Note: Descriptions are shown in the official language in which they were submitted.
20~8688 1
IMPROVEMENTS IN FLUID-BAS~D EXCAVATING
This invention relates to fluid excavating. The
invention is particularly applicable to fluid excavating
trenches for burying cables or pipelines in the seabed.
In laying undersea pipes or cables it is
advantageous to bury them beneath the surface of the sea
bed to afford protection. To do this it is known to use
water emitted from a nozzle to fluidise a non-cohesive
or soft cohesive material making up the sea bed. In
this way the fluidised material can be dredged away
allowing the pipe or cable to be lowered into the trench
thus created. However, fluidisation is only practicable
when used on non-cohesive or soft cohesive materials,
such as sand and very soft clays.
It is also known to use water emitted from a nozzle,
to cut into cohesive material making up the sea bed to
define more easily removable blocks as part of a
procedure for cutting a channel in which an undersea
cable or pipe is to be lowered. The blocks are removed
by a dredging unit.
It is an object of the present invention to provide
an improved excavating method and apparatus particularly
for use on stiff cohesive materials as well as non-
cohesive and soft cohesive materials.
According to the present invention there is provided
a method of excavating material the method comprising:
mounting on a carrier at least one nozzle for producing
a jet of fluid, moving the nozzle relative to the
carrier and the material to cause the jet to cut spaced
apart kerfs whereby castellations are created between
said kerfs.
The invention also extends to apparatus for
excavating which apparatus includes a carrier and a
plurality of nozzles (12) for producing jets of fluid,
said nozzles being movably mounted on the carrier
wherein the nozzles are spread apart suoh that movement
2 ~ 07 8 688
of the nozzles reLative to the carrier causes the jets
to move along spaced apart tracks whereby spaced apart
kerfs with a castellation between are produced.
The acute angle of impingement may be parallel to a
plane which is normal to the direction of movement of
the jet or at an angle thereto. By directing the jet at
an angle with respect to the said plane, such that the
outlet lags the point of impingement of the jet on the
cutting face, the jet may also serve to expel material
from the excavated area.
By passing the jet in a succession of runs, or a
series of spaced jets in a single pass, a deeper channel
may be formed than that simply created by the single jet
alone. The material between the kerfs may not be
completely detached but be connected at its root. Thus,
preferably, a second pass of the jet, or a second jet,
preferably parallel to the first, serves to create the
second kerf and to sever the first in one action. Thus,
successive passes of the jet or jets will create a kerf
with a width that is proportional to the jet spacing.
In this way, a channel may be created either by
longitudinal runs of the jet or jets with respect to the
line of the channel or, alternatively, lateral runs.
Preferably, the jet or set of jets is moved at a
constant rate relative to the material to be cut. This
rate in part determines the depth of cut in a material
of constant density. On the other hand a non-constant
rate may be imparted to the jet, for example sinusoidal.
The movement may be linear. However, any other path
or movement may be adopted in order to create the kerf.
Another factor governing the depth of cùt of the kerf is
the distance of the outlet from the surface. Thus, it
is also preferable that the nozzle is maintained at a
small and substantially constant distance from the
material being cut.
As mentioned above, any pattern of movement of the
jet or jets may be adopted as required. One particular
3 ~0~8~88
way is to sweep the jet in an arc or parabola across the
cutting face of the material. In this case, the axis of
the sweep is conveniently generally vertical when
exc~vating, for example, a trench ln a horizontal
seabed.
Proposals for using such a jetting technique also
include cutting slits in the cohesive material to make
them more easily removable as comminuted lumps by means
of a following plough arrangement. The cutting of slits
therefore breaks up the consistency of the seabed in
advance of the plough arrangement, hence reducing tow
forces required to pull the plough.
It is ound that removal of the ker is most
suitably achieved in the excavating process by directing
the jet at an angle of about 30 to the surface of the
material being cut into. In suitable materials, such as
clays, each kerf is in the manner of a scallop or scroll
of material similar to the shaving created by a chisel.
In harder materials the kerf may fragment as it is
forced to curl out of the path of the jet. In any case,
it is the effect of the stagnation pressure at the root
between the parted material and the newly created
surface which forces the waste kerf away from the
excavated area.
The parameters which determine the successful
removal of a kerf, instead of simply cutting into the
clay, are presently considered to be the pressure of the
cutting fluid, the flow rate, the nozzle profile, the
vertical angle of the jet and the speed at which the jet
travels across the surface.
When a set of jets are used the cutting
characteristics are also dependent on the number of jets
and the spacing of the jets both in the direction of
movement and normal to that direction.
