An Indirect Method for the Quantitative Identification of Unstable Rock

Under the influence of continuous external factors (rainfall, earthquake, construction, etc.), the slope rock mass in a stable state gradually transited to an unstable rock, and then the unstable rock collapsed. However, a safety factor can identify the occurrence of failure but cannot identify the transition of stable rock to unstable rock; thus, it cannot realise the quantitative identification of unstable rocks. In this study, safety factor of adhesion (SFA ) and a relatively objective analysis method are proposed to effectively identify unstable rocks. SFA can be calculated by natural vibration frequency and applied as a mechanical index to judge unstable rock. When SFA is less than 1, the rock is defined as an unstable rock. Compared with the traditional method, the new method has the merits of simple operation, low cost and higher efficiency, and provides a relatively complete quantitative evaluation index and judgment criteria for quantitative identification of unstable rocks for engineers who are engaged in early warning and prevention of rock collapse.

Fracture mechanism of rock collapse in the freeze-thaw zone of eastern Sichuan-Tibet Mountains under seasonal fluctuating combinations of water and heat

In the freeze-thaw zone of eastern Sichuan-Tibet Mountains, the phases of water in cracks show strong seasonal variations, which significantly affect the stability of perilous rocks in mountains. However, few works have clearly addressed the role of water/ice in crack development from a fracture mechanics viewpoint to explain the seasonality of rock collapse. In this study, we built physical models from a fracture mechanics viewpoint to calculate water-freezing stress, hydrostatic pressure, and their combinations induced by water/ice in cracks, and show the crack propagation mechanism under temperature fluctuations in different seasons in mountainous regions. Based on the models, we calculate fracture conditions, simulate the crack process, and illustrate the rock collapse mechanism in different seasons by the extended finite element method. The results indicate that different phases of water, which induce stress under spatiotemporal fluctuations of temperature, determine the various propagation styles and influence what kind and when a collapse will occur. The collapse of fractured rocks in different seasons generally results from rock damage accumulation owing to the initiation, propagation, and connection of primary cracks under freezing stress or hydrostatic pressure or their different combinations.

ANALYSIS OF PRODUCTION RISK FROM CRUSHES OF ROCKS AT EXCAVATION SITES, TAKING INTO ACCOUNT WAYS OF PROTECTION

Purpose. To assess the production risk of rock collapse in a deep coal mine to identify hazards in the workplaces of the excavation site, taking into account different methods of protection of workings. Methods. A comprehensive approach was used, which included: analysis and generalization of known research; expert evaluation; use of the basic provisions of probability theory and set algebra (Venn diagrams), the method of estimating the production risk of Fine-Kinney; processing, analysis and interpretation of the obtained results. Results. Problems and sources of industrial risk from rock collapses during maintenance of workings, risk-forming factors that contribute to the threat of dangerous events at the excavation site are analyzed. The decision-making model is considered, which is based on the description of situations when the production risk of the dangerous factor “landslides and collapses” in the maintenance of preparatory workings depends on the result of choosing an alternative method of protection of the retractable lane. For excavation sites under the same mining and geological conditions for all workplaces, the probability of receiving consequences from dangerous events due to uncertain conditions of their implementation has been established. It is fixed that the realization of this production risk is influenced by low reliability and inefficiency of the practiced methods of protection of excavations. Risk analysis is defined as the systematic use of available information to identify hazards in the maintenance of long workings. Novelty. A model for monitoring the production risk of rock collapses in excavations of deep coal mines is proposed, which allows assessing the dynamics of the threat at the stage of technical decisions related to the choice and justification of the method of protection of workings taking into account the interaction of risk factors. Practical significance. When formulating measures to reduce the risk of dangerous events at the excavation site, it is necessary to take into account that the production risk of rock collapse while maintaining the workings depends largely on the method of protection and effectiveness of technological measures.

ASSESSMENT OF THE CONDITION OF THE ROCK MASSIVE ABOVE THE SUBMERGED SALT MINE ON THE SALT DEPOSIT IN TUZLA IN THE POST-EXPLOITATION PERIOD

This paper assesses the condition of the "rock massiv" above the closed Tušanj salt mine based on the results of monitoring in the post-exploitation period of the salt deposit in Tuzla. The results of individual monitoring segments realized from 2002 until today, geodetic, hydrogeological, engineering-geological, chemical and geophysical, were analyzed in order to assess the condition of rocks above the mining premises of Tušanj mine, in the rock collapse zone above mine well B-31. The results will be used to assess the condition of the massiv in the post-exploitation period in the Tušanj district and will be the basis for conducting additional research.

Analysis of the 2017 June Maoxian landslide processes with force histories from seismological inversion and terrain features

SUMMARY A devastating landslide occurred in Maoxian (China) on 2017 June 24, which generated strong signals that were recorded by a regional seismic network. We determined the landslide force history from long-period seismic waves and identified eight subevents. For each subevent, we obtained an independent force history and calculated its sliding path. The shape of the terrain before and after the landslide was found to play a critical role in the motion of the sliding mass. A combination of seismic and terrain data was used to discriminate between or relate the subevents to each other, and to locate the initiation point of each sliding path. We explain the Maoxian landslide dynamics as the combination of the rock collapse, centripetal acceleration of the sliding body, deceleration and acceleration once again after overcoming obstacles along the sliding path.