IRTG ppt.pptx

BACKGROUND
As desired by ME vide letter dated 02.12.11, following projects on
Design, Construction, Inspection & Maintenance of Tunnels have
been undertaken by GE Directorate:
S. No. Guidelines Date of
Completion
1. Guidelines for Safety in Tunnels during
Construction (RDSO/2012/GE:G-0016)
June 2012
2. Guidelines for Design & Construction of
Tunnels (RDSO/2012/GE:G-0017)
June 2012
3. Guidelines for Civil Engg. Inspection,
Maintenance and Safety in existing
Tunnels (RDSO/2012/GE:G-0015)
August 2012

 Indian Railways (IR) is presently undertaking many challenging
construction projects involving construction of tunnels under difficult
conditions. The subject of tunneling is however not comprehensively
covered in “Indian Railway Bridge Manual”; which only prescribes
stipulations for Inspection & Maintenance of Tunnels.
 Thus, necessity of separate Manual/Guidelines on design,
construction & maintenance of tunnels for guidance of field
engineers is being felt.
 Considering the importance of the subject, Geo-technical Engineering
Directorate/RDSO has brought out a comprehensive Indian Railway
Tunnel Guidelines.
 The guidelines cover the key components of a tunneling project
including Geotechnical investigation, Design Philosophy, Construction
methodology and safety during tunnel construction which includes:

 Geo-Technical Investigations
 Rock Mass And Soil Classification
 Tunnel Excavation Methods
 Tunneling Methods
 Design Aspects
 Ground Improvement And Ground Reinforcement
 Tunnel Safety During Construction
 It is expected that the guidelines will enable engineers on Indian
Railways to develop understanding about design aspects of the
tunnel and help them immensely to maintain safety during tunnel
construction.

TABLE OF CONTENTS
Chapter-1 GEO-TECHNICAL INVESTIGATIONS
Chapter-2 ROCK MASS AND SOIL CLASSIFICATION
Chapter-3 TUNNEL EXCAVATION METHODS
Chapter-4 TUNNELING METHODS
Chapter-5 DESIGN ASPECTS
Chapter-6 GROUND IMPROVEMENT AND GROUND
REINFORCEMENT
Chapter-7 TUNNEL SAFETY DURING CONSTRUCTION

Chapter 1 Geo-Technical Investigations
101 General
102 Assessing Exploration requirements of a
Tunneling Project
103 Geotechnical investigation Program for
tunnels should involve/include
104 Phases of Geo-technical Investigation
Program

 General
Planning, design and construction of a tunneling project requires
various types of investigative techniques to obtain a broad
spectrum of pertinent topographic, geologic, subsurface, geo-
hydrological, and structure information and data.
 Assessing Exploration requirements of a Tunneling
Project
(1) Because of the complexities of geology and the variety of
functional demands, no two tunnels are alike. It is therefore
difficult to give hard and fast rules about the required
intensity of explorations or the most appropriate types of
exploration. Nonetheless, following can help in the planning of
explorations:
 Plan explorations to define the best, worst, and average
conditions for the construction of the tunnel; locate and
define conditions that can pose hazards or great difficulty
during construction.

 Use qualified geologists to produce a geological model that
can be used as a framework to organize data and to
extrapolate conditions to the location of the tunnel.
 Determine and use the most cost-effective methods to obtain
the desired information.
 Anticipate methods of construction and plan to obtain data
relevant to these methods.
 Anticipate potential failure modes for the completed tunnel
and obtain the necessary data to analyze them.
 Special problems may require additional explorations.

(2) Frequently, even the most thorough explorations will not provide
sufficient information to anticipate all relevant design and
construction conditions. Here, the variation from point to point
may be impossible to discover with any reasonable exploration
efforts.
(3) The specific scope and extent of the investigation must be
appropriate for the size of the project and the complexity of the
existing geologic conditions; must consider budgetary constraints;
and must be consistent with the level of risk considered
acceptable.
(4) Since unanticipated ground conditions are most often the reason
for costly delays, claims and disputes during tunnel construction, a
project with a more thorough subsurface investigation program
would likely have fewer problems and lower final cost.

 Geotechnical investigation Program for tunnels
should involve/include:
(1) Active consultation with experienced geotechnical engineers,
geologists & designers.
(2) “What”, “Why”, “Where”, “How” & “How much” for each
Geotechnical parameter to be tested/investigated.
(3) Phasing the investigations.
(4) Keeping the investigation program and contract flexible
enough so as to enable taking up of additional investigations
as per unexpected requirements that emerge during course
of work.

 Phases of Geo-technical Investigation Program
Due to factors like high cost, lengthy duration and limited
access, investigations should be carried out in phases to
obtain the information necessary at each stage of the
project; as illustrated in the figure below:

1) Preliminary Geo-technical investigations for
Feasibility Studies
In this phase, the emphasis is on defining the regional geology and
the basic issues of design and construction. Investigations at this
stage are largely confined to:
a) Collection, organization & study of available data
 Topographical maps of Survey of India.
 Geological maps & reports of GSI.
 Geological maps and reports from agencies other than GSI.
 Geo-technical investigation reports from other agencies.
 Case histories of other underground works in the region.
 Details of land ownership (Government, Private, Forest), Access
routes, hydrological information and environmental sensitivity
from State Govt./Local bodies

 Satellite images and aerial photographs from public or private
sources
 Seismic Records.
 Records of landslides (caused by earthquakes or other reasons),
documented by the other agencies: can be useful to avoid locating
tunnel portals and shafts at these potentially unstable areas.
b) Preliminary Survey
c) Conducting investigations to compare alternative alignments
and for arriving at a conceptual preliminary design
I. Preliminary Geological field mapping
II. Exploratory borings
III. Geophysical Explorations
IV. Hydrological survey

(2) Preconstruction Planning and Engineering Phase
More detailed geotechnical investigation should be carried out in
this phase to refine the tunnel alignment and profile once the
general corridor is selected, and to provide the detailed information
needed for design of tunnel & selection of appropriate tunneling
methodology.
As the final design progresses, additional geo-technical
investigations might be required for fuller coverage of the final
alignment and for selected shaft and portal locations. Investigations
carried out during this phase are:-
a) Topographical Surveys
b) Subsurface Investigations
• Borings
• In situ testing
• Geophysical investigations
• Laboratory testing

 Laboratory Testing for soil:
Table below shows common soil laboratory testing for tunnel design
purposes:
Parameter Test Method
Soil
Identification
 Particle size distribution
 Atterberg limits wl, wp
 Moisture Content
 Unit weights γ ,γd , γz
 Permeability k.
 Core recovery
Mechanical
properties
 Unconfined compressive strength
 Triaxial compressive strength for
determination of Friction angle Φu , Φ
and Cohesion cu, c.
 Consolidation Test for determination of
Compressibility mv, cv

 Rock Testing: Table below shows common soil laboratory
testing for tunnel design purposes:
Parameter Test Method
Index
Properties
o Density
o Porosity
o Moisture Content
o Slake Durability
o Swelling Index
o Point Load Index
o Hardness
o Abrasivity
Strength
o Uni-axial compressive strength
o Tri-axial compressive strength
o Tensile strength (Brazilian)
o Shear strength of joints
Deformability o Young’s modulus
o Poisson’s ratio
Time dependence o Creep characteristics
Permeability o Coefficient of permeability
Mineralogy and grain
sizes
o Thin-sections analysis
o Differential thermal analysis
o X-ray diffraction

c) Detailed Geological Mapping
The purpose of detailed geological mapping is to define the regional
geology and site geology in sufficient detail so geological questions
critical to the tunnel can be answered and addressed. Detailed geologic
mapping should include mapping & plotting of Joints, faults, and
bedding planes.
Projected Geology and ground classes along a tunnel (based
on various investigative techniques)

(d) Groundwater investigation
Groundwater is a critical factor for tunnels since it may not only
represent a large percentage of the loading on the final tunnel lining,
but also it largely determines ground behavior and stability for soft
ground tunnels; the inflow into rock tunnels.
Groundwater investigations typically include most or all of the following
elements:
 Observation of groundwater levels in boreholes
 Assessment of soil moisture changes in the boreholes
 Installation of groundwater observation wells and piezometers
 Borehole permeability tests
 Geophysical testing
 Pumping tests

(e) Structures & Utility survey
 Structures located within the zone of potential influence may
experience a certain amount of vertical and lateral movement as a
result of soil movement caused by tunnel excavation and
construction in close proximity (e.g. cut-and-cover excavation,
shallow soft ground tunneling, etc.).
 If the anticipated movement may induce potential damage to a
structure, some protection measures will be required, and a detailed
preconstruction survey of the structure should be performed.
3) Geo-technical Investigations During Construction phase
It sometimes becomes necessary to perform additional subsurface
investigations and ground characterization during construction. Such
construction phase investigations serve a number of important
functions like:

 To verify initial ground support selection& for design/redesign.
 Documenting existing ground conditions for reference in case of
contractual claims.
 Assessing ground and groundwater conditions ahead of the
advancing face to reduce risks and improve the efficiency of
tunneling operations. This enables forewarning of adverse tunneling
conditions like potential high water inflow, very poor ground etc.
 Verification of conditions assumed for final tunnel lining design,
including choice of unlined tunnel.
 Mapping for the record, to aid in future operations, inspections, and
maintenance work.

A typical construction phase investigation program would include some
or all of the following elements:
 Subsurface investigation (borings and geophysical) from the ground
surface.
 Additional groundwater observation wells and/or piezometers.
 Additional laboratory testing of soil and rock samples.
 Geologic mapping of the exposed tunnel face: with due safety
precautions.
 Geotechnical instrumentation.
 Probing in advance of the tunnel heading from the face of the tunnel:
typically consists of drilling horizontally from the tunnel heading by
percussion drilling or rotary drilling methods.

