| The coal mine roadway tunneling work is the most important and dangerous front-end production process and geological disasters as water inrush, rock burst, collapse and fire, etc. are great threat and frequent accidents to the safety of the tunneling miners. The threat of water damage is very serious and one of the major geological disasters(gas, dust, water, fire and roof disaster) in coal mine. The contradiction of mutual restraint between the four processes of detection, excavating, supporting and anchor should be solved reasonably in order to eliminate safety hazards, improve the work efficiency and safety coefficient of tunneling work face, realize the remote automatic control and the unmanned operation of the excavation process, and break through three key technologies of advanced detection, fast supporting and automatic control of the roadheader.In a certain specific coal roadway comprehensive tunnelling for advanced detection, it has become an urgent technical problem in coal production to identify the concealed dangerous geological structures(water-bearing geological structure, faults and collapse column geological structure) in front of tunneling face effectively and accurately, especially water-bearing geological structure, which is difficult to be found out and accurately located in the process of macro geological exploration. The conventional drilling method have the shortcomings of high cost, heavy equipment, long operating time and low efficiency, therefore cannot get satisfactory results. Compared with the drilling method, geophysical exploration methods have become an important technical means to detect mine geological structures and security risks, which is faster, more convenient, more economical, of higher resolution, larger control range and other technical advantages. The geophysical exploration methods are now widely used in the field of prevention and treatment water in coal mine. The existing advanced detection geophysical methods of coal roadway mainly include mine direct current method, transient electromagnetic method, mine geological radar method and seismic exploration method. There are some problems of these geophysical methods for advanced detection in the coal mine: low detection accuracy, poor real-time, poor directivity, low efficiency, high cost, poor anti-jamming capability and separation of detecting and excavating steps, which result in the increasingly prominent contradiction between exploration and excavation and seriously restrict the mine mechanization level and production efficiency.With the theory proposition and successful application of the DC focusing resistivity method, the DC focusing IP method and AC focusing IP method in the advanced detection field of ground or tunnel, the study of focusing electrical method theory is greatly promoted. To solve defects of the existing geophysical technology of coal roadway, China University of Mining & Technology(Beijing) proposed a new method for advanced detection in coal mine roadway-the focusing dual-frequency IP method advanced detection technology of coal roadway tunneling on the basis of the above detection theories and methods, combining the special coal mine geological environment. The method is a kind of advanced detection technology method based on the dual-frequency IP method and focusing electrical method, taking advantages of lightweight device, strong anti-interference ability, high efficiency, good stability and high observation precision of dual-frequency IP method and combining the strong penetration capability and suppression of surface interference of focusing electrical method.This paper improved design of the detector and made the key technology researches of advanced detection in coal mine roadway based on the principle prototype and existing detection mechanism researches of the focusing dual-frequency IP method. Firstly, the paper finished the tests of prototype based on resistor-capacitor network model, proposed the improved design scheme and finally designed the experimental prototype. Secondly, according to the geological conditions of coal roadway surrounding rock, the paper researched the grounding resistance calculation method and its influence factors, determined the size parameters of the electrode and finally proposed the methods of reducing grounding resistance for advanced detection in coal mine roadway. Thirdly, the paper studied effects of medium parameters on spectral characteristics of the Cole-Cole model and determined the operating frequency of emitter electrode through simulation analysis of apparent frequency with the operating frequency and Cole-Cole model parameters. Fourthly, the paper designed different electrode combination way, analyzed IP parameters variation of homogeneous and water-bearing geological structure model with the finite element method and determined the optimal electrode combination way for advanced detection in coal mine roadway. Fifthly, the paper built the physical model test platform of resistor-capacitor and soil bin with water-bearing geological structure to study characteristics of the dual-frequency IP effect and to verify the feasibility and effectiveness of the focusing dual-frequency IP method detection mechanism. This research lays a good foundation for development of project prototype and industrial test in coal mine and contributes a great value to the realization of focusing dual-frequency IP method in coal mine. It is of great significance to make the detection and excavation work together and ensure safe and efficient production in coal roadway comprehensive tunneling. The main research results are as follows:(1)The paper tested the performance of principle prototype based on resistor-capacitor model network, in view of the existing problems, put forward the improved design scheme and completed the experimental prototype which can be used in the physical model test detection.Based on the principle prototype design of focusing dual-frequency IP instrument, this paper built a resistor-capacitor network model test device, in accordance with the design requirements of system functions, tested the charge and discharge IP effect, constant current and limiting voltage, multi-channel controllable current amplitude of the transmitter and output square wave control signal of the receiver, etc. In view of the problem that the transmitter's single channel current amplitude cannot set arbitrarily, this paper put forward the improved design scheme and designed respectively the signal acquisition and square wave current control isolation circuit of the transmitter by using linear optocoupler technology. Test results show that the experimental prototype developed can meet the detection requirements of physical model test, the measurement of amplitude and phase has high precision and good stability, and the accuracy of measuring phase is higher than that of measuring amplitude. These lay a good foundation for further exploration of physical model test.