Excavation-induced deep hard rock fracturing: Methodology and applications

To analyze and predict the mechanical behaviors of deep hard rocks, some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed. First, a series of apparatuses and methods have been developed to test the mechanical properties and fracturing behaviors of hard rocks under high true triaxial stress paths. Evolution mechanisms of stress-induced disasters in deep hard rock excavations, such as spalling, deep cracking, massive roof collapse, large deformation and rockbursts, have been recognized. The analytical theory for the fracturing process of hard rock masses, including the three-dimensional failure criterion, stress-induced mechanical model, fracturing degree index, energy release index and numerical method, has been established. The cracking-restraint method is developed for mitigating or controlling rock spalling, deep cracking and massive collapse of deep hard rocks. An energy-controlled method is also proposed for the prevention of rockbursts. Finally, two typical cases are used to illustrate the application of the proposed methodology in the Baihetan caverns and Bayu tunnels of China.