Study on Bidirectional Blasting Technology for Composite Sandstone Roof in Gob-Side Entry-Retaining Mining Method

The traditional gob-side entry-retaining mining method has problems such as difficulty in roof collapse and large deformation of the entry, which may affect the safety of mine production. In this study, we introduced a bidirectional blasting technology (BBT) to make the roof collapse smoothly and to improve the traditional gob-side entry-retaining mining method. A theoretical model of the BBT was established and the stress propagation of the BBT was analyzed by numerical simulation. The gob-side entry-retaining mining method was then applied in a composite sandstone roof condition. Compared with ordinary blasting, the concentrated stress and directional cracks can be generated in the set direction after using the BBT technology. Field monitoring data suggested that the deformation of the retained entry met the requirements of mining, verifying the effectiveness of the proposed technology for composite sandstone roof. The results of the study have an important significance in solving the high pressure and large deformation problems in the coal mine roadway and saving coal resources, which also provided a reference for similar geotechnical mines.

Effect of the Installation Process on the Pullout Capacity of Helical Anchors

In this paper, an advanced numerical method called Coupled Eulerian-Lagrangian (CEL) method is used for the prediction of the behavior of helical anchors in sandy soil under ultimate limit state ULS including the effect of anchor installation process. The CEL analysis allows one to overcome the drawback of the classical finite element FE method in the case of large deformation problems as it takes the advantages of both Lagrangian and Eulerian methodologies. Results have shown that the CEL analysis is relevant for the computation of the helical anchor pullout capacity. Indeed, the CEL analysis was able to rigorously determine the ultimate capacity of the anchor contrary to the classical FE method; the calculation via the CEL approach has been carried out for relatively large displacement values without encountering any problem of convergence. Furthermore, CEL analysis was able to simulate the installation process of the anchor and thus enables one to consider the effect of the soil disturbance induced by the installation process on the computed pullout capacity. The numerical simulations have shown that the pullout capacity of the helical anchor may be significantly decreased when considering the anchor installation effect.