Triger process

The trigger process is a shaft-sinking method used to drive through water-saturated or unstable ground by maintaining a pressurized work chamber. A steel tubbing (lining) is installed as the shaft descends, and an airlock at the top creates a seal. Compressed air is pumped into the chamber below the working level, keeping water and loose material out while miners or machines excavate the shaft bottom. The air pressure must equal or slightly exceed the hydrostatic pressure of groundwater at depth to prevent inflow.

The process requires careful management of air pressure, typically ranging from 0.3 to 3 bar depending on depth and ground conditions. A pressure chamber (or decompression chamber) allows workers to transition safely between atmospheric and pressurized zones. The tubbing itself, usually made from cast iron or steel rings bolted together, must be strong enough to resist both internal air pressure and external soil and water loads as it descends.

Decompression and operational hazards

Workers spending prolonged periods in pressurized chambers face the risk of decompression sickness (the bends) if they ascend too quickly. Staged decompression in the airlock, sometimes over hours for deeper work, is essential. The confined, pressurized environment also demands careful monitoring of air quality, removal of excavated material, and structural integrity of the tubbing as it moves downward. Ground collapse, air leaks, and pressure loss all threaten both safety and progress.

The trigger process was widely used in the 19th and early 20th centuries for mine shafts and deep wells, particularly where other dewatering methods proved impractical. It remains viable for specialized applications in difficult geology, though modern alternatives such as ground freezing or chemical grouting have reduced its use. The name derives from the triggering or release of air pressure to maintain working conditions, distinguishing it from open-pit or dry-shaft methods.