Cutting device for dislodging an underwater bottom and corresponding method

Abstract

 Described is a device for dislodging an underwater bottom. The device comprises the combination of a cutter suction dredger (1) for dislodging the underwater bottom (9) and an excavator (30) for discharging the dislodged ground portions. The cutter suction dredger (1) is provided with a cutting device (10) which comprises attaching means (103) for attachment to a ladder (2) of the cutter suction dredger (1) and in attached state is moved through the underwater bottom (9) in a lateral sweeping movement (13) of the ladder (2), wherein the cutting device (10) comprises a revolving body (106) which is rotatable around a rotation axis (102) running substantially perpendicularly of a longitudinal direction (21) of the ladder (2), wherein the cutting device (10) comprises elongate members (105) extending outward from an outer surface of the revolving body (106) and the elongate members (105) are provided with one or more cutting tools (115). The invention likewise relates to a method in which the device is applied.

Description

[0001] The invention relates to a cutting device for dislodging an underwater bottom, which cutting device is suitable for attaching to the ladder of a cutter suction dredger and for movement therewith over the underwater bottom in a lateral sweeping movement of the ladder.

[0002] Dredging operations are a usual part of hydraulic engineering operations, such as for instance in port development, tunnel construction, urban expansion, beach replenishment, coast protection, installation of power stations such as wind turbines, mining, environmental improvement and the like.

[0003] It is of course important during dredging to operate efficiently and to remove as much bottom material as possible per unit of time using the least possible power. More and more emphasis has however been placed in recent years on the effect of dredging on the surrounding environment, particularly the flora and fauna. This is particularly the case when performing dredging operations in the vicinity of nature reserves.

[0004] A significant problem is formed here by sediment spill. During the excavation, dredging, transport and/or dumping of excavated bottom material a part will remain behind in the water as relatively fine sediment. Such sediment clouds can make the water highly turbid, and this increased turbidity disrupts the natural environment. In addition, it is increasingly the case that the storage capacity for the excavated bottom material in the immediate vicinity of the work is limited.

[0005] A known device for dredging an underwater bottom is described in NL-1031253. The known cutting device comprises a cage construction which is rotatable around a central axis and provided with cutting tools such as teeth. The cutting device is attached during use to a ladder of a cutter suction dredger (or cutter dredger), a vessel which is anchored in the underwater bottom by means of spud poles and the ladder of which comprises a suction conduit along which dredged ground portions are discharged with suctioned-in water. During dredging the cutting device attached to the ladder is lowered onto the underwater bottom and subsequently dragged through the bottom in rotating state. Using winches the ladder is hauled alternately here from port side to starboard side, wherein the cutting device makes a lateral sweeping movement. A whole bottom surface can be dredged by moving the cutter suction dredger over a determined distance at a time and repeating the above stated sweeping movement. Connected to the suction conduit attached to the ladder is a pump which pumps up the dredged mixture and then pumps it through a pressure conduit to a dumping site.

[0006] The present invention has for its object to provide a cutting device for dislodging an underwater bottom which particularly makes it possible to dredge underwater bottoms in an efficient manner without diluting the material too much and causing a great deal of sediment spill, and this particularly at greater depths and in the case of harder grounds, with a considerably higher efficiency than would be feasible with a mechanical dredging vessel without this preliminary dislodging operation.

[0007] The device according to the invention comprises for this purpose the combination of a cutter suction dredger for dislodging the underwater bottom and an excavator for discharging the dislodged ground portions, wherein the cutter suction dredger is provided with a cutting device which comprises attaching means for attachment to a ladder of a cutter suction dredger and in attached state is moved through the underwater bottom in a lateral sweeping movement of the ladder, wherein the cutting device comprises a revolving body which is rotatable around a rotation axis running substantially perpendicularly of a longitudinal direction of the ladder, wherein the cutting device comprises elongate members with a free outer end extending outward from an outer surface of the revolving body. The elongate members therefore extend away from the rotation axis. The revolving body is preferably cylindrical.

[0008] It has been found that the cutting device according to the invention allows an underwater body to be dislodged such that the dislodged ground portions can be carried relatively easy to the surface with the excavator. The cutting device and the method according to the invention therefore result in a high dredging efficiency, this being represented by the quantity of ground portions dredged per unit of power.

[0009] Provided in a method according to the invention is a device comprising the combination of a cutter suction dredger and an excavator, wherein the cutter suction dredger is provided with a cutting device and, in a situation where it is attached to a ladder of the cutter suction dredger, the cutting device is moved through the underwater bottom in a lateral sweeping movement of the ladder, wherein the cutting device is rotated around a rotation axis running substantially perpendicularly of a longitudinal direction of the ladder, wherein the elongate members (arms) make contact with the ground and penetrate at least partially therein under the weight of the ladder and the cutting device, whereby the underwater bottom is dislodged, and wherein the dislodged ground portions are preferably not suctioned up by a suction conduit - which would result in a strong dilution of the material - but are carried by means of the excavator to the surface.

