Trenchless Technology
ABSTRACT
Trench less technology is the science of installing, repairing and renewing
underground Pipes, ducts and cables using techniques which minimize or eliminate
the need for excavation. It can reduce environmental damage, Social costs and
produce an alternative to open trench method of installation, renewal and repair .It
includes in, development of all kinds of underground napping techniques, tunneling
devices and specialist materials and equipment. Trench less technology is
basically making a tunnel below the surface and staling service lines like water or
gas pipes, electric or telecommunication cables etc. with out any disruption to the
public. It also makes it possible to install the utilities under rivers canals and other
obstacles with no disruption of flow and with minimum or no damage to the
environment.
REFERENCES
1) Jagadish Chandra, “Trenchless Technology in India: Need of the New
Millennium.”
Civil Engineering and Construction Review October 2009-
page 48
2) Maninder Singh, “Techniques of Trenchless Technology In Use In India.” Civil
Engineering and Construction Review October 2009- page 43
3) Dr.Neeraja Lugani Sethi, “Pre- Requisites for Trenchless Technology.” Civil
Engineering and Construction Review October 2009- page 21
4) Sarkar A.K, “Trenchless Technology and INDSTT In India.” Civil Engineering
and Construction Review October 2009- page 13
5) The Construction Journal of India November 2009- page21
6) www.google.com
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2. TRENCHLESS TECHNOLOGY METHODS
Trenchless technology methods system have been categorized in to two groups :
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1)
2)
2.1)
New installation
Rehabilitation and Renovation
NEW INSTALLATION
Methods for installation of a new pipeline or duct, including dealing with
service connection are:
1) Microtunelling
2) Horizontal directional drilling
3) Short drive system
4) Guided drilling
2.1.1 MICRO TUNNELING
Controlled excavation – steerable –Less than 1000mm diameter –Medium length
Micro tunneling is a term which is used to describe remotely controlled
mechanical tunneling systems where the spoil is removed from the cutting head
with in the new pipe line which is advanced by pipe jacking.
Micro tunneling machines have now been developed to work from drives
hafts in almost all types of ground conditions. The cutting head has to be carefully
selected to deal with the expected ground conditions, with the appropriate cutting
tools and crushing devices for the range of gravels, sands, slits, and clays.
The only excavating required from the service is for drive and receptions
shafts. Spoil may be removed from the face by an auger running through the newly
installed pipeline to a skip in the base of the drive shaft.
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Alternatively, water or bentonite may be used to convert the soil into slurry
at the cutting face. The slurry is less then pumped to the surface where the solids
are separated before disposal .
Microtunneling is used extensively for sewerage work where surface
disruption has to be minimized. Machines are now available to drive 100mm or
more in soft ground for sizes 100mm diameter upwards. from drive shafts of less
than 3mm diameter.
Micro tunneling system has been developed in which temporary steel tubes
are jacked in and removed at the next manhole position, the new pipeline following
in the established bore. In microtunnelling, the only indication on the surface is the
presence of a control container with a hoist for lowering pipes into the drive shafts.
Noise levels and traffic disruption are minimised
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Horizontal Directional Drilling
2.1.2 HORIZONTAL DIRECTIONAL DRILLING
Steerable heavy, powerful rig-Large size range –Long distances
Horizontal drilling systems are nowadays widely used for installing pressure
pipes under major obstacles such a motor way intersections, large rivers and
airports runways.
A small rotating and steerable drill bit is launched from the surface at an
angle 10-15 and is used to drill 90mm mud filled diameter hole. During the drilling
operation a 125mm diameter washover pipe is drilled over the pilot string and
following some 100mm behind the head. Alternate drilling then continues on the
pilot string is removed and the bore is enlarged by a rotating barrel reamer
attached to and pulled back by the wash over pipe, drilling mud being used to
llushed away the cuttings and to support the reamed hole. Subsequent caming
continues until required diameter is achieved. The product pipe is less than
attached to the reaming head and pulled through the bore drives of more than
1.5km and of up to 1200mm diameter have been carried out.
2.1.2 SHORT DRIVE SYSTEMS
Essentially unsteered –Soil displacement
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Auger Boring utilizes a rotating head to excavate the soil, which is transported by
auger flights operating in a casing to the drive pit. The head is recovered at an exit
pit or in the trench cut for the adjacent length of pipe line. Auger boring is used in
the range of 100-1000mm diameter
Augur Boring
Impact Moling in which a percussive mole is launched from a drive pit to displace
the soil and from a bore is widely used. The new conduct is normally drawn in
behind the mole. They are used to install services for all utilities.
