NATM (Sprayed Concrete Lining) Safety

NATM (New Austrian Tunnelling Method) uses sprayed concrete to stabilise the ground immediately after excavation.
The method relies on the ground itself as the primary structural element, supported by sprayed concrete and rock bolts.
Sprayed concrete (shotcrete) is applied at high pressure, creating risks from rebound, dust, and chemical accelerators.
Accelerator chemicals used in shotcrete are highly alkaline and cause severe burns on skin and eye contact.
Ground conditions must be continuously monitored as NATM relies on controlled ground deformation.
Convergence monitoring using survey instruments detects unsafe ground movement before collapse occurs.
The confined working environment creates exposure to dust, fumes, noise, and restricted ventilation.
NATM tunnels require immediate support — any delay in applying shotcrete increases collapse risk.
Emergency refuge chambers and evacuation routes must be maintained as the tunnel face advances.
The HSE has issued specific guidance on NATM safety following historical tunnel collapses in the UK.

Prevent collapse	NATM relies on timely support application — delays or incorrect thickness can lead to catastrophic tunnel collapse.
Chemical burns	Shotcrete accelerators are corrosive. Skin and eye contact causes severe chemical burns requiring immediate treatment.
Health protection	Dust, rebound, accelerator fumes, and noise inside NATM tunnels cause long-term occupational health damage.
Legal duty	CDM 2015 and HSE tunnel safety guidance require specific risk controls for all NATM construction methods.

Do

Don't

Monitor ground convergence continuously using installed survey instruments and targets
Apply sprayed concrete within the time limits specified by the tunnel designer
Wear full chemical-resistant PPE including goggles when working near shotcrete application
Ensure ventilation systems are running effectively before and during all spraying operations
Maintain emergency refuge chambers and keep evacuation routes clear at all times
Test sprayed concrete thickness and strength in accordance with the design specification
Brief all operatives on the evacuation plan and alarm signals before each shift
Report any cracking, water ingress, or unusual ground movement to the shift engineer
Use RPE with appropriate filters during shotcrete spraying to protect against dust and fume
Keep emergency eyewash stations within the tunnel at designated intervals

DON'T delay sprayed concrete application after excavation — ground stability depends on it
DON'T enter the freshly excavated face area without authorisation from the shift engineer
DON'T handle shotcrete accelerator chemicals without chemical-resistant gloves and goggles
DON'T ignore convergence monitoring results that show movement beyond trigger levels
DON'T obstruct emergency refuge chambers or evacuation routes with plant or materials
DON'T work at the tunnel face without confirmed ventilation and atmospheric monitoring
DON'T apply shotcrete below the specified minimum thickness to save time
DON'T remove or relocate survey monitoring points without the engineer's approval
DON'T re-enter the tunnel after an evacuation alarm without clearance from supervision
DON'T stand in the rebound zone during shotcrete spraying operations

See also: Tunnelling Safety Awareness | Sprayed Concrete (Shotcrete)

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