TBM declines for underground mine access in Australia

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1 TBM declines for underground mine access in Australia Brendan Henry GHD, Brisbane, Queensland, Australia ABSTRACT For the first time, an Earth Pressure Balance TBM is driving two mine access declines for Anglo American s Grosvenor coal mine in Australia. Bandanna Energy are currently in an Early Contractor Involvement process to develop a bankable cost before obtaining their mine license to develop a 4 million tonne per annum thermal coal mine with over 6km of mine access declines to depths of 300m. Oz Minerals has purchased a used gripper TBM to provide mine access and exploration tunnels to over 1000m depth. These projects are part of a growing trend to deliver mine access tunnels using Tunnel Boring Machines. This paper discusses the projects, their details and the drivers behind the use of TBMs and how risks such as methane are managed. 1 INTRODUCTION While many in the mining and tunnelling industries may consider the use of a Tunnel Boring Machine (TBM) to create mine infrastructure to be a near new development, they have been used for many years in all areas of the globe with examples as early as the 1950s at Steep Rock Iron project in Canada. However, the use of tunnel boring machines in mines in Australia has been limited to a few examples in the 1970s. 2 TIME FOR CHANGE The use of TBMs in mining has not been a popular choice in Australia until very recent times. This is largely due to the lead time required for TBM procurement and the relative inflexibility of TBMs in terms of excavation shape and ability to change direction. In addition, the layout of the mine often requires steep and curved declines and in a coal mine, the ability to work in-seam to create mine infrastructure for ventilation and egress requirements means the usefulness of TBMs in limited. Health and safety legislation has also changed, particularly for coal mines, due to risks associated with explosions and the requirements to always work under supported ground making roadheaders less flexible and drill and blast too high risk. The cost of roadheaders has always been less than TBMs but with the requirements for fully flameproof roadheaders and safe and speedy operation of such including the addition of bolting rigs and shotcrete robots, the cost difference and lead time is lessening. In addition, tunnel boring machine configurations allow operation and ground support in soils, meaning the location of the drift access is not limited to good ground conditions or very deep box cut portals. The flexibility of roadheader excavation is a definite advantage, but mining companies are starting to realise the production rates for roadheaders are far inferior to TBM advance rates. Bandanna Energy engaged MineCraft Consulting to produce a bench marking study of TBM, Roadheader and Drill and Blast excavation rates at the start of the Springsure Creek Coal Mine Project. MineCraft found the following advance rates applied across the mining and civil construction industry. Roadheader 9 to 25m per week. Drill and Blast 21 to 63m per week. TBM 54 to 350m per week. They found that in the Queensland mining industry, roadheader drift construction projects were often contracted to produce 20m or greater per week of completed drift but generally did not achieve the required rate. Even if TBM advance rates were at the low average noted above, the production rate would be twice that of a roadheader, making the use of TBMs more attractive for the right project. 3 CURRENT AND PLANNED PROJECTS The author is aware of four projects in Australia that are either in execution, advanced planning phase or are currently on hold due to the economic downturn of the last 5 years. 3.1 Carrapateena Decline Tunnel, Australia OZ Minerals is developing a copper and gold mine in South Australia that has a cylindrical ore deposit 500 to 1,500m below ground. To investigate and excavate the ore body, an exploratory TBM access tunnel 1,000m deep is required. A refurbished 5.8m diameter Robbins Main Beam TBM was procured to excavate the exploration tunnel at 1:6.5 making the tunnel 6.5km long. The TBM is owner procured and was delivered to site in March Oz Minerals is currently conducting further studies before deciding whether to proceed with the project. The

