Assessment of the risk of loss of stability of the steel arch support of the underground excavations

The stability of underground excavations depends on many natural, mining, technical and technological factors. The conducted research has shown that the data accepted for design are often characterized by considerable variability both in time and in space. In order to take into account the variability of parameters characterizing the conditions of maintaining the excavation stability, the probabilistic structure analysis method was used in which the probability of failure was assumed as the risk measure and the values of parameters accepted for analysis as random variables with normal distribution. The paper presents solutions for assessing the safety of excavations based on probabilistic methods of level II and level III. For practical purposes, classification of the degree of risk of loss of excavation stability was proposed, in which the probability of loss of stability (level II method) and probability of dangerous state (level III method) were assumed as a criterion. The general characteristics of the excavation support behaviour were indicated for individual stages. The whole is supported by practical examples from over 20 exploitation fields in several mines of the Upper Silesian Coal Basin. The proposed method can be used both at the stage of design and use of the excavation.