Investigation of fracture mechanisms in smooth blasting of limestone samples: numerical and experimental approaches

Abstract

This paper presents a comprehensive study on the numerical and experimental simulation of smooth blasting in limestone. The calibration of the numerical model was initiated through Brazilian and uniaxial compression tests on limestone samples. Compressive strength and Brazilian tensile strength of limestone were 70 MPa and 8 MPa. This enabled the determination of essential micro-parameters. Subsequently, smooth blasting scenarios were simulated under two distinct conditions: with and without confinement. Under confinement conditions, models with dimensions of 600 mm * 900 mm were constructed. The blasting hole was strategically positioned at varying distances from the free boundary, accompanied by a row of parallel holes positioned behind it. A confining pressure of 10 MPa was applied. Appropriate values for normal and shear damping, as well as the allocation of a viscous boundary, were established. Normal and shear damping values were equal to 0.4 and 0.3, respectively. Throughout different stages of blasting, critical parameters such as crack growth patterns, particle velocity, and induced loads near the blasting hole were meticulously recorded. Measuring circles were strategically placed in proximity to both the blasting hole and free boundary to capture induced forces. Parallel to the numerical simulations, an unconfined experimental test was conducted on limestone samples with similar dimensions. However, it was observed that the reflected tensile stress wave at the surface of the empty hole exacerbated damage to the rock mass between the blast hole and the empty holes. The presence of multiple empty holes significantly influenced the extension of the blasting-induced main fracture. Various factors, including the distance between the explosion source and the empty holes, played a pivotal role in the reflection tensile failure on the surface with no holes. Furthermore, it was found that increasing the separation between the empty holes and the blasting hole led to a reduction in kinetic energy and high friction energy. Conversely, widening the blasting holes amplified both peak friction energy and kinetic energy. Elevating the confining pressure resulted in a decrease in both peak friction energy and kinetic energy, while simultaneously increasing the strain energy. Additionally, extending the distance between the blasting hole and the free border led to a reduction in flying rock. Confining the area had a dual benefit of reducing induced force and mitigating the quantity of flying rock. The results from the experimental test and numerical simulation exhibited a consistent trend.