Adding capacity to the over-tasked wastewater system in Mexico City, an alignment through changing ground conditions is a likely candidate for Robbins’ Crossover TBM, Nicole Robinson reports.In the mountains northwest of Mexico City, the soft rock is self-supporting and very consolidated, a dream to mine. "Even the face is self-supporting," says Roberto Gonzalez, Robbins' general manager in Mexico. "You could use a normal backhoe and excavate like that. It's a beautiful ground to bore."But the alignment crosses valleys of tuff, faults and finishes with a stretch of soft ground with low cover. This is the scenario for Túnel Emisor Poniente II (TEP II), or the English translation of West Drainage Tunnel II.Conagua, Mexico's national water commission, is building the 5.9km-long tunnel with a 7m i.d. to reduce flooding in the area, and increase wastewater capacity. Across three municipalities, some 2.1 million people will benefit from the tunnel project.The contractor joint venture of Aldesa, Proacon and Recsa chose an 8.7m diameter, dual-mode type machine capable of "crossing over" between rock and EPB. With the August 2015 tunnel boring machine (TBM) launch on TEP II, manufacturer Robbins has supplied its first Crossover machine in Mexico.End gameRobbins draws comparisons to the Kargi Kizilirmak hydroelectric project in Central Turkey. The design of the TEP II machine was based largely on experience from past projects, and that TBM in particular. While initial reports on the Turkey project showed fractured hard rock, Robbins explains, within 80m of launch the geology became substantially more difficult than expected, consisting of blocky rock, sand, clays and water-bearing zones. The machine required multiple bypass tunnels and major modifications before it could resume excavation.Robbins says these modifications proved instrumental to the design of its Crossover TBMs, including the TEP II machine.In Mexico, the contractor JV expects to convert the machine from hard rock to EPB mode due to changing ground conditions in the last kilometre of the alignment. "Initially the proposal was a hard rock machine but they found they have 800m of water-more EPM conditions-that's the reason we proposed a Crossover," explains Javier Alcala, job site engineer for Robbins on TEP II.The ground conditions at TEP II are complex, from competent to weathered volcanic rock to clay, and sand. The final 800m is also the portion of the alignment with the lowest cover, some 12m, and the most populated. This is one of the reasons for using a Crossover machine. The rest of the drive has between 50-60m of cover on average with some stretches up to 150m."We try not to convert unless it's completely necessary because you stop, you have to drain the screw conveyor inside the machine, and you have to make a lot of changes, for example on the cutterhead," Robbins' Gonzalez explains.As an open mode machine boring in rock, the TBM is equipped in the event of entering running ground, he says. "These closure doors are able to maintain the material in the cutting chamber. They're just a safety." In smaller valleys of tuff there is potentially some water, but it's unknown for now, he explains."For these cases we believe that these closure doors will be held to see what we have to do with the material, if we have to consolidate in the front."Tight fitAldesa's Castillo says one of the biggest accomplishments on the project so far has been organising the logistics in such a small work space-fewer than 10,000 sq m. The JV excavated a 30m deep launch shaft supported by 800mm-thick Milan walls (slurry walls), and used on-site first time assembly, he says, to start excavation as soon as possible.Once assembled by gantry crane, the machine bored 100m before adding back gantries. When completely assembled the machine has nine gantries for a total length of 1,030m.At the time Tunnels & Tunnelling visited the project, the crews were still adjusting to having the full machine in operation, and had only recently started using the continuous conveyors for muck.The TBM was mining through a transition zone between tuffs and dacites, and had excavated 435m by mid November 2015. At the time of publication the TBM has bored 1,417.5m, which equates to 945 rings. The best day has seen an advancement of 42.8m and the best week is 185.1m. Robbins' Mexico office reports the TBM has reached softer geology and is boring very well.Tunnelling is expected to finish within this year and a second lining of reinforced concrete will be installed following excavation to extend the life of the tunnel. "Once we arrive to the final bit, it's a very close curve of 400m radius," Alcala explains.The tunnel alignment ends along the rivers of San Javier and Xochimanga in Atizapan de Zaragoza.
