Buffer Blasting: an overview

Buffer blasting is most successful when the rock is quite competent or on slopes designed with a higher factor of safety. However, the buffer row, which involves modifying the loading and pattern for the last row of the final production blast, is essential to good pre-split blast results (Verma, 2015).

The primary disadvantage of buffer blasting that the wall is not protected from crack dilation, gas penetration and block heaving. In buffer blasting, the energy level is decreased adjacent to the wall to reduce over break. This is often achieved by simply reducing the charge weight (30 to 60%) in the row nearest. However, most rock types require additional design modifications to minimize damage (Verma, 2015).

These modifications can include air decking, reducing the burden and spacing dimensions (by 25%), minimizing sub drill and increasing the delay interval between the last two rows of blastholes (Verma, 2015).

One of the key elements in the success of buffer blasting is standoff of the last row of holes. The blast hole standoff is the distance from the last row of holes to the final slope. This offset controls both the wall stability and ease of excavation of the toe. The optimum standoff distance will depend on the strength and structure of the rock mass and should be determined by carefully analysing blast performance (John, 1998).

Following are the guidelines for designing buffer blast (Verma, 2015):

1. Locate the modified production row 1 mouth from toe of the slope
2. Reduce production charge weight by 50% in the last row
3. Use air decks and minimize the stemming length in the last row
4. Minimize sub-drill when drilling adjacent to the next catch bench
5. Reduce the burden and spacing of the last row by 25% 6. Increase the delay timing between the last two rows of holes

Reference

John, L. F. (1998). The development and implementation of efficient wall control blast designs. Proc. Intl. Conf. onExplosive & Blasting Techniques, Florida, USA, 88–92.

Verma, H. K. (2015). CONTROLLED BLASTING TECHNIQUES FOR DEVELOPMENTOF ROADINFRASTRUCTURES IN HILLY TERRAIN. https://www.semanticscholar.org/paper/CONTROLLED-BLASTING-TECHNIQUES-FOR-DEVELOPMENTOF-IN-Verma/6c9733bad33da0e106ef16e0037d291f4ec4cb16