WO2004074586A1

WO2004074586A1 - Dredge device and dredge method

Info

Publication number: WO2004074586A1
Application number: PCT/NL2004/000130
Authority: WO
Inventors: Dirk Albertus Bodegom; Arnold Johannes Nobel; Willem Floris Rosenbrand
Original assignee: Baggermaatschappij Boskalis B.V.
Priority date: 2003-02-20
Filing date: 2004-02-20
Publication date: 2004-09-02
Also published as: EP1597439A1

Abstract

Dredge device for removing a layer (107) of soil material from underneath an upper layer (106), comprising a pipe set to be positioned substantially vertical having a first pipe, which in the lowermost portion is provided with at least one nozzle and with means for supplying pressurised liquid, particularly water, to the nozzle, as well as with means for rotation of the first pipe about its centre line, wherein the pipe set comprises means for discharge through the pipe set of soil material eroded by the liquid discharged by the nozzle.

Description

Dredge device and dredge method

The invention relates to a device and a method for dredging soil material from an earth stratum, particularly form an earth stratum covered by an upper layer of material that has to remain in situ.

Managers of lakes and waterways are responsible for keeping their waters at the correct depth. When these waterways have to be deepened, the upper layer is a problem. Said upper layer may consist of several meters of (polluted) sludge, peat and/or soft clay. Underneath it there usually is a sand layer. On the other hand the upper layer may contain valuable flora and fauna, such as shellfish.

In traditional methods (first) the upper layer is dredged. Storage of the removed soil requires quite a lot of space. When said soil moreover is polluted, this constitutes a serious limitation for re-use. The total costs of the project are considerably affected by all this. If, on the other hand, the upper layer contains flora and fauna it will be destroyed in the course of removing said upper layer.

During dredging the upper layer is disturbed to a large extent, which may mean an environmental burden or be disadvantageous to the usable sand, or damage life in the surroundings. Obtaining permits for this type of work is not seldomly met with great resistance and/or long procedures. Extracting sand from underneath for instance layers of peat or clay is known per se, particularly for extracting sand with relatively high productions, such as with a standard suction dredger. During this process the upper layer is disturbed and partially sucked up.

From Dutch patent application 89.02028 a dredge device is known, having a double pipe assembly, of which the outer pipe is reciprocally rotatable and at its lower end provided with an unfoldable drill head, and the inner pipe is used for discharge of soil material. The drill head is kept closed and the outer pipe is reciprocally rotated during passing the pipe assembly through an upper layer of soil that cannot be used and through a part of the layer to be extracted. Simultaneously pressurised flush water is inserted in the drill head range through apertures in the drill head. The flush water with loosened material escapes upwards along the outer pipe. A considerably disturbance of the soil thus occurs.

It is an object of the invention to provide a device and a. method of the type mentioned in the preamble, wherein the upper layer is disturbed as little as possible or remains intact as much as possible.

It is a further object of the invention to provide a device and a method of the type mentioned in the preamble, with which soil material from a layer situated underneath an upper layer can be removed in a controlled manner.

A further object of the invention is to provide a device and a method of the type mentioned in the preamble, with which a water bed can be lowered in a controlled manner by extracting soil material from an earth stratum situated underneath it.

At least one of said objects is achieved from one aspect of the invention, using a dredge device for removing a layer of soil material from underneath an upper layer, comprising a pipe set to be positioned substantially vertical having a first pipe, which in the lowermost portion is provided with at least one nozzle and with means for supplying pressurised liquid, particularly water, to the nozzle, as well as with means for rotation of the first pipe about its centre line, wherein the pipe set comprises means for discharge through the pipe set of soil material eroded by the liquid discharged by the nozzle.

In this way an excavation cavity can simply and effectively be. realised at the wanted depth in the layer of soil material to be excavated. An optimal radial range can be realised. Due to rotation of the inner pipe a surrounding area is eroded with pressure jets. In that way a surrounding area can be loosened at the wanted depth, from which surrounding area a mixture of soil material and water can be discharged via the pipe set. The liquid may be water, but for instance also a mixture, such as a sand/water mixture.

Preferably the nozzle is at least substantially radially oriented, for an eroding activity reaching radially as far as possible.

Preferably the discharge means have an entrance that is situated below the nozzle.

Preferably the dredge device is furthermore provided with means for determining the volume or flow rate of water discharged by the nozzle and volume liquid otherwise introduced into the process (for instance for an ejector pump yet to be discussed) and with means for determining the volume or flow rate of the mixture carried away by the discharge means, as well as with regulating means for by controlling the liquid supply means and/or discharge means keeping both volumes or flow rates substantially equal. It is thus counteracted that also in case the layer of soil material to be removed is positioned at little depth, in case of a thin upper layer, the upper layer does not collapse as a result of too great a pressure difference over that layer. When an open connection is created between the excavation cavity and the space above the upper layer, the creation of unwanted flows is counteracted. Thus mixing of material of the upper layer with soil material to be extracted is counteracted. In the excavation cavity created by removal of soil material, the supplied water discharged by the nozzle forms an incompressible water (mixture) body.

Alternatively or additionally a pressure relief passage may be formed between the excavation area and the area above the upper layer. A pressure equalising channel is thus created. In the pressure relief passage means for determining the flow rate or volume may also be incorporated, which means are in operative connection with the aforementioned regulating means.

In a simple embodiment of the dredge device according to the invention, the aforementioned discharge means comprise a discharge pump, particularly a (slim) ejector pump having a supply line for ejector water and a parallel discharge line, accommodated in the pipe, said pump being placed in the pipe set, particularly the first pipe, particularly a lower half thereof. These lines and parts may thus be accommodated in a screened way in the first pipe, and easily be brought into rotation with it.

For reasons of simplicity of structure it is preferred that the discharge means comprise a stationary positioned pump placed at the top of the pipe set, wherein a rotational connection is incorporated in the line towards the pump, preferably above the upper end of the first pipe. The weight of the pump can be utilised for the lowering process of the pipe set.

From a further aspect the invention provides a method for removing soil material, such as sand, from an earth stratum situated underneath an upper layer, wherein a pipe set with a first pipe having at the lower end one or more nozzles to be fed with a pressure fluid, is lowered to some distance under the upper layer, pressurised liquid, particularly water, is jetted out of the nozzle to make a radial breach in the layer of soil material, the eroded soil material is discharged via the pipe set through pumping action, after a while the first pipe is rotated over a small angle and kept still, or after some time the first pipe is rotated at low speed, to expand the radial breach in tangential direction, all this until at least one full revolution is completed.

In this way a tangentially expanding breach is made in a controlled manner and the eroded material is discharged.

