A few months ago one of my colleagues and yours truly presented a two day seminar to the Dongah Geological Company of South Korea on Robbins Hard Rock TBMs. The following is our story of the ensuing trip: Fueled by copious amounts of South Korean hospitality known as Soju (for those of you who don’t know Soju or Shōchū is a Japanese distilled beverage. It is usually distilled from barley, sweet potatoes, or rice. Typically, shōchū contains 25% alcohol by volume. It’s weaker than whiskey or standard-strength vodka but stronger than wine and sake. It does actually taste like weak vodka, at least the first one or two do, after that…well you should get the picture!) our agent Mr. Kim in South Korea suggested that we should further develop our relationship with our hosts and provide some on-site practical training for our hosts.
We needed to find a project that would be similar to the potential project in South Korea–similar meaning, similar in purpose, design and diameter. The machines in South Korea we learned could be up to 12m in diameter and possibly larger. Someone, I am not sure who, volunteered the West Qinling project in Gansu Province, China as the project most similar to the ones in South Korea.
Robbins currently has two 10m diameter hard rock main beam type machines in operation there. With the Soju in full effect we all thought this was a great idea and it was decided that West Qinling would be our next port of call. (For more on this project, view our news release and case study).
After a day or two of recovery and not expecting to hear anything more (Soju has that affect on you) there followed a flurry of E-mails, a few phone calls and before you knew it we had arranged a trip to the West Qinling project.
Gansu province is located in the northwest of the People’s Republic of China. It lies between the Tibetan and Huangtu plateaus. The landscape in Gansu is very mountainous in the South and flat in the North. The mountains in the South are part of the Qilian mountain range. At 5,547 meters high, Qilian Shan Mountain is Gansu’s highest elevation. The West Qinling Project is located in the mountainous region to the South. Similar to the great expedition in 1845, it’s only about 500km (310miles) from Chengdu to the jobsite.
I have been to the West Qinling site before; there is no way to get there other than by a four wheel drive vehicle. You have to drive; the nearest airport was severely damaged by the deadly 7.8 earthquake in the region in 2008. On a good day the drive could take 8 hours. Generally it takes at least 10 hours. On my first trip it took over 13 hours. If it rains you can expect landslides and mudslides, it has taken some field service personnel nearly two days to get off the mountain and back to Chengdu. In a weak attempt to dissuade Mr. Kim from actually going ahead with the visit to the jobsite, we tried to paint as black a picture of the journey as we could. No matter what we told him he always replied “Guk-jung-ha-jee-ma!” which in Korean literally means “No worries!” or “Don’t worry!” To which we replied, “But Mr. Kim are you aware that this is the rainy season?” And to that we got the same answer “Guk-jung-ha-jee-ma!”
After meeting and greeting our party of seven guests, accompanied by Mr. Kim from South Korea, at Chengdu Airport on the evening of 12th May we held a briefing on the same evening about the journey and the schedule for the days ahead. Arrangements were made to meet in the hotel lobby the next morning. “Any questions?” I asked. “Guk-jung-ha-jee-ma!” was the now familiar reply.
8am Friday 13th May:
I thought I wasn’t superstitious, but setting off on Friday 13th on a 10-hour journey in the rain to a remote jobsite in the mountains gets you thinking a little. So with Mike (our field service training supervisor), Andy (the Robbins China project manager for the project) and myself in the lead vehicle we set off in convoy, 4 vehicles in total, for West Qinling. Four hours into the journey and lunchtime is approaching. As some of you will be aware meal times are sacred in China–the drivers are getting short tempered and need to stop. We’re driving through Sichuan province and we’re close to the last major town before we hit the mountains and dirt roads.
The majority of food in Sichuan is spicy. The locals love nothing more than Chilies of any and all kinds with their food. We stop at a local restaurant in Baolun, (this is one of the small number of places where you will see few, if any, American style fast food joints, a rarity in itself these days). Andy orders food and leaves instructions ‘not too spicy’ with our smiling waitress. It seems as though something got lost in translation and most of the food is spicy. There are a few newcomers in our group to this part of China and the last thing you need on a long road trip into the mountains is to be looking for restrooms. Even some of the more experienced travelers have been known to get caught out once or twice (myself included).
In the more remote parts of non-Westernized countries or parts of countries that have had limited exposure to Westerners or “lao wai” (foreigners in China) you shouldn’t expect Western style facilities either; a hole in the floor type convenience would be the norm…if you’re lucky.