In one form, the invention comprises directing a
plurality of oscillating fluid jets at the surface to be
excavated at the acute angle to sh-e~r off a succession
~ 2~78688 4
of kerfs to form the trench. The channels may be formed
longitudinally with respect to the overall lie of the
trench being cut or be formed laterally with respect
thereto.
In another form the cut may be achieved by means of
a set of nozzles arranged in a helical pattern on a
rotatable drum. The drum may be horizontally or
vertically disposed. In either case it is necessary
that the jets impinge on the material at an acute angle
with respect to the material to create the kerf.
The present invention can be put into practice in
various ways some of which will now be described by way
of example with reference to the accompanying drawings
in which:
Figures lA) and B) are schematic representations of
an excavating arrangement according to the present
invention;
Figure 2 is an illustration of a nozzle drum
assembly for use in one embodiment of the present
invention;
Figure 3 is a valve arrangement used in one
embodiment of the invention;
Figures 4A and 4B are end and side views of a
components of the valve of Figure 3;
Figures 5A, 5B, 5C and 5D are side and end views of
another component of the valve of Figure 3; and
Figure 6 is a side view of a modified excavating
assembly.
Figures 7A), B) and C) are illustrations of parts of
alternative forms of the invention;
Figure 8 is an illustration of part of a further
alternative form of the invention;
Figure 9 is a schematic representation of the
function of the invention according to another variant;
and
Figure 10 is an illustration of a further form of
the invention.
~ s 2078688
Figures 11 and 12 show an alternative embodiment o
the excavating arrangement to the invention.
Referring to Figures lA) and B) and 2, a trenching
apparatus comprises a submersible frame (not shown)
having hydraulically driven positioning and driving
propellers which are powered by a hydraulic power motors
source (also not shown) on the frame. A hydraulic motor
also rotates a 36mm diameter nozzle drum 10 of the
excavator head about its axis which is generally near
vertically disposed when the rame is arranged on a
horizontal surface. In general, the frame is adapted to
orientate the drum 10 so that its axis of rotation is
substantially normal to the attitude at which the frame
rests. The angle of the nozzles may be more or less
than 30, for example between 20 (or less) and 40~. Each
of a set of nozzles 12 in the drum is orientated to
direct a jet of water from the drum downwardly at an
angle of 30 with respect to a cutting face 13 of the
cohesive material in whi~h the trench is to be dug.
Commonly, on a horizontal seabed this will result in a
substantially vertical axis of rotation. The nozzles
have a 2mm outlet diameter and are angularly spaced,
with respect to the drum axis, at a 30mm pitch over an
axial length of 600mm on the drum. ~.
The nozzles 12 are arranged on the drum in a helical
pattern. This presents an overlap of the cutting effect
which each individual nozzle presents in order to
provide an overall effective cutting width equal to the
spacing between the upper and lower-most nozzles 12a and
12b on the drum.
Referring particularly to Figures la) and b) it is
the purpose of the jet of water from each nozzle to cut
into the cutting face at least to create a kerf. It may
be that a single nozzle could be used with sufficient
water pressure to create and sever its own kerf.
However, using a plurality of nozzles, as depicted in
Figure lB), the pass of nozzle 1 has cut the kerf
2078688 6
beneath it away. At the same time it defines the lower
surface of the next kerf to be removed. As nozzle 2
then passes its jet penetrates above the lower surface
deflned by nozzle 1 and forces the kerf defined between
the planes of penetration of the jets away from the
cutting face.
As the nozzles rotate a complete layer of the
cutting face is removed. On the next pass of the
nozzles the same action takes a further layer off and so
on. In this way the trench cutting progresses.
The nozzles 12 are fed with water pumped from a
hydraulically driven pump and filter arrangement on the
submersible frame to a series of conduits in the drum
leading to the nozzles. Clearly, the rotating nozzles
will only be used for a limited amount of each turn of
the drum. Thus, a kidney valve arrangement 14 is used
to interrupt the flow of the water to the nozzles so
that fluid is passed only to the nozzles in the relevant
cutting portion of each turn of the drum, i.e. when they
are adjacent the cutting face 13.
The kidney valve is shown in Figures 3, 4 and 5. It
comprises a circular valve plate 16 which is secured to
the frame and a distribution member 18 which bears on
and is rotatable relative to the valve plate 16. The
valve plate 16 is formed on one mating side 25 with a
pair of radially spaced, angularly coincident curved
channels 20 set in annular raised guides 22. The
channels 20 are referred to in this description as
kidney ports. The kidney ports are coaxial with the
axis of rotation of the distribution member which, in
turn, is coaxial with the axis of rotation of the drum
itself. Both kidney ports communicate with outlet ports
24 which open on to the other side of the plate. The 26
nozzles 12 communicate with the kidney ports in upper
and lower groups of 13. Thus, by directing water to one
or both ports the active region of the drum is
selectable.
