Tunneling methods in softsoil

1. Submitted by:
•Durgesh Kumar Yadav

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

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

4. Soft soil
Running
Ground
Soft Ground Firm Ground
Self supporting
ground
•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.  Preventing soil movement.
 Soil pressure.
 Water seepage

6. 1. Which requires timbering.
2. Other methods.
 Which requires timbering :
i. Fore-poling method
ii. Needle beam method
iii. Belgian method
iv. Austrian method
v. American method
vi. English method
vii. Army method or Case method
viii. German method
ix. Italian method

7. • 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

9. • 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

11. 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

12.  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.

15.  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.

17. • 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

19. • 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

21. • 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 .

23. MERITS :
 Simple,economic
 Unskilled labour can driven
DEMERITS :
 Only for short tunnel

24. • 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.

25.  Other methods :
i. Linear plate method
ii. Shield method
iii. Compressed air method

26. • 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.

27. 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.

29.  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

30. • 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.

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

33. 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.

35. • 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.

36. • 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 :
I. Earth pressure varies from top to bottom in a
tunnel.
II. Pressure in floor depends upon the nature of
soil strata.
III. Value of pressure varies with moisture content
of soil strata.
IV. Compressed air will escape continuously
through the pores of soil , thus air pressure
will have vary time to time to get balanced.