| Ground penetrating radar is an effective, non-destructive, rapid detection technology. Ithas been widely used in the engineering field. The stability of cemented tailings backfill iscrucial to the mining method which is called underhand cut-and-fill stoping. Different crackswere found in the roof and the presence of cracks may cause the roof falling and rib spalling.Aiming at the shortcomings of the existing roof detection technology, the ground penetratingradar (GPR) technology is firstly introduced into the cemented tailings backfill for detectingthe crack in the roof. In this paper, the characteristics of ground-penetrating radar images ofcracks are researched from various angles respectively. These angles include the principle ofthe electromagnetic response, forward modeling, laboratory test and field test. The paper wasfunded by the support of the Jiangxi Province Graduate Student Innovation Project Fund―AStudy of detecting the crack in the cemented tailings backfill roof by GPR‖. The maincontents and results are as follows:(1) Dielectric properties of cemented tailings backfill are tested. Feasibility of thedetection of the crack in the cemented tailings backfill roof by GPR is demonstrated in theory.(2) Radar Response characteristics of vertical crack and inclined crack are analysed intheory. Mathematical formulas are derived which explain the law of the hyperbolic wavediffraction. The electromagnetic response of different cracks is revealed under the conditionof different factors. These factors contain the relative dielectric constant of the medium, thedepth of crack, the horizontal position and the singular position of crack.(3) Forward electromagnetic responses of different factors for cracks in the roof byforward modeling are consistent with the theoretical analysis. Under other conditions remainunchanged, the relative dielectric constant of the dielectric material is smaller, the wings ofresponse hyperbolic diffraction wave more flatten out.. The crack is deeper, the generatedhyperbolic diffraction wave is along with the depth of the crack down and the wings ofhyperbolic diffraction wave expand gradually flattens out. Changes of crack in the horizontalposition will only cause the movement of hyperbolic diffraction wave in the horizontaldirection and the changes have no impact on the ductility of hyperbolic diffraction wave.Characteristics of crack by forward modeling are analyzed under conditions of layered media.(4) Crack models which are composed of the material of cemented tailings backfill aretested. The results demonstrate that the crack in cemented tailings backfill roof can be detected and the state of cracks is further identified. The field test of roof crack is carried outin one mine. The imaging features in the field remain consistent with laboratory test results.(5) Based on orthogonal experimental results by GeoStudio2007numerical models, thestability of cemented tailings backfill roof is analyzed when the crack is existed in the roof.The width and depth of crack are considered in the analysis. Depending on the results of theorthogonal experiment, the stability of cemented tailings backfill roof which exists differentcrack is divided into three levels. The corresponding treatment measures are established.In this paper, according to theoretical analysis and forward modeling research andlaboratory research, the characteristics of ground-penetrating radar images of cracks areresearched respectively. It provides theoretical guidance and basis for the practical applicationof ground penetrating radar (GPR) to identify cracks. It is strengthened that the GPR signalrecognition and interpretation skills for the crack detection.In field, application is proved thatit is feasible to identify the crack in cemented tailings backfill roof by ground penetratingradar (GPR). |
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