This document presents a case study on tunneling using the New Austrian Tunneling Method (NATM). It begins with an abstract that provides an overview of NATM and its advantages. The main body of the document then discusses key aspects of NATM, including its broad principles, rock mass classification systems, and typical sequence of execution. It describes surveying, drilling, blasting, and defuming procedures used during NATM tunnel construction. Classification systems like RQD, RMR, and Q factor are also explained for assessing rock mass quality.

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245
ISSN 2231-3907 (Print) www.enggresearch.net
ISSN 2231-3915 (Online) www.ijtonline.com
RESEARCH ARTICLE
A case study on Tunneling using NATM
Raviprasad Gupta1
, Prof. B. Ravinder2
1
PGPQSCM XII Batch, NICMAR, Hyderabad
2
Assistant Professor, NICMAR, Hyderabad
*Corresponding Author Email: ravicivil.nita@yahoo.in, bravinder@nicmar.ac.in
ABSTRACT:
The new Austrian tunneling method (NATM) is widely applied in design and construction of underground engineering
projects. The NATM is also known as sequential excavation method (SEM). The NATM is a construction method, which is
very adaptive according to changing subsoil conditions and changing shapes of cross-sections. NATM/SEM enhances the
self-supporting capacity of the rock or soil by mobilizing the strength of the surrounding ground. It is today by far the most
resistant tunnel support system in earthquake endangered zones. Experience from past projects has helped to identify several
critical success factors for safe and cost effective NATM/SEM tunneling. According to actual site conditions the design of
NATM is with a certain degree of flexibility for adjustments .Unit price contracts to support flexibility, adaptability and
balance risk sharing - a proven way to a cost effective and state-of-the-art product. Skilled contractors are familiar with the
principles of NATM/SEM and the utilization of the ground support measures. Basic idea behind NATM is that immediate
rocks are self-supporting and this method is economical. Here the cycle time achieved is 12 hrs. for class I, II and III but for
the rock classes IV and V the cycle time achieved normally is 16-18 hrs. The NATM is most appropriate support system for
tunneling in soft ground i.e. rock class IV and below. The installation of reinforced lattice girder with wire mesh, shotcrete
and rock bolting provides a uniform load bearing structure in soft rocks.
KEYWORDS: Underground, self- supporting, cost effective, flexibility, lattice girder.
INTRODUCTION:
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 varying geologic strata.
BROAD PRINCIPLES OF NATM:
NATM broadly based on the following principles:
 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 – Shotcrete is defined as a mixture of cement, aggregate, water and accelerators in correct proportions
with maximum size of aggregate less than 10mm projected at high velocity from a spray nozzle on to surface to form a layer of
pneumatically applied concrete on that surface. Loosening and excessive rock mass deformation should be minimized by
applying a layer 25-50mm of sealing shotcrete immediately after opening of the face.
 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 reflectors.
 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.
 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.
 Dynamic Design – The deigning is dynamic during the tunnel construction. Every face opening classification of rock is done
and the supports are selected accordingly. Also the design is further reinforced based on the deformation as noticed during the
monitoring.

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Classification of Rock Mass type:
Rock mass encountered during excavation cannot be said to be favorable or unfavorable only on the basis of the type of the rock.
The excavation of the rock is depends on the rock class based on several factors such as – compressive strength of rock, water
condition, number of cleavages, condition of cleavages, dip and strike of the rock etc. There are various approaches of
classification of the rock mass and most predominantly are Rock Quality Designation (RQD), Rock Mass Rating (RMR) and
Quality of the Rock Mass (Q) factor of the rock mass.
Rock Quality Designation index (RQD)
The Rock Quality Designation index (RQD) was developed by Deere (Deere et al 19671
) 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 (4 inches) in
the total length of core. The core should be at least NW size (54.7 mm or 2.15 inches in diameter) and should be drilled with a
double-tube core barrel.
RMR Value:
RMR value depends 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.
Based on this the rock mass classification as per RMR is as under:
RMR VALUE 100-81 80-61 60-41 41-20 <20
ROCK CLASS I II III IV V
DESCRIPTION Very Good Good Fair Poor Very Poor
Quality of the rock (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
The Q-value is determined with
Where,
RQD = Rock quality designation
Jn= Joint set number
Jr = Joint roughness number,
Jw = Joint water parameter and
SRF = Stress reduction factor.
Q factor varies from 0.01 to 1000 i.e. from exceptionally poor rock to exceptionally good rock.
