Tunnelling methods

Tunneling methods in softsoil

1. Tunnel engineering Submitted by: Durgesh Kumar Yadav

2. Contents Soil classification Soft soil classification Challenges in tunneling Methods of tunneling in soft soil

3. Soil classification Methods adopted for tunneling may vary with soil present in the construction site. Soil present on site can be classified as : Soft soil , which requires temporary support during and after excavation. Hard rocks or Fully self supporting soil

4. Soft soil classification Needs instant support during excavation. Dry sand, gravel ,silt etc. Roof needs instant support after excavation. Walls can withstand for few minutes only without support Soft earth, clay, damp sand. Roof can withstand without support for few minutes. Walls can stand for 1 or 2 hours after excavation. Dry earth, firm clay, cemented sand etc. Ground can stand unsupported while excavation is done for 1.5m to 5m. Sand stones, hard clay etc.

5. Challenges in tunneling Preventing soil movement. Soil pressure. Water seepage

6. Methods of tunneling in Soft soil Which requires timbering. Other methods. Which requires timbering : Fore-poling method Needle beam method Belgian method Austrian method American method English method Army method or Case method German method Italian method

7. Fore-poling method Ancient method, used for running ground Now replace by compressed air tunneling method Slow, tedious method but safe. Skilled labours and strict provision required.  Sequence of operations for 1.52x1.52 m. “A” frame prepared and placed near facing of tunnel. Poles are inserted at top which are supported by vertical posts. Bent is placed from the sheeting Now the excavation can be done under forepoles Fore pole consist of plank with wedge ends are entered one at a time Driven through half length at 15 cm/m inclination

8. Needle beam method Suitable for firm ground Needle beam consist of a stout timber beam from main temporary support SEQENCE OF OPERATION : a drift of about 1m. is driven on working face roof of this drift is lagged with sheeting apply trench jack on it a needle beam of 5 to 6m. is inserted and one end is carried on plank and other on stout post. with help of jacks , drift is widened side ways

9. Needle beam method  MERITS : economical works all right on brick lining  DEMERITS : heavy beam pushed foreward by hand no. of trench jacks required difficulties in concrete lining with machine

10. Belgian method It is used for moderately firm or hard soils.  SEQUENCE OF OPERATION : A top heading abcd for the full rise of the arch is driven & supported. Heading is widened sideways , and supported by additional crown bars on sill. Lining the arch Inserted the shore at side and excavate the mnop . Shoring is removed and space is filled with masonary .

11. Austrian method It is also known as “sequential excavation method”. A center cut is taken for full height . Cut is widened to full face. Permit short section of masonry to be completed.

12. American method It is used for railway or highway tunneling.  SEQUENCE OF OPERATION : A top drift is driven and supported by laggings,cap timber and parts Side are widened Walls plates are introduced at the springing supporting the arch set Vertical posts are driven Sides and benching are clared & tunnel lining is started

13. English method The main characteristic of this method is excavation of full section of the tunnel at once using longitudinal strutting and alternate of masonry work and excavation  SEQUENCE OF OPERATION : Top head is driven up to 5 m. It is supported on crown bars Then widening of the heading is then done by digging away the earth at each side. Then started excavation of part -2 and put the sill Part -3 in same manor and started masonry

14. Army method or Case method It is derived by USA army for constructing small tunnels at shallow depth.  SEQUENCE OF OPERATION : A common gallery of wood 1.1x1.8x0.05 mtr . Of wood is used. A top braced is removed and ground is excavated for a short distance. The box is moved ahead and set next cap. After that remove the breast one by one and excavate .

15. Army method or Case method  MERITS : Simple,economic Unskilled labour can driven  DEMERITS : Only for short tunnel

16. German method In this method 3 drifts are used to support the roof and side . One at the crown and rest two are at bottom along the wall.

17. Methods of tunneling in Soft soil Other methods : Linear plate method Shield method Compressed air method

18. Linear plate method It is presented steel plates ,plain or corrugated are used to support the soil during excavation. The size of plates are 0.91 x 0.41m with flange of .05 m. The plates are bolted to each other through holes in flange.  SEQUENCE OF OPERATION : a hole of 0.4 m depth is cut at crown and liner plate “ a” is inserted.

19. Excavated sides and place “b” and “c” plates Now two wooden wall plates of size about 20 cm. x 5 cm. And placed on each side of the bench Jacks are removed The bench is then cleared and the wall plates are under pinned at bottom.

20. Linear plate method LINEAR PLATE WITH STIFFNERES : For strenthen the plate “I” or “T” section rib is used as stiffners .  MERITES : Lighter, economical Erected with unskilled labour Fire proof Require less number of joints

21. Shield method It is used for driving a tunnel through water bearing strata. It is an equipment which acts as a bridge with roof for workers. A shield is a movable frame and it is used to support the face of the tunnel. The excavation & lining of tunnel can be carried out under protection of shield.

22. Shield method  COMPONENTES OF SHIELD : 1.The skin 2.Cutting edge 3.Propelling jack 4.The hood 5.The tail 6. Port holes

23.  SEQUENCE OF OPERATION : The ground is excavated ahead of the shield of .45 to .75 meter. The shield is jacked forward.  PRIMARY LINING : It is the name given to the heavy cast iron lining used in conjunction with the shield.  SECONDARY LINING : 5 to 7 cm. Concrete is placed over the flange of iron.  MERITS : Full dimension available Speedy Moving with constant support to the advanced tunnel.

24. Shield method

25. Compressed Air method Most modern method used for tunneling in soft grounds having water bearing strata. Timber support is not required. Support is provided by compressed air into enclosed space to prevent the collapse of roof and sides of tunnel. Usually air is used in conjunction with a shield and air-tight locks. Air pressure adopted is approximately 1kg/cm^2.

26. If pressure will be more than working hour will reduce which will increase the cost of labours and the construction cost as well. Challenges occurs in maintaining air pressure : Earth pressure varies from top to bottom in a tunnel. Pressure in floor depends upon the nature of soil strata. Value of pressure varies with moisture content of soil strata. Compressed air will escape continuously through the pores of soil , thus air pressure will have vary time to time to get balanced.

27. The End Thank you..!!