 Pilot Tunnels: are small size tunnels (typically at least 2m
by 2 m in size) that are occasionally used for large size
tunnels in complex geological conditions.
Pilot tunnel may also be located adjacent to the proposed
tunnel, using the pilot tunnel for emergency exit, tunnel
drainage, tunnel ventilation, or other purposes for the
completed project.
*****

Chapter-2 Rock Mass and Soil Classification
201 General
202 Terzaghi’s Rock Mass Classification
203 Rock Quality Designation index (RQD)
204 Rock Mass Rating (RMR)
205 Rock Mass Quality (Q)
206 Tunnelman’s Ground Classification for Soils

 General
 Rock mass classification systems can be used at preliminary feasibility
and design stages of a tunneling project, when very little detailed
information is available on the rock mass and its stress and hydrologic
characteristics.
 The use of Rock mass classification design procedures require success
to relatively detailed information on in-situ stresses, rock mass
properties and planned excavation sequence, none of which may be
available at an early stage in the project. As this information becomes
available, the use of the rock mass classification schemes should be
updated and used in conjunction with site specific analysis.
 It should be noted that Rock mass classification based design
procedures have inherent limitations and their use does not (and
cannot) replace more elaborate design procedures.
Important Rock mass classification systems are discussed below:

202 Terzaghi’s Rock Mass Classification
Terzaghi (1946) considered the structural discontinuities of the rock
masses and classified them qualitatively into nine categories as
described in Table below:
Terzaghi’s Rock Mass Classification
Rock Class Rock Condition Description
I Hard and intact The rock is unweathered. It contains neither joints no rhair cracks. If
fractured, it breaks across intact rock. After excavation, the rock may
have some popping and spalling failures from roof. At high stresses
spontaneous and violent spalling of rock slabs may occur from the
side or the roof. The unconfined compressive strength is equal to or
more than 100 MPa.
II Hard stratified and
schistose
The rock is hard and layered. The layers are usually widely separated.
The rock may or may not have planes of weakness. In such rocks,
spalling is quite common.
III Massive, moderately
jointed
A jointed rock, the joints are widely spaced. The joints may or may
not be cemented. It may also contain hair cracks but the huge blocks
between the joints are intimately interlocked so that vertical walls do
not require lateral support. Spalling may occur.

Rock
Class
Rock
Condition
Description
IV Moderately
blocky and
seamy
Joints are less spaced. Blocks are about 1m in size. The rock may or may not be
hard. The joints may or may not be healed but the interlocking is so intimate
that no side pressure is exerted or expected.
V Very blocky and
seamy
Closely spaced joints. Block size is less than 1 m. It consists of almost
chemically intact rock fragments which are entirely separated from each other
and imperfectly interlocked. Some side pressure of low magnitude is expected.
Vertical walls may require supports.
VI Completely
crushed but
chemically
intact
Comprises chemically intact rock having the character of a crusher-run
aggregate. There is no interlocking. Considerable side pressure is expected on
tunnel supports. The block size could be few centimeters to 30 cm.
VII Squeezing rock
–moderate
depth
Squeezing is a mechanical process in which the rock advances into the tunnel
opening without perceptible increase in volume. Moderate depth is a relative
term and could be from 150 to 1000 m.
VIII Squeezing rock
–great depth
The depth may be more than 150 m. The maximum recommended tunnel
depth is 1000 m.
IX Swelling rock Swelling is associated with volume change and is due to chemical change of the
rock, usually in presence of moisture or water. Some shales absorb moisture
from air and swell. Rocks containing swelling minerals such as montmorillonite,
illite, kaolinite and others can swell and exert heavy pressure on rock supports.

 Terzaghi's computed rock load factors(i.e. height of loosening zone
over tunnel roof which is likely to load the steel arches) in terms of
tunnel width and tunnel height for each of these classes and
recommended corresponding support systems. [Refer para 503 (1)]
 Rock Quality Designation index (RQD)
1) The Rock Quality Designation index (RQD) provides 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.
%
100
run
drill
total
mm
100
pieces
core
of
sum
RQD 


Appendix 1 for sample calculations of RQD

 Rock Mass Rating (RMR)
(1) The geomechanics classification also known as Rock Mass Rating
(RMR)was developed by Bieniawski using following six
parameters to classify rock mass:
a) Strength of Intact Rock Material (Point Load Strength
Index or Uniaxial compressive strength of rock material)
b) Rock Quality Designation (RQD).
c) Spacing of discontinuities.
d) Condition of discontinuities.
e) Groundwater conditions.
f) Orientation of discontinuities.

(2) For applying this classification system, the rock mass should be
divided into a number of structural regions having their boundaries
usually coinciding with a major structural feature such as a fault or a
change in rock type. Each region should then be classified
separately. In some cases, within the same rock type division of the
rock mass into a number of small structural regions may be required
due to significant changes in discontinuity spacing or characteristics.
(3) Ratings for each of the six parameters listed above are summed to
give a value of RMR. Tables for assessment of RMR are given in
Appendix 2. Sample calculation of RMR is available in Appendix 3.
 Rock Mass Quality (Q)
 Barton et al (1974) of the Norwegian Geotechnical Institute
proposed a Tunnelling Quality Index (Q) for the determination of
rock mass characteristics and tunnel support requirements.

 The numerical value of the index Q varies on a logarithmic scale
from 0.001 to a maximum of 1,000. Classification of rock mass
based on Q-values is as under:
Group Q Classification
1
1000-400 Exceptionally good
400-100 Extremely good
100-40 Very good
40-10 Good
2
10-4 Fair
4-1 Poor
1-0.1 Very poor
3
0.1-0.01 Extremely poor
0.01-0.001 Exceptionally poor

Where:
RQD = Deere’s Rock Quality Designation≥10,= 115 − 3.3 Jv≤ 100
Jn = Joint set number,
Jr = Joint roughness number for critically oriented joint set,
Ja = Joint alteration number for critically oriented joint set
Jw = Joint water reduction factor,
SRF = Stress reduction factor to consider in-situ stresses
 The parameter Jn, representing the number of joint sets, is often
affected by foliations, schistocity, slaty cleavages or beddings, etc.
 The parameters Jr and Ja, represent roughness and degree of
alteration of joint walls or filling materials. These parameters should
be obtained for the weakest critical joint set or clay-filled
discontinuity in a given zone.
SRF
J
J
J
J
RQD
Q w
a
r
n



 Calculation of Q Value:

 The parameter Jw is a measure of water pressure, which has an
adverse effect on the shear strength of joints. This is due to
reduction in the effective normal stress across joints. Water in
addition may cause softening and possible wash-out in the case
of clay-filled joints.
 The parameter SRF is a measure of
I. Loosening pressure in the case of an excavation through
shear zones and clay bearing rock masses,
II. Rock stress σc/σ1 in a competent rock mass, where σc is
uniaxial compressive strength of rock material and σ1 is
the major principal stress before excavation and
III. Squeezing or swelling pressures in incompetent rock
masses. SRF can also be regarded as a total stress
parameter.

 Tables for Assessment of Rock Mass Quality (Q)are given in Appendix
4. Sample calculation of Q value is available in Appendix 3 Support
Selection based on Q-System of rock mass classification is discussed
in chapter-5.
 Tunnelman’s Ground Classification for Soils
 Anticipated ground behavior in soft ground tunnels was first defined
by Terzaghi (1950) by means of the Tunnelman’s Ground
Classification, a classification system of the reaction of soil to
tunneling operation. Heuer (1974) modified the Tunnelman’s
Ground Classification, as shown in Table below:

Classification Behavior Typical Soil Types
Firm Heading can be advanced without initial
support, and final lining can be
constructed before ground starts to
move.
Loess above water table; hard clay, marl,
cemented sand and gravel when not highly
overstressed.
Raveling Slow
raveling
Chunks or flakes of material begin to
drop out of the arch or walls sometimes
after the ground has been exposed, due
to loosening or to over-stress and
“brittle” fracture (ground separates or
breaks along distinct surfaces, opposed
to squeezing ground).
Residual soils or sand with small amounts of
binder may be fast raveling below the water
tale, slow raveling above. Stiff fissured clays
may be slow or fast raveling depending upon
degree of overstress.
Fast
raveling
In fast raveling ground, the process
starts within a few minutes, otherwise
the ground is slow raveling.
Squeezing Ground squeezes or extrudes plastically
into tunnel, without visible fracturing or
loss of continuity, and without
perceptible increase in water content.
Ductile, plastic yield and flow due to
overstress.
Ground with low frictional strength. Rate of
squeeze depends on degree of overstress.
Occurs at shallow to medium depth in clay of
very soft to medium consistency. Stiff to hard
clay under high cover may move in
combination of raveling at excavation surface
and squeezing at depth behind surface.

Running Cohesive
running
Granular materials without cohesion
are unstable at a slope greater than
their angle of repose (approx 30°-
35°). When exposed at steeper slopes
they run like granulated sugar or
dune sand until the slope flattens to
the angle of repose.
Clean, dry granular materials. Apparent
cohesion in moist sand, or weak
cementation in any granular soil, may allow
the material to stand for a brief period of
raveling before it breaks down and runs.
Such behavioris cohesive-running.
Running
Flowing A mixture of soil and water flows into
the tunnel like a viscous fluid. The
material can enter the tunnel from
the invert as well as from the face,
crown, and walls, and can flow for
great distances, completely filling the
tunnel in some cases.
Below the water table in silt, sand or gravel
without enough clay content to give
significant cohesion and plasticity. May also
occur in highly sensitive clay when such
material is disturbed.
Swelling Ground absorbs water, increases in
volume, and expands slowly into the
tunnel.
Highly pre-consolidated clay with plasticity
index in excess of about 30, generally
containing significant percentages of
montmorillonite.

 Anticipated ground behavior has been further expanded by various
researchers/authors for various soil conditions (clays to silty sands,
cohesive soils, silty sands, sands, gravels) above/below the water
table. Standard technical literature may be referred to for more
details in this regard.
 Determination of load on the initial supports for circular and
horseshoe tunnels in soft ground of different classifications is
detailed under Para 505 (5) of chapter-5.
*****

Chapter 3 Tunnel excavation methods
301 General
302 Excavation Methods for Rock Tunnels
302 (1) Drill and Blast (Full Face or Partial Face Excavation)
302 (1) (a) Full-Face Excavation
302 (1) (b) Partial Face Excavation
302 (1) (b) (i) Heading and Benching
302 (1) (b) (ii) Multiple drift Advance
302 (2) Excavation by Roadheader
302 (3) Excavation by Tunnel Boring Machine
303 Excavation Methods for Soft Ground Tunnels
303 (1) Multiple Drift Method
303 (2) Excavation by Tunnel Shields

 General
Selection of a particular tunnel excavation method depends on
various factors; such as:
I. Geological conditions
II. Size of tunnel
III. Length of tunnel
IV. Ground water condition and expected water inflow
V. Vibration restrictions
VI. Allowable ground settlements
VII. Availability of resources (machinery/equipment, funds &
time)
Commonly used Tunnel excavation methods can be grouped under
the following categories:
I. Excavation Methods for Rock Tunnels
II. Excavation Methods for Soft Ground Tunnels
These are discussed below:-

 Excavation Methods for Rock Tunnels
The three commonly used excavation methods for rock tunnels are:
1. Drill and Blast (Full Face or Partial Face Excavation)
2. Road Header (Full Face or Partial Face Excavation)
3. TBM (Full Face)
(1) Drill & Blast (Full Face or Partial Face Excavation):
The drill and blast method is the most typical method for medium to
hard rock conditions. It can be applied to a wide range of rock
conditions. Some of its major advantages are fast start-up and relatively
low capital cost tied to the equipment. On the other hand, the cyclic
nature of the drill and blast method requires good work site
organization. Blast vibrations and noise also restrict the use of drill and
blast in urban areas.
This excavation method has been used since a long time & still remains
the conventional method for non-circular cross sections and also for
short length circular tunnels.