Components and Sequence of Execution in NATM:
a) Surveying: Keeping the fact in mind that tunnel is concrete lined, so shape was to be maintained to have good profile and to
keep a check on over break. Meticulous survey was done after each blast and Profile was marked properly in the minimum
excavation line in hard strata and modified the Drilling pattern. As a result we achieved accuracy for maintaining center line and
limiting the over break much below then admissible over break 7%. Theodolite, lazer beam analyser and total stations were used
to keep the alignment (Photo 1) in order.
Photo 1: Profile marking and surveying.
International J. Technology; July – December, 2015; Vol. 5: Issue 2
246
Classification of Rock Mass type:
Rock mass encountered during excavation cannot be said to be favorable or unfavorable only on the basis of the type of the rock.
The excavation of the rock is depends on the rock class based on several factors such as – compressive strength of rock, water
condition, number of cleavages, condition of cleavages, dip and strike of the rock etc. There are various approaches of
classification of the rock mass and most predominantly are Rock Quality Designation (RQD), Rock Mass Rating (RMR) and
Quality of the Rock Mass (Q) factor of the rock mass.
Rock Quality Designation index (RQD)
The Rock Quality Designation index (RQD) was developed by Deere (Deere et al 19671
) 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 (4 inches) in
the total length of core. The core should be at least NW size (54.7 mm or 2.15 inches in diameter) and should be drilled with a
double-tube core barrel.
RMR Value:
RMR value depends 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.
Based on this the rock mass classification as per RMR is as under:
RMR VALUE 100-81 80-61 60-41 41-20 <20
ROCK CLASS I II III IV V
DESCRIPTION Very Good Good Fair Poor Very Poor
Quality of the rock (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
The Q-value is determined with
Where,
RQD = Rock quality designation
Jn= Joint set number
Jr = Joint roughness number,
Jw = Joint water parameter and
SRF = Stress reduction factor.
Q factor varies from 0.01 to 1000 i.e. from exceptionally poor rock to exceptionally good rock.
Components and Sequence of Execution in NATM:
a) Surveying: Keeping the fact in mind that tunnel is concrete lined, so shape was to be maintained to have good profile and to
keep a check on over break. Meticulous survey was done after each blast and Profile was marked properly in the minimum
excavation line in hard strata and modified the Drilling pattern. As a result we achieved accuracy for maintaining center line and
limiting the over break much below then admissible over break 7%. Theodolite, lazer beam analyser and total stations were used
to keep the alignment (Photo 1) in order.
Photo 1: Profile marking and surveying.
International J. Technology; July – December, 2015; Vol. 5: Issue 2
246
Classification of Rock Mass type:
Rock mass encountered during excavation cannot be said to be favorable or unfavorable only on the basis of the type of the rock.
The excavation of the rock is depends on the rock class based on several factors such as – compressive strength of rock, water
condition, number of cleavages, condition of cleavages, dip and strike of the rock etc. There are various approaches of
classification of the rock mass and most predominantly are Rock Quality Designation (RQD), Rock Mass Rating (RMR) and
Quality of the Rock Mass (Q) factor of the rock mass.
Rock Quality Designation index (RQD)
The Rock Quality Designation index (RQD) was developed by Deere (Deere et al 19671
) 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 (4 inches) in
the total length of core. The core should be at least NW size (54.7 mm or 2.15 inches in diameter) and should be drilled with a
double-tube core barrel.
RMR Value:
RMR value depends 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.
Based on this the rock mass classification as per RMR is as under:
RMR VALUE 100-81 80-61 60-41 41-20 <20
ROCK CLASS I II III IV V
DESCRIPTION Very Good Good Fair Poor Very Poor
Quality of the rock (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
The Q-value is determined with
Where,
RQD = Rock quality designation
Jn= Joint set number
Jr = Joint roughness number,
Jw = Joint water parameter and
SRF = Stress reduction factor.
Q factor varies from 0.01 to 1000 i.e. from exceptionally poor rock to exceptionally good rock.
Components and Sequence of Execution in NATM:
a) Surveying: Keeping the fact in mind that tunnel is concrete lined, so shape was to be maintained to have good profile and to
keep a check on over break. Meticulous survey was done after each blast and Profile was marked properly in the minimum
excavation line in hard strata and modified the Drilling pattern. As a result we achieved accuracy for maintaining center line and
limiting the over break much below then admissible over break 7%. Theodolite, lazer beam analyser and total stations were used
to keep the alignment (Photo 1) in order.
