NATM
NEW AUSTRIAN
TUNNELING METHOD
Prepared by- Suman Paul
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.
 The first use of NATM in soft ground
tunnel in Frankfurt (Europe) metro in
1969.
 The basic aim of NATM is for getting
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Prepared by- Suman Paul
Need of Pandoh Takoli Bypass
Project
Social Benefit: The project would help
expedite the improvement of infrastructure
in Himachal Pradesh and reduce the time
and cost of travel for traffic plying on the
stretch.
 Travel Time: Travel time would be reduced
by 1.3hr to 2 hrs.
 Infrastructure: Construction of 10 new 2
lane tunnel for a total length of 16.8km and
1 existing tunnel and 19km of 4 Lane
Highway.
 Safety: Safety of traveler will be increased
because of Tunnel infrastructure and 4
Lane Highway infrastructure.

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DEFINITION OF NATM

The New Austrian Tunneling Method is a
support method to stabilize the tunnel
perimeter by means of sprayed concrete
,anchors and other support and uses
monitoring too control stability.
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BROAD PRINCIPLES OF
NATM

The NATM integrates the principles of
the behavior of rock masses under load
and monitoring the performance of
underground
construction
during
construction.
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7 FEATURES OF NATM
Mobilization of the strength of rock mass
 Shotcrete protection
 Measurements
 Primary Lining
 Closing Invert
 Rock mass classification
 Dynamic Design

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FEATURES OF NATM
Mobilization of the strength of rock
mass - The method relies on the inherent
strength of the rock mass being conserved
as the main component of tunnel support.
Primary support is directed to enable the
rock to support itself.
 Shotcrete protection - Loosening and
excessive rock mass deformation should
be minimized by applying a layer 25-50mm
of sealing shotcrete immediately after
opening of the face.
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FEATURES OF NATM
Measurements - Every deformation of the
excavation must be measured. NATM
requires installation of sophisticated
measurement
instrumentation.
It
is
embedded in lining, ground such as load
cells, extensometers and relectors.
 Primary Lining - The primary lining is thin.
It is active support and the tunnel is
strengthened not by a thicker concrete
lining but by a flexible combination of rock
bolts, wire mesh and Lattice girders.

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FEATURES OF NATM
Closing of invert – Early as far as
possible closing the invert so as to
complete the arch action and creating a
load-bearing ring is important. It is
crucial in soft ground tunnels
 Rock mass classification - The
participation of expert geologist is very
important as the primary support as well
as the further designing of supports etc
during the excavation of rock requires
the classification of the rock mass.
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FEATURES OF NATM

Dynamic Design – The deigning is
dynamic during the tunnel construction.
Every face opening classification of rock
is done, and the support are selected
accordingly. Also the design is further
reinforced based on the deformation as
noticed during the monitoring.
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PSYCOLOGY BEHIND
NATM


a “design as you go” approach to
tunnelling providing an optimized
support based on observed ground
conditions.
a “design as you monitor” approach
based on observed convergence and
divergence in the lining as well as
prevailing rock conditions.
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WHY NATM
Flexibility to adopt different excavation
geometries and very large cross
sections.
 Flexibility to install additional support
measures, rock bolts, dowels, steel ribs
if required.
 Easy to install a waterproof membrane.
 Easy to install primary support, i.e.
shotcrete.
 TBM (Tunnel Boring Machine) is not an
effective method as compared to NATM
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SEQUENCE OF EXECUTION
OF NATM
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Portal Development
Survey and Profile making
Drilling Hole and Rock bolting
Loading Explosive
Charging (20 to 30 min)
Blasting
Defuming Through Ventilation Pipe
Removal Of Muck
Scaling/Chipping With Boomer
SHOTCRETE Ist Layer ( Upto 50mm )
SURVEY
SUPPORT SYSTEM (Wire Mesh , Steel Rib/Lattice
Girder )
SHOTCRETE 2ND LAYER (150 – 200mm)
Systematic Rock Bolting
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PORTAL DEVELOPMENT

Portal development is the process to
stabilize the entrance and exit of the
tunnel
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SURVEY AND PROFILE
MAKING
The basic procedure of tunnel surveying
is to align the center line in the ground
and transfer that to the tunnel.
 Marking of profile as per design and
drawing of that tunnel.

