Actively heated fiber optics method to monitor grout diffusion range in goaf.

• An actively heated fiber optics method is proposed to monitor the grout diffusion range in goaf. • The grid installation method of AHFO is designed, and the calculation formula of grid size is deduced. • The two-dimensional positioning of optical fiber is realized, the grouting diffusion range is quantified, and the measurement accuracy is improved. • The visualization of slurry diffusion morphology is realized. The invisibility of grouting has always been one of the most challenging problems related to the research of grouting theory, but it has not been solved. An actively heated fiber optics (AHFO) method is proposed in this paper to realize the visualization of slurry diffusion morphology. The grid installation method of AHFO is designed, and the calculation formula of grid size is deduced. Based on the self-developed spatial positioning algorithm and Kriging spatial interpolation algorithm, the temperature anomaly in the AHFO temperature profile is used to locate and quantify the range of grouting diffusion in goaf. To verify the applicability of this method, a large-scale three-dimensional grouting model test was carried out. The test results show that the grouting diffusion mode is elliptical, consistent with the previous research results. Compared with the theoretical calculation results, the maximum relative error of the monitored grouting diffusion radius is 18 %. Therefore, the monitoring method can monitor the grouting diffusion. [ABSTRACT FROM AUTHOR]