Depending on the actual conditions the entire radial area can be treated in one revolution or it can be treated in several revolutions.

When the flow rate of supplied water and the flow rate of discharged mixture is at least kept substantially equal, the upper layer can remain temporarily supported and will not collapse during the extraction process.

Preferably soil material is extracted until the removed quantity of soil material at least corresponds with a desired quantity, possibly with an intended lowering of the upper layer.

From another aspect the upper layer can be stabilised by supplying water via the pipe set to the area from where the soil material is being removed to replace said soil material.

Alternatively soil material substituting material, for instance gypsum, can be supplied to the cavity made, via the dredge device according to the invention.

Preferably, after the wanted quantity of soil material has been removed, water is extracted in a controlled manner via the pipe set to lower the upper layer.

The aforementioned dredge device according to the invention is particularly suitable for carrying out the method according to the invention.

With the dredge method according to the invention usable soil, such as physically and chemically clean sand is selectively extracted directly from underneath an upper layer. Said upper layer is disturbed to a minimum degree and a minimal mixture of the soil material to be extracted occurs.

As a result of this dredge method a desired bed lowering may occur, wherein the layer situated above is left behind. Said bed lowering has additional purposes such as: better navigability, water transport capacity, and through- flow ability for the water quality.

From a further aspect the invention to that end provides a dredge device that may or may not also be provided with the characterising measures described above, such as the nozzle, comprising a pipe assembly to be positioned with a vertical directional component, preferably substantially vertical, wherein the pipe assembly at the lower end defines a flush chamber, which is bounded by a circumferential wall and open at the bottom, wherein the pipe assembly at the lower end is provided with means for supplying flush fluid, particularly liquid, such as water, to the flush chamber, as well as with means for discharging fluidised soil material from the flush chamber and/or its immediate surroundings through the pipe assembly.

In this way the bearing capacity of the soil material can be reduced at the location of the lower end of the pipe assembly which enhances the lowering of the pipe assembly. Because fluidisation mainly takes place within the lower edge of the pipe assembly, disturbance of the soil material, particularly the upper layer, remains highly limited. Such a lowering method is also known from caissons. This device, however, can also be lowered in the same manner through the next layer of soil material to be extracted, to the point of extraction. Preferably the pipe assembly comprises a first, inner pipe and a second outer pipe surrounding the first, wherein the outer pipe is stationary in circumferential direction and provided with the supply means for flush fluid and wherein the discharge means comprise a pump placed near the lower end and in the inner pipe. Due to the stationary outer pipe the disturbance of the surrounding soil is further limited, because no frictional forces are exerted in circumferential direction on the surrounding soil and the locations of discharge of the flush fluid -slowly- move substantially vertical.

Preferably the outer pipe near the lower edge and at the inner surface is provided with apertures for discharge of the flush fluid. Advantageously the outer pipe is double-walled, wherein the passage formed through it may be used for flush fluid.

Preferably the inner pipe at the lower end is provided with excavation means and is rotatable within the outer pipe. During excavation the outer pipe, which is in contact with the soil above the location of excavation, can remain standing still, due to which the soil at that location is disturbed to a minimal degree as well.

Preferably the dredge device is furthermore provided with means for adjusting the mutual position of both pipes with respect to each other in axial direction. In this way, when desired, -by axially moving the pipes- certain parts having certain functions and provided at the lower end, can easily be correctly positioned.

Preferably the adjustment means are adapted for relative movement of the lower end of the first pipe between a first position inserted in the lower end of the second pipe for forming the flush chamber, and at least one second position at least partially extended out of the lower end of the second pipe. Advantageously the excavation means are at least partially arranged at the lower end of the first pipe in order to in the second position extend beyond the lower end of the second pipe and to actively act on the soil.

The adjustment means preferably are adapted for moving the lower end of the second pipe with respect to the lower end of the first pipe between the first and/or second position, and a third position, extending widely out of the lower end of the second pipe, in which the excavation means are freely exposed.

For the actual process of the removal of the soil material, the excavation means preferably comprise one or more of the aforementioned nozzles, that are connected to a line for pressure fluid and are arranged at the first pipe in order to extend below the lower end of the second pipe when in the third position.

Preferably the nozzles are arranged above the entrance of the discharge means, due to which a flow of eroded soil material is enhanced.

When the aforementioned flush apertures are arranged to be in open connection with the area adjacent to the lower end of the pipe assembly when in the third position, said apertures may be utilised for pressure equalising. To that end it is furthermore preferred that the aforementioned passage in the second pipe has an upper end that can be brought into connection with the surroundings above the upper surface of the soil. Thus undesirable pressure differences over the upper layer, that might lead to its instability, can be equalised via a pressure relief.

In a simple embodiment the adjustment means comprise a cylinder assembly which substantially extends in pipe axis direction.

The dredge device according to the invention may furthermore comprise a holder, such as a kings post, for the pipe assembly and first and second locking means for securing the first and the second pipe, respectively, in position with respect to the holder. The holder provides a holding and guiding means for the pipe assembly and may -in a manner known per se- in turn be held by a device or work vessel, depending on the location of the layer to be removed and the (possible) water level.

Preferably the first and second locking means can be operated independent from each other, as a result of which the one pipe can be secured and then by operating the adjustment means the other pipe can be moved relative (with respect to the one pipe) and absolute (with respect to the kings post or something like it).

If necessary, the adjustment means can be utilised for pressing the pipe assembly, or one of its pipes, into the soil, wherein the locking of one of the pipes with the holder forms a fixed take-off point. It may for instance be utilised when the soil properties render a lowering of the pipe assembly merely in the aforementioned caisson manner difficult.

It is preferred here that the adjustment means are adapted for in absolute sense moving the second pipe for moving with respect to it the lower end of the first pipe between a primary first position, inserted into the lower end of the second pipe for forming the flush chamber, and at least one secondary first position inserted further into the lower end. The lowering may thus by complemented by pressing the outer pipe downward and subsequently bringing the inner pipe from the secondary into the primary first position, by discharge of the material in the initially enlarged flush chamber. The flush chamber may continue to exist here.

Preferably the excavation means comprise one or more vanes, blades and the like that are rotatable about a pipe axis of the pipe assembly, and placed at the lower end of the first pipe. Said excavation means can be used in the discharge of the soil material fluidised in the flush chamber. The vanes and the like may be situated immediately below an end wall, in which a passage is formed for passing on soil excavated by the vanes, wherein preferably means are present for supplying flush water to the area immediately below the vanes. The -fluidised- soil in the area below and near the vanes and the like may then almost immediately be carried away.