2078688 7
The distribution member 18 is formed with a
plurality of distribution ports 26 which extend from its
mating face 28 to the other side. The distribution
member is also formed with an annular flange by which
the member is secured relative to the one end of the
drum to rotate with it to distribute the pumped water to
the nozzle heads. The mating face 28 of the
distribution member 18 is sealingly engaged with that of
the valve plate 16.
The drum and attached distribution member are
rotated together by means of a conventional hydraulic
motor (not shown). In so doing, a selection of the
distribution ports is in registry with the adjacent
kidney port. Thus, nozzle water is supplied only to
those distribution ports in registry for as long as they
remain so. By correctly adjusting the orientation of
the valve plate, nozzle water is fed only to those
nozzles within the effective working part of each cycle
corresponding to the period when a particular nozzle is
at the cutting face. In this way, the amount of pumped
water required is considerably reduced.
Following on from the general description of the
excavating apparatus of Figure 2 a modified arrangement
is illustrated in Figure 6. The drum 10 is powered by
a hydraulic motor and gearing arrangement not
specifically illustrated in Figure 6 but which is
enclosed in a housing 29.
The drum 10 is also provided with a spoil scavenging
arrangement comprising a trailing suction pipe 30,
having an inlet towards the base of the drum 10 and
communicating with a venturi ejector 32. The arrow in
Figure 6 denotes the direction of travel of the drum
when cutting a trench. The suction pipe 30 is formed
with a shroud 33 which consists of an open metal box
structure in which the sides defining the open face
conform generally to the adjacent curved surface of the
drum 10 but leaving a small gap along all edges of about
2078688 8
25mm between the edges of the shroud and the drum. The
ejector 32 has an ejector water inlet pipe 34 and a back
flushing pipe 36. Both of these pipes 34 and 36 are
attached to a further sea water pump system on the
submersible frame respectively for creating the ejector
vacuum to create suction at the open end of the suction
pipe 30, adjacent the drum 10, and to flush out
blockages if they occur in the ejector.
The scavenged spoil drawn into the scavenging
arrangement is exhausted through an outlet pipe 38 which
is rotatable relative to the fixed suction pipe and
ejector assembly to direct the spoil as required out
from the area of the cutting face. The outlet pipe 38
is orientatable about an upright axis by means of a worm
drive and a hydraulic motor 40 which moves an engaged
gear wheel 42. This orientatability is particularly
useful in sub-sea applications in which the excavator
and frame are remote controlled using video cameras.
Strong currents can be encountered and by directing the
spoil to flow with the current the chance of it drifting
back into the trench is removed and the problems
associated with clouding up the water, thus obscuring
the view, can be avoided.
The device is mounted on the submersible frame by
means of a mounting block 44, and a pair of locating
pins 46. Preferably, the orientation of the excavator
with respect to the submersible frame is adjustable. In
a particular situation the angle of the axis of the drum
may be better tilted away from the vertical.
In this embodiment, the drum is designed to rotate
to pEoduce a linear speed of about 14 metres/sec. The
water is pumped to the nozzles at 200 litres/min to
develop 210 bar at the lower 13 nozzles for cutting
400kPa shear strength clay or at 300 litres/min to
develop 137 bar at all 26 nozzles for cutting 200kPa
clay. Using the arrangement the excavator is able to
2078688 9
cut a trench 300mm deep using the lower 13 nozzles alone
or a trench 600mm deep using all 26 nozzles.
By actuating the motor by hydraulics and pumping the
filtered water to the nozzles, via the distribution
valve, the helical arrangement of nozzles will cut a
succession of adjacent kerfs from a wall of cohesive
clay or the like. each nozzle jet except the top-most
or bottom-most nozzles impinges on the wall constituting
the cutting face opposite the root 34 of the previously
formed kerf. The force of the jet makes and shears off
a kerf in a sliver at the same time as the base of a new
kerf is made. A large amount of the spoil created by
the excavating operation is forced out of the way by the
pressure of water. However, some will tend to fall back
into the created trough. This loose material is removed
by means of the following spoil scavenging system.
Alternatively, referring to Figures 7A), B) and C)
the cutting fluid constituting the jet is fed to a
column 50 of axially spaced outlet nozzles 52 or groups
of outlets. The column 50 is oscillatable through an
arc 54 to effect a cut. More than one oscillatable
column can be used to effect the cutting of a trench.
The spacing of cutting jet outlet nozzles 52 on the
column is such that the penetration of the jet of one
outlet extends past the point of initial penetration of
the lower adjacent nozzle. In this embodiment the
nozzles 52 create and cut kerfs contemporaneously and
not in succession as the columns oscillate in antiphase.
When sets of nozzles are most closely spaced there
is a region between the columns 50 that is not as
agitated as that directly in line with the nozzles.