2 tunnel will intersect rock with temperatures of above 40 Celsius. 3.2 Oaky Creek Mine XSTRATA (now Glencore) In 2012, Oaky Creek North coal mine, a subsidiary of XSTRATA (now Glencore), was in the process of expanding their operations with two new decline drifts, a man and materials drift and a conveyor drift. The project was placed on hold before XSTRATA became Glencore in May The mine development proposed involved the construction of two decline drifts from a single TBM drive 5km long at a grade of +/- 1:8. The drift has a maximum overburden height of approximately 260m and was to be constructed with a Main Beam Gripper TBM of approximately 8m diameter. 4 OPERATIONAL ENVIRONMENT 4.1 Regulation Australian coal mines work under regulatory frameworks developed by each state. In New South Wales (NSW), mines operated under the NSW Coal Mine Health and Safety Act 2002 and Regulations In Queensland (QLD), mines operated under the QLD Coal Mine Health and Safety Act 1999 and Regulations Operating under these frameworks, Australian underground coal mines are possibly the safest in the world. Sections of the legislation are prescriptive, such as for the management of high risk activities, but in general the legislation requires the mine operator to apply a vigorous risk management process. 4.2 Explosion Risk All coal mines are considered to be an explosion risk and are zoned in accordance with this risk, even after coal seam gas has been drained from the coal body prior to mining operations. In Queensland, the Regulations define the criteria for designating an area as ERZ1 or ERZ0 (Explosion Risk Zone) or NERZ (Nil Explosion Risk Zone) and the corresponding compliance requirements. The location of the ERZ/NERZ boundary has implications to the ongoing machine operability and the Capex and Opex costs. An ERZ0 zone is defined as a location where the concentration of methane is known to be, or is identified by a risk assessment as likely to be, greater than 2%. An ERZ1 zone is defined as a location where the concentration of methane is known to range, or is shown by a risk assessment as likely to range, from 0.5% to 2%. All electrical equipment within the ERZ must be certified as suitable for use in and explosive environment. A NERZ is defined as a location where the concentration of methane is known to be, or is identified by a risk assessment as likely to be, less than 0.5%. All electrical equipment in NERZ must be rated IP55. Tunnelling projects in Queensland must be executed to the requirements of the QLD Tunnelling Code of Practice which is also a legislative requirement. Although there is no clear directive to work to this Code when complying with Coal Mining legislation, it is generally accepted that complying with the Tunnelling Code should be standard practice. 4.3 Requirements for TBM manufacturers TBM manufacturers must develop a full understanding of the operational environment of a mine, which differ significantly from a civil construction project, as well as the Mining Acts and Regulations. The requirements can have significant impact on the cost and set up of the TBM. Coal mining regulations preclude the use of aluminium alloy underground if it contains more than 6% by mass of combined magnesium and titanium, or 0.6% for rotating or reciprocating parts. A person must not work in a place at the mine where the effective temperature exceeds 29.4 degrees Celsius meaning the ventilation system will usually require a chiller and access to the cutterhead will benefit from a well-designed ventilation system that will allow access in as short a timeframe as possible for tool changes. External surface temperature of any item or machinery component within the drift must not exceed 150 degrees Celsius. Emergency egress and refuge requirements are complex and must be considered during decline development and operations. In a coal mining environment, the number of persons in the tunnel at one time is higher than in a civil tunnelling application. Regulatory compliance is non-negotiable. A fully compliant TBM attracts a significant premium to that of a TBM designed for civil operations. 5 GROSVENOR COAL MINE The Grosvenor project is a A$1.95 billion growth project in Moranbah, Queensland. It involves developing a greenfield underground coal mine, producing up to seven million tonnes per annum (Mtpa) of run-of-mine (ROM) coal, which would be processed to produce approximately five Mtpa of metallurgical (coking) coal for export. The project site is located approximately 190 kilometers south-west of Mackay and will use the longwall mining method to mine coal with an anticipated mine life in excess of 30 years. Product coal from the Grosvenor Mine would be transported by rail from the existing Moranbah North Mine rail load-out facilities to the Abbot Point Coal Terminal for export. No upgrade of the rail or port facilities are required. The project secured its mining lease in June 2012 and is 100% owned by Anglo American and forms a major part of the group s strategy to triple metallurgical coal production by Site construction commenced in 2012 on bulk earthworks, access roads and the cut and cover tunnels (Armco tunnel in box cut; Figure 1) for the two drifts from the surface. Longwall mining will commence in 2016.

