Note: Descriptions are shown in the official language in which they were submitted.
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IN--GROUNI) SECITRE:MRNT OF PIPl~LINES AllD T~B LIKE
The present invention relates to the locating and
securing o~ a pipeline and other devices in a
subterranean location.
Pipelines for the transportation of fluids, such as
natural gas, petroleum products or waker, are often
buried underground for a signi~icant distance in a
variety of terrains. Usually, a ditch is dug in the
terrain, the pipeline laid in the ditch and the ditch
and pipeline backfilled with the material dug out to
form the ditch.
The pipeline is intended to remain buried for a
significant period of time. This requirement can be a
problem, particularly when traversing low lying areas
subject to inundation by water, such as in muskeg
terrain. The buoyancy force produced on the pipeline by
the aqueous environment in such areas tends to shift
the position of the pipeline towards the surface with
the potential for the pipeline eventually to break
through the surface. For this reason concrete weights
of various designs have been traditionally placed at
intervals along the ditch to resist the buoyancy forces
on the pipeline caused by the water or other
encompassing fluid medium.
A novelty search has been conducted in the
facilities of the United States Patent and Trademark
Office and the following UOS. Patents were noted as the
closest prior art:
687,389 3,793,845 3,903,704
4,126,012 4,166,710 4,242,010
4,338,045 4,477,706
These prior patents show a variety of pipeline anchoring
arrangements, some to maintain the pipeline submerged in
an aqueous environment, such as a seabed, and some to
maintain the pipeline buried in-ground.
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In the former category fall U.S. Patents Nos.
3,793,845, 4,242,010, 4,338,045 and 4,477,706. The
characteristic of these arrangements is the provision of
an element which engages the upper portion of the
submerged pipeline and an element contacting the seabed
to resist the upwardly-buoyant forces on the pipeline.
The pipeline lays flat on the seabed surface and an
unlimited space is available on the sides of the
pipeline for location of the seahed contacting elements
of the devices.
In the latter category fall U.S. Patents Nos.
687,389, 3,903,704, 4,126,012 and 4,166,710. The
characteristic of these arrangements is the provision of
some form of weighting element directly engaging at
least the upper portion of the pipeline buried in a
ditch.
U.S. Patent No. 687,389 describes a series of bags
of beton covering and adhered to the pipeline. U.S.
Patent No. 4,126,012 describes a series o~ spaced pipe
carriers in the form of an upright body driven into the
undisturbed ground at the bottom of the ditch and having
prongs which extend from the upright body to engage and
hold the pipeline.
U.S. Patent No. 3,903,704 is particularly concerned
with anchoring underground pipelines in wet and flood
lands with swelling ground. This arrangement employs a
pair of anchors secured to the ground, a fastening
element attached to and engaging the upper portion of
the pipeline and resilient connectors connecting the
fastening element to the ground anchors. When ground
swelling occurs, any forces tending to effect transverse
and/or upward movement of the pipeline are resisted by
the resilient connectors.
U.S. Patent No. 4,166,710 describes the employment
of ballast weights having contact shoes which engage the
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pipeline and which are interconnected above the pipeline
by an articulated joint.
In accordance with th~ present invention, there is
provided a novel weighting device for improving the
resistance of a pipeline to upward movement in a
subterranean aqueous environment and a novel method of
effecting the securement of pipelines which effects a
secure location resistant to upward movement of the
pipeline in the subterranean environment, particularly
in low lying areas subject to inundation with water.
The present invention provides a method of locating
and securing a pipeline in a subterranean environment
comprising a plurality of steps. The first step
involves digging a ditch having a depth to the ditch
bottom exceeding the diameter of the pipeline and having
a width between sidewalls significantly exceeding the
diameter of the pipeline. The pipeline then is laid on
the bottom of the ditch approximately equidistant from
the sidewalls of the ditch. Then, at a plurality of
predetermined intervals along the length of the
pipeline, a length of flexible inelastic fabric material
is draped down the sidewalls, across the bottom of the
ditch and over the pipeline. The ditch then is
backfilled with suitable backfill material, usually
material previously removed from the ditch.
By using a ditch width significantly wider than the
pipeline diameter and lengths of flexible fakric
material which overlie the pipeline and which are
secured by backfilling the ditch, the resistance to
upward movement of the pipeline is increased because of
the additional weight of backfill material acting on the
fabric both directly on top of and to the sides of the
pipeline, as well as the shear strength of the
fabric/soil interface.
While the present invention is particularly
directed to and is particularly described with respect
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to maintaining buried pipelines in their subterranean
location, the present invention also is applicable to
b~lried containers and vessels and similar tubular fluid-
enclosing devices.
The invention is described further, by way of
illustration, and reference to the accompanying
drawings, in which:
Figure 1 is a perspective sectional view showing a
pipeline located in a trench under the influence of
lo forces due to buoyancy;
Figures 2 and 3 are perspective and end sectional
views showing a conventional pipeline weight before and
after backfill;
Figures 4 and 5 are perspective and sectional
views of a novel pipeline weighting device before and
. after backfill;
Figure 6 is a force diagram of the submerged
pipeline; and
Figure 7 is a graphical illustration of the effect
: 20 of the fabric strips on the resistance to buoyant forces
applied to the pipeline in its submerged environment.
Referring to the drawings, Figure 1 shows the
buoyant effect of water levels above a pipeline 10 which
is not held in place at the bottom of a backfilled ditch
: 25 12. The buoyant effect on the pipeline 10 causes the
pipeline to rise in the ditch 12. The pipeline 10 may
be designed to carry any o~ a wide variety of fluids
from one location to another, as is well known in the
art.
