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Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguaçu, Brazil.

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1 INTRODUCTION

The economic and safe design of tunnel projects is based on the following aspect:

• qualified experts for planning, design and

construction • interaction between structural engineers and

geotechnical engineers • adequate soil investigation combined with

laboratory and field tests • design and deformation analysis using e.g.

Finite-Element-Method (FEM) • quality assurance by an independent peer

review (4-eye-principle) combined with the observational method These aspects have a particular importance

for tunnel constructions in difficult soil respectively rock and groundwater conditions and in urban areas.

Many tunnel projects have to be realised in urban areas. These underground constructions have to be carried out in a context of a very sensitive neighbourhood (Kastener et al. 2010), for e.g. high-rise buildings and World Heritage Properties.

The quality control management has to be defined in the first planning stage and covers all stages of planning, design and construction. In special situations the quality control management can be extended to the first years of the service time.

2 INDEPENDENT PEER REVIEW

PROCESS

The independent peer review is part of the 4-eye-principle and the basis for quality assurance. The process of independent peer review is shown in Figure 1. It consists of 3 divisions. The investor, the experts for planning and design and the construction company belong to the first division. Planning and design are done according to the requirements of the investor and all relevant documents to obtain the building permission are prepared. The building authorities are the second division and are responsible for the building permission which is given to the investor. The third division consists of the publicly certified experts. They are appointed by the building authorities but work as independent experts. They are responsible for

Independent peer review processes regarding stability and serviceability during planning, design and construction of underground structures

R. Katzenbach, S. Leppla Technische Universität Darmstadt, Institute and Laboratory of Geotechnics, Germany

ABSTRACT: The increasing size and population density of metropolitan areas and the along going traffic demands lead to the construction of large infrastructure projects. The construction of new underground structures has an influence on existing superstructures and the deconstruction of existing buildings has an influence on existing underground structures. To guarantee the stability and the serviceability of underground structures and the influenced neighbouring buildings independent peer review processes during planning, design and construction are necessary. The independent peer review is based on the 4-eye-principle and helps to avoid time delay in the construction process, modifications of the construction, additional expenditure and in extreme cases even damages and accidents. The paper explains the independent peer review processes and focuses on the application at challenging tunnel projects in urban areas.


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the technical supervision of the planning, design and construction.

In order to achieve the license as a publicly certified expert for geotechnical engineering by the building authorities intensive studies of geotechnical engineering in university and large experiences in geotechnical engineering with special knowledge about the soil-structure-interaction are required.

Figure 1.Indpendent peer review process (4-eye-principle).

In case of a defect or collapse the publicly certified expert can be involved as an independent expert to find out the reasons for the defect or damage and to develop a concept for stabilization and reconstruction (Katzenbach & Leppla 2013a, Katzenbach et al. 2013b). For all difficult projects an independent peer review is essential for the successful realization of the project.

3 OBSERVATIONAL METHOD

At all tunnel construction projects the observational method is applied, especially for deformation analysis in the tunnels and on the surface.

The observational method is always a combination of the common geotechnical investigations before and during the construction phase together with the theoretical modeling and a plan of contingency actions (Figure 2). Only monitoring to ensure the stability and the serviceability of the structure is not sufficient and, according to the standardization, not permitted for this purpose.

Overall the observational method is an institutionalized controlling instrument to verify the soil and rock mechanical modeling (Katzenbach et al. 1999, Rodatz et al. 1999).

The identification of all potential failure mechanisms is essential for defining the measurement concept. The concept has to be designed in that way that all these mechanisms can be observed. The measurements need to be of an adequate accuracy to allow the identification of critical tendencies. The required accuracy as well as the boundary values needs to be identified within the design phase of the observational method. Contingency actions need to be planned in the design phase of the observational method and depend on the ductility of the systems.

Figure 2. Principle of the observational method.

The observational method is applied to projects with difficult boundary conditions for verification of the design during the construction time and, if necessary, during service time.


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The requirements on infrastructure projects with regard to precision and the minimisation of impacts on neighbouring properties are extremely high. The interaction between existing buildings, tunneling processes, groundwater and subsoil is very complex. The quantity of the impacts cannot be easily predicted, even with the existing state of the art calculation methods (Knitsch 2010).