In this embodiment it may be advantageous -by way of alternative for the caisson method of lowering- to provide the device with means for selectively driving the vanes and the like in two opposite directions of rotation, in the second position of the first pipe. In this way it is possible to let the vanes and the like rotate in an opposite soil displacing direction when lowering the dredge device through the upper layer, wherein no flush water needs to be supplied. The surroundings are disturbed as little as possible as well. As a result a good connection of the soil of the upper layer with the outer surface of the pipe assembly can furthermore be realised. This is particularly so in the case of an upper layer consisting of granular material. Dispersion of the material of the upper layer is thus counteracted, whereas an upward leakage path is also prevented.

In case of highly cohesive soil the vanes and the like may be used for as it were peeling the soil, to which end they will be suitably designed. In that case they are rotated in the usual direction.

From a further aspect the invention provides a dredge device which may or may not also be provided with the characterizing means described above, such as the nozzle, comprising a pipe assembly to be positioned with a vertical directional component, preferably substantially vertical, having soil excavation means at the lower end and means for upward discharge through the pipe assembly of the soil excavated with the excavation means, wherein the pipe assembly comprises a first inner pipe and a second pipe placed coaxially around the first pipe, wherein the dredge device is furthermore provided with means for adjusting the mutual position of both pipes with respect to each other in axial direction. In this way, -by axially moving the pipes- certain parts having certain functions and provided at the lower end, can easily be correctly positioned when desired.

Preferably the adjustment means are adapted for relative movement of the lower end of the first pipe between a first position inserted into the lower end of the second pipe, and at least one second position extended out of the lower end of the second pipe. Advantageously the excavation means comprise first, preferably mechanically operating, excavators that have been arranged at the lower end of the first pipe in order to extend beyond the lower end of the second pipe when in the second position. This position is advantageous when lowering the lower end of the pipe assembly through the upper layer. The outer pipe can be held against rotation, as a result of which no frictional forces are exerted in circumferential direction on the surrounding soil.

Preferably the second pipe at the lower end is provided with flush apertures for in the first position supplying flush water in the area below the excavator and preferably within the lower end of the second pipe. The -fluidised- soil in the chamber-shaped area below the excavator can then almost immediately be discharged by means of the excavator. Under conditions the pipe assembly can be lowered further caisson-like (a known possibility of lowering caissons) in the upper layer and/or the earth stratum, until at a desired depth, wherein the surrounding soil is disturbed as little as possible. In this way a (tight) abutment of upper layer material or soil material, such as sand, against the outer side of the pipe assembly can be realised.

Preferably the second pipe is double-walled and forms a passage extending in pipe direction for flush water to the flush apertures.

Preferably the adjustment means are adapted for exerting a penetration force on the second pipe, wherein the adjustment means are adapted for in absolute sense moving the second pipe for moving the lower end of the first pipe with respect to the second pipe between a primary, first position inserted into the lower end of the second pipe for forming the flush chamber, and at least one secondary first position further inserted into the lower end. The lowering can thus be complemented by pressing the outer pipe downwards and subsequently bringing the inner pipe from the secondary into the primary first position, by discharge of the material in the initially enlarged flush chamber. The flush chamber may continue to exist here.

Preferably the adjustment means are adapted for relative movement of the lower end of the first pipe between the first and/or second position, and a third position extended out of the lower end of the second pipe, wherein a further function (such as excavation with the aforementioned nozzle(s)) can be carried out.

According to a further aspect the invention provides a dredge device which may or may not be provided with the characterising parts described above, such as one or more nozzles, comprising a pipe assembly to be positioned with a vertical directional component, preferably substantially vertical, with a soil excavator at the lower end and means for upward discharge through the pipe assembly of the soil excavated with the excavator, wherein the excavator comprises a number of vanes, blades and the like, that are rotatable about a pipe axis of the pipe assembly, as well as means for selectively driving the vanes in two opposite directions of rotation, wherein the vanes and the like are formed to be operative in an excavating manner in the one direction and in a displacing manner in the opposite direction.

The abutment of the soil against the outer side of the pipe assembly is further enhanced when the pipe assembly defines a pipe profile within which the vanes and the like rotate.

Preferably the vanes and the like are situated immediately below an end wall, in which a passage is formed for passing soil excavated by the vanes and the like, wherein preferably means are present for supplying flush water to the area immediately below the vanes. The -fluidised- soil in the area below and near the vanes and the like that can now be oppositely rotated, can then almost immediately be carried away. As discussed above under conditions the pipe assembly can be lowered further caisson-like in the earth stratum, down to a desired depth, wherein the surrounding soil is disturbed as little as possible. A (tight) abutment of the -this time- soil material, such as sand, against the outer side of the pipe assembly can thus also be realised.

Preferably a transverse plate, which is provided with a cutting edge, is attached on the lower edge of the vanes and the like, which edge may project substantially in downward direction. This plate reinforces the projecting vanes and may form a peeling blade, by which means for instance highly cohesive soil can be cut.

From a further aspect the invention provides a method for removing soil material, such as sand, from an earth stratum situated underneath an upper layer, wherein a pipe assembly having at the lower end a set of vanes, blades and the like excavating in a first direction of rotation, is lowered through the upper layer, particularly under the influence of the pipe assembly's own weight, while the vanes and the like are rotated in soil displacing direction of rotation that is opposite to the first direction of rotation. The lowering of the pipe set here takes place with a minimum of disturbance of the upper layer, because the soil without adding water is urged away simply in situ over a short distance and is not discharged. The urged away soil ensures sealing along the pipe wall.

Preferably, after the lower end has reached the upper side of the earth stratum, flush water is supplied to the lower end of the pipe assembly to fluidise the area underneath it and the vanes are driven in the first direction of rotation, wherein the fluidised material is discharged by the vanes and further by discharge means incorporated in the pipe assembly, wherein the pipe assembly is lowered, particularly under the influence of the pipe assembly's own weight. It is particularly advantageous when a radially outward screened-off space is created at the lower end of the pipe assembly, which space is situated immediately below the vanes. In this way the above- mentioned caisson conditions can effectively be realised. During lowering, the soil material can be discharged using a pump positioned in the lower end of the pipe assembly.

Thus the lower end of the pipe assembly can be lowered down to for instance a lowermost area of the earth stratum to be extracted, in order to subsequently keep it at the same level for the actual process of removal of soil material. In a further development of the method according to the invention the lower end of the pipe assembly is held at a location below the upper side of the earth stratum by means of one or more nozzles provided at the lower end of the pipe assembly and driven in rotation water is forcefully jetted in radial outward direction for eroding the surroundings, wherein the eroded soil material is discharged through the pipe assembly.

When the flow rate of supplied water and the flow rate of discharged mixture is kept substantially equal, the upper layer can remain temporarily supported and will not be lowered during the extraction process.