Photo 1: Profile marking and surveying.

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247
b) Drilling Loading and Blasting: Face drilling was done using Twin Boom drill jumbo (Electrically operated). Appropriate
drilling pattern need to be selected so that powder factor and pull achieved is maximum. There are many types of drilling pattern
but in tunnels two types of drilling pattern are adopted i.e. Burnt Cut and Wedge cut.
Powder factor can be expressed as a quantity of rock broken by a unit weight of explosives.
i) Burnt Cut: A series of parallel holes are drilled closely spaced at right angles to the face. One hole or more at the centre of the
face are uncharged. This is called the burn cut. Since all holes are at right angles to the face (Fig.1 and Photo 2), whole placement
and alignment are easier than in other types of cuts. The burn cut is particularly suitable for use in massive rock such as granite,
basalt etc.
Fig.1: Burnt Cut
Photo 2: Face Drilling.
ii) Wedge Cut: Blasthole are drilled at an angle to the face in a uniform wedge formation (Fig.2) so that the axis of symmetry is at
the centre line of the face. Hole placement should be carefully preplanned and the alignment of each hole should be accurately
drilled.
Fig.2: Wedge Cut
International J. Technology; July – December, 2015; Vol. 5: Issue 2
247
b) Drilling Loading and Blasting: Face drilling was done using Twin Boom drill jumbo (Electrically operated). Appropriate
drilling pattern need to be selected so that powder factor and pull achieved is maximum. There are many types of drilling pattern
but in tunnels two types of drilling pattern are adopted i.e. Burnt Cut and Wedge cut.
Powder factor can be expressed as a quantity of rock broken by a unit weight of explosives.
i) Burnt Cut: A series of parallel holes are drilled closely spaced at right angles to the face. One hole or more at the centre of the
face are uncharged. This is called the burn cut. Since all holes are at right angles to the face (Fig.1 and Photo 2), whole placement
and alignment are easier than in other types of cuts. The burn cut is particularly suitable for use in massive rock such as granite,
basalt etc.
Fig.1: Burnt Cut
Photo 2: Face Drilling.
ii) Wedge Cut: Blasthole are drilled at an angle to the face in a uniform wedge formation (Fig.2) so that the axis of symmetry is at
the centre line of the face. Hole placement should be carefully preplanned and the alignment of each hole should be accurately
drilled.
Fig.2: Wedge Cut
International J. Technology; July – December, 2015; Vol. 5: Issue 2
247
b) Drilling Loading and Blasting: Face drilling was done using Twin Boom drill jumbo (Electrically operated). Appropriate
drilling pattern need to be selected so that powder factor and pull achieved is maximum. There are many types of drilling pattern
but in tunnels two types of drilling pattern are adopted i.e. Burnt Cut and Wedge cut.
Powder factor can be expressed as a quantity of rock broken by a unit weight of explosives.
i) Burnt Cut: A series of parallel holes are drilled closely spaced at right angles to the face. One hole or more at the centre of the
face are uncharged. This is called the burn cut. Since all holes are at right angles to the face (Fig.1 and Photo 2), whole placement
and alignment are easier than in other types of cuts. The burn cut is particularly suitable for use in massive rock such as granite,
basalt etc.
Fig.1: Burnt Cut
Photo 2: Face Drilling.
ii) Wedge Cut: Blasthole are drilled at an angle to the face in a uniform wedge formation (Fig.2) so that the axis of symmetry is at
the centre line of the face. Hole placement should be carefully preplanned and the alignment of each hole should be accurately
drilled.
Fig.2: Wedge Cut

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248
c) Defuming: It means removing of foul gases by ventilation. Defuming activity shall be carried out immediately after the face
blasting. Fresh air will be pumped inside the tunnel from outside using installed ventilation system Ventilation system shall be
designed to meet the requirement of fresh air inside tunnel, systems consist of Blower fan and ducts (Photo 3).Blower fans are
fixed outside i.e. near portal for pumping fresh air in heading through flexible duct.
