Solutions for Mechanized Tunneling

Dipl. Ing. Lars Langmaack

BASF Construction Chemicals (Europe) Ltd, Zurich, Switzerland

Amit Kaul

BASF India Limited

1  GENERAL

The correct use of soil conditioning additives is very important for tunnelling security and efficiency.

The success of EPB machines - especially running through non-homogeneous, highly porous or adhesive ground conditions - depend on good mechanical engineering combined with highly efficient soil conditioning additives and their laboratory testing. 

2  TBM DESIGN VS GEOLOGY

EPB tunneling is used in homogeneous as well as heterogeneous ground conditions. Famous examples for EPB drives in very heterogeneous geological formation are BPNL Lyon with a 10,98m diameter NFM machine (Bentz et al 1997) and Barcelona Metro L9 with a 12,06m diameter Herrenknecht machine (Gabarró et al 2003). The soil distribution of these two projects is indicated in Figure 1.

Figure 1: soil distribution of Lyon and Barcelona (Langmaack 2004) 

As  a  consequence  of  the  soil  heterogeneity,  the TBMs cannot be designed for the optimum of a specific geology, but for the overall optimum (Rehm 2004). This implicates a compromise from the machine technology point of view that has to be opti- mized by using different soil conditioning agents.

The 3 most important factors for soft ground tunneling - apart from the hard rock geology - are the

• Soil permeability
• Ground water pressure
• Risk of clogging and adhesion 

2.1  Soil Permeability

The soil permeability for EPB drives can reach val- ues of up to k=10-3 for the most porous soils (BPNL Lyon, Turin) and comes down to practically imper- meable clay (Heathrow T5).

The TBM drives in clay soil - either full face or mixed face - often face clogging and adhesion prob - lems as described in 2.3. In porous soils, the faced problems are very in - stable tunnel face, uncontrolled soil and water income as well as loss of face pressure through the soil. These problems were lately described for the Milan  Metro  project  (Grandori  et  al,  2003).  Important for a successful TBM drive is the mechanical adaptation of the TBM itself including shield open- ing factor, number and choice of tools and finally the right soil conditioning with foams and polymers combined with a complete filled working chamber. The use of pure foams will not be successful - details see in chapter 3.2. 

2.2  Ground water

An important influence for the EPB drives in soft ground  is  the  ground  water level  respectively the ground water pressure. The higher the water pres- sure, the more difficult uncontrolled water income and settlement risks can be avoided. From the ma- chine technique point of view only few things can be done like long screw conveyors to decrease the pres- sure gradient, installation of piston pumps after the screw conveyor ... The most important factor to con- trol successfully the water is to fill the TBM work- ing chamber completely with a homogeneous and impermeable soil paste by help of Foams and Poly- mers. Site examples therefore are Botlek Tunnel and Alives Sewage Tunnel as described in the literature (Fernandez et al 2002) and in chapter 6.1 

2.3  Clogging and adhesion

EPB drives in clay formations - either full face or mixed face - often run into clogging and adhesion problems. Cutterhead openings can be easily closed and cutterhead tools can be turned ineffective by clogging clay. The problem of clay clogging and ad- hesion will always lead to difficult TBM guiding, slow advance rates and extensive cleaning. From the machine technique point of view only few things can be done like the design of an open cutterhead - especially in the center - and well placed mixing devices in the working chamber. Again one of the most important factors to reduce successfully the clay clogging and adhesion is the use of Foams or / and special anti-clay Polymers (details in chapter 3.3). 

3  NECESSISITY OF SOIL CONDITIONING

Only the EPB mode of advance is suitable for instable ground and sensitive surface areas (Babendererde 2003) as shown in figure 2. This driving mode can only be achieved by using efficient soil conditioning additives: reducing the TBM torque, reducing the abrasion of the cutterhead tools, the cutterhead structure and the screw conveyor, creating an impermeable soil paste. 

Figure 2: EPB mode (Babendererde 2003)

The earth pressure equilibrium can only be achieved if the TBM working chamber is filled completely with  soil  (Herrenknecht  et  al  2003,  Steiner  et  al 1994). Therefore the soil must be treated during excavation with soil conditioning agents:

• Foams
• Polymers for porous soil
• Polymers for clay soil

either separately or in combination.