We set off again after lunch, the first few hours are on black top. Although the road is winding up and over the first mountain range it’s a relatively smooth ride and the views are spectacular. We enter Gansu province around 3:30pm in the afternoon.
Relative to the food we’ve eaten and the roads we’re traveling on, the condition of the digestive system is, in weather related terms, (refer to the Beaufort Scale) around Force 7: ‘High Wind, moderate gale, near gale.’”
Again for those of you who don’t know, The Beaufort Scale (pronounced bou–fart, need I say more) is an empirical measure for describing wind speed based mainly on observed sea conditions (on land it is categorized by the physical effects it has on vegetation and structures). Its full name is the Beaufort Wind Force Scale.
Not long after we’re on the dirt roads, top speed is roughly 20km/h (12mph) about an hour in we stop at a small village, where wind speed for some of the group has increased to force 8 (gale, fresh gale), and all of our guests need a pit stop. We find a ‘restroom’ in a small village, the wind dies down and we set off again.
We pass through an area that has just been cleared of a landslide (see photo below), which had closed the road for 2 days prior to us travelling. If the landslide had not been cleared we would have had a four hour 150km detour to endure.
Unexpectedly the wind starts to increase again, Mike is feeling it the worst, without warning we (he) experiences Force 11 (Violent storm) – we need to stop immediately!
Luckily we’re not far off another camp about 2 hours from our destination. We pull in and Mike calms the storm. There’s a lot of curiosity when we arrive at this camp. It’s not often you see four vehicles in convoy travelling these roads. Add to this the fact that we’re all ‘lao wai’ and pretty soon we’re surrounded by curious onlookers. A bit of ‘Chinglish’ (Chinese English) with the crowd, they hand out cigarettes to those who want them, we have a laugh and joke (‘laugh and joke’ by the way is cockney rhyming slang (slang mainly used in London in the UK) for ‘smoke’, and head on up the mountain.
We arrive at the camp at around 6:30pm, where we’re greeted by our host from MOR18, Mr Wang. Everyone is shown to their rooms. We throw the bags in, wash up and head for a welcome dinner. We’re all weary after the long journey, a few beers take the edge off and the expedition team starts to relax.
Saturday May 14th:
First day of training, we split up into two groups. Mike takes a group for some classroom study, Andy & I with the other group head into the tunnel. First of all we explain some general rules on safety and what to watch out for when we’re in the tunnel. “Any questions?” – same answer: “Guk-jung-ha-jee-ma!”
When we were on site the previous year we were there to assemble, test and commission the machines. Due to bad ground at the start of the tunnel we had to walk the machines some 2.5km from the portal to the starting point of the bored tunnel. Since then the machine we’re visiting has advanced another 4.5km. Average production on the machines is close to 500m per month. Considering the location and the logistical nightmare that this project is, this is an excellent achievement. By anyone’s standards 500m per month on a 10m main beam machine is good going.
These tunnels form part of a massive project that will eventually cut rail transportation times between two major cities in the region from 12 hours to roughly 4 hours.
It takes us an hour on the loco to get to the machine, along the way we see several slip forms that are used by the contractor to complete the final lining of the tunnel. There are two rail tracks all the way to the back of the machine. There are currently nine rail switches at roughly 500m distance throughout the tunnel, and we constantly switch from the left line to the right line as we progress towards the machine to prevent any hold ups to the works.
On this project excavation, preliminary ground support consisting of rock bolts, mesh, ring beams and shotcrete is done at the machine and the final lining using the slip forms is carried out simultaneously in both tunnels. The excavated material is transported out of the tunnel on a continuous conveyor also supplied and installed by us.
We spend the whole morning on the machine and our guests get to see a lot of activities being carried out, ask a lot of good questions and get a good feel for hard rock tunnel boring. We manage to get into the cutterhead and witness a cutter inspection. For most of our guests it is the first time they have seen a hard rock boring machine in action. In South Korea tunnels in hard rock have typically been excavated by drill and blast methods and metro tunnels have been excavated by EPB machines. I think everyone is taken aback by the sheer size of the machine, the heat and noise and the amount of activities being carried out in the tunnel.
We see first-hand the machine boring whilst the crew installs ring beams and mesh and drill for rock bolts. Behind us in the L2 zone shotcreting is ongoing.
