In September, the BTSYM lecture on the Implementation of the Tamoios Highway in Brazil took place virtually. The talk was held in collaboration with the Brazilian CBTym and was held online due to the ongoing safety issues associated with the coronavirus pandemic.
Thiago Perez of CBTym and BTSYM introduced the main speaker, Pedro Paulo Soares dos Anjos, project engineer and design coordinator at Queiroz Galvão Constructor. Dos Anjos is responsible for coordinating designers, topographic teams, information and geologists on the project. Commentary also came from his colleague Gustavo Santos. Both belong to CBTym. Dos Anjos began by introducing Queroz Galvao Group (QGG) and its portfolio of infrastructure projects in Brazil which includes metros, road tunnels, sewers and power stations.
Project Background and Overview
Construction of the Nova Tamoios Highway project involves the addition of a second carriageway (‘duplication’) to mountain route SP99 Rodovia Dos Tamoios in Caraguatatuba on the north coast of Sao Paulo.
The project comprises 21.5km of highway, 12.85km of main tunnels (including the longest road tunnel in Brazil at 5.5km), 12km of service tunnels and 2.65km of bridges and viaducts.
Around 85% of the project is located in the Serra do Mar state park, a protected environmental area of rain forest.
Duplicating the existing highway will alleviate heavy traffic flows, provide more safety for users, smoother ramps, less sinuous roads and gentler curves. It will also improve the flow capacity of products through the port of São Sebastião thereby contributing to the Brazilian economy.
In recognition of the different technologies adopted to reduce the impact on the Atlantic rainforest, the company was awarded the ECO Sustainability Award from the American Chamber of Commerce (AMCHAM) in 2017.
The new highway will comprise two lanes and a hard shoulder and will duplicate the existing highway. Once it is in operation, it will be used for the uphill direction while the existing highway will be used for the downhill route. The road will link to an existing coastal highway that leads to the port of São Sebastião – an important logistical port in the region. As of August 2020, 78% of the project had been completed, well on target for its scheduled completion date of March 2022.
Conditions
The mountainous terrain dissected by valleys and heterogenous geological conditions in a protected area makes building tunnels difficult. Bringing the highway from sea level to a plateau 650m ASL was an enormous challenge, as was the tropical weather: workers have endured variable weather conditions in their bid to keep the construction on track.
Emergency Tunnels
Brazilian fire regulations stipulate that tunnels over 3km must have pedestrian cross passages every 250m for use in the event of fire or accident. In this case, 16m-long cross passages link the parallel service tunnel to the main tunnel. Although tunnels T5, T3-T4 and T1 (main cross section 120m2) all have parallel service/emergency tunnels, tunnel T2 does not because it is under 1km long.
Due to the 5.5km length of tunnel T3-4, the fire department required a large air extraction chamber and an extraction tunnel located between the main and service tunnels. It is equipped with six 150hp fans which activate in the event of fire or high gas concentrations.
Methods and Technologies
The project employed the full drill-and-blast cycle, from loading, detonation, ventilation and scaling to bolting/ shotcreting, mapping, and also topographic marking.
Sandvik drill rigs proved to be crucial in this cycle. Queiroz Galvao Constructor (QGC) bought five drill rigs, each equipped with three booms and the TCAD system, which enables the export of critical drilling data, including drill speed and water pressure.
TCAD allowed significant improvements in drilling accuracy, decreasing the amount of under- and overbreaks, and minimising the material waste resulting from drilling. QGC partnered with Sandvik to train the operations, maintenance and control teams in order to optimise the entire cycle of activities undertaken by the jumbo.
Geopositioning of jumbos was achieved by robotic total station. This enables the location of drilling holes and maps the excavation section.
Using an autonomous system allows information to be collected and tunnel sections to be compared in real time. The technology can determine the treatment of underbreak points and drilling adjustments for the subsequent blast, thereby minimising rework and losses from over excavation.
Importance of The Topographic Team
The topographic team was deemed critical in undertaking the underground works, taking part throughout the excavation cycle. It provided:
- Automatic tunnel setting out: drill pattern, rig positioning, profile contour, steel-arch positioning.
- Real-time profile control: excavation, steel arch.
- Excavation documentation and analysis: excavation, shotcrete.
- Backup set-out: rock support, cross passages, niches.
- Quality control of the outer lining: shotcrete profile and surface undulation.
- Rework quality profile checks: critical spots.
- Final tunnel surface QC: profile and surface undulation.
- Inner lining set-out: construction joints, reference heights.
- Formwork acceptance control: profile.
