A tunnel is excavated by means of a shield and uses a liquid to support the walls and roof around the shield. The liquid is also used as a means of removing the excavated material, consisting of clay and loam, which is suspended in the liquid. The solid material is separated from the liquid by first passing it through a vibrating sieve (1). The sieve has housing (3a,3b) equipped with an upper screen (4a) and a slotted vibrating lower screen (4b). The lower screen is vibrated by a vibrator (9). After passing through the screen the liquid is pumped to a cyclone separator (2) which removes the solid particles to enable the liquid to be re-used. USE/ADVANTAGE - Separation of escavated material from the liquid which holds it in suspension. The liquid can then be re-used.
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