Abstract: A barrier forming apparatus for forming a barrier between an exposed tunnel face (107) and a tunnel boring machine (100), the barrier being formed by the application to the tunnel face of a barrier mixture comprising two highly reactive first and second components. The barrier forming apparatus (10) includes a first reservoir (11) for storing the first component, a second reservoir (12) for storing the second component, and a plurality of applicators (13, 14 and 15). The barrier forming apparatus (10) also includes a third reservoir (56) that is used to store a clearing fluid and a piston flow divider (58) having an inlet (59) and three chambers having respective outlets, (61, 62 and 63) that are in fluid communication with a respective applicator (13, 14 and 15). The applicators are maintained in a state of readiness by a regular supply of clearing fluid passing there through.

Abstract: A barrier forming apparatus for forming a barrier between an exposed tunnel face (107) and a tunnel boring machine (100), the barrier being formed by the application to the tunnel face of a barrier mixture comprising two highly reactive first and second components. The barrier forming apparatus (10) includes a first reservoir (11) for storing the first component, a second reservoir (12) for storing the second component, and a plurality of applicators (13, 14 and 15). The barrier forming apparatus (10) also includes a third reservoir (56) that is used to store a clearing fluid and a piston flow divider (58) having an inlet (59) and three chambers having respective outlets, (61, 62 and 63) that are in fluid communication with a respective applicator (13, 14 and 15). The applicators are maintained in a state of readiness by a regular supply of clearing fluid passing there through.

Abstract: A flexible capacitor is used in a switch circuit arrangement for activating a vehicle horn. The switch circuit arrangement includes an astable circuit having a flexible capacitor. The astable circuit generates a signal having a frequency that varies in response to force applied to the capacitor. A programmed frequency sensor activates a horn activation signal if the frequency of the signal falls below a programmed threshold.