Abstract
In the whole life cycle of the extraction structure in block caving mine from the beginning of roadways excavation to the end of ore drawing, there are many factors affecting the stability of the extraction structure. The investigation in the mine site shows that the extraction structure often presents the law of repeated instability. In order to reveal the mechanism of repeated instability of the extraction structure, the whole life cycle of extraction structure can be divided into three stages, namely, the formation stage of extraction structure, the undercutting stage without initial caving, and the ore caving and drawing stage. The three-dimensional finite difference software FLAC3D was used to establish the numerical model of the extraction structure in the whole life cycle in the block caving method. The process of ore caving and ore drawing was replaced by manual excavation of the caving area above the undercut space and applying stress on the major apex. The stress and displacement evolution laws of the extraction structure in three stages of the whole life cycle were studied and compared with the instability characteristics of the extraction structure on mine site. The whole life cycle instability mechanism of the extraction structure in Tongkuangyu mine is revealed; the research results show that the extraction structure near the advancing undercut front is prone to producing compressive stress concentration under the action of the surrounding rock stress arch in the stope; if the rock mass shear failure condition is reached, the instability of the extraction structure occurs. The extraction structure near the advancing undercut front is gradually transferred to the area under the undercut space with undercut increase, and the tensile stress concentration gradually appears in the sidewall of ore loading roadway and the tip of major apex; if the tensile strength of the rock mass in the extraction structure is exceeded, the instability occurs again. It is helpful to reduce the probability of the instability of the extraction structure to promote the overburden ore caving as soon as possible after the undercutting begins.
Highlights
With the increasingly fierce market competition in recent years, the use of efficient mining methods and large-scale automatic equipment has become a trend in mining industry
The extraction structure of the block caving method is the general term of a series of roadways and chambers used for ore drawing between the undercut level and the production level [4, 5]
A combined support form of bolt mesh cable shotcreting and floor concrete reverse arch should be established before the high stress formation in front of advancing undercut front, which could effectively control the loose deformation of the surrounding rock of the ore drawing roadway, and increase the stability of the extraction structure
Summary
With the increasingly fierce market competition in recent years, the use of efficient mining methods and large-scale automatic equipment has become a trend in mining industry. Rojas et al [9, 10] monitored the stress and microseismic events of the production roadways to explore reasons of the instability of the extraction structure during the ore caving stage. In the whole life cycle of the extraction structure of the block caving mine from the beginning of roadways excavation to the end of ore drawing, there are many factors affecting its stability. Previous studies have not really revealed the repeated instability mechanism of the extraction structure in the whole life cycle in the block caving method. Xia et al [16,17,18] revealed the reasons for the repeated instability mechanism of the extraction structure during the process of undercutting but did not take into account the influence of the ore caving stage. The instability mechanism of the extraction structure in the whole life cycle is revealed, which is of great significance to ensure the safety of block cave mining
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