| The hidden geological structure under the floor of goaf is an important factor causing water inrush.Before,during and after mining,it is necessary to find out its position and monitor the water abundance to ensure the safety of the whole mining process.Due to the limitation of traditional detection technology and interpretation accuracy,it is difficult to identify some small-scale concealed structures.Meanwhile,under the influence of mining,the stress balance of floor is destroyed,which may lead to the formation of water conduction channels connecting concealed geological structures with the development of fractures and triggering water inburst from floor.In order to track and detect the hidden geological structure of the goaf floor for a long time,the single point and double point power supply is used to supply power to the goaf floor,the electromagnetic sensor is arranged in the goaf floor by the three-dimensional direct current method,and the oblique borehole is set up to work towards the goaf.The primary field potential and polarization potential were observed within one emission period,and the acquired data were used for real-time imaging to monitor the position of the floor collapse column and the change of water level in the goaf.Through forward calculation,the floor potential and polarizability changes caused by the water-bearing collapse column under the goaf floor are simulated in the process of water level rising,position moving towards the working face and position moving towards the goaf boundary.First of all,it can be concluded from the forward simulation results of potential parameters that,in the case of single point power supply,the floor potential anomaly is extremely worthy of location,and its size can directly delineate the approximate location of the abnormal body.The water level change of the abnormal body can be obtained through the abnormal borehole curve,and the connection of the extreme point can also delineate the approximate location of the abnormal body.When the two-point power supply is supplied,the midpoint position and abnormal size between the maximum and minimum potential can reflect the position of water-bearing collapse column and the change of water level.Secondly,on the basis of potential parameters,the polarizability parameters are used to carry out forward modeling of horizontal and longitudinal changes of water-bearing collapse columns at different water levels and positions in floor.The results of single point power supply are similar to the results of potential parameters,and the location of abnormal bodies can be delineated basically through the isoline map of floor polarizability and borehole survey.When the two-point power supply is applied,the response of the polarizability to the water-bearing abnormal body in the floor is not obvious,and the position of the abnormal body can be roughly found,but the law of water level information is not obvious.The result shows that the single point power supply effect is better than the double point power supply effect,which is convenient for underground construction.Finally,based on the similarity criterion,the actual physical model is established according to the floor distribution of the mined-out area,and the three-dimensional monitoring physical model experiment of the polarizability is carried out on the model.The experiment adopted the comparison of the resistivity and the three-dimensional graph of the polarizability,the change of the polarizability of the section of the polarizability and the monitoring of the oblique borehole survey line.The results showed that with the rise of the water level,the abnormal polarizability gradually increased,and the change of the position of the abnormal body and the value of the polarizability with the water level was observed through the borehole survey line.The feasibility of monitoring technology for water inrush process of concealed structure based on polarizability parameter is verified,which provides reference basis for mine safety production. |
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