A Review Study on Methods of Tunneling in Hard Rocks

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 8, 2013 | ISSN (online): 2321-0613
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A Review Study on Methods of Tunneling in Hard Rocks
Chirag J. Shah1
Hiren A. Rathod2
1
M. E. Student (Construction Management) 2
Assistant professor
1, 2
Civil Engineering Department
1, 2
S.N.P.I.T. & R.C, Umrakh, Bardoli, Gujarat, India.
Abstract— This article presents a review on the different
methodologies that are used for tunnels excavations in hard
rocks in present era. Growing needs for modern
transportation and utility networks have increased the
demand for a more extensive and elaborate use of
underground space or through high mountains / hills. As a
result, more projects have to be completed in various ground
conditions and one of which is more challenging is to carry
out excavation work in hard rocks. Significant technological
advances have rendered these projects possible, but have
also given rise to new challenges as many of these projects
have to be completed in difficult conditions, with very strict
environmental constraints, particularly in urban areas where
the potential impact of tunneling on existing structures is a
major concern. This paper addresses the main aspects of
tunneling and underground works performed in hard rocks.
A summary is presented of the more recent advances and
widely adopted techniques in these regards.
Key words: Hard rock, Excavation, Tunnel Boring Machines
(TBM)
I. INTRODUCTION
Tunnel is an underground passage through a mountain,
beneath a city or under a waterway or tunnels are enclosed
roadways, railways, waterways, etc. with vehicle, trains,
ships, etc. access that is restricted to portals regardless of
type of structure or method of construction. Tunnels are
structures that can require special design considerations that
may include lighting, ventilation, fire protection systems,
and emergency egress capacity, as documented in design
standards or based on the owner’s determination.
Tunnelling can be define as ”the continuous
excavation of a hole through the earth’s crust”. The portion
where the work is carried out while its construction is called
the face (heading) and all efforts are made in advancing this
face as fast as possible till the end of tunnel is reached. The
man at the face are called heading crew. The heading crew
is supplied with fresh air, compressed air, water, explosives,
drills, mucking and hauling equipment, support and other
accessories. Tunnel excavation produces a re-distribution of
stresses in the rock and a tendency for closure of the void
produces a tendency counteracted by the tunnel support
shell.
Modern tunneling work is best regarded as the
repetition of a cycle comprising of number of operations and
each operation makes a contribution in the controlled
advance of a tunnel face. It is essential that tunnel works
should be organised on a scientific basis. Factors such as
size of the tunnel and the quality of rock will influence
details, but the basic order of progressing in all types of
tunnels (whether large or small or whether hard or soft), is
to:
 Excavate
 Dispose of the muck and
 Line the excavated ground
II. WORLD WIDE SCENARIOS
Some of the examples of carrying out challenging work of
tunnel construction through hard rock are highlighted over
here. The 1036 m long Eupalinos water supply tunnel was
built in 530 BC on the Greek island of Samos. This is the
first known tunnel to have been built from two portals and
the two drives met with a very small error.
The oldest underground sections of the London
underground were built using the cut-and-cover method in
the 1860s, and opened in January 1863. What are now
the metropolitan, Hammersmith & city and circle lines were
the first to prove the success of a metro or subway system.
Thikri tunnel length 800 meters, shape of tunnel d-
shape, internal diameter 6.0 meter, longitudinal gradient is 1
in 2500, rock cover 14 metres to 44 metres [>3d as per IS
code], existing G.L. (at entrance) is 224.015, existing G.L.
(at exit) is 221.695, invert level (at entrance) 203.671, invert
level (at exit) 203.349, general geology hard rock strata with
RQD value > 75%, method used was drill blast method.
Veligonda tunnel length is about 19.2 km. The
TBM method of tunneling was used on the Veligonda
project. The bore diameter and segment diameters were 10.0
m and 9.2 m respectively. The whole of the Veligonda
tunnel geology has been given an expected RQD value of
between 61 and 75 which remains firmly within the Rock
class-II category.
Ghatkopar high level Tunnel, Mumbai was
constructed for the purpose of Sewage. Geology of soil was
Massive & Weathered Basalt. Length of tunnel was 2600 m
& its Diameter was 3065 mm. TBM method was used with
machine type Single Shield TBM. Support system used was
Segmental Lining.
III. PURPOSE & IMPORTANCE
Tunnels are the underground passages which are constructed
without distributing the ground surface. They may be
constructed through hills, below the ground, streams, etc.,
for various purposes which may be summarized as follows
along with its importance as compared to other means of
conveyance:
 To provide passage for roads and railway tracks, access
to mines, conduits for water, etc.
 Tunnels protect the railway track, highway, sewer line,
oil line, etc., from weathering effects such as rain, snow
and other elements.
 Tunnels also protect them during war time from
destruction due to bombarding.

