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Tunnels Konusunu
Araştıran , Geliştiren Akademi Yetkilisi
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HOW TO BUILD A TUNNEL- English |
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Erdinç Özkara - (İnş. Müh.) |
HOW TO BUILD A TUNNEL WITH TUNNEL BORING MACHINE (TBM)
This method has been used since the early 1900 in United States, it is fast, safe and it makes it possible to drive tunnels anywhere and under any conditions without any time delay. The information I am going to give you is based on my experience having finished 8 km of tunnel in turkey and 2 km of tunnel in United States.
There are two types of tunnel machines one for the soft ground and one for the rock.
I will write my experience on the soft ground tbms. All I know about the rock type tbms is that you do not need concrete lining for the support of the ground which is rock and push against the lining to move forward (push itself ahead). The machine uses, which it is called shoes against the rock ground and the tbm pushes itself by pushing against these shoes to move forward. You can advance as fast as u can take the muck out (which is cutted or excavated crushed rock material). You can use conveyor belt or train cars to take the muck out which totally effects the drive time for the tunnel. So everything the progress of the tunnel drive depends on the design of the muck removal from the tunnel and the driving capacity of the tbm.
Soft ground tbms A B C. Lets start with where they are used mainly. Most of the metro projects prefer this method due to the ground conditions and the locations of the tunnels. Tunnels usually goes under the buildings or main highways where there is always traffic running and where there is concern about settlement of the ground. Ofcourse, there is always a limit for settlement and it should be noted in the design (up to 5 cm for the roads and virtually nothing may be up to 2 cm for the ground around or underneath the buildings). This is possible with this method . To my knowledge maximum slope you can have is up to 4 % in metro projects which determines the type of structure for the line which in return will determine the length of the tunnel in that project. For the soft ground tunnel with tbm ground cover should be minimum of diameter of the tunnel which is cut diameter roughly. And for the thickness of the pre fabricated concrete linings is around 28 cm and the rebar should be designed for the stresses due overburden soil and water pressure. And it is usually made out of 5 + 1 sections which 1 is the key . it should be tapered another words this 5 +1 makes a complete circle which is called a ring this ring width should be 4 cm less on one side than the other side to follow the tbm where driving a tunnel. Design does not mean it will be a straight or as designed because it all depends on the performance of the tbm and this ring must follow the tbm where ever it goes I mean where ever it goes because the tbm will advance by pistons which is pushing against the last erected ring which should be erected and bolted 100 % before any advance can be made. These rings are erected inside the tbm and pushed outside when advancing forward to make room for the next one. Now the outside diameter comes into effect with the diameter of the tail section of the tbm which in return effects the cutting diameter of the tbm and these all are effected by the clear diameter of the tunnel which is decided based on the dynamic envelope the train and the safety standarts so this means one should decide on the clear inner diameter of the ring and order the machine accordingly. Before we go further this is very important there should be a 2 cm clearance between the outer diameter of the ring and the inner diameter of the tail section of the tbm where it is erected and pushed out without damaging the tail brushes plus giving some tolerances for the erection. There is no such thing as make up for the last ring erected it should be perfect so that there wont be any problem with the next ring erected. If you can not erect a ring you can not advance it is that simple. The good thing about these tbms is that one never sees the ground you are always either inside the machine or inside the lining or finished tunnel. The only time you see the muck or soil is that when it is coming in front of the machine to the conveyor belt. Now lets talk about the design of the system now , it should always be designed so that muck removal system which are called muck cars locomotive with enough vagons to carry the excavated material at one trip this is important because your advancement depends totally on this if u can not take the muck out at one time you have to wait for the second trip the erect you ring which also depends on the time of travel length of tunnel etc. So one should always design the system to make one trip for one advance of the tunnel and it should not make any difference how long is the tunnel. This can be overcome by installing switches inside the tunnel. There are a lot of things involved in tunneling we shall start with grouting first, there should be a grout batch plant outside the tunnel which is called portal this should be designed so that when the train gets out of the tunnel it should take 10 minutes to empty the vagons ( muck cars) , wash the grout pump, loading of the segments (which makes one ring complete) and the loading of the grout , the amount of the grout is cutting diameter minus the outside diameter of the ring and it is made of fine sand (0- 4 mm), cement and lime stone powder it has no carrying effect and it is just a fill material to fill the gap. It should be noted that also it has no water proofing purpose if it helps no problem. Water proofing is done by the gaskets around the segments which is put together with the bolts to make it water tight. There is no water proof tunnel there will always a water seepage or leak but it should be controlled and under the allowed tolerance. There are chemicals now to seal the leaking segments to have water proof tunnel if wanted. Now for the principles of driving a tunnel if it is possible you always drive tunnel up grade plus slope this will help you a lot when excavating there will be water coming from the conveyor belt and leakage around the rings when this happens you know that water will run away form the face of the tunnel to outside so you don’t have to pump or worry about flooding or slurry by the machine. If it is not possible you make a provision for the pump and the piping to pump it out. As we mentioned earlier that we have to bolt the segments to each other and to the previous ring to make a ring but these bolts can be taken out and reused after the 50 ring behind the machine. This depends on the pressure of the tbm when it is pushing itself forward and around the ring is filled with grout primary and secondary. Primary grout is done during the advance on the 3 rd ring from the tbm and the secondary or the final grouting is done at the end of the shift which is just a mixture of cement and water and the pressure is about 4 bar and the pressure for the primary one is around 2 bars and should be filled with theoretical value or close to it to make sure that all the gap is filled with grout. Tunnel should be planned 3 shifts based on 24 hrs ,30 minutes maintenance between the shifts. Each shift is around 25 people and one engineer per shift and one electrical and mechanical engineer for the project. Key to the straight tunnel within the tolerance is a good tbm driver and a good computer program. At every push of the tbm where the tbm is heading versus the alignment and grade so the operator can adjust the tbm and push accordance to that there are a lot of things involved in driving a tunnel but as we mentioned if it is planned right and with right people tunnel can be done without any major problems. Tunnel guidance is done with the laser and it is moved forward as the tunnel advances.
When planning a tunnel where there is a water problem tbm should have option of epb (earth pressure balance) what it does is it controls the muck coming inside the tbm that applies a pressure at the face in front of the tbm and this pressure pushes the water away from the machine allowing the mud come inside the tbm to the conveyor belt. This can be adjusted according to the ground conditions and how dry you want the muck to fall on the belt. What this means is that it does not make how much water you have on top of the tunnel 2 meters or 10 meters you just design the tbm and the segment seals according to this. This makes it possible of drive tunnel anywhere and under any conditions. This is not a known subject in our country and we are thinking of many complicated solutions but it is as simple as A B C and we have done it and we can do it even if it is under the Istanbul bogazi without any problems and with out paying billions of dollars. We can do it ourself and better than anybody else.
Zorlara dağlar dayanmaz, Turk atasözü
Thank you very much
Mustafa Sahin
Civil Engineer - Insaat muhendisi
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Tunnels Konusunu
Araştıran , Geliştiren Akademi Yetkilisi
Kimdir? |
| |
HOW TO BUILD A TUNNEL- English |
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Erdinç Özkara - (İnş. Müh.) |
 English | Tunnels | Yazim: 26.3.2005 | Hit : 581 BU SAYFAYI YAZDIR
Anasayfa >> ENGLISH >> HOW TO BUILD A TUNNEL- English
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