(a)Full-Face Excavation:
Excavating the complete tunnel section in one operation is
termed as Full Face Excavation. Wherever practical Full Face
Excavation is preferred mainly for its superior rate of progress &
ease in construction. The decision for excavating full-face has to
be taken after careful consideration of the geology, the size (or
span) of the opening, and the stand-up time.
(b)Partial Face Excavation:
Large openings or openings in weak rocks are less stable than
small ones. Therefore, in many cases the tunnel cross section is
not excavated at once, but in parts. This type of excavation is
called Partial Face Excavation.
The various types of partial face excavations are:

(i) Heading and Benching.
This method involves excavation of top heading first. Excavation of
the bench is done only after securing the top heading. With the
stand-up time problem eliminated (unless there will be a problem
with wall stability), longer increments of bench can be excavated.
A ramp needs to be constructed for accessing the heading face if the
gap between faces of top heading & bench warrants so. If the
heading and the bench are excavated simultaneously, then the ramp
must be every now & then moved forward.
Installation of rock reinforcement in a top heading presents no
special problems. However, when steel ribs are used, the necessity
for a full-strength steel rib arch creates a problem at the abutments.
The arch must have a temporary foundation while the bench
beneath it is excavated.

Wall plates are installed longitudinally beneath the ribs at the top
heading invert. A wall plate is a horizontal structural steel
member placed under the arch to act as an abutment and spread
the reaction while the bench is being taken.
For smaller or lightly loaded ribs, the wall plate is a single wide
flange beam with its web horizontal; arch and post segments fit
inside its flanges. For heavier loads or larger spans, a pair of
beams joined together, with webs vertical, is located directly
beneath or over the arch/post flanges.

(ii) Multiple drift Advance:
If the stand-up time is insufficient for advance by heading and bench
method, because of either the geology or large spans, the top heading
and/or benches must be divided into two or more drifts.
This is advantageous because the reduced span increases stand-up time,
the reduced volume decreases mucking time, and time required to
install support or reinforcement is also reduced. When using steel sets,
the appropriate final arch segment is used and supported temporarily
on one or more steel posts. When the adjacent drift is excavated, the
next arch segment is erected, connected, posted, and so on. Once the
wall plates are in place and the full arch erected, the temporary posts
are removed.
While tunnel excavation from top down is preferred, in exceptionally
poor ground it may be necessary to work from the bottom up. Driving
bottom sidewall drifts first permits concreting abutments and eliminates
having to establish, undercut, and reestablish support.

Some well-established schemes of multiple drift excavation are:-
Core heading
This is also known as the German heading method. It consists of
excavating and supporting first the side and top parts of the cross
section and subsequently the central part (core). The ring closure at
the invert comes at the end. The first gallery also serves for
exploration. The crown arch is founded on the side galleries thereby
keeping the related settlements small.
Sidewall drift
The side galleries are excavated and supported first. They serve as
abutment for the support of the crown, which is subsequently
excavated. This method is preferred in soils/rocks of low strength.
Note that a change from top heading to sidewall drift is difficult to
accomplish.
In addition to above, many other variations of multiple drift
sequence are also in practice.

 Drill-and-blast are best suited for hard rocks, non-circular cross
sections & relatively short tunnels (where use of TBM/
Roadheader is uneconomical) & can also be used when
encountering too great a variety of geologies or other specific
conditions such as mixed face, squeezing ground, etc.
 It is suited to any type of tunnel cross section. Appropriate
controlled blasting technique needs to be implemented at site to
reduce overbreaks & minimize damage outside the minimum
excavation line.

(2) Excavation by Roadheader:
A Roadheader, is a piece of excavating equipment consisting of a boom-
mounted cutting head, a loading device usually involving a conveyor,
and a crawler travelling track to move the entire machine forward into
the rock face.
The cutting head can be a general purpose rotating drum mounted in
line or perpendicular to the boom, or can be special function heads such
as jack-hammer like spikes, compression fracture micro-wheel heads like
those on larger tunnel boring machines, a slicer head like a gigantic
chain saw for dicing up rock, or simple jaw-like buckets of traditional
excavators.
Roadheaders are used for moderate rock strengths and for laminated or
joined rock. The cutter is mounted on an extension arm (boom) of the
excavator and cuts the rock into small pieces. Thus, overprofiling can be
limited and also the loosening of the surrounding rock is widely avoided.
One has to provide for measures against dust (suction or water
spraying). The required power of the motors increases with rock
strength.

The width of tunnel excavated varies from slightly more than the width
of the machine body plus treads to twice that width. Much less heading
equipment is required and start-up costs are only a fraction of that for
TBM excavation. The compactness, mobility, and relatively small size of
the roadheader combined with simultaneous mucking makes it practical
to install rock bolts and/or shotcrete quickly and easily.
The principal constraint on roadheaders is that they currently are usable
only in rock of less than about 12,000 psi compressive strength.
Somewhat stronger rock can be cut, or chipped away, if it is sufficiently
fractured.
This method could also be called partial face mechanization. Whereas
TBMs are generally purpose-built, roadheaders are nearly "off-the-shelf’
equipment requiring relatively little lead time.
Excavation by roadheader is suited for any type of tunnel cross sections
& may be done either partial-face or full face.

(3) Excavation by Tunnel Boring Machine:
 Tunnel boring machines are used as an alternative to drilling &
blasting (D&B) methods in rock. TBMs excavate circular cross
sections with a rotating cutter head equipped with disc cutters.
 TBMs have the advantages of limiting the disturbance to the
surrounding ground and producing a smooth tunnel wall. This
significantly reduces the cost of lining the tunnel, and makes them
suitable to use in heavily urbanized areas.
 TBM tunnels have very high start-up (pre-excavation) costs and
accompanying long lead time; the high rate of advance reduces
the per-m excavation cost. The decision on undertaking excavation
by TBM requires careful consideration of techno-economic factors.

 Excavation Methods for Soft Ground Tunnels:
Two principal Methods for tunneling in soft ground are:-
1) Multiple Drift Method
This method has already been under “Excavation methods for rock
tunnels”. Forepoling is normally done before doing excavation
particularly in heading portion.
2) Excavation by Tunnel Shields
The shield is a steel tube with a (usually) circular cross section. Its
front is equipped with cutters. The shield is pushed forward into the
ground by means of jacks.
The control of ground water is of utmost importance in soft ground
tunneling. To control groundwater, dewatering & grouting are the most
common methods. Methods using “compressed air” & “freezing” are
also sometimes used.
*****

Chapter -4 Tunneling Method
401 Tunneling Methods
401(1) Conventional Tunneling
401(2) Mechanized Tunneling
401(3) NATM
401(4) Norwegian Method of Tunneling
401(5) ADECO-RS
402 Tender Documents for Tunneling Contracts
403 Stipulations recommended to e included in Contract
Documents

 General
Tunneling methods can be broadly categorized into following
three methods:
1) Conventional tunneling
2) Mechanized tunneling and
3) New Austrian Tunnelling Method (NATM)
4) Norwegian Method of Tunneling (NMT)
5) Advance Control of Deformation Method (ADECO)
(1) Conventional Tunneling
(a) The definition of “Conventional Tunneling” is rather arbitrary, and
subject to variations, depending on the context. For Indian Railway
context, the term conventional tunneling applies to any method
other than Mechanized tunneling & NATM; involving cyclic
construction process of:

 Excavation, by using the drill and blast methods or mechanical
excavators except any full face TBM
 Mucking
 Placement of the primary (initial) support elements such as
 Steel ribs or lattice girders
 Soil or rock bolts
 sprayed concrete (shotcrete) or cast in situ concrete, not
reinforced or reinforced with wire mesh or Fibres.
 Final or secondary lining (if required).
(b) Principles of Conventional Tunneling
i. Conventional Tunneling is carried out in a cyclic execution process of
repeated steps of excavation followed by the application of relevant
primary support, both of which depend on existing ground
conditions and ground behavior.

ii. The Conventional Tunneling Method mainly using standard
equipment and allowing access to the tunnel excavation face at
almost any time is very flexible in situations or areas that require a
change in the structural analysis or in the design and as a result of
this also require changes in the support measures.
iii. A standard set of equipment for execution of Conventional
Tunneling may consist of the following items:
 Jack Hammers/Drilling jumbo to drill holes for blasting, rock
bolting, water and pressure release, grouting etc.
 Road header or excavator in cases where blasting is not
possible or not economical.
 Lifting platform allowing the workers to reach each part of the
tunnel crown and of the tunnel face.
 Lifting equipment for handling/erection of steel sets.
 Loader or excavator for loading excavated material onto dump
trucks.

 Dump trucks for hauling excavated ground.
 Shotcrete machines (robotic/non-robotic).
(iv) Using this standard set of equipment the following changes can
easily be applied during construction if ground conditions change or
if monitoring results require action:
 Increase or decrease of support, e.g. the thickness of shotcrete,
number and/or lengths of rock bolts per linear meter of tunnel,
spacing and dimensions of steel arches, number and lengths of
fore poles, application of shotcrete at the tunnel face, bolting the
face etc.
 Variation of ring closure time.
 Variation of explosives charge per blasting round and variation of
detonator sequences.
 Increased or decreased length of excavation round (common
round lengths vary from 0.5 m to 4.0 m).