3 5.2.1 Geology Both the conveyor drift and Man and Material Drift pass through a sequence of alluvial sediments, weathered basalt, tertiary sediments and weathered and fresh sandstone and siltstone of the Permian era TBM Figure 1. Conveyor Drift box cut and TBM sliding cradle. 5.1 Project drivers In July 2012, coking coal was approximately A$220/mt, around the same time as China overtook Japan as the world s largest importer. In the preceding years, as Queensland was experiencing widespread flooding disrupting supply, the price rose as high as A$330/mt in mid-2011 due to undersupply. With high commodity prices and the receipt of the mining license the development of Grosvenor started in earnest in mid-2012 with the aim of reaching and producing coal in as short a time as possible. At this stage Arrow Energy had completed the coal seam gas extraction program and started the handover of the project site to Anglo. Currently, coking coal spot prices have reached as low as A$99.5/mt just after Anglo American fixed its 3 rd quarter price with Japan of approximately A$122/mt FOB east coast ports. 5.2 Surface to Coal Grosvenor coal mine will operate as a single long wall mine. To develop the long wall mine, two access drifts are required from surface to approximately 160m depth. Anglo American engaged Redpath Mining to construct the drifts in an early contractor involvement process. Redpath had recently completed an access drift at Kestrel Mine with a Roadheader. Anglo also engaged GHD to provide advice on tunnelling methodology, geotechnical investigation, detailed design and construction assistance / verification services throughout the development of the drifts. The Grosvenor Coal Mine requires two access drifts, a Conveyor Drift and a Man and Materials Access Drift. The Conveyor Drift runs at a grade of 1:6 down to the Goonyella Middle coal seam at 135m depth and as such is approximately 960m long with approximately 830m of TBM tunnelling from the bottom of the box cut. As the name suggests, the Conveyor Drift will house the mines permanent conveyor, bringing the long wall coal to surface. The Man and Materials (M&M) Drift is used for mine access of personnel and equipment and is at a shallower grade of 1:8, requiring approximately 1000m of TBM tunnelling. The Goonyella Middle Seam is approximately 3 to 4m thick. As stated above, due to the tertiary sediments (alluvium) and weathered Permian below the water table in the M&M Drift, an EPB TBM was chosen. However, as the majority of the drift is in fresh silt/sandstone, a hybrid rock EPB was considered appropriate. In the ECI process, Anglo and Redpath engaged with Robbins to develop the TBM technology and design. Robbins provided the TBM (Figure 2), moulds and segment design. Figure 2. Robbins 8m Hybrid EPBM assembled on surface. Due to the ground conditions and other reasons discussed later in the paper, a precast segmental lining was adopted. However, the design of the TBM was considerably more complex than dealing with the standard ground condition issues as it had to be designed to work in a coal mine environment and meet the operation requirements discussed in Section 4. To comply with the regulations and its risk assessed methodology, Anglo, Redpath, Robbins and GHD executed a series of risk workshops. One of these workshops was in development of the ERZ/NERZ boundary. This boundary was established in a multi-phase risk assessment process that looked at the possible sources of explosive gas (methane) ingress into the TBM and tunnel and how that gas could be managed. Possible sources of methane ingress are leaks through the tunnel lining, the screw conveyor discharge area, the tailskin brush seals and the shield articulation joint. To reduce the risk of free gas (the ability to discharge from the muck) being able to escape up the screw conveyor, a long, two stage screw conveyor was adopted (Figure 3), providing the ability to form a good plug along the screw and have multiple injection locations for muck conditioning.

