Note: Descriptions are shown in the official language in which they were submitted.
132~7~ ~
"Method of pipe replacement"
THIS INVENTIO~ relates to a method of replacing an existing
old pipe, such as water service pipe~ gas pipe or the like,
with a new pipe and, in particular, to a method oE replacing
an old pipe with a new one without digging up the ground.
When an old pipe, in particular a cast :iron pipe, has
deteriorated with age and become unable satisfactorily to
perform its func-tion or when it is required to replace -the
old pipe with a new due -to new re~uirements, it is desirable
to replace the old pipe by a new one without digging up -the
~round, because great labour and cost is involved in
; excavating the old pipe and because such digging woxk
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unavoidably obstructs traffic or affec-ts means of transport
and communication.
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According to a known method of pipe replacement called
"plpe-in-pipe", a new pipe is simply inserted into the old
one under the ground, but this inevitably means that the
internal diàmeter of the new pipe mu~t be smaller than that
of the old pipe, resulting in a reduction in the capacity for
transporting gas or water. ~
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An attemp-t has already been made to ovexcome the
above-discussed drawhack of the "pipe-in-pipe" method, as
disclosed in UK Patents ~B 2152624B "Pipe Replacement
System", GB 21243~5B and GB 20~270:LB "Mains Insertion".
The aforesaid prior art discloses a method and an
apparatus for pipe replacement in wh:ich a new pipe is
attached -to a rear end of a bursting mole having a
cylindrical body with an external diameter which is larger
than an old pipe to be replaced. The bursting mole and -the
new pipe move forward together, and a front end or head of
the bursting mole in-trudes into the old pipe and.
progressively burst the old pipe to form an enlarged space
to receive the new pipe following behind -the burstiny mole,
so that the old pipe is replaced with the new one.
The known method descrihed above may be said to
constitute a rational way of replacing buried pipes.
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However, when the abo~e known ~ethod is studied in de-tail,
several drawbacks are found therein. Tha-t is, the
following drawbacks exist whether a new pipe or a sheath is
towed into position by the mole:
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1. When no sheath is used ~i.e., a new pipe is
connected to the rear end of the mole for direct renewall:
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(a) Because an air hose and possibly other items are
inserted thxough the new pipe, any paintwork or lining on
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the internal surface of the new pipe may be damaged by the
coupling of the hose a-t the time of working or drawing the
hose.
~b) Because exhaust air is discharged insicle the
new pipe, lubricating oil in the air ~mixing of lubricating
oil with the air is necessary for sliding motion of piston)
may adhere to the internal surface of the new pipe and soil
it. If an exhau~t air hose is provided in an a-ttempt to
obviate this problem, not only is the working efficiency
lowered but the performance of the air cylinder is also
affected due to the reduced discharge cross-section,
Moreover, an increased number of hoses is then required, and
the danger of damage to the internal surface of the new pipe
may increase correspondingly.
~; 15 2. When a sheath is used (i.e., a new pipe is inserted
into a sheath aFter the sheath is installed in place of the
old pipe):
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Because the sheath attached -to the mole should have an
internal diameter which is larger than the external diameter
of the new pipe, the external diarneter of the mole is obliged
; to be rather large as compared with the former case where no
sheath lS used. Accordingly, greater pressure has to be
applied to the surrounding ground and working efficiency is
thereby lowered. Further, the conse~uences of such greater
pressure on the surrounding ground tpressure, Yibration~
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132~4~9
cannot be ignored~ In particular, where there is another
existing buried pipe line in the vicinity, then is a serious
possibility of disloca-ting the other pipe line or loosening a
pipe joint -thereof due to such pressure.
The present invention aims to solve -the above-discussed
problems and to provide an improved pipe replacement method
by which the internal surface of the new pipe is protected
from damage, stain or pollution, while minimizing the adverse
consequences on the corresponding ground.