Metro projects and hydropower schemes continue to drive India’s tunnelling market, and more opportunities are yet to come but challenges remain in the competitive market, Bernadette Ballantyne reports.Until the turn of the new millennium, India's tunnelling market was dominated by hydropower and irrigation tunnels, many of which meant drilling into the challenging geology of the Himalayas. "These are the toughest ground conditions in the world, closely followed by the Andes and then the Alps," says Manoj Verman, president of the Indian National Group of the International Society for Rock Mechanics (ISRM) and an independent consultant on tunnelling and rock mechanics. "The geology is very varied.It is not uncommon to encounter weak zones, shear zones, fault zones and water in the same path," he says noting that the high overburden stresses from the mountain can also cause problems. Combined with the inaccessible nature of some of the locations and the climatic extremes that include snow and flash flooding, working conditions are inhospitable at best and impossible at worst. It is clear to see why projects here are so challenging.Early TBM hurdlesDealing with the hard and changeable Himalayan rock has traditionally been a drill and blast affair, but the use of tunnel boring machine (TBM) appears to be gaining momentum despite an inauspicious start. "In mountainous regions TBMs have been used and the first three projects were a disaster," says Verman. "There is frequently changing geology and if a TBM goes fast it can get stuck and that is a nightmare. If the height of the mountain is very high it stresses too much and if the rock is soft then it squeezes, under the same height of overburden if the rock is strong then it will burst so these two are extreme cases and they both happen under high stress."An early example of a stranded TBM was on the Dul Hasti hydropower project in the Kishtwar district of Jammu and Kashmir, which began preliminary construction in 1985 and became operational in 2007. Shear zones regularly crossed the 9.64km head race tunnel alignment and water seepage was high leading to tunnel roof collapses that eventually buried the TBM, leaving it beyond salvation.Better progressHowever there have been some more positive breakthroughs. In June 2014 contractor and TBM manufacturer Seli announced that it had completed 14.7km of tunnelling on the Kishanganga hydropower project in Kashmir, mainly for construction of the 12km headrace tunnel. Revealing average rates of over 400m per month and a maximum of 816m in a single month, the scheme has been widely recognised as a huge breakthrough for mechanised tunnelling in the Himalayas. "This tunnel was a tremendous success," says Verman pointing to other forthcoming schemes that are planning to use TBMs. Client THDC India has appointed Hindustan Construction Company (HCC) to use a TBM for delivery of a 10m diameter, 12km long head race tunnel for the 444MW Vishnugad-Pilpakoti hydropower scheme in Chamoli in the state of Uttarakhand. The TBM is scheduled for delivery and assembly on site in February 2016.Long awaited success in the mountains combined with a huge demand for TBMs to build a growing number of city wide metro schemes, means that TBM manufacturers are upbeat about the prospects. TBM manufacturer Robbins established its Indian subsidiary in New Delhi in 2005."We started by supplying 10m double shield TBMs to contractors for an irrigation water supply tunnel which is 43km long. It would be the world's longest tunnel without intermediate access once completed," says Kapil Bhati, general manager for Robbins India, noting that the company's 10m-diameter machines are the largest in operation in India today. "The tunnel will take the water from a river and then over to a drought affected areas irrigating 500,000 hectares of land and further providing drinking water. We have completed around 25km as of now with two TBMs. We are still continuing and expected to complete 2.5 years from now," he says.Of course such a huge job has not been without its challenges and although boring of the outlet began in 2007 access to the inlet end was not available until 2011 due to land acquisition issues."After that advancements were pretty good even with geology being more difficult than anticipated. We are still doing around 300m/month average on each side of the tunnel so the production average is good in spite of the hard rock and tough geology," says Bhati.Another water tunnel transferring flows from the same river, is also underway using a third Robbins 10m-diameter machine. The tunnel is half way through with three years to go, says Bhati. A fourth 10m-diameter machine is also building a 12km water transfer tunnel.Metro growthAs these schemes roll on, Robbins has also been busy supplying and supporting machines for metros in India's bustling cities. "Soon after the irrigation tunnels the metro projects started," says Bhati and the company began by supplying machines to Delhi and then Chennai. "Delhi Metro was totally soft ground so we supplied a spoke type of earth pressure balance (EPB) machine. Those machines performed very well and had very good advance rates."The geology of Chennai is mainly soft but there are a couple of areas where there is rock or mixed ground and then we have supplied a mixed face EPB machine for that geology," he says."The result has been a more challenging bore in Chennai with rock at the bottom and soft ground at the top combined with ingress of water. Cutter changes and interventions were challenging but we have still been successful. There are around 200m left to bore."In Jaipur which is currently building the first phase