Nature surprises Engineering

Interview with Julio Cláudio Di Dio Pierri, Coordinator of Engineering of the Consortium for Construction of Line 4 South of the Rio de Janeiro Metro

“Building a subway line in a densely populated urban center, such as the South Zone of Rio de Janeiro, is like a giving a patient who is already debilitated a coronary bypass: you only do it when the situation is already very complicated.” The comparison with critical surgery made by engineer Julio Cláudio Di Dio Pierri, Coordinator of Engineering of the Consortium for Construction of Line 4 South of the Rio de Janeiro Metro, illustrates the sheer complexity of the challenge of this venture. Building a new commuter system to enhance mobility in a large urban center, interfering as little as possible with other existing mobility systems, requires surgical precision, high technical expertise, the latest in equipment and, above all, a lot of planning.

In this interview, Julio Cláudio Di Dio Pierri draws a panorama and acknowledges the importance of combining these factors, but admits that, on many occasions, that is not enough. The geological profile of the region, formed by a large stretch of sandy soil with the interference of portions of rock can mean surprises that technique and best practices alone do not resolve. It takes a good dose of intuition, ability to improvise, flexibility and resourcefulness’. Perhaps this is precisely the difference that makes Brazilian engineering stand out on the world stage: the ability to learn from nature respecting it, consolidating that knowledge and advancing at each new surprise.

Grandes Construções – The construction of Line 4 of the Rio de Janeiro Metro resulted in innumerable challenges for engineering. A major complication in the project is its location, crossing certain stretches of Rio’s South Zone where there is heavy traffic, a large amount of interference caused by utilities networks and a high concentration of inhabitants, most of whom have a high social and cultural standard and are highly demanding. Did the profile of this population affect, to any extent, the definition of the construction methods in seeking to reduce the impact on the lives of the local population?

Julio Cláudio Di Dio Pierri – For sure this is a high income population and that has a considerable influence. We had to ‘invert’ some construction methods to facilitate acceptance of the work by the population. Some of the major challenges happened when the need arose to detour traffic on some streets in the area, for example. But some impacts were inevitable. All construction methods affect, in some respects, the public and the target community. That applies to the route of the metro line, where the stations are located, the type of the stairs, the project as a whole. In this project, we had to solve an equation or rather a statement of inequality which is executing the project, meeting deadlines and meeting the demands of the population. Imagine what it’s like to carry out a giant piece of urban mobility work with the least possible interference in the present mobility. That’s why we strived to define a methodology of construction that would impact the day-to-day lives of these people as little as possible. I usually say that implanting a Metro is like implanting a coronary bypass: we only do it when the situation is already very complicated. So, the way to minimize impact is to do many tests before starting the work, to do a lot of planning. We spent a long time, more than a year, planning before starting the works. And that is the path, even though we know that at the last minute surprises will arise requiring adjustments. But the main concept will persist. It has persisted until now. In this work, a major concern was to avoid expropriations, preserving city squares and routes of traffic on the surface.

GC – In this project, in the South Zone, there were almost no expropriations, isn’t that right?

Julio Cláudio – No, there weren’t. One reason was that it would make the project too expensive. We only had a few tentative changes, such as changing a few of the fences of buildings. But this was a concept that we sought right from the beginning - we did several studies, analyzed the work along with the government, exchanged ideas, had the advice of the Fundação Getúlio Vargas (FGV) because we knew that the main issue to be confronted would actually be meeting the demands of the population and, at the same time, meet deadlines. We always established in these meetings that the ideal thing to do would be to simplify things

GC – Is this combination of technologies for construction of the South line, using the cut-and-cover method to build the Metro stations and the Tunnel Boring Machine (TBM) for the tunnels, established worldwide or is it something new?

Julio Cláudio – It is usual. What we changed here was the construction of stations closer to the surface. The tunnels excavated by the TBM are deep, but the stations are shallow. Normally, operating with a TBM, making two Metro ways together, causes stations to be made deeper. But we chose to bring them closer to the surface.

GC – What’s the advantage of doing that?

Julio Cláudio – There are several indirect gains such as fewer escalators; users have to move around less, etc. But our problem is that we had to use shoring in the excavations, which wound up turning into shoring of the stations. We combined both to simplify things, we ‘fused’ the structures, so that the span that the shoring had to withstand was enough for the passage of the TBM without interruption. Because, based on the characteristics of the soil, I had to have multiple locking points for the containments. We had to eliminate that. So we overloaded on the structures, we super-sized them. And one way to achieve this was to raise the stations, otherwise we wouldn’t succeed. One of the biggest diaphragm walls in Brazil is 1.20 meters wide. Another option would be to do them with 1.20 meters, but in “T”, which would increase the rigidity. But, in this sand, it would be very risky. Then we raised the stations closer to the surface.

