The document provides details on executing tunnel drives using the New Austrian Tunneling Method (NATM) in Manipur, India. It describes the various support elements of NATM including forepoling, drilling, blasting, mucking, shotcreting, installing wire mesh and lattice girders, and systematic rock bolting. A typical drive sequence is also outlined, beginning with forepoling installation and ending with rock bolting after two layers of shotcrete have been applied. The document emphasizes controlling deformation, stabilizing the surrounding rock mass, and providing flexible but active support during tunnel drives when using the NATM approach.

1. DRIVE DIRECTIVE FOR TUNNEL
EXECUTION IN MANIPUR REGION
(NORTH-EAST ) INDIA
By
Mr. Pradeep Goswami
Chief Geologist, Coastal Projects Ltd. Manipur
Presented in Jiribam-Tupul(Manipur) New BG Line,
North-East Frontier Railway
P. Goswami

2. Introduction
The NATM method has been developed basically in
Austria so its name make use of providing flexible
primary lining in shape of shotcrete, wire mesh, rock
bolts ,lattice girder. In case of weaker rock mass the
use of pipe forepole/pipe roofing is also restricted for
crown support which in turn lead to less over break as
well as ensure safety during the execution. The main
aspect of the approach is dynamic design based on
rock mass classification as well as the in situ
deformation observed. Hence more economical use of
the tunnel support system along with the rational
approach of execution.
P. Goswami

3. The name New Austrian Tunneling method (NATM) is a
misnomer as it is not a method of tunneling but a
strategy for tunneling which does has a considerable
uniformity and sequence. The NATM is based on
philosophy of ‘Building as you go’ approach with the
following caution. “Not too stiff, nor too flexible
Not too early, nor too late”.
The NATM accomplishes tunnel stabilization by
controlled stress release. The surrounding rock is
thereby transformed from a complex load system to a
self-supporting structure together with the installed
support elements, provided that the detrimental
loosening, resulting in a substantial loss of strength, is
avoided.
P. Goswami

4. Cont…
The self stabilization by controlled stress release is
achieved by the introduction of the so called
“semi-Rigid Lining” i.e. systematic rock bolting
with the application of shotcrete lining. On one
side, this offers a certain degree of immediate
support, and the flexibility to allow stress release
through radical deformation on the other hand.
The development of shear stress in shotcrete lining
in ached roof is thus reduced to minimum.
P. Goswami

5. History of NATM
The term New Austrian Tunneling Method
Popularly Known as NATM got its name from
Salzburg (Austria). It was first used by Mr.
Rabcewicz in 1962. It got world wise recognition
in1964. This method has been evolved as a result of
experience gained in Austrian Alpine tunneling
condition. The first use of NATM in soft ground
tunneling is done in Frankfurt metro in 1969. The
basic aim of NATM is for getting stable and
economic tunnel support systems. This method
has been very useful in complex diversified
geological condition where forecasting of the rock
mass is difficult due to rapidly changing geology.
P. Goswami

6. The Basic principles of NATM
I. Mobilization rock mass strength
II. Shotcrete protection to preserve the load-carrying
capacity of the rock mass,
III. Monitoring the deformation of the excavated rock
mass.
IV. Providing flexibility but active supports, and
V. Closing of invert to form a load-bearing support ring
to control deformation of the rock mass.
P. Goswami

7. Rock support system based on Rock
Classification

8. NATM Support Elements
 Fore Poling
 Drilling
 Loading
 Blasting
 Mucking
 Scaling/Chipping
 Face Sealing
 Wire Mesh
 Steel Rib/Lattice
 Shotcrete
 Systematic Rock Bolting

9. Forepoling
Function:
Forepoling and lagging are support measures
installed in the tunnel longitudinal direction prior
to excavation. They shorten the FREE SPAN of the
unsupported excavation surface. Forepoling and
lagging are only support aids for the excavation
and will have less function after installation of
initial supports(Rib, Shotcrete, Wire Mesh, Rock
bolt etc.).

