1. Project work For Integrated Course No- 10109 Presented By Sri M. K.Chattopadhyay AEN/HQ/ Fairlie place /E Rly /Kolkata Sri N.C.Mondal ADEN/ Works/ Nagpur S. E. C. Rly

2. Project - Blade Shield Tunneling Under Railway tracks At Dumdum Underpass section/Metro Railway - Kolkata

3. Blade Shield Tunneling Definition- It is a system of Tunneling on soft soil constructed by a no of Moveable Steel blades (Front&Rear) supported on two nos of circular shaped Iron rings connected with the steel plates covering the entire circumference called as Shield. RCC rings is cast in situ inside the Rear blades to form tunnel

4. Tunnel Engineering Tunnel is just a hole in ground or mountain made for moving people or materials where no other means practical or adequate or to accomplish the required movement more directly,more quickly or less obstructively. The Tunnel serves myriad functions –Highway, Railway, pedestrian passage way, fresh water conveyance, waste water transport i.e Utility Corridor

5. Basic Principle- The tunnels can be made either by cut and cover method or by drilling progressively in soil Cut and cover method is suitable for smaller overburden depths For drilling, it is desirable that soils shall be good so that it stands till the arching action of the tunnel starts. –Soft soils are worst from this point of view –Keeps on falling Tunnel Engineering

6. Various methods of soft soil Tunneling (A) Blade shield – Suitable for soft soil within a reasonable depth where soil is cutted of by manual labour (B) Blind Shield - Used in Harbor and river crossing in soft soils (C) Open face, hand-dug Shield- Good for Short,small Tunnel, in hard, non Collapsing soil

7. Continued--- (D) Semi Mechanized- The Most Common Shield Equipped with “Pie plate ”Can have troubled in soft, loose or Running ground soil. Compressed air may be used For Face Stability in poor ground (E) Mechanized- A fully Mechanized machine excavates with full face cutter wheel and pick or disc cutter for various soil. It may also used with compressed air in poor ground for face stability

9. Brief Description of the Shield Shield is formed by two nos mechanized circular Iron beams 2.5 Metre apart Connected by steel plate covering the entire circumference to form a rigid structure. Altogether 23 nos of moveable blades (both at Front&Rear end) are attached with the Shield.Front blades act as cutter &rear blades acts as Outer Shutter of the Ring (Also acts as a supporting arrangement to the Earthen embankment/Soil above the tunnel) over which RCC Tunnel Ring(M25) is cast after providing necessary circular Reinforcement (Double Layer) with inner steel shutter covering the reinforced ring.

10. Continued--- Each front blade is operated by individual hydraulic jack(23 Jacks )Supported on the Shield ring at front. At the centre of the shield one platform is exists from which entire operation is carried out. Vertical /horizontal alignment of the tunnel is checked by Laser ray focused to a fixed plate on shield. Besides these front jacks,another 12 nos of hydraulic jacks are provided at the front to support the wooden planks over the face soil against any collapse.

11. Continued--- Inner Steel Shuttering arrangement (length 2.00 metre) is fabricated in the form of segments( Three nos) connected by three hinges at middle of the ring(both sides) with top segment. Bottom shutter is in the form of Semi-circular segments fixed with inner steel shutter to complete the entire shuttering arrangement.

13. Mode Of operation After assembling of entire shield with front blades& necessary Jacks (connected with the shield) over concrete base, the Diaphragm wall at the front is dismantled by jack hammer, the front blades is inserted into the face soil by 600 mm at a time and soil is protected by wooden planks through 12 nos of face jacks. Then soil in the annular space is cutted off by manual labour segment wise

15. Continued--- Initially the shield is pushed form behind by separate jacks until it is totally entered into the soil base by continuous cuttings of soil strips up to a length of 2.5 meter. Rear Blades are then connected with the shield. As the Shield advances by systematic insertion of front blades one after another followed by cuttings of soil, the blades behind the Shield occupies a clear space (These rear blades are also acts the supporting arrangement of soil/embankment above the tunnel). This vacant space the tunnel ring segment of 2.00 metre(300mm thick) was cast by RCC(M-25) over 300mm thick CC M -10 base concrete after Providing necessary steel reinforcement and inside steel shutter fitted with surface vibrator over the reinforcement Casting is done by air compressed concrete mixture machine connected with flexible pipes to the mould. Filling up the mould by flow able Concrete mixture( higher Slump by admixture) from Bottom to Top by changing the position of the flexible pipe & concrete is compacted by surface vibrator

