Numerical Prediction of the Bridge Subsidence Induced by Longwall Mining: A Case Study of the Majiagou Bridge

The Majiagou Bridge comprising four sub-bridges is adjacent to the Weiqiang coal mine, Yulin City, Shaanxi Province, China. The mining of the longwall panel No. 1307 may damage the Majiagou Bridge. In this study, we predicted the mining-induced bridge movements using the finite element method (FEM) to examine whether the progressive mining of the longwall panel will pose a negative impact on the Majiagou Bridge. We reconstructed detailed three-dimensional models of the four sub-bridges by considering the superstructures and substructures. The input mechanical properties of the strata are estimated by calibrating with available field monitoring data. Effect of traffic load on the bridge subsidence is also accounted. The numerical predictions are: (1) after the panel No. 1307 is mined, the maximum vertical and horizontal displacements of the four bridges are 61.2 mm and 84.8 mm respectively, which occur on the sub-bridge D that is closest to the longwall panel, (2) traffic load has much less pronounced effect on the Majiagou Bridge than that due to mining, and (3) the maximum tilt and horizontal strain of the sub-bridges are 3.42e⁻⁵ m/m and 2.19e⁻⁵ m/m, which occur on sub-bridge B and sub-bridge A, respectively. In terms of tilt, the Majiagou Bridge is safe whereas it is to be damaged in terms of horizontal movement that is more critical in causing structural damage. Therefore, we suggest that a reasonably wider protective coal pillar should be set if the panel No. 1307 is to be mined, to ensure the safety of the Majiagou Bridge.