The South African Institute of Mining and ~Metallurgy RISE OF THE MACHINES THE ADVANTAGES, PERFORMANCE AND POTENTIAL OF THE HYDROPOWERED LONG HOLE RIG FOR DEVELOPING ROCKP ASSES AND OTHER EXCAV ArIONS Abstract Phillip Tobias Gold Fields Ltd. Peter Fraser Hydro Power Equipment (Pty.) Ltd. The Long Hole Rig utilizing a high-pressure water hammer is a safe, cost-effective method of developing 20 to 60m long rockpasses. This paper examines the fundamental advantages of this approach, key factors for success, its limitations, its achievements and the potential of the Long Hole Rig for rockpasses and other types of development such as travelling ways, drain holes etc. Background Traditionally in South Africa, rockpasses from the raise to the cross cut narrow reef gold and platinum mines have been developed using hand-held drills, chain ladders and temporary platforms. This method is dangerous, slow, inaccurate and produces an excavation of poor or variable quality. The traditional alternatives to hand-held drilling methods were drop raising using air-hungry top hammers which are limited to short holes (say, less than 20m) or raise boring which is expensive. The Long Hole Drill Rig (LHR) was born of the significant need to drill long rockpass blastholes safely, accurately and quickly without a person having to enter excavation. It was made possible by the bringing together oftwo elements-a water-powered In-The-Hole (ITH) hammer developed and proven in Sweden and the 100% water-powered motor and valve technology developed in South Africa by Hydropower Equipment (Pty) Ltd (HPE). The ITH hammer provided the opportunity to bring considerable percussive power to the bit without have to suffer the energy losses associated with having impact strain pulses travel through many rod couplings and drill steels. High power at the rock-breaking face translates into high penetration rates and fast drilling. The motor and valves allowed the rotation, thrust and other control functions to be 100% water driven necessitating a single water power pack and eliminating the need for an oil hydraulic unit. p The hammer developed in Sweden from 1993 onwards by Wassara (a subsidiary of LKAB and Sandvik) comes in sizes 80, 100, 150 and 200mm-l00mm being the most commonly used size. This size of hammer allows holes from 95 to 115mm to be drilled and these can be reamed to 165mm. This size hammer is usually connected to 89mm drill pipes which are rigid (compared with say a 32mm drill rod) thus aiding direction control and producing straight holes. Page 1
Figure 1 (a) and (b) Water-powered In-The-Hole (ITH) hammers and rotation motor Additional synergistic advantages of bringing the hammer together with the water rotation and controls are the excellent flushing, the high energy efficiency and the known advantages of hydropower (cool, quiet, oil-free environment, free of dust and oil mist in the air and the absence oil to cause slippery footwalls or contaminate the ore). The European Hammer Experience The need for a hydraulic ITR hammer was first understood by LKAB who operate the largest underground iron ore mines in the world. They mine a massive ore body that necessitated drilling long holes accurately, but were limited in length and accuracy by what could be achieved with top hammer drilling from conventional top hammer electro-hydraulic mobile drill rigs. They realized that a water hydraulic ITR hammer was the solution to their problem. They estimate that the development and introduction of the hammer has reduced their drilling cost by about O.5billion SKr per year. Furthermore, the additional accuracy and length of hole they could achieve allowed them to double their spacing between levels and thereby significantly reduce development costs and time. The hammer has also enabled and number of other types of drilling to be achieved such as slot drilling and cluster drilling of large holes as shown in figure 2 and 3. The Wassara hammer is also finding new uses in civil engineering applications such as pile and geothermal drilling. Page 2
Figure 2 (a) and (b) Slot drilled using a Wassara hammer and blasted excavation Figure 3 Two hammers in a cluster capable of drilling a 700mm hole The key point from the European experience is that a reliable, powerful, efficient and flexible tool has been developed and is used to drill over 1300km annually. Page 3