 Partial excavation by splitting the excavation face into the crown,
bench, and invert excavation steps or even further in pilot and
sidewall galleries.
(v) In case exceptional ground conditions are encountered - regardless
of whether predicted or not - the Conventional tunneling Method
can react with a variety of auxiliary construction technologies like
 Grouting: consolidation grouting, fissure grouting, pressure
grouting, compensation grouting.
 Technologies to stabilize and improve the ground ahead of
the actual tunnel face like fore poling, pipe umbrella,
horizontal jet grouting, ground freezing etc.

(c) Construction Methods for Conventional Tunneling
I. Excavation Methods
II. Excavation Sequence
III. Primary Support
IV. Auxiliary Construction Measures
V. Placement of final (secondary) lining
VI. Instrumentation and Monitoring
(d) Conventional Tunneling in connection with the wide variety of
auxiliary construction methods enables making the most
appropriate choice to achieve safe and economic tunnel
construction even in situations with changing or unforeseen
ground conditions.
The Conventional tunneling Method is preferred choice for
tunneling under highly variable ground conditions or for projects
with variable shapes.

Conventional tunneling enables:
 A greater variability of the shapes.
 Better knowledge of the ground by using systematic
exploratory drillings at tunnel level ahead of the face.
 Greater variability in the choice of excavation methods
according to the ground conditions
 Greater variability in the choice of excavation sequences
according to the ground conditions.
 Easier optimization of the primary support using the
observational method in special cases.
 A greater variability in the choice of auxiliary construction
methods according to the ground conditions

(2) Mechanized tunneling
(a) Mechanized tunneling offers many advantages; some of these are:-
 Industrialization of the tunneling process , with ensuing
reductions in costs and construction times
 the possibility some techniques provide of crossing complex
geological and hydrogeological conditions safely and
economically,
 the good quality of the finished product
 enhanced health and safety conditions for the workforce
However, there are still risks associated with mechanized tunneling,
for the choice of technique is often irreversible and it is often
impossible to change from the technique first applied or only at the
cost of immense upheaval to the design and/or the economics of the
project.

(b) “Tunneling Shields” & “Tunnel Boring Machines” are the two
principal types of machines employed for mechanized tunneling. Strictly
speaking, TBMs are “unshielded” (i.e. are of Open type) and are used in
hard rock whereas Shields have “shield/s” under the protection of which
the ground is excavated and the tunnel support is erected. Shields are
used in soft ground.
But quite often these two terms are used interchangeably as distinction
between two is getting blurred.
(i) Tunneling shields
In its simplest form a tunneling shield is a steel frame with a cutting
edge on the forward face. For circular tunnels this is usually a circular
steel shell under the protection of which the ground is excavated and
the tunnel support is erected. A shield also includes back-up
infrastructure to erect the tunnel support (lining) and to remove the
excavated spoil.

There are two main types of tunneling shield, one with partial and one
with full face excavation.
In partially-mechanized shields, an excavator or a partial cutterhead/
roadheader works on the face. Partially-mechanized shields (also
called boom-in-shield tunneling machines) are used where the cost of
full face tunnel boring machines cannot be justified.
Manual excavation, i.e. by ‘hand’, is only considered for very special
applications, e.g. very short advances, due to the low advance rate.
This type of tunneling is called the manual shield technique.
Full face Shield are discussed under Shielded TBMs & Soft Ground
TBMs; however basic working principle of the same is being briefly
described below:-
Tunneling shields do not have an ‘engine’ to propel themselves
forwards, but push themselves forward using hydraulic jacks. In order
to create the necessary force to push the tunnel shield forwards, jacks

are placed around the circumference of the shield. These jacks push
against the last erected tunnel segment ring and also push the shield
against the tunnel face in the direction of the tunnel construction. The
jacks can be operated individually or in groups, allowing the shield to be
steered in order to make adjustments in line and level and to be driven
in a curve if required.
When the shield has advanced by the width of a tunnel segment ring,
the jacks are retracted leaving enough room in the tail of the shield to
erect the next tunnel segment ring.
The support usually adopted with shield tunnelling these days is circular
segments. These segments form, when connected together, a closed
support ring. As the tunnel segments are connected together inside the
shield tail, the diameter of the completed tunnel segment ring is smaller
than that of the shield tail, the diameter of the completed tunnel
segment ring is smaller than that of the shield.

This creates a gap between the ground and the tunnel lining. When
the shield is jacked further into the ground the size of this gap is
between approximately 50 and 250 mm.
In less supporting soft ground it has to be expected that the ground
settles by this value. This can result in the softening of the ground and,
especially with shallow tunnels, in the settlements reaching the
ground surface and having undesirable consequences on surface or
near surface structures. In order to avoid these settlements, the gap is
generally injected with mortar.
(ii) Tunnel Boring Machines (TBM)
a) Introduction
TBMs exist in many different diameters, ranging from microtunnel
boring machines with diameters smaller than 1 m to machines for
large tunnels, whose diameters are greater than 15 m (the largest
TBMs are now in excess of 19 m).

TBMs are often grouped under categories of “Hard Rock TBMs” & “Soft
Ground TBMs”.
b) Hard Rock TBMs
Hard rock TBMs comprise of following four key sections:-
i. Boring section, consisting of the cutterhead,
ii. Thrust and clamping section, which is responsible for advancing
the machine,
iii. Muck removal section, which takes care of collecting and
removing the excavated material, and
iv. Support section, where the tunnel support is erected.
Hard Rock TBMs primarily fall under following categories:-
i. Gripper TBM: Open hard rock TBM - suited for boring in stable rock.
ii. Shielded TBM: shielded hard rock TBM - suited for tunneling in
varying rock formations that alternate between stable and unstable
formations.

c) Soft ground TBMs/Shields
The application of a TBM technique in less stable soft ground
commonly requires the face to be supported. This is in contrast to
the open face TBMs (often used in hard rocks) where the ground is
able to support itself during excavation by virtue of its significant
strength and stand-up time.
 Mechanical-support TBM/Shield
 Compressed-air TBM/Shield
 Slurry shield TBM/Shield
 Earth pressure balance TBM/Shield
 Reaming Boring Machines
 Raise Borer
 Mixed Face TBMs
 Multi-Mode TBMs

(d) Selection of TBM
Careful and comprehensive analysis should be made to select proper
machine for tunneling taking into considerations its reliability, safety,
cost efficiency and the working conditions. In particular, the following
factors should be analyzed:
 Suitability to the anticipated geological conditions
 Applicability of supplementary supporting methods, if
necessary
 Tunnel alignment and length
 Availability of spaces necessary for auxiliary facilities behind
the machine and around the access tunnels
 Safety of tunneling and other related works.

(3) NATM
 Background
The New Austrian Tunnelling Method (NATM) was developed by the
Austrians Ladislaus von Rabcewicz, Leopold Müller and Franz Pacher in
the 1950s. The name was introduced in 1962 (Rabcewicz 1963) to
distinguish it from the ‘Austrian Tunnelling Method’, today referred to
as the ‘Old Austrian Tunnelling Method’.
Loosening pressure was conventionally considered to be the main
active force to be reckoned with in tunnel design. NATM approach
emphasized the importance of avoiding loosening almost entirely.
Whereas the earlier methods of temporary support were bound to
cause loosening and voids by yielding of the different parts of the
supporting structure, a thin layer of shotcrete together with a suitable
system of rock bolting applied to the rock face immediately after
blasting entirely prevents loosening and reduces decompression to a
certain degree, transforming the surrounding rock into a self-
supporting arch.

 Definition of NATM
Austrian National Committee defines NATM as “a concept which
makes the ground (rock or soil) surrounding the void a supporting
construction element through the activation of a ground supporting
arch.”
 Principles of NATM
The main principles of NATM are:
• The main load-bearing component of the tunnel is the
surrounding rock mass. The sprayed concrete has only a secondary
supporting function. Maintain strength of the rock mass and avoid
detrimental loosening by careful excavation and by immediate
application of support and strengthening means. Shotcrete and
rock bolts applied close to the excavation face help to maintain
the integrity of the rock mass.

• The support must not be installed too early or too late. It should not
be too stiff or too weak.
• The tunnel is to be seen as a composite system consisting of the
ground, and the support and stabilizing measures, e.g. sprayed
concrete, anchors, steel ribs and similar.
• Rounded tunnel shape: avoid stress concentrations in corners where
progressive failure mechanisms start .
• Flexible thin lining: The primary support shall be thin-walled in order
to minimize bending moments and to facilitate the stress
rearrangement process without exposing the lining to unfavourable
sectional forces. Additional support requirement shall not be added
by increasing lining thickness but by bolting. The lining shall be in full
contact with the exposed rock. Shotcrete fulfills this requirement.

• In situ measurements: Observation of tunnel behaviour during
construction is an integral part of NATM. The choice of support
and construction sequence is made on the basis of monitoring of
tunnel behavior. Observational method requires:
 Determination of acceptable limits for the behaviour of a
construction
 Verification that these limits will (with sufficient
probability) not be exceeded
 Establishing a monitoring programme that gives
sufficient warning of whether these limits are kept
 Providing measures for the case that these limits are
exceeded.

 Construction Sequence
The construction process is as follows:
• Excavation: The tunnel advance can be achieved using blasting, a
partial face boring machine or simply using an excavator,
depending on the ground conditions. Generally, the advancement
is spatially and timely staggered in the heading, benching and
invert.
• Sealing the exposed ground if necessary.
• Mucking.
• Installation of lattice girders or mesh reinforcement, and
application of shotcrete. Depending on the quality of the ground
the support might be installed first before the spoil is removed.
• Potential installation of a second layer of reinforcement and
application of shotcrete.
• Installation of anchors.
• Construction of inner lining

 Limitation
NATM assumes that the ground has sufficient stand-up time itself for
the construction cycle. In order to use NATM, the ground has to be
capable of supporting itself over the length of each advance section,
which means that the ground must have a stand-up time.
The limit of this construction technique is reached when the stand-up
time of the ground has to be improved by artificial measures, such as
freezing or grout injection.

 Pre-requisites for NATM
 Balanced Contract Structure:- providing for equitable risk
sharing & flexible approach as per varying technical
requirements.
 Qualified Personnel: particularly for ensuring quality of
shotcrete, rockbolts.
 Better Site Management: for –
• Coping with unseen events
• Proper application of the observational method
• Elimination of human errors
 Continuous Monitoring of geology:- by qualified & experienced
geologists- for interpretation of exploration data & keeping
thorough geological record.

