Research On Very Low Frequency Method For Detecting Goaf Of Coal Mine

The development of the current world and the progress of the new era have increased the demand for natural resources.Natural resources such as coal,iron,and petroleum are constantly being mined and excavated.China's main energy coal plays a vital role in the rapidly developing economy and society.Mineral resources were excavated in an uncontrolled manner,and countless mine goafs were formed underground.Due to the uncertainty of the underground depth and range of the goaf,it is easy to cause ground collapse,threaten people's lives,affect the construction of houses and roads,and prevent crops from being cultivated.Therefore,it is urgent to focus on strengthening the exploration of coal mines' goafs.This paper proposes a new idea for the detection of the goaf of coal mines using the very low frequency electromagnetic method.The very low frequency electromagnetic method,developed in the mid-1960 s,is a geophysical exploration method for inferring formation information based on detecting electrical differences in rocks at different depths underground.This method is based on the principle of electromagnetic induction,and can be measured either from the magnetic vector(magnetic dip method)or from the electrical vector(resistivity method).It uses the electromagnetic wave signals emitted by communication stations or navigation stations distributed in various parts of the world as a field source to receive and process radio frequency signals without the need to create additional signal stations by itself.There are a large number of VLF radio stations distributed around the world,so they can always receive electromagnetic signals transmitted by one or more transmitting stations,which provides convenient conditions for prospecting,lava,faults or geological exploration,and solves the bulky and difficult equipment.A series of problems such as portability and high cost.As a result,very low frequency electromagnetic methods are gradually being valued and applied in today's society.This thesis uses very low frequency electromagnetic method combined with software radio technology.The receiver receives the high-power and high-precision electromagnetic waves emitted by the very low frequency navigation station as the signal field source.When it propagates underground and meets the underground geological body,it will produce electromagnetic induction phenomena,resulting in thecombination of the primary field and the induced secondary field.The amplitude and phase have changed.The system filters and amplifies the received electromagnetic waves and transmits them to the computer.Based on the mathematical relationship analysis,the apparent resistivity is calculated.At the same time,we also used the experimental method to measure the resistivity of common underground materials,and also used Simulink simulation to verify the system we designed.Finally,the apparent resistivity calculated in the computer is combined with our experimental results to determine the location of the goaf based on the abnormality of the resistivity value.This method has low cost,easy to operate instruments,easy to carry and carry,and it is convenient for field measurement.And the measurement operation is simple,with good results is a meaningful geophysical method.