China is one of the nations suffering most serious water inrush disasters in tunnel and underground engineering, casualties and economic losses caused by water inrush and mud inrush disasters are in the forefront of geological disasters of various tunnel and underground engineering, and heavy casualties and severe economic losses and environmental disruption are generally caused. In order to prevent the water inrush and mud inrush disasters in tunnel and underground engineering, advanced geological prediction work needs to be implemented in the construction period, and the purpose of the advanced geological prediction work is to explore the geological conditions within a certain range in front of the excavation surface of tunnel and underground engineering. However, due to the strong imperceptibility and complexity of the water inrush and mud inrush disaster sources, no effective method or instrument is available for three-dimensional location of the water inrush disaster sources and quantitative prediction of the water quantity, and it is a key problem to be solved urgently in the engineering field of tunnel and underground engineering at home and abroad.
Since 70's in last century, advanced prediction research work on unfavorable geology in a construction period of tunnel and underground engineering has been begun internationally, and multiple geophysical exploration methods have been developed after development of nearly 40 years, for example, seismic reflection method, electrical method, electromagnetic method, etc. For the advanced geological prediction of a water inrush disaster source, a seismic reflection advanced prediction method and equipment thereof (for example, TSP method, TRT method, and the like) are insensitive to response of a water body and can not effectively recognize and locate the water inrush disaster source. An electromagnetic advanced prediction method and equipment thereof (for example, geological radar method, transient electromagnetic method, and so on) are sensitive to spatial position information of the water body and have a certain effect of locating the water body, yet, the electromagnetic method is very weak in anti-interference ability and is unable to predict the water quantity.
In electrical method type geological prediction methods, an induced polarization method is relatively effective, the induced polarization method is proved to have good reaction to the spatial position and water quantity of the water body and provide an effective and feasible way to solve the problems on the three-dimensional location and water quantity prediction in advanced prediction of water inrush disaster sources in underground engineering construction such as tunneling and the like. However, the existing advanced exploration induced polarization equipment in tunnel and underground engineering is fixed point source non-focusing type induced polarization equipment based on an electrical sounding theory. An exploration line of the non-focusing type induced polarization advanced prediction equipment is arranged on a tunnel side wall or bottom plate, and side interference near the exploration line generally covers useful information in front of the tunnel excavation surface, so that the location and water quantity prediction precision on the water inrush disaster source is low and the credibility is poor, thereby often resulting in a wrong geological exploration result to affect the tunnel construction safety.
The following key problems exist in the invention of the three-dimensional focusing type induced polarization equipment: (1) a shielding electrode and a source electrode need to simultaneously output current of the same polarity, and the invention of a multiplex large-constant-current transmitter with an automatic modulation function is the key problem; (2) in a three-dimensional focusing type induced polarization exploration method, an observation electrode system composed of tens of electrodes needs to be arranged on the excavation surface, and an automatic multichannel observation data collection device, namely an intelligent multichannel receiver, needs to be developed; (3) a large number of data of the observation electrode array need to be measured by the equipment, the electrodes need to be continuously switched in the collection process, and meanwhile, the switch of large current is a problem to be solved urgently, and an automatic electrode converter needs to be developed; (4) the equipment needs to have a comprehensive collection function of multi-element induced polarization information, including shielding current, supply current, apparent resistivity, ground resistance, apparent polarizability, induced polarization decay time, etc.