4 Figure 3. First stage of extended screw being assembled Figure 4. TBM GA showing ERZ/NERZ boundary and extended screw conveyor The first stage ERZ/NERZ boundary assessment concluded that the likely ingress of gas through the tunnel lining had a very low potential and that as gas ingress through the discharged muck was a certainty, the boundary should be located just behind the screw discharge area. All electrical equipment forward of this point, including the segment erector and main drives, would have to be explosion proof. Therefore at this stage a mechanical (not vacuum) segment erector was considered. In developing the ventilation strategy, it was deemed possible to manage any gas discharge from the screw conveyor by addition of a snuffing box that would extract any explosive gases directly into a ducted ventilation system with no source of ignition available. With a triple row of brush seals in the tailskin that would be continually fed tailskin grease, the use of a tailskin grout injection system and the ring build areas being relatively open for good air circulation to prevent gas build up, it was considered that the potential for gas ingress and build up in the tailskin would be low and therefore the ERZ/NERZ boundary could be moved forward of this point (Figure 4). This meant the erector system could be changed back to a vacuum lifting device. Although the potential for gas ingress through the sealed articulation point could be considered relatively low, the forward shield itself is full of equipment (including the variable frequency electric drives) and is difficult to adequately ventilate. It was therefore concluded that all equipment in front to articulation point should be explosion proof (flameproof). The main drives were developed, tested and certified by ATB Morley Motors in the UK. To convert to hard rock mode, a hydraulically operated muck chute would be deployed around the screw. The muck is then picked up by paddles installed in the plenum to load the screw conveyor. The whole conversion process would take approximately 7 to 10 days. In rock mode, the same gas ingress issues exist and there is a higher likelihood for free methane being discharged. Therefore the screw conveyor still provided the same level of gas containment with discharge directly at the snuffer box. As the cutterhead is unidirectional in rock mode, a skew ring is used to twist the thrust cylinders in order to react to the torque of the machine in hard rock. Mini grippers on the rear shield allow the machine to bore forward and then be retracted slightly for cutter changes. The main body and drive of the TBM are designed sit inside an adaptor ring. The core of the machine is a bolted design that separates from the shield, in a process that does not require hot works (cutting or grinding tools). The core of the TBM and the backup can be walked back up the tunnel for reuse Long term strategy In 2011, the roof of the Conveyor Drift at Anglo s adjacent Moranbah North mine collapsed, halting coal production. Delay in coal production quickly runs into millions of dollars of lost revenue. As an example, in full production the mine will produce approximately 14,000t per day. For each day lost, at (for example) $200/t, lost revenue is $2.8M/day. The mine was at a standstill for more than one month. The mine had been in production since 1998 and as such the conveyor drift was around 15 years old. Utilizing an EPB TBM with precast segmental lining means that the mine can operate with what is effectively a zero maintenance access tunnel with a lining designed to last for over 50 years. Although the capital cost of a segmentally lined tunnel is higher than that of a roadheader tunnel (in reasonable rock), the savings from avoiding downtime can be significant. At the outset, Anglo decided to design the TBM for reuse on other projects such as Moranbah South and the expansion of Grosvenor leading to the TBM having the following specification: High powered TBM to deal with higher strength rock Hybrid EPB/Rock TBM Capable of executing curves TBM can be extracted from its shield and reset in new shield for each new drive. Capable of operating at a grade of 1:6

5 5.2.4 Time is of the essence In order to access the coal in as short a timeframe as possible, Anglo chose to develop the Conveyor Drift first using a flameproof roadheader. The ground conditions for the M&M Drift has highly weathered rock to a much greater depth (90m) under the groundwater table (40m). As such, Anglo opted to employ a Tunnel Boring Machine for the M&M Drift. With the lead time required for purchasing a TBM, excavating the Conveyor Drift by roadheader should have allowed a much earlier start to tunnelling and the potential to reach coal before a TBM could be supplied. Initial offerings from contractors approached to develop the Conveyor Drift showed extremely low advance rates through the tertiary sediments, which lead to a tactical rethink of the tunnel design. GHD were engaged by Anglo to work with them and Redpath to rethink the roadheader tunnel design. In parallel, Anglo worked with Hatch to develop a deeper box cut, allowing the tunnel portal to be located in better ground where higher advance rates could be achieved. These works were driven on a fast track basis with the desire to reach and produce coal in the shortest possible timeframe as the main driver. Towards the end of 2012, the coking coal price was dropping at a significant rate leading Anglo to reassess the project development timeframe. As a TBM was already on order and in production for the Transport Drift, and escalating issues relating to ground conditions for the Conveyor Drift, Anglo made a bold decision. The decision was to continue to develop Grosvenor as a strategic Coking Coal development but to delay project capital expenditure by deferring the development of the Conveyor Drift to the following financial year. This decision allowed the TBM to be utilized for both drifts. Figure 5. Conveyor Drift operational layout Construction Program Excavation for the Conveyor Drift box cut began in Q3 of 2013, with the concrete cradle, Armco tunnel and back fill complete for TBM official launch ceremony in October 2013 (Figure 6) Drift design To accommodate a production conveyor, sufficient maintenance space around the conveyor and access for a drift runner (personnel carrier / maintenance vehicle), the required floor width and clearance envelope requires a tunnel with internal diameter of 7m (Figure 5). The tunnel lining was designed as a six (equal) piece universal ring 1.4m wide with full sized key (to match the predetermined thrust ram and skew ring assembly) capable of a four hundred meter radius curve. The segments are reinforced with steel fibers and circumferential joint reinforcing cage (for the machines considerable available thrust) and radial joint bursting cage at greater depths. At refuge bay locations (every 100m), GHD designed the tunnel lining as fully reinforced with special shear dowels between rings to allow the segments to be opened up without the addition of any internal temporary works. The floor requires three separate concrete areas. A precast invert piece for the TBM back up and MSV to run on, a secondary precast floor for mine development drives, and a cast in place top up slab for the life of mine production. Figure 6. Armco tunnel partially backfilled. From there, the TBM named Lucia, was moved into the Armco tunnel and to the launch face where the multi stage commissioning was completed. By January 2014, Lucia started in earnest and completed in approximately six months. The TBM finished where the top of the coal seam is approximately at spring line. The TBM was extracted by August and relocated to the Transport Drift to start the second drive. After installation of the second level precast concrete floor and modification of the ventilation and services, the mine development is executed with continuous miners. The first section of in seam drivage and development drive intersections was designed by GHD (Figure 7).

