New Tunnel Boring Machine

28 july 2010 Mining EnginEEring

New tunnel boring machine accelerates tunnel construction

in deep mining operationsAs openpit copper operations transition from surface

mines to underground, the speed of underground infrastructure construction prior to production is

critical for maximizing the value of the project. Typically, the preferred underground bulk mining method is block caving.

In preparation for future underground projects, Rio Tinto made the strategic decision to invest in a step-change program that would develop system solutions to reduce the construction time of block caves. The program focused on improving safety and doubling or more the construction speed of both vertical shafts and horizontal infrastructure compared to existing drill-and-blast rates.

After an extensive selection process, Rio Tinto selected the Atlas Copco mobile miner machine as one of the concepts to proceed with for construction of horizontal infrastructure for access and footprint. In addition to un-derground drilling and hauling equipment, Atlas Copco’s Robbins mobile miner concept (a previous attempt at horizontal mechanical excavation) completed trials at Mount Isa, Pasminco and Taisei.

Rio Tinto selected the new Atlas Copco mobile miner machine concept for a number of reasons including the use of proven technology from the three previous mobile miner machines and other commercial products, as well as the ability to install complete ground support typical with high rock stress conditions at approximately 1,500 to 2,000 m (4,900 to 6,500 ft) depth.

Atlas Copco, with support from Rowa, the Swiss company that specializes in back up systems for tunnel boring machines (TBM), is advancing the detail design of the access version of a tunneling system on behalf of Rio Tinto. Because of the different requirements between an excavation system for access tunnels and that for tunnels on the footprint, two different versions of the mobile miner

machine technology were envisioned. The access and the footprint versions of the Atlas Copco mobile miner machine share a major-ity of key technologies and systems. Therefore, it was possible to conduct a perfor-mance confirmation test us-ing a full-scale version of the access machine that would also mitigate the technical risks for the footprint ver-sion. To alleviate confusion, this article focuses on the access version of the Atlas

Copco mobile miner machine technology. Tunnels have been excavated by drill-and-blast, tunnel

boring machine (TBM) methods and, on rare occasions, other mechanical methods. TBMs are considered advan-tageous for high speed tunneling. TBM’s provide a higher advance rate, a very smooth profile and a careful excavation, reducing demands for rock support. The drawbacks for a TBM include the cost of the machine, its limited ability to change profile as well as difficulties handling small curve radii. These are all aspects in which drill-and-blast has a number of advantages. The TBM profile has strengths and weaknesses. The arched roof is a benefit, but the nonflat invert is not ideal for all applications. Cutting crosscuts and branching is difficult with TBMs, and normally requires extensive, extra measures. The choice between the two methods is, therefore, a complex exercise involving many different parameters and complex calculations.

Based on performance estimates and observed real performance, a “brutal tool” is sometimes used for an initial quick selection of the preferred tunneling method for a normal tunnel with length L (m), diameter D (m) and rock compressive strength UCS (Pa). It was found that when using the simple formula: Q = L/ (D* 3√UCS), if the result is a value larger than 1.5, then the TBM method has to be considered the prime candidate. If the result of the formula was below 1.5, then the drill-and-blast method would be better. The result, Q, is a sort of feasibility index, but this is just a first suggestion that must be verified through a more detailed analysis.

Using this formula with all of its limitations, one can still find some conclusions. Obviously, tunnel length is important. Capital cost is also important, as are startup time and the first months of typical “running in” low per-formance of a TBM tunnel. The negative influence of the

Fig 1

Robbins MM130 (Willoughby, 1993).

UNDERgROUND MiNiNg

Sverker Hartwig and Fred Delabbio

Sverker Hartwig is vice president Technology for Atlas Copco Construction and Mining Technique, Fred Delabbio,

member SME, is general manager innovation - underground, Rio Tinto,

Brisbane, Australia e-mail [email protected], Sverker.

[email protected].

MIN_028_043.indd 28 6/22/10 3:15 PM

Mining EnginEEring july 2010 29

diameter can be explained in different ways. One obvious way is that the cutterhead speed has to be reduced with increasing diameters, leading to fewer meters per hour of advance. The influence of the rock strength is remarkable. In this formula, its weight has been reduced by the “cubic root” function. In essence, this means that “rock hardness” is not the “one and only” determination factor. It also points to the fact that a hard rock TBM can cut almost any type of hard rock, even rock as hard as 300 MPa. This is unlike some other mechanical methods, like roadheaders, where there is a clear limit, never to be exceeded. There may ex-ist different opinions of exactly where the limit for road headers is; 80,100 or 120 MPa.

