hybrid epb tunnelling in rio de janeiro 2015

„SEE Tunnel:Promoting Tunneling in SEE Region“ ITA WTC 2015 Congress and 41st General Assembly

May 22-28, 2015, Lacroma Valamar Congress Center, Dubrovnik, Croatia

First experiences gained with the hybrid EPB technology in the Rio de Janeiro sands

Author: Ulrich MAIDL, Maidl Tunnelconsultants GmbH & Co KG, Germany, [email protected]

Co-author: Carlos Henrique TUROLLA MAIA, Consórico Linha 4 Sul, Brazil, [email protected]

Marc COMULADA, Maidl Tunnelconsultants GmbH & Co KG, Germany, [email protected]

Alexandre MAHFUZ, Consórico Linha 4 Sul, Brazil, [email protected]

Aluisio de Abreu COUTINHO, Consórico Linha 4 Sul, Brazil, [email protected]

Mechanized tunnelling in use

Keywords: hybrid EPB shield, metro, sands, data management

1. Introduction

The shield-driven tunnel of Metro Rio Line 4 between the General Osório II and Gávea stations has an approximate length of 5.2 km. The double-track tunnels have an internal diameter of 10.33 m with a 0.40 m thick segmental lining. The excavation is carried out using an Earth Pressure Balanced shield with an excavation diameter of 11.53 m.

2. Project overview The Metro Rio Line 4 project, also called Line 4 South, runs parallel to Ipanema Beach, between the beach and the inner lagoon. The project is executed by the joint venture Consórcio Linha 4 Sul (CL4S) leaded by Odebrecht. The tunnel excavation is planned to start at General Osório II station and will end at Gávea Station. The total length of the tunnel is 5,200 m including the stations. Figure 1 shows the layout of the tunnel alignment. The excavation of soils will be approximately 3 km long and the excavation in rock approximately 2 km long.

3. Geological setting The Metro Rio Line 4 project, also called Line 4 South, runs parallel to Ipanema Beach, between the beach and the inner lagoon. The tunnel excavation is planned to start at General Osório II

Fig. 1 Tunnel alignment layout



station and will end at Gávea Station. The total length of the tunnel is 5,200 m including the stations. Figure 1 shows the layout of the tunnel alignment. The excavation of soils will be approximately 3 km long and the excavation in rock approximately 2 km long. 3.1 Section in sands

The 3 km tunnel stretch in soils is mainly excavated in alluvium sands and marine sands. At some sections, silty and clayey sands are described. Occasionally, there are clay and silt layers embedded in the sands. At both ends of the soil section, mixed face conditions of rock and soil will prevail as the rock approaches. The groundwater table always lies over the tunnel crown and is between 2 m and 5 m below the ground surface.

The fine content of the relatively dense sands is low and generally between 2% to 7%. In a few boreholes, the fine content increases to maximum values of 8% to 12%. The geological studies have shown that the expected permeability is k = 10-4 m/s (4x10-2 cm/s). The grain size distribution that characterise the sands are shown in Figure 3 in chapter 4 where the applicability of EPB shield technology is discussed. The stretch in sands follows the alignment of streets. However, in the dense urban areas of Ipanema and Leblon where the tunnel is built, residential buildings, generally at least 5-storey high, are always in the influence area of the tunnel (Figure 2). 3.2 Section in rock The 2 km tunnel stretch in rock will be totally excavated in gneiss. Table 1 summarises the minimum, maximum and average values of the UCS, tensile strength and CAI parameters of the rock section. The gneiss rock can be classified as a very strong, highly abrasive rock.

Table 1. Rock test results

Parameter Unit No. of samples

Min. Max. Avarage

UCS* Mpa 6 76 236 174 Tensile strength

Mpa 8 8,5 14,4 11,5

CAI - 4 4,6 5,2 5,0

4. TBM selection The applicability of the EPB and slurry method can be verified on the basis of the German Recom-mendations for the Selection of TBM (Daub, 2010). The key geotechnical parameters for the selec-tion of the TBM are the grain size distribution, relative density and permeability. The shear resis-tance parameters and the soil permeability are influenced by the above mentioned parameters. Also, the expected face support pressure is a relevant parameter to be considered. In the sands, the required shield operational pressures at crown will range from 0.9 bar to 2.1bar. The main findings for the TBM selection are listed below: -The permeability in sands is partly high. -The sands contain low amounts of fine content. -The tunnel face needs active support. -The rock is a very strong, highly abrasive rock.