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SURVEY AND PROFILE
MAKING
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DRILLING HOLE & ROCK
BOLTING
Process of making hole in rock surface
for blasting and rock bolting.
 Equipment used- Drill Jumbo, Crawler
Drill

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DRILLING HOLE
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LOADING EXPLOSIVE
TYPES OF EXPLOSIVES Explosives based on chemical nature

 High or detonating explosives- Process is
extremely rapid, almost instantaneous.
 Low or deflagrating Explosives- Low velocity
of burning and produce pressure by
progressive burning

Explosives based on availability
 Powder explosives
 Disruptive explosives or Dynamites
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LOADING EXPLOSIVE
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CHARGING
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A exporter having a red light/button used for blasting
Start charging face at least 15 minutes after start
drilling out a safe position.
Charging should be done always from the top to
bottom , it should be done 200m away from the
explosive area.
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.
Push red light for blast after it give signal.
Wheel-loader and Dumper trucks have to be
organized before blasting and placed inside Tunnel.
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BLASTING
Definition- The process of breaking rocks
into smaller pieces by use of explosives. A
picture of phase with explosive loading
Ready for blasting.
 Control Blasting

 Volume excavation difficult to achieve
 Permission & license is must for usage, storage
& transportation
 Limited permission available for usage, when its
must
 Usage is still restricted like drill & blast
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BLASTING
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VENTILATION IN TUNNEL

Ventilation is required because of :
 Remove Dust and Gas caused by drilling,
blasting, loading of excavated materials and
Shotcreting.
 Exhaust gas and smoke discharged by
diesel
 Poison gas made from explosive or organic
solvent
 Poison gas, flammable gas or oxygen
shortage gas in ground
 High temperature and high humidity
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VENTILATION IN TUNNEL
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FACE MAPPING
After the blast, geological mapping of
excavated face are being done with
their orientation with geological features
(Joints, Faults & Folds) w.r.t tunnel is
prepared.
 Based
on Geological observation
support system is decided, and support
is being installed.
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MUCKING

Mucking is a process in which muck is
carried in the dump truck after blasting
and throw outside the tunnel. Mucking
has to be not lower than the bottom
plate of last lattice girder.
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MUCKING
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SACLING/CHIPPING
Scaling/Chipping
in
progress
of
removing lose rock from heading of
tunnel and it helps to make space for
tunnel support by remove under cut after
blasting.
 Scaling/chipping is done with boomer
machine to remove the muck which stick
to the phase
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ROCK MASS
CLASSIFICATION
The excavation in the rock is dependent
on the rock class based on several
factors such as – compressive strength
of rock, water condition, number of
cleavages, condition of cleavages, dip
and stike of the rock etc.
 There are various approaches of
classification of the rock mass and most
predominantly are RQD,RMR and Q
factor of the rock mass.
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ROCK QUALITY
DESIGNATION INDEX (RQD)

The Rock Quality Designation index
(RQD) was developed to provide a
quantitative estimate of rock mass
quality from drill core logs. RQD is
defined as the percentage of intact core
pieces longer than 100 mm in the total
length of core. The core should be at
least NW size (54.7 mm in diameter)
and should be drilled with a double-tube
core barrel.
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RMR VALUE

RMR value dends upon the following
factors:
 1. Uniaxial compressive strength of rock
material. 2. Rock Quality Designation
(RQD). 3. Spacing of discontinuities. 4.
Condition of discontinuities. 5. Groundwater
conditions. 6. Orientation of discontinuities.
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Q FACTOR

Q Factor: It depends on the following:
 i) Block size
 ii) Inter block shear
 iii) Active stress
 iv) Reduction for joint water flow
 v) Presence of weakness zones

Q factor varies from 0.01 to 1000 i.e.
from exceptionally poor rock to
exceptionally good rock
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ROCK SUPPORT SYSTEM
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COMPONENTS AND
SEQUENCE OF EXECUTION
AFTER
BLASTING
I.
Sealing Shotcrete – Shotcrete 25-50mm
II.
III.
IV.
V.
VI.
generally
Fixing of Lattice Girder – lattice girder is 3
Bars of steel reinforcement placed at three
corners of triangle with 8mm steel bar for
connection. Easy to handle comparison of
steel ribs.
Fixing of wire mash – generally used 6mm
thick wires (fig 6 )
Primary Lining with Shotcrete – In layers
each not thicker than 150mm
Rock Bolting – discussed separately
Pipe Fore poling – Used for crown support
for next Excavation cycle ( for Rock Class
after III only)
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SHOTCRETE
Shotcrete is the generic name for cement,
sand and fine aggregate concretes which
are applied pneumatically and compacted
dynamically under high velocity”.
 Pre-shotcrete

 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
sprayed 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.
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TYPE OF SHOTCRETE

Wet Mix Shotcrete:
 All ingredients, including water are thoroughly
mixed and introduced in the delivery equipment.
Wet material is pumped to the nozzle where the
compressed air is added to provide high velocity
for placement and consolidation of the material
into the receiving surface.