Preferably soil material is extracted until the removed quantity of soil material corresponds with a desired quantity, possibly with an intended lowering of the upper layer.

From another aspect the upper layer can be stabilised by supplying material, such as gypsum, through the pipe assembly, to the area from which soil material is being removed, to replace said soil material.

Preferably after the desired quantity of soil material has been removed, water is extracted in a controlled manner via the pipe assembly in order to lower the upper layer.

With the dredge method according to the invention usable soil, such as physically and chemically clean sand, is selectively extracted directly from underneath an upper layer. Said upper layer is disturbed to a minimum extent and a minimal mixing with sand occurs.

As a result of this dredge method a soil lowering occurs, wherein the layer situated above is left behind. This soil lowering has additional purposes such as: better navigability, water transport capacity, through flow ability for the water quality.

The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:

Figure 1 shows a schematic vertical view, partially in cross-section, of an important part of an exemplary embodiment of a dredge device according to the invention;

Figures 1 A and 1 B, show the upper portion and the lower portion, respectively, of figure 1 , enlarged;

Figures 2A, 2B, 2C and 2D show the lower end of the device according to figure 1 , in various, consecutive stages of use;

Figures 3A-3D show cross-sections according to, respectively, III A-D in figure 1 B and figure 2C;

Figure 4 shows the device according to figure 1 , at the start of a project; Figure 5 shows the device according to claim 4, during penetrating an upper layer;

Figure 6 shows the device according to claim 4, during penetrating an upper layer of usable sand;

Figure 7 shows the device of figure 4, during removal of sand from a sand layer over a longer period of time;

Figure 8A and 8B, show a top view on a work flow of the process according to figure 7 and a vertical cross-section of a part of figure 8A, respectively.

The device 1 shown comprises a pipe assembly 5, having an outer pipe 20 and an inner pipe 30, which will be further discussed. The device 4 comprises a bracket 6, on which the parts of the upper end of the device 4 have been fixedly attached, and which form a vertically movable unity with the inner pipe 30. All this is further shown in figure 1 A.

The outer pipe 20 forms a fixed (movable) unity with bracket 9. A hydraulic cylinder 1 1 extends between the brackets 6 and 9, which cylinder is hinged to the bracket 6 at 7 and hinged to bracket 9 at 8. By operating cylinder 1 1 the relative vertical position between the inner pipe 20 and the outer pipe 30 can be changed. In figure 1 the cylinder 1 1 is entirely retracted and the outer pipe 30 is in the highest position with respect to the inner pipe 20. The configuration of the lower end 89 of the pipe assembly 5 can be changed with the cylinder 1 1 , compare the figures 2A-C.

For securing the vertical position of the device 4 with respect to the kings post 2 and also the mutual vertical position of the parts connected to the inner pipe 20 and the parts connected to the outer pipe 30, the brackets 10 and 6 are provided with pawls 1 5a, 1 5b, respectively, that are rotatable in a vertical plane and hingable about hinge points 16a, 16b and for operation are engaged at the location of hinges 14a, 14b by separately operable hydraulic cylinders 13a, 1 3b that are hinged at the location of 1 2a, 1 2b to the brackets 10 and 6, respectively. The pawls 1 5a, 1 5b are provided with locking ends 1 8a, 1 8b that are able to engage in locking openings 1 7, that are regularly distributed along the height of the kings post 2.

Referring to figure 1 A, it can be seen that the inner pipe 30 at the top is attached with flange 30a to lower plate 64 of a worm/circular rack 65 to be driven with driving means that are not further shown, in which circular rack a ring chamber 66 is defined, which is radially bounded in inward direction by circular wall 69. In the lower plate 64 two holes 67a, b are arranged, on which stubs 62a, b are attached, which by means of valves 62a, b are connected to upper ends 33a,b of supply line 33 for ejector pump 37 yet to be discussed, which supply line 33 is accommodated in the bore 32 of the pipe 30, and to the upper end of a supply line 39 for erosion jets 42 (figure 2A), respectively. The ring chamber 66 is upwardly bounded by upper plate 66a, in which an annular series of openings 68 is arranged, which are in connection with the ring chamber 70, which is bounded radially to the inside by circular wall 72 and is bounded radially to the outside by ring wall 71 , which at a location is provided with a radial opening 73, on which by means of connection piece 74 the end 75 of a supply pipe 76 is connected, which supply pipe is provided with a connection flange 77 to a supply line of pressurised water that is not further shown. By means of the connection pipe 76 and by suitable operation of the controllable valves 60 and 61 water for either the ejector pump 37 or the erosion jet 42, or both can be supplied in the direction M, and flow under pressure in accordance with the arrows shown in figure 1 A.

As can be seen in figure 1 A a mixture discharge pipe 38 has also been placed in the boring 32 within the inner pipe 30, which mixture discharge pipe 38 with flange 38a is attached to the lower plate 64 as well, but further connects to pipe 80, which is coaxial to the vertical centre line S of the inner pipe 30 and stationary with respect to the inner pipe 38 and the circular rack 65. The pipe 80 is rotatable within the circular wall 72. The passage 73, connection 74 and 75 are also stationary with respect to the inner pipe 30 and the circular rack 65.

The pipe 80 continues upwards in order to connect to inlet 81 of a centrifugal pump 82, which by means of downward bent exit 83 is able to discharge a mixture in the direction N to a downward discharge pipe 84, which is provided with a lower opening 85, that can be connected to a discharge pipe that is not further shown for discharging dredged materials elsewhere.

The centrifugal pump 82 is accommodated in a casing 90, in which hydraulic drive 92 for the pump is accommodated. All this is accessible for repair purposes via opening 91 .

For performing the repair activities and realising connections to further lines, the device 1 is further provided with a platform 95 with railing 96 (figure 4).

The pump 82, the drive 91 , the supply and discharge lines 76, 84, etcetera, are supported on the inner pipe 30.

Further downwards, as shown in figure 1 B the inner pipe 30 extends in the outer pipe 20. At the location of the bracket 9 a stub 27 is connected to the outer pipe 20, with a valve 23 and a connection piece 24. As can be seen in figure 3D, a second pipe stub 28 extends along side it, provided with valve 29 (that is not depicted). As can be seen in figure 1 B the outer pipe 20 becomes double-walled at that location, having an extra outer wall 22, with which a vertically continuing ring space 21 is defined with the wall of the outer pipe 20. At the top of figure 1 B and in figure 3D a pipe 57 is also shown which pipe has a valve 58, which at the location of 59 debouches in connection piece 24 and with the other end opens in the ring space 31 that is formed between the inner pipe 30 and the outer pipe 20.

In order to keep the inner pipe 30 centred within the outer pipe 20 a number of centring rings 23a-c are provided on the inner pipe 30, which rings corotate with the inner pipe 30.