Fig. 2 Typical cross-section in sands



The first brief assessment based on the German Recommendation for the Selection of TBM (Daub, 2010) gives a clear picture. The main experience of the South American contractors is with the operation of Earth Pressure Balanced shields and not Slurry shields. Moreover, the slurry technol-ogy requires an amount of space that is not available in the project area and carries a risk of high volume collapses in case of operation failures. Because of these reasons, MTC was mandated to analyse the feasibility of an Earth Pressure Balance shield.

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Metro Rio L4

Based on the analysis performed, the geotechnical conditions indicate that the use of slurry shield technology is slightly more suitable in the given soils. The sands with very low fine contents are particularly suitable for the slurry shield technology. In rock, both EPB and slurry shield technologies are compromised solutions. The material flow from the face, through the cutter head openings and through the excavation chamber, will be hin-dered by the accumulation of rock chips in these areas. This will cause additional grinding of the rock chips and increased secondary wear. However, assuming that excavation in rock can take place in open mode, both technologies would be feasible in the rock stretch. Due to high rock strength and abrasiveness, high wear should be expected not only on the cutting tools and cutter head, but also on the screw conveyor (EPB shield) and the outflow slurry pipes and pumps of the hydraulic conveyance system (Slurry shield). Therefore, it would be advisable to use a convertible machine that allows the allocation of a conveyor belt behind the cutter head at the centre of the TBM. In this case, if a Slurry shield is used, the conveyance system should be completely changed from a hydraulic system to an additional belt conveyor. In terms of system behavior in soils, the selection of a Slurry shield would be the traditional choice. However, with the latest developments EPB technology is also suitable for the Metro Rio Line 4 ground conditions. From the point of view of cost effectiveness in soils, a detailed cost analysis was performed to compare the two technologies. Moreover, in this part of the city of Rio de Ja-neiro it is impossible to find areas to install a necessary slurry separation plant and all the equip-ment that is needed to perform the excavation. All findings lead to the conclusion that an innovative Hybrid TBM combining the advantages of Slurry Shields, Earth Pressure Balanced Shields and Open Shields (for the rock section) has to be developed to deal with the project and ground conditions.

5. Innovative hybrid TBM Hybrid Shields, which are designed to switch operation modes, were already produced in the 1980s by Japanese manufacturers and contractors. For the tender of the Miami Port Tunnel, Ode-brecht (one of the Consortium CL4S partners) and Maidl Tunnelconsultants developed a technical

Fig. 3 Typical cross-section in sands Application ranges of EPB shield technology depending on the grain distribu-tion (Maidl, 1994) with all the average curves of Metro Rio L4



approach based on an EPB transporting the muck behind the screw conveyor with an open belt or a closed slurry system. The Botlek Tunnel in the Netherlands running in similar sands was success-fully finalized with a Hybrid TBM where two piston pumps are connected to the screw conveyor. The Slurry TBMs for the Grauholztunnel in Switzerland (1993-94) were equipped with a separation plant system on the backup gantries and a belt conveyor system for the muck discharge to the portal. 5.1 Multimode muck discharge and separation solution Normally, the muck will be transported by belt conveyor. However, in a case where the volume of slurry injected into the face is so high that the muck turns liquid, that not would be feasible. A high-density pumping system will make the transportation of this muck possible. As a high quan-tity of slurry will be injected, a separation plant will be installed in order to recover the condition-ing agent to reuse it.

6. Foam testing program Due to the complexity of the conditioning requirements, special care will has been taken in regard to the quality and combination of conditioners to be applied. For that purpose, prior to the begin-ning of the excavation works tests were carried out at the Ruhr University of Bochum (Thewes, 1999) for the selection of the final product. Further suitability and parameter tests were carried out in at the lab site in Rio. Furthermore, during excavation tests are performed with the excvated and conditioned muck. These test are focused on the behavior and quality of the foam, the condi-tioning behavior of the ground and the sealing of the tunnel face. 6.1 Foam behavior and quality The mixing of water, air and surfactant leads to the formation of the foam. The following tests were carried out: - Foam Expansion Rate (FER). Ratio of the liquid phase volume (water and surfactant) and the total foam volume. In other words, how wet or dry the foam is. -Drainage behavior. It measures the foam quantity, which drains over time. -Bubble size. It is measured over time, and then the cell skeleton transformation can be studied. An explanation for the drainage behavior can be derived. 6.2 Conditioning behaviour of the ground Regarding the conditioned soils, the tests carried out are:

-Workability. This parameter gives an idea of how well the ground will flow through the ex-cavation chamber and is studied by means of a slump test as shown in Figure 4. -Drainage behavior. A water head is loaded on a soil-foam sample and the drainage of 3 liters is recorded, as showed in Figure 4. -Permeability. An adequate permeability is re-quired in order to prevent uncontrolled groundwater inflow. The methodology differs, but the information provided by this test is similar as the information of the drainage be-havior test. This test is shown in Figure 4.