Extensive analytical analyses and numerical simulations based on high-level soil investigations and combined with a qualified, comprehensive construction supervision and the consistent application of the observational method can guarantee for the safety and serviceability of new and existing structures.

The observational method generally covers the following aspects:

• predictions with computational models • definition of acceptable limits • plan of contingency actions • carefully and permanently monitored

construction / deconstruction works • safety systems at the influenced

constructions, independent from the construction / deconstruction works

Figure 3. Admissible settlements according to MINTRA.

Limits have to be defined for the parameters of the construction / deconstruction and the displacements of the influenced structures.

One example is the use of the MINTRA criteria for monumental buildings, applied at the

tunnel construction in Barcelona, Spain. There for example admissible settlements are given in three steps, green, amber and red (Figure 3).

The observational method must not be seen as a potential alternative for a comprehensive soil investigation program. Additionally the observational method is a tool of quality assurance and allows the verification of the parameters and calculations applied in the design phase. The observational method helps to achieve an economic and save construction (Katzenbach et al. 2010).

4 CONSTUCTION OF A HIGH-SPEED RAILWAY TUNNEL CLOSE TO WORLD HERITAGE PROPERTIIES OF THE UNESCO

4.1 Project overview In the years 2010 to 2012 a double tracked

tunnel with a length of 5.6 km was built under the city centre of Barcelona as a part of the new Spanish high-speed railway line (AVE) connecting Madrid, Barcelona and the French border.

The tunnel passes directly next to the famous church of Sagrada Familia and the building “Casa Milà”. Both were planned by the architect Antoni Gaudí and belong to the World Heritage Properties of the UNESCO. Special requirements in control and surveillance had to be fulfilled during the tunnel construction to ensure the entire safety of these two outstanding buildings.

The tunnel has an outer diameter of 11.55 m and is built with a tunnel boring machine (TBM), using an earth pressure balanced shield (EPB). The bottom of the tunnel is located in a depth of at most 40 m under the ground surface. The average groundwater table is approx. 19 m above the bottom of the tunnel. The TBM was working and monitored continuously 24 hours a day.

4.2 Soil and groundwater conditions The project is located in the comparatively

plain area in the City Centre of Barcelona. Most of the soil layers passed by the TBM are tertiary layers (Figure 4). In the first kilometre of the tunnel the TBM passed tertiary clay followed by a section of tertiary silty sands. In this section


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the World Heritage Properties Sagrada Familia and Casa Milà have been passed.

The soil and groundwater conditions at Sagrada Familia Casa Milà are as follows:

• artificial filling up to 2 m depth • quaternary sandy silts and silty sands with

thickness of 4 m to 10 m • tertiary sand down 60 m with tertiary clay

layers of various thickness of 0.4 m to 2.0 m

Because of these dense clayey interceptions various aquifers are underlying the city of Barcelona. The highest aquifer is a free aquifer, the lower ones partly have confined groundwater conditions. In vicinity of Sagrada Familia the free groundwater level is about 16.5 m below the surface.

Figure 4. Geotechnical longitudinal section.

4.3 Tunnel construction at Sagrada Familia The basilica of Sagrada Familia is a church

still under construction. The construction of this outstanding building began in the year 1882. In 1883 it was re-designed by the architect Antoni Gaudí. He planned a totally new supporting structure and combined the architectural styles of many different eras.

Antoni Gaudí planned a church with a 50 m high main nave with a length of 90 m and 18 large steeples, the highest is planned with a height of 170 m.

The church of Sagrada Familia has a pile foundation. The piles under the main nave are estimated to have a depth of approx. 20 m, but the exact pile length is unknown since most of the original plans have been lost.

Until his death in the year 1926, Gaudí could finish the apse and the so called Nativity façade. The parts of the church built in Gaudí’s lifetime belong to the world heritage property of the UNESCO since 1984.

The works on the church of Sagrada Familia have been continued after the death of Gaudí. The end of the construction works is currently planned for 2026. Until today, the main nave, the Nativity and the Passion façade with altogether 8 steeples are finished. The construction works on the 6 central steeples and on the so called Glory façade have been started.