Photo 3: Defuming
d) Scaling: It means removal of loose rocks after blasting. Scaling is carried out after Defuming to remove the loose boulders
hanging at roof and on vertical faces of the tunnel by using the excavator.
e) Shotcreting 1st
Stage: Shotcrete is defined as a mixture of cement, aggregate, water and accelerators in correct proportions
with maximum size of aggregate less than 10mm projected at high velocity from a spray nozzle on to surface to form a layer of
pneumatically applied concrete on that surface. Shotcreting (Photo 4) will be carried out immediately after the scaling is over as
an immediate rock support. Shotcrete mix of required grade shall be prepared in batching plant outside of tunnel and will be
transported to the discharge location through transit mixers. The mix is unloaded in to the shotcrete pump from where it is
conveyed to the spraying nozzle by means of positive displacement or compressed air. During shotcrete operation operator will
ensure that accelerator is passing at the spraying end and spraying nozzle is placed perpendicular to the surface approx. 1.5mtr
away during Shotcreting which is essential to minimize wastage/rebound. Approved accelerators will be added in the shotcrete
mix at the end of spraying nozzle for quick setting.
Photo 4: Tunnel Profile after Shotcrete and rock bolt.
f) Mucking: All the scattered/spread muck of heading will be collected towards heading prior to start of mucking using the
excavator. Water will be sprinkled over the muck to avoid dust formation during mucking. Excavator and haulers of required
capacities should be deployed during mucking operation. The excavated muck will be loaded into the dumper by using excavator.
The loaded muck will be transported to the approved dumping yard for disposal.
g) Rock anchoring/ bolting: A rock bolt is a long anchor bolt for stabilizing rock excavations. It transfers load from the unstable
exterior, to the confined (and much stronger) interior of the rock mass.
i) Resin grouted type and cement type Rock Bolt: Resin grouted type and Cement type rock bolts of required diameter and
length should be preferred. Each bolt should have one end chamfered and the other end threaded over a length of 200 mm. The
rock bolt will have a bearing plate, washer and nut for tightening to fix the plate perpendicular to the surface. Tightening should
International J. Technology; July – December, 2015; Vol. 5: Issue 2
248
c) Defuming: It means removing of foul gases by ventilation. Defuming activity shall be carried out immediately after the face
blasting. Fresh air will be pumped inside the tunnel from outside using installed ventilation system Ventilation system shall be
designed to meet the requirement of fresh air inside tunnel, systems consist of Blower fan and ducts (Photo 3).Blower fans are
fixed outside i.e. near portal for pumping fresh air in heading through flexible duct.
Photo 3: Defuming
d) Scaling: It means removal of loose rocks after blasting. Scaling is carried out after Defuming to remove the loose boulders
hanging at roof and on vertical faces of the tunnel by using the excavator.
e) Shotcreting 1st
Stage: Shotcrete is defined as a mixture of cement, aggregate, water and accelerators in correct proportions
with maximum size of aggregate less than 10mm projected at high velocity from a spray nozzle on to surface to form a layer of
pneumatically applied concrete on that surface. Shotcreting (Photo 4) will be carried out immediately after the scaling is over as
an immediate rock support. Shotcrete mix of required grade shall be prepared in batching plant outside of tunnel and will be
transported to the discharge location through transit mixers. The mix is unloaded in to the shotcrete pump from where it is
conveyed to the spraying nozzle by means of positive displacement or compressed air. During shotcrete operation operator will
ensure that accelerator is passing at the spraying end and spraying nozzle is placed perpendicular to the surface approx. 1.5mtr
away during Shotcreting which is essential to minimize wastage/rebound. Approved accelerators will be added in the shotcrete
mix at the end of spraying nozzle for quick setting.
Photo 4: Tunnel Profile after Shotcrete and rock bolt.
f) Mucking: All the scattered/spread muck of heading will be collected towards heading prior to start of mucking using the
excavator. Water will be sprinkled over the muck to avoid dust formation during mucking. Excavator and haulers of required
capacities should be deployed during mucking operation. The excavated muck will be loaded into the dumper by using excavator.
The loaded muck will be transported to the approved dumping yard for disposal.
g) Rock anchoring/ bolting: A rock bolt is a long anchor bolt for stabilizing rock excavations. It transfers load from the unstable
exterior, to the confined (and much stronger) interior of the rock mass.
i) Resin grouted type and cement type Rock Bolt: Resin grouted type and Cement type rock bolts of required diameter and
length should be preferred. Each bolt should have one end chamfered and the other end threaded over a length of 200 mm. The
rock bolt will have a bearing plate, washer and nut for tightening to fix the plate perpendicular to the surface. Tightening should
International J. Technology; July – December, 2015; Vol. 5: Issue 2
248
c) Defuming: It means removing of foul gases by ventilation. Defuming activity shall be carried out immediately after the face
blasting. Fresh air will be pumped inside the tunnel from outside using installed ventilation system Ventilation system shall be
designed to meet the requirement of fresh air inside tunnel, systems consist of Blower fan and ducts (Photo 3).Blower fans are
fixed outside i.e. near portal for pumping fresh air in heading through flexible duct.