6.3 Sealing of the tunnel face This aspect is especially important in coarse-grained soils such as the sands of the Metro Rio Line 4 South because of the risk of uncontrolled pressure losses, both in advance and in short-term standstills. The tests carried out aim to study the feasibility of face sealing and how long this seal-ing can be maintained. These tests are:

Fig. 4 Tests for the conditioning behavior of the ground. From left to right, slump, permeability and drainage test.



-Foam penetration. The progress of foam infiltration is studied, which can inform about the effects of sealing and the void water expulsion over time. -Slurry penetration. This procedure is the same as the foam penetration test. Compared to the foam, the slurry forms a filter cake which brings stability to the excavation face. When carried out, a test which applies pressurised air after removing the filter cake aims to study the seal during the application of compressed air. Three kinds of slurries were studied: polymer-filler slurry, bentonite slurry and bentonite-filler slurry.

7. First experiences in the shield drive in sands Several operation modes have been foreseen to deal with the cohesionless sands as discussed in detail in [9]. To date the TBM has excavated the first 470 metres in full face sands, all the way from the transition from rock to sand until the first stations Nossa Senhora da Paz. We summarise in this chapter the main shield drive parameters. 7.1 Foam and polymer conditioning The excavation in sands in EPB mode with stable face pressure control and muck conveyance through the screw has been possible with polymer foams. Conditioning in combination with added polymer to further stabilize the foams and to adsorb the water in the muck has proved useful to also reduce sedimentation effects during standstill. Optimum face pressure control and muck characteristics have been attained with injection rates around 80% at the cutterhead. Face pressure control and muck flow has also been enhanced by injection foam and polymer through the bulkhead stators in rates of approximately 10 %. Figure 5 left shows the typical consistency of the sand extracted by the screw, attained with foam and polymer conditioning. The sand is very dry and it hardly presents a plastic consistency.

Compared to a more plastic conditioning attained without the use of polymers and with a wetter foam composition (Figure 5 right) it seems as though this muck is more suitable as EPB support medium. The dry consistency shown in Figure 5 left is not desired for muck flow and face pressure control. However, this is the

end product resulting of mixing foam and polymer in the chamber. The muck does have the re-quired plasticity when immediately conditioned at the face, but the effect of the polymer slowly makes effect while the muck flows through the chamber and the screw conveyor. The final con-sistency of the muck is optimum to assure the formation of a controlled plug in the screw. On the other side, the more plastic and wetter consistency of the muck shown in Figure 5 right whilst it also allowed a good face pressure control, it did not allow to attain a controlled plug in the screw and face pressure control had to be adjusted by the opening and closing of the rear screw gates. 7.2 Muck conveyance As mentioned above, the excavation in sands was possible to convey entirely through the screw conveyor. Muck was transferred from the rear screw gate onto a slightly inclined belt conveyor on gantry number one. The belt conveyor transports the muck all the way to the muck pit located at the portal cavern.

Fig. 5 Left: muck with dry consistency (dry foam and polymer conditioning). Right: muck with plastic consistency (wet foam without polymer)



A critical aspect in difficult EPB shield tunnelling as well as a performance driver, is the transfer of the muck from the screw onto the belt. A too liquid, i.e. overconditioned, muck will slip from the inclined belt. This avoids an immediate transport of the muck on the first stretch of the inclined belt, the muck then accumulates on the belt right below the screw gate. This makes the shield operator to have to close the screw and stop the advance until the liquid muck is finally trans-ported by the belt. Additionally, in this situation part of the liquid muck flows down the belt to-wards the shield invert. This requires additional cleaning works at the invert that may also have an impact on global performance. The successful conditioning of the sands made it possible to avoid any hindrance at the transfer from the screw onto the belt. Furthermore the dry consistency of the muck allows to use most of the belt conveyor´s capacity for transport of sand, without any excessive additional products. Additionally, the number of trucks required for muck disposal is minimised both by the low content of conditioning agents and water and by the fact that trucks can be loaded more compared to wetter muck consistencies. 7.3 Face pressure control Face pressure control has been possible by means of conditioning with good quality and stable polymer foam. Distribution of the face pressure inside the chamber is homogeneous as indicated by the uniform distribution of the earth pressures measured at different levels in the chamber (Figure 6) and the calculated average density in the chamber always in the range 13 to 17 kN/m3, generally 15 kN/m3 on average (Figure 7).