3.1  Polymerized Foam

The main demand of polymerized foam as conditioning additive is to obtain the suitable rheology of the soil in order to build up and to maintain the necessary support pressure in the working chamber and to prevent high pressure variations. Foam incorporated in the earth paste has got the same effect as the big air bubble in Slurry machines. The reduction of torque and abrasion are very important additional effects, too. Foam is produced by turbulent mixing of a surfactant solution with air (Langmaack 2000). The main surfactant properties are:

•  fluidising effect on soils because of the decrease of surface tension. Soil particles are no longer bound to each other by linked water
• electrostatic repulsion effect which can separate  two  particles  attracting  each  other  by electrostatic forces.

Laboratory tests as well as the site experience show, that often each soil type, from stiff clay to sandy gravel, requires more or less an own type of foam to reach its best effectiveness. The reduction of the angle of internal friction as well as the cohesion is of high importance. In clay soil, the reduction of cohesion is one of the main tasks of foam. The type of surfactant that shall be used for a specific site has to be determined by preliminary laboratory tests with the original in situ type of soil, see chapter 3.4.

3.2  Anti-Clay-Agents for clay soils

As indicated already in the foam chapter 3.1, soil conditioning additives  shall  decrease  the  clogging and adhesion characteristics of clay soil. Therefore anti-clay polymers have to adsorb on the clay particle surface. They have to carry a high charge density to separate the soil particles and they should furthermore be able to create a steric barrier in order to avoid re-agglomeration effects. These demands can be fulfilled by some surfactants and special polymers, where as polymers are much more efficient. Anti-clay Agents are mainly used to support the de - structuring properties of the foam. Figure 6 illustrates the effect of those anti-clay polymers in clay soil. 

Figure 3: clay behavior without and with anti-clay agents

Using only foam and water, the clay particles ag- glomerate immediately and show extensive adhesion to metal surfaces (figure 3 left part). Using a TBM in this  mode,  the cutterhead  as  well  as  the  working chamber will get plugged. Only the additional use of anti-clay  polymer  results  in  separated  clay  lumps and decreases to a minimum their adhesion (figure 3 right part). A proper EPB mode with a reasonable TBM speed and reasonable maintenance work is on- ly possible under these conditions.

3.3  Structuring Polymers for porous soils

In contrast to the anti-clay polymers, the polymers for porous soil have to create cohesion in order to obtain a pasty soil rheology. 

Figure 4: comparison of original pure dry porous soil  and  as  homogeneous  paste after mixing with foam and polymer

A couple of polymers can be used in porous soils:

• water binding polymers to dry out (liquid) soils
•  soil structuring polymers which are useful in loose, coarse soils to change the soil rheology and which prevent sedimentation.
•  foam stabilising polymers

Some polymer developments are based on hydrocar- bon chains and are produced by bacterial fermentation. These polymers are water soluble, biodegradable and compatible to the foam surfactants. Both of them are safe for the foaming generator, in consequence they can be mixed with the foaming solution and passing the foam generator. Polymers also in- duce a more stable support pressure in the working chamber during boring and when stopping the machine.

All Polymers should be preferably in liquid form to avoid dosing problems and additional installation to get a solution or suspension out of the powder.  

 3.4  Importance of Laboratory testing

The necessity of soil conditioning has been de- scribed at length. One of the remaining issues is to find the best soil conditioning additives for the start of  the  project  and  provide  suitable  solutions  for each geology of the project, especially for known difficulties. Therefore, BASF can use a quite ad- vanced test method - SGAT - the soft ground abra- sion tester (Figure 5).

This  test  has  been  developed  together  with  Pal Drevland from NTNU Trondheim University, Norway. 

Figure 5: soft ground abrasion tester SGAT

This soft ground abrasion test is designed to work very similar to a TBM: boring takes place with a cutterhead-like tool into a consolidated soil. Adding the conditioners at the cutting tool - as it takes place on a real TBM - simulates the soilconditioning.

Figure 6: Benefits of good soil conditioning, SGAT test results for an Asian soil sample. 

Figure 6 illustrates how powerful modern soil condi- tioning additives can be:

drastic reduction in the above case of

- thrust > 30%

- (cutterhead) torque > 20%

- wear > 80% 

4  SITE EXAMPLES

The following chapters introduce a couple of TBM sites with difficult geologies: 

4.1  Aviles Sewer (Spain)

The Aviles Site worked with a Lovat EBP machine, diameter 3,40 m. After facing stiff clayey silt, the soil changed over a length of approximately 1.000m to pure gravely beach sand with a seawater pressure of up to 3,0 bar.

Only the use of foam in this type of geology resulted in incorrect pressure in the working chamber, uncontrolled water inflow and very slow TBM advance rates (Figure 7). 