Photo 3: Defuming
d) Scaling: It means removal of loose rocks after blasting. Scaling is carried out after Defuming to remove the loose boulders
hanging at roof and on vertical faces of the tunnel by using the excavator.
e) Shotcreting 1st
Stage: Shotcrete is defined as a mixture of cement, aggregate, water and accelerators in correct proportions
with maximum size of aggregate less than 10mm projected at high velocity from a spray nozzle on to surface to form a layer of
pneumatically applied concrete on that surface. Shotcreting (Photo 4) will be carried out immediately after the scaling is over as
an immediate rock support. Shotcrete mix of required grade shall be prepared in batching plant outside of tunnel and will be
transported to the discharge location through transit mixers. The mix is unloaded in to the shotcrete pump from where it is
conveyed to the spraying nozzle by means of positive displacement or compressed air. During shotcrete operation operator will
ensure that accelerator is passing at the spraying end and spraying nozzle is placed perpendicular to the surface approx. 1.5mtr
away during Shotcreting which is essential to minimize wastage/rebound. Approved accelerators will be added in the shotcrete
mix at the end of spraying nozzle for quick setting.
Photo 4: Tunnel Profile after Shotcrete and rock bolt.
f) Mucking: All the scattered/spread muck of heading will be collected towards heading prior to start of mucking using the
excavator. Water will be sprinkled over the muck to avoid dust formation during mucking. Excavator and haulers of required
capacities should be deployed during mucking operation. The excavated muck will be loaded into the dumper by using excavator.
The loaded muck will be transported to the approved dumping yard for disposal.
g) Rock anchoring/ bolting: A rock bolt is a long anchor bolt for stabilizing rock excavations. It transfers load from the unstable
exterior, to the confined (and much stronger) interior of the rock mass.
i) Resin grouted type and cement type Rock Bolt: Resin grouted type and Cement type rock bolts of required diameter and
length should be preferred. Each bolt should have one end chamfered and the other end threaded over a length of 200 mm. The
rock bolt will have a bearing plate, washer and nut for tightening to fix the plate perpendicular to the surface. Tightening should

5. International J. Technology; July – December, 2015; Vol. 5: Issue 2
249
be done by suitable torque winch. Resin capsule should be filled 1/3rd
of the hole and remaining should be filled with cement
capsule or grouted.
ii) Cement Grouted Anchor bars/ Anchor bolts: Anchor bar/bolt is an intentioned element consisting of a rod embedded in
cement/sand grout filled hole; the anchor bar/bolt will have a bearing plate nut for tightening to fix the plate perpendicular to the
surface. The drilled hole should be filled with grout constituting cement/sand mix with lower w/c according to the technical
specifications. Admixtures for fast setting and shrinkage may be added in grout mix as required. Anchor bar/bolts will be inserted
centrally into the grout filled hole prior to initial set of grout.
iii) Self-Drilling anchor (SDA): These are self-drilling type of Rock bolts with sacrificial bit at start, suitable for rapidly
collapsing soils. SDA are the solution for the reinforcement of the tunnel circumference and advanced roof support for tunnel
excavation in the overburdened and soft fractured rock conditions.
iv) Expansion rock bolts: Swellex type, the rock bolt is inflated after insertion with the water pressure for better anchorage.
h) Wire mesh with Shotcreting 2nd
Stage: Welded wire mesh conforming to the technical specifications should be installed in
underground tunnel surface over the first layer of shotcrete as per the geological conditions .The wire mesh should be held in
position by providing hilti Pin/ steel rod anchors. As soon as the wiremesh installation is completed final layer of shotcrete
should be sprayed. Proper curing of shotcrete should be done for achieving desired strength within specified time period.
i) Steel rib support (For Class IV and V): Steel rib supports should be installed where rock class- IV, V and squeezing rock is
encountered. Proper supporting and strengthening should be done as per drawing and technical specifications.
 Forepoling: In tunnel excavation to support the heading roof horizontal reinforced bar of 25 dia. or higher dia. are inserted
which forms an umbrella (Fig.3) and ensure the stability of the perimeter and allows for neat excavation cycle.
