An inflatable tunnel plug 20 for blocking a tunnel 10, the tunnel plug comprising at least a first inflatable portion 24 and a second inflatable portion 26 that is inflatable to support the first inflatable portion against the interior surface of the tunnel, wherein the first portion is inflated to a lower pressure than the second portion. The tunnel plug may also comprise an inflation device 21.The plug may comprise a pressure relief valve 28 configured to pass fluid from second portion to first portion and a exhaust pressure relief valve 28a to exhaust fluid from first portion to atmosphere. The first portion and second portion may each comprise chambers 25 27 into which fluid can be passed. The second portion may be inside the first portion. The tunnel plug may comprise a centre 22 and an outer periphery that is formed by the first portion. The second portion extends around the centre between the centre and the periphery. The second portion may provide structural strength and the first portion may deform against the interior of the tunnel. The tunnel plug may further comprise a third and forth inflatable portions.
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