Figure 7: sand excavation only with foam

There was no possibility on the machine to introduce additional filler suspension into the working chamber. An extra installation had been too costly and too time intensive. The alternative solution was to use additional Polymers - in order to make the soil as plastic as  possible to  be able to  install  a counter pressure against the seawater and to reduce the water content of the outcoming soil. The result is shown in  figure 8 and visualises the tremendous change. Figure 8: sand excavation with Foam & Polymer With the above mentioned soil conditioning by using a combination of foam and structurising polymer, the average daily progress achieved 27 meters with a maximum daily performance of 50,50 meters with fully filled and pressurized working chamber up to 3 bars and without any trouble with water income. Details concerning this jobsite are given by Fernan- dez 2002 and Langmaack 2001.

4.2  Toulouse Metro (France)

The Herrenknecht 7,72 m diameter EPB TBM S-208 operated by Vinci / Eiffage JV was working on the Toulouse metro extension project Lot 2 in France. The geologic formation is dry clayey silt with incor- porated sand lenses under water pressure. In ho- mogenious clay formation it was possible to exca- vate in dry mode under air pressure, but as soon as the sand lenses were hidden, the face support col- lapsed and water ingress was observed. This resulted in overall slow advance rates, extensive TBM clean- ing, conveyor belt difficulties and last but not least in doubts on face stability and surface settlements.

Only by using foam and antic lay polimwr together with water it was possible to create a non adhesive and non dogging soil paste to fill the working chamber completely and work in EPB mode. Figure 9 illustrates the quality of the exavated soil.

figure 9: Soft but not Adhesive soil after excavation 

The TBM showed reasonable advance rates of 40 - 50mm/min also in the EPB mode, no water ingress occurred any more and the face support could be secured. Figure 10 shows the clean cutterhead after the TBM breakthrough. 

Figure 10: clean cutterhead after breakthrough

4.3  Case Studies from India

Delhi Metro phase II consists of two major lines: Central Secretariat to Badarpur and Central Secretar- iat to Gurgaon. With the completion of these two lines, Delhi central is now connected with Badarpur Border at one end and Gurgaon City Centre on the other end.

Central Secretariat to Gurgaon City Centre, BC 18 Project of Delhi Metro Rail Corporation

Approximately 35 km of rapid transport system was being constructed during the year 2007 to 2010 between Central Secretariat and Huda City Centre Gurgaon.  The metro  line has  to  pass  through  the densely populated localities and some very important  areas  like  Safdarjung  Airport  and  AIIMS, hence the major part of the metro line had to constructed underground. Whilst most of the project lied in  Delhi  Silts,  highly  compacted,  and  the  above ground conditions, the majority of the construction was carried out by the use of Tunnel Boring Machines. The project consisted of 18.5 km of underground   works   between   Central   Secretariat   to Mehrauli and balance was elevated section. 

Figure 11: BC 24 station

Out of 9.5 Km underground construction, 3.25 Km of twin tunnel job was awarded to M/s Metro Tunneling Group, a joint venture between Dywidag, L&T, Samsung, IRCON International and Shimizu, as the main contractors. The project consisted of 3.1 Km long metro twin tunnel bored with 2 No Her-renknecht EPB's (6.64 m diameter) and two under ground stations at Hauz Khas and Malviya Nagar. The tunnels were constructed with  around  25,000 pre-  cast  concrete  segments,  constructed  40  km away from the site and transported during the night times to avoid any traffic blockages during the day times. The project, BC 18, was connection between Green Park and Saket (both stations excluding). 

TBM Main Drive:

1) Malviya Nagar Station to Hauz Khas Station: 1.454 m

2) Hauz Khas Station to Green Park Station: 983 m

3) Malviya Nagar Station to Saket Station: 716 m

The tunnel alignment was approximately 18 m below the ground level. Predominantly the tunnel was constructed  in  highly  compacted  Silty  Sands with water table generally below the tunnel alignment. BASF  was  involved  with  the  project  right from the start of the project with its solutions for TBM tunneling, like use of soil conditioning foams (MEYCO SLF 30: more than 200 tons used) and tail skin greases (MEYCO TSG 7 & 6: more than 80 tons used). The best advance rates in such ground conditions achieved was 27.6 m/day. The tunneling was started in December 2007 and the total tunnel- ing was successfully completed in mid of 2009. 