Fig.3 Forepoling
 Pipe roofing:
Pipe roofing – the technique of pre-reinforcing the ground ahead of the tunnel face to ensure that the excavation can proceed
safely until permanent support structures can be installed. Used for crown support for next Excavation cycle ( for Rock Class
after III only)
 Lattice Girder:
Lattice girder (Photo 5) shall consist of 25mm or greater dia. reinforcing bars forming an equilateral triangle (or square) of
150mm or greater depth laced together by 12mm dia. or greater dia. reinforcing bars. In order to improve the tunnel cycle time
and expedite the rate of progress the alternative is comprising of lattice girders embedded in shotcrete. Due to their light weight
they provide major reduction in erection time and thus safety. Its structural compound when fully embedded in the shotcrete is
reliable than the steel arches in soft ground. After introduction of lattice girders rate of excavation has improved as compared to
support system with steel sets.
Photo 5 Installation of Lattice Girder
International J. Technology; July – December, 2015; Vol. 5: Issue 2
249
be done by suitable torque winch. Resin capsule should be filled 1/3rd
of the hole and remaining should be filled with cement
capsule or grouted.
ii) Cement Grouted Anchor bars/ Anchor bolts: Anchor bar/bolt is an intentioned element consisting of a rod embedded in
cement/sand grout filled hole; the anchor bar/bolt will have a bearing plate nut for tightening to fix the plate perpendicular to the
surface. The drilled hole should be filled with grout constituting cement/sand mix with lower w/c according to the technical
specifications. Admixtures for fast setting and shrinkage may be added in grout mix as required. Anchor bar/bolts will be inserted
centrally into the grout filled hole prior to initial set of grout.
iii) Self-Drilling anchor (SDA): These are self-drilling type of Rock bolts with sacrificial bit at start, suitable for rapidly
collapsing soils. SDA are the solution for the reinforcement of the tunnel circumference and advanced roof support for tunnel
excavation in the overburdened and soft fractured rock conditions.
iv) Expansion rock bolts: Swellex type, the rock bolt is inflated after insertion with the water pressure for better anchorage.
h) Wire mesh with Shotcreting 2nd
Stage: Welded wire mesh conforming to the technical specifications should be installed in
underground tunnel surface over the first layer of shotcrete as per the geological conditions .The wire mesh should be held in
position by providing hilti Pin/ steel rod anchors. As soon as the wiremesh installation is completed final layer of shotcrete
should be sprayed. Proper curing of shotcrete should be done for achieving desired strength within specified time period.
i) Steel rib support (For Class IV and V): Steel rib supports should be installed where rock class- IV, V and squeezing rock is
encountered. Proper supporting and strengthening should be done as per drawing and technical specifications.
 Forepoling: In tunnel excavation to support the heading roof horizontal reinforced bar of 25 dia. or higher dia. are inserted
which forms an umbrella (Fig.3) and ensure the stability of the perimeter and allows for neat excavation cycle.
Fig.3 Forepoling
 Pipe roofing:
Pipe roofing – the technique of pre-reinforcing the ground ahead of the tunnel face to ensure that the excavation can proceed
safely until permanent support structures can be installed. Used for crown support for next Excavation cycle ( for Rock Class
after III only)
 Lattice Girder:
Lattice girder (Photo 5) shall consist of 25mm or greater dia. reinforcing bars forming an equilateral triangle (or square) of
150mm or greater depth laced together by 12mm dia. or greater dia. reinforcing bars. In order to improve the tunnel cycle time
and expedite the rate of progress the alternative is comprising of lattice girders embedded in shotcrete. Due to their light weight
they provide major reduction in erection time and thus safety. Its structural compound when fully embedded in the shotcrete is
reliable than the steel arches in soft ground. After introduction of lattice girders rate of excavation has improved as compared to
support system with steel sets.