Thus it is advantageous to install wash jet outlets 56
between the cutting jet nozzles. The wash jets are
directed at the space between the cutting jets and of
the cutting face to agitate the water and assist in
removal of spoil.
2o~8688 10
The number of columns of jets can be varied to suit
the width or trench to be cut. Similarly, the amount of
overlap between adjacent jets in a column can be varied
to accommodate, for example, different densities of clay
to be removed.
It is found that the dislodged spoil can clog the
oscillating mechanism for the columns 50. To overcome
this the column and nozzles 52 are enclosed in a metal
shroud shown in Figure 7C). The shroud has groups of
arcuate apertures 57 which allow the jets to impinge on
the cutting face throughout their sweeps. The shroud
can equally well be used with one column or any number
of columns disposed side by side.
In a further alternative illustrated in Figure 8, a
jet 58 (or jets) can be mounted on an extensible and
retractable arm 60 which can be adjusted to optimise the
cutting angle relative to the cutting face 13.
In another form of the invention, illustrated in
Figure 9, a single jet is movable to progress in the
direction of the trench to be cut, illustrated by the
horizontal arrow in the drawing, while creating a series
of progressively cut kerfs either by rotating or
oscillating as the radius of the cycle or sweep moves
forward.
Figure 10 illustrates a further embodiment of the
invention in which the plurality of nozzles 62 are
equally angularly spaced about the axis of a rotatable
drum 64. The nozzles direct jets from the end face of
the drum to impinge at an acute angle to the surface.
This embodiment can be used to break up and loosen
material which can be necessary in applications other
than trench cutting where the sea bed has to be rendered
more easily workable, for example to allow structural
supporting members to be worked into the sea bed more
easily.
2078~88 11
Figures 1 - 10 were filed with the priority
document. An extra embodiment will now be described
with reference to Figures 11 and 12.
The apparatus illustrated in this embodiment
comprises two circular, parallel discs, 100 and 101
which have inwardly facing nozzles spaced apart around
their circumferences. In operation, the inwardly facing
nozzles provide inwardly directed jets 102.
In use, the discs 100 and 101 progress along the two
sides of a trench which is required to be created. The
discs are rotated, preferably by oscillation to a small
angle of rotation. This causes the jets 102 to follow
curved spaced apart tracks so as to cut curved, spaced
apart kerfs with curved castellations between the kerfs.
As the apparatus progresses the castellations break away
and they may be further comminuted by following jets.
As described with reference to other embodiments, the
discs are conveniently followed by suction apparatus for
disposing of the spoil.
In modifications, not illustrated in any drawing,
the nozzles are located only around the forward part of
the discs. In addition, the discs may be provided with
radially directed jets extending forward in order to cut
thin slots to allow the discs to progress leaving
substantial amounts of material remaining between the
discs for cutting into castellations.
The method of this invention relates to the use of
jets of fluid (water) for excavation, e.g. of trenches,
on the sea-bed.
The direct effect of a jet causes thorough
disintegration of the material onto which the jet
impinges and, in accordance with practice as established
by the prior arts, jets have been used to disintegrate
substantially all the material lying in the region to be
excavated.
This invention differs from this prior usage in that
it uses a jet or jets to create castellations, e.g.
20786~8 12
slabs of material. The castellations are removed, but
the material forming the castellation is not directly
disintegrated by the jet nor is it disintegrated to the
same extent as material upon which the jet impinges. In
order to create a castellation, it is necessary to cut
kerfs on both sides thereof, or, in the case of a
castellation at the surface, on the side away from the
free surface. This invention uses a jet or jets to cut
the kerf by preferentially directing the jet or jets at
the region where kerfs are intended (and preferably
avoiding the regions where castellations are intended).
The cutting of the kerf or kerfs creates the
castellations but a jet directed into the kerf creates
a high-pressure therein, and this high pressure produces
a mechanical load which causes the castellation to break
up. It will be appreciated that directing a jet into
the kerf necessarily creates a corresponding outflow
from the kerf and the detritus, e.g. both material
comminuted by the jet and material arising from the
breakup of the castellation, is removed from the slot by
said outflow. It is usually convenient to provide a
suction inlet near the workface to assist in this
removal. If necessary, the detritus can be deposited a
substantial distance from the working region.
Apparatus according to this invention includes means
for moving a jet or jets along spaced apart tracks.
This produces spaced apart kerfs along the spaced apart
tracks and the castellations are formed between the
kerfs. A preferred arrangement for producing the spaced
apart jets comprises nozzles which are helically
arranged about the axis of a rotatable drum.
(Note "KERF" means a cutting into solid material,
e.g. the cut made by a saw, axe or similar instrument).