Around 1pm we’re out of the tunnel. After a light lunch Mike and I swap teams and once again we head back into the machine with the second group. More questions, more explanations and all in all a productive educational day.
We have two machines on this project that are boring parallel tunnels, we’ve been on the left side machine all day, due to the way the project is organized this is actually the right line machine. This machine is operated by MOR18, our other machine is operated by CRTG. We think it only proper that we visit both machines. Two different contractors, two different ways of working, it’s good for our guests to see & understand that there are many different ways to approach this kind of work.
Saturday evening we get invited to dinner by CRTG, Mr. Dai is our host and knows how to throw a good reception. The food is excellent: Mike and myself demolish a large plate of bull frogs (tastes and looks just like Chicken) our guests however don’t seem too fond of them. They are washed down with Mr. Dai’s special Baijiu. Baijiu is almost the Chinese version of Korean Soju but around 50% stronger. Literally translated Baijiu means ‘white liquor’. For the most part Baijiu is an acquired taste; it kind of percolates out of you for around 3 days after you’ve been drinking it. Mr Dai has a special Baijiu that contains herbs and spices that make it good for the health, or so they say (and who am I to argue). I don’t want to upset our host and join with him in several toasts to the health of our guests — there’s no need for translation this evening. Baijiu is a wonderful translation tool — it’s funny how we can all understand each other so well. Our guests reciprocate with several toasts of their own, we sleep well that night!
Sunday May 15th:
Sunday morning is spent looking around the jobsites as a group. We visit the segment plant (all segments are fabricated on site), the ring beam plant, the wire mesh plant, the cutter workshop and the three batching plants. Three batching plants are needed as the invert segments, the shotcrete and the final lining concrete all require different quantities of sand, cement and aggregates for each application.
We take a look at the continuous conveyor installations and explain to our guests how it all works and ties in with the boring machine.
Sunday afternoon we visit the right side machine (left line), as they have just come off an 800m plus month. We think it’s a record for this size of machine, an outstanding performance.
Later on in the day we’re invited to a question and answer session by the contractors. Our guests get a lot of useful information from them as do we.
We get a weather report for the next few days, not so good, rain is forecast. We need to change plans and decide to make a run for it down the mountain before the rains start. Sunday evening we attend another excellent dinner, this time hosted by Mr. Wang of MOR18. Once again the Baijiu replaces our translators and we communicate in a common language. We need to be cautious though; wind is also forecast for the next morning especially after a large dinner. We don’t need a repeat of our inbound journey!
Monday May 16th
We cannot thank our hosts enough for their hospitality; we have been welcomed with open arms, a great experience for our guests. We set off down the mountain at 7am. Winds are Force 0 – Calm!!
Around 6pm we’re back in Chengdu. A bit of rest and recuperation is in order—a couple of hectic days & hard nights takes its toll on you.
Tuesday May 17th
We pay a visit to one of the workshops in Chengdu. We are currently assembling the 2nd machine for the Chengdu metro project there. It’s an EPB machine and is nearly completely assembled. The shop is impressive and our guests are very interested in the unit. They have a lot of experience with EPB machines and ask a lot of pertinent questions.
Later that morning we stop off at the jobsite and see the sister machine in the workshop being assembled in the pit at site. Most of the back-up is completed, the middle shield is standing up and the site crew are preparing for the arrival of the forward and tail shields.
Monday afternoon is spent taking in all the information from the visit. We have a final question and answer session with our guests and arrange a farewell dinner.
Wednesday morning 5:30am, we put our guests on the bus for the airport. We made it back from the mountains safely and the expedition is over. Mike gets on a plane for the US, Andy flies back to Shanghai; I jump on the high speed train from Chengdu to Chongqing, we have two hard rock single shield machines to build there. The first is about a month away from completion…back to reality, we’re on a tight schedule and there’s work to be done. All of a sudden I get the familiar feeling of a Force 11 (violent storm) coming on, must be something I ate at the farewell dinner. Luckily I’m on the train, there is a decent restroom and the storm is over before we know it. Winds return to Force 0 – Calm!
The Oldest Robbins TBM still in Action? We visit a jobsite in Canada that may be using the World’s Ultimate Workhorse TBM
It’s a long-standing question in the world of tunneling: Which TBM has been operating the longest? What makes it so durable?