17. Continued--- After 24 hours of casting, advancement of Shield was started by systematic cutting of face soil. Now the shield completely is in the soil bed with rear end blades partially on newly cast concrete Ring& front blades on face soil mass. Here the Advancement/Movement of Shield is carried out by the reverse action of 23 Nos face jacks against frictional resistance of soil mass with the entire surrounding surface outside the shield when the front blades were stuck well into the face soil surface (Reverse pulling action of Face jacks). Annular space between steel plate bottom &concrete top is filled up by cement grout through grout pipes (kept before casting) immediately after the leaving of the rear blades from the concrete ring area

22. Continued--- At the Junction of two tunnel Rings, necessary dowel bar is provided and Chemical grouting was injected to prevent leakage of subsoil water. During any advancement of shield, level &alignment of shield position was taken more preciously by laser &leveling machine and accordingly movement of the shield was guided. In case proper thickness of ring was not achieved due to adjustment of ring position to a correct level and alignment, additional Reinforcement were provided to that location of lesser thickness.

24. Problem Faced during Execution The shield had to move to a steeper grade as per designed data. But, due to soft soil, the automatic nose dive tendency of shield could not be controlled to the correct alignment/level of the tunnel for which the tunneling works was stopped after execution of 18 metre length. The front face of the shield was dipped into (Nose Dived) the soil. After necessary soil test, it was identified that the bearing capacity of the soil at the bottom of Tunnel ring was not sufficient to carry such huge load of the Shield assemble including the RCC tunnel rings. Hence it was decided to provide Jet Grout piles through out the length of tunnel for the improvement/increase the bearing capacity of the soil.

25. Measures for the improvement of bearing capacity As it was a busy track zone, hence a number of cement grout piles through out stretches of 120 metre were Driven by imported Rig machine where grout piles (Cement &water 1;1) at any angle were driven through the mechanically operated imported Rig and by air compressor including water jet at high velocity through concentric imported bore hole pipes of 150 mm Dia, from the both side of the embankment. Cutting of bore holes was carried out by water jet with compressed air through concentric pipe fixed on a imported Rig followed by casting

26. Continued--- Grout piles were driven at any required angle and at any depth through this machine as per site condition. Grout piles were done only up to the bottom of ring for the improvement of the bearing capacity. The nose dived shield was lifted up by hydraulic jack supported on RCC pile cap on cement grout piles driven inside the ring area. The ballast of the existing track was removed by cinder (with the imposition of necessary speed restriction) reduced the load on the Shield ultimately helped to the lift of shield

28. Continued--- On improved Bearing capacity of the soil mass throughout the stretches, RCC tunnel had been completed successfully without any hindrance.

29. Material used Cement conforms to IS 8112 (Gr-43) Steel conforms to IS 1786 Stone chips 20 mm down Sand Course graded Bentonite For boring of piles Chemical grout For leak proof joint Admixture Super plasticiser

30. Machines at site Weigh batching mixture Air compressor Shuttering vibrator Compressed air concrete machine Specially imported Rig machine for piles Laboratory at site. Lifting crane for lowering of heavy loaded imported shield Air compressor and water jetting machine for Rig Shield Assemble &other accessories imported from Italy

31. Precautions Continuous watching of track for any settlement Continuous watching of face supporting arrangement inside tunnel Closely controlled of level &alignment of shield position compared with theoretical position after any movement. Precaution during driven of Jet Piles from the top of embankment close to Track

32. Problems of Soft soil tunneling Soil Subsidence due to Water- table Depression will occur because of external dewatering as the Tunnel itself function as Ground water drain Subsidence due to Lost Ground in a soft soil tunneling operation may occur in different ways such as :- Face losses- Soil movement out in front of the shield by means of Raveling, Caving, Flowing, Running etc

33. Continued--- Shield losses- Soil movement towards the shield body between cutting edge &the tail results plowing pitching etc from the voids created by over cutters Tail loses- Soil movements towards the supporting system as it leaves the shield tail results soil moving to fill the tail voids that is created by the volume of tail skin plate plus incomplete support expansion

34. Conclusion No tunnelling work should be carried out without correct knowledge of soil strata & its bearing capacity. No tunnel should not be provided with steep gradient including provision of both vertical as well as horizontal curves. No tunnel should be allowed to move in downward direction i.e no nose dive shall be allowed. Due to necessary care had not taken, the work was completed with substantial delay and cost

35. Thank you