An advancing face requires continuing review
Excavation redistributes stresses and can leave unstable ground. Temporary and permanent support must suit the geology and excavation method, including how it can be installed without exposing workers beneath unsupported ground. Repeating a support arrangement from another section is not enough.
Unexpected water, fractures or different materials require the design assumptions to be reviewed before further advance. Inspections should cover the face, walls, crown and travel routes, rather than only the production area. Excavations and trenches provides related stability principles, but a tunnel still needs its own engineering design.
Deliver air and services to the workplace
Air must reach occupied areas and remove contaminants produced by the work. Dust, engine emissions and fumes require assessment of both sources and exposure. Control of Respirable crystalline silica is not demonstrated simply by feeling an air movement at the entrance to the tunnel.
Duct length and layout change as the tunnel advances. Damage, leaks and alterations can reduce effectiveness. Ventilation design must also address heat and possible oxygen deficiency. Environmental monitoring and conditions requiring work to stop must be specified for the actual tunnel rather than borrowed from generic airflow figures.
Know who is underground and maintain contact
Entry and exit records allow surface personnel to determine who is underground during an emergency. Contractors and visitors must be included. Communications between the face, access points and surface need to function in the intended environment, with a defined response if they fail.
Pedestrian routes need protection from vehicles, construction trains and mobile equipment. Shift handovers should communicate developments involving ground conditions, water, atmosphere and machinery. Important changes cannot remain only in the memory of the person finishing a shift.
Prepare for an underground emergency
The Emergency plan should consider fire, flooding, collapse and loss of essential services. Escape routes, lighting, wayfinding and rescue resources must account for distance and escape time. Where refuges or self-rescuers are needed, they form part of an engineered strategy supported by training. Exercises test coordination with specialist assistance; being able to telephone the emergency services does not establish that rescue from the particular tunnel is practicable.
