Study On Dynamic Monitoring Technology For Water Inrush From Coal Floor With Grounded Wire Source Electromagnetic Method

The lagging water inrush from floor is harmful to mine safety for it’s concealment and emergent. Small buried faults and subsided columns can’t be detected for most of the traditional geophysical methods are static detection before mining and their data accuracy is limited, while the stress balance may be destroyed, which can cause the development of fracture, and partial buried structure may be developed into water conducting channel during mining process. In order to monitor the development of water-bearing fracture, we transmit periodic pulse square wave with grounded wire source, the potential and the magnetic field intensity could be observed by multi-channel electromagnetic sensors, thus we defined it as dynamic monitoring technology for water inrush from floor with multi-parameters grounded wire source electromagnetic method.The distribution of potential and vertical magnetic field intensity with abnormal bodies in different positions, sizes and depths are researched through forward modeling. From anomalous potential contours it can be known the location of extreme points, extreme value and its change trend can reflect the distribution, development and upward trend of each abnormal body in the 3D DC system. The diffusion process of transient field and factors which have effect on zH, including source waveforms, length of grounded wire, offset and geoelectric structure are analysised in the grounded wire source TEM observing system. We calculate the zH plane contours of each model at the same time and its multi-channel profile, both of them can reflect the distribution, development and upward trend of abnormal body.We define the water inrush coefficient of fixed source 3D DC resistivity method and grounded wire source TEM. Three pre-alarm levels coefficients of the theoretical geological model has been calculated based on the forward result of abnormal body in different depths, they are grade Ⅲ, ⅡandⅠ. The water inrush coefficients was calculated to obtain the thickness of aquifer through real-time variation of potential and magnetic field intensity, so it can be used to monitor floor safety. And we have made a test of 3D DC resistivity method in a mine, the results showed it can measure the safety of the floor effectively,which provides a reference for safe mining.