Numerical analysis of the upper frozen layer fracture in plateau open-pit bench.

The upper frozen layer is one of the main factors affecting the blasting effect of the plateau open-pit bench. To clarify the fracture law of the upper frozen layer of the open-pit bench under the blasting load in the cold area of the plateau, this paper uses the particle flow code method to simulate the fracture process of the natural single frozen layer and the artificial composite double-frozen layer under the action of single and double rows of blast holes respectively. The frozen layer s speed, impact pressure, and fragmentation characteristics were analyzed. The results show that the frozen layer undergoes the failure process of cracking-local uplift-macro fracture. For the artificial composite frozen layer,the thickness increases due to the increase of the gravel soil in the upper part, which weakens the overall uplift trend of the frozen layer and leads to increased fragmentation. The impact pressure on the frozen layer in the middle of the double-row blast hole first reaches the peak, but the peak value on the frozen layer near the free surface is higher. The fracture problem of single and double frozen layers under blasting load can be simplified as the structural fracture mechanics problem under impact pressure. The large block rate of double-frozen-layer bench is 4% to 6% higher than that of single-frozen-layer. It is suggested that in the blasting of plateau open-pit mines, the area that needs special treatment should be preliminarily determined by the thickness of the frozen layer, and the large block rate should be reduced by adjusting the delay time to improve the efficiency of shovel-to-digging. [ABSTRACT FROM AUTHOR]