In May 2011, I visited the site of the Centennial Parkway Sanitary Sewer Tunnel in Hamilton, Ontario, Canada to find some answers. The rock portion of the tunnel, located in the shale of the Niagara Escarpment, is being bored by a Robbins Main Beam TBM in operation since 1968. The 2.7 m (8.8 ft) diameter machine was first used for a Hydroelectric Tunnel in Tasmania, and is now owned by McNally Construction, who has used it on multiple sewer tunnels in Toronto and Ottawa since 1972.
I arrived at the Centennial Parkway site on a sunny Friday afternoon along with Tunnels & Tunnelling North America editor Nicole Robinson, where we were greeted by McNally Project Sponsor Dave Bax and Field Technician Kenny Baxter.
After giving us some safety instructions, we were handed full rubber suits and boots. “You’re going to need these,” said Kenny. “It’s muddy on the shaft floor, and the material is red. It gets everywhere.” A quick look around the jobsite confirmed his statement—red clay-like material caked nearly everything, from trailers to trucks to boots.
We climbed down a long ladder into the shaft, and were given a tour of the small diameter tunnel. Kenny explained that the ring beams and wooden lagging installed at the tunnel entrance were due to the softer clay material encountered at that point. The rest of the rock portion of tunnel was being supported with rock bolts and steel straps. “The shale material is being recycled to use as brick. The clay was used by a local gun club for berms on their grounds.”
Single track muck cars rolled out as we walked out of the tunnel, carrying more heaps of reddish shale, before they were lifted by a crane and dumped on the surface.
Bax and Kenny mentioned that daily maintenance shifts have helped keep the veteran machine in good working order. Crews regularly check the 12-inch (304 mm) diameter disc cutters, and inspect the cutterhead and critical sub-systems. “We are not expecting a lot of wear. Our estimated completion for this tunnel is about two months,” said Bax. At the time of our Centennial visit, the TBM had advanced 200 m, at 1.8 to 2.1 m (6.0 to 7.0 ft) per hour, with no major issues.
The competent shale rock is certainly also a factor in limiting wear to the machine’s cutterhead and main bearing. Robust core components, including the main beam and gripper system, are key in keeping a TBM running for a long time (43 years, in this case).
Overall, the machine looked to be well equipped for its latest tunnel drive, and though it is impossible to know if it’s the world’s oldest working Robbins machine, it is certainly on the list. If you know of a Robbins machine that’s been operating longer, drop us a line in the comments section. We’d be interested to hear about it, and maybe even visit it!
Being in Field Service can have some interesting moments, particularly when working overseas and in countries where the English language might not be the first language. We are a department of personnel drawn from all over the world, so we each have our own take on English and the way to speak it. Add to this workers who speak a local dialect, and even communicating with each other can be confusing or comical, to say the least. Read below for some lighthearted moments at field service projects around the world.
Field Service personnel often get by with sign language, drawings on the back of cigarette packets (a rarely used device these days as most of us have quit!) and by any means possible to get a point or question across. In some of the more frustrating conversations we resort to shouting the same question, as it would appear we think people can understand English by raising our voices.
On occasion we could be in a scene from a Monty Python Sketch–A reply to the question “Do we have no cutter wedges?” was met with a positive “yes” answer. “So where are they then?”, “We have none.” It’s all very confusing, but the way the question was asked prompted the answer, so “Yes, we have no cutter wedges,” would appear to be correct when taken literally. A few years ago one of our guys (no names mentioned) was trying to explain to the waitress that we wanted one of those fancy Italian Ice Creams for dessert. Imitating holding the ice cream and moving it to his mouth several times didn’t go down too well, with a somewhat embarrassed waitress as I recall, but it was all taken in good humor (we got the ice cream by the way).
Lost in Translation
When we try to get smart and speak the local language the results are even worse…or better depending on your outlook. In Spain while ordering lunch, Macaroni with Tomato Sauce (Maccarones con tomate) came out as ‘Maricones con tomate’, which turned out to be ‘Gays with Tomatoes’…that brought more than a few smiles to the table and a bewildered look to the waiter’s face. We still talk about it to this day.
During a lunchtime chat between three of our guys, two Americans and a Scottish guy, the topic of conversation came around to hunting. The two American guys mentioned that they had been hunting Moose somewhere in the USA a few years back and that they had needed special ammunition for the rifle. “Hunting Moose!” said the Scotsman in his strong dialect, with a confused look on his face, “Where I come from a Moose (dialect for a Mouse) is only 3 inches long!”
