Sidewall rockburst of highly stressed D-shape hole tunnel triggered by impact load: An experimental investigation

This study aims to clarity the failure mechanism of sidewall rockburst of highly stressed D-shape tunnel triggered by impact load. Using the biaxial Hopkinson pressure bar (BHPB) system, we have developed experimental capabilities to study the sidewall rockburst of D-shape tunnel by applying various prestresses, including horizontal and vertical static stresses, to sand prefabricated D-shape hole specimen, followed by impact loads. High-speed (HS) camera and digital image correlation (DIC) were used to tracked the process and strain field of the sidewall rockburst. The test results reveal that the process of sidewall rockburst can be summarized as: calm stage, crack initiation, propagation, and coalesce stage, spalling stage and rock fragments ejection stage. During the rockburst process, the surrounding rock experienced spalling and violent ejection, involving both tensile and tensile-shear failure. The mechanism of sidewall rockburst under the coupled of static stress and impact loads has been elucidated, i.e., the static prestress determines the initial stress and strain distribution, and the horizontal prestress influences the affected range and strain values of strain concentration zone; the impact load disrupts the original static stress equilibrium, inducing alterations in the stress and strain of the surrounding rock and triggering sidewall rockburst.