6 Figure 7. Fracture height analysis for coal mine development workings 6 SPRINGSURE CREEK The Springsure Creek Coal Mine Project is a Central Queensland underground thermal coal project, located in the Bowen Basin approximately 47km south-east of Emerald. It is owned and managed by Springsure Creek Coal, a wholly owned subsidiary of Bandanna Energy Limited. The underground mine has an anticipated operational life of 40 years and is expected at peak performance to produce up to 11Mtpa of thermal coal. Underground mining will occur using the longwall method. Rail facilities for the project will transport coal from the mine site to connect with existing networks servicing the Bowen Basin. The Project will export the coal through the Wiggins Island Coal Export Terminal (WICET) at the Port of Gladstone. Bandanna is a 14% shareholder in WICET with an allocation of 4Mtpa. Springsure Creek Coal has a 15 year take or pay arrangement with PN Coal and WICET to haul up to 4Mtpa of coal from the mine and export. 6.1 Project Drivers Thermal coal prices rose sharply in the second half of 2009 from below A$100/mt (FOB) to above A$125/mt at the beginning of 2011 and remained high for the whole year, hitting a high of approximately A$142/mt. With the coal price consistently above $100/mt for the 2010/2011 financial year, Bandanna Energy was successful in raising $76M of capital to fund project development with coal export expected to be achieved within Confident of delivery, and needing to secure coal transportation certainty, Bandanna Energy entered into a 15 year agreement in February 2012 to haul 4mtpa of coal from the mine to WICET. Since then, Bandanna has continued with focused exploration and engineering works to achieve first coal by a slightly later date of late Shortly after February 2012, the price slumped to approximately A$92/mt and stayed at a similar average rate for two years. By June 2014, the price was back down to just over A$80/mt, a seven year low. 6.2 Surface to Coal Springsure Creek Coal Mine will operate as a single long wall mine during the first few years of operation, with additional long walls being added at staged intervals. To develop coal in as short a timeframe as possible, Bandanna with MineCraft have developed a single drift short term solution. The initial M&M drift reaches coal after 2,200m (linear drivage at 1:8) and then the TBM continues 1,350m in coal at 1:13. This coal drivage enables the TBM to develop the main gateroads whilst the

7 Figure 8. Conceptual Mine Plan and TBM Drivage. CM s develop the pit bottom area and also hole through to the main ventilation shaft. At the completion of the M&M drift the TBM will be fully extracted and reinstalled to drive the conveyor drift which will be developed to 250m depth (Figure 10). To engineer and construct the drifts, Bandanna received proposals from a number of underground development contractors as well as 3 major civil tunnelling contractors. John Holland Tunnelling was chosen to enter into an Early Contractor Involvement process with respect to the Mine Access. Bandanna then engaged John Holland to provide concept engineering of the drifts and the TBM to develop a cost and construction program. As part of this process, GHD were engaged directly by Bandanna to provide peer review and technical assistance. To meet the target operational dates and take or pay commitments, Bandanna entered into an aggressive mine development program that requires the TBM to be procured during the ECI phase. To achieve this during the ECI process, John Holland and Bandanna with GHD entered into a competitive process with TBM suppliers who were invited to submit proposals for a main beam gripper TBM of approximately 8.7m diameter. Of particular importance in these offers were supply costs, delivery program and collaborative development of the TBM with staged progress payments at key procurement timeframes and delivery timeframes. Herrenknecht were chosen to provide the TBM and have entered into a design phase to develop the machine to a suitable level to provide cost and delivery schedule certainty Geology The two drifts will be constructed through a range of geological conditions. Tertiary basalt is present close to surface up to approximately 40m deep. The basalt overlies over 100m depth of Triassic age Rewan Group; an inter-bedded sequence of mudstone, siltstone and sandstone. The Aries 2 coal seam lies beneath the Rewan Group in the Bandanna Formation. This formation is from the Permian age and has similar composition to the Rewan Group, with laminated sedimentary strata. The Aries 2 coal seam is 2.5 to 3.5m thick and has an average gas content in the range 2m 3 /t to 3m 3 /t.

