Shani Wallis. Matching the machine to the task // Tunnels & Tunnelling. July, 1983, Vol 15, No 7

MATCHING THE MACHINE TO THE TASK

To spend more money and guarantee the very best tunnel driven on time or spend less money and hope for the best— that is the question. The engineer must arrive at a compromise too and Voest-Alpine, the Austrian road-header manufacturer, puts for¬ward a strong case for using a roadheader wherever possible.

Choosing an excavation method to drive a tunnel is an exercise in finding a balance between ability to do the job on one end of the see-saw arid the final cost on the other. The ingredients which tip the scale, be they fixed (the dimensions and location of the tunnel, the geology and ground conditions), or flexible (time and labour), will always be in conflict and only a compromise on price will keep the balance.

The Austrian manufacturer, Voest-Alpine, has been producing and develop¬ing electrically driven, hydraulically operated roadheaders at its Zeltweg works since 1965, starting with the F6-A, a light weight machine still used in countries of the Third World. The range now includes the AM 100, the largest, the AM75 and the popular AM50 introduced in 1970. Over 500 AM50s have been produced and are now working in all parts of the world.

For ease of transport, the roadheaders are made up of eight components: boom and cutter head, turret, loader with two gathering arms, chain conveyor, crawler assembly and frame, electrical system, hydraulic system and rear clamp unit. They all feature the twin cutter head which rotates on the horizontal axis as opposed to the conical type cutter. This increases the applied pressure/pick and ensures that rock fragments are directed down towards the gathering apron. The long low chassis absorbs vibrations and provides a working platform on which rock bolting devices or arch erectors can be assembled. A conveying back-up system can also be attached to the rear.

Of all the roadheaders produced by Voest-Alpine, about 70% are working in the mining industry and 30% on civil construction projects. The AM50 is most frequently used for tunnelling as its cutting cross section of up to 18.1m2, (or 20.3m2 with turret and cutter boom extensions), is most applicable for both pilot tunnels or final outside diameters. They work most economically in rock with compressive strengths of up to 80MPa. Only one operator and one assistant are required to work the machine and back-up personnel require¬ments depend on the mucking out system used.

Recently, Tunnels & Tunnelling visited two sites where an AM50 roadheader was in operation. The Tanzenberg road tunnel project in Austria and the Hesslach road tunnel project in Stuttgart, West Germany.

In the Tanzenberg tunnel, which forms part of the Mur-Murz Express Roadway, the Austrian consortium Rellei/TBG/ Universale is using an AM50 to drive four ventilation and escape route connecting tunnels between the two parallel main road tunnels.

Drill + blast, which is being used to drive the main tubes, could not be used to drive the cross tunnels for fear of cracking or damaging the concrete lining of the first tube which was completed early in 1982. The AM50 with a swivel belt conveyor was hired from Voest Alpine to do the job.

The geology in this area consists of gneiss, quarzite, marble and amphibolite mixed with different types of schists. The average compressive strength is about 50MPa with peaks of 100MPa plus. The first two 65m long cross tunnels were com¬pleted successfully and achieved cutting averages of 15 bank mVh and a pick wear of 0.2 to 0.3 picks/m3, which was expected. However, the compressive strengths of the amphibolite andquartzite encountered in the third and fourth drives was around 150MPa making it too hard and abrasive for economical use of the roadheader. The pick wear was averaging 1.5/m3. The third tunnel advanced 1m and the fourth 3m before it was decided that the roadheader must be withdrawn.

In the Hesslach project in Stuttgart, the Strabag/Baresel/Sanger & Lanninger joint venture is using an AM50 to drive a 2.2km X 12m2 horseshoe shaped pilot tunnel which will be enlarged to a 60m2 two lane road tunnel. The AM50 began tunnelling in February 1980 and has completed 2km passing through areas of marl, sandstone, claystone, gypsum, anhydrite and recent backfill material. As a result the whole excavating system consisting of the AM50, the railbound conveying system with Haggliind loading cars and the support system, be it reinforced shotcrete, roof bolts or forepiling with steel arches, had to be adapted constantly to the changing conditions.

In sections of the tunnel consisting of gypsum which had a compressive strength of 50M Pa, an average rate of 6 to 7m/22h (twoX llh shifts/day) was achieved with one machine operator and six assistants/ shift. Pick wear averaged five picks/12m3.

When Tunnels & Tunnelling visited, the machine was in the last 100m of the drive. The ground had deteriorated as expected and some 0.5 to 1.5 litres of water/s were seeping into the face. The ground was too wet and weak for excavation with the roadheader. Work is now continuing by hand methods with the machine remaining in place to remove the muck via the gathering apron and conveyor. Better ground is expected to reappear after the next 20m and progress rates will improve.

Herr Rathei, the project manager, told Tunnels & Tunnelling during the visit that maintenance for the two years had cost DM40000, which was expected and reasonable. He is also pleased with the cutting rates, although the machine could have cut more if the mucking out facilities were more efficient. "The back-up was lacking so I have been restricted to the l00mV22h capacity of the mucking out system", he said.

When asked about the machine itself, Herr Rathei confessed: "I would have liked a telescopic boom on the road-header to give it a longer reach before having to move the machine forward and a deeper undercutting facility." The machine can undercut the floor by 500mm below the apron at present, making the need to incorporate a down grade in softer ground, as in the later part of this particular tunnel, inconvenient. Usually the rear hydraulic clamp is engaged to realign the machine but in soft ground this clamp has little to push against. Therefore it is reversed to an area of good ground to be manoeuvred, the grade then being corrected at the next stage, in this case benching to a larger o.d. or in the final lining.

"But on the whole I am very pleased with the performance of the AM50 so far and the service given by Voest-Alpine has been very impressive. I expect to hole through as planned by the end of May I983," Herr Rathei concluded. Given the statistics and the performance to date, the roadheader has proved the most economic method of driving this tunnel.

As a manufacturer and supplier of roadheaders, Voest-Alpine has adopted a comprehensive customer service policy. Dr Gehring, head of the tunnelling department of Voest-Alpine Zeltweg works, explained this policy to Tunnels & Tunnelling: "The life expectancy of an AM50 is approximately 8 to 10 years, but we place great importance on service and operator training. We also believe that potential users of an AM roadheader must be provided with all necessary figures for calculating performance and consumption of the machine in the rock being encountered or expected on a proposed project," he said. To achieve this, Voest-Alpine established its own rock testing laboratory and developed specific testing methods to judge cuttability and abrasivity of different types of rock. These methods as well as standard tests of mechanical behaviour and investigation of petrography help Voest-Alpine give the best service to anyone interested in installing an AM roadheader.

Alpine Miners are operating world wide and were used on the Paris and Marseille Metros in France, the Melbourne Under¬ground in Australia and are at present working on a sewer in Paris, subway systems in Pusan, Lisbon and Prague, hydro power schemes in Algeria, Fiji Islands and Romania, drinking water tunnels in Madeira and road tunnels in Spain, Italy, West Germany and Austria as well as enlarging the cross section of the Aumal rail tunnel in Switzerland.