158 / 2021-10-25 14:43:55

Modelling and optimization studies in support of blasting work in the copper ore mines

Finite Element Analysis (FEA),optimization analysis,drilling and blasting

The most common method for excavating copper ore in Polish mining industry is a blasting technique, which involves drilling holes in the mining face.​ Its effectiveness is influenced by many factors, including: ​actual number of holes,​ their relative position,​ charging sequence, etc. Any optimization of this process is extremely difficult as it is almost impossible to obtain any field data other than an amount quantity of rock excavated.​ ​ A solution may be to use computer mechanics methods to simulate the interaction of the blast wave with rock volume and thus describe the process of cracking and fragmentation of the rock [1-3].



Numerical studies of the blast-induced fracture and fragmentation of the rock were carried out using Finite Element Method (FEM) and mesh-free Smooth Particle Hydrodynamics (SPH) coupled method with an explicit integration procedure. Massively parallel processing (MPP) LS-Dyna code, which uses explicit central difference time integration, was adopted. In the models previously validated Johnson-Holmquist II (JH-2) constitutive models were used to describe the dolomite behaviour. The parameters responsible for damage and fracture were iteratively obtained based on a proposed drop-weight impact laboratory stand method and numerical simulations [4]. The emulsion HE was described using the Jones-Wilkins-Lee (JWL) equation of state and the High Explosive Burn constitutive model (HEB). All required parameters of the HE used in the mining industry were defined based on the results of a so-called cylindrical test.



The research was aimed at optimising the effectiveness of blasting operations. The main objective was therefore to minimise the number of blast holes per mine face and the amount of detonation material (HE) used, while maintaining a defined level of rock fragmentation. The numerical analyses were divided into two stages. In the first stage parallel cut-hole blasting with different patters including large-diameter central boreholes were simulated using 2D models. The second stage was the analysis of representative model of rock volume with production holes detonated after cut-hole blasting and a free surface created. For this purpose the parametrically generated FE-SPH model with variable hole spacing and hole fill fraction was developed. Finally, the numerical simulations carried out made it possible to determine the relationships between blasting parameters and to optimise blasting procedures.



The results obtained allowed the development of an algorithm for generating optimised blasting metrics. This algorithm is accessible to the user from a web application. Once the mining face size, thickness of rock layers, basic mechanical parameters (compressive strength Rc) and type of explosive used have been specified, a full blast metric is generated with dedicated blast holes layouts and amounts of HE material.



References

[1]. Baranowski P, Mazurkiewicz Ł, Małachowski J, Pytlik M., 2020. Experimental testing and numerical simulations of blast-induced fracture of dolomite rock, Meccanica (2020) 55:2337–2352.

[2]. Baranowski P, Damaziak K, Mazurkiewicz Ł, Mertuszka P, Pytel W, Małachowski J, Pałac-Walko B, Jones T. 2019. Destress blasting of rock mass: multiscale modelling and simulation. Shock Vib. 2019:1–11

[3]. Mazurkiewicz L, Małachowski J, Baranowski P, Damaziak, K, Pytel W, Mertuszka P (2016) Numerical modelling of detonation in mining face cut-holes, in: Adv. Mech. Theor. Comput. Interdiscip. Issues—3rd Polish Congr. Mech. PCM 2015 21st Int. Conf. Comput. Methods Mech. C. 2015, CRC Press/Balkema, pp 393–396

[4]. Baranowski P, Kucewicz M, Gieleta R, Stankiewicz M,  Konarzewski M, Bogusz P, Pytlik M, Małachowski J. 2020. Fracture and fragmentation of dolomite rock using the JH-2 constitutive model: Parameter determination, experiments  and simulations. Int J Impact Eng.