Face pressure oscillations are very low as shown in Figure 8, which illustrates in red the average value of face pressure and in grey the minimum and maximum pressure oscillations area. . As mentioned before the use of added polymer has also made it possible to almost minimise sedi-mentation effects and maintain face pressures constant during ring building sops (in average ap-proximately 30 min) without the need of injecting foam or polymer or slurry bentonite during standstill to maintain face pressure over target.

Fig. 6 Earth pressure distribution in the excavation chamber measured at different levels.



7.4 Settlements The overburden in the excavated stretch until station Nossa Senhora da Paz started with 20 me-ters right after the transition from sands to rock and it ended with merely 8 meters (0,7 x D). At the beginning of the sand stretch the groundwater level lied 8 meters below the surface, i.e. 11 meters over the tunnel crown. As the shield approached the station, not only the cover decreased, but also the groundwater level decreased, since it had been lowered until under the tunnel invert right before the station in order to avoid water flow into the station during TBM reception at the shaft. Face support and grout injection pressures were adjusted as cover and groundwater level de-creased. The target pressure values were determined from face stability and finite element settle-ment calculations. Pressures were determined in order to keep settlement at tunnel axis, i.e. on the middle of the street, within the admissible range defined by the planner. Settlements along this stretch remained always within admissible range, namely always below 15 mm. Figure 9 shows the settlement development in time for monitoring cross-section at km 11+437. At this cross-section the overburden is 10 m high and the groundwater level was located exactly at tunnel crown level. Settlements at thi cross-section stabilized at 9 mm after passage of the 11.5 m excavation diameter shield. Face pressure at crown during this passage was 1.1 bar.

Fig. 8 Pressure oscillations in the excavation chamber, earth pressure sensor 1, top sensor. Min max range shown here are 1.26 bar to 1.36 bar (+/- 0.05 bar)

Fig. 7 Average density of the muck in the excavation chamber during shield advance(Range 1.3 kN/m3 to 1.7 kN/m3; Average aroung 15 kN/m3)



7.5 Net advance rates and global performance The shield performance in sands is attaining average values of 13 rings/working day (i.e. 23.4 m/working day). Maximum attained performance to date has been 16 rings/day (i.e. 28.8 m/day). High utilization factors, as high as 95% are being attained by shift (Figure 10). Average penetration amounts 15 mm/rev and advance speed 30 mm/min.

Penetration is governed by the resistance of the ground. Thrust and steering force adjustment allows increasing penetration up to values that are only limited by the maximum operative cutter-head torque. Figure 11 plots steering force vs. penetration. Actively increasing the steering force up to values around 27,000 kN to 29,000 kN, penetration values of 20 mm/rev can be reached.

Fig. 11 Correlation between increasing steering force (horizontal axis) and penetration (vertical axis)

Fig. 10 Activity distribution during a 8 hrs shift (blue: tunnelling 62.8% ; green: ring building 32.7% ; red: down time 4.5 %)

Fig. 9 Settlement development cross-section km 11+427



8. Data Management and Process Controlling Whereas the mechanized tunnelling process depends on the interaction and collaboration of sev-eral partial processes starting from casting the lining segments via a large number of production and logistics steps to the final deposit of extracted material, the fundamental core process of the

whole process is the tunnel boring machine. This machine comprises a manifold of complex compo-nents and devices that require a constant supervi-sion and controlling in order to ensure a flawless operation and, thus, an optimal construction per-formance. For this reason, modern shield ma-chines are equipped with many different sensors that provide a continuous monitoring of the state and condition of the machine. Here, a large amount of data is generated that may sum up to 1.5 to 3.5 million data items per day over the full project duration (Maidl & Stascheit, 2015). If these data are put into the whole context of the tunnelling process, they can provide insight to the

assessment and optimization of the performance and to the prediction of potential risks and hazards. The various data sources that