Rod Pushing is a technique in which a bore of about 50mm diameter is formed by
displacement. A rod is advanced by a straight hydraulic push and the pilot hole
may be back reamed to the required size. The technique is used for the installation
of pipes and conduits up to 15mm diameter over lengths of 30-40mm.
Pipe ramming and Thrust boring are similar processes where a casting, usually
steel, is driven through the ground from the drive pit to the exit pit. Accumulating
spoil is removed by compressed air and water after completing the bore. Pipe
ramming is suitable for most types of soil but not suitable where there are solid
rock formations.
It is said to be a cost saving alternative to open trenching,
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angering or pipe jacking methods. Usually pipes up to 2000mm diameter can be
laid using this technique depending upon the equipment uses.
2.1.4 GUIDED DRILLING
Steer able small rig-Sallow drilling-Medium length
Guide drilling employs an excavation or soil displacement with compact
lightweight rig for rapid mobilization. Small diameter jets mechanized cutting tools
or displacement heads attached to a flexible drill string are positioned to form a
bore as the head is thrust forward. The drilling head is launched from the surface
at an inclined angle. Controlling the orientation of a slant face at the head effects
steering in both vertical and horizontal planes. Monitoring of the alignment takes
place using a transmitter in the head and a locating device at ground level.
Guided Drilling
I having established the pilot bore; back reaming equipment is drawn
through the hole to enable it to accept the product pipe, duct, or cable using an
impact mole.
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2.2 REHABILITATION AND RENOVATION
Methods including are:
1) Pipe bursting
2) Pipe eating
3) Retaining the existing pipes
4) Localized repair
Mini Burst
2.2.1 PIPE BURSTING
New for old without trenching – Size for size and upsize capability
In this method an existing pipeline can be replaced with a pipeline of the
same or larger dimension without opening up the ground. It is especially useful in
areas where the load on the system is more than the existing pipe can handle and
replacement is required.
The method uses a mole as a bursting head that is drawn through the
existing pipe crushing it as it moves forward and replacing it with a new PE
(polyethylene) pipe. The main advantage of this system is that a small power
source can be used to drive the mole with minimum time. Upsizing from 100mm
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diameter to 225mm diameter is now well established, and pipes of up to 600mm
diameter have been replaced.
2.2.2 PIPE EATING
New for old without trenching – Enlargement - Steer able
Pipe eating is an online micro tunneled replacement technique. The existing
defective pipeline is crushed and removed through the new pipeline.
Lateral
connections must be disconnected in advance and may be replaced by rider
sewers or reconnected by angled drilling.
2.2.3 RELINING THE EXISTING PIPES
This method requires access, usually by manholes, at both ends of pipe. A
flexible liner is places into the defective pipe and with the use of water under
pressure finds its own way and can pass bends of 90o . In places where joints have
moved or sections are missing, but the passage is available, the liner creates a
smooth transition. When the liner is in place, it is heat cured to create a rigid,
tough, and smooth inner surface.
2.2.4. LOCALISED REPAIR
Resin injection and chemical grouting at trouble spots
Local defects may be found in pipes due to cracking or joint failures.
Systems are available for resin injection to seal localized defects in the range
100mm-600mm diameter.
Chemical grouting with urethane and similar materials are used in sewer
rehabilitation. Remote and man entry grouting of defective joints and cracks may
prevent infiltration in pipelines.
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This is an inexpensive method of rehabilitating existing systems up to
several hundred meters of length everyday from manhole to manhole.
Pipe Slip lining is another method used that involves inserting new smaller pipes
in to older, damaged sewers thereby replacing the old pipe. But the new pipe is in
reduced diameter.
Modified slip lining often called close fit lining utilize the properties of PE or PVC
to allow temporary reduction in diameter or change in shape prior to insertion in the
defective pipe.
The method includes Roll down, Swage lining and Deformed lining. The
inserted pipe is subsequently expanded to form a tight fit against the wall of the
original pipe, thus avoiding the need for annular grouting as in conventional slip
lining.
For Roll down and Swage lining, temporary reduction in diameter is
achieved either by mechanical rolling (Roll down) or drawing through a reduction
die (Swage lining).
For Deformed linings, the pipe is deformed and folded
immediately after extrusion and is coiled on a drum. After insertion in the defective
pipe, the lining is expanded using steam and a re-rounding device to form a close
fit.
These systems are suitable where the existing line is of good shape.
As
compared to conventional slip lining , in this method there is little or no loss of
hydraulic capacity.
3. PRE-REQUISITES
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Through surveys and site investigations are essential to the success and
efficiency of trench less installations and repair techniques.
(a) The survey results help top determine the most appropriate systems.
(b) The investigations methods include geophysical surveys, boring and
sampling, measurement of ground water table, test pits and trenches,
penetration tests, examinations and investigations of existing structures
using ground penetration testing etc.