Accordingly, the invention provides a method of
replacing an old buried pipe with a new pipe, comprising
attachiny a temporary pipe having an external diame-ter
which is substantially the same as the new pipe to the rear
` end of a bursting mole having a cylindrical body whose
external diameter is larger than -the old pipe moving
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n the mole forward so that a head of the mole intrudes
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into the old pipe and bursts it to provide an enlarged space
for receiving the temporary pipe following -the mole,
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~` applying the new pipe to ~ end of the temporary pipe, and
withdrawing the temporary pipe such that it is procJressively
replaced by the new pipe.
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A method embodying the invention obviates such problems
as damage to the paintwork and lining of the internal surface
of the new pipe wikh which the old pipe is replaced. Even
when khe drive unit is equipped with an air cylinder, the
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~32~L47~
internal surface of -the new pipe is prevented from stain and
damage due to the adherence of foreign materials ~lubricating
oil in the exhaust air), and cleaning of the new pipe after
the replacement is no-t required.
S Moreover, since a -temporary pipe having an external
diameter almost the same as -the new pipe is used in the
; replacemen-t, the external diameter of the temporary pipe can
be one size smaller than a comparable sheath for the same
- size of new pipe, so that the driving force necessary for the
foxward movement can be correspondingly smaller. As a
result, detrimen-tal influences on -the surrounding ground can
be reduced.
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Furthermore, the temporary pipe once used can be
repeatedly used for future replacements, and therefore the
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; 15 method according to the invention may be said to be more
^ economical as compared with a sheath which is used only once
and left buried.
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In order that the inven-tion may be more readily
understood, embodiments thereof and the prior art, will now
be described by way of example with reference to -the
a~companying drawings, in which:
Figures l and 2 are diagrammatic sectional views
illustrating a method of pipe replacement embodying the
; present invention;
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1~21479
Figure 3 is a diagrammatic sectional view illustrating
an example of a temporary pipe employed in -the method o
Figures 1 and 2;
Figure 4 is a sectional view illustrating the wall
construction and coupling arrangement o an example of a
new pipe;
Figures 5 and 6 are diagrammatic sectional views
illustrating respective further embodiments of the
; invention; and .
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Figures 7 to 9 are diagrammatic sectional views 10
. illustrating a prior art pipe replacemen-t method.
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Apparatus in accordance with -the prior art is
illustrated in detail in Figure 7 of the accompanying
drawings, Figures 8 and 9 illustrating a manner of actual
~:; 15 use of this prior apparatus.
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As shown in Figure 7, a rear end of a mole 4a having a
body with a laryer external diameter than that of an old
pipe la is connected to either a new pipe 9a for directly
replacing the old pipe or to a sheath 14 for receiving and
- 20 protecting -the new pipe.
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In Figures 8 and 9, -the mole 4a incorporates an air
cylinder serving as a drive unit for the mole, and an air
hose 7a for actuating the air cylinder is connected to a
pressure source ~compressor 8a) and passes through the new
pipe or shea-th. A cable 3a attached to the tip end of the
mole passes through the old pipe and is connected -to a win~h
2a.
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` The mole 4a is impulsively driven forward by the
~: lO driving force applied by the pressure source while being
.: subjected to a tractive for~e by the winch -thereby
bursting the old pipe. Since the maximum ex-ternal
diameter of the mole body is larger -than the external
diameter of the old pipe, the fragments o~ the old pipe
are pushed outwardly to form a space larger than the
external diameter of the new pipe or the sheath which Eollows
the mole. In this manner, by utilising the gap corresponding
to the difference in the external diameters of the mole and
the new pipe, the pipe replacement can be smoothly carried
out using a new pipe of substantially the same diameter as
the old pipe. The disadvantages of this apparatus are
outlined above.
: An embodiment of -the invention will now be described
with reference to ~igure 1 (showing the replacement of an old
; 25 pipe with a temporary pipe) and Figure 2 (showing the
replacement of the temporary pipe with a new pipe).
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The steps involved in the illustratecl pipe replacement
method are as follows:
1. A starting pi-t Kl and a destination pi-t K2 are dug
at respective ends section of an old buried pipe whi.ch is to
be replaced and existing pipe members in the pi.ts are
removed.
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r~ 2. A winch :is installed a-t the destination pi-t, ancl a
cable 3 of the winch is passed from the destination pit K2 to
-the s-tarting pit Kl throwgh -the inside of the old pipe 1.