Photo 5 Installation of Lattice Girder
International J. Technology; July – December, 2015; Vol. 5: Issue 2
249
be done by suitable torque winch. Resin capsule should be filled 1/3rd
of the hole and remaining should be filled with cement
capsule or grouted.
ii) Cement Grouted Anchor bars/ Anchor bolts: Anchor bar/bolt is an intentioned element consisting of a rod embedded in
cement/sand grout filled hole; the anchor bar/bolt will have a bearing plate nut for tightening to fix the plate perpendicular to the
surface. The drilled hole should be filled with grout constituting cement/sand mix with lower w/c according to the technical
specifications. Admixtures for fast setting and shrinkage may be added in grout mix as required. Anchor bar/bolts will be inserted
centrally into the grout filled hole prior to initial set of grout.
iii) Self-Drilling anchor (SDA): These are self-drilling type of Rock bolts with sacrificial bit at start, suitable for rapidly
collapsing soils. SDA are the solution for the reinforcement of the tunnel circumference and advanced roof support for tunnel
excavation in the overburdened and soft fractured rock conditions.
iv) Expansion rock bolts: Swellex type, the rock bolt is inflated after insertion with the water pressure for better anchorage.
h) Wire mesh with Shotcreting 2nd
Stage: Welded wire mesh conforming to the technical specifications should be installed in
underground tunnel surface over the first layer of shotcrete as per the geological conditions .The wire mesh should be held in
position by providing hilti Pin/ steel rod anchors. As soon as the wiremesh installation is completed final layer of shotcrete
should be sprayed. Proper curing of shotcrete should be done for achieving desired strength within specified time period.
i) Steel rib support (For Class IV and V): Steel rib supports should be installed where rock class- IV, V and squeezing rock is
encountered. Proper supporting and strengthening should be done as per drawing and technical specifications.
 Forepoling: In tunnel excavation to support the heading roof horizontal reinforced bar of 25 dia. or higher dia. are inserted
which forms an umbrella (Fig.3) and ensure the stability of the perimeter and allows for neat excavation cycle.
Fig.3 Forepoling
 Pipe roofing:
Pipe roofing – the technique of pre-reinforcing the ground ahead of the tunnel face to ensure that the excavation can proceed
safely until permanent support structures can be installed. Used for crown support for next Excavation cycle ( for Rock Class
after III only)
 Lattice Girder:
Lattice girder (Photo 5) shall consist of 25mm or greater dia. reinforcing bars forming an equilateral triangle (or square) of
150mm or greater depth laced together by 12mm dia. or greater dia. reinforcing bars. In order to improve the tunnel cycle time
and expedite the rate of progress the alternative is comprising of lattice girders embedded in shotcrete. Due to their light weight
they provide major reduction in erection time and thus safety. Its structural compound when fully embedded in the shotcrete is
reliable than the steel arches in soft ground. After introduction of lattice girders rate of excavation has improved as compared to
support system with steel sets.
Photo 5 Installation of Lattice Girder

6. International J. Technology; July – December, 2015; Vol. 5: Issue 2
250
Cycle time and sequence of operation in Class (I, II and III)
Sl.No. Description Hrs.
1 Survey and profile marking 0.50
2 Drilling 2
3 Charging and Blasting 1
4 Defuming 0.5
5 Scaling/Mucking and bottom cleaning 4.5
6 Rock support /Shotcreting 2.5
7 Miscellaneous 1
Total 12
CONCLUSION:
NATM approach of design and execution of the tunneling in varied geology and especially in soft ground tunneling is
advantageous and scientific way of tunneling in comparison to the old /conventional way of tunneling. This system monitors the
rock mass deformation and designs the support system with reference to the rock mass type and deformation. The NATM
represents the state of art in modern tunneling. Its concept makes NATM more economical than conventional means of tunneling.
NATM is a technique suitable for tunneling in all types of rock but, in the case of rock class IV and poor value of rock it is
required to provide lattice girder in addition to wire mesh provision, shotcreting and rock bolting provides a uniform load bearing
structure in soft rocks. Further the use of Lattice Girder with shotcrete has been found to be more effective as an alternate support
system in poor and very poor/soft rock conditions as compared to steel sets for reducing cycle time. The cycle time achieved 12
hrs. For class I, II and III but for the rock classes IV and V the cycle time achieved normally is 16-18 hrs.
REFERENCES:
1. 50 years of NATM Experience reports by Jahre NATM, Publisher ITA – Austria Karlsgasse 5, 1040 Wien, Austriaoffice@ita-aites.at,
www.ita-aites.at
2. http://www.dr-sauer.com/technical-info/912
3. http://miningandconstruction.com/construction/completepackageforpiperoofingsolutions-1070/
Received on 10.11.2015 Accepted on 20.12.2015
© EnggResearch.net All Right Reserved
Int. J. Tech. 5(2): July-Dec., 2015; Page 245-250
DOI: 10.5958/2231-3915.2015.00028.0