Prediction of strainburst risks based on the stiffness theory: Development and verification of a new rockburst indicator

Abstract

Strainburst is an unstable rock failure phenomenon that occurs at deep excavations' boundaries due to the excavation-induced stress concentration and a “soft” loading environment. A critical task for researchers is to predict the possibility or risk of strainburst occurrence. In this paper, the local mine stiffness (LMS) of a tunnel determined by a novel calculation method is compared to the post-peak characteristic stiffness (PCS) of surrounding rock masses having different brittleness to discriminate strainburst occurrence, which is verified with simulated stable and unstable rock failure occurring in a calibrated deep tunnel model established by UDEC. The reliability and accuracy of the LMS calculation method are further examined by comparing excess energy's analytical and numerical results. The relative difference is 11.3 % and 2.5 % regarding the measurement of the Richter magnitude. As a result, a new rockburst indicator, called strainburst stiffness factor (SSF), is proposed to predict strainburst risks based on the analysis of stiffness differences. The prediction results of SSF were successfully validated on two real-life examples where the data was matched with the “5.5″ rockburst event in the Zofiowka Coal Mine and the “11.28″ rockburst event in the Jinping II Hydropower Station. The proposed indicator provides an effective tool to predict strainburst risks, which can further improve the safety of workers and equipment when constructing deep excavations in mining and civil engineering projects.