A few months ago we were working in China and came across this sign in Shanghai:
I did as instructed, went down the stairs, turned around and walked backwards… I couldn’t find the restroom or a Policeman??
So as you can see, communication in the field is important. There is no need to shout. Be humble and respectful, and think about the question and the way to ask it–whatever country or situation you’re in. Sometimes what you say or the sign language you use to get your message across can be misinterpreted, often with unexpected results.
As is often said: “When in Rome, do as the Romans do.” And a final word of advice…be careful of any sign language you use, especially when asking for ice cream, more so if you’re in Italy, you’d probably end up with a slap there!!
Visiting Mexico City’s Newest Metro Tunnel: How the Country’s Capital is Upgrading its Aging Infrastructure
I was lucky enough to visit the jobsite of the Mexico City Metro Line 12 tunnel in October, along with Tunnels & Tunnelling International’s features editor Nicole Robinson. The country’s largest TBM, a 10.2 m (33.5 ft) diameter Robbins EPB, is excavating Mexico’s first new rail route in 10 years, below southern areas of the city. The 7.7 km (4.8 mi) long Mexico City Metro Line 12 is being excavated just 7 m (23 ft) below downtown areas in mixed ground including watery clay and boulders up to 800 mm (32 in) in diameter. The project is one of two major tunnels being constructed in Mexico City, the other being the 62 km (39 mi) long Emisor Oriente wastewater project, using six TBMs including three 8.93 m (29.3 ft) diameter Robbins EPBs.
During our visit to the site, the machine was between its first and second cut and cover station sites (it will hole through into seven such sites during the course of tunneling). We walked through the tunnel to view the machine, and later sat down with metro director Enrique Horcasitas of the Mexican Federal District for an interview on the current state of tunneling in Mexico.
Interview with Metro Director Enrique Horcasitas
Q: Were other methods besides tunneling with an EPB TBM considered for this tunnel?
A: Originally, the line was envisioned to be constructed using a technique of slurry walls cast in place. Most of Mexico City’s underground lines were built using this method. However, opening and closing city streets was not possible for a large portion of this route, while open cutting would interfere with existing municipal facilities and fragile archeological sites. In addition, cost estimates placed open cut excavation of the entire 24 km (15 mi) line at 19.5 billion pesos (USD $1.57 billion).
Our engineers needed a solution that would reduce risks and adverse impacts to traffic flow, as well as reduce project cost. For several weeks, methods were studied, and it was ultimately determined that a solution using multiple methods would work best. The 7.7 km (4.8 mi) long tunnel between Mexicaltzingo and Mixcoac would be excavated using a mixed ground EPB TBM, while the rest of the line between Atatonilco and Tláhuac, in much more difficult ground, would be constructed on the surface. Smaller portions of the tunnel would be constructed using cut and cover methods. The overall plan has a budget of 17.58 billion pesos (USD $1.41 billion).
Q: What does the city forecast for future ridership?
A: In the short term, it is expected this project will meet an average demand of 437,000 users per weekday. By 2030, this number is expected to grow to 600,000 users.
Q: How was the route of this line determined?
A: There is a long history associated with Mexico City’s metro plan. Engineers used to think it was impossible to excavate underground, given Mexico City’s highly complex geology. But in the 1950s and 60s, crews hand-mined the city’s main wastewater line, Emisor Central, about 100 m (330 ft) below ground. After the encouraging results, about 41 years ago, the project’s current contractor ICA (Ingenieros Civiles Asociados) began to make feasibility studies about metro lines running through the city. ICA was contracted to excavate the capital’s first metro lines, and 10 years later ICA gave the Federal District a gift: A master plan with over 300 km (185 mi) of rail that would serve as our template for decades to come.
The master plan is reviewed every 10 years, and it was most recently determined to build Line 12. The alignment is almost entirely true to the master plan, though it was made a bit longer after being reviewed by advisors, to match public demand for transportation.
Q: Are there any other metro expansions that the city is considering?
A: We are looking at doing an extension of the new Line 12, depending on the available budget. This extension would include 1,400 m (4,600 ft) of tunnels west of Mixcoac.
The next line we are considering in the master plan is Line 15, which would run directly below Insurgentes, the longest avenue in the world (18.8 km/11.7 mi), which goes straight through the city. A metro is absolutely needed on this route, as there are currently about 10,000 people per hour riding on just buses alone in each direction.