As already mentioned before, and as can also be seen in the cross-section of figure 3A and in figure 1 , two water supply lines 33, 39 and a discharge line 38 are placed in the inner pipe 30, which lines corotate with the inner pipe. The supply line 33 for water for the ejector pump 37 changes via narrowing 34 into a 1 80 -bend 35, which with vertically oriented mouth 36 is situated in the inlet narrowing 37a of the ejector pump 37. The ejector pump 37 is further provided with a cylindrical portion 37b and with widened exit portion 37c, that connects to the mixture discharge pipe 38, which extends vertically upwards.

The inlet 37a of the ejector pump 37 is placed in line above a hole 51 , below which a space is situated which is surrounded by circumferential wall 53, provided with grid-shaped apertures 54, which space is bounded downwards by a plate 55, in which a mixture passage opening 55a is arranged (see figures 3B and C) situated in line with the opening 51 . At the lower side of the plate 55 vanes 56 are arranged, the shape of which is further shown in the cross-section according to figure 3C, in which it is also schematically shown that a plate 55b can be attached to the end edges of the vanes, for reinforcing and/or forming a peeling blade.

Just above the transverse plate 50 the lower end of the inner pipe 30 is provided with a centring ring 23a, which can be fittingly accommodated in the ring space 31 . As shown in figure 1 B the lower end of the outer pipe 20 is formed with an edge 24 that is shaped inclined and tapering at the inner side, which ends in pilot edge 25. Just above it a number of apertures 26 is formed in the wall 20, which holes open radially to the inside and form a connection between the ring space 21 and the ring space 31 . Above the holes 26 there are holes 1 0 (also see figure 2D), which form the same connection.

Adjacent to the supply pipe 33, as also indicated in figures 2A and 3A, the supply pipe 39 is situated, which via narrowing 40 changes into nozzle 41 , having jet opening 42, and which is oriented radially to the outside of the inner pipe 30.

The device 1 is particularly suitable for removing/dredging a layer of usable soil, such as for instance sand, without an upper or top layer of unusable soil, for instance in case the level of the upper layer has to be lowered, for instance in case of wanted deepening of a waterway or navigation channel. The unusable earth stratum is left behind and disturbed as little as possible during removing the indeed usable substratum.

For a comparable situation on land (that may or may not be temporarily unflooded) the use of the device described above is shown in figures 4-7. A hydraulic crane 1 00 is placed at the ground level 105, which crane is provided with an engine/operating section 1 01 and is supported on caterpillar tracks 102. The crane is provided with an boom 103, at the end of which a parallelogram connection 104 is present to which the connection plate 3 of the device 1 is attached, such that a kings post 2 is at all times kept vertical.

The ground surface 1 05 forms the upper side of a layer 106 of peat and/or clay, which for instance is polluted. Below the upper layer 1 06 there is a usable sand layer 1 07, which extends to some depth. When starting the project it is ensured that the pipe assembly 5, in particular its lower end 89, is in the condition as shown in figure 2A. The cylinder 1 1 is extended almost halfway, due to which the outer pipe 20 is moved slightly downwards with respect to the inner pipe 30. The centring ring 32a closes the lowermost opening of the ring space 30a. The lower plate 55 is situated at approximately the same level as the pilot or cutting edge 25 of the outer pipe 20. As a result the impeller 56 extends to below the cutting edge 25.

The vanes 56 extending into ground surface 1 05, and the locking pawls 1 5a, 1 5b out of engagement with the locking openings 1 7, the inner pipe 30, together with the parts that have been accommodated in there, is brought in rotation in direction B. The vanes 56 will urge the soil to the outside, wherein, also under the influence of the full weight of the device 4, the pipe assembly 5 in a manner comparable to a drill, moves downwards through the upper layer 1 06. The soil material urged outwards in direction L by the vanes 56, however is not discharged upwards, as is the case with a common drill, but is as it were pressed radially to the outside in the bore hole made. As a result a radially inward ring tension is created in the bore hole, which is yet enlarged because the diameter of the outer pipe 20 is larger than the diameter of the vanes 56. As a result the soil will tightly contact the outer surface of the outer pipe 20, so that a leakage path along it is prevented.

During penetrating the upper layer 106, the pumps for water supply are not yet operated, due to which the disturbance of the upper layer can be kept to a minimum. Once arrived at the upper side of the sand layer 107, the cylinder 1 3a is operated to bring the pawl 1 5a with locking end 1 8a in a locking opening 1 7 and thus to secure the vertical position of the outer pipe 20 and the cylinder 1 1 is then operated again to relatively retract the inner pipe 30, until in the condition shown in figure 2B. Subsequently the centrifugal pump 82 is started and pressurised water is supplied via the supply pipe 76, the ring chamber 70, the ring chamber 66, the open valve 61 a and the supply pipe 33, in the direction M, G, until it flows out in the direction H from nozzle 36 in the ejector pump 37. When the water in the vertical pipe 38 reaches the pump 82, a mixture flow K will arise. Then (with closed valves 29 for stub 28) pressurised water is supplied in the direction D via pipe 27, which flows downwards in the direction E through the ring space 21 , in order to flow out at the lower end of the outer pipe 20 in radial inward direction F through the holes 26. The holes 10 are now closed off by the ring 23a. The sand in the chamber formed by the plate 55 and the wall of the outer pipe 20 will come in suspension, and can be included in the mixture flow, in the direction I, through holes 55a and 51 , through the ejector pump 37, in the direction K through the discharge pipe 38, now suction pipe. Then the pawl 1 5b is retracted again, so that the full weight of the inner pipe 30 and the parts supporting on it is released. In a way comparable to the lowering of a caisson the pipe assembly 5 will now go down through the sand layer 1 07, wherein the sand situated outside of the path of the outer pipe 20 will to a large extent remain undisturbed and closely contact the outer surface of the outer pipe 20, so that a leakage path along the outer pipe 20 is prevented to a large extent. The cutting edge 25 here enhances the lowering process.

For enhancing this process the inner pipe can be rotated, now in opposite direction C, wherein the vanes 56 will be operative for enhancing the sand mixture flow through the opening 55a.

It is observed that the caisson method just described can also be utilised for the penetration in the upper layer, when its soil is not highly cohesive. The vanes and the like, however, are then rotated in the excavating direction C.

