The town of Maumee is located along the Maumee River in Lucas County, it is a suburb about 10 miles southwest of Toledo. The Stoneco mine is at the heart of Maumee, surrounded by a dense population of residents, commercial businesses, and industrial complexes on all sides of the mine site boundaries.
Over the many years of mining at this site, geology and rock structure have brought challenges to the drilling and blasting process. One of these challenges led to a peninsula of rock 54 feet in height totaling 35,000 tons that contained several caves and voids within the rock. Drilling and blasting through and around these caves and voids is extremely difficult and creates hazardous and even dangerous conditions. Shooting all 3 open sides for this blasting event poses a threat of increased levels of ground vibration, high air over pressure (air blast) and an increased chance of fly rock ejections.
Utilizing drone technology, a GPS system, sophisticated industry designed software (3GSM Blast Metrix 3D), Shelly Company Drill & Blast engineer creates a 3D model designing the production blast to a predetermined elevation (MSL).
Once the georeferenced model is created, the blast design is built using the correct burden and spacing based upon type of rock, height of the rock face, geological structure, and borehole size. After careful examination of the 3 open faces and cave’s burden profile, hole positioning was finalized, and their locations were exported as GPS Coordinates.
The shot pattern was then laid out with a GPS system connected to Ohio State plain connected through the national survey system. A meeting between site management, engineering, and vendors occurred to discuss the design, the tasks at hand and look at the potential risks of such a blast. Once all parties were satisfied, the drill log, shot design and burden profile were provided to the drilling and blasting vendors and drilling commenced.
On blast day a prework meeting and inspections took place where a review of the drilling logs and blast plan were conducted with all participants of the workday. A safety discussion about specific site needs and bench conditions occurred with all participants.
The shot was loaded with multiple decks of explosives and inert materials strategically placed and charged with programable electronic detonators and primers. The intent of all this work is to fracture the rock to a specific grade elevation, keeping vibrations (< 2” per second), and air over pressure at a minimum (< 132 decibels), while eliminating any chance of flying rock to produce rock that is efficient for the crusher and easy on the equipment and operators to handle.
Once all safety procedures were completed by the mine site and the blasting vendors, the shot was fired.
This was a very challenging blast due to several reasons. The rock contained many voids, and caves, the rock wall contained many dips and valleys on all 3 sides making the burden (the distance in feet from borehole to open face) heavy in some places and very light in others. Heavy burden leads to oversized rock, uneven floor grade, excess wear on equipment, increased risk of injury to the operators, and higher production costs. Light burden creates increased risks of air blasts, fly rock, energy loss in the shot, poor performance. The goal is to blast this rock in a way that can be efficiently moved and loaded into the crusher for production needs while staying within the state regulations and company standards.
The fragmentation of blasted rock is extremely important to longevity of equipment, health of all operators in the process of moving the blasted rock and speed the rock flows through the primary crusher to the conveyor systems.
Management, engineering, drilling contractor, and blasting contractors all working together as a team made this shot possible, and ensured the job got done in a safe and efficient manner.
