Tunnelling in Rock Mass

Tunnelling in rock mass –
I NST R U M E NTATIO N A ND SU PP O R T SY STE M
PRESENTED BY PRESENTED TO
SHYAM BABU REBAKA DR.SHAILNDER KUMAR
M.TECH(Geotech) SVNIT
P23GTOO3
TUNNELING
CONTENTS
INTRODUCTION TO TUNNELLING IN
ROCK MASS
TUNNEL INSTRUMENTATION USES
TUNNEL INSTRUMENTATION
SUPPORT SYSTEMS
REFERENCES
• Rock Excavation: Excavation technology is primarily driven by rock
excavation machine technology.
• Rock Support: Support technology is largely driven by rock
mechanics science together with support material technology.
INTRODUCTION TO TUNNELLING IN ROCK MASS
• Tunneling in rock mass is a difficult engineering

discipline due to the high requirements, e. g. in
terms of dimensional accuracy, water
tightness, long-term stability and
serviceability.
• Extensive measurements and observations are
inherent parts of the construction process.
• Due to the uniqueness of rock masses, each
tunneling project demands a creative strategy
for planning and construction.
• Rock tunneling involves:
Rock excavation – to make a hole.
Rock support – to sustain the hole.
TBM AND NATM
• It is important to note that the selection between TBM and NATM
methods depends on various factors, including the geological
conditions, project requirements, budget, and expertise available. In
some cases, a combination of both methods may be used, such as using
a TBM for main tunnels and NATM for cross-passages or smaller
sections. No matter which method you wish to use, DeepEX is the
ultimate software for the design and analysis of tunnel systems. From
metro stations and tunnel section design and optimization to whole
metro systems design – transportation analysis, cost-benefit analysis,
city buildings damages and repair costs, and more – DeepEX can assist
you and help you gain a competitive advantage!
TUNNEL INSTRUMENTATION USES
.instrumentation may be used for the following applications:

(a) identifi cation of rock and soil mass properties, such as,
strength,deformability, anisotropy etc.
(b) observation of state of stress in rock mass

(c) observation of response of rock mass to disturbances by
construction and operation of the structure
(d) observation of adjacent structures or services either aff ected or
at risk due to tunnel construction
(e) identifi cation of hazards
(f ) working out remedial measures and verifi cation of their effi cacy.
TUNNEL INSTRUMENTATION NEED
• instrumentation → a scientific way to ensure safety of workers,
stability of the opening and quality of workmanship besides optimizing
the time and cost of construction.
• * possible to know maximum and failing stress and weak planes so
that we can provide better support or alternative
• * Possible to observe movement stabilization, or, in the case of
acceleration, by means of instrumenatioin
• Comparison of measured values with design values enables the
monitoring of tunnel stability and the possibility of implementing
corrective measures at the appropriate moment.
• * The importance of monitoring programs widely accepted →
many historical cases where early warning signs of failure might
have been detected if a good monitoring program had been in
place.
• * Monitoring: better understanding of performance of structure.
• Level of instrumentation:
• depends on type of rock mass/soil condition and also method of
tunneling
• → a) Classical method: used up to last half of 19th century.
Instrumentation not needed!
• b) Mechanical drilling and cutting, drill and blast method:
minimum instrumentation.
• c) Shield method by TBM: ground movement monitoring,
temperature, vibration (accelerometers), hydraulic pressure and
electrical current sensors are used.
• Level of instrumentation:
• depends on type of rock mass/soil condition and also method of
tunneling –
• d) NATM (design as we go!), NTM: dynamic design needs
extensive monitoring.
• Not only before but also during service
• * In-service performance of tunnel: seepage, pore water
pressure and deformations. * Loads on rock bolts and
movements within tunnel shape.
• Instrumentation
• → consists of various electrical and mechanical devices → to
measure parameters such as movement, stress, strain, and
temperature.
• * Monitoring → collection, reduction, presentation, and evaluation of
the instrumentation data. * Effective surveillance program
• → relates the identified symptoms to specific problems at an early
stage of development by ongoing examination of the collected
instrumentation data combined with a review of operation and
maintenance records to decide if a dangerous trend is developing or
appears likely to develop
TUNNEL INSTRUMENTATION
• Measurement of rockmass deformation
• Direct methods
tape meters( used to measure the distance between two reference
points)
• Indirect methods
Borehole extentiometer
TUNNELING
INSTRUMEN
TATION
TUNNELING
INSTRUMEN
TATION
Borehole extensometer
Tunneling
instrumentat
ion
Tunneling
instrumentat
ion
TUNNELING
INSTRUMEN
TATION
Tape extensometer
SUPPORT SYSTEMS
It is the structure erected in the tunnel to support the strata surrounding the
excavated space until the permanent lining is placed.
The basic functions of a tunnel support system are to keep the tunnel stable
and to make the opening usable.
The support systems in tunnel are classified into two types
(a) Temporary Support System
(b) Permanent Support System
Temporary support is defined as any system designed and installed to
support the perimeter of an underground opening between the time it is first
excavated up to the time that a permanent lining is in place.
Permanent support is defined as the support that is designed and installed to
guarantee the long term stability of the underground structure.
STEEL SUPPORT SYSTEMS
Rock tunnel support systems of steel may be generally classified into

the following principal types:
a) Continuous ribs
b) Rib and post
c) Rib and wall plate
d) Rib, wall plate and post
e) Full circle rib
load
cell
ROOF BOLTS
• Roof bolts we usually use to stabilize underground openings and rock
anchors to stabilize natural and excavated slopes.
• Roof bolting follows the principle of fastening the loose rocks near
the surface to the solid rock above, by means of anchor bolts instead
of supporting it from below.
• Roof bolts not only support the surface rock but also assist it to act as
a load carrying element.
SHOTCRETE
• Shotcrete is often used in tunneling and mining to seal freshly
uncovered surfaces and for the support of cavities.
• Shotcrete for tunnel supports may be used by itself as a thin skin type
reinforcement or used in combination with rock bolts, wire mesh and
other more conventional tunnel reinforcements.
• Shotcrete is forced into open joints, fissures, seams and irregularities in
the rock surface and in this way serves the same binding function as
mortar in a stone wall.
• Shotcrete hinders water seepage from joints and seams in the rock and
thereby prevents piping of joint filling materials and air and water
deterioration of the rock.
SHOTCRETE
• Shotcrete’s adhesion to the rock surface and its own shear strength
provide a considerable resistance to the fall of loose rock blocks from
the roof of a tunnel.
• A thicker shotcrete layer 150 to 250 mm provides structural support,
either as a closed ring or as an arch type member.
Watch it for better understanding!
Watch it for better understanding!
REFRENCES
• IS 15026 (2002): Tunnelling Methods in Rock Masses – Guidelines
• IS 5878-4 (1971): Code of practice for construction of tunnels
conveying water, Part 4: Tunnel supports
• https://miningandblasting.files.wordpress.com/2009/09/tunnelling_in
_rocks_present_technology_future_challenges.pdf
• https://old.amu.ac.in/emp/studym/1056.pdf
• NPTEL_IIT ROORKEE

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Tunnelling in rock mass –

I NST R U M E NTATIO N A ND SU PP O R T SY STE M

TUNNEL INSTRUMENTATION USES

• Tunneling in rock mass is a difficult engineering

.instrumentation may be used for the following applications:

(b) observation of state of stress in rock mass

Rock tunnel support systems of steel may be generally classified into

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