of its metro starting with a 12km east-west connection, 2.8km of which are underground, the company met with soft ground. "The contractor had two old Robbins machines in stock so we refurbished those machines for the contractor and those are being used. The main challenge here is the heritage structures over the top. It is an old city," he says noting that in the areas where the metro transitions from elevated to underground there is just 5m of cover and yet the marginal tolerance is just 1mm.Tip of the icebergThese are just the tip of the metro iceberg. "Right now there are metros being built in New Delhi, Chennai, Calcutta and Bangalore. Elevated and underground both," says Sanjib Bhattacharya, chief of TBM tunnelling at ITD Cementation India, which is comprised of Italian Thai Development Public Company Limited with the Indian branch of the UK's Cementation. In his 22 years with the company Bhattacharya has delivered 50km of traditional tunnelling with NATM and 21km of TBM routes. "We just completed 7km of TBM tunnelling in Delhi. I was the project manager and out of 7km there were four EPB TBMs, two mixed shield and two soil all from Herrenknecht. In Delhi out of 36 machines, some 19 were Herrenknecht," he says. The Delhi metro is now undertaking its third phase of construction which will result in a further 160km of new lines 54km of which are underground. At its peak in mid-2014 there were 26 TBMs working simultaneously. The tunnelling is over 80% complete as Tunnels and Tunnelling goes to press and has not been without its challenges. Bhattacharya says that one particularly tough section was a 1.25km drive that ran beneath Delhi airport's runway for a distance of 400m meaning that the contractor was not able to carry out geotechnical investigations."This was very unpredictable because the geological data was not there. We designed our machine cutterheads and cutting tools on the basis of available geological parameters. It was around rock, we encountered quartzitic rock of around 200-210Mpa. Very, very hard. So in accordance with that we designed our machine to 250MPa. But unfortunately when we entered the airport area where the survey was not possible we encountered 350MPA," says Bhattacharya. As a result the construction costs ballooned from USD 14 to USD 15 per metre to around USD 35 as the hard rock quickly ate up the cutters. "It was a huge cost and meant that we were only getting four or five metres per day."As a result progress on this section was two to three months behind schedule, says Bhattacharya, however he points out that better progress on another drive where they avoided the rock and used the soil EPB machine made back the time.Despite having taken cores every 50m the nature of the airport site prevented investigation in this area and Bhattacharya says that the client accepted this when the contractor made a claim for the additional costs. "In India contracts are very rigid. 400m survey was not possible so we put a claim in and this was (logically) accepted by DMRC as the data couldn't be got in advance."Critical geological dataAs this experience shows, obtaining geological data is critical for any tunnelling project and is an area where Verman says that clients themselves need to put in more effort in the planning stages if they want to see their projects succeed. "The biggest lesson I would offer clients is 'please investigate more'. What is absolutely lacking in the country is proper site investigation or geotechnical investigation before the project," he says pointing to a World Bank study which he led five years ago which reached the same conclusion. "In state of the art projects 3–5% of cost is spent on investigations but in India it is not even 0.5%. People always say they have had geological surprises. They are surprises because they are not investigating. That is the biggest lesson that should be learned.""I fully agree," says Bhati. "There is hardly any sufficient data available before the tendering process commences. We understand regarding areas which have the limitations like Himalayas wherein the cover above the TBM is as high as 1 to 2km. On the other hand, water transfer tunnel projects or metro projects have the accessibility of lands which clients want to cut short by not providing the proper information or doing proper geographical mapping which results in the award of the tender to the contractor as it is," he says."The contractor in turn has to gather that information by himself which takes time therefore delaying the project and losing more time. Better and earlier information on geological details allows the manufacturers to design the machines and give them provisions to equip the machine to encounter all the problems in front."One of the side effects of this is that projects are less attractive to international contractors who are not prepared to take the risks pushed onto the contractors under the design and build arrangements. "For the time being, due to aggressive local competition and actual contract versions comprising unacceptable risks for the contractor, we refrain from tendering for tunnel projects in India," a spokesperson for contractor Strabag says.Yet ironically clients are demanding that international