Research on the Application of Surface Wave Method for the Precise Detection of Shallow Coal Seam Mined-Out Area and Overburden

Abstract

To finely detect the boundary of a shallow coal mined-out area, as well as the extent of the overburden affected by the mined-out area, and to analyze the factors and interrelationships between the detection depth and lateral resolution of the multichannel analysis of surface waves (MASW) method, a low-frequency focusing factor is introduced into the phase-shift method, and a low-frequency focusing phase-shift method is proposed to improve the detection depth and lateral resolution of the MASW method. The method is applied to the processing and analysis of measured active-source surface waves. The results show that the low-frequency focused phase-shift method has the significant advantage of extracting the dispersion energy at low-frequency side from the short receiver spread. The receiver-spread length of the measured data used to calculate the dispersion energy is 35 m, which meets the 70 m detection depth of the target coal mined-out area. The measured data were processed to obtain high-precision horizontal slices of the shear wave velocity along the coal seam and in the overburden at different depths. The former clearly identify the boundaries of the coal mined-out areas and the locations and geometries of the security coal pillars and estimate the main coal mining direction to be approximately 23° NW, which is in general agreement with the actual direction of 21° NW of the back workings in the mining area of the study site. One mined-out area of approximately 30 m in width, one mined-out area greater than 50 m in width, and one roadway of approximately 10 m in width are inferred. The latter directly shows the extent of the overburden affected by the coal mined-out area gradually decreasing as the depth becomes shallower. The severe influence extent on the surface is delineated and mutually supported by the surface cracks in the village east of the research site. The effectiveness of the low-frequency focused phase-shift method in improving the depth and lateral resolution of the MASW method and the feasibility of the MASW method in precise detection of shallow coal mined-out area and overburden are confirmed.

Research on Elevation Survey Method of Sea-Crossing Bridge under Adverse Conditions

“…Jianzhou Li et al [20] deduced the error formula of the survey result through the error propagation law according to the rigorous calculation formula of precision trigonometric leveling and proved that controlling the vertical angle and survey distance of the instrument can improve the survey accuracy and achieve second-class leveling accuracy. Jianzhou Li et al [21] developed TriLevel, a precision triangulation elevation survey system that realizes the automatic measurement and quality control of precision triangulation elevation. Refs.…”