Q: Do you think current opinion about TBMs is changing in Mexico? What is the current climate towards TBMs?
A: I think the public can see the success of this tunnel—we arrived into the first station with precision, only 1 cm (0.4 in) to the side. We are monitoring settlement, and have detected only about 2 cm (0.8 in) at maximum—well within the limits and not enough to affect buildings. The public voted on where to excavate the next new line, they decided where to go, and so there is a consensus in society. I think that is why there has been a high degree of acceptance.
The operation of TBMs is seen as more favorable than hand mining or open cut, because there is less inconvenience at the surface, and building the tunnel itself is safer. For this reason, I think TBM tunneling will continue to increase in Mexico.
With the six TBMs currently excavating or being readied to excavate the new Emisor Oriente wastewater line, we now have seven TBMs operating in the country—this has never happened before. I think this is a tunneling boom!
Offshore oil production is an important sector of business worldwide, but recent events have highlighted its inherent risks. We have witnessed catastrophic accidents on offshore drilling platforms that damaged the delicate marine environment and hurt businesses and families. Inclement weather and technological unreliability compound the problems that come with accessing oil fields in deep water.
Making offshore oil drilling as safe as possible is a high priority task—and one that could be advanced through TBM tunneling. Building oil production facilities in controlled environments underground has the potential to take at least some of the variables out of the equation. The tunnels would provide human access to the well head in deep water, and could be monitored for leaks and other malfunctions.
Extensive sub-sea tunnels for this purpose are being investigated in Norway, where schematics were drawn up for tunnel access to offshore oil fields in the early 1980s. Personnel access, transportation of drilling equipment, exploration and drilling for oil, and eventual piping of oil to the shore are all performed in tunnels and caverns underground. This enables access to the drilling sites and intervention by humans, rather than by remotely controlled and operated machines thousands of feet below water. Some concepts, such as the one below, feature a triple cross section—one tunnel would be used for materials transport, one is used for transport of personnel, and the third would be used as the oil supply pipeline.
More than 40 subsea tunnels have been completed in Norway since their excavation was first proposed: 25 road tunnels, 8 oil pipeline tunnels, and 8 water supply tunnels. All of these tunnels were excavated by conventional drill & blast methods (D&B). The longest tunnel was 7.9 km (4.9 mi) (Bømlafjord), and the deepest is 287 m (942 ft) below sea level (Eiksund). Most of the tunnels were excavated in hard gneiss rock, with a few in shale and sandstone.
The slow relative excavation rates of drill and blast excavation, however, make this method of excavation on long sub-sea tunnels impracticable. Many new underground oil fields up for development will require long subsea tunnels of up to 50 km (31 mi) in length. These long tunnels must be excavated in the shortest possible time and as inexpensively as possible to make economical sense. At these tunnel lengths, mechanical full-face tunneling is the most realistic option. TBM technology for seabed excavation has been used on multiple projects since the 1980s, from the Channel Tunnel to the Boston Harbor Outfall and multiple tunnels worldwide.
New tunnels, as in the schematic below, would be built far below the sea bed, out of unstable regions that might experience sea water infiltration.
In addition TBM tunneling would control the amount of over-break compared to drill and blast, by limiting the amount of material removed from the tunnel.
With today’s experience and know-how it is possible to excavate long tunnels under the sea in good time and with reasonable cost. The technology exists to improve oil and natural gas production from offshore oil fields, all that remains is for the method to gain acceptance in the industry.
It has been argued that the majority of good ground for tunneling in the world already has a tunnel going through it. While this might be an overstatement, it is true that more and more of today’s tunneling projects are being proposed in difficult, mixed ground conditions. Hybrid TBMs, specifically EPB/Slurry and EPB/Hard Rock machines, are increasingly becoming the best solution for these challenging conditions.
Hybrid machines have the potential to lower risk and make difficult excavations possible, as long as accurate geologic information is available. For example, a hybrid EPB/Open-Type machine can be optimized towards either end of the scale—depending on whether the majority of the drive is in soft soils or majority in hard rock—to produce the fastest possible advance rate over the entire project. If the tunnel is 80% soft ground and 20% hard rock, the overall machine design will be optimized towards EPB.