 Advantages of NATM
 Flexibility to adopt different excavation geometries and very
large cross sections.
 Lower cost requirements for the tunnel equipment at the
beginning of the project.
 Flexibility to install additional support measures, rock bolts,
dowels, steel ribs if required.
 Easy to install a waterproof membrane.
 Flexibility to monitor deformation and stress redistribution so
that necessary precautions can be taken
 NMT (Norwegian Method of Tunneling)
A variant of NATM using steel-fiber reinforced shotcrete (SFRS) instead
of mesh-reinforced concrete is referred to as the Norwegian Method of
Tunnelling (NMT).

 ADECO-RS (Analysis of Controlled Deformation in Rocks and
Soils) method:
This method is based on the principle that a previously consolidated
core in front of the face and an inner lining concreted immediately
behind it has a favorable effect on the deformation curve and also on
the settlement at the surface.
The method enables undertaking full face excavation even under
squeezing ground conditions.
Excavation of full face in combination with advance support of the face
(normally in the form of glass fibre anchors and/ or jet grouting)
enables early closure of ring as compared with the excavation of the
entire cross-section in parts.
This keeps the deformation of the rock mass low. As only one step is
necessary for the entire excavation, management of tunneling
operation becomes much simpler.

 Tender Document for tunneling contracts should not restrict the
method of tunneling to certain particular types like conventional,
NATM, NMT etc. Tender Document should offer the engineer and
contractor the flexibility to use a broad spectrum of available
methods (either separately or in combination) for execution of
work.
 Stipulations recommended to be included in contract
documents:
Except in rare instances, the contractor should be entrusted with
responsibilities for all surveying conducted for the construction
work, including control of line and grade and layout of all facilities
and structures. Railway officials must conduct verification surveys
at regular intervals and also ensure that the work is properly tied
to adjacent existing or new construction.
*****

Chapter 5 Tunnel Design
501 General
502 Design of Initial Support System
503 Empirical Approach
503 (1) Support Selection based on Terzaghi’s Rock-load
503 (2) Support Selection based on Rock Quality Designation (RQD)
503 (3) Support Selection based on Geomechanics Classification (RMR
System)
503 (4) Support Selection based on Q-System of rock mass classification
503 (4) (a) Support Categories
503 (4) (b) Excavation Support Ratio (ESR)
503 (4) (c) Length of Rockbolts
503 (4) (d) Maximum unsupported span
503 (5) Support selection for soft ground
503 (6) Limitations of empirical approach
504 Numerical Approach
505 Design of Permanent Support
506 Excavation and Support Classes for New Austrian Tunneling Method
(NATM)

 Reliable and sufficient knowledge of the structural properties
of the ground likely to be met with during tunneling is
prerequisite for assessment of quantum of loads that the
tunnel is likely to be subjected to.
 Detailed geological and geotechnical investigation should be
carried out under close monitoring of field engineers and in
consultation with design engineers/consultant.
 Tunnel support systems mainly include initial ground support
as well as permanent support system.

 Design of Initial Support System
 Initial or primary ground support is installed shortly after excavation
in order to make the tunnel opening safe until permanent support is
installed. The initial ground support may also function as the
permanent ground supporter as a part of the permanent ground
support system. The initial ground support must be selected in view
of both its temporary and permanent functions.
 Initial ground support systems are usually not subject to rigorous
design but are selected on the basis of a variety of rules. There are
three basic approaches (viz. Empirical, Analytical & Numerical)
employed in selecting initial ground support, and one or more of
these approaches should be used.

 Empirical Approach
Most commonly used empirical approaches for design of initial
support system are:
1) Support Selection based on Terzaghi’s Rock-load
a) Terzaghi (1946) defined rock load factor Hp as the height of
loosening zone over tunnel roof which is likely to load the steel
arches.
Rock load factor Hp was computed in terms of tunnel width Band
tunnel height Ht for each of the nine rock classes and made
recommendations for support system to be adopted.
b) Terzaghi’s recommendations are tabulated below: (giving Rock Load
Hp in feet of rock of support in tunnel with Width B (ft) and Height
Ht (ft) at depth more than 1.5C, Where C = B + Ht)

Rock Class Rock Load Hp in feet Remarks
i Zero Light lining, required only if spalling or popping occurs.
ii 0 to 0.5B Light support.
iii 0 to 0.25B Load may change erratically from point to point.
iv 0.25B to 0.35C No side pressure.
v (0.35 to 1.10)C Little or no side pressures.
vi 1.10C Considerable side pressure. Softening effect of seepage toward bottom of tunnel
requires either continuous support for lower end of ribs or circular ribs.
vii (1.10 to 2.10)C Heavy side pressure, invert struts required.
viii (2.10 to 4.50)C Circular ribs are recommended.
ix Up to 250 feet
irrespective of value
of C
Circular ribs required. In extreme cases use yielding support.
Terzaghi’s recommendations for Rock-load in tunnels
Note: The roof of the tunnel is assumed to be located below the water table. If it is located permanently above the water
table, the values given for types IV to VI can be reduced by 50%.
a Some of the most common rock formations contain layers of shale. In unweathered state real shales are no worse than
other stratified rocks. However, the term shale is often applied to firmly compacted clay sediments which have not yet
acquired the properties of rock. Such so called shale may behave in the tunnel like squeezing or even swelling rock. If a rock
formation consists of a sequence of horizontal layers of sandstone or limestone and of immature shale, the excavation of the
tunnel is commonly associated with a gradual compression of the rock on both sides of the tunnel involving a downward
movement of the roof. Furthermore the relatively low resistance against slippage at the boundaries between the so-called
shale and rock is likely to reduce very considerably the capacity of the rock located above the roof of bridge. Hence in such
rock formations the roof pressure may be as heavy as in a very blocky and seamy rock.

(c) Terzaghi’s rock load estimates were derived from an
experience of tunnels excavated by blasting methods and
supported by steel ribs or timbers. Ground disturbance and
loosening occur due to the blasting prior to installation of
initial ground support, and the timber blocking used with
ribs permits some displacement of the rock mass. As such,
Terzaghi’s rock loads generally should not be used in
conjunction with methods of excavation and support that
tend to minimize rock mass disturbance and loosening, such
as excavation with TBM and immediate ground support
using shotcrete and rock bolts.

(2) Support Selection based on Rock Quality Designation (RQD)
(a) Several methods of using the RQD for design of rock tunnels have
been developed. Deere et al. (1970) modified Terzaghi’s
classification system by introducing the RQD and distinguishing
between blasted and machine excavated tunnels. He proposed
following support system for 6 to 12m diameter rock tunnels:
 Support recommendations based on RQD is given table below:

Rock Quality Tunneling
Method
Steel sets3 Rockbolts3 Shotcrete
Excellent1
RQD>90
TBM None to occasional light set.
Rock load (0.0–0.2)B
None to occasional None to occasional local
application
D&B None to occasional light set.
Rock load (0.0–0.3)B
None to occasional None to occasional local
application 2 to 3 in.
Good1
75<RQD<90
TBM Occasional light sets to pattern on 5 to 6
ft center.
Rock load (0.0 to 0.4)B
Occasional to
pattern, 5 to 6ft
centers
None to occasional local
application 2 to 3 in.
D&B Light sets 5 to 6 ft center.
Rock load(0.3 to 0.6)B
Pattern,
5 to 6 ft centers
Occasional local application
2 to3 in.
Fair
50<RQD<75
TBM Light to medium sets,
5 to 6 ft center.
Pattern,
4 to 6 ft centers
2 to 4 in. crown
D&B Light to medium sets, 4 to 5 ft center.
Pattern,
3 to 5 ft centers
4 in. or more crown and
sides
Poor2
25<RQD<50
TBM Medium circular sets on 3 to 4 ft center.
Rock load (1.0 to 1.6) B
Pattern,
3 to 5 ft center
4 to 6 in. on crown and
sides. Combine withbolts.
D&B Medium to heavy circular sets, 2 to 4 ft
center.
Pattern,
2 to 4 ft center
6 in. or more on crown and
sides. Combine with bolts.

Very poor3
RQD<25 (Excluding
squeezing or
swelling ground)
TBM Medium to heavy circular sets
on
2 ft center.
Pattern,
2 to 3
ft center
6 in. or more on whole selection.
Combine with medium sets.
D&B Heavy circular sets on 2
ft center.
Pattern,
3 ft center
6 in. or more on whole selection.
Combine with medium sets.
Very poor3
(squeezing or
swelling)
TBM Very heavy circular sets on
2 ft center.
Rock load up to 250 ft.
Pattern,
2 to 3
ft center
6 in. or more on whole section. Combine
with heavy sets.
D&B Very heavy circular sets on
2 ft center.
Rock load up to 250 ft.
Pattern,
2 to 3
ft center
6 in. or more on whole section. Combine
with heavy sets.

Notes:
 1In good and excellent rock, the support requirement will be, in
general, minimal but will be dependent upon joint geometry,
tunnel diameter, and relative orientations of joints and tunnel.
 2Lagging requirements will usually be zero in excellent and will
range from up to 25 percent in good rock to 100 percent in very
poor rock.
 3Mesh requirements usually will be zero in excellent rock and
will range from occasional mesh (or strip) in good rock to 100
percent mesh in very poor rock.
4B = tunnel width.
TBM: Tunnel Boring Machine
D&B: Drilling and Blasting

 (3) Support Selection based on Geomechanics Classification (RMR
System)
(a) Bieniawski (1989) provided following guidelines for selection of
tunnel supports based on the RMR system.
Rock mass
class
Excavation Rock bolts
(20 mm dia, fully
grouted)
Shotcrete Steel sets
I– Very good
rock
Full face
3 m advance
Generally no support required except spot bolting
II – Good rock Full face,
1-1.5m advance.
Complete support 20 m from
face
Locally, bolts in crown
3 m long, spaced 2.5 m
with occasional
wiremesh
50 mm in
crown where
required
None
III – Fair rock Top heading and bench 1.5-3
m advance in top heading.
Commence support after each
blast. Complete support 10 m
from face.
Systematic bolts 4m
long, spaced 1.5-2 m
in crown and walls with
wire mesh in crown.
50-100 mm in
crown and 30
mm in sides
None
IV – Poor rock Top heading and bench 1.0-
1.5 m advance in top heading.
Install support concurrently
with excavation, 10 m from
face.
Systematic bolts 4-5 m
long, spaced 1-1.5 m
in crown and walls with
wire mesh.
100-150 mm in
crown and 100
mm in sides
Light to medium ribs
spaced 1.5 m where
required

V – Very poor
rock
Multiple drifts.
0.5-1.5 m advance in top
heading. Install support
concurrently with
excavation. Shotcrete as
soon as possible after
blasting.
Systematic bolts 5-6
m long, spaced 1-1.5
m in crown and walls
with wire mesh. Bolt
invert.
150-200 mm
in crown, 150
mm in sides,
and 50 mm on
face
Medium to heavy
ribs spaced steel
lagging and
forepoling if
required.
Close invert.
Note: Shape: Horseshoe; Width: 10 m; Vertical stress < 25 MPa; Construction: Drilling & blasting.
Note:
 The recommendations are applicable to only tunnels excavated
with conventional drilling and blasting method.
 The support measures recommended in this table are the
permanent and not the temporary or primary supports.
 Double accounting for a parameter should not be done in the
analysis of rock structures and in estimating the rating of a rock
mass. For example, if pore water pressure is being considered in the
analysis of rock structures, it should not be accounted for in RMR.
Similarly, if orientation of joint sets is considered in stability
analysis of rock slopes, the same should not be accounted for in
RMR.