(2)According to the actual geological conditions of coal roadway, this paper determined the size parameters of the electrode, simulated and analyzed the grounding resistance and electromagnetic coupling interference effect on dual-frequency IP measurement, and put forward the methods of reducing grounding resistance for advanced detection used in coal mine roadway.According to the basic requirements of electrode design in coal roadway tunneling detection, this paper selected electrode material, studied the grounding resistance calculation method of rod electrode, analyzed various factors of surrounding rock medium resistivity, electrode buried depth, electrode radius effect on the grounding resistance value, and determined the size parameters of the electrode. In order to improve the accuracy of IP measurement and reduce the grounding resistance and electromagnetic coupling interference effect on dual-frequency IP measurement, the equivalent circuit network complex impedance of the polarized element model is calculated on the basis of the similar mechanism between electric double layer capacitor and IP. Using the dimensional theory verifies the equivalence between complex impedance and electric double layer capacitor. By building an IP effect test device of simple resistor-capacitor model given parameters, this paper analyzed its accuracy and reliability, and then completed the test scheme design of resistor-capacitor model network IP effect. An ultra-low frequency signal generator produces a modulated square wave with combination of high and low frequency as the excitation signal through the resistor-capacitor model network. Though the high precision data acquisition analyzer for data acquisition and processing, the experiment simulated and analyzed the influence degrees and variations of the grounding resistance value for apparent frequency with and without electromagnetic coupling respectively, and obtained whether or not to reduce the grounding resistance and how to effectively suppress the electromagnetic interference. At the same time, combined with the actual geological conditions of coal roadway, reducing grounding resistance methods for advanced detection used in coal roadway are put forward.(3)The operating frequency and frequency ratio coefficient of emitting electrodes for tunneling detection in coal roadway are determined through simulating and analyzing complex resistivity and apparent frequency changes with the operating frequency and the Cole-Cole model parameters.Firstly, the paper defined the concept of normalized anomaly amplitude and analyzed the operating frequency effect on IP abnormal amplitude and observation accuracy of the anomaly. Secondly, according to the theory of Cole-Cole model and the definition of apparent frequency, using MATLAB software simulated complex resistivity and apparent frequency changes with the operating frequency and Cole-Cole model parameters(including charge ratio m, frequency correlation coefficient c and time constant ?). It is concluded that the charge and discharge time constant ? under different geological conditions effect on characteristic frequency of apparent frequency extreme value is the most significant. In the actual measurement, the operating frequency is selected mainly according to parameter ?. Finally, under the condition of the instrument measuring accuracy unchanged, the proper selection of operating frequency can improve the relative observation precision of detector through analyzing the measured apparent frequency value influence on the measurement accuracy. According to IP characteristics of actual geological conditions in coal roadway, considering the efficiency and the influence of electromagnetic coupling effect, this paper determined that the operating frequency of detector emitting electrode was 1/13 Hz and 1Hz and frequency ratio coefficient was 13.(4)The best advanced detection method of electrode assembly is put forward by using the finite element method to calculate the three-dimensional space potential distribution and simulate and analyze numerically focusing detection effect of different electrode assemblies.Firstly, the equivalent variational problem of multi-points source field anomaly potential of focusing dual-frequency IP method is derived on the basis of boundary value conditions and equivalent variational problem of 3-D point source field in coal roadway. Hexahedral element and three linear interpolations are adopted to carry out regional divisions and calculate the parameters of apparent frequency and apparent resistivity under different frequency square wave excitation current. The numerical solution and analytical solution of geoelectric model are compared and analyzed by building three-dimensional detection model of homogeneous media and water-bearing geological structure in coal roadway. The calculation results verify that the finite element numerical simulation has high precision by using the MATALB software and fully meet the forward precision requests. Different electrode assemblies are designed for emitting electrode number, measuring electrode observation device, constraint plane orientation of the constraint electrodes and relative position with the main electrode, and shield current coefficient between the constraint electrodes and the main electrode to analyze IP parameter variation curves of homogeneous media and water-bearing geological structure for three-dimensional detection in coal roadway. By comparing the focusing detection effect of different assemblies, this paper determined the best electrode assembly detection method that the emitting electrodes use five channels focusing device with five electrodes, the constraint electrodes are arranged at the midpoint of the cross section four edges, the measuring electrodes use observation device with three electrodes, the shield current coefficient is 1:2.(5)The dual-frequency IP effect variation characteristics of different scale water-bearing geological structure are obtained through carrying out the resistor-capacitor and soil bin physical model test of water-bearing geological structure in coal roadway. The test results verify the feasibility and effectiveness of the focusing dual-frequency IP detection technology.Firstly, according to the ideal physical model of water-bearing geological structure, the paper built the test device of equivalent resistor-capacitor model network, simulated the detection process with different scale water-bearing geological structure by changing the parameters of resistor-capacitor model, and obtained the variation of IP effect characteristics. The results show that when the measuring electrodes close to the water-bearing anomaly, the apparent frequency values increase and the apparent resistivity values decrease; when the scale of anomaly changes from big to small, under the same measuring point, the apparent frequency decreases, while apparent resistivity increases, namely the apparent frequency measurement is more sensitive to the change of the anomaly scale. Secondly, on the flat earth, excavating the geoelectric model is similar to the tunneling detection in coal roadway to carry out respectively experiment simulations of unconstrained IP effect and focusing IP effect detection with different scale and orientation water-bearing geological structure. The test results show that using the focusing dual-frequency IP method for advanced detection can greatly shorten the measurement time, not only can determine the specific direction of anomaly in front of the excavation face, but also can estimate the actual distance from the anomaly to the excavation face according to the distance between the adjacent multiple excavation faces and the current strength of extreme value point of IP anomaly parameters. |
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