Figure  12:  Excavated  soil  collected  in  the  Loco

(treated with BASF Foam MEYCO SLF 30) 

Central Secretariat to Badarpur Border, BC 24 project of Delhi Metro Rail Corporation:

Package BC 24 of Phase II of Delhi Metro, be tween  Central  Secretariat  and  Lajpat  Nagar  (both excluding), was awarded to M/s ITD - ITD Cem Jv. The project BC 24 was a part of Central Secretariat to Badarpur Border line with total length of around 20 Km. The alignment of the track line was running through  very busy and  VIP  areas  such  as  Udyog Bhawan, Khan Market, Golf Link and in close vicinity of India Gate, which forced DMRC to go under- ground for almost 4.5 Km.

The project consisted of 4.1 Km twin tube tunnel bored with 4 Herrenknecht EPB’s (6.64 m L) and three underground stations namely Khan Market, Jawahar Lal Nehru Stadium and Jungpura. Around 35,000 concrete segments were used to construct more than 8 km of tunnel.

The tunneling was carried out >15 m below the ground level. Predominantly the tunneling was done in clayey silt with pebbles and the water table was above the rail levels. BASF was involved in the pro ject right from the beginning of the project and sup- ported ITD to carry out the lab trials with the soil samples taken from the launching shafts. 

Figure 13: geology for BC 24

With the help of BASF range of Soil Conditioners, MEYCO SLF 30, ITD- ITD Cem Jv constructed the tunnels before time with the record 37.5 m tunneling per day as the best advance rate, which also stands as an Asian record now.

Figure 14: muck cars at shaft level

5  CONCLUSION

As demonstrated by the site examples, it is possible to drive a TBM successful and quick also through difficult  geologies.  In  addition  to the choice of a well-adopted TBM machine, the use of the right soil conditioning additives is vital - for very permeable soil under ground water table as well as for clay soil with high clogging and adhesion potential. Additionally, neither during construction nor on the disposal sites negative influence of the soil condi- tioning additives could be observed. 

6  REFERENCES

• Babendererde 2003 : TBM mit Slurry- oder Erddruckstützung - Einsatzbereiche und Zuverlässigkeitsanalyse ,Felsbau 21 (2003), No.5, p. 155 ff
• Bentz et al 1997 : Optimierung des schaumgestützten EPB-Vortriebs, Boulevard Périphérique Nord de Lyon STUVA Tagung Berlin 1997, Alba Verlag Berlin, 1998, Volume 37, p. 88, ISBN 3 87094 636 9
• Fernandez 2002 : Aviles Sewage Tunnel, a tunnel below sea water level AFTES 2002 Toulouse, p. 131 ff, Specifique ISBN 951 04 16 2 4
• Gabarro et al 2003 :  Metro Barcelona Linea 9 - Europe's greatest metro project with tunnel boring machines of large diameter, ITA 2003 Amsterdam, p 637 ff, Balkema ISBN2: 90 5809 542 8
• Grandori et al 2003 Turin Metro Systems - Design and operation of EPB TBMs beyond the limits of this technology Felsbau 21 (2003), No.6, p. 34 ff
• Herrenknecht et al 2003 : Geotechnische und mechanische Interaktion beim Einsatz von Erddruckschilden im Fels STUVA Tagung  2003,  Dortmund, p.  175  ff,  Bauverlag ISBN 3 7625 3602 3
• Jancsecz et al 1999 : Advantages of soil Conditioning in shield tunneling: Expe- riences of LRTS Izmir , ITA 1999 Oslo, p. 865 ff., Balkema ISBN 90 5809 063 9
• Langmaack 2000 : Advanced Technology of Soil Conditioning North American Tunnelling Congress, Boston 2000, A.A. Balkema, Rotterdam, Brookfield, 2000, p. 525 ISBN 90 5809 162 7
• Langmaack 2001 Application of new TBM Additives BAUMA 2001, 6th int. symposium for tunnel construction , Verlag Glückauf GmbH, Essen, 2001, p. 27, ISBN 3 7739 5964 8
• Langmaack 2004 : EPB-Vortrieb in inhomogenen Böden: Möglichkeiten neuer Konditionierungsmittel , Tunnel- und Tiefbautagung 2004, Györ, p. 121 ff
• Marchionni et al 2002: Galleria Quattro Venti in Rom Tunnel No.8, 2002, p. 8 ff
• MBT Online Madrid MetroSur : www.degussa-ugc.com
• MBT Online Roma 4 Venti : http://www.degussa-ugc.com
• Rehm 2004 : maschineller    Tunnelvortrieb    unter    sehr    schwierigen geologischen Verhältnissen Tunnel- und Tiefbautagung 2004, Györ, p. 99 ff
• Steiner et al 1994 : Face support for a large Mix - Shield in heterogeneous ground condition Proc. of Tunnelling '94. London : Chapman & Hall