It is further observed that the outer pipe 20 and the inner pipe 30 during lowering through the soil can also be moved between the positions shown in the figures 2B and 2D, when the soil has too great a resistance against the lowering of the pipe assembly 5. From the position shown in figure 2B the outer pipe 20 is then forcefully pressed downwards (cylinder 1 1 ), but the inner pipe 30 is left standing, so that the position in figure 2D is achieved, in which the flush chamber is enlarged. Flush water keeps being supplied, and fluidised material is discharged via the inner pipe 30, which as if of its own accord may then sink to the position shown in figure 2B. It is also possible to urge the inner pipe downwards using the cylinder 1 1 (retracting) and suitable manipulation of the locks 1 5.

Once the lower end 89 has reached the desired depth in the sand layer 1 07, particularly its lowermost area, the supply of flush water via the pipe 27 and thus through the holes 26 is stopped. Said water is now passed on to the supply pipe 39, to forcefully flow out radially from the nozzle 42 in the direction O (figure 7), wherein the inner pipe 30 with contents is rotated in the direction C. Immediately prior to that, the outer pipe 20 has been pulled up to the position with respect to the inner pipe 30 shown in figure 1 B and figure 2C, by operating the cylinder 1 1 (wherein first the pawl 1 5b has been extended again in a locking opening 1 7).

The pipe 57 connected to the inner space 30a can be used, in case of an open valve 58, for keeping the inner space 30a at a certain water pressure, higher than the ambient pressure, in order to prevent that sand will enter past the centring rings 23a-c.

The nozzle 42 jets water in the direction O, from below the cutting edge 25, as a result of which the sand in the surrounding area will be eroded. The ejector pump 37, with supply water through pipe 33, and dredge pump 80 remain being operated, as a result of which a mixture flow arises to the suction openings 54 in the circumferential wall 53, after which the mixture flows through opening 51 and in the ejector pump 37.

As a result of the upward shift of the outer pipe 20 the lower opening 30a of the ring space 31 has come to lie exposed. Via the openings 26 and 1 0 and the ring space 21 and the pipe 28, in case of an opened valve 29, a pressure equalising channel can be created for equalising the pressure differences between the area near the lower end 89 of the pipe assembly 5 where the sand is eroded and discharged, to the top water and/or the atmosphere. As a result pressure differences are prevented over the upper side of the excavated area, so that the cavity cannot collapse there.

The cavity can be made in the manner shown in the figures 8A and 8B. In radial direction O water is forcefully jetted in radial, substantially horizontal direction, from a nozzle 42 that is initially kept still. The fluid can be jetted at a constant, alternating or adjustable pulse. At an ever increasing radial distance soil material is eroded, along the upper side of the breach, then downwards (V), and then radially to the inside flowing past the lower side of the breach, to the discharge holes 54, in order to via pump 37 be discharged upwards. After for instance a tunnel-shaped breach having a length T of for instance 4 m has been made, slow rotation of the inner pipe in the direction C is started with, see figure 8B. The side 1 08 of the breach is then eroded by the water jet exiting in radial direction. The speed of rotation is selected taking the soil conditions into account. It can also be opted for to remove the entire disc and extractable soil material situated above it shown in figure 8B in one revolution, which may for instance take many minutes, for instance in the range of 10-60 minutes, in a continuous rotation. The rotation may however also take place discontinuously.

During removal of the sand it is seen to that the supplied volume of water through the nozzle 42 and the ejector pump 37 is at least equal to the volume of the discharged mixture.

When a predetermined volume of soil material has been extracted the process is terminated. In a controlled way the remaining water is sucked out of the formed cavity, wherein the upper layer 106 will be gradually lowered (Q), in a process that is controlled by adjusting the suction flow rate to it. In figure 7 the upper layer 106 that has already been lowered is shown. When sufficient soil material has been extracted from the cavity, the cylinder 1 1 is operated again to lower the outer pipe 30 until in the position shown in figure 2A, and the pipe assembly 5 is slowly lifted.

Claims

1 . Dredge device for removing a layer of soil material from underneath an upper layer, comprising a pipe set to be positioned substantially vertical having a first pipe, which in the lowermost portion is provided with at least one nozzle and with means for supplying pressurised liquid, particularly water, to the nozzle, as well as with means for rotation of the first pipe about its centre line, wherein the pipe set comprises means for discharge through the pipe set of soil material eroded by the liquid discharged by the nozzle.

2. Dredge device according to claim 1 , wherein the nozzle is at least substantially radially oriented.

3. Dredge device according to claim 1 or 2, wherein the discharge means have an entrance that is situated below the nozzle.

4. Dredge device according to claim 1 , 2 or 3, furthermore provided with means for determining the volume or flow rate of water discharged by the nozzle and volume liquid otherwise introduced into the process and with means for determining the volume or flow rate of the mixture carried away by the discharge means, as well as with regulating means for by controlling the liquid supply means and/or discharge means keeping both volumes or flow rates substantially equal.

5. Dredge device according to claim 4, wherein a pressure relief passage is formed between the excavation area and the area above the upper layer, wherein preferably means for determining the flow rate or volume are incorporated in the relief passage, which means are in operative connection with the aforementioned regulating means.

6. Dredge device according to any one of the preceding claims, wherein the aforementioned discharge means comprise a discharge pump, particularly a (slim) ejector pump having a supply line for ejector water and a parallel discharge line, accommodated in the pipe, said pump being placed in the pipe set, particularly the first pipe, particularly a lower half thereof.

7. Dredge device according to any one of the preceding claims, wherein the discharge means comprise a stationary positioned pump placed at the top of the pipe set, wherein a rotational connection is incorporated in the line towards the pump, preferably above the upper end of the first pipe.

8. Method for removing soil material, such as. sand, from an earth stratum situated underneath an upper layer, wherein a pipe set with a first pipe having at the lower end one or more nozzles to be fed with a pressure fluid, is lowered to some distance under the upper layer, pressurised liquid, particularly water, is jetted out of the nozzle to make a radial breach in the layer of soil material, the eroded soil material is discharged via the pipe set through pumping action, after a while the first pipe is rotated over a small angle and kept still, or after some time the first pipe is rotated at low speed, to expand the radial breach in tangential direction, all this until at least one full revolution is completed.

9. Method according to claim 8, wherein in one revolution the entire radial area is treated.

1 0. Method according to claim 9, wherein the entire radial area is treated in several revolutions.

1 1 . Method according to claim 8, 9 or 1 0, wherein the flow rate of supplied water and the flow rate of discharged mixture is at least kept substantially equal.

1 2. Method according to any one of the claims 8-1 1 , wherein soil material is extracted until the removed quantity of soil material at least corresponds with a desired quantity, possibly with an intended lowering of the upper layer.

1 3. Method according to any one of the claims 8-1 2, wherein the upper layer is stabilised by supplying water via the pipe set to the area from where the soil material is being removed to replace said soil material.

14. Method according to any one of the claims 8-1 3, wherein through the dredge device according to the invention soil material substituting material, for instance gypsum is supplied to the cavity made.

