Investigating the backbreak and reduction in the bench dip with respect to the blastholes dip in surface mines

The broken area between last row of blastholes and remained bench crest at the top part of the blastholes is displaced and attached to the muck pile existing in most of the common blasting operations.  The broken area at the top of the blastholes and unbroken rock at the bench toe rerduces the bench dip with respect to the blasthole dip. Backbreak and reduction of the bench dip with respect to the blasthole dip play important roles on the stability and design of the remained bench wall after blasting.The effects of blastholes and charging parameters have been investigated in this study by various blasting operations in Eyvughly gypsum mine, Rashakan limestone mine, Sungun copper mine and Gholghohar iron mine.including: blasthole diameter, blastholes spacing, burden, stemming, blasthole length, blasthole dip, charge quantity and number of rows in each delay and powder factor on the backbreak distance and varying the reduction of bench dip angle (a) respect to the blastholes dip angle (b).  
The results show that backbreak distance (L_b) rises with an increase of the blasthole diameter, blastholes spacing, burden, stemming, blasthole length, number of rows in each delay while it has the best correlation (R=0.880) with the blasthole diameter.  However, the backbreak distance (L_b) has no correlation with each of the three parameters of powder factor (q), ratio of the burden -to- blasthole diameter and blastholes dip (a).  The backbreak distance as a function of six parameters of diameter (f_h), blastholes spacing (S), burden (B), stemming (S_t), blasthole length (H) and number of rows in each delay can be predicted by a multivariable function (R=0.979).  Reduction of bench dip respect to the blastholes dip (a-b) increases with an increase of blasthole diameter, blastholes spacing, burden, stemming, blasthole length and blastholes dip.  Reduction of bench dip respect to the blastholes dip (a-b) as a function of six parameters of diameter (f_h), blastholes spacing (S), burden (B), stemming (S_t), blasthole length (H) and blastholes dip can be predicted by a multivariable relationship with a  high correlation (R=0.986).  Reduction of bench dip respect to the blastholes dip (a-b) has no correlation with each of the three parameters of powder factor (q), number of rows and charge quantity in each delay.