Monitoring critical stress conditions in mines and tunnels - using geophones and staggered frequency-time signal distribution evaluation

The method is for monitoring critical stress conditions, esp. in large geological layers of mining and tunneling constructions, enables the accuracy of measurement to be increased w.r.t. conventional methods in combination with equivalent or reduced cost of measurement equipment. Seismoaconotic signals, including any noise signals arising, are acquired by geophones before being evaluated in staggered frequency band and time distributions. Macro, medium, and micro results (13"', 13", 13') are separately counted and evaluated. Noise signals occurring are suppressed outside the stagger limits and below each residual level. Associated with each geophone (1) are an amplifier (5), band filter (7), a threshold switch (9), a time discriminator, (11) and a result counter. The geophones used are either broad band types or those with three resonance systems.