- Setout for installation works: banquettes, installations
- Tunnel quality control: profile, assets.
Sprayed Concrete
The tunnel lining must resist not only mechanical loads but also the effects of spalling under fire load. The Tamoios project is the first in Brazil to use polypropylene fibres – both micro and macro – in the shotcrete mix. The tunnel lining is applied with 100% synthetic fibres to improve the shotcrete. The project is also noteworthy in that it is helping to develop a Brazilian standard for the use of polymeric fibres in shotcrete
Drainpack System
The engineers chose the Drainpack system to facilitate adherence between the first shotcrete lining and the second one, preserving the friction between both layers. This allowed a significant reduction in the final thickness, leading to savings in cost and time. The system is claimed to have numerous benefits over waterproofing membranes:
- Not a systematic treatment, so cheaper and easier to apply.
- Can cope with high flow-rate infiltrations commonly found in tropical regions.
- Reduces groundwater pressure over the lining surface, avoiding overload due to extreme climatic events.
- When necessary, the system efficiency is maximised by combining the use of short drains and polymeric mortar.
The Innovative Cable Crane
Constructing a cable crane to transport materials and equipment to a difficult to access area is seen as one of the most important and innovative aspects of the project. It also marks an important engineering solution that helped achieve the project’s environmental goals.
The solution arose from the company’s desire to avoid the construction of a winding, sinuous service way adjacent to Portal T3 that would decimate around 40,000m2 of Atlantic rainforest. Because of the tight schedule, construction of T3 and viaduct 3 (V3) had to start simultaneously, which is why the pioneering technology was employed – the first cable crane assembly in the country and a challenging maiden project undertaken in an environmentally protected area.
The position of the track cable was suspended from two towers, T1 and T2, 42m- and 35m-high respectively. The cable would carry trucks, excavators and materials. Aligned with the main bridge supports, it would help the construction of the viaduct’s foundations, columns and other structural components. It would also transport spoil out of the tunnel.
A total of 35 sections were hoisted in place by helicopter to form the two cable-frame towers, some weighing up to 3.2t a piece. In all the operation took 20 days to complete.
Tower 2 was assembled by a conventional crane because there was sufficient onsite space. But tower 1, which was located in an area that was difficult to access, required the use of a helicopter as well as confirmation that it would not impact the park’s ecology. QGC partnered with Omni for the helicopter work and LCS Cable Cranes.
Spaced 394m apart, the two towers linked by a 65mmdiameter cable, could carry items weighing up to 20t at a speed of 4m/sec. From March 2019 to August 2020, the cable crane worked a total of 7,200 hours transporting more than 220,000t of soil and rock, and 10,500m3 of concrete. With its 90% availability, it proved to be a very efficient and important mechanism for completing the viaduct’s construction: all steel, concrete, frameworks and other materials were transported by it.
A reinforced concrete pedestrian walkway was also constructed with the aid of the cable crane around 36m below viaduct 3 and roughly parallel to it. It not only allowed workers to access the main supports and so minimise their downtime, but also carried a line for pumping concrete.
Water Treatment Stations
During tunnel excavation, a boomer’s water consumption can be around 40m3/excavation cycle so a project like this can consume around 400m3/day. To deal with such high water volumes, a closed-circuit system was developed so that all captured tunnel effluents (both infiltration and post-drilling water) passed through a treatment station to avoid the escape of polluted water. This protected the environment and helped reduce operational costs.
Each tunnel had its own water treatment station. In 2019, nearly 288,000m3 of water was treated, 119,000m3 reused and 160,000m3 discarded. More treated water than fresh was used on the project, avoiding unnecessary water consumption. The total water treated in 2019 was the equivalent of 115 Olympic-sized swimming pools. The main water uses included tunnel jumbos, equipment washing, water sprinklers at crushing plants and the wetting of access routes to suppress dust.
Crushing Plants
A total of two million cubic metres of rock was excavated from the tunnels, much of which was processed by crushing plants and used for concrete, asphalt surfacing and other civils’ works.
The total volume of concrete used for civils’ works was more than 300,000m3. To reduce waste, tunnel spoil was crushed into gravel and used for shotcrete and other concrete.
Tunnel 2 Breakthrough
Environmental limitations made access to the T2 portal inaccessible. This resulted in the tunnel breakthrough coming from one side, i.e. from the inside outwards. To save time in constructing bridge V1a, it was assembled inside the tunnel and then jacked hydraulically over the supports.
Good Practice
Various good practice measures benefited the project and included:
- Minimal connecting tunnel lengths between principal and service tunnels helped lower the total work area and the environmental impact.
