flood Sump Seal

Pressurized Survivor Cavity

Rescue Percussion Borehole

Atmosphere & Survival Envelope Dynamics

Closed-pocket metabolic depletion modeled for 2 workers over 9 days at 14°C ambient headrace temperature.

• Partial Pressure O₂: 17.4 kPa (Hypoxia limit: 12.0 kPa)

• Partial Pressure CO₂: 2.8 kPa (Hypercapnic toxicity: 5.0 kPa)

• Cavity Air Trapped: 1,662.5 m³ (Compressed from 1,930 m³)

• Hydrostatic Pressure: 135.8 kPa (1.34 atm)

Acoustic Geophone & Drill Trajectory

Seismic sensor detection threshold through gneiss bedrock versus muddy silt slurry.

• Overburden Depth: 280 m vertical shaft

• Penetration Rate: 7.2 m/hr (Down-The-Hole Hammer)

• Geophone SNR: +14.8 dB (Bedrock acoustic transmission)

• Status: VOICE SIGNALS DETECTED

Parameter Controls

Elapsed Entrapment 9 days

Trapped Survivors 2 persons

Flood Slurry Elevation 14.5 m

Overburden Depth 280 m

Tunnel Incline Gradient 3.5°

Operational Scenarios

Operational Summary

The 3.5° ascending grade of this 4.2m diameter headrace tunnel creates a self-sealing trap. As floodwaters submerge the portal, trapped atmospheric air cannot vent down-gradient, establishing a pressurized survival pocket where O₂ depletion and CO₂ accumulation determine the intervention window.

Incident Background & Engineering Rationale: Following the severe flash flood disaster along the Nepal-Tibet border watershed resulting in over 1,200 fatalities and 5,000 missing, rapid geotechnical mobilization achieved the extraction of two workers trapped nine days subterranean in a hydropower headrace tunnel. Surface geophones detected structural tapping and vocal signatures through solid metamorphic gneiss, providing exact coordinates for emergency rotary percussion drilling.