TABLE OF CONTENTS X.M.AN and G.W.MA*
School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798
(* e-mail of corresponding author: cgwma@ntu.edu.sg )
Fracture control technique has many practical applications in rock blasting engineering, especially in underground excavation where smoother and undamaged walls are of concern. There are mainly two kinds of fracture control techniques, namely 1) notching along blasthole or drilling satellite holes beside the blasthole; 2) using pre-split charge holder. For the former one, the stress concentration in the tip of the notch will lead to the extension of the notch and the fracture can be controlled, For the latter one, the fracture initiates and propagates along the direction of the pre-split of the charge holder and the rock in other directions is protected by the charge holder. In the present study, the Johnson-Holmquist (JH) material model, which includes a strength model, a polynomial equation of state and a damage model, is implemented into LSDYNA to analyze the effectiveness of the fracture control techniques. Parametric studies are carried out. It is found that these two fracture control techniques are effective in controlling the initiation and propagation of fractures only when the blasthole load meets certain conditions. Stem can improve the efficiency of the notch. For 2-slits charge holder, fracture initiates and propagates exactly at the position of the slits. The 2-slits charge holder may be effectively adopted in pre-splitting operation, For smooth blasting, multiple slit charge holder may be used to...