10. Forepoling Driving Method
Start drilling out of the center with two booms. Prepare
Grouting Equipment now. As soon as the gap between
the booms is as big that the bucket will fit in, go up with
the loaded forepole bars at the basket and start installing
them, after you have filled up the Drilled-holes with the
grout. As soon as one boom is finished with drilling for
Forepoling it will switch over immediately to drill blasting
holes. The second boom will push forpoling bars into the
deepest depth as possible into the hole, if necessary, than it
will switch over also to drilling for blasting. Amount and
depth of the needed holes find in present site instruction
and follow instructions strictly.

11. Fixing of Forepoling
P. Goswami

12. Types of Forepoling
 Pipes (Diameter 1¼ - 1¾ inch)
 Rods ( Diameter around 32mm)
 Self drilling bolts
 Channel Forepoling
P. Goswami

13. Three different methods of forepoling
can be mentioned-
1. Sub- horizontal jet grouting method
2. Spiling method
3. Pipe roof method
Forepoling is generally employed under the following
conditions :
- The existence of shallow overburden above the
tunnel
- The need to restrict ground surface settlement
- Poor ground conditions
P. Goswami

14. The Jet grouting method
Jet grouting is used in especially difficult conditions
where both weak soils and thin over burden occur. Jet
grouting is normally used in sandy or gravel
formations. It should be noted that jet grouted,
reinforced column and a drilled or driven pipe ( pipe
roof method) work as a beam, while treated soil in the
spiling method makes the structure function as an
arch.
P. Goswami

15. The Spiling Method
The Spiling method consists of four different parts:
- Drilled steel pipe
- Grout inside the pipes and in voids outside
- Treated ground by permeation or fracture grouting
- Steel arch supports
P. Goswami

16. Drilling for Blasting
Both booms start drilling profile out of the top centre,
one left, and one right down to knee hole. After
finished Profile Line start again on the Top centre
drilling from inside to out side horizontal for open up
ASAP gap for basket. Then finish middle and lower
part including Cut. Meanwhile drilling Lower Point,
the bottom area needs to be cleaned out by hand.
After that drill bottom-line. Make sure that all holes
are cleaned nicely to have easy charging after. Depths
of drilling holes find into present site instruction and
follow instruction strictly.
P. Goswami

17. Drilling in Progress
P. Goswami

18. Charging
Start charging face at least 15 minutes after start
drilling out a safe position. Charging should be done
always from the top to bottom (above booms, about
safety reasons) charging upto 2m heights should be
done always in safety distance to drilling boom. Take
blasting cord with in the basket and correct detonator
straight after hole is finished charged. As soon as
charging out of the basket is done prepare ignition-
cable and correct electrical dets. Wheel-loader and
Dumper trucks have to be organized before
blasting and placed inside Tunnel.
P. Goswami

19. Explosive Loading in Progress
P. Goswami

20. Drilled Hole Ready to Loading
P. Goswami

21. Mucking
Important during mucking is to have enough Dump Truck
running, so that there is no delay in between mucking
itself while waiting for Trucks. Truck has to be as close as
possible to Muck Pile(Max.10m) waiting trucks have to be
placed close to loading bay to guaranty that the replacing
of unloaded and loaded truck is possible meanwhile the
wheel-loader is loading itself at Muck Pile. Mucking has to
be not lower than the bottom plate of last lattice girder.
Latest after 50% of mucking time it needs to organize
the shotcrete robot and the shotcrete itself, so that the
robot is connect and transits miller is standing
behind robot close to the face when the excavator,
after scaling, is leaving the face.
P. Goswami

22. Mucking in Progress
P. Goswami

23. Scaling/Chipping
The Excavator is standing more or less close to the
face. As soon as the wheel-loader is moving out, it’s
going in and start scaling loose rocks down from the
face and preparing the rough profile so that there is no
“under-profile”. Then preparing also a rough stand for
the robot and if necessary a small drainage etc.
P. Goswami