The AVE tunnel has a horizontal distance of only 4 m parallel to the Glory façade, the bottom of the tunnel is in a depth of 37 m (Figure 5).

Figure 5. Cross section at Sagrada Familia and AVE tunnel.

In order to guarantee the safety of Sagrada Familia and to avoid settlements soil improvements were executed and a bored pile wall was constructed between Glory façade of Sagrada Familia and the AVE tunnel. The diameter of the piles is 1.5 m. The axial distance is 2 m and the length approx. 40 m.

4.4 Tunnel construction at Casa Milá Another building designed by Antoni Gaudí is also close to the AVE tunnel. The Casa Milà was built from 1905 to 1910 and belongs to the World Heritage Property of UNESCO as well (Figure 6).


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Figure 6. Casa Milà and drilling works.

The minimal horizontal distance between the AVE tunnel and Casa Milà is approx. 4 m (Figure 7). A bored pile wall has been installed between Casa Milà and the AVE tunnel to fulfill the special requirements in control and construction of the AVE tunnel. The diameter of the piles is 1.2 m. They are approx. 37 m deep. The drilling works for this redundant safety margin have been complicated due to the form of the balconies (Figure 7).

The settlements due to the construction process of the bored pile wall were about 0.1 cm. The TBM passed in February 2011 and induced settlements below 0.1 cm.

Figure 7. Cross section at Casa Milà.

4.5 EPB tunneling method The tunnel is built with a tunnel boring

machine with an earth pressure balanced shield (EPB shield), shown in Figure 8. At the cutter head the soil is conditioned with water and foam injections. The homogenized earth slurry is used as support medium (Göbl 2010, Herrenknecht et al. 2010). The gap between the TBM shield and the excavated soil is injected with bentonite (Maidl et al. 2011). The gap behind the tail of the shield is permanently grouted with mortar to provide a compensation grouting procedure (Kastner et al. 2010).

Figure 8. TBM with EPB shield.

In order to reduce the subsidence risk, earth pressure balanced shield machines are preferred in an urban environment in comparison to other tunnelling methods (Saczynski et al. 2007).

Settlements occur due to changes in the stress conditions or changes in pore water pressure. With an active support pressure of the face, of the gap between shield and surrounding soil and of the gap behind the tail of the shield, these changes can be reduced to a minimum (Maidl et al. 2011). Nevertheless, settlements or ground subsidence occur in every tunnel construction process. To characterize the settlement trough evolution in width and depth over a tunnel section, the volume loss factor Vl can be used. Vl describes the volume of the settlement trough related to the theoretical tunnel volume (Burghignoli et al. 2010, Kastner et al. 2010).

As shown in Figure 9, Vl is an instantaneous value, changing with the position of the TBM and the analysed tunnel section. The final Vl usually ranges from 1 % to 2 % for tunnels excavated with the conventional method. In the case that the tunnel is constructed using an earth pressure balanced shield lower values can be


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observed, sometimes below 0.5 % (Kastner et al. 2010).

Figure 9. Settlement trough and volume loss factor V1.

The factors influencing the shape, the depth and the length of the settlement trough related to EPB tunnelling are numerous. Tthey can be divided into geotechnical, geometrical and operational parameters (Boubou et al. 2008).

4.6 Geotechnical parameters The determining factors for the tunnelling

process are given by the geotechnical parameters, i.e. the soil characteristics as for example rigidity, friction angle, cohesion, deformability, permeability and abrasiveness. Based on a good soil investigation, the choice of the tunnelling method and the specification of operational parameters can be done efficiently.

4.7 Geometrical parameters The depth and the diameter of a tunnel and

the lining geometry, meaning the thickness and shape of the lining, and the width of the gaps are the significant geometrical tunnel parameters.

Besides the geometry of the tunnel, the distance and geometry of adjacent buildings and structures have a significant influence on the magnitude of settlements (Mair 2005).

Also the geometry of the TBM itself influences the development of settlements; especially the conical shape of the shield has to be mentioned in this context (Kastner et al. 2010).