- Regulating shotcrete technology saw the use of 100% filler and polypropylene fibres in the mix design. No natural sand was used, improving results, quality and minimising the need for raw material.
- The cable crane assembly reduced environmental impacts and rendered the overall project schedule viable.
- The breakthrough at tunnel 2 /viaduct 1a proved to be a novel solution which saved time and protected the environment.
End of Presentation
The speaker ended the presentation with a quote from Winston Churchill: “The pessimist sees difficulty in every opportunity; the optimist sees opportunity in every difficulty.”
Dos Anjos thanked the BTSYM for the opportunity and also CBT. He also thanked Gustavo Santos who then gave tribute to the more than 1,000 people who worked on the project.
Questions and answers
Q. Divik Bandopadhyaya: Was the contract a cost plus or a ‘pain and gain’ share mechanism, so if you exceed the budget the contractor then shares some of that?
Dos Anjos: The project was a turnkey lump-sum contract and completed to budget.
Q. Andre Pereira: Did you only use shotcrete for support or was there any anchoring?
A: Both were used but only for temporary support to take the initial load.
Q. Divik Bandopadhyaya: Was there a reason you didn’t opt for steel fibres, for example, cost?
A: Both types of polypropylene fibre were used; the second layer is the fire-resistant layer so the microfibres are for that. The first layer is a structural layer for which the macro polypropylene fibres satisfy the requirements.
Q. Thiago Pereira: What is the thickness of the tunnel lining?
A: It varies from 15-40cm, depending on the geological conditions.
Q. Thiago Pereira: What did you use to classify the rock mass, RMR or Barton’s Q-System?
A: Barton’s Q-System.
Q. Mehdi Hosseini: What type of environmental study was carried out prior to the project? What were the major risks and what was the performance compared to the study?
A: The major risk was the environmental impact in the park which had virgin forest, particularly the possibility of contaminating a local river. From the start, we sent the client monthly reports to control risk. We also had a good team and the diligent client meant we had to be more aware.
Q. Divik Bandopadhyaya: How dry is your tunnel and do you get substantial water ingress? And if you do, how does it replicate in changing the water levels in the adjacent areas?
A: We map the tunnel and identify any localisation to carry out any treatment. Some regions are drier than others, depending on the type of rock and other factors.
Q. Thiago Pereira: Did you start tunnelling without knowledge of water levels?
A: We had all information and instrumentation in place.
Q. Mehdi Hosseini: Have you seen any impact on the local water levels?
A: No, no impact on ground water.
Q. Rogério Pinto Ribeiro: How did the rock mass impact on the lining thickness?
A: For the worst rock quality we applied something like 40cm of shotcrete and for the better quality around 13cm of shotcrete. We have a rock quality scale of 1-5 and the shotcrete thickness depends on that and on other factors.
Q. Thiago Pereira: Have you crossed any rock faults during the alignment and if so which treatment did you use across the fault?
A: We didn’t cross faults but we had rockbursts, some instances with more than 200m of cover. In some cases we applied steel-mesh reinforcement and NATM, depending on the rock instrumentation we had available, so we could adjust the treatment. One of the reasons we chose NATM is because of this type of situation.
Q. Ana Paula Ruiz: What sort of advances did you achieve?
A: The best was 5m/day in good quality rock; the worst in poor soil ranged between 50cm -1m.
Q. Divik Bandopadhyaya: Did you get any substantial convergence or was it always within tolerance?
A: The convergence of this tunnel was normal and within tolerances.
Q. Casio Moura: The first layer of shotcrete lining was part of the permanent tunnel support – do you have a measure of the economy led by the solution or the reduction of the total lining thickness? Do you have a comparison of what the cost would have been had you have used steel mesh?
A: We achieved good economies. Compared to steel mesh, synthetic fibre reduces the excavation cycle and the equipment required to install steel mesh. We reaped many benefits and economies when we used the fibre but I don’t have cost comparison data or the amount we saved; it depends on many factors and it is not that easy to evaluate.
Winding up
Divik Bandopadhyaya: Once again Pedro and Gustavo thanks for your great presentation, I think it’s evident from our comments section how much people enjoyed it, and rightly it appears to be a very challenging project to which you have found a really good engineering solution which delivers what is required within budget and also reducing the impact on the local ecology. So congratulations to you and your organisations for achieving this.
Tiago Perez thanked presenters and BTSYM for presenting and sharing the knowledge.
Next BTS lecture:
The next BTS lecture is on 17 September 2020; the BTSYM committee applications for 2020/21 will also open in September.