The length and diameter of the tunnel are also im-portant. But would a number of shorter tunnels, more or less at the same place, do the trick? Yes, but only with the assumption that the TBM could move by itself to the next section, in a matter of hours or days. A reasonable tunnel size, less than 6 m (20 ft), would be ideal. Therefore, a mine would be the perfect marketplace because there are many tunnels, not too big, difficult rock and high stresses.

To accomplish this, a machine would have to be able to change profile; make a flat invert; be able to back up after ground support was installed and tunnel closure completed; be able to make small radius curves; do cross cuts, travel by itself; be easy to launch with shaft access; and also maintain a large part of TBM speed and gentleness to adjacent rock.

In short, this is the basis for the “mobile miner dream.”

Start of the dreamThe dream, as such, may very well have been around

for hundreds of years. In the dream, the hope for a continu-ous mole, that is controlled remotely, with limited ventila-

Fig 2

Mini machine tunnel, circa 1970.

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tion and other support and utilities, keeps on delivering a precrushed, steady stream of high-grade ore at shaft. The first ideas of how to make it true appeared in the 1970s. Primus motor here was Dick Robbins and The Robbins Company (Robbins). Robbins delivered many concepts for shaft sinking, tunneling, box holing and raise boring. An entirely new idea evolved using TBM-type disc cut-ters arranged on a cutterhead enabling most of the dream functions. The machine type, best known throughout the world as the mobile miner (Fig. 1), has given its name to any other attempt to realize something similar. Atlas Copco and Robbins manufactured three machines of this type and the latter two were still active or under manufacture when Atlas Copco acquired Robbins Co. in 1993.

“Wild ideas” like the mobile miner were not new to Atlas Copco in any way.

Atlas Copco’s history in mechanical rock cuttingEven as a 130-year-old company, Atlas Copco remains

closely related to the Swedish method of tunneling. The Swedish method is “the one man, one machine” rock drill technique developed around the time of World War II. These machines, having built-in rotation, tungsten carbide bits and the pusher leg, revolutionized not only rock drill-ing, but also Atlas Copco. However, after 10 to 15 years, it became obvious that step-change development goes on, and further innovations were needed. Since then, the development has followed two directions. The first was mechanization and later automation of the drill-and-blast process including all unit operations, drilling, charging, blasting, scaling, bolting and mucking.

Atlas Copco realized that there could be further tech-nical developments that could differentiate it from other competitors in the market. Could rock be drilled by means other than rotary or percussive? Could these options include microwaves, high-pressure water, thermal lances and plasma burners? Then, the ultimate opportunity was the possibility that the machines tried in the late 1800s, the tunnel boring machines, would develop into something that not only advanced drill-and-blast methods, but replaced it.

It should be noted that Atlas Copco had a research institute in Switzerland, CERAC, that for many years tried any possible (and some impossible) ways to make a hole or a slot in rock. Techniques such as high-pressure water and lasers were tried as well as rapid tunneling using battle cruiser ship cannons. The latter works, but is rather expensive and noisy. A couple of water jet drilling and or slot-cutting machines were actually sold.

During the 1960s, Atlas Copco acquired the Swiss com-pany Habegger, which became Atlas Copco TBM Machines based in Thun, Switzerland. This company focused on use of professor Wohlmeyer’s undercutting method that included large tungsten carbide cutting picks, running at very low speed with high forces in a “get in under and rip out” type of operation. Many machines, some extremely successful, were built of this type model, including the Mini and Midi, as shown in Figs. 2 and 3.

There was, however, certain rock types (particularly those with high ductility) where the machine type per-formed poorly. Similar machines have been tried most recently in the platinum industry.

Atlas Copco needed a machine whose performance was

Fig 4

The Atlas Copco shaft borer MBM, circa 1987.Fig 5

Robbins MM 120, circa 1992.

Fig 3

A midi for White Pine and a Mini for Sidney Harbour, circa 1974.

