GROUND SUPPORT
friction bond length is retained at both ends of the bolt. The Dynamic Omega-Bolt associates the well-known advantages of inflatable friction bolts such as fast, clean and safe installation, with an improved capacity of energy / deformation absorption from the internal point anchored element.
The sessions of dynamic drop tests performed at Canmet laboratories confirmed the validity of the concept of adding a pointanchored element to an inflatable friction rockbolt. In particular, this new rockbolt offers an interesting combination of a relatively stiff initial response, followed by a secondary ductile behaviour associated with an improved capacity of energy absorption. The specific version of the dynamic inflatable bolt tested at Canmet showed an energy absorption capacity in line with the 30 kJ class of dynamic rockbolts, a level normally considered sufficient for hard rock mines subjected to rockburst. Energy absorption measured( 35 kJ) and plate deformation( on average 350 mm), position this new friction bolt within the cluster of‘ yielding support’( Potvin, Y, Wesseloo, J & Heal D 2010,‘ An interpretation of ground support capacity submitted to dynamic loading’, in M Van Sint Jan & Y Potvin( eds), Proceedings of the Fifth International Seminar on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth).
‘ Continuous tube configuration’ tests performed at Canmet in Q4 2016, measured the rockbolt’ s performance at its lower end( close to the ace plate). The static test confirmed the validity of the analytical model, with a peak tensile strength of 237 kN in average, and a residual tensile strength( inner element) of average 68 kN. The dynamic test indicated that this dynamic inflatable bolt is able to absorb on average a dynamic energy of 22 KJ.
Two series of static pull tests performed during November and December 2016, respectively at the LKAB Malmberget mine and at Outokumpu’ s Kemi mine, were able to confirm and validate the static behaviour of this dynamic inflatable bolt and the values measured at the Canmet laboratory.
Global success with D-Bolts
The Normet D-Bolt is a rock reinforcement element comprised of a smooth steel bar with a number of deformed sections that act as anchor points along its length. The collar end of the D- Bolt is threaded and is designed to be used with a face plate, spherical washer and a nut that fastens the bolt. The bolt is fully encapsulated in a borehole, but it is only constrained to the grout or resin along the anchor points. This allows the smooth sections of the bolt, between the anchor locations, to deform without constraints and absorb energy as the rock mass dilates.
The Kidd copper / zinc mine started to test the
Few tasks in underground mining are as demanding as mechanical scaling. The ScaleBOSS from Breaker Technology Inc( BTI) the company says represents a new generation of mining productivity and safety. Its five axis boom offers enhanced flexibility and superior coverage, while a heavy-duty, compact construction makes it easy to manoeuvre while withstanding severe conditions. An ergonomic ROPS / FOPS certified operator cabin and HVAC system maintains excellent personnel safety while providing high visibility and comfort.“ Built with our Hydraulic Wheel Drive( HWD) powertrain and braking system, the ScaleBOSS Scaler gains more traction and power with fewer emissions than conventional mechanical systems.” Hydraulic braking also means no brake pads to service or replace.
D-Bolt for rock burst control in 2009, in small quantities. In 2012, Xstrata Copper decided to test the D-Bolt for squeezing ground conditions and following the original success, it is now the specified rock bolt for mining below 8,500 ft. Since 2012, the D-Bolt has also been subjected to seismicity, with good results. It is now also the standard rock bolt for seismic conditions below 7,000 ft depth.
In 2012, a long hole blast was detonated close to an opening where D-Bolts were used. The D-Bolts located 1 m away had not been broken and were still performing adequately; with the only visible damage in that some plates were flattened by the blast waves.
Since November 2011, Nickel Rim South mine has been using D-Bolts to control squeezing in soft copper deposits, and dynamic conditions in hard nickel deposits at the site in Garson, Ontario Canada. D-Bolt is the preferred bolt for squeezing and dynamic conditions and is used systematically in ramp development. In 2012, a small rock burst followed by squeezing was well handled by the D-Bolts installed in that area; the shotcrete cracked but the support system kept its functionality and no rehabilitation or repairs were necessary.
Lucky Friday Mine in Idaho, USA, used D-Bolts to rehabilitate most of its damaged working areas from high stress and dynamic events. D- Bolt is the preferred bolt for long term development. Hecla Mining started to use D- Bolts in 2012 and the repaired excavations are in very good condition still.
In Chile, the D-Bolt system has been used at El Teniente since 2013. The Pilar Norte and Dacita operations were selected to apply the D- Bolt as complementary ground support due to evidence of seismic risk on site. To date 23,000 D-Bolts have been acquired and there has not been any incident with installed bolts.
Since Q3 2011, hundreds of thousands of D- Bolts have been installed in the largest LKAB iron ore mine, Kiruna, in Sweden, mainly for securing the infrastructure of the new, main level at 1,365 m depth. D-Bolt has been the preferred dynamic bolt for the new main level project, but is also being installed as part of the overall mine operation.
The Frog ' s Leg gold mine is located 20 km directly west of the city of Kalgoorlie in Western Australia. The Frog ' s Leg deposit is robust, consistently returns strong exploration results, and has a reported attributable gold resource of 500,000 oz ensuring a long lifespan. In 2012, the resource was extended by drilling to a depth of 800 m. Following a comprehensive tender process in 2014, La Mancha has chosen the D- Bolt as the bolt to be used for dynamic support in its mine.
MacLean Engineering face bolting trials complete
A key feature of MacLean Engineering’ s 975 Omnia Scaler-Bolter is the capability to‘ bolt the face’ from a safe distance. With this new design, operators can install ground support while remaining a minimum of 6 m from the face.
62 International Mining | AUGUST 2017