[0010] Because hydraulic transport of the dislodged ground portions through a suction conduit does not take place, the bottom material is either not or only moderately diluted with water during the dredging, and relatively few fine clay, sludge or organic particles are brought into an aqueous suspension. These particles can only be removed from such a suspension with great difficulty and/or much time, and this can result in a relatively large amount of sediment spill during the loading of containers or during pumping into a dumping zone. The inventive method does not have this drawback and can therefore be advantageously utilized in the vicinity of nature reserves, particularly also when not much storage capacity is available. The dislodged ground portions are after all brought to the surface in relatively dry state.

[0011] According to the invention the rotation axis of the cutting device runs substantially perpendicularly of a longitudinal direction of the ladder, and therefore substantially tangentially to the direction of the sweeping movement. The rotation axis of the cutting device running substantially perpendicularly of the longitudinal direction of the ladder is understood to mean that the rotation axis of the cutting device according to the invention makes an angle with the longitudinal direction of the ladder which varies by no more than 20% from an angle of 90 degrees, more preferably by no more than 10% and most preferably by no more than 5%. During the sweep of the cutting device the rotation axis of the cutting device according to the invention preferably runs substantially parallel to the underwater bottom surface.

[0012] An embodiment of the invention provides a cutting device wherein elongate members extend parallel to a plane running perpendicularly of the rotation axis. It is possible for all or some elongate members to extend parallel to a plane running perpendicularly of the rotation axis.

[0013] In order to further increase the efficiency of the cutting device during the lateral movement through the underwater bottom, a cutting device is provided in an embodiment wherein elongate members extend at an angle other than zero to a plane running perpendicularly of the rotation axis. It is also possible here for all or only some elongate members to extend at an angle to the rotation axis. Particularly suitable angles range between 5 and 25 degrees.

[0014] In order to further increase the efficiency of the cutting device during the lateral movement through the underwater bottom, a cutting device is provided in an embodiment wherein elongate members are 'twisted' at an angle in their longitudinal direction. The blades must after all move at an ideal cutting angle through the underwater bottom at each cutting point. This angle is determined by the lateral speed, the rotation speed of the revolving body and the distance between this cutting point and the rotation axis.

[0015] An elongate member is understood in the context of this application to mean a member with a length dimension at least twice as great as, more preferably at least three times greater than, and most preferably at least five times greater than a width dimension.

[0016] The members are in principle configured to dislodge the underwater bottom in any possible manner. The members can thus form excavating members, scraping members, scooping members, cutting members, tearing members and the like, and the operation of the members is not limited to specific operating principles of dislodging.

[0017] The members can in principle be positioned in all possible ways in the rotation direction of the cutting device, wherein it can be advantageous for adjacent members to be arranged offset relative to each other in the rotation direction. A greater working width can hereby be covered.

[0018] It is important for the dredging efficiency that the cutting device can penetrate with the revolving body (and the members) relatively deeply into the underwater bottom. In an embodiment the cutting device has for this purpose the feature that the revolving body has a diameter and a width in the direction of the rotation axis, and the width/diameter ratio lies between 0.1 and 5, and more preferably between 0.5 and 2.

[0019] Another embodiment of the invented cutting device comprises a revolving body, the organs of which are provided with one or more cutting tools. Suitable cutting tools comprise teeth, bits, fins and the like and can be connected fixedly to an associated member, for instance by welding or one-piece casting. It is also possible for an associated member to comprise holders in which the cutting tools can be received.

[0020] It has been found advantageous for the dredging efficiency to provide an embodiment of the cutting device wherein a cutting tool has a longitudinal axis and the cutting tool extends substantially perpendicularly of the elongate members.

[0021] In another embodiment of the invention a cutting tool runs - or substantially all cutting tools run - substantially tangentially to the rotation direction of the revolving body. The members can function here as spacer from the outer surface.

[0022] The length of the elongate members can be selected within broad limits, depending for instance on the properties of the underwater bottom to be dredged. An efficient embodiment relates to a cutting device wherein an elongate member has a length and the revolving body a diameter, and the length/diameter ratio lies between 0.1 and 2.0, more preferably between 0.3 and 0.8. It is perhaps unnecessary to state that the diameter of the revolving body is defined as the diameter excluding the additional diameter due to the presence of the elongate members.

[0023] The diameter of the revolving body can also be selected within broad limits, wherein the properties of the underwater bottom to be dredged can for instance again be a factor. A suitable embodiment relates to a cutting device wherein the diameter of the revolving body lies between 0.5 and 10 m, more preferably between 1 and 5 m, and most preferably between 1.5 and 3 m.

[0024] The attaching means of the cutting device for attachment to a ladder of a cutter suction dredger can be embodied in any manner, wherein it is recommended to embody the attaching means such that the cutting device can be attached fittingly onto the outer end of the ladder of a known cutter suction dredger, preferably by a simple connection.

[0025] The cutting device can be rotated in two directions around its rotation axis. For a determined rotation direction the members protruding from the outer surface of the revolving body will according to an embodiment strike into the ground with a front side provided with protruding cutting tools. An embodiment can be provided in which the members strike with the front side and the cutting tools penetrate into the ground from a position lying higher than the rotation axis (in the manner of a cleaver). This is also referred to as overcutting. In another embodiment the cutting tools penetrate into the ground from a position lying lower than the rotation axis (in the manner of a spade). This is also referred to as undercutting.