firms participate in main contracts. "Indian clients are putting a condition [in place] that the tunnelling manager must be an expert from outside of India," says Bhattacharya who says that the international financing provided to the metros also pushes for European consultants to be involved."It is true that they have more experience than us but the fact is that we are building experience. I have a team now running four TBMs simultaneously and now I am looking at Mumbai and Kolkata. We have the resources. Only problem is that the Indian companies don't have the technical credentials so they can't pass the technical bids so that is why we are making JVs."However he says that this is changing and that for smaller bores of 1-2km Indian contractors are wining projects without international partners. Another advantage that local firms have is their proximity to clients and their long term market positions which mean that local companies are more willing to accept delayed payments through claims. International firms however see this as too risky.One way of reducing risk, says Bhati is to have the TBM manufacturer support the project through its life, not just at the beginning. "Most of the time delays are because manufacturers are not supporting the project and the contractor is not capable of coping with the difficult geology. On most of the jobs what we are doing we are supporting them on execution on a per metre basis," he says.This strategy has been particularly important to the Bangalore metro for which delays have been widely reported in the local media. Mumbai Metro Line three"On Mumbai Metro there are seven packages and we got package four," says Bhattacharya whose firm ITD Cementation are in joint venture with Continental Engineering Corporation of Taiwan and Tata Projects. Financial bids were opened in October and Tunnels and Tunnelling International understands that the client Mumbai Metro Railway Corporation is currently scrutinising the project budget which is lower than the forecast costs. One of the major issues which will be faced in the execution of metro tunnels in Mumbai city will certainly be the rock strata which will push up the tunnelling costs. The entire 32.5km line is underground."Geological survey suggests 90% rock which will vary from 50 to 150MPa," says Bhati who has first-hand knowledge.Contracts for this line are yet to be signed . Other MetrosMumbai may be the next major project set for award but there are many more on the horizon. "Phase four of Delhi is coming with 90km of tunnelling. Bangalore phase one is about to complete and phase two is coming next year. Chennai phase three coming next year. Kolkata has another two underground packages coming," says Bhattacharya also pointing to forthcoming schemes in Lucknow in Uttar Pradesh, Hyderabad and Puna."The market is very promising perhaps one of the best in the world at this time, says Verman. "Now is the time that the country has to start moving into delivering infrastructure in difficult areas. Many projects are already sanctioned but procedures are such that they are not tumbling out in the way that we expected. However remain very optimistic. I am expecting 2016 to be a crowded year."Data from the Timetric Construction Intelligence Center places the value of work underway with a tunnelling element at USD 31bn however given the scale of projects planned — Verman says there are 3,000km of tunnels in the pipeline, the figure seems likely to rise substantially over the next five years."I was involved in planning a railway through the Himalayas from Rishikesh to Karnaprayag, 125km long alignment of which 105km is in tunnels so that is the kind of project you are looking at and for this kind of distance you have to use TBMs, especially for the longer tunnels," he says.Bhati of Robbins points to four main growth areas for the TBM tunnelling market. "We have hydropower projects in the pipeline which we see being awarded in 2016 and a couple of them will be using heavy provision of TBM. Then the metros like Mumbai which will be awarded in the next few months.Bangalore and Chennai are planning phase two. Seeing the success of Delhi, Bangalore and Chennai everyone sees that it is the best solution possible. For the next 10-15 years one city after the other will keep having metros come up," he says.Water transfer tunnels to divert much needed resources is also a priority, as are road tunnels. "These are the future. People have realised that there is limited space available above ground so we have to go under. There is a 22km underground tunnel in Mumbai which is going to come from the southernmost part of the city through the coast to the airport. It is entirely underground and will be about 12m diameter, and has now been approved.”Learning from the pastExpectations are therefore high for India's growing and maturing tunnelling industry, but challenges remain and Verman urges government to learn from the past in terms of better planning and reducing bureaucracy so that contractors are able to get on and deliver. "There are huge projects coming forward and government should support this industry and nurture it because it is in the government's interest that these projects are built.”