This autumn people continued to die in mines around the world. Some of the tragedies were caused by non-compliance with safety rules, while others were caused by rockbursts, i.e. the destruction of seams caused by excessive concentration of energy in the surrounding rocks of the mine. Forpost decided to find out whether scientists can predict and prevent such cataclysms.
In mid-September the roof of the Rudyłtowy mine in Poland collapsed, killing one person who was crushed by rocks. A week earlier, at least 12 miners died in an accident at a marble mine in northwest Pakistan. And in Congo, where illegal mining is a major source of livelihood for local people, 50 young people failed to get out of the ground. They were working in gold mines.
Such large numbers of victims are unfortunately not uncommon in many resource-rich countries in Africa and Asia. Even those companies that operate officially there often do not pay any serious attention to the safety of their employees. Even the artisanal miners do not think about it at all. After all, the rate of those who are willing to go underground for double or triple their wages in the absence of social or any other guarantees remains high, regardless of the number of accidents.
Of course, everything is different in Russia. The death and injury figures are going down across the country as a whole, but life threatening accidents still happen from time to time. So, at the end of last year, 21 people died in 18 such accidents. Is it possible to reduce this figure to zero or at least minimise it?
The St. Petersburg Mining University is currently carrying out scientific research in this field. Its scientists, for example, periodically visit mines, take rock samples and then test them in the laboratory. They simulate rock bumps in order to understand the risk of destroying each mine. And then they test their findings in the Earth's interior.
"At the moment I am working with samples of the igneous rocks that surround the ore body. They are called urtites. I am identifying seismic signs of rock shock preparation by acoustic emission. I'm determining the shock hazard criteria in order to make recommendations later to the company's rock-burst forecasting and prevention service, with which we have a cooperation agreement," explained Alexander Rozanov, a senior researcher at the geodynamic safety laboratory.
This experiment should determine how dangerous it is to be in a tunnel under normal conditions. If the risks are high, scientists at the Mining University point this out and justify the need for a series of preventative measures. For example, by drilling the so-called unloading string, i.e. a series of holes that will lead the source of damage away from the excavation deep into the massif. But is it really possible to identify the vulnerability of a mine from a small cylindrical specimen of rock?
"We load the sample into a special machine and simulate a mining strike. In doing so, acoustic sensors pick up high-frequency signals formed by pressure - a crackling sound that cannot be heard by the human ear. This is acoustic emission. In order to make an objective picture and give an accurate prediction about 10 thousand such signals need to be received, then summarize the data and draw certain conclusions. If we observe the process of acoustic emission sources densification and growth of signal energy, this indicates the beginning of a dangerous stage, i.e. the tendency of rocks to rock bumps," says Alexander Rozanov.
The scientist cites statistics from one of his recent investigations. Every fifth measurement in the host rock - that is, that which surrounds the mine but is not a mineral - showed a probable danger to people and machinery. After measurements in the ore body itself, such a verdict was given less frequently, in only 6% of cases.
The reliability of the experiments is guaranteed not only by the painstaking work of the scientific team, but also by the rich instrumentation and laboratory base. In particular, British equipment with a program for calculating the coordinates of emission sources and a data collection system. But to interpret the obtained data, scientists from St. Petersburg write their own software, taking into account local geological conditions.
"The methodology of shock hazard forecasting was put into commercial operation in 2018. This happened as a result of cooperation between leading specialists from three organizations - St. Petersburg Mining University, Khabarovsk Federal Research Center of the Far Eastern Branch of the Russian Academy of Sciences, and the Kirov branch of Apatit JSC. Our main task is to give an advance forecast, but at the same time a correct one. This, of course, is not easy, because the earlier in relation to a probable dangerous event, the less accurate it will be. Nevertheless, modern technology makes it possible to be proactive and detect the propensity of rocks to rockbursts with a high degree of reliability. And then to divert the focus of destruction to the side before the dangerous event occurred. This is a very important part of the occupational safety prevention system," emphasized Alexander Rozanov.
He reminded that researches in the field of miners' safety have been conducted at the Mining University for over a hundred years. The founder of this scientific trend was the professor of the Petersburg university Alexander Skochinsky. He, in particular, created the theory of movement of air and gases in mine workings, which brought clarity to the understanding of the physical and mechanical nature of the complex process of ventilation of mines. The scientist found out that under certain conditions it leads to dustiness of the air flow, ignition of dust and explosions.
As a result of his research Skochinsky was the first to formulate a theory of anti-dust aerodynamic regimes for mines. Modern engineers when calculating ventilation systems of any complexity for mines of any depth rely exactly on theoretical provisions and experimental results obtained by Aleksandr Aleksandrovich and his students.
