Abstract
This paper presents the results of laboratory tensile testing of segmentally-installed glue-in roof bolting. We studied roof bolting of the type Olkusz-16A (Boltech Sp. z o.o., ZGH Bolesław S.A., Bukowno, Poland), additionally equipped with a steel rod coil, which was mounted in steel cylinders filled with a concrete mixture using multi-part resin cartridges with a diameter of 0.024 m and length of 0.045 m. The mounting depths were 0.1 m and 0.2 m, respectively. Our main purpose was to determine the effect of the bolt hole diameter, which assumed the values 0.028 m, 0.032 m, 0.035 m, and 0.037 m, respectively, on the load-bearing capacity of the roof bolting in relation to the mounting depth. We found that the mounting depth of 0.2 m was sufficient for the roof bolting to exhibit its full load and displacement properties for all four diameters of the bolt hole. To determine whether the roof bolting was capable of transferring the load in situ, we presented the results of the predicted load on the roof bolting applied in a room and pillar mining method in an underground mine of zinc and lead ore deposits. Our objective was to determine the influence of the room and pillar mining method geometry on the range of the fault zone of rocks around pits. We designed the deposit excavation model using the Examine3D numerical modeling software, which is based on the boundary element method. We created three-dimensional models for three variants of working space opening widths: featuring two, three, and four rows of rooms. The geometry of rooms and pillars corresponded to the mine conditions; the width, height, and length parameters were all 5 m. We determined the strength, strain, and structural parameters of the rock mass on the basis of laboratory studies of the drill core and rock forms collected from the room longwall. We used the strength factor to specify the maximum range of the fault zone of rocks around pits. In the last stage of research, we compared the load value obtained based on numerical testing with the maximum load obtained in the tensile strength tests of the roof bolting and determined the safety factor of the segmentally-installed roof bolting.
Highlights
Roof bolting, both adhesive and sleeve-anchor installed, is very common in room and pillar mining methods for protecting pits against roof rock cave-ins
Some doubts arise from the fact that in a fractured rock mass, the resin cartridge may not be correctly mixed, as the resin will have a tendency to move towards the cracks
Room and pillar mining methods are4.commonly used in the underground mining of mineral deposits
Summary
Both adhesive and sleeve-anchor installed, is very common in room and pillar mining methods for protecting pits against roof rock cave-ins. The diameter and length of the cartridge should be selected in such a way as to reach the full load and displacement properties of the roof bolting. This type of optimization is a significant factor in reducing production costs. The same kinds of rocks may be softer or harder, more or less fractured, fractures may be filled with stronger or weaker material, separated or compacted, wet or dry. All these features may affect the final quality of the roof bolting. Campbell et al [2] found that an important issue to be considered is the packaging of the resin cartridge, which might serve as a plug that prevents the full utilization of the cartridge mass
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