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Hu J.-H.,Hunan Key Laboratory of Mineral Resources Exploitation and Hazard Control for Deep Metal Mines | Hu J.-H.,Central South University | Lei T.,Hunan Key Laboratory of Mineral Resources Exploitation and Hazard Control for Deep Metal Mines | Lei T.,Central South University | And 4 more authors.
Journal of Central South University | Year: 2014

The pre-crack blast technology has been used to control the induction caving area in the roof. The key is to form the pre-crack seam and predict the effect of the seam. The H-J-C blast model was built in the roof. Based on the theories of dynamic strength and failure criterion of dynamic rock, the rock dynamic damage and the evolution of pre-crack seam were simulated by the tensile damage and shear failure of the model. According to the actual situation of No. 92 ore body test stope at Tongkeng Mine, the formation process of the pre-crack blast seam was simulated by Ansys/Ls-dyna software, the pre-crack seam was inspected by a system of digital panoramic borehole camera. The pre-crack seam was inspected by the system of digital panoramic borehole in the roof. The results of the numerical simulation and inspection show that in the line of centers of pre-hole, the minimum of the tensile stress reaches 20 MPa, which is much larger than 13.7 MPa of the dynamic tensile strength of rock. The minimum particle vibration velocity reaches 50 cm/s, which is greater than 30-40 cm/s of the allowable vibration velocity. It is demonstrated that the rock is destroyed near the center line and the pre-crack is successfully formed by the large diameters and large distances pre-crack holes in the roof. © 2014 Central South University Press and Springer-Verlag Berlin Heidelberg.


HU J.-H.,Central South University | HU J.-H.,Hunan Key Laboratory of Mineral Resources Exploitation and Hazard Control for Deep Metal Mines | YANG C.,Central South University | YANG C.,Hunan Key Laboratory of Mineral Resources Exploitation and Hazard Control for Deep Metal Mines | And 6 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2016

Undercut is one kind of important spaces to place the mining blocks in the mass underground mining. This structure is also used as a compensation space during blasting. In the process of underground mining in the fragment orebody, it is important and critical to analyze the stability and blockage of the three-dimensional wedges created around the undercut space. The wedge stability is mainly controlled by factors including geometry (i.e., the size, shape and spatial location of the wedge and undercut), the strength (shear and tensile) of the discontinuities that created the wedge, and the stress distribution within the rock mass. The Unwedge software was used to conduct the orthogonal simulation tests (three factors and five levels) that considered different cross sections, trends, and plunges of the undercut space. The results demonstrate that the control value of the safety factor of wedge is set to be 1.2. The optimal parameters are determined in the undercut space, such as the blasting fragmentation, orientation of the fluid flow, and the equipment gradeability; the wedge stability can be evaluated in the light of the block images and continuous falling; the stability of the key block meets the needs of the undercut space, the parameters gained are reasonable and optimal. Cross section is 27°, trend is from 315° to 325° (it is 320° at in-suit test) and plunge is 5°. © 2016 The Nonferrous Metals Society of China

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