A Review Study on Methods of Tunnelling in Hard Rocks
(IJSRD/Vol. 1/Issue 8/2013/0007)
 Tunnels have proved cheaper for crossing the mountain
or river than open cut or bridges.
 The use of tunnel under a river bed is often economical
and convenient than providing a bridge over the river.
 The cost of maintenance of a tunnel is lesser as
compared to a bridge or a heavy open cut.
In most congested urban areas, underground railway or
highway is the best alternative to provide the means of
transportation. Also in soft ground it seems to be cheaper
than open cut due to possibility of a large numbers of slips.
Tunnels reduce the length of railway line in a circuitous
route to reach the other side of the hill. In busy and
congested cities due to scarcity of load, tunnels are used for
providing underground system, which provide rapid and un-
obstructed transportation.
IV. METHODS OF TUNNELLING
GENERALA.
Tunnelling in hard rock is safe, easy and the cost of
maintenance of tunnel is also very less. Many of the primary
rocks which are categorized under the hard rocks are
granite, feldspar, basalt, et. all.
Various methods used for the excavation purpose
in such types of rocks are:
 Full face method.
 Heading and bench method.
 Drift method.
 Pilot tunnel method.
 Drill & Blast method.
 Hard TBM method.
 Cut-Cover method.
 Immersed tube method.
Some of the above listed techniques are conventional and
not covered under the scope of this paper; only few of the
techniques which are predominantly adopted worldwide and
have its importance in excavation through hard rocks as
compared to other are prescribed here with its brief
introduction, procedure, merits and demerits.
Drill & Blast Method of TunnellingB.
Modern Drill and Blast excavation for civil projects consists
the basic approach of:
 To drill a pattern of small holes,
 Load them with explosives,
 Then detonate those explosives
Fig.1: Drill & Blast Method
Hence, creating an opening in the rock. The blasted and
broken rock (muck) is then removed and the rock surface is
supported so that the whole process can be repeated as many
times as necessary to advance the desired opening in the
rock.
Procedure:
1) Drilling
The drilling should be ensuring minimum overbreak and use
of least amount of explosive per unit volume of excavation.
Holes are drilled by using pneumatically operated rock drills
in conjunction with pneumatic pushers or drifters mounted
on column bars or drill carriages as may be found suitable.
The size of drill bits used should be such that the diameter
of the hole will be about 6 mm greater than the diameter of
explosive cartridge to be inserted.
2) Blasting
a) Explosives:
Blasting explosives are divided into two classes: high
explosives and low explosives. Gelignites, Gelatines and
Dynamites are the examples of high explosives, whereas,
Black powder is low explosive. Most commonly, high
explosives are used for tunnelling operations. The strength
of these explosive is expressed as a percentage of strength of
the blasting gelatine which is the most powerful commercial
explosive. The following explosive are used in tunnelling:
 Blasting gelatine used for blasting very hard and tough
rocks. This is fully water proof and can also be used in
wet locations.
 Special gelatine 9% to 40% is selected to suit the rock
requirements.
 Ammonia dynamite is available in strength from 15% to
60% used for soft rock.
 Semi-gelatine is bulkier than other varieties and come
in 45% to 60% strength.
b) Detonators:
There are primarily two types of detonators namely, Lead
azide aluminium detonator and electric detonators. Lead
azide aluminium detonators are used in conjunction with
safety fuses and give efficient detonation with all types of
blasting explosives. The electric detonators are suitable for
singles or simultaneous firing in series or parallel.
c) Detonating Fuse:
It contains a high explosive core with a water proof
covering. It is used for shooting a large number of holes in
one blast. It is denoted by the use of one or two blasting
caps securely attached alongside it.
d) Primer:
It is the cartridge containing the detonator. The primer is
supplied with the explosive and is attached with the
explosive. It is denoted by Prima cord, which is a high
explosive use.
e) Circuit Testers:
To test an electric detonator, it should be placed inside an
iron pot or tube to guard against accidental explosion.
3) Loading & Stemming
Loading means charging the drill holes. Before loading,
each hole is blown out with a high pressure air jet to remove
loose cuttings and water. Then, primer cartridge is gently
placed into drill hole next to the bottom. A full cartridge is
inserted first, tamped well into bottom, then the primer is
inserted with the end containing detonator pointing towards