are required for assessment are shown in Figure 12 that visualizes the software PROCON II as a central data warehouse that collects and combines information from various partial processes. 8.1 Data Visualization and User Interface All of the TBM operational data are stored in a unified time-and-space-correlated reference system. However, to access the data and to gain actual knowledge from it, a suitable visualization is re-quired. For this purpose, PROCON II, the software implemented at Line 4 South project, offers various options that will be addressed below. In order to assess, evaluate and further exploit the data, PROCON II offers tools for data analysis. The most important of these tools is the incorporation of formulae for the generation of computed values. An additional data analysis is the correlation diagram (see Figure 11). This diagram helps with detecting and verifying correlations between arbitrary parameters. This can help with the in-vestigation of excavation problems or to evaluate the occurrence of certain geological features. Employing the geotechnical layers along the tunnel alignment and comparing this to the actual position of the machine, the sensor readings, the target parameters and the current status can be related to the geotechnical conditions and the current location of the machine. Figure 13 shows the geotechnical section and the map feature, respectively. Related images, PDF documents can be assigned that appear in the map and in the geotechnical section at their respective positions. Furthermore, potential hazards or warnings can be marked in the map and provide more detailed information on click.

Fig. 13 Map feature indicating the tunnel alignment, settlement measurements (green and red dots), streets, buildings with different vulnerability colour codes, executed jet-grouting treatments and warning messages along the alignment

Fig. 12 Data sources for the context-aware collection of process data.



Additionally, as data management tool, based on shift and intervention reports, graphs are gener-ated that allow for a detailed analysis of standstills and tool wear. The downtimes can be assigned to categories. Here, the amount of time lost for different reasons can be assessed. Monitoring data visualisation is also implemented in the system with different types of representations: settlement curve in time (Figure 9), position ad value of settlement markers on the groundview map (Figure 13), representation of transversal settlement troughs and correlation with TBM data. Additionally, aiming for rapid information transfer and decision taking, the software manages the warning and alarming system. On the basis of the alarm levels defined by the project for the key parameter indicators, messages are automatically sent by e-mail to the operation and TBM man-agement team as soon as a threshold is exceeded for a given time interval.

9. Conclusions The present paper summarises the first experiences of EPB shield drive in full face sand excavation of Metro Line 4 south in Rio de Janeiro. TBM is prepared to handle situations in which face pres-sure control or muck conveyance in the conventional EPB mode is not feasible. However, until now the excavation in middle-coarsed grained sand is possible with efficient polymer foam conditioning. The addition of polymer to the foam injection is proving efficient to create a watertight plug in the screw conveyor, minimise sedimentation during standstill and minimise the volumes to be trans-ported for disposal. Face support pressure control and pressure-volume control of the grout injection is also enabling to keep settlements within admissible values over the axis (<15 mm) as well as the nearby build-ings despite the low overburden.

10. References

[1] Essex, R. J. 2007. Geotechnical Baseline Reports for Construction. American Society of

Civil Engineers.

[2] Önorm, B. 2005. Untertagebauarbeiten – Werkvertragsnorm Teil 2: Kontinuierlicher

Vortrieb, Ausgabe.

[3] Maidl, U. 1994. Erweiterung des Einsatzbereiches von Erddruckschilden durch

Konditionierung mit Schaum. Diss. Ruhr-Universität Bochum. Technisch-

Wissenschaftliche-Mitteilungen des Instituts für konstruktiven Ingenieurbau. 1995.

[4] Daub. 2010. Recommendations for selecting and evaluating tunnel boring machines. Köln.

[5] Thewes, M. 1999. Adhäsion von Tonböden beim Tunnelvortrieb mit Flüssigkeitsschilden;

Diss., Bergische Univ. Gesamthochschule Wuppertal, Fachbereich Bauingenieurwesen.

[6] Maidl, U. Wingmann, J. 2009. Predicting the performance of Earth Pressure shields in

loose rock. Geomechanics and Tunnelling 2.

[7] Oskar Sigl and Hiroshi Yamazaki. 2007. Predicting New Metrorail City Project. Under-

ground Structures, Perth Seminar.

[8] J.C.D.D. Pierri, Ulrich Maidl 2014. Innovative Hybrid EPB Tunnelling in Rio de Janeiro.

Proceedings ITA World Tunnelling Congress 2014.

[9] U. Maidl, J. Stascheit .Web-based Process Controlling of Shield Tunnelling. International

Conference and Exhibition of Tunnelling and Underground Space IEM Kuala Lumpur 3-5

March 2015

hybrid epb tunnelling in rio de janeiro 2015

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