1 5. Dredge device comprising a pipe assembly to be positioned with a vertical directional component, preferably substantially vertical, wherein the pipe assembly at the lower end defines a flush chamber, which is bounded by a circumferential wall and open at the bottom, wherein the pipe assembly at the lower end is provided with means for supplying flush fluid -particularly liquid, such as water- to the flush chamber, as well as with means for discharging fluidised soil material from the flush chamber and/or its immediate surroundings through the pipe assembly.

1 6. Dredge device according to any one of the preceding claims, wherein the pipe assembly comprises a first, inner pipe and a second outer pipe surrounding the first, wherein the outer pipe is stationary in circumferential direction and provided with the supply means for flush fluid and wherein the discharge means comprise a pump placed near the lower end and in the inner pipe.

17. Dredge device according to claim 16, wherein the outer pipe near the lower edge and at the inner surface is provided with apertures for discharge of the flush fluid.

1 8. Dredge device according to claim 1 7, wherein the outer pipe is double- walled, wherein a passage for flush fluid is formed.

1 9. Dredge device according to claim 1 6, 1 7 or 1 8, wherein the inner pipe at the lower end is provided with excavation means and is rotatable within the outer pipe.

20. Dredge device according to any one of the claims 1 6-1 9, furthermore provided with means for adjusting the mutual position of both pipes with respect to each other in axial direction.

21 . Dredge device according to claim 20, wherein the adjustment means are adapted for relative movement of the lower end of the first pipe between a first position inserted in the lower end of the second pipe for forming the flush chamber, and at least one second position at least partially extended out of the lower end of the second pipe.

22. Dredge device according to claim 21 , wherein the excavation means are at least partially arranged at the lower end of the first pipe in order to in the second position extend beyond the lower end of the second pipe and to actively act on the soil.

23. Dredge device according to claim 20, 21 or 22, wherein the adjustment means are adapted for moving the lower end of the second pipe with respect to the lower end of the first pipe between the first and/or second position, and a third position, extending widely out of the lower end of the second pipe, in which the excavation means are freely exposed.

24. Dredge device according to any one of the claims 1 6-23, wherein the excavation means comprise one or more nozzles, that are connected to a line for pressure fluid and are arranged at the first pipe in order to extend below the lower end of the second pipe when in the third position, preferably substantially radially oriented, so that an optimal radial range can be achieved.

25. Dredge device according to claim 24, wherein the nozzles are arranged above the entrance of the discharge means.

26. Dredge device according to claim 1 8 and 23, wherein the aforementioned flush apertures are arranged to be in open connection with the area adjacent the lower end of the pipe assembly when in the third position.

27. Dredge assembly according to claim 26, wherein the aforementioned passage in the second pipe has an upper end that can be brought into connection with the surroundings above the upper surface of the soil.

28. Dredge device according to any one of the claims 20-27, wherein the adjustment means comprise a cylinder assembly which substantially extends in pipe axis direction.

29. Dredge device according to any one of the claims 1 6-28, wherein the excavation means comprise one or more vanes, blades and the like, that are rotatable about a pipe axis of the pipe assembly, and placed at the lower end of the first pipe.

30. Dredge device according to claim 29, wherein the vanes and the like are situated immediately below an end wall, in which a passage is formed for passing soil excavated by the vanes, wherein preferably means are present for supplying the flush water to the area immediately below the vanes.

31 . Dredge device according to claim 30, provided with means for selectively driving the vanes and the like in two opposite directions of rotation, in the second position of the first pipe.

32. Dredge device comprising a pipe assembly to be positioned with a vertical directional component, preferably substantially vertical, having soil excavation means at the lower end and means for upward discharge through the pipe assembly of the soil excavated with the excavation means, wherein the pipe assembly comprises a first inner pipe and a second pipe placed coaxially around the first pipe, wherein the dredge device is furthermore provided with means for adjusting the mutual position of both pipes with respect to each other in axial direction.

33. Dredge device according to claim 32, wherein the adjustment means are adapted for relative movement of the lower end of the first pipe between a first position inserted into the' lower end of the second pipe, and at least one second position extended out of the lower end of the second pipe.

34. Dredge device according to claim 33, wherein the excavation means comprise first preferably mechanically operating excavators that have been arranged at the lower end of the first pipe in order to extend beyond the lower end of the second pipe when in the second position.

35. Dredge device according to claim 33 and 34, wherein the second pipe at the lower end is provided with flush apertures for in the first position supplying flush water in the area below the excavator and preferably within the lower end of the second pipe.

36. Dredge device according to claim 35, wherein the second pipe is double- walled and forms a passage extending in pipe direction for flush water to the flush apertures.

37. Dredge device according to any one of the claims 33-36, wherein the adjustment means are adapted for exerting a penetration force on the second pipe, wherein the adjustment means are adapted for in absolute sense moving the second pipe for moving the lower end of the first pipe with respect to the second pipe between a primary, first position inserted into the lower end of the second pipe for forming the flush chamber, and at least one secondary first position further inserted into the lower end.

38. Dredge device according to any one of the claims 33-37, wherein the adjustment means are adapted for relative movement of the lower end of the first pipe between the first and/or second position, and a third position extended out of the lower end of the second pipe.

39. Dredge device according to claim 38, wherein the first pipe at the lower end is furthermore provided with second excavators in the shape of one or more nozzles for discharging pressurised fluid for eroding the soil, as well as with means for rotating the nozzles about the pipe axis, wherein the nozzles are arranged in order to extend below the lower end of the second pipe when in the third position.

40. Dredge device according to claim 38 or 39, wherein the flush apertures are arranged to be in open connection with the area adjacent to the lower end of the pipe assembly when in the third position.

41 . Dredge device according to claim 40, wherein the passage in the second pipe has an upper end that can be brought into connection with the surroundings above the upper surface of the soil.

42. Dredge device according to any one of the claims 32-41 , wherein the adjustment means comprise a cylinder assembly extending substantially in pipe axis direction.

43. Dredge device according to any one of the claims 32-42, comprising a holder, such as a kings post, for the pipe assembly and first and second locking means for securing the first and second pipe, respectively, in position with respect to the holder.

44. Dredge device according to claim 43, wherein the first and second locking means can be operated independent from each other.

45. Dredge device according to claim 34 or a claim depending thereon, wherein the first excavator comprises a number of vanes or the like.

46. Dredge device according to claim 45, wherein the vanes and the like extend downwards from the end of the first pipe, in order to be operative in downward and sideward direction.