(c) Closed circuit televisions, ground penetration radar, utility detection
equipments
leak detection techniques are available for below ground activities.
4.TECHNIQUES OF TRENCIILESS TECHNOLOGY IN INDIA
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The main trenchless techniques which are in use in India (included in the
above mentioned methods) are described below.
4.1. DIRECTIONAL DRILLING
Directional drilling involves steerable tunneling systems for both small and
diameter lines. In most cases, it is a two-stage process. The first stage consists of
drilling a small diameter pilot hole along the desired centre line of a proposed line
and in the second stage, the pilot hole is enlarged to the desired diameter to
accommodate the utility line and to pull the utility line through the enlarged hole.
The pilot hole is of approximately 3 inches in diameter and is drilled with a specially
built rig up with an inclined carriage typically adjusted to between 5 and 30
degrees, which pushes the drill rods into the ground. However the optimum angle
is 12 degrees. As the pilot hole is being drilled, bentonite-drilling mud is pumped
down the center of the drill rods. The drill head consists of either a jetting head or
drill bit. In the case of a jetting head, small diameter high-pressure jets of bentonite
actually cut the soil and facilitate spoil removal by washing the cuttings to the
surface where they settle out in a reception pit. In case of drill bit, the bit is driven
by a down hole mud motor located just behind the drill bit from energy derived from
the pumped drilling fluid. Before the start of back reaming the pipeline has to be
positioned on rollers in line with the hole to minimize any axial load on the line.
Advantages
(1) The major advantage is the speed of installation combined with the
minimum environmental and social impact.
(2) Long and complicated crossings can be accomplished with a great degree
of accuracy since it is possible to monitor and control the drilling operation
so that utilities can be fit into small corridors where little place is available
between existing utilities.
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(3) Another advantage is that sufficient depth can be accomplished to avoid
other utilities.
(4) Limitation of access and reception pits is another advantage.
Disadvantage
(1) Special equipment and very high degree of operation skill is required.
(2) As the cost of the equipment and the operation are high, bore length should
be sufficient in order for it to be economical.
(3) Mainly steel pipe is being installed by the method.
4.2 RAMMING
In this method, the pipe is rammed through the soil by using a device
attached to the end of the pipe to drive the pipe through the soil. In this method,
the tool does not create a borehole. It acts as a hammer to drive the pipe through
the soil.
Compressed air supplied from an air compressor is generally used as a
power source. When ramming pipe, the leading edge cuts a borehole, the spoil
enters the pipe and is compacted as it is being forced to the rear of the pipe. After
the whole length of the pipe is rammed in place, the tool is removed and the pipe is
cleaned out.
The type of pipe installed by the pipe ramming method is limited to steel due
to the application of cyclic impact loads on the pipe. The size of the pipe ranges
from 2 inches to 55 inches. This method is capable of installing pipes to over 200
feet (60 meters) in length.
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Advantages
The pipe ramming is an effective method for installing medium size pipes.
The method is economic since the equipment cost is not very high and the
operation is simple. The pipe can be installed in one piece or segments. This can
be used in almost all types of soils. The method does not require any thrust
reaction structure.
Disadvantages
The major disadvantage is that there is no control over the line and grade
and in case of obstructions like boulders, the pipe may be deflected. Then work
should be stopped immediately.
For small diameter pipelines, the method is
economical, but for large diameter pipes, the equipment cost is high.
4.3. MOLING
Moling is a method, which forms the borehole by compressing the earth that
immediately surrounds the compacting device which is an underground piercing
(mole) is propelled by a power source.
The tool is streamlined into bullet or
shape. The method is restricted to relatively small diameter lines in compressible
soil conditions.
Compressed air or hydraulic fluid, transmitted to the toot through the flexible
hoses, imparts energy at a blow frequency of 100 to 600 strokes per minute to a
reciprocating piston located inside the nose of the tool. This action results in the
tool propelling itself through the ground. It is applicable in most ground conditions
from loose sand to firm clay. The method required the use of boring and receiving
pit. After the operation the unit can be backed out of the borehole. The tool is
removed and the cable is attached to the air hose and pulled back through the
borehole. In the case of rigid pipe, it can simply be pushed through the open
borehole. Any type of pipe or cable can be installed by the method.
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Moling Equipment
Pipe size is generally limited to 6 inches or less. However, modern
techniques in mole manufacturing have increased the ability to make bores of large
sizes. Even though 200 feet (60 meter) bores have been successfully made by
this method, the span lengths were limited to 60 feet (18 meter) with 40 feet being
optimum.
Again span lengths have increased with modern advances in mole
design.