In Figures 2 and 3, there are shown a typical
concrete weight 14 which is positioned at intervals
along the length over the pipeline 10 before the ditch
12 is backfilled. The weights 14 resist upward buoyant
forces acting on the pipeline.
In Figures 4 to 6, there is illustrated the
novel geotexile buoyancy restraint device o~ the present
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invention. The procedure of the invention for the
laying and locating of a pipeline in a submerged
environment involves a plurality of steps. The ditch 12
first is dug in the earth of a length as desired for the
pipeline 10. The ditch 12 is illustrated as being
formed in a muskeg environment, which may have an upper
organic material layer 18 overlying a mineral layer 20,
but the principles of the invention are applicable to
other low lying environments subject to inundation by
water, and thus tending to subject the pipeline to
buoyant forces.
The material dug from the ditch is intended to be
used as the backfill for the ditch after the pipeline
has been positioned in the ditch. In the svent that the
material dug from the ditch does not have sufficient
weight, it may be necessary to import backfill material.
The ditch 12 preferably is formed with a
rectangular cross section. The depth (d) of the ditch
12 from the ground surface to the bottom wall 22 exceeds
the diameter of the pipeline 10, so that the pipeline 10
will be submerged following backfilling. For regulatory
and backfill weight reasons, the depth of the ditch 12
is dug so that the pipeline is burie~ generally to a
depth of about 0.8 to 1.3 m.
The ditch 12 also has a width (w) between the
sidewalls 24, 26 which significantly exceeds the
diameter of the pipeline 10, for reasons which will
become apparent below, and to some extent, i5 affected
by the density of the backfill material.
The pipeline 10 next is positioned by any
convenient pipeline laying technique on the bottom 22 of
the ditch 12 approximately equidistant from the
sidewalls 24 and 26.
The next step involves positioning, at
predetermined intervals along the length of the pipeline
10, a strip of flexible, inelastic, water-pervious and
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water-resistant non-biodegradable geotextile-typ2
material 28. The geotextile material 28 has a length
which enables it to drape down the sidewalls 24 and 26
of the ditch 12, and across the bottom 22 and over the
pipeline lo.
The geotextile material 28 has a width as
determined for force application on the pipeline and the
spacing and location of the strips of geotextile
material 28 similarly are determined by the same
consideration.
The strips 28 may be secured at one or both upper
ends to the ground adjacent the sides of the ditch 12 by
any suitable securement means, such as spikes 30. The
securement of the ends of the strips 28 also is assisted
by the backfill material 16 upon refilling the ditch.
The ditch 12 then is refilled with the backfill
material, which may be mounded up over the ditch 12 and
the edges of the strips 28, thereby filling with
backfill material 16 all the space of the ditch 12
except for that occupied by the pipeline 10, engaging
the strips 28 against the sidewalls 24, 26, the bottom
wall 22 and the pipeline 10. Hence, the ditch 12 is
filled with backfill 16 along the length of the pipeline
10 and strips 28.
Since the pipeline 10 is buried in a low lying
environment subject to inundation, water tends to infill
the ditch 12 to the level of the static ground water
level which is approximately at the surface of the
formation. The water in the ditch tends to apply a
buoyant force to the pipeline. This buoyant force B,
which varies with the diameter of the pipe and the
weight per unit length of the pipe and its contents,
may, if the buoyant force is not exceeded, cause the
pipeline 10 to rise (see also Figure 1~.
However, this force is counteracted by a variety of
forces. First, there is the weight of backfill
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material 16 of weight W~ in the zone of backfill
material 16 corresponding to the diametér of khe
pipeline 10. There is also the weight of backfill
material 16 of weights W1 and W3 in the pipeline zones
of backfill between the pipeline 10 and the sidewalls 24
and 26. The buoyancy force B produces a tension T in
the fabric strip 28 depending on the shear ~orce between
the fabric and the soil, the magnitude of which is
dependent on the net buoyancy forces, and the weight
components of the backfill W1, W2 and W3. As the upward
displacement of the pipeline 10 tends to increase, the
fabric strip 28 is subjected to increasing tension. The
weight of the backfill 16 is distributed over the whole
width (w) of the ditch 12 by the action of the textile
strip 28, thereby increasing the resistance of the
uplift forces provided by the backfill. In this way, a
greater resistance force is achieved than has heretofore
been possible.
The anti buoyancy forces which act on the pipeline
in the present invention contrast with those
achievable with a conventional concrete weight 14, where
the only forces applied are from the weight 14 itself
and the weight of filler material (w) immediately above
the pipeline 10.
In the method of the present invention, more of the
ditch backfill material is employed to resist buoyancy
fGrces than has hitherto been the case. The present
invention is much more inexpensive than known systems.
EXAMPLE
Tests were carried out using a system as
illustrated in Figures 4 to 6 as compared with the
absence of the fabric. The load obtained on the pipe
for varying pipe displacement in the subterranean
environment was determined and plotted as Figure 7. As
may be seen, a signi~icantly increased uplift resistance
is achieved with the fabric in place.
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SIJMMARY OF DISCLOSURE
In summary of this disclosure, the present
invention provides a novel system for ensuring that
pipelines and conduits carrying a wide ranye of products
as well as other buried containers and vessels buried in
areas subject to inundation, such as swampy or other low
lying environments are maintained in their subterranean
location. Modifications are possible within the scope
of this invention.
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