The Ural Department of Rostechnadzor has completed an investigation into the fatal accident that occurred last November at the Tsentralnaya mine of Yuzhuralzoloto. Then a 28-year-old drift operator died during drilling operations as a result of a rockfall.
According to the press service of the ministry, the reasons for the tragedy were “violations of the requirements of safety instructions and occupational safety”, as well as “imperfect fixing technology”. In other words, mistakes were made during the erection of the excavation structure that protects people from falling boulders.
Similar cases that lead to miners’ deaths or injuries, or, more often, do not lead to any unfortunate consequences and remain practically unnoticed, occur rather regularly. The opposite is also true when the management of mining corporations reinsures itself and erects excessively resistant and expensive supports. This, of course, minimizes the probability of roof collapse, but it also leads to additional capital investments, increased production costs, and, consequently, reduced competitiveness of the business.
But are there ways to find the “golden mean”? To guarantee (as much as possible) the stability of underground facilities on the one hand, and to avoid excessive financial costs of building supports to prevent the collapse of rocks on the other hand? The answer to this question is not just relevant, but strategically important for core companies, especially during economic downturns and low prices for raw materials, such as during the 2019 lockdown.
Scientists of the Scientific Center of Geomechanics of St. Petersburg Mining University traditionally deal with this area of research. Analytical data obtained by its specialists in the course of field and laboratory surveys, as well as thanks to the creation of digital twins, allow them to effectively determine the zones of possible collapse at underground ore deposits, reliably predict the development of geomechanical processes in strata and, as a result, to calculate the loads on supports concerning specific geological conditions. As a result, the university’s partner enterprises receive optimal solutions, some of which are even implemented in their normative documentation.
“Today we observe a clear tendency towards intensification of production processes. The demand for raw materials is growing. In connection with this the volume of production increases, the depth and scale of mines increase, the stressed state of rock masses changes, the degree of structural disturbance changes, i.e. mining and geological conditions gradually become more complicated. All this leads to the need to review and supplement the existing approaches to assessing the development of geomechanical processes in the contour massif. In other words, in the areas which are in the zone of technogenic impact, their natural field of stresses therefore changes,” says a postgraduate student of Mining University Maria Willner.
She also specifies that an underground mine is not a corridor built from point "A" to point "B", but an extensive system of mutually intersecting excavations, similar to the street and road network. According to studies, up to 40% of the total number of collapses occurs precisely at the intersection of junctions, i.e. at the intersection of tunnels with each other, or at their crossing. Nevertheless, under the existing normative base, the loads on the lining in such sections are determined by the methodology adopted for single excavations.
“At the intersections of mine workings, the prediction of the stress-strain state of the contour massif is complicated by their spatial geometry, as well as by the overlap of their influence zones. That is why it is necessary to propose a new approach to the assessment of the stability of junctions, based on the representation of the massif as a discrete medium, where the process of deformation and collapse of rocks is predicted within a unified calculation model,” explains Maria Willner.
The postgraduate student co-authored her research with colleagues from the Scientific Center for Geomechanics and the Department of Mining Construction and Underground Structures at St. Petersburg Mining University. As part of it, she revealed new regularities that determine the relationship between the stress state of the massif, its structural disturbance, and the intensity of the development of negative processes during the construction of conjugate mine workings. Based on the data obtained, justification of correction factors, taking into account such factors as parameters of fracturing, the configuration of the conjugation, the angle between the intersecting tunnels, and several others were carried out.
“The shape and size of the zone of possible collapse at the junction of mine workings depend on their geometric parameters and physical and mechanical properties of the massif. And the greatest influence is exerted by the stressed state of rocks and the spatial geometry of structural disturbances. The result of our research will be the development of methodological regulations, which allow estimating the size of the potential collapse zone with the highest possible accuracy today, taking into account all these factors,” summarized the representative of Mining University.
The scientists of St. Petersburg Mining University are sure that their study will significantly increase the accuracy of forecasts. Recommendations made on the basis of improved calculations will significantly improve geomechanical safety during construction and operation of workings in structurally disturbed rock massifs. Several domestic mining companies are already interested in the results of this project.