4.8 Operational parameters of the TBM There are a lot of operational parameters of

TBMs with earth pressure balanced shields that have an influence on the reaction of the soil around the TBM. The following 10 parameters have the greatest influence on the magnitude of surface settlements (Boubou et al. 2008):

• face pressure • torque on the cutting wheel • total thrust force • power excavating 1 m³ • back filling pressure • grouted volume of mortar • rate of advancement • time for boring and installing 1 ring • change in vertical angle of the TBM • change in horizontal angle of the TBM A numerical study showed that essentially

the rate of advancement, the torque on the cutting wheel, the face pressure and the change in vertical angle of the TBM correlate to surface settlements (Vanoudenheusden et al. 2006).

4.9 Monitoring In order to ensure a safe construction of the

AVE tunnel and to give the maximum possible security for the sensitive buildings in vicinity the construction works had to be executed under special control and supervision requirements following the observational method according to Eurocode EC 7 (Katzenbach & Strüber 2003). The monitoring in Barcelona was realized with a dense grid of geodetic and geotechnical measurement devices combined with a permanent monitoring of the most important operational parameters of the TBM.

4.10 Influence of geotechnical parameters The final surface settlements above the

tunnel axis after the TBM passage for a part of the tunnel are shown in Figure 10. The depth of the tunnel below groundwater level and the zones of significantly different soil conditions, i.e. tertiary clay in the first part and then a change to tertiary silty sands, are marked.

The measured surface settlements do not exceed 0.5 cm over the whole tunnel length. The volume loss factor Vl is in the range of only 0.1 %. The biggest settlements occurred at the start of the TBM between PK 5+400 and


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PK 4+700 in the tertiary clay. It is possible to explain the decrease of the settlements over the tunnel length by the adaptation of the gained experiences during the first part of the tunnelling process concerning the definition of adequate thresholds and limits for the TBM operation.

Figure 10. Settlements in geotechnical parameters.

Small heaving of less than 0.1 cm occurred between PK 3+800 and 3+400, directly after the change from tertiary clay to tertiary silty sands.

An influence of the groundwater height over the bottom of the tunnel on the displacements cannot be remarked.

In all reflections about the magnitude of the displacements the measurement accuracy of approx. 0.1 cm has to be considered.

4.11 Influence of geometrical parameters Figure 11 shows the change of the depth of

the tunnel in comparison to the measured surface settlements above the tunnel axis. Because the distance of the adjacent buildings is almost the same over the whole tunnel length, just the positions of Sagrada Familia and Casa Milà are marked.

Other significant buildings are the vertical maintenance shafts for planned maintenance stops of the TBM that will be emergency shafts in the final operation of the tunnel.

There is no noticeable effect of the depth of the tunnel below the surface, but it is remarkable that the settlements in vicinity of Sagrada Familia and Casa Milà are quite small in comparison to the other sections. This effect may be caused by an effect of the bored pile wall or an especially careful operation of the TBM.

Close to the maintenance shafts at the crossing of Padilla Street (PK 3+930) and Bruc

Street (PK 2+500) bigger settlements than in the neighboured sections occurred. Although the maximum values are only about 0.3 cm an influence of the complex procedure of the TBM for entering and leaving the shafts – including measures for groundwater drawdown inside – can be remarked

Figure 11. Settlements and geometrical parameters.

4.12 Influence of operational parameters The operational parameters of the TBM that

are expected to be the most important ones, in comparison to the surface settlements above the tunnel axis are shown in Figure 12.

Figure 12. Settlements and operational parameters.

-40 m

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Displacements[cm]

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ada

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xant

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A correlation between the comparatively low face pressure and the comparatively high settlements (max. 0.4 cm) in the starting section of the tunnel can be remarked. The used face pressure was smaller according to the lower weight of the vertical cover above the tunnel crown and the soil parameters of the tertiary clay in the first section of the tunnel. The other operational parameters show no significant influence on the measured settlements.

The three larger steps in the graph at the top of Figure 12 (construction time vs. tunnel length) show the three planned maintenance stops in the shafts. The smaller steps in the section beginning at approx. PK 3+900 show additional maintenance stops of the TBM to change the cutting tools caused by the higher abrasion in the sandy soil. These works were made under hyperbaric conditions.

5 DECONSTUCTION OF A HIGH-RISE BUILDING LOCATED ABOVE AN UNDERGROUND STATION

5.1 Project overview The city of Frankfurt am Main, Germany,

plans to reconstruct the historic centre. To cre-ate the necessary space on the surface an up to 14 storeys high-rise building was deconstructed.

