Tensile fracture characteristics and directional fracturing mechanism of 2D blasting: Experimental investigation and theoretical modelling

Blasting is a crucial technique for rock breaking in geotechnical engineering, with directional fracture-controlled blasting being one of its most important applications. To advance this field, a novel non-explosive blasting method, termed two-dimensional blasting (2D blasting), has been developed. This innovative technique utilizes high-temperature, high-pressure gas generated by expansion agent to induce tensile stress along the splitting direction of the borehole wall, facilitating directional rock mass rupture. The research and theoretical modelling of the directional fracturing mechanism for 2D blasting are extremely challenging, but this is crucial for the field application and parameter design of 2D blasting technology. In this study, comparative experiments were conducted using concrete specimens subjected to both 2D and conventional blasting. Dynamic crack propagation behaviour was recorded with a high-speed camera, and tensile fracture characteristics were analysed using the Digital Image Correlation (DIC) method. The experimental results revealed that conventional blasting generates random, disordered radial cracks around the borehole, forming a three-dimensional (3D) fracture network. In contrast, 2D blasting employs an energy-gathering device to regulate stress distribution on the borehole wall, transforming the 3D fracture network into a two-dimensional (2D) fracture plane in the preset direction. Building on these experimental findings, mechanical models for both conventional and 2D blasting were established. The stress concentration effects around the borehole wall under 2D blasting were analysed, and criteria for crack initiation and propagation in 2D blasting were proposed. The results confirmed the directional fracturing efficacy of 2D blasting, characterized its tensile fracture behaviour, and provided valuable insights into its underlying mechanisms, offering a reference for further advancements in directional fracture-controlled blasting technologies.