Rational frequency range and criteria for diagnosing endogenous fire zones in coal massifs by using the georadiolocation method

Abstract

Relevance. The necessity to improve the accuracy of analysis and prediction of potential fire hazard of rock-coal massifs by using electromagnetic methods of endogenous fire detection. Taking into consideration that the increase in coal temperature changes a number of its parameters, such as dielectric permittivity and electrical resistivity, it is reasonable to use the method of electromagnetic reconnaissance in locating the focus of fire. Aim. To analyze the theoretical and practical knowledge about the anomalies formed in the area of spontaneous combustion and to evaluate the effectiveness of electromagnetic methods for locating the spontaneous combustion zones of a coal massif. Objects. Physical parameters of the ignition zone of the coal massif, such as dielectric permittivity and electrical resistivity, as well as the range of the GPR central frequency, allowing clearly defining the boundaries of the ignited zone. Method. Reviewing the proposed methods of determining the parameters serving for correct location of the fire zone. For GPR it is necessary to determine the center frequency of the standard antenna unit and resolution, then to estimate the rational frequency range of GPR. Results. Allow us to draw conclusions about the methods used to determine the rational range of GPR center frequency – it can be calculated by solving the system of equations of the signal attenuation function and energy potential of GPR, by the experimental value of the target function, including the depth and detail of sounding as a function of frequency, or on the basis of a complex parameter of GPR, including the radiated power of the antenna, the number of accumulations and the reflection coefficient from the boundaries. Taking into account such physical features of the fire zone as drying the rock-angle massif and the shape of the anomalous zone, the rational range of the center frequency for the GPR "OKO-2" was determined.

Keywords

• endogenous fires
• coal spontaneous combustion
• geophysical monitoring
• georadiolocation sounding
• electrical sounding
• center frequency