Figure 13. Overview of the project area.

Figure 14. Cross section of Figure 13.

The high-rise building and its underground parking overlay 2 tunnels and an underground

station of the urban metro system. The loads of the superstructures are directly transferred onto the tunnels and underground station. Figures 13 and 14 give an overview on the primary situa-tion before the deconstruction. The sealing of the structures is made of outside layers of bitu-men-based materials. It must be guaranteed that during the deconstruction of the existing high-rise building and the construction of the new buildings the sealing of the underground struc-tures and the sublevels remain intact. For this purpose especially the uplifts due to the decon-struction and the deformations of the under-ground structures and the sublevels are moni-tored during the execution of the project according to the observational method.

5.2 Soil and groundwater conditions The soil and groundwater conditions are as follows:

- 0 m to 7 m: quarternary sands and gravel - 7 m to 30 m: Frankfurt Clay - below 30 m: Frankfurt Limestone - groundwater level in a depth of 6 m

The groundwater level is influenced by the

river Main which is 180 m far away. In the course of the geotechnical survey two aquifers have been encountered. The top aquifer is located in the noncohesive soil. The lower confined groundwater layer is located in the Frankfurt Clay and in the Frankfurt Limestone.

For the construction project the strongly time dependent behaviour of the Frankfurt Clay has to be taken into account (Katzenbach & Leppla 2013a).

5.3 Monitoring of the deconstruction works According to the classification of the project

into the Geotechnical Category 3, that is the Category for very difficult projects in Eurocode EC 7, an extensive geodetic monitoring program with 580 measuring points was installed. 220 measuring points are located around the deconstructed building, 110 are located in the underground parking and in the sublevels of the deconstructed building, 30 are in the underground station and the remaining 220 are located in the tunnels. The existing buildings were deconstructed down to the 2 sublevels.

The uplift that occurred due to the unloaded soil is shown on selected points (Figures 15 and


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16). The selected measuring points 1 to 4 are in the sublevel of the former high-rise building. Measuring point 5 is at the transition of the underground station to the tunnel. At the measuring points 1 to 4 an uplift between 1 cm and 5 cm was detected in the deconstruction time (March to December 2010). The measured uplift of measuring point 5 is less than 0.5 cm. After the deconstruction down to the sublevels in December 2010 began the modification of the sublevels. In that phase the loads only were changed insignificantly.

The uplift of the whole project area and the neighbourhood in Summer 2013 is drawn in Figure 17. The uplift due to the reduced stress level of the Frankfurt Clay is continuously raising due to the consolidation processes. A maximum uplift of 8.5 cm was measured in the area where the most storeys were deconstructed. The uplifts fade down related to the distance very quickly. No dangerous deformations of the neighbourhood were measured.

Figure 15. Selected measurement points.

Figure 16. Measurement results of selected measurement points.

Figure 17. Measured uplift of the project area.

6 CONCLUSION

The presented case studies from Barcelona and Frankfurt show that only high-level analyses and the observational method according to Eurocode 7 compared with an independent review are the guarantee for safe planning, design and construction phases for the project itself and the influenced structures. The influence of the arising deformation of the soil has to be taken into account during an early planning stage and has to be considered during analyses, design and construction. For verification of the analyses and to proof the design all projects with large soil deformations have to be monitored by means of the observational method.

The analysis of the data from the EPB drive in Barcelona show that the observed, very small surface settlements, that did not exceed 0.5 cm, cannot clearly be correlated with some special parameters. Among the geometrical parameters the position of the maintenance shafts seems to have an influence. Among the chosen operational parameters the face pressure shows the biggest influence on the displacements. The observed data shows that the surface settlements can be reduced to a minimum with a carefully and highly supervised TBM performance.

The case of the project in Frankfurt demonstrates that during the deconstruction of existing buildings the soil is unloaded and relaxes due to the reduced stress level. Cohesive soil materials like clay react strongly time dependent. For example the tertiary Frankfurt Clay relaxes time-delayed due to the unloading in the dimension of centimeters and years.