24. Scaling/Chipping in Progress
P. Goswami

25. Pre Shotcrete/Face sealing
First the profile and the after needs to be washed down so
that there will be a good connection between rock and
shotcrete. Areas where are over break situations should be
sparyed first with a thin layer(max 10 cm). The shotcrete
needs to be sprayed from the bottom upwards to have a
good abutment for upper shotcrete. After a while it needs
to go back to “over Break” area for the next thin layer. Two
third of the face needs to be sprayed I between as face
support. Pre shotcrete has to finish at least 80% of the total
needed shotcrete, preparing the rough profile as much as
possible, so that after wire mesh and lattice girder the
second shotcrete is more or less only the final polishing.
Maximum thickness of shotcrete read out of present site
instruction.
P. Goswami

26. Face recently opened sealed
with Shotcrete
P. Goswami

27. WIRE MESH
FUNCTION:
1. Stabilization of applied shotcrete until setting and
hardening
2. Increase of shear strength
3. Reinforcement of construction joints
4. Reduction and limitation of shotcrete cracking due
to creep and overstressing
5. Preventing dropping of shotcrete portion after
cracking or failing of the lining.
SIZE:
Standard size is 150 x 150 x 6 mm
P. Goswami

28. Wire mesh placing method
Place wire mesh at the bottom of left hand profile and
connect with overlapping from last wire mesh. Lift up
Jumbo Basket and bring it into the finally position.
Press it close to the rock and tie it with 2 mm wire at
the overlapping. Do the same with the right hand
profile. Last wire mesh needs to be installed on top
with overlapping of three squares to left and right
hand wire mesh. Don’t wire up the three units in
between, just at the overlapping area!! Wire mesh
needs to be movable during the installing of the
lattice girder.
P. Goswami

29. Wire Mesh
P. Goswami

30. Wire Mesh Fixing
P. Goswami

31. Method of Placing Lattice
Girder
Lift up the LG by basket and chain around two meter
and drop it against the face. Release chain install “T-
Piece” at basket and lift up LG exactly to centerline
check correct heights by supervisor. Install
immediately spacers in Top-shoulder and bottom area
hold these position by basket and right-hand shoulder
area should hold in present position by right-hand
boom. Now bring the left-hand shoulder with left-
hand boom into the position given by the supervisor.
Measure from the marked centerline at face the
needed space between centerline and left-hand
bottom plate of L.G.(3.03m).
P. Goswami

32. Bring bottom plate to exact position and secure it with
stones, timber etc. elevation is not relevant at this
moment. Still hold the position by basket and now
left-hand shoulder area should hold correct position
by left-hand boom. Now bring the right-hand
shoulder with right-hand boom into the position given
by surveyor.
Measure from the marked centerline at face the
needed space between centerline and right-hand
bottom plate of L.G.(3.03m). Bring bottom plate to
exact position and secure it with stones, timber etc.
elevation is not relevant at this moment. Connect the
wiremesh at LG, tie the spacers to the wiremesh .
P. Goswami

33. Lattice Girder
P. Goswami

34. Functions of Lattice Girder
1. Steel Rib/Lattice Girder Composite structure of
lattice girder and concrete confined to load
distribution.
2. Carrying of “Green” shotcrete.
3. Profile control
4. Support for forepoling
P. Goswami

35. SECOND SHOTCRETE
Start spraying at the bottom area of previous lattice
girder move in direction to new lattice girder to secure
the girder at bottom area first. Spray around 1m high,
than switch over to other side of Lattice Girder and do
the same over there. Without doing these, the
possible overloading with shotcrete at one side,will
push the whole Lattice Girder out of direction. Now
spray the area of the old LG and old overlapping first to
secure the new Wiremesh. After that do the same with
the area at new LG.ter the LG is covered nicely with
shotcrete spray the profile from one side bottom to
another side bottom, so that the wiremesh is covered
with shotcrete max. 3 m inside. Make sure that the
thickness of shotcrete is as written in present site
instruction. P. Goswami

36. FUNCTIONS OF SECOND SHOTCRETE
1. As sealing Shotcrete:
 Avoids first loosening of the surrounding ground.
 Closes joints and prevents fall-downs; so activating
the rock arch.
 Seals the surrounding ground (air sensitive grounds).
2. As main shotcrete (carrying member)
 To carry the load introduced by the ground in the
lining (mainly normal forces, no bending moments
if tunnel shape optimal).
P. Goswami

