Shotcreting plays an essential part of today’s mining industry; especially in underground mines where a roof collapse is a real risk that needs to be mitigated.


“Shotcreting is all about enhancing safety outcomes to personnel working underground,” Macmahon Underground Commercial Manager Gordon Leslie told National Mining Chronicle.


“It provides surface coverage to secure smaller loose material that steel mesh simply can’t cover economically or productively.


“Further, shotcrete provides a smoothed, ‘locked-in’ surface that could result in improved ventilation outcomes, especially in ventilation shafts, and reduce the need to bog out the shaft into the future.”


Macmahon provides contract services for shotcreting in the traditional mining ground-support process and also for shaft lining processes.


The contractor’s remote shotcrete shaft-lining machine can reach to a depth of up to 380m, with a diameter of 1.8m to 6.5m.


This process is another example of how shotcreting enhances the safety of a minesite, with the whole process conducted in a control room.


“The Macmahon shaft liner is a zero-exposure system where no personnel are exposed to the risk of falling into the shaft,” Mr Leslie said.


“The monitoring and operation are carried out by CCTV network.


“The container and winch are fitted out with the appropriate equipment to allow both the operator and the supervisor to view and control the application via TV screens.”


The shaft liner incorporates technology to enable pre and post-scanning of the shaft to gauge an accurate thickness measurement of the applied shotcrete.


Infrared cameras monitor the spraying, relaying images to the operator in real time.


The shaft lining process is similar to traditional shotcreting methods, according to Macmahon Underground Mining Engineer David Willey.


“Once the module and umbilicals have been assembled and tested, the unit is connected to the winch rope and lowered into the shaft to perform a survey, with the client being shown a video for approval to spray,” he said.


“Once lines are primed and tested, the application is performed as a similar principle to conventional shotcreting – concrete bands are sprayed in layers, with the previous pass supporting the new coat.


“Total thickness does not have to be achieved on the initial pass, a second or third pass may be required to achieve the specification thickness.


“Further, over-break in the strata may require the operator to manually control the nozzle to  ll any voids that may be present.”


Image: Macmahon shaft liner.