But what happens when the divisions are not so clear cut, or when the geology is 50% rock and 50% soft ground? A real example is the upcoming Sleemanabad Carrier Canal project, which will utilize a 10.0 m (32.8 ft) diameter Hybrid EPB/Hard Rock TBM. The 12 km (7.5 mi) long water transfer tunnel in Madhya Pradesh, India consists of shorts sections of hard rock and soft ground. Geology includes clay, gravel, marble, and hard rock up to 180 MPa (26,000 psi) UCS.
The solution at Sleemanabad is to provide three modes of tunneling: pressurized EPB tunneling, non-pressurized EPB tunneling, and open hard rock tunneling. The first half of the tunnel will be excavated using a specially designed screw conveyor, which can operate well in both the pressurized and non-pressurized environments. The oversized screw can be rotated faster to handle short sections of hard rock while minimizing any loss in efficiency.
When a longer section of rock is encountered, the screw conveyor is removed and switched out for the TBM belt conveyor. Additional welded steel is added to the cutterhead to close up the open soft ground design, and the machine operates as a Single Shield TBM.
In other conditions, such as sections of soft ground and rock mixed with sections of high water content, a Hybrid Slurry/EPB Type machine is desirable. The machines can similarly be optimized towards slurry or EPB depending on the amount of groundwater expected. An interesting example of this type of hybridization took place at the South Central Hillsborough Intertie Tunnel in Tampa Bay, Florida, USA. The machine excavated limestone with significant groundwater using both a screw conveyor and modified slurry removal system. See the case study here.
Hybrid machines are becoming more common, and are likely to gain in popularity over the near future. With greater experience will also come greater optimization of conversion times between modes—one of the biggest challenges during tunneling. While these machines do have some negatives, as all machine types do, the solution of Hybrid TBMs in mixed ground vastly outweighs any difficulties over the life of the project.
Settlement. It is one of the biggest risks in urban tunneling and the cause of sinkholes, cracked building foundations, and tunnel collapses. Surface subsidence and upheaval have vexed contractors and equipment suppliers worldwide, but there are some proven ways to minimize ground movement, even in low cover tunnels.
Tunneling at Mexico City Metro’s Line 12 provides a good, recent example of settlement prevention. The 7.7 km (4.8 mi) route is being excavated just 7.5 to 14 m (25 to 45 ft) below downtown Mexico City. The 10.2 m (33.5 ft) diameter Robbins EPB is surfacing into eight cut and cover station sites during excavation, all along major downtown streets.
The ground, which consists of watery clays, sand, and large boulders up to 800 mm (2.5 ft) in diameter, makes settlement a concern. Ismail Benamar, Tunnel Manager for contractor Ingenieros Civiles Asociados (ICA), spoke about the measures they are taking to control the ground: “We have an extensive monitoring program to detect displacements and pore pressure on the surface, underground, inside the tunnel, and in the most critical structures next to the tunneling line.” The risk of surface subsidence and vibration is also being controlled by regulating the rate of advance and controlling earth pressure at the front of the machine, as well as the back-fill grouting pressure.
In particularly low cover areas, Benamar cited a reduction in EPB cutterhead rotation as one of the primary means of avoiding ground disturbance. Cutterhead rotation is kept low (around 1.5 RPM) while torque is kept relatively high.
In addition, the machine’s two-component back-filling system is used to further stabilize the space between concrete segments and bored tunnel. The liquid mixture consists of water and bentonite cement plus an accelerant, which are combined in the tail shield and harden rapidly after injection. Because the two liquids are kept separate, high pressure concrete pumps, which can disrupt the surrounding geology, are not needed.
By May 21, 2010, the machine had broken through into Mexicaltzingo Station—the first of eight cut and cover station sites along the tunnel route. Little to no settlement issues were recorded during tunneling.
Taken together, the methods at Mexico City Metro show the best ways to minimize settlement in urban EPB tunneling. Settlement can be due to multiple factors, including over-excavation, improper ground conditioning, inadequate back-filling, or loss of face pressure. Despite the risks, proper machine design, continuous monitoring, and a knowledgeable crew can keep ground under control.
For more about the causes of settlement and tunnel collapse, visit an online forum at tunneltalk.com
Multiple Machines: The Challenges and Successes of Delivering Three TBMs for Malaysia’s Longest Water Tunnel
Simultaneous delivery of TBMs, some of the most complex machines in the construction industry, is no easy task. Robbins TBM assembly is most often a local process—one that requires skilled workers with knowledge of components designed and manufactured all over the world.