The Long Hole Drill Rig Figure 4 Long Hole Drill Rig The LHR was developed initially for the purpose of drilling blastholes for rockpasses up to about 60m long, although it is flexible and can do more than this primary function. To drill long blastholes for 1.5m rockpasses the following principles were adopted: The rig must be able to operate with the main sizes of hammer in use, namely 80, 100 and 150mm with the ability to do slot drilling. This meant that the rig had to be designed for the largest forces generated by the 150mm hammer. The base was to be a rigid frame providing a reference for the drilling direction and bringing all the force due to drilling and the weight of the machine to the footwall. The base incorporates slides so that drill feed can be moved in the horizontal plane in the x and y directions without introducing errors. These slides must also move freely. This approach provides a stable and safe platform that is independent of the position or angle of the hangingwall. The LHR must be transportable on the level and between levels. This necessitated that it be disassembled into modules that can be fitted into mine cages and manually handled. The base frame is fitted with wheels and becomes another module. The tool-and-pipe car and the power pack are also wheeled modules. To ensure accurate holes, the LHR must be able to collar gently and be hammer-guided during collaring. To ensure this is possible for a wide range of hammer and drill pipe sizes, a variable gripping diameter "iris" collar guide was developed. Page 4
To ensure easy drill pipe handling, screwing and unscrewing, the drill pipes are removed from the underside of the drill feed with the aid of and arm which magnetically clamps the drill pipe as is lowered to the drill pipe handler. Key Factors for Success Fundamental to drilling multiple long, accurate and parallel holes is the initial set-up. This is carried out on the basis of the direction and inclination determined by the mine surveyor off pegs. Although expensive direction instruments are available, the initial set up can be done simply using strings, a spirit level and a digital inclinometer to better than 0.5% (l-in-200). Figure 5 Drilling Pattern Figure 6 Straight hole Aligning subsequent holes thereafter is a matter of moving the drill feed on the x-y base arrangement. To ensure easy movement and to guarantee mechanical alignment the latest LHR model has rollers on a "V" guide. Once the drill feed is correctly directed, it is then important to collar gently without misalignment and thereafter to control the thrust and rotation optimally. Page 5
Stabilizers to assist guiding the drill hammer and the drill pipe ensure hole straightness. These consist of eight flatbars welded longitudinally along 'a drill pipe such that they fit snugly in the hole, but allow sufficient space between them for the chippings to be flushed out. Typically, drill pipes with stabilizer bars will be fitted just behind the hammer and thereafter on every sixth drill pipe. Stabilizers combined with the rigid drill pipe go a long way to providing straight holes. Typically, the straightness of a 40m hole is better than half the diameter of the hole. This can easily be checked using a light, but has also been checked with borehole survey instrumentation. An important factor in drilling good holes is the operator position and visibility. To this end the controls have been mounted on a separate consol that can be positioned in a safe position with good visibility. Because the hammer is water-powered and the spent water is flushed out of the hole in the annulus around the drill pipe, cuttings are effectively removed. Of course, the drilling operation is dust free. Critical to the success of drilling is bit control and sharpening. A series of circular hole gauges is used to measure the diameter of the bits and the bits must be used in a sequence with the largest bits at the start of the hole and the smallest bits at the end if jamming of the bits in the hole is to be avoided. Bits must be marked and stored in a logical manner. The life of the bits is one of the key costs of drilling and care must be taken to minimize this cost. To do this the number of sharpenings over the life of the bit must be determined for the type of ground. Thereafter the bit must be removed from the hole when the estimated distance between sharpenings has been drilled to avoid excessive wear and/or unsharpenable bits. Typically wear flats must be less than 2mm on a bit between sharpenings. Water quality is important for hammer life. This is primarily a function of the type of valve incorporated in the Wassara hammer. As the hammer wears internally so it demands more water. Monitoring the water flow to the hammer allows the user to estimate the condition of the hammer. Accurate drilling of the long blastholes is only part of the requirement for excavating long rockpasses. Charging and blasting is the other key factor. To produce a 1.5 x 1.5m rockpass typically 11 x 9Smm holes are drilled, three of which are reamed to 16Smm. These are normally charged and blasted in stages to prevent a hang up. Typically the first round might be 10m and Srn thereafter, although sections as long as 20m have been blasted at once. To support the operational staff who set-up and drill with the rig it is necessary to ensure the correct maintenance and logistics support. Also necessary is a training and implementation programme required at the start of the project. These services are best provided by the supplier in the form of an OEM Maintenance Contract. Performance The penetration rate depends primarily on the rock type and bit size. Typical instantaneous penetration rates are 0.8 mlmin in the Bushveld Complex and O.Smlminute in quartzite. With Page 6