Advantages
It is a rapid, economic, and effective method of installing small diameter
lines. Any type of utility line can be installed using the method. The stability of the
soil around the borehole is increased due to compaction.
equipment is minimum.
Disadvantages
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Compaction methods are limited in their length by reliability because basic
systems are unintelligent, unguided tools that tend to bury themselves, surface in
the middle road or damage existing utility lines.
4.4 AUGER BORING
The auger horizontal earth boring is a process of simultaneously jacking
casing through the earth while removing the spoil inside the casing by means of a
rotating flight auger. The auger is a flighted tube having dual functions, firstly it has
couplings at each end that transmit torque to the cutting head from the power
source located in the bore pit and secondly, it serves to transfer spoil back to the
machine.
Augur Blades
This method requires bore pit both at the entry and exit points of the bore.
The auger-boring machine consists of the boring machine, casing pipe, cutting
head and augers as the major components. The power source creates the torque,
which rotates the auger, which in turn rotates the cutting head. The cutting head
cuts the soil and the soil is transported to the machine through the casing by
means of the auger, which acts as a screw conveyor.
The pipe size that can be installed by this method ranges from 4 inches
(100mm) to over 60 inches (1500 mm). However, the most common size range is 8
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inches(200 mm) to 36 inches(900 mm) and the average bore length ranges
between 53 meter and 68 meter, though with experience and the use of latest
techniques up to 180 meter of boring is possible using auger boring.
Advantages
The major advantage is that the casing is installed at the same time as the
borehole excavation takes place. This method can be used in a wide variety of soil
types.
Disadvantages
This method requires different sized cutting heads and auger sizes or each
casing diameter, which increases the investment in equipment. The investment in
bore, pit construction, and the initial setup is also required.
In case of soils
containing large boulders, this method cannot be used advantageously.
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5. NEED FOR TRENCILESS TECHNOLOGY
(1) The disadvantages and difficulties encountered in conventional trenching
methods have resulted in thinking of the need for trenchless technology.
(2) The advantages of the no-dig technology are also responsible for the need of
this technology to be adopted in mainly urban areas
5.1 OPEN TRENCH METHOD
It is a traditional met6hod of trenching for laying the utility lines below the
surface. In present days, there are many disadvantages and difficulties in adopting
this method, mainly in urban areas. Those are described below:
(a) As the open trench is going to create obstruction roads, busy areas,
diversions have to be provided before start of any digging word.
(b) As the obstruction is created, the traffic has to be rerouted causing
traffic jams.
(c) Original users of the road have to undergo hardships in the form of
additional mileage as well as time.
(d) Many a time, while cutting deep trenches in congested areas appear
in the adjacent buildings.
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(e) Another difficulty, which is encountered very often is the damage
caused to other service lines or cables present underground,
providing temporary supports to these lines during the construction is
cumbersome and costly affair.
(f) Trenches left open overnight should be fenced and barricaded. Hand
of mechanical signs should be used where necessary.
(g) While cutting open trenches, trees, shrubs, gardens etc. may have to
be destroyed damaging the environment.
(h) If any rehabilitation or renovation is required, the trenches once cut
and refilled should again be cut through out and refilled causing
difficulties to the public; that is, cutting and refilling is required at
frequent times
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5.2 ADVANTAGES OF NO-DIG TECHNOLOGY
(a) It reduces damages of valuable surface.
(b) It reduces the danger of improperly compacted excavations.
(c) It saves resources.
(d) It is accident free.
(e) It avoids traffic jam.
(f) It makes the use of the line(track) of the old pipe possible.
(g) It saves underground space (pipe busting).
(h) It reduces the impact on the environment.
(i) It provides the hassle-free road surface.
(j) It is possible to lay service lines across railway track, narrow lanes etc.
When open trenching is impossible.
(k) Presence of a canal, pond, river etc. across the root poses no problems to
the trench less technology systems.
(l) Without disturbing the traffic and life on the surface, the lines can be laid
below ground in a much shorter time by using this technology.
(m)For replacement, repair and rehabilitation of old water and sewer lines in
cities, it is very helpful to use trench less technology without disturbing the
normal life on the surface.
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6. CONCLUSION
With all round developments in various fields like petrochemicals where
conveyance of gas, crude and refined products over long distances is common,
telecommunication and power, water supply and sewerage etc. and
mushrooming growth of high- rise buildings in and in and around the cities is
becoming increasingly necessary that these lines are laid underground leaving
space above surface comparatively free. i.e., Adoption of
trench less
technology is the only remedy. Also if costs benefit analysis of the two systems
(i.e. open trenching methods and trenchelss technology methods) is conducted,
considering both direct and indirect costs, it will help us make informed
divisions on technology selection, under different circumstances.
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