GC – Did the type of soil complicate things?

Julio Cláudio - Yes, because we are working in sand. This sand is actually is very compact as of about 8 meters deep. But when you cut that sort of land, it has no cohesion. To complicate matters even further, most of the nearly 600 buildings located along the line’s route are built with foundations directly in this sand. When you move this ground, settling can be immediate. This sand can be very treacherous.

GC – What is the solution for working in that kind of soil?

Julio Cláudio - You have to keep moving forward in the excavation of the tunnel, and as you go, you treat the soil. And the faster you work, the better. You go on excavating the tunnel and at the same time place the concrete rings for containment. But the methodology for treatment of the soil is ‘cone-like’ or tapered in shape, and that leaves some gaps. So if you are the least bit careless, the street above you can be gone (cave in). Besides that, you have to consider that above you there are networks of water mains, gas, all the utility networks. Settling of the ground may generate a problem, a leak or something.

GC – How fast is the work expected to progress? How many meters of tunnels will be prepared per day?

Julio Cláudio - The TBM advances as many meters as we can complete. There is no limit. We’re the ones who hold it back. I do not move ahead from the point where it stops until the next part on the verge of being ready. I need to make sure that it will get to the other side. It would be possible to stop midway, it would be possible to perform a few specific treatments, but the idea is to have that at a higher speed, so I wait until the next stopping point is almost done to be able to OK the part that is behind us. That way the tunnel ceases to be a critical point. The limiter is the station which has to be ready for the TBM to pass.

GC – Considering the large amount of probing that you carried out on this line segment, is there any chance there may be a surprise along the way that could slow down this process?

Julio Cláudio - In geology, anything is possible. We might find, for example, a protrusion  of rock underground, in the middle of the sandy soil. If that happens, the TBM itself can cut that rock. It has been designed to handle this possibility. In fact, this land in Rio de Janeiro, for the most part, consists of sandy terrain with rock protrusions. The Sugar Loaf, the Morro da Urca,are rock protrusions or outcroppings. Some are apparent, others are buried and you don’t see them. And you do not know if, between one probe sample and another there is a protrusion of rock. The risk exists. Something local may appear that even the good practices used in probing did not detect.

GC – Along the entire South zone line segment, how many soil probes or surveys were performed?

Julio Cláudio – Over 120 geological probes were carried out by specialized subcontracted companies. That’s how we did the mapping to generate the basic project design. It was a lengthy process, we had to get permission to do the work in front of commercial establishments, or in front of churches. Often it was not possible on that day and we had to return the next day, or we weren’t allowed to do it there and we had move to another spot. That complicated the probing process.

GC – Did you come up against a large amount of ground water (water tables) in this region, similar to what happened in the ‘Barra da Tijuca’?

Julio Claudio – Yes we did, in most of the stretch, at about 1.5 meters deep, after all we are digging between the sea and the ‘Lagoa Rodrigo de Freitas’. And that was a gigantic challenge. Normally, we drawdown (drain and lower) the level of water . But one consequence of lowering the water table is settling of the land. And with this sand, there is a risk of immediate and large settling. We had to find a process of construction that would reduce that risk. And, most of the buildings in that region are 30, 40 years old, with foundations directly in the sand. Thus, the methodology changed. Especially because the volume of water was very large, equivalent to a water mains with a flow of 400 cubic meters per hour, to remove the water that gushed.

GC – And what was the solution?

Julio Cláudio – We decided to isolate the water, to not interfere in the water, so we treated the bottom to seal it.

GC – Did that in any way affect the architecture of the stations?

Julio Cláudio – Absolutely. It altered, for example, the thickness of the walls of the Metro stations.

GC – We know that the TBM was custom made for the project considering the geological profile of the region, the width and height of the tunnels and stations, among other factors. What was the presentation of the project and the development of the equipment by its manufacturer in Germany like?

Julio Cláudio - That required several technical missions, several visits by our teams to the manufacturer. In 2010 we started the soil probing initiative. In mid-2011, we completed these surveys with enough collected information to begin studies for the manufacturing of the equipment. That finally happened in 2012.

