Abstract:  In order to accurately predict the occurrence of coal seams in front of the tunnel face and realize the threedimensional visual display and dynamic measurement of coal seams, the Huangjiagou highgas tunnel of LanzhouHaikou expressway expansion project is taken as the engineering background. First, advance drilling is carried out in the gas drainage face and the drilling parameters are recorded in detail. Then, the obtained drilling parameters are used for data processing using the Malab software, so as to acquire the spatial threedimensional coordinates of coal seam floor and roof. On this basis, a threedimensional visual coal seam occurrence model is constructed and the occurrence of coal seam is analyzed. The research results show that, the average true thickness of the coal seam crossed by Huangjiagou tunnel is about 3.35 m, the dip angle of the coal seam is about 33°, and the included angle between the coal seam strike and the axial direction of the tunnel is about 64°. The research results are almost consistent with the actual coal seam occurrence detected in the project, which shows the correctness of the established model and provides a suitable means for the advance detection of coal seam of gas tunnel.

Key words: gas tunnel, tunnel coal seam；advance detection technology, threedimensional visualization; Matlab