47. Dredge device according to claim 45 or 46, wherein the vanes and the like are rotatable with the first pipe about a pipe axis of the pipe assembly, wherein the device is furthermore provided with means for selectively driving the vanes in two opposite directions of rotation, wherein the vanes and the like are formed to be operative in an excavating manner in the one direction and in a displacing manner in the opposite direction. >

48. Dredge device comprising a pipe assembly to be positioned with a vertical directional component, preferably substantially vertical, with a soil excavator at the lower end and means for upward discharge through the pipe assembly of the soil excavated with the excavator, wherein the excavator comprises a number of vanes, blades and the like, that are rotatable about a pipe axis of the pipe assembly, as well as means for selectively driving the vanes in two opposite directions of rotation, wherein the vanes and the like are formed to be operative in an excavating manner in the one direction and in a displacing manner in the opposite direction.

49. Dredge device according to claim 48, wherein the pipe assembly defines a pipe profile, and the vanes and the like rotate within said pipe profile.

50. Dredge device according to claim 48 or 49, wherein the vanes and the like are situated immediately below an end wall, in which a passage is formed for passing soil excavated by the vanes, wherein preferably means are present for supplying flush water to the area immediately below the vanes.

51 . Dredge device according to claim 48, 49 or 50, wherein a transverse plate is attached on the lower edge of the vanes and the like, which transverse plate is provided with a cutting edge.

52. Dredge device according to any one of the claims 48-50, wherein the vanes and the like project substantially in downward direction.

53. Dredge device according to claim 52, wherein the pipe assembly at the lower end is furthermore provided with nozzles for discharging pressurised fluid for eroding the soil, as well as with means for rotating the nozzles about the pipe axis, wherein the nozzles preferably are oriented with a radially outward component with respect to the pipe assembly.

54. Dredge device according to any one of the claims 48-53, wherein the pipe assembly comprises a first pipe on which the excavator is arranged, particularly on an end plate thereof, and which is rotatable about a central pipe axis.

55. Dredge device according to claim 53 or 54, wherein the nozzles are arranged on the first pipe for co-rotation therewith and/or wherein the discharge means are arranged in the first pipe and are rotatable therewith.

56. Dredge device according to claim 55, wherein the discharge means comprise a pump, particularly an ejector pump, placed in the lower end of the pipe assembly, said pump having a supply line for ejector water and a parallel discharge line.

57. Dredge device according to claim 55 or 56, wherein the discharge means comprise a stationary positioned pump placed at the top of the pipe assembly, wherein a rotational connection is incorporated in the discharge line towards the pump, preferably above the upper end of the first pipe.

58. Dredge device according to any one of the claims 48-57, wherein the pipe assembly comprises a first inner pipe and a second pipe placed coaxially about the first pipe, wherein the dredge device is furthermore provided with means for adjusting the mutual position of both pipes with respect to each other in axial direction.

59. Dredge device according to claim 58, wherein the adjustment means are adapted for relative movement of the lower end of the first pipe between a first position inserted into the lower end of the second pipe, and at least one second position at least partially extending out of the lower end of the second pipe.

60. Dredge device according to claim 59, wherein the vanes and the like are arranged at the lower end of the first pipe in order to extend beyond the lower end of the second pipe when in the second position.

61 . Dredge device according to claim 59 or 60, wherein the second pipe at the lower end is provided with flush apertures for in the first position supplying flush water in the area below the said excavator and preferably within the lower end of the second pipe.

62. Dredge device according to claim 61 , wherein the second pipe is double- walled and forms a passage extending in pipe direction for flush water to the flush apertures.

63. Dredge device according to any one of the claims 59-62, wherein the adjustment means are adapted for moving the lower end of the second pipe with respect to the lower end of the first pipe between the first and/or second position, and a third position extending out of the lower end of the second pipe.

64. Dredge device according to claim 53 and 63, wherein the nozzles are arranged to extend below the lower end of the second pipe when in the third position.

65. Dredge device according to claim 63 or 64 and claim 61 or 62, wherein the flush apertures are arranged to be in open connection with the area adjacent to the lower end of the pipe assembly when in the third position.

66. Dredge device according to claim 65, wherein the passage in the second pipe has an upper end that can be brought into connection with the surroundings above the upper surface of the soil.

67. Dredge device according to any one of the claims 58-66, wherein the adjustment means comprise a cylinder assembly extending substantially in pipe axis direction.

68. Dredge device according to any one of the claims 58-67, comprising a holder, such as a kings post, for the pipe assembly and first and second locking means for securing the first and second pipe, respectively, in position with respect to the holder.

69. Dredge device according to claim 68, wherein the first and second locking means can be operated independent from each other.

70. Method for removing soil material, such as sand, from an earth stratum underneath an upper layer, wherein a pipe assembly having at the lower end a set of vanes, blades and the like excavating in a first rotational direction, is lowered, particularly under the influence of the pipe assembly's own weight, while the vanes and the like are rotated in soil displacing direction of rotation that is opposite to the first direction of rotation.

71 . Method according to claim 70, wherein after the lower end has reached the upper side of the earth stratum, flush water is supplied to the lower end of the pipe assembly to fluidise the area underneath it and the vanes and the like are driven in the first direction of rotation, wherein the fluidised material is discharged by the vanes and further by the discharge means incorporated in the pipe assembly, wherein the pipe assembly is lowered, particularly under the influence of the pipe assembly's own weight.

72. Method according to claim 71 , wherein a radially outward screened-off space is created at the lower end of the pipe assembly, which space is situated immediately below the vanes and the like.

73. Method according to claim 72, wherein the soil material is discharged using a pump, particularly an ejector pump, positioned in the lower end of the pipe assembly.

74. Method according to claim 71 , 72 or 73, wherein the lower end of the pipe assembly is held at a location below the upper side of the earth stratum and by means of one or more nozzles provided at the lower end of the pipe assembly and driven in rotation water is forcefully jetted in radial outward direction for eroding the surroundings, wherein the fluidised soil material is discharged through the pipe assembly.

75. Method according to claim 74, wherein the flow rate of supplied water and the flow rate of discharged mixture is kept substantially equal.

76. Method according to claim 74 or 75, wherein soil material is extracted until the removed quantity of soil material corresponds with a desired lowering of the upper layer.

77. Method according to claim 74 or 75, wherein water is supplied via the pipe assembly to the area where soil material is being removed to substitute said soil material.

78. Method according to claim 77, wherein after the desired quantity of soil material is removed, water is extracted via the pipe assembly in a controlled manner in order to lower the upper layer.

79. Method according to any one of the claims 70-78 using a dredge device according to any one of the claims 1 -7, 1 5-69.

80. Dredge device provided with one or more of the characterising measures described in the attached description and/or shown in the attached drawings.

81 . Method comprising one or more of the characterising steps described in the attached description and/or shown in the attached drawings.