8 6.2.2 Conceptual Drift Layout As stated, the conceptual drift layout was developed to allow in-seam TBM tunnelling and CM development drives from the single drift. With such a layout, the ventilation strategy must allow for the methane polluted return air to avoid working areas. The basic concept at this stage was to place an intermediate floor in the tunnel that has fresh air supply to the tunnelling face on the upper level, and contaminated air return flow below a sealed deck (Figure 9). Figure 10. Example layout of Gripper TBM with forward fixed bolting rig assembly. Figure 9. Conceptual Drift Layout. 6.3 TBM Using the concept drift layout and the available geotechnical information, John Holland and Herrenknecht developed a main beam gripper TBM layout that allows adequate and timely ground support installation, road deck installation with logistics that do not govern advance rates and electrical and ventilation systems that meet the regulatory and tunnel excavation requirements (Figure 10) Ground support installation Within the laminated strata and in-seam drivage, installation of ground support at as early a stage as possible is important to prevent ground movement. As such, fixed forward bolting rigs (2) are envisaged that sit just behind the cutting head and can install support within 2.5m of the face. These bolts cannot be installed during forward advance and affect production rates in most strata. Sitting just behind the shield are four bolting rigs that install the main support during the excavation cycle Road deck For the conceptual layout, the road decks are turned and lifted into position behind the main beam by a travelling crane after delivery into the tunnel and through the backup on MSVs ERZ/NERZ and Ventilation The ventilation concept (Figure 11) has been developed in conjunction with an ERZ/NERZ boundary risk workshop. Of importance in an unlined tunnel with in coal seam drivage is the gas content and permeability of the coal and surrounding strata. As the below deck area is designated the return airway, any gas released from the tunnel ribs or the coal on the belt will be extracted towards the TBM and personnel working areas. It was assessed that the proposed ventilation system was adequate to dilute any gas to below 0.5% concentration and can therefore be designated a NERZ. The workshop established that the concentration of methane could be managed by ventilation at all places behind the bulkhead. However, this presented a level of uncertainty and some practical risks. In addition, the Regulations state that a place where holes are being drilled underground in the coal seam or adjacent strata for exploration or seam drainage is designated as ERZ1. This could be interpreted as being applicable to the probe drill on the TBM and the risk of non-acceptance by the mines inspectorate is real. Therefore, at this early stage of the process, all areas inbye of the rear of the probe drill are designated ERZ1. All areas outbye of this location above the road deck are designated NERZ. The area below the road deck being the return airway is designated ERZ1 and the TBM ventilation system is ducted to release contaminated air below the roadway.