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more predictable and acceptable in hard rock. So it was decided that Atlas Copco should get involved with more classical TBM machines. It acquired Jarva in Solon, OH. This company had a range of successful Jarva MK x TBMs, which today are difficult to beat in competent hard ground. Jarva further developed shield machines, raise boring machines (RBM) and some special shaft machines. An interesting machine started to be developed in Solon, but finished after Atlas Copco moved this business to Stockholm, the mobile boring ma-chine (MBM). Notice the similarity between the Atlas Copco MBM from 1986 with later developments in the business (Fig. 4).

In parallel, with these TBM activities, Atlas Copco joined forces with Gbr Eickhoff in Germany for the development of heavy roadheading machines, which had applications in civil en-gineering projects. Not hiding the fact that a roadheader can do remarkable jobs in softer ground, again Atlas Copco entered into a situation in which it was clear that these types of machines could not be used as a universal mining tool like drill-and-blast.

After the move of Jarva to Sweden, Atlas Copco flour-ished for 10 years in this business, developing a number of hard rock TBMs, new cutters, the variable speed drive (VSD) technique and many more features. To further en-hance this business, Atlas Copco acquired Robbins in 1993. Atlas Copco decided to sell off the TBM part of the business in 1998 and keep RBM’s and the other mining machines portion. Atlas Copco has since been involved in a number of more or less detailed developments of special mining machines, for shafts, narrow vein excavation and more.

Atlas Copco has worked actively with novel rock exca-vation techniques since the late 1950s with noticeable and sometimes very successful efforts.

Robbins/Atlas Copco mobile minersThree machines of this type were built in the late 1980s

and early 1990s. They all worked with a vertical narrow cutterhead that was sumped into the rock and then in a sweeping movement under rotation was swung +/- 45°. The last machine could also lift the cutter head in a “ranging” type mode. Different configurations were tested to hold the machine stationary in the drift while cutting and also to propel them forward.

The first was a machine tried at Mt. Isa Mines, Queensland, Australia, the MM 120 (Fig. 5).

This machine was followed by the MM 130 Pasminco, Broken Hill machine (Fig. 1).

The Pasminco machine made several projects and a clas-sical picture is, of course, this beautiful drift. The last of the three mobile miners was the Taisei MM130R. Some sum-mary data on these three machines is outlined in Table 1.

Some observations from these machinesGiven the conditions, the Pasminco machine was very

successful. Performance measured in meters/month was handicapped by basically two circumstances. First, was an experimental machine, it was the one that always had to stand back when there was risk of interference with im-portant mining operations. Therefore, average standstill delays accounted for 47 percent of total available time.

And there was the exceptionally hard rock, with a UCS that approached 300 MPa (45 kips) in many places. The cutters became a long Golgotha walk for the machine and everything known was tried to improve the situation. Actual boring time reached an average 23 percent of total time with cutter changes and related issues accounting for 17 percent of total time. Adding the above three percentages 47, 23 and 17 (87 percent), it was realized that little time was lost for other reasons. But, of course, being a prototype, several small and a few large breakdowns were reported. Also, other operational problems occurred, such as the machine not being able to clean the invert perfectly, so it started to climb itself on the muck left behind.

There was one fundamental problem with the machine. A good stable classical TBM maintains the kerfs for the cutters in neat rings on the face. Simplified, all of the energy applied to the machine goes into making fine powder of the rock in these kerfs. But all the rock in between the cutter kerfs falls out free of charge. A narrow cutter and a large spacing will, before other factors are taken into account, give an improved result. The mobile miner does not follow in its own kerfs. In essence, it mills the whole face into fine dust and gets nothing for free because of its sweeping mode of operation. This observation is supported by a very high reported specific power consumption reported in kWh/m3 for this machine compared to a TBM in similar rock. Obviously, this will influence cutter wear as well. Here, it is clear that cutter consumption was many times higher per m3 of rock than for a conventional TBM. Add to this the applied power to each cutter was on average almost three

Mt. Isa Pasminco Taisei MM 120 MM 130 MM 130 (ranging)Tunnel height (m) 3.7 fixed 4.1 fixed 6.1-8.1Tunnel width (m) 4.9-7 5.5-7.9 9.0-12Cutterhead diameter (m) 3.7 4.1 4.1Cutterhead power (kW) 300 500 500Cutterhead speed (RPM) 12.7 15 15Number of cutters 20 18 18Load per cutter 35 23 23Stroke length (m) 0.75 0.75 0.75Best consistent performance 0.15 m/h 83 m/ month 0.5 m/h

Table 1

Data on MM120 and MM 130 machines.

