Quantitative prediction of water abundance in rock mass by transient electro-magnetic method with LBA-BP neural network

The existence of water in the rock stratum in front of the roadway seriously threatens the safe driving of the mine roadway. Mine Transient Electromagnetic Method is the main method in advanced detection of roadway. Current- ly,apparent resistivity is the only way to qualitatively evaluate the water abundance of rock stratum in front of road- way. In order to realize a quantitative prediction of water abundance in rock stratum,the first step is to establish the mathematical model of the uneven water abundance of rock stratum in front of the roadway based on Archie formula. Then numerical simulation can be carried out by 3D finite difference time domain (FDTD) and its results can be used to extract the features needed in prediction. According to the selected features and the geological parameters related to the water abundance of rock stratum,the water abundance can be determined to predict the structure of neural net- work. The BP neural network was optimized by the bat algorithm based on Lévy flight improvement,and the simulation test and field test of water abundance prediction were carried out by using the LBA-BP method. In the simulation test, in order to approach the actual situation,different degrees of noise were added to the numerical simulation results. By comparing the test results,it was found that although the prediction error fluctuated significantly with the increase of noise,the mean square error of rock porosity and water saturation prediction was less than 1% ,and the prediction ac- curacy was at a high level. In the field test,according to the classification criteria of water abundance evaluation based on the field geological data,it can be seen from the prediction results and the apparent resistivity interpretation results that the accuracy of the LBA-BP prediction method is significantly better than that of the conventional apparent resis- tivity interpretation method in predicting the water abundance of stratum in front of the roadway. The results show that the induced electromotive force,sampling time,apparent resistivity,detection distance and induced electromotive force attenuation rate in logarithmic co-ordinates can be used as the characteristics of water abundance prediction. The LBA- BP method realizes the near quantitative or quantitative prediction of water abundance in rock stratum,and improves the interpretation accuracy of the advance detection data for water abundance in rock stratum.