Zhi Chen

This article presents the results of deformation characteristics and crack stress thresholds of cement stone under different acid treatment times. A series of true triaxial tests were conducted on cement stones under four sulfuric acid treatment times (0, 7, 14, and 28 days). The microstructures of cement stone under different acid treatment times were examined. In the range of 0 to 14 days, the damaging effect of sulfuric acid dominated, and the structural integrity was damaged by sulfuric acid. In the range of 14 to 28 days, the strengthening effect of calcium sulfate precipitate dominated, and the structural integrity was enhanced by calcium sulfate precipitate. The cement stone exhibited anisotropic deformation characteristics under true triaxial stress states. With an increase in acid treatment time, the deformation modulus of cement stone first decreased and then slightly increased. The crack stress thresholds first increased and then decreased with an increasing intermediate principal stress coefficient. With an increase in acid treatment time, the crack stress thresholds first decreased and then slightly increased. Substantially, the ratio of crack stress thresholds was analyzed. The proportion of the unstable crack growth stage and crack growth stage increased with minimum principal stress. Additionally, the proportion of the unstable crack growth stage and thecrack growth stage first increased and then decreased with increasing acid treatment time. However, the proportion of the stable crack growth stage had the opposite variation law to that of the unstable crack growth stage and crack growth stage.

The overlap winding system of coils in a multiturn small loop device in the transient electromagnetic method makes the mutual inductance coefficient large, and the measurement data are seriously affected by the turn-off effect. The conical source has the advantages of low mutual inductance effects and strong secondary fields. This study conducts an inversion of an improved particle swarm optimization (PSO) algorithm for this device. The new PSO algorithm improvement strategy (PSO-GIS algorithm) has the advantages of high success rate of optimization, fast convergence speed, high calculation accuracy, and low calculation elapsed time. The inversion results of the theoretical model and the measured mine data show that the PSO-GIS algorithm does not depend on the initial model setting, and the inversion of the layered full-space geoelectric model has a fast convergence speed and enhanced calculation accuracy. The PSO-GIS algorithm inversion is applied to the measured data of coal mine wells, which can achieve the effect of abnormal separation of roof and floor. The reflection of low-resistivity anomalous bodies is refined, and the drilling verification results agree well with the inversion interpretation. The PSO-GIS algorithm inversion in this article can be applied to the processing of real measured mine data to improve the interpretation effect of full-space inversion of mines.