Fig 6

Drift cut by MM130 at Pasminco Mine, circa 1993.

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times higher than on a TBM, due to the fact that very few cutters at any given moment were in contact with the rock. It was clear that the cutters would become a problem. Rio Tinto´s requirements

Rio Tinto, facing the challenge of going underground with block caves (less than 100 kt/d or 110,000 stpd), is fo-cused on advancing tunnel construction systems for safety and development rate. Due to the massive developments needed for starting up a block caving operation, the old expression “need for speed” is particularly well placed. For the latter reason, Rio Tinto and Atlas Copco have several ongoing discussions and projects to speed up tunneling in traditional drill-and-blast operations.

Additionally, Rio Tinto decided to seriously develop a step-change program in rapid mine construction that would look at technologies, concepts and systems that could double or more tunneling and shaft sinking speeds in Rio Tinto mining operations of the future. This included a fresh look at mechanical excavation since the conditions and requirements for underground copper operations are different to those that previous machines, such as the mobile miner, had been designed for. Having a continuous excava-tion process that can eliminate explosives, blast gases and scaling of loose ground should increase worker safety by eliminating risks with a process change. The other positive aspect is the dramatic increase in development rate that is possible versus drill-and-blast. The key reason behind this advantage is that ground support can be installed in parallel with rock excavation. The net result of these two factors is that Rio Tinto will have the ability to make mine

construction safer and also reduce the time for constructionSeveral companies were invited to bring ideas and to

work with Rio Tinto during a concept development stage. After a comprehensive analysis and selection process, two tunneling concepts and one shaft-sinking concept were selected for further detail engineering. One of the selected tunneling machines was the Atlas Copco modular mobile mining (MMM) machine. The MMM machine is based on all Atlas Copco’s previous experience with the MMM.

To comply with Rio Tinto’s demands, some compro-mises were needed from the true versatility of the original MM concept. The new machine is much bigger and more powerful than the mobile miner. On the other hand, it is not so flexible in changing tunnel widths or negotiating narrow turns. Instead, the machine is based on modules so that, even if not used during one tunnel, components can be added, or changed, to adapt the vehicle to new challenges in the same mine or another mine entirely.

What properties is Rio Tinto looking for to be mastered by the Atlas Copco mobile miner machine?

Two versions of the Atlas Copco mobile miner machine technology were envisioned. The access and the footprint versions of the Atlas Copco MMM machine share a ma-jority of key technologies and systems. Therefore, it was possible to conduct a performance confirmation test using a full-scale version of the access machine that would mitigate the technical risks for the footprint version. In terms of the access tunnels, it is ideal to have a flat invert, straight or slightly curved sidewalls and a “Roman” arched roof. The dimensions can vary, larger and smaller, than the base machine that would be 5.5-m- (18-ft-) wide with a height (center) of 5.5 m (18 ft). Curve radius is less than 90 m (295 ft) preferably down to 30 m (98 ft). Slope should be +/- 15°. Rock conditions are expected to range from 40 MPa up to 150 MPa (in different mines). Fault and other difficult zones expected from 0-5 percent of the overall length.

The machine must have the means to handle extraor-dinarily bad rock by installing rock support at face, and for all other types of rock continuous systematic bolting and shotcrete (two layers), most of which is to be applied between 1 and 10 m (3.3 and 33 ft) from the face. The

Fig 8

Cutting profile using three bottom cuts, plus five top cuts.

Fig 9

Cutting profile using three bottom cuts and three top, out of which two have revolving heads.

Fig 7

Robbins MM130 destined for Taisei, circa 1993.

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machine will be self-propelled and self-supporting with everything onboard except muck trucking from the rear of the machine. Under these conditions the machine will perform on average 8 to 12 m/d (26 to 39 ft/d) of advance. High in situ stresses as well as high rock temperatures are expected in some applications.

The Atlas Copco mobile miner machineThe approach for the Atlas Copco proposal was to reuse

the working principles of the previous mobile miners as much as possible. It was clear from the beginning that the machine must operate in a mode where the cutters follow their own tracks (significant difference to mobile miners). So, instead of swinging the cutterhead sideways when work-ing the cutterhead, it must be advanced straight or almost straight forward. This is a partial face machine (only a por-tion of face is excavated at one time). This means that the head has to be retracted out of the rock and then moved sideways or vertical in the air and then sumped forward again to cover the entire drift face. In order to reduce the lost time for this necessary repositioning, the machine should have a longer stroke than the mobile miner.