37. Shotcreteing in Progress

38. Rock Bolting
Mark the position of rockbolts with spraypoint. Start
drilling from the top down, so that the basket is able to
work above the boom, as soon as the first hole is
drilled. Depend on what kind of rockbolt needs to be
installed carry on like explained below -

39. Types of Rock Bolts
SN-Bolt:
Fill up the holes with a stiff grout. Install the rockbolt by hand or by
boom. Install the plate and screw the nut on by hand.
SDR-Bolts:
Install the Rockbolt at the Boom and drill it in the full length, after
that pull back 5 cm to make sure that the grout is able to squeeze out of
the drill bit. Disconnect SDR FROM hammer and do the next SDR the
same way. Now you have to close the gap around the installed SDR
(empty cement bag etc.) so that no Grout is flowing out. Than
Grouting Crew is connecting Grout hose to SDR and is pumping in the
Grout into the SDR until Grout is flowing out through the “cement
bag”. Then place and tie the Nut by spanner. Now pump again until the
Grout will squeeze out between Rock and Plate.

40. SYSTEMATIC ROCK BOLTING
ANCHOR MORTAR:
1. Rock bolts must be fully grouted(except expansion bolts)
2. Behavior of the anchor mortar is of significance:
 Its ultimate strength must not be reduced to any great
extent as result of displacements, affecting the mortar
during the setting time.
 The quality of the mortar influence considerably the
success of the anchoring system.
MORTAR TYPES:
 Special anchor mortar with expanding agent
 Cement – sand mixture(1:2)
 Net Cement (for injection bolts)

41. DIRECTION OF ROCK BOLTS
In general the direction of rock bolts shall be radial, i.e.
perpendicular to the lining (±10 degrees). It may deviate from the
general radial direction to cope with unfavorable bedding, etc.
P. Goswami

42. Systematic Rock Bolting In Progress
with Rocket Boomer

43. Drive Direction for 1.00M Pull
Sr. No. Item Works Duration Remarks
1 Fore Poling 1 Hour
2 Drilling For
Blasting
1 Hour
3 Charging, Blasting
& Defuming
1 Hour and 40
Minutes
Wheel-loader & Dump Trucks have to be organized
before blasting & placed inside Tunnel.
4 Mucking 3 Hour Latest after 50% of Mucking Time it needs to organize the
shotcrtete Robot and the shotcrete itself, so that the robot is
connect and the Mix Truck is standing behind Robot close to
the Face when the Excavator, after scaling , is leaving the
face.
5 Scaling 20 Minutes
6 Pre
Shotcrete/Face
Scaling
1 Hour As soon as the Pre shotcrete is running wire mesh and Lattice
Girder has to be prepared and placed close to the face,
needed equipment (Jumbo) has to be arranged as close as
possible to Plugbox.
7 Wire Mesh 30 Minutes Don’t wire up the three unites in between, just at the
overlapping area! Wire mesh needs to be movable during the
installing of the lattice girder.
8 Lattice Girder 1 Hour Meanwhile the lattice girder will set up into right position
make sure that the robot is waiting close to the switchbox &
Mixtruck with shotcrete is inside tunnel.
9 Second Shotcrete 30 Minutes During spraying the second layer of shotcrete prepare
Rockbolts, Plates etc. and place everything close to Face.
Make sure that the Equipment like Grout pump and Jumbo is
as close as possible to the switchbox, ready to be connected.
10 Rock Bolting 45 Minutes
Total Duration 10 Hr. 45 Min.

44. TIME CYCLE PATHS

45. Start at Point one the Next cycle!!
These directives has to be seen more as Guide Line than as
Directive. It shows the standard Cycle in standard
conditions. Depends on different rock conditions and other
circumstances it may change into other priorities of doing
the cycle. In the summary of experience it will help to set
up a system in doing tunnel the NEW AUSTRIAN
TUNNELING METHOD.
CHIEF ENGINEERING GEOLOGIST
PRADEEP GOSWAMI
Coastal Projects Ltd.
MANIPUR (India)

46. THANK YOU
P. Goswami