1.5m drill pipes and allowing for the fitting and removal of pipes and the need to drill only as far as one sharpening of the bit will allow, a 60m hole can be completed in a shift. This means that including set-up and relocation a typical 14 pass (11 holes +3 reamings) can be completed in 2 weeks. The time to blast the holes will take just under two weeks. The longer the rockpass, the more important it is to maintain accuracy and parallelism of the holes. Accuracy of the holes ultimately determines the quality ofthe final rockpass. The LHR is designed to deliver this accuracy through its sturdy base design. The complete cost of invert drop raising a rockpass is estimated by Sachse and Westgate (SAIMM December 2005) to average R 3 670/m over a range of lengths from 15 to 90m as shown in Table 1 below. LENGTHOFROCKPASS'CQ$'rPER..Mt'l'ER.()FtCOS'rTOCOMRhE'fE,. '(NI).'r,:>,' :com.lileteproduct ~r2~:;:. >t. '. :.s{... c;;;t(ra.nijlm} <'\.:' _~ ~ ""';\>~".......... ' 15 3483 53000 30 3242 98000 45 4156 187000 60 3867 232000 75 3693 599000 90 3578 702000 Table 1 Estimated RIm costs Total cost for complete rockpasses of different lengths These costs include capital cost amortization and set-up costs and are based on typical rates in the industry and contactors' rates. The performance of this method in comparison with other methods (hand-held drilling, raise climber, conventional drop raising, blind boring and raise boring) are compared on a number of criteria (e.g. safety, site preparation, overall excavation period, risk of not achieving an acceptable rockpass etc.) by Sachse and Westgate (SAIMM December 2005). The LHR method offers the most cost-effective method of excavating ore passes over the widest range of lengths while at the same time being safe, quick and with a low risk of a failure compared with the other methods considered. pi A completed rockpass is shown in figure 7 below. Page 7
HYDRA ULIC TRANSPORTATION AND COMMUNICATIONS Figure 10 Drilling a decline from the surface with the LHR supported on a frame Cover Drilling Cover Drilling is possible, but has not yet been tried. This could be drilled 50m or more ahead off the face and would require a special anchor to ensure that the drill pipe and rig can be clamped and held in position in the event of encountering high-pressure ground water. Another advantage of the LH R for cover drilling is that the drill pipes have non-return valves installed inside them which would prevent a reverse flow through them. A long 100mm cover hole could be completed in a few shifts without having drill and blast a cubby. This hole could also be reamed to provide a cut hole for subsequent development. Pre-conditioning In areas with a high Energy Release Rate it can be desirable to blast the ground ahead of the face to relieve some of the stress by allowing fracturing to occur. Again the ability to drill long holes may be advantageous in this case. Page 10
HYDRA ULIC TRANSPORTATION AND COMMUNICATIONS Future Developments A more compact unit with a smaller drill feed is planned. This unit will be designed to use the 80 and 100mm hammers. It is envisaged that this drillfeed will also be suitable for long-hole stoping. Conclusions The Wassara high-pressure water powered hammer is a proven In-the-Hole hammer both in South Africa and Europe. When employed in the Long Hole Rig it is capable of drilling long, straight and parallel holes accurately when correctly set up without the necessity of an oilhydraulic power pack. Although the LHR was initially designed to drill rockpass blast-holes safely in an invert drop-raising configuration, thereby eliminating the need for hand-held drilling in rockpasses, it is a flexible and efficient drilling tool that has found other uses. In its primary function it offers the most cost-effective solution to excavating rockpasses up to about 55m. No doubt, it will become more widely used in the future. References U. Sachse and N: Westgate, Rockpasses: a guide to excavation methodology, Journal of the SAIMM, Volume 105, Page 759-763, December 2005. Page 11