The second issue that needed to be addressed was muck collection in front of the machine. Roadheader aprons with collector wheels/arm and chain conveyors are not free from problems, but were regarded as the more suitable answer than the previous mobile miner solution.

The third issue was related to the extensive rock rein-forcements called for in the Rio Tinto requirements. The machine had to be stretched length-wise in order to provide enough room for rock bolting and shotcrete equipment. The rock support must be installed simultaneously with the rock boring. Finally, the expected performance is to reach an average advanced rate of 240 to 360 m/month (790 to 1,200 ft/m) versus the MM130 Pasminco machine’s best month of 83 m (272 ft). For these reasons, more power, more cutters and a much heavier machine for stability reasons was needed.

It can be said that the design of a machine of this na-ture always starts with the cutters and cutterhead. Using proven cutter technology, the size and numbers needed will be determined rather quickly. That, in turn, leads to a cutterhead size. Tunnel shape and cutterhead width and diameter will define how many of these repeated part cuts

need to be done to complete the face. If 3.5 cuts are needed to make full width, it means four cuts. Iterating this a few times the basic cutterhead size, power, speed and number were established. The machine will, in normal operation, cut the lower cuts at full depth and width. Then the whole center part of the machine will be lifted (still horizontal, not tilted) and three or five top cuts will be done, each with much less cut volume than the bottom three. Actually two of them are more “polishing” type cuts to generate the desired arch. Examples of profiles are illustrated in Fig. 8 and 9.

This type of cutterhead has pros and cons versus a TBM. A weakness is that only maximum half of the cutters are active at the same time and, in the top cuts, much less. But there are some strong points as well. All these cutters travel with the same speed, not like a TBM where the center cut-ters run slow and vice versa. Another strong point is that on this drum, there is room for two cutters per kerf. On a TBM, this is not true for the positions near the center and that will define the rate of penetration (ROP) per revolu-tion for the whole machine. In all, 56 cutters (two cutters mounted in 26 positions) are installed, placed in classical TBM manner with angled gage cutters and “center” but with a slight difference in the meaning of center. The cut-terhead will have a diameter of 4.5 m (15 ft) and a cutting width of 1.8 m (6 ft). Having such a wide head provided the opportunity to mount all needed motors and gearboxes inside the head, which avoided the complex angled drive line of the mobile miner. At the same time, power has now been increased from the old machines 300 to 500 kW (403 to 670 hp) to 1,260 kW (1,690 hp). The drive system is based on VSD technique and the speed can be altered from 0-15 rpm in both directions.

Atlas Copco is using a fairly advanced statistical model of the cutter loads. The model is based on extensive mea-surements determined from individual cutter positions on TBMs. In the model, each cutter presents a load as function of time (reference to pink noise). This is math-ematically explained with the help of rain flow statistics transformed into a total cutter head load in all directions (time and frequency). The design criteria used thereafter is based on an average plus a suitable number of added σ (variance). Using this method, safety factors can be kept at a low number. This does not lead to a lighter machine, but instead a heavier one.

The basic concept can now be described by Fig. 10.To the left, the cutterhead is mounted in a fork. This

Fig 10

Cross section of cutter head.

Fig 11

3D functional view of Atlas Copco mobile miner machine.

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Summary data - access version of Atlas Copco MMM (all numbers are preliminary)

Atlas Copco MMM Access Version paratmeter Atlas Copco MMM Comments mining tunneling machine Tunnel width (m) 5.3-6.3 Without change of modules.Tunnel height (m) 5,25-6.1 Can be increased by spacers.Horizontal curve radius (m) 70 /30 30 with increased tunnel width.Slope (degrees) +/-15 Cutterhead size (m) 4.5x 1.8 (Diameter x width)Cutters number and size (in) 2 x 28 x 17” Installed power (kVA) 2500 (6/10/16 kV)Cutterhead power (kW) 1,260 at 12 RPM Cutterhead speed (RPM) 0-15 , both directions Forward thrust static (kN/lbf) 3,500 / 780 000 Load per cutter (kN) 183 -270 Machine weight (ton) 350 Complete machine with backup (ton) 675