the bottom of drill hole. Both the primer and next placed
cartridge are tamped lightly with a wooden rod. When the
tamping material is being inserted, the leading wires or
safety fuse should be held to one side, to facilitate the action
of the tamping rod and prevent damage to fuse.
The remaining portion of the drill hole is filled with
an inert material and tightly tamped by wooden rod. Soft
rolled plugs of clay, damp mixture of sand and clay or a
rubber plug with a wooden core may be used as inert
material.
4) Firing
a) Firing by Safety Fuse:
After charging or loading the holes, personnel and
everything liable to injury must be placed to a safe distance.
When necessary, the blast may be covered with rope
blasting mats or a heavily weighted blanket of scrub. Special
fuse-lighter should be used for ignition.
b) Firing by Electricity:
Before attempting to connect up an electric circuit, it should
be ensured that the main cables are intact and that the
exploder is working correctly and capable of supplying
sufficient current to fire the number of charges in the circuit.
No naked wire should be left touching the ground. Also, the
exploder is not connected to the firing circuit until all men
have left the danger area and signal to fire has been given.
5) Inspection & Handling Misfire
After completion of firing, the site is examined by the
foreman before he gives the all-clear signal. If a misfire has
occurred, no person shall approach the site for one hour if
safety fuse was used or 15 minute, if electrically fired.
Misfires may occur due to improper primers, use of non-
water resistance explosive in wet condition or improper
loading.
Immediately after the smoke is cleared away from
a blast, inspection is carried out by a competent and
experienced tunnel foreman. All loose rock is removed
carefully by barring to ensure that the access to the face is
safe.
Merits:
 Potential environmental impacts in terms of noise, dust
and visual on sensitive receives are significantly
reduced and are restricted to those located near the
tunnel portal;
 Compared with the cut-and-cover approach, quantity of
C&D materials generated would be much reduced;
 Compared with the cut-and-cover approach, disturbance
to local traffic and associated environmental impacts
would be much reduced;
 Blasting would significantly reduce the duration of
vibration, though the vibration level would be higher
compared with bored tunnelling;
Demerits:
 Potential hazard associated with establishment of a
temporary magazine site for overnight storage of
explosives shall be addressed through avoiding
populated areas in the site selection process.
 There is a high risk of over breaking the tunnel profile
and damaging the surrounding rock
 High levels of noise and vibration make this unsuitable
for an urban area.
Cut Cover Method of TunnellingC.
Cut and cover tunneling is a common and well-proven
technique for constructing shallow tunnels. The method can
accommodate changes in tunnel width and non-uniform
shapes. Cut and cover is a simple method of construction for
shallow tunnels where a trench is excavated and roofed over
with an overhead support system strong enough to carry the
load of what is to be built above the tunnel.
Fig. 2: Cut Cover Method
Procedure:
1) Excavation and support
The initial “cut” is undertaken to facilitate the tunnel
construction. This uses similar technology to road cuttings.
Prior to excavation, buried utilities and services crossing the
route have to be protected, temporarily raised or
permanently diverted to avoid the tunnel alignment where
possible. For gravity sewers this may involve pump
installation. The cut is constructed in a number of ways,
depending on the support requirements of the ground. In
hard rock this may be vertical walls supported by rock bolts
and sprayed concrete, in soft rocks and soils stable slopes
may be created by constructing benches. If surface space is
restricted, or the disturbance caused by construction needs to
be minimized, then retaining walls can be used to stabilise
the excavation. These may be permanent, incorporated into
the final structure or temporary and removed or abandoned
after the tunnel structure has been completed.
2) Tunnel fabrication
Once a stable open cut has been constructed, the tunnel
structure is fabricated in the trench. This structure is
generally constructed from reinforced concrete using large
tunnel forms. As considerable materials and excavated fill
storage is required this operation requires a significant work
site.
3) Reinstatement
After construction, fill is used to reinstate the ground
surface. Where possible this fill may be reserved material
from the trench excavation. Additional fill may be required
to assist with compaction and drainage, or if the trench
material is unsuitable. Reinstatement may be to the original
topography and land use. In some cases this offers the
opportunity to improve surface conditions, such as utility
and drainage improvements or local road upgrades.
Demerits:
 More dust and noise impact may arise, though these can
be mitigated through implementation of sufficient
control measures;

