Optimization of blast design for better fragmentation & reduction of ground vibration at Khao Mai Nuan pyrophyllite mine, Saraburi province, Thailand

Abstract

Control blasting with better fragmentation is very important to decrease the environmental impacts of blasting and the cost of downstream mining operations such as loading, transportation, crushing, and milling. Proper blasting designs with optimized parameters such as burden, spacing, stemming, sub-drilling, and amount of explosive ensure the required fragmentation with ground vibration within the standards set by different monitoring agencies.

This study dealt with the blasting design parameters, fragmentation, and ground vibration at the Khao Mai Nuan Pyrophyllite quarry Saraburi province, Thailand. First, grab samples were collected from the quarry's active benches and tested in a lab for strength, compositions and other rock characteristics. The obtained rock characteristic data such as rock type, rock description, uniaxial compressive strength (UCS), tensile strength, and density were used to optimize blast design parameters and build the predictive models. Based on the rock parameters data, four blast designs were proposed and then executed in the field.

A digital image processing method, image J software was employed for the size distribution analysis of each blast muckpile. The average size distribution results were obtained both in tabular and graphical form, which showed that the fragmentation performance had been increased from the average size of 25 inches to 14 inches with less noticeable boulder productions. On the other hand, blast-induced vibrations were measured carefully for all blasts conducted on-site using the Instantel Micromate seismograph device. Based on the statistical evaluation of the data pairs obtained from a scaled distance and peak particle velocity (PPV), the ground vibrations generated and propagated were very low to cause any kind of damage to any nearby structures within the vicinity of the mine. The highest peak particle velocity was recorded at 1.65 mm/s, and the lowest peak particle velocity (PPV) was 0.37 mm/s. Hence, it can be concluded that the proposed modified blast designs used for test blasts were suitable for the production of required size fragmentation, and it will be very unlikely that the PPV in such a range can affect any structure in the vicinity of the mine.