fork can be moved along the curved front plate +/-15°. This movement is normally done under no load and then the fork is locked in position, for the left, right or center cut. The whole yellow part, the main body with internal torque tube can within the gray gripper frames is lifted horizontally 1.5 m (5 ft) for the upper cuts. The advance for each part cut is a stroke of 1.75 m (5.75 ft) achieved by cylinders inside the yellow square tube forcing the bent front plate forward. In the side cuts, the cutterhead will, thus, advance with a small skewed angle, but always in line with the tunnel. After all of the six or eight cuts, the whole machine with a trailing backup system will move forward for next set of strokes.

The machine is modular and, as such, can use spacers beneath the grippers to handle larger tunnels. Also, the front plate can be adopted for different maxi or mini tunnel widths. In any case, this machine cannot cut a lower profile then 4.5 m (15 ft) since that is the size of the head. However, larger and smaller machines can be designed using similar components. Other modules that can be added are a cut-terhead revolving unit that can tilt the head sideways +/- 30° and also an articulation that can be fitted between the front and rear grippers. These aspects enable this technology to ideally cover all present and future requirements of access and footprint excavation of horizontal infrastructure.

Backup systemThe backup system was developed with close coopera-

tion between Rowa, Rio Tinto and Atlas Copco. It should be regarded as a full TBM backup with all such facilities. It is crawler based, with individually steerable crawlers mak-ing it possible to negotiate narrow curves when boring and when backing out for repositioning to a new face. Muck is collected in front of the machine and transported to the rear of the backup with several conveyors. The muck can then be delivered to mine trucks or possibly into extendable conveyor systems. The backup hosts a 2,500 kVA system for the MMM’s VSD and hydraulic systems, shotcrete pumps, compressors, ventilation fans and dust suction fans. Mate-rial transportation of bolts, wire mesh, spares and cutters

is provided all the way from the rear to the final destination. Due to the expected hot ambient temperatures that will be encountered, the backup has extensive built in heat exchang-ers for water, lube oil and hydraulic oil. In the rear end, there exist drums for trailing cable, water hose and further ventilation duct storage.

Apart from the normally re-tracted “emergency” bolting and shotcrete boom in front of cutter wheel, the first set of bolts and shotcrete is applied as soon as pos-sible after first gripper system (Fig. 11). The machine has two remote controlled bolt feeds. In a third ad-ditional bolting station, application of shotcrete and wire mesh can be completed. Each of these stations is separated from the other with a dust wall. The machine includes the latest technology for emergency refuge chamber and dust filtration system.

Performance Rio Tinto and Atlas Copco estimate the average perfor-

mance of this technology will be between 10 to 16 m/d (33 to 52 ft/d). This is based on a combination of conventional cutter performance from RBM’s and TBM’s combined with the results of a detailed discrete event simulation. The simulation individual process steps of this machine, along with supporting equipment, includes allowances for probe hole drilling, extending services, truck and transmixer movements and all ground support activities. As rock cut-ting rates change with different rock conditions, the critical path (rate limiting activity) will change in the process. As an example, a typical cycle in 150 MPa rock for a full ad-vance of 1.75 m (5.7 ft), inclusive of rock support, will take 2 hours 45 minutes. This corresponds to 0.64 m/h (2.1 ft/hour) instantaneous rate of penetration. When considering factors that delay cutting and ground support activities, such as planned and unplanned downtime, maintenance, services and trucking delays, an advance rate of 12 m/d (39 ft/d) is predicted. It is important to note that, in weaker rock, the advance rate speed will be increase significantly. Since rock support is installed concurrently with rock excavation, reaching advance rates of around 16 m/day (52 ft/d) will be possible, with the time required for rock support being the process limiting task (critical path). n

AcknowledgmentsThis project has only been possible due to the support

and vision of Rio Tinto and Atlas Copco executive and management teams. The technical work presented here is the result of a large collaborative global team that consists of members from Atlas Copco, Rio Tinto Innovation, Rio Tinto Copper Projects and external consultants. The effort of many is greatly appreciated.

ReferencesSales material and internal documentation from TRC and Atlas Copco 1960 -1999.Principal Arrangement of Access Version of Atlas Copco MMM Machine and Back-up System.

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New Tunnel Boring Machine