Research On Radar Detection Technology Of Top Coal Thickness In Caving Mining

Due to the large changes in coal seam occurrence conditions and the large differences in the thickness of the top coal,uniform coal caving procedures and instability of worker experience often lead to over-and under-cutting of the top coal.The existing coal thickness detection technology still uses drilling as the main method,although the drilling detection has high accuracy,it is time-consuming and labor-intensive,and is not suitable for efficient production.At the same time,the accurate detection of coal thickness is an important part of the fine research of coal geography information system.The components are directly related to the advancement process of unmanned working face.Therefore,how to quantitatively measure the thickness of the top coal at a high speed and accurately is an urgent problem to be solved.The goal of this paper is to develop an on-line detection device for top coal thickness based on ground penetrating radar to achieve precise detection of top coal thickness,and finally integrate the device into the tunneling system or coal mining system to achieve real-time detection of top coal thickness.Make certain contributions to intelligent and unmanned coal mining.First of all,this article theoretically analyzes the propagation mode and energy attenuation characteristics of radar signals in the top coal system;studies the electromagnetic characteristics(permittivity,permeability,conductivity)of the top coal system on the propagation of radar signals.The influence of speed and amplitude attenuation;based on the research of the former two,combined with the ground penetrating radar numerical simulation software gprmax and numerical analysis software Matlab,the best detection center frequency of the radar in the ultra-thick top coal system with known media parameters has been carried out the study.At the same time,a numerical simulation of top coal thickness detection was carried out with the center frequency(80～120 MHz)as a variable,and the optimal center frequency of the ground penetrating radar for the detection of extra-thick coal seams(10 m)with known media parameters was determined.Then,using FDTD(Finite Difference Time Domain Algorithm)for numerical simulation,the research on the influence of key media(gangue)in the coal seam on the detection of ground penetrating radar coal thickness is carried out.Through the establishment of different gangue-containing composite top coal models,the radar image response of the ground penetrating radar under different gangue thicknesses,layers,and lithologies are explored.It is found that the number of layers of gangue only affects the detection thickness,while the lithology and overall thickness of gangue have a greater impact on the accuracy of radar detection of coal thickness,showing a positive correlation trend.Secondly,build a gangue compound top coal model in the laboratory and carry out physical experiments.Through the use of LTD-2600 ground penetrating radar and an antenna with a center frequency of900 MHz for detection,the radar image response caused by the gangue(thickness,number of layers,and lithology)is explored.Finally,in terms of radar images and detection errors,the law of gangue influence shown by physical experiments and numerical simulations is consistent.At the same time,in view of the important influence of coal seam water content,physical experiments with different water saturations(natural state,dryness,and complete water saturation)of coal quality have been added to study the response characteristics of electromagnetic waves under different water saturations.The results show that when the coal is completely saturated with water,the propagation speed of electromagnetic waves in the coal is greatly improved.Finally,based on the above research,a correction model for radar detection of top coal thickness error is proposed: the correction model of velocity compensation method.And carrying out the corresponding numerical simulation and physical experiment is to verify its correction effect.The results show that the correction model is feasible within a certain range.Compared with the detection results of the classic radar thickness measurement model,the accuracy is greatly improved.