9 John Holland are responsible for developing the design as a design and build contractor Ground support PSM were engaged by John Holland to develop the probable support types based on the limited data available and previous projects. Five support classes have been developed with only the most favourable (A) not requiring bolted support from the static drill rigs behind the cutterhead. This support type is limited to the basalt and fresh sandstone. The majority of the drifts will require support Types B and C, consisting of standard bolting patterns and represent approximately 80% of the alignments. Further geotechnical investigations are required and are underway and once complete, further design work and support type distribution will take place to develop a target price and schedule. During the ECI phase it was identified that further investigations and ground water pumping tests be undertaken (now completed) and a baseline inflow established for TBM/drift dewatering design Road deck Figure 11. Concept ventilation schematic TBM removal The TBM must be designed to allow removal back up the driven tunnel and above the road deck (Figure 12). John Holland and Herrenknecht are working closely together to produce a bankable scheme. The road deck was conceptualised by NOMA and relies on its support on sloped rock. The precast concrete deck represents a very large portion of the cost of drift development and is subject to further design optioneering as well as further detailing of the connections at the supports. Further studies include detailed assessment of the vehicular loads that will travel on the road ways, their speed and frequency. 6.5 Surface works The TBM will be launched from the bottom of a box cut (Figure 13). The box cut requires the excavation of approximately 220,000 cubic metres of soil and rock to a depth of approximately 30m. A precast concrete arch will be installed on a concrete slab and the whole excavation backfilled. The arch is sized to allow the TBM to be walked down to the tunnel face. Mine blast doors, access doors and ventilation systems are installed as part of the box cut works. Figure 12. TBM removal concept. 6.4 Drift design Figure 13. Conceptual box cut TBM launch area section. Concept design of the drifts includes the design of ground support and road deck as well as layouts for the box cut.

10 6.6 Construction Program Bandanna Energy is currently working through items that will lead up to the issue of the Mine Lease. From then, it is expected the TBM will be on site and ready to bore within approximately 10 months. Development of the first drift is expected to take approximately 6 to 8 months and the second drift is expected to be driven in approximately 4 to 6 months. 6.7 Long terms development Bandanna is also assessing using the same tunnel boring machine to create a further 7km or more of mine infrastructure at a later date. Options being considered include moth balling of the TBM underground or extraction of the TBM to be cleaned and stored at site and then reinstalled underground at a later date. The delay between the first and subsequent developments may be 10 years. 7 ALL EYES ON GROSVENOR For the first time in Australia, underground coal mine access is being developed by TBMs at Grosvenor Coal Mine at the same time as Aquila mine develops 2 x 2km long drifts with flameproof roadheaders. Anglo American Coal has already successfully completed the Conveyor Drift and although progress was relatively slow for TBM production, the drift was completed in a timeframe that is more than two times faster than average roadheader production rates. If the execution of the M&M Drift is equally as or more successful, it is likely that the use of TBMs by mining companies will become the preferred methodology for development of mine access drifts. The civil tunnel construction industry is also hoping that the Grosvenor project is successful. 8 OTHER DEVELOPMENTS Aside from the mining companies mentioned, Peabody Coal, Vale and Hancock GVK are known to be considering TBMs as an alternate delivery technology for development of underground mine access drifts and infrastructure. Civil tunnel construction companies such as McConnell Dowell are teaming with mine development contractors such as Mastermyne to present TBM solutions for mine development and are actively working with TBM manufacturers to develop mechanical excavation solutions that combine the smarts and speed of TBM technology with roadheader technology to develop flat floor drifts (Figure 14). Figure 14. Concept in-seam mining machine 9 CONCLUSIONS Development by TBM manufacturers of alternative means of mechanised excavation for the mining industry is gaining momentum with faster and more efficient ways of developing underground mine infrastructure being developed. With successful completion of the first tunnel drive at the Grosvenor Coal Mine, the coal mining and underground mining industry in Australia is on the verge of realising a more efficient and faster method of reaching underground resources. Tunnel boring machine manufacturers are developing more equipment for the mining industry and with successful completion of both drives at Grosvenor, the Australian mining industry is likely to adopt TBM mining infrastructure development on a more frequent basis especially if the roadheader drifts at Aquila achieve poor production. Currently, resource commodity prices are low. However, when prices start to recover, the impetus on reaching underground resources in as short a timeframe as possible is likely to ensure the use of TBMs in Australian mining. ACKNOWLEDGEMENTS The writers would like to acknowledge the contribution of a number of individuals to the paper: Minecraft, Bandanna Energy, Anglo American Metallurgical Coal, John Holland Tunnelling, Herrenknecht and McConnel Dowel Mastremyne JV. REFERENCES Brox, Dean Technical considerations for TBM tunneling for mining projects