 (3) (b) Stand-up time vs. unsupported span for various rock mass
classes as per RMR
For the tunnels with arched roof, the stand-up time is related with the
rock mass class as given in figure below:
Stand-up time vs. unsupported span for various rock mass classes as per RMR (Bieniawski, 1989)

Note:
• There should not be unnecessarily delay in supporting the roof in
the case of a rock mass with high stand-up time as this may lead
to deterioration in the rock mass which ultimately reduces the
stand-up time.
• Stand-up time improves by one class of RMR value in case of
excavations by TBM (Lauffer, 1988).
• RMR system is found to be unreliable in very poor rock masses.
Care should therefore be exercised to apply the RMR system in
such rock mass. Q-system is more reliable for tunnelling in the
weak rock masses.

 (4) Support Selection based on Q-System of rock mass classification
(a) Estimated support categories based on the Rock mass quality Q are
indicated in the nomogram as shown in Figure below (The bolt
length l is not specified in the support):

Estimated support categories based on the rock quality index Q
(NGI, 2013)

 (b) Excavation Support Ratio (ESR)
The value of ESR (Excavation Support Ratio) is related to the intended use of the
excavation and to the degree of security which is demanded of the support system
installed to maintain the stability of the excavation. ESR values for different types of
excavation are tabulated below:
ESR Values for Different Types of Excavation (NGI, 2013)
Excavation Category ESR
A Temporary mine openings. 3-5
B Vertical shafts*: i) circular sections
ii) rectangular/square section
2.5
2.0
*Dependant of purpose. May be lower than given values.
C Permanent mine openings, water tunnels for hydro power (excluding highpressure penstocks), pilot tunnels,
drifts and headings for large excavations.
1.6
D Minor road and railway tunnels, surge chambers, access tunnels, sewage tunnels. 1.3
E Power houses, storage rooms, water treatment plants, major road and railway tunnels, civil defence
chambers, portals, intersections.
1.0
F Underground nuclear power stations, railway stations, sports and public facilities, factories. 0.8
G Very important caverns and underground openings with a long lifetime, = 100 years, or without access for
maintenance.
0.5
Note:
i) ESR should be increased by 1.5 times and Q by 5Q for temporary supports.
ii) Ratio of Excavation span, Diameter or height (m) to ESR is also termed Equivalent Dimension De of the
excavation

where:
L – Length of rockbolts
B - Excavation width
ESR -Excavation Support Ratio
(c) Length of Rockbolts
The length of rockbolts can be estimated from the following formulae
(Barton et al. , 1974):
ESR
0.15B
2
L 

(d) Maximum unsupported span
The maximum unsupported span can be estimated from following
formulae:
0.4
Q
ESR
2
Span
ed
Unsupport
Maximum 

 (5) Support selection for soft ground
A simplified system of determining the load on the initial support for
circular and horseshoe tunnels in soft ground is given in Table (Terzaghi,
1950) below. However, It is important that the experience and judgment
of the engineer also be applied to the load selection.
Geology Circular Tunnel Horseshoe Tunnel
Running ground Lesser of full overburden or
1.0 B
Lesser of full overburden or
2.0 B
Flowing ground in
air free
2.0 B
4.0 B
Raveling ground
 Above water
table
 Below water
table
Same as running ground
Same as flowing ground
Same as running ground
Same as flowing ground
Squeezing ground Depth to tunnel springline Depth to tunnel springline
Swelling ground Same as raveling ground Same as raveling ground

 (6) Limitations of empirical approach
a) The empirical methods of ground support selection provide a
means to select a ground support scheme based on parameters that
can be determined from explorations, observations, and testing.
They are far from perfect and can sometimes lead to the selection
of inadequate ground support. It is therefore necessary to examine
the available rock mass information to determine if there are any
applicable failure modes not addressed by the empirical systems.

b) A major flaw of all the empirical systems is that they lead the user
directly from the geologic characterization of the rock mass to a
recommended ground support without the consideration of
possible failure modes. A number of potential modes of failure are
not covered by some or all of the empirical methods and must be
considered independently, including the following:
• Failure due to weathering or deterioration of the rock mass.
• Failure caused by moving water (erosion, dissolution,
excessive leakage, etc.).
• Failure due to corrosion of ground support components.
• Failure due to squeezing and swelling conditions.
• Failure due to overstress in massive rock.

c) The empirical systems are largely based on blasted tunnels.
System recommendations should be reinterpreted based on
current methods of excavation. Similarly, new ground support
methods and components must be considered.
 Numerical Approach
A number of commercial computer programs are available in the
market for undertaking design of tunnels through numerical
analysis. Some of the most commonly used numerical modeling
programs for tunnel design and analysis areas are PHASE II and
PLAXIS.

 Design of Permanent Support
1) Permanent support system for tunnels is provided by tunnel
linings. Tunnel linings are structural systems installed after
excavation to provide ground support, to maintain the tunnel
opening, to limit the inflow of groundwater and to provide a
base for the final finished exposed surface of the tunnel.
2) The materials used for tunnel linings are cast-in-place concrete
lining, precast segmental concrete lining, steel plate linings, and
shotcrete lining.
a) Cast-in-place concrete linings are generally installed some
time after the initial ground support and are used in both soft
ground and hard rock tunnels and can be constructed of
either reinforced or plain concrete.
b) Precast concrete linings are used as both initial and final
ground support. Segments in the shape of circular arcs are
precast and assembled inside the shield of a tunnel boring
machine to form a ring.

c) Steel plate linings (liner plates) are a type of segmental
construction where steel plates are fabricated into arcs that
typically are assembled inside the shield of a tunnel boring
machine to form a ring. The steel plate lining may form the
initial and final ground support.
d) Shotcrete is a pneumatically applied concrete that is used
frequently as an initial support but now with the advances
in shotcrete technology permanent shotcrete lining is
designed and constructed in conjunction with NATM
tunneling. Shotcrete can take on a variety of compositions,
can be applied over the exposed ground, reinforcing steel,
welded wire fabric or lattice girders. It can be used in
conjunction with rock bolts and dowels, it can contain steel
or plastic fibers and it can be composed of a variety of
mixes. It is applied in layers to achieve the desired
thickness.

 (3) The following codes can be referred to for the design of tunnel
linings
• IS:4880 (Part 4)-1971:Structural design of concrete lining in rock
• IS:4880 (Part 5)-1972: Structural design of concrete lining in soft
strata and soils
• IS:4880 (Part 6)-1971: Tunnel supports
• IS:4880 (Part 7)-1975: Structural design of steel lining
 (4)
Numerical methods can also be applied to design permanent support
systems.

 Excavation and Support Classes for New Austrian Tunneling
Method (NATM)
1) The design process for NATM tunnels is represented in figure below:
Concept
Design can
follow either the
“Empirical”
approach or the
“Analytical”
Approach.

 2)
Tables indicating basic concepts to derive Excavation and Support
Classes (ESCs) for for tunneling in rock and soft ground are placed as
Appendix 5 & Appendix 6 respectively.
*****

Chapter 6 Ground Improvement and Ground Reinforcement
601 General
602 Ground improvement
603 Methods of Ground improvement
603 (1) Grouting
603 (2) Jet Grouting
603 (3) Ground freezing
604 Ground Reinforcement
604 (1) Pipe umbrella
604 (2) Spiles
604 (3) Face bolts
604 (4) Dewatering and drainage

 In special cases, the excavation work can only be carried out by
means of additional auxiliary construction measures. The
auxiliary construction measures can be classified in categories
of Ground improvement and Ground Reinforcement.
 Ground improvement
1) Ground improvement means the application of methods
that improve the mechanical or hydraulic properties of the
ground.
2) Ground improvement has normally to be carried out
alternately to the excavation and leads to interruptions of
the excavation work. In special cases ground improvement
can be carried out from the surface or pilot tunnels
outside the future tunnel cross section.

 The main methods of Ground improvement
(1) Grouting
The different techniques for grouting are consolidation
grouting, fissure grouting, pressure grouting and
compensation grouting.
Grouting can be carried out in the tunnel excavation as face
grouting or as radial grouting from the excavated tunnel or
from a pilot tunnel. The most commonly used grout material is
cement. In special cases chemical products such as resins or
foams are also applied. In these cases the environmental and
safety restrictions have to be considered specially.

(2) Jet Grouting
 Jet grouting is applied mainly horizontally or at a slightly
upward or downward angle from within the face of the
tunnel. An improvement of the roof arching behavior is
achieved by applying one or more layers of jet grouting
columns in stages corresponding to the excavation operations.
 An improvement of the stability of the face is achieved by
placing individual jet columns parallel to the direction of
advance in the working face.
 Less common in tunneling is vertical or steeply inclined jet
grouting, except in shallow tunnels where it is applied from
the surface. From within the tunnel vertical or steeply inclined
jet grouting is mainly applied to underpin the bottom of the
roof arch.