3. A temporary pipe 5 composed of interconnect.ecl
temporary pipe members and having almost the same length as
the section of the old pipe to be replaced is attached to -the
: rear end of a mole 4, and the mole and the temporary pipe are
. coupled together by means of a wire 6 inserted through the
temporary pipe 5. The wire is tensioned between the rear end
of the mole and -the rear end of the temporary pipe. At this
time, an air hose 7 is inserted through the inside of the
temporary pipe, and the ends of the air hose are connected to
the mole 4 and a compressor 8 respectively.
4. The cable 3 of the winch is connected to the front
end of the mole to guide the mole to -the end of -the existing
pipe in the starting pit.
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5. The existing buried pipe is burst by a head of the
mole as a result of forward motion o~ the mole 4 under the
action of the tractive force of -the winch ancl the impulsive
drive of the air cylinder clisposecl in the mole, whereby -the
temporary pipe towed by the mole is progressively installed
within the fragmented old pipe as the mole progxesses from
; the starting pit to the destina-tion pit.
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6. Upon reaching the destination pit, the mole 4 is
uncoupled from the temporary pipe 5 ancl the air supply hose
and others inside the temporary pipe are also removed. The
foregoing steps 1 to 6 corresponcl to Figure 1.
7. A new pipe member 9 is connected to the end of the
temporary pipe in the starting pit and is pushed in toward
the destination pit by means of a jacking device 10 disposed
in the starting pit/ whereby the temporary pipe S is thrust
out of the ground at the destination pi-t by a corresponding
amount as the new pipe is inserted.
8. New pipe memhers are inserted one by one from the
star-ting pit and pushed toward the destination pit, whereby
the temporary pipe is progressively replaced with the new
pipe extending from the starting pit -to the destination pit.
When short temporary pipe members are used, as illustra-ted,
they are removed one by one at the destination pit. The
foregoing steps 7 to 8 correspond to Figure 2.
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The above steps remain almost unchanged when a device
other than an air cylinder is usecl as a drive uni-t
incorporated in the mole, because a drive source is required
to be connected -to any such device by way of a hose or
cable.
Figure 3 illustrates the construction of a -temporary
pipe 5 which may be used in the above described method. As
can be seen, the temporary pipe 5 is composed oE
interconnected members each having a reduced diameter spigot
portion at one end and an enlarged diameter socket por-tion at
the other end for receiving -the spigot portion of an adjacent
pipe member. Because the temporary pipe moves under -the
ground, it is preferable for the external surface oE the
; pipe to be smooth, although the configuration and
material of the temporary pipe does not matter so far as it
is durable enough against traction applied by the mole,
compressive force applied by the jacking device as the new
pipe is inserted, and pressure from the s~rrounding ground.
Figure ~ is a view illustrating an example of a nu-t and
bolt joint between adjacent pipe members of the new pipe 9.
The body of the pipes composed of a ductile cast iron
processes by centrifugal casting, the internal surface of the
pipe is lined with a cement mortar 11, and the external
surface of the pipe is coated with an armoured concrete 13
which includes reinforcing bas~et members 12 (composed of
welded steel bars) r both internal and external surfaces
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composing of a ductile cast iron pipe for use in propulsion
working for the replacement, which is the most preferable
embodiment o~ the inven-tion.
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In another embodimen-t of the method according to the
inven-tion illustrated in E'igure 5, -the new pipe ~ is
connected to the rear end of -the te~lporary pipe 5 so as to be
pulled through the ground to the destination pit K2 behind
the temporary pipe 5 at the latter is pulled ou-t of -the
ground by the winch 2, thereby obviating -the head for a
jacking device in the starting pit K1. In this embocliment,
since the temporary pipe and the new pipe move forward
through the space left by the passage of the mole 4, an
advantage is that no large propulsion ~i.e.. jacking device)
is needed in addition to the propulsion system for the
temporary pipe.
Figure 6 illustrates a further embodiment of the pipe
replacement method, in which the temporary pipe members are
successively connected together within the starting pit K1
where there is insufficient space for the connection to take
place at ground level.
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