Robbins use of local or nearby shops can often cut down on delivery times. A partial video of the TBM assembly process in the Robbins China-Shanghai facility is available here:
The video depicts the recent assembly of one of three 5.2 m (17.2 ft) diameter Robbins Main Beam TBMs. The machines are being built simultaneously for Malaysia’s Pahang Selangor Raw Water Tunnels, and are a good example of the assembly process.
Each machine is built at a workshop in Shanghai from components manufactured in the U.S. and China. After assembly of each machine is complete, the TBM and continuous conveyor system are shipped from Shanghai to Port Kelang in Malaysia. Once at the port, the components are trucked to the jobsite.
“One of the most difficult processes is finding a single shop that can manage the volume of fabrications and machining. The delivery times for the Malaysian TBMs are one month apart, which means that at one point you are disassembling and shipping the first machine, testing the second machine and starting assembly of the third machine,” said Kolenich. On average, each TBM requires a skilled crew of 20-30 fabricators, welders, and technicians, but shorter delivery schedules can require up to 60 people in two shifts. “We have an experienced group in China that has been building machines for many years,” he added.
Assembly of TBM #3, the first machine to be built, was completed in early July 2010. Assembly of the machine began with core components, including the main bearing and back-up structures, and finished with installation of the electrical and hydraulics systems, as well as outer components including cutterhead pieces and ground support.
“We perform all of the same quality inspections in our shops, regardless of location,” adds Kolenich. “At the end of assembly there is a two to three week no-load testing period to ensure that each machine is set up and functioning properly per the contractual and engineering requirements.”
The two other Robbins Main Beams will be completed later in 2010, with the factory acceptance for TBM #1 scheduled in August and TBM #2 in mid-September. The three machines will be launched between December of 2010 and March 2011.
For more about the Pahang Selangor Raw Water Transfer tunnels, visit the Malaysian Government’s Ministry of Energy, Green Technology, and Water.
View a short video about the project here:
Conditions in high cover tunnels are often challenging. At the Olmos Trans-Andean tunnel, crews face 2,000 m (6,500 ft) of hard quartz porphyry, andesite, and other volcanic rocks under high stress. At two rail tunnels in China’s Gansu Province, open-type machines are boring beneath 1,400 m (4600 ft) of weak phyllite and sandstone.
Ground support, particularly in deep tunnel projects, is a highly debated topic. However, recent successes have pointed to several systems that work in a variety of situations. The Robbins Main Beam at Olmos was launched in 2007, and began to experience significant rock bursting and cathedralling under sections of high cover. “We encountered a 1,200 m (4,000 ft) section of highly fractured ground, with over 8,500 recorded rock bursts. Cavities also formed during tunneling that had to be injected with grout,” said John Simm, Robbins Field Service Superintendent.
To better contain the fractured rock, the machine’s roof shield fingers were removed and replaced with the McNally Support System, supplied by C&M McNally Engineering of Toronto, Ontario, Canada. The McNally support System provides the benefit of continuous support along the roof area of the tunnel, which protects workers from falling rock. The system works by replacing the curved finger shield plate for a curved assembly of pockets with rectangular cross-sections. Steel or wood slats are extruded from the pockets and bolted to the tunnel crown using a steel strap, effectively supporting and minimizing collapsing ground. As the machine advances, slats are reloaded into the pockets.
The below video shows the crew loading McNally slats into the pockets:
The system successfully contained numerous high-pressure rock bursts at Olmos, as seen in the below video courtesy of Dean Brox from Hatch Mott MacDonald:
For the machines at China’s West Qinling tunnels, the answer is a versatile ground support system that can be adapted depending on the ground conditions. The two 10.2 m (33.5 ft) diameter Main Beam TBMs are the first Robbins Main Beam machines built with specialized ground support and no finger shields. Instead of the roof fingers, the machines are designed with mesh pockets beneath a protective shield for workers to safely install mesh panels.
The machines can also use the McNally Support System if needed. Modified pockets can be bolted inside the mesh windows, allowing space for short slats of steel or wood.
In addition, streamlined materials handling and separate roof and probe drills allow for improved progress in high cover conditions. Redesigned ring beam installers allow for loose assembly and expansion against the tunnel walls, and can be easily converted to install steel straps rather than full rings.
Both machines are currently excavating 16.6 km (10.3 mi) long rail tunnels.
For more information on ground support in large diameter tunnels, check out this recent technical paper: Large Diameter TBMs_WTC2010
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