(3) Ground freezing
 The following ground freezing techniques are known to
waterproof or stabilize temporarily the ground.
a) Continuous frozen bodies
 which provide long-term load-bearing. The freezing is
achieved by a drilled tube system, through which coolant is
pumped.
b) Short-term, immediately
effective local freezing
 Damp zones close to the face
or in the immediate vicinity
outside the excavated cross
section. This is achieved by
means of injection lances with
liquid nitrogen cooling.

 Ground Reinforcement
 Ground reinforcement involves the application of methods
that use the insertion of structural elements with one
predominant dimension. Bolts, anchors, micro piles and spiles
are such elements. The main methods of application are pipe
umbrellas; face bolting or radial bolting from a pilot bore.
(1) Pipe umbrella
 Pipe umbrellas are specified to supplement the arch structure
in the roof and spring line regions as well as stabilization of
the face and in advance of the face immediately after the
excavation.

Pipe Umbrella
Pipe forepole umbrella

(2) Spiles
 Spiles are steel rods left in the ground for the local short-term
stabilization of the roof section and at the working face on the
boundary of the excavation.
 The spiles rest on the first steel arch in front and should be at
least 1.5 times as long as the subsequent advance in the
excavation. Depending on the type of soil, the spiles can be
jacked, rammed or inserted in drill holes.

(3) Face bolts
 Face bolts are often necessary to stabilize or reinforce the face.
Depending on the anticipated ground condition/behaviour, the
relevant bolt type and length have to be determined in the
design. Practically any bolt type or length is possible. As a
protection against rock fall, spot bolts may be sufficient whereas
in difficult ground conditions (e.g. squeezing rock and soils)
systematic anchoring with a high number of long, overlapping
steel or fiber glass bolts may be necessary. Face bolts are placed
during the excavation sequence, if necessary in each round or in
predefined steps.

(4) Dewatering and drainage
 In some cases the tunnel construction is only possible with the
application of special dewatering measures. According to the ground
conditions and other boundary conditions conventional vertical or
horizontal wells or vacuum drains can be used.
 In the design of the dewatering measures environmental aspects
have to be considered, such as limits on lowering the ground water
table, settlements, etc.
 In the case of low overburden, dewatering measures can be carried
out from the ground surface. In the other cases, dewatering has to
be done from the tunnel cross section or from pilot tunnels.
******

701 Safety at the design and planning Stage
701 (1) General
701 (2) Risk Assessment
701 (3) Health and Safety Plan (HSP)
702 Safety Management & Training
703 General Safety Measures
703 (1) Medical facilities
703 (2) Stacking of Material
703 (3) Telephone system
703 (4) Warning signals
703 (5) Ventilation & Protection from Noise
703 (5) (a) Ventilation
703 (5) (b) Protection from Noise
703 (6) Lighting
703 (7) Protection against fire
703 (8) Electrical installations
703 (9) Personal Safety Equipment

703 (10) Use of explosives
703 (10) (a) Transportation of Explosives
703 (10) (b) Handling and use of explosives
703 (10) (c) Explosives Disposal
703 (10) (d) Explosive Accountal
703 (11) Safety while working with Construction
Machinery& equipment
703 (12) Access Control
703 (13) Insects-leeches-Vermins-Snakes
703 (14) Tunnel Instrumentation
704 Safety Requirements for various activities during
construction
704 (1) Underground Excavation
704 (1) (i) Drilling Equipment
704 (1) (ii) Drilling operations
704 (1) (iii) Loading & Blasting
704 (1) (iv) Inspection after blasting
704 (1) (v) De fuming
704 (1) (vi) Scaling
704 (1) (vii) Mucking
704 (1) (viii) Installation of Temporary Supports

704 (2) Structural Steel Erection
704 (3) Fall Protection
704 (4) Scaffolds
704 (5) Working Platforms
704 (6) Concreting
704 (6) (a) Cement Handling
704 (6) (b) Formwork
704 (6) (c) Mixing Plant
704 (6) (d) Pumped Concrete
704 (6) (e) Reinforcement
704 (6) (f) Concrete Placement
704 (7) Grouting, Guniting & Shotcreting
704 (8) Welding and Cutting
704 (8) (a) General Safety Precautions
704 (8) (b) Fire Protection for oxy-acetylene cutting and
welding
704 (8) (c) Gas Cylinders
704 (8) (d) Hoses and Torches
704 (8) (e) Gas Welding and Cutting Operations
704 (8) (f) Electric Arc welding and Cutting
704 (9) Paints

705 Presence of water
705 (1) General
705 (2) Dealing with Water
706 Planning for emergencies
707 Shafts & Hoists
708 Working with specialized machinery like Tunnel Boring
Machine
709 Safety Signage

 Safety at the design and planning Stage
1) General
 The design and planning stage of any tunnelling project should be
adequately resourced in terms of money, staff and time.
 It is recommended that preliminary research/investigation works
like those mentioned below be done during planning/design stage
to have a proper appreciation of ground &site conditions:
 Research of available historical data, existing regional and site
specific geological data etc.
 Consultation with concerned National/State bodies (like GSI,
CWC, Irrigation & Water Supply departments etc.)
 Consultation with utility service providers, particularly in urban
areas, including the electricity, gas, water, communications,
highway etc.

 Survey of the condition of adjacent buildings or subsurface
structures whose structural integrity may be affected by the
proposed tunnelling works
 Adequate Ground/site investigation by means of seismic
methods, boreholes, trial pits, exploratory shafts and tunnels
etc. (in accordance with advice of experts/designers).
 An assessment of the geology & hydrology of the area.
 An assessment of the risk of encountering methane or other
hazardous gas in the ground or hazardous substances such as
asbestos or industrial waste - solid or liquid. An estimate of the
levels of atmospheric and other contamination in the tunnel
during construction e.g. dust from rock drilling, concrete
spraying etc.
d) Thorough review should be made of the preliminary
research/investigation results and how they may affect:
 The selection of the most appropriate tunnelling shape.
 The selection of the most appropriate tunnelling methodology..

 The selection of suitable tunnelling machinery.
 The selection of appropriate support &lining methods.
 The monitoring scheme to be put in place to evaluate the
safety of the working environment during the construction
phase.
(2) Risk Assessment
a) Once the tunnel construction has been awarded but before any
construction work takes place, risk assessment should be
undertaken after identification of likely hazards and for each risk
occurrence an estimate of the possible resulting consequences
should be determined.
b) Based on that assessment appropriate risk mitigation and control
measures should be taken to control or minimise the risks.
c) On-going risk assessment will be needed during the construction
phase, particularly if design changes are made or unforeseen
ground conditions encountered.

(3) Health and Safety Plan (HSP)
a) Before actual commencement of work, occupational health and
safety strategy for the work should be drawn up and set out in a
Health and Safety Plan. The Health and Safety Plan should form
the basis for the identification and management of all health
and safety risks arising from the works. The engineer-in-charge
for the work should join with the designers and contractors for
developing the HSP & monitoring its implementation.
b) Tunnelling involves both the general construction risks and risks
specific to the tunnelling environment and therefore HSP
should be developed by competent staff.
c) The plan should also contain details of emergency procedures,
workers welfare measures and medical facilities. A copy of the
plan should be made available to all supervisors/engineers at
site. Workers should regularly be briefed/educated about
provisions of HSP relevant to their work area.

d) Careful consideration should be given to the design and safety
of any temporary works associated with the tunnelling project.
These could include: temporary access shafts and adits, pilot
tunnels, any temporary ground support etc. along with materials
storage areas, working areas and site offices.
e) While many of the main hazards to be addressed in the plan are
covered in some detail in the following sections, it is expected
that site specific HSP will cover all the identified risks &
corresponding avoidance, control & mitigation measures.

 Safety Management & Training
1) Safety policies should be established for all the parties involved in
the project which will include a clear chain of command and
communication. These policies should also specify responsibilities
for safety.
2) All operations inside the tunnel or shaft shall be carried out under
the supervision of a competent engineer. The engineer shall be
responsible for ensuring safety stipulations laid down for the work,
to enforce the rules, guard against the use of defective safety
appliances, tools and materials, to see that no man is permitted to
do work for which he is not qualified and to brief all workmen on
the plan of work before it is started with special emphasis on all
potential hazards and on the ways to eliminate or guard against
them. In larger jobs these responsibilities and function in respect of
safety arrangements may be delegated to an independent qualified
and competent safety officer working under the overall control of
the engineer-in-charge. Periodically meetings preferably once every
month shall be conducted to review the effectiveness of safety
measures.

3) Appropriate training courses should be designed and put in place
for people unfamiliar with the nature of the tunnelling work to
be undertaken. No workers should be deployed to work
underground unless they have undergone a safety and health
orientation programme to acquaint them with all the hazards
associated with all the operations.
4) For a tunneling operation where 25 or more employees have to
work underground at any one time, at least one rescue crew of 5
employees per shift must be trained in rescue procedures and
resuscitation, the use, care and limitations of oxygen breathing
apparatus, and the use and maintenance of fire fighting
equipment.
5) For a tunnelling operation where less than 25 employees work
underground not less than 5 employees must have such training
in rescue work.

6) Workmen shall be thoroughly instructed in safety rules and shall
be required to follow them at all times. All workers should also
be trained in use of safety devices and appliances provided to
them. Workers who are not aware of hazards, peculiar to the
work should not proceed to work without being properly
instructed and they should obey the instructions of qualified
and authorized person under whom they would work. They shall
be required to report immediately if any unsafe conditions
observed. In case any worker feels that he cannot perform a
work safely he should immediately inform the site in charge of
his inability to carry on with the work.
7) The engineer in-charge may also seek guidance about the bad
reaches expected to be met in the tunnel from the geologists so
that necessary safety measures could be adopted.

8) Where the geological data collected so warrants, advance probe
holes drilling shall be drilled ahead of the tunnel faces to locate
any flowing mass of rock, auriferous strata, geological
disturbances, gas etc. In case presence of gases like methane is
detected, further tunnelling work shall be stopped and the
advice of Director General Mines Safety (DGMS) shall be sought.
9) The occurrence of any accident, involving personal injury or of any
dangerous incident, such as serious break-down of or damage to
any apparatus / equipment shall be reported to the supervisory
staff / officers and adequate precautionary measures shall be
taken by the engineer-in-charge to prevent recurrence. An
accurate record of such accidents shall be properly maintained in
format approved by Engineer-in-charge. Probable reasons of
accidents shall be investigated and precautionary measures
taken to avoid further recurrence.

