ON THE FEASIBILITY OF PRETENTION REBAR IN UKRAINIAN CONDITIONS
DOI:
https://doi.org/10.34185/1991-7848.2026.01.15Keywords:
metal-polymer anchor, preload, condition of the excavation surfaceAbstract
Placing a part of industrial and social facilities underground, for a long time of operation and the influence of external sources of seismic energy of various origins has become an urgent problem of today.
Frame-anchor fastening is the most common fastening system of underground workings, including for long-term operation of underground industrial structures. The fastening procedure begins with fastening the workings with metal-polymer anchors (AKM). Then, under the protection of the anchor fastening (AK), the workings are fastened with frames. The features of such a combination are that the anchor fastening counteracts any movement of rocks in the workings. At the same time, with minor movements of rocks in the working space, the frame fastening has not yet begun to counteract the rock pressure. With significant movements for the AKM, the frame fastening is forced to take on the load of the weight of the rocks of the volume of the compressed shell. This situation is not acceptable for fastening excavations with a long service life. Taking into account the factor of long-term operation of underground structures leads to a detailed analysis of the factors that may have an impact on it.
One of the most important factors that has an impact on the load-bearing capacity of rocks in the vicinity of the excavation is the preload (PR) of AKM anchor rods. An analysis of literary sources showed the absence of a consistent opinion on its value and even on its feasibility in general. According to existing regulatory documents in Ukraine, it is accepted at the level of 5 tons. According to these documents, PR should be carried out by compressing rocks by tightening a nut on the tail section of the anchor rod. However, this method of creating PR has changed now. Given the technological complexity of the thread rolling operation, it was abandoned. Currently, the operation to create PR of anchor rods is carried out by tightening a cast nut on periodic protrusions on the surface of the anchor rod. As a result, the regulatory value of PR is not achievable. As calculations show, the maximum value of PN does not exceed 2t. The value of PN cannot be controlled, since it is determined by stopping the procedure for tightening the nut due to the impossibility of its further execution. Since the landings in the screw-nut pair are widely movable, that is, free, and as a result, the nut bites on periodic protrusions of the anchor rod. It is not worth talking about achieving the design values of PN. For fastening industrial facilities for a long period of operation, such a state of affairs is not permissible.
To clarify the importance of fulfilling the PN regulatory values, it is necessary to conduct an experimental study in industrial conditions. Such a study was conducted and its results are presented in this article.
Graphic images of the condition of the roof surface of the excavations that were subject to investigation are presented and conclusions are drawn.
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