| Similar material model experiment is an important means to study mining subsidence and damage,and it is very important to obtain model deformation information with high precision in the experiment.There are still some limitations in the accuracy and efficiency of data acquisition of existing model deformation measurement methods.In this paper,the 4105 working face of No.4 coal seam in Wenjiapo Coal Mine,Binchang,Shaanxi Province is used as the model to carry out the similar material simulation experiment.The high-resolution sequence images are obtained by taking a close shot of the model with a non-metric camera,and the feature points are extracted by image distortion correction,automatic stitching and improved Faster R-CNN(Faster Regions with Convective Neural Network Features)algorithm,so that the deformation information in the mining process of the model can be obtained with high precision.The main research contents and results are as follows:(1)By comparing and analyzing the different characteristics of four close-range photogrammetry methods existing in deformation measurement of similar material models,a technical scheme of sequence image acquisition with similar aerial photography mode is adopted.The results show that the existing panoramic fixed imaging methods take short time,but the accuracy is low.The precision of single-point digital imaging is high,but it takes a long time for field shooting;Digital close-range industrial photogrammetry system can work efficiently,but it has high requirements for equipment and can’t display the deformation of specific points.The aerial photography-like sequence image acquisition method adopted in this paper has obvious advantages in operation efficiency,image resolution and measurement accuracy.(2)According to the characteristics of experimental models of similar materials,based on the analysis of the influence of measuring point mark,size,number of image control points,object distance and image overlap on the measurement accuracy of the model,the technical process of aerial photography integrated operation of experimental models is determined.In the process of model excavation,non-metric camera was used to take close-range orthophoto shots,forming image sequences with horizontal overlap greater than 70%and vertical overlap greater than 50%.Bilinear interpolation method was used to correct image distortion,automatic and robust image stitching algorithm was used,Harris corner detection operator was used to extract feature points,RANSAC algorithm was used to classify pseudo-matching points,and color interpolation method was used to join edges,so as to further splice the image sequences.The results show that the resolution of the generated panoramic image is about 10 times higher than that of the panoramic image of the fixed camera.(3)An improved Faster R-CNN algorithm is proposed in sequence image processing,and the actual effect of this algorithm on improving the accuracy of measuring point extraction of the model is analyzed.In the process of image processing,the measuring point mark is used as the training network,the confidence level is added based on Faster R-CNN algorithm,the appropriate sliding template is selected for region analysis,and then the accurate coordinates of the measuring point are obtained by using the correlation image matching algorithm.The results show that this method can improve the detection accuracy by 4.7%and the detection efficiency by 2.3%,and the accuracy of coordinate extraction of measuring points in model experiment is better than 0.027mm,which is equivalent to the field measurement accuracy of 5.4mm,which meets the requirements of model experiment of similar materials in mines.(4)Based on the geological mining conditions of No.4105 working face in Wenjiapo Coal Mine,a similar material model is made,and the deformation information extracted by this method is used to preliminarily reveal the characteristics of strata and surface deformation caused by mining in this working face.A 1:200 scale model was made for 17 simulated excavations,and 17 image sequences were obtained.The improved Faster R-CNN algorithm was used for feature point extraction and deformation analysis.The results show that the surface subsidence curve of the model is basically consistent with the field observation data,and the maximum subsidence is-3.767mm,which is equivalent to-753mm in the field.The model experiment also reveals the basic characteristics of periodic weighting and caving and fracture zone development in overburden.The research results have certain reference value for the safety protection of surface reservoirs in mining areas. |
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