10) There should be procedures for the handing over of critical
safety related information from the outgoing to the incoming
shift. A written record of this information should be
maintained.
11) Accidents occurring during the fortnight shall be discussed in
the safety meetings and adequate publicity shall be given to
the causes of these accidents and their preventive measures.
12) Display of names, contact numbers and addresses of
officials/organisations to be contacted in case of emergency
should be done at prominent locations of the site.
13) Mock drills should be conducted periodically (preferably once
every six months) to assess the level of safety preparedness/
awareness. Appropriate state Govt./District administration
authorities should also be briefed about and involved in
conducting of mock drills. Mock drill can include scenarios for
evacuation and rescue/ relief in case of “fire accidents” serious
injuries to workers etc.

 General Safety Measures
1) Medical facilities
a) First-Aid Arrangements: Arrangements for rendering prompt and
adequate first-aid to the injured persons shall be maintained at
every work site under the guidance of a medical officer. Depending
upon the magnitude of the work the availability of an ambulance at
a very short notice (at telephone call) shall be ensured.
b) First-aid arrangement commensurate with the degree of hazard and
with the number of workers employed shall be maintained in a
readily accessible place throughout the whole of the working hours.
At least one experienced first-aid attendant with his distinguishing
badge shall be available on each shift to take care of injured
persons. Arrangements shall be made for calling the medical officer,
when such a need may arise. It is recommended that engineer or
foreman who is normally present at each working face in each shift
be given adequate training on first-aid methods to avoid
employment of a separate attendant.
c) Stretchers and other equipment necessary to remove injured
persons shall be provided at every shift and portal.

(D) Where there are more than 50 persons working in a shift,
effective artificial respiration arrangements shall be provided, with
trained men capable of providing artificial respiration.
(2) Stacking of Material
Only the materials required for work in progress shall be kept inside
the tunnel. All other materials shall be kept in a planned & organized
manner to avoid mishaps& to enable the workers to get out of the
tunnel quickly in case there is any collapse or any other mishap inside
the tunnel.
Following special precautions should be followed for storage/handling
of flammable material:
a) All storage, handling and use of flammable liquids shall be under
the supervision of qualified persons. Unless totally unavoidable,
flammable liquids shall not be stored inside the tunnel.
b) All flammable liquids shall be kept in a secure fire resistant store
protected from electrical sparks, welding sparks, open flames and
smoking.
c) Only such amounts of flammable liquids should be issued as are
required for immediate use. Cans for carrying flammable liquids
should be leak proof and properly stoppered and clearly marked
“FLAMMABLE LIQUID.”

d) All sources of ignition shall be prohibited in areas where
flammable liquids are stored, handled and processed. Suitable
warning and “NO SMOKING” signs shall be posted in all such
places. Receptacles containing flammable liquids shall be
stacked in such a manner as to permit free passage of air
between them.
e) All combustible materials like rubbish shall be continuously
removed from such area where flammable liquids are stored,
handled and processed. All spills of flammable liquids shall be
cleared up immediately. Containers of flammable liquid shall be
tightly capped.
f) Fire extinguishers and fire-buckets appropriate to the hazard
should be conveniently located and identified.

(3) Telephone system
A telephone system shall be provided to ensure a positive and quick
method of communication between all control locations inside tunnel
and portal of the tunnels when longer than 500m and for shafts when
longer than 50m.Maximum distance between two telephone should
preferably not exceed 500m.
(4)Warning signals
Irrespective of length and bends in the tunnel, arrangements shall be
made for transmitting of warning signals by any one of the following
means:
 By electrically operated bells, operated by battery / dry cells with
the bell placed outside the tunnel and the position of the switch
shifting with the progress of the tunneling work. The position of
the operating switch although temporary shall be so chosen as to
ensure proper accessibility and easy identification.

 By the use of two field (magnet type) telephone.
 Any other suitable arrangement like walkie-talkie.
 For up to 100m length of the tunnel, only one of the systems
mentioned above shall be provided whereas in tunnels of length
more than 100 m at least two systems shall be installed; the
wires running along opposite sides of the tunnel, if practicable.
 Red and green lights of adequate size and brightness shall be
provided at suitable intervals on straight lengths and curves etc.
to regulate the construction traffic.
In all the cases as above the system(s) shall be subject to daily
checks regarding proper serviceability. These checks shall be carried
out under the supervision of a responsible person.
(5) Ventilation& Protection from Noise
a) Ventilation
(i) Measures to keep workers safe from harmful effects of dust, gas,
smoke and high temperature in tunnel during construction fall
under any of the following three categories:

 Management to reduce the generation of dust, gas and
smoke.
 Individual protection.
 Adoption of appropriate ventilation system.

• The selection of explosives generating less gas/fumes, the
adoption of wet type shotcreting having less rebound, the
adoption of mechanical excavation system without using
explosive, etc, belong to the first category.
• The requirement of workers using personal protective equipment
like safety goggles, gas masks, falls under second category.
• The adoption of ventilation system using a fan or blower, and dust
collector falls under the third category.
ii) In general, fresh air must be supplied to all underground work
areas in sufficient amounts to prevent any dangerous or harmful
accumulation of dusts, fumes, mists, vapors, or gases. A minimum
of 200 cubic feet of fresh air per minute is to be supplied for each
employee underground. Mechanical ventilation, with reversible
airflow, is to be provided in all of these work areas, except where
natural ventilation is demonstrably sufficient.

iii) Where blasting or drilling is performed or other types of work
operations that may cause harmful amounts of dust, fumes, vapors,
etc., the velocity of airflow must be at least 30 feet per minute.
iv) For gassy or potentially gassy operations, ventilation systems must
meet additional requirements
V) The exposure to airborne contaminants of an employee working in a
tunnel or shaft should not exceed the specified exposure limits.
Vi) Employees should be removed from any area in which there is an
airborne contaminant at a concentration which exceeds the
exposure limit for that contaminant.
Vii) Portable instruments should be provided to test the atmosphere
quantitatively for carbon monoxide, hydrogen sulphide, nitrogen
dioxide, flammable or toxic gases, dust or other toxic contaminants
that occur in the tunnel or shaft. Tests should frequently be
conducted to ensure that the required quality of air is maintained.
A record of all tests should be maintained and be kept available for
inspection.

(b) Protection from Noise
(i) Deafness caused by noise at the working place is a recognized
occupational illness, and tunneling is one of the noisiest
occupations. Exposure to a noise level of 85 dB(A) can cause
damage to hearing. Steps must therefore be taken to reduce the
noise.
(ii) As far as possible noise in the environment should be reduced
through a number of measures like:
 Reduce noise from a machine at source.
 Fit larger mufflers to exhaust and ventilation fans.
 Erect screens to separate the source of noise from the rest of
the working area.
 Improved maintenance of machine.
 Improvements in design of machines

iii) The risk from, exposure to noise can be reduced by reducing the
exposure time however this leads to increased labour costs and
may not be commercially viable for tunneling. Consequently the
measures outlined above should be taken.
iv) Where this cannot be done for technical reasons, personal hearing
protective equipment must be provided. As proper protection is
only possible when the protective devices are properly fitted and
worn, an effective assessment, fitting and training program should
be put in place.
(6) Lighting
a) Adequate lighting shall be provided at the face and at any other
point where work is in progress, at equipment installations, such as
pumps, fans and transformers. A minimum of 50 lux shall be
provided at tunnel and shaft headings during drilling, mucking and
scaling. When mucking is done by tipping wagons running on trolley
tracks a minimum of 30 lux shall be provided for efficient and safe
working. The lighting in general in any area inside the tunnel or
outside an approach road, etc. shall not be less than 10 lux.

b) Emergency lights shall be installed at the working faces and at
intervals along the tunnel to help escape of workmen in case of
accidents. All supervisors and gang-mates shall be provided with cap
lamps or hand torches. It shall be ensured that at least one cap lamp
or hand torch is provided for every batch of 10 people.
c) Any obstruction, such as drill carriages, other jumbos and drilling
and mucking zones in the tunnel shall be well lighted.

(7) Protection against fire
a) As far as practicable, combustible material shall not be used in the
construction of any room or recess containing electrical
apparatus.
b) No flammable material shall be stored in rooms, recesses or
compartments containing electrical apparatus (other than
telephone & lighting apparatus).
c) Fire Fighting Equipment: Clearly visible Fire Points shall be
established inside the tunnel (near any room, recess or
compartment etc.)for use in an emergency.
d) Each fire point should have available as a minimum the following
type of equipment:
i. Dry Powder Extinguisher
ii. Water Type Extinguisher
iii. Bucket of Sand.

e) Recharging of fire extinguishers and their proper maintenance
should be ensured and as a minimum should meet Indian
Standards. These equipment's shall be tested at least as per
manufacturer’s specifications.
f) Water supply for fire fighting purposes should be provided at the
construction site. This may be in the form of static water tank of
adequate capacity or a hydrant line with adequate water pressure at
outlet points.
g) Sufficient number of fire hoses with branch pipes should be
provided at site so that the fire can be controlled until the arrival of
the Fire Brigade.
h) The contractor shall need to give consideration to the provision of
adequate fire fighting arrangements within the underground and
tunnelling operations including the provision of Fire Service
compatible hose connections and emergency lighting.
i) The Telephone Number of the local fire brigade should be
prominently displayed near each telephone on site. Fire Alarms
should be provided at appropriate locations inside the tunnel.

j) Supervisors and workmen at the site should be trained in the use of
fire fighting equipment provided at the site.
k) On the occurrence of a fire caused by any electrical apparatus or a
fire liable to affect any electrical, the supply of electricity should be
cut off from such apparatus or installation as soon as practicable.
l) All places where electrical apparatus is installed shall be adequately
ventilated in order to ensure proper cooling of the apparatus and
dilution of flammable gases.

(8)Electrical installations
a) The entire electrical installation shall be carried out according to
the existing Indian Electricity Rules as modified from time to time.
(9)Personal Safety Equipment
a) Personal safety equipment serves as an additional measure to
ensure safety where it is not possible to improve the environment
by engineering means. Following Personal Safety Equipment
should be provided to workers working in the tunnel. Hard hats
for head protection should be issued to every person entering the
works and the wearing of hard hats should be made compulsory.
b) Eye protection for activities such as welding, Shotcreting etc.
c) If noise levels are excessive and cannot be reduced, hearing
protection should be used e.g. ear muffs or ear plugs.

IRTG ppt.pptx

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