 Temporary decks are often installed before bulk
excavation to minimise the associated environment
impacts;
 Larger quantity of C&D materials would be generated
from the excavation works, requiring proper handling
and disposal.
Hard TBM Method of TunnellingD.
In hard rock, either shielded or open-type TBMs can be
used. All types of hard rock TBMs excavate rock using disc
cutters mounted in the cutter head. The disc cutters create
compressive stress fractures in the rock, causing it to chip
away from the rock in front of the machine, called the tunnel
face. The excavated rock, known as muck, is transferred
through openings in the cutter head to a belt conveyor,
where it runs through the machine to a system of conveyors
or muck cars for removal from the tunnel.
Procedure:
1) Excavation Advance:
The cutting head is rotated against the ground to commence
cutting
 Thrust is applied by the rams or side gripper pads in the
drive section to assist cutting and maintain face pressure
 Cutting and advance continues until enough space is
created in the tail shield to construct the next lining ring
the gap between the ground and the previous lining ring
is grouted as it leaves the tail shield.
Fig. 3: Excavation Advance
Fig. 4: Lining erection
2) Lining erection:
 The thrust rams are withdrawn into the drive section
leaving clear space for the erection of the lining
 Each segment forming the lining is maneuvered into
position and bolted together to form a completed lining
ring the thrust rams are then reengaged to commence
the next excavation cycle
Merits:
 Potential environmental impacts in terms of noise, dust
and visual on sensitive receives are significantly
reduced and are restricted to those located near the
launching and retrieval shafts;
 Compared with the cut-and-cover approach, disturbance
to local traffic and associated environmental impacts
would be much reduced;
 Compared with the cut-and-cover approach, quantity of
C&D materials generated would be much reduced
Demerits:
 The major disadvantage is the upfront capital cost.
TBMs are expensive to construct, difficult to transport,
require significant backup systems and power.
 Their applicability is limited to long tunnels where the
high rates of advance and tunnel quality can offset their
high capital cost.
V. CONCLUSION
Referring to the various literatures mentioned below and the
contents mentioned above in the paper the importance of
tunneling can be clearly understood as compared to other
means of conveyance such as bridges, open cuts, etc. i.e.
through tunnels we can get many benefits such as low
maintenance cost, no need for acquiring the land & it can be
used in any type of area such as in congested cities. Also
referring to many recent methodologies in tunnels we found
that most suitable method was the method using TBM.
Though it is very costlier than all other methods, but it also
has many advantages compared to others like it is easier in
operation, very fast, can be used in any ground conditions
depending on cutterhead with little modifications, perfection
of work, safety etc.
ACKNOWLEDGMENT
The authors are thankfully acknowledge to Mr. J. N. Patel,
Chairman Vidyabharti Trust, Mr. K. N. Patel, Hon.
Secretary, Vidyabharti Trust, Dr. H. R. Patel, Director, Dr.
J. A. Shah, Principal, S.N.P.I.T. & R.C., Umrakh, Bardoli,
Gujarat, India for their motivational & infrastructural
supports to carry out this research, Dr. Neeraj D. Sharma,
HOD Civil Department, SNPIT & RC, Umrakh.
REFERENCES
[1] Doctoral thesis at NTNU , Hard Rock Tunnelling
[2] “Fracturing Excavation Method for Hard Rock
Tunnelling” By: Fon Drill & FASE Method.
[3] “Tunnelling in Rocks – Present Technology & Future
Challenges” By: ZHAO Jian, Inaugural lecture, May
2007.
[4] S. Seetharaman “Tunnel & Airport Engineering”
Umesh Publication.
[5] Tunnel wikipedia.
[6] Tunnel Boring Machine (TBM) in action in Kuala
Lumpur & Robbins Hard Rock Disc Cutters,
youtube.com.
[7] IS: 5878 ( Part 111) – 1972: Underground Excavation
Soft Strata.
[8] “Construction safety in hard rock tunnelling” By: Dr.
Zhou Yingxin Programme Manager (Underground

Technology & Rock Engineering), Defence Science &
Technology Agency.
[9] “Tunnelling in Rocks – Present Technology & Future
Challenges” By: ZHAO Jian, Inaugural lecture, May
2007.
[10]Engineering Survey System for TBM (Tunnel Boring
Machine) Tunnel Construction, By: Andrew Hung
Shing Lee, Hong Kong.
[11]“Tunnel Boring Machines”, IMIA Working Group
Paper WGP 60 (09) Tunnel Boring Machines.

A Review Study on Methods of Tunneling in Hard Rocks

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