Dry Mix Shotcrete:
 Pre-blended dry or damp materials are placed
into the delivery equipment. Compressed air
conveys material through a hose at high velocity
to the nozzle, where the water is added. Material
is consolidated on the receiving surface by high
impact velocity.
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DRY VS WET SHOTCRETE
Dry Shotcrete
I.
Less power input
is required.
II. Low initial cost,
low maintenance
and cheaper
III. Productivity is
comparatively
low
IV. Rebound is
greater

Wet Shotcrete
I.
Greater power
required.
II. Costlier process.
III. Higher
productivity
about 10-16
cum/hr
IV. Rebound is less
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SHOTCRETE
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TUNNEL SUPPORT
SYSTEM

Support acting by applying a confining
pressure to the surrounding ground
 Shotcrete
 shotcrete with lattice girders

Support applying both a confining
pressure and acting as reinforcement of
the surrounding ground
 Un-grouted mechanically or chemically
anchored rock bolts
 Grouted (resin or mortar) rock bolts
 Driven anchor bars
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TUNNEL SUPPORT
SYSTEM

Systems providing plain "brute strength”
support
 heavy steel ribs
 lattice girders
 steel linings
 concrete segments
 driven tubes (umbrella arch)
 Shields

Systems which consolidate the ground to
amend its geotechnical and/or hydrological
properties
 consolidation grouting
 compressed air
 freezing
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SUPPORT SYSTEM AS PER
ROCK CLASSIFICATIONS
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WIRE MESH

Wire mesh
 Wire mesh is used to support small pieces of
loose rock or as reinforcement for shotcrete.
 Stabilization of applied shotcrete until setting
and hardening
 Increase of shear strength
 Preventing dropping of shotcrete portion
after cracking or failing of the lining.
 SIZE: Standard size is 150 x 150 x 6 mm
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FOREPOLING
The Forepoling Umbrella System (FUS)
has proved to be an efficient soil
reinforcement method in open face
tunneling.
 . The system comprises steel pipes
installed from the tunnel face to form a roof
above the tunnel heading thereby
contributing to decreasing the deformations
caused by tunneling and increasing the
tunnel heading stability.
 Generally forepoling is used for soft ground
rock conditions.
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FOREPOLING
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LATTICE GIRDER
It is used when rock is loose.
 It is used in class C , D and F of rock.
 Functions of Lattice Girder

 Steel Rib/Lattice Girder Composite structure
of lattice girder and concrete confined to
load distribution.
 Carrying of “Green” shotcrete.
 Profile control
 Support for fore poling Placing of lattice
girder
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LATTICE GIRDER
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ROCK BOLTING
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A rock bolt is a long anchor bolt, for stabilizing
rock excavations, which may be tunnels or
rock cuts. It transfers load from the unstable
exterior, to the confined (and much stronger)
interior of the rock mass.
Rock bolt are used to support the upper part of
the tunnel.
It is inserted at an inclined angle 40-60 degree
in the rock.
Type of Rock bolt
 SDA :- Self Drilling Anchor
 SN :- Store Norphus Rock bolt
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TYPES OF ROCK BOLTS
1) SN Type – Normal steel tor steel bars of
dia 28mm and above (generally used as
32mm) with cement grout, some time the
resin pouches can be used for better
anchorage.
 2) SDR – These are self drilling type of
Rock bolts with sacrificial bit at start,
suitable for rapidly collapsing soils where
the drilled hole collapses when drill bite is
withdrawn.
 3) Expansion Rock Bolts – Swellex type.
The rock bolt is inflated after insertion with
the water pressure for better anchorage.
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SECOND LAYER OF
SHOTCRETE
2nd layer of shotcrete is sprayed to cover
lattice girder and standard thickness of
shotcrete is 150 mm to 200 mm.
 Function of 2nd 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.

2. As main shotcrete (carrying member):
 To carry the load introduced by the ground in the
lining.
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TUNNEL LINING &
PAVEMENT
Fixing of Reinforcement / Waterproofing
Membrane
 Erection of Concrete Lining Gantry
 Concreting in Tunnel
 GSB laying in invert
 DLC laying in invert
 PQC laying in invert
 E&M works

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FIXING OF REINFORCEMENT
/ WATERPROOFING
MEMBRANE
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ERECTION OF CONCRETE
LINING GANTRY
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CONCRETING IN TUNNEL
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GSB LAYING IN INVERT
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DLC LAYING IN INVERT
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PQC LAYING IN INVERT
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CONCEPT OF 3D
MONITORING
3d monitoring is new technique using for
taking the right alignment of the tunnel
 Optical targets are used for determining
the coordinates for measurements
 The coordinates should be checked
daily
 It is necessary for the tunnel as by it we
know any displacement and wrong
alignments

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POINTS TO CARRY OUT A
SUCCESSFUL NATM
PROCESS
 Consideration of rock mechanics
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Selection of a proper profile
Design of flexible support and slender lining (in
rock)
Careful excavation
Maintenance of rock strength, avoidance of
loosening and over-breaks
Direct contact of rock/soil and support
Continuous
control
by
geotechnical
measurements
Installation of support without delay and in
correct
sequence
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General
Optical Target
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General
Optical Displacement Monitoring
Free Stationing
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