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REFERENCES

Babou, R.; Emeriault, F.; Kastner, R. 2008. Correlation between TBM parameters and ground surface settlements, neural network method. International Workshop TC 28, 12.-13. September, Budapest, Hungary, presentation slides.

Burghignoli, A.; Di Paola, F.; Jamiolkowski, M.; Simonacci, G. 2010. New Rome metro line C: approach for safeguarding ancient monuments. International Conference Geotechnical Challenges in Megacities, 7.-10. June, Moscow, Russia, Vol. 1, 55-78.

CEN European Committee of Standardisation 2008. Eurocode 7: Geotechnical design – Part 1: General Rules.

Göbl, A. 2010. The interaction of ground, TBM and segment lining with closed shield machines. Geomechanics and Tunnelling 3, 491-500.

Herrenknecht, M.; Wehrmeyer, G.; Bäppler, K.; Burger, W. 2010. Zukünftige Möglichkeiten und Grenzen der maschinellen Tunnel-Vortriebstechnik. 50 Jahre STUVA: Vergangenheit trifft Zukunft, 17.-18. June, Düsseldorf, Germany, 304-321.

Kastener, R.; Emeriault, F.; Dias, D. 2010. Assessment and control of ground movements related to tunnelling. International Conference Geotechnical Challenges in Megacities, 7.-10. June, Moscow, Russia, Vol. 1, 92-119.

Katzenbach, R.; Bachmann, G.; Leppla, S.; Ramm, H. 2010. Chances and limitations of the observational method in geotechnical monitoring. 14th Danube-European Conference on Geotechical Engineering, 2.-4. June, Bratislava, Slovakia, 13 p.

Katzenbach, R.; Leppla, S. 2013a. Deformation behaviour of clay due to unloading and the consequences on construction projects in inner cities. 18th Conference of the International Society for Soil Mechanics and Geotechnical Engineering, 2.-6. September, Paris, France, Vol. 3, 2023-2026.

Katzenbach, R.; Leppla, S.; Weidle, A.; Choudhury, D. 2013b. Aspects regarding management of soil risk. 4th International Seminar on Forensic Geotechnical Engineering, 10.-12. January, Bengaluru, India, 12 p.

Katzenbach, R.; Schmitt, A.; Turek, J. 1999. Co-operation between the geotechnical and structural engineers – experiences from projects in Frankfurt. COST Action 7, Soil-Structure-Interaction in urban civil engineering, 1.-2. October, Thessaloniki, Greece, 53-65.

Katzenbach, R.; Strüber, S. 2003. Schwierige Tunnelvortriebe im Locker- und Festgestein – Anforderungen an Erkundung, Planung und ausführung. Geotechnik 4, 224-229.

Knitsch, H 2010. Steering Supporting Measures for Urban Tunnelling. Tunnel, 2/2010, 43-49.

Maidl, B.; Herrenknecht, M.; Maidl, U.; Wehrmeyer, G. 2011. Maschineller Tunnelbau im Schildvortrieb. Ernst & Sohn Verlag, Berlin, Germany.

Mair, R.J. 2005. TC 28 – tunnelling: reflections on advances over 10 years, Geotechnical Aspects of Underground Construction in soft soil. 5th International Symsposium TC 28, 15.-17. June, Amsterdam, Netherlands, 3-10.

Rodatz, W.; Gattermann, J.; Bergs, T. 1999. Results of five monitoring networks to measure loads and deformations at different quay wall constructions in the port of Hamburg. 5th International Symposium on Field Measurements in Geomechanics, 1.-3. December, Singapore, 4 p.

Saczynski, T.M.; Pearce, M.; Elioff, A. 2007. Monitoring Earth Pressure Balanced Tunnels in Los Angeles. 7th International Symposium on Field Measurements in Geomechanics, 24.-27. September, Boston MA, USA, 1-12.

Vanoudheusden, E.; Petit, G.; Robert, J.; Emeriault, F.; Kastner, R.; Lamballerie, J.-Y.; Reynaud, B. 2006. Analysis of movements induced by tunnelling with an earth-pressure balance machine and correlation with excavating parameters. Geotechnical Aspects of Underground Construction in soft ground, Bakker et al. (Eds.), London, England, 81-86.

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