GC – Does the manufacturer provide you with a period of monitoring assistance following the delivery of the TBM?

Julio Cláudio - Yes, all the time. On account of the complexity of this project itself, this is a challenge even for the manufacturer. The manufacturer will monitor the operation all the time and, in the beginning, it will even provide the staff to do the start-up. According to the contract, this will be done for the first 100 meters, in an assisted operation. We are already studying the possibility of hiring them to perform the whole operation.

GC – When is the TBM expected to begin to operate?

Julio Cláudio – In October of this year.

GC – Is the part of the machine that performs the installation of the concrete shield arch sections (segments or voussoirs), which will constitute the lining of the tunnel that was bored by the TBM, part of the structure of the TBM and included in this assisted operation? Is it a component of the equipment or a separate, distinct structure?

Julio Cláudio – It’s an adjacent structure but it interacts with the main equipment structure. There is interaction of size, weight, position, meshing details, etc.

GC – But is that structure also manufactured by Herrenknecht?

Julio Cláudio – It is manufactured by a member company of the Herrenknecht group.

GC – How are the arch sections applied and fastened? Is it done by pressure?

Julio Cláudio – It is a meshing, puzzle-type assembly somewhat like Lego ©. They are concrete structures (sections) that are placed in parts. The placement of the sections is all automatic. As the machine advances, it selects and applies the parts. It is the process of a ‘universal ring’. The same form is appropriate for curved and straight segments of the tunnel. The TBM is directed by laser – the equipment’s command system is programmed with the entire route. From these data, the system tells you what the next concrete part will be and where it will be placed. In the past, this process was done manually.

GC – Are these concrete rings prefabricated?

Julio Cláudio - Yes, they are pre-cast elements with special characteristics that will be produced at the construction site of the Leopoldina railway station. They are made of high-strength concrete and have to be waterproof since the structure will be submerged in aggressive soil. Besides the concrete structure there are the ‘supplements’. Between the concrete sections there’s rubber which will constitute the seal. There are notches, indentations; there are the details of the notches that, if they’re not done right, can lead to leaks because the pressure is high.

Grandes Construções – Has the prefabrication of the concrete arch sections begun well in advance of the startup of operation of the TBM?

Julio Cláudio – That’s going to depend on the size of the plant you’ll have, the number of forms you purchased, etc.. Our forecast is that, at the beginning of the operation of the machine, at least 800 concrete arch sections will be ready in stock. Ideally we should have a whole segment’s worth of sections ready for placement because the TBM works very fast and cannot stop to wait for production. Our idea is to start production of these concrete structures in late April.

Grandes Construções – How many sections will be required for the entire length of the South zone tunnel?

Julio Claudio – It will be 2,800 sections for the whole stretch, and the production capacity of our prefabricated element plant, which will be established at the Leopoldina construction site, will be 10 sections per day, working two shifts. But we can set aside a third shift of operation as a ‘Plan B’.

Grandes Construções – How long do expect the TBM to take to conclude the 5.7 kilometers of tunnels?

Julio Cláudio – We expect to advance 15-18 meters per day, with the setting of 10 rings in place each day. That’s if there are no geological surprises along the way, and no problem at a station. But you cannot be absolutely sure of anything. A surprise can always happen. If we find a boulder in the path of the TBM, for example, we have to stop work and remove the rock. The machine can even cut the rock but only if it is locked into place. Otherwise it will just keep turning along with the machine and it won’t be cut. So, you must take the rock out of the way. We need to be especially careful, because when we remove the rock, it can bring down more sand and that can cause substantial settling. But we'll only find out about that during the execution of the work. Therefore we cannot accurately say how much the tunnel will advance per day. We make an estimate and try to stay within it.

Grandes Construções – While it’s operating, does the TBM generate any sort of noise on the surface?

Julio Cláudio – None at all. We don’t even notice that it’s working down there underneath us. What we might be able to notice is possible settling, but even so, it would be perceived slightly. That is actually verified  later, with instruments.

Grandes Construções – Once the tunnel is dug, can the TBM be reused in another project? Can it be adapted to be used in performing another similar job?

Julio Cláudio – If the geology is similar, you may even be able to. In São Paulo they are adapting the TBM that was used in the construction of the city’s Line 4 for the expansion of Line 5. They are adapting the diameter of the boring head to the new works. We have to see whether the engines can withstand the increase in diameter. You must review everything to see if it can cope with load or not. This experience of São Paulo will tell us whether it is actually possible.