[0026] The rotation of the revolving body is brought about in an embodiment of the invention by providing the cutting device for this purpose with drive means. In a preferred embodiment the drive means comprise a mechanical converter configured to convert a rotation of a cutter suction dredger shaft on which the cutting device is mounted to a rotation of the revolving body. The rotation of the cutter suction dredger shaft will preferably take place here around an axis running parallel to the longitudinal direction of the ladder, while the cutting device according to invention is rotated around an axis running substantially perpendicularly of the longitudinal direction of the ladder.

[0027] It is advantageous to characterize the cutting device according to the invention in that the revolving body is symmetrical relative to a plane running perpendicularly of the rotation axis and is provided with the members on both sides of the plane. A symmetry is hereby achieved during dredging wherein there is substantially no difference between dredging with a port sweep or dredging with a starboard sweep.

[0028] The cutting device preferably comprises a revolving body provided on one or both end faces with guide fins. Dislodged ground portions can if desired be carried away with such guide fins. Clogging of the cutting device with ground portions, which can be a particular problem in clayey soils, is also further prevented.

[0029] In a further embodiment of the cutting device the members are distributed regularly over the revolving body in the rotation direction. Possibly occurring peak loads on the members are hereby reduced, this resulting in a smoother operation of the cutting device. It is advantageous here for the intermediate distance between two successive members in rotation direction to be a maximum of five times the length of the members, more preferably a maximum of three times the length, and most preferably a maximum of once the length.

[0030] The mutual distance between the cutting tools is determined, among other factors, by the dimensions of the cutting tools themselves and by the overall underwater weight of the cutting device, the ladder and other components. The hauling force developed can also be of importance. In addition, the properties of the underwater bottom for dredging are important, for instance the compression strength/tensile strength ratio thereof.

[0031] Another embodiment of the invention provides a cutting device comprising a scraper blade configured to remove dislodged ground portions from the outer surface of the revolving body. Clogging can hereby be prevented.

[0032] Yet another embodiment provides a cutting device which comprises a guide device configured to carry dislodged ground portions a distance away from the cutting device, and preferably to already dislodged ground. A furrow made by the cutting device in a sweeping movement of the ladder is hereby left clear of dislodged ground portions, whereby the dredging efficiency is increased and the sweeping forces can be reduced.

[0033] A suitable guide device comprises in an embodiment a conveyor belt or screw conveyor, an entry side of which is located in the vicinity of or even connecting to the revolving body and an exit side of which is located at a distance from the revolving body.

[0034] With a view to a further reduced turbidity, a further embodiment of the cutting device according to the invention is at least partially covered from the surrounding water by means of a cap.

[0035] The invention relates to the combination of a cutter suction dredger provided with an embodiment of the above described cutting device and an excavator which preferably comprises a backhoe dredger, a dragline or a grab crane, or a combination thereof. A particularly suitable excavator comprises a grab crane.

[0036] The invention will now be further elucidated with reference to the following figures and description of preferred embodiments, without the invention otherwise being limited thereto. The figures are not necessarily drawn to scale. In the figures:

Figure 1 is a schematic side view of a cutter suction dredger with a ladder attached thereto provided with a cutting device according to an embodiment of the invention;

Figure 2 is a schematic top view of the cutter suction dredger according to an embodiment of the invention shown in figure 1;

Figure 3A is a schematic perspective front view of a cutting device according to an embodiment of the invention;

Figure 3B is a schematic perspective rear view of the cutting device according to an embodiment of the invention shown in figure 3A;

Figure 4 is a schematic side view of an excavator which can be applied in a method according to an embodiment of the invention.

[0037] Referring to figures 1 and 2, a cutter suction dredger 1 is shown on which a ladder 2 is mounted for pivoting around a horizontal axis 3. In the known cutter suction dredger 1 ladder 2 can be provided with a suction tube, although this is not essential for the present invention. In the embodiment shown in figures 1 and 2 the suction tube is not present. For the purpose of dredging an underwater bottom 9 the ladder 2 provided on a free outer end with a cutting device 10 is lowered underwater at an oblique angle using a hoisting cable 5 running over a winch 6 until cutting device 10 comes into contact with the underwater bottom 9. Winch 6 is mounted on a platform 4 situated on the bow side of cutter suction dredger 1. From platform 4 a cutting device 10 in the raised position can optionally be repaired or maintained. The angle of ladder 2 can be easily adjusted depending on the depth 8 of the ground to be dislodged.

[0038] During use ladder 2 is hauled in the lowered position shown in figure 1 over the bottom surface 9 to be dredged by means of traction cables (70a, 70b) running between the free outer end of ladder 2 and anchors (7a, 7b) arranged in the underwater bottom. By hauling in the traction cables (70a, 70b) alternately the cutting device 10 is hauled in a sweeping movement 13 along a line 11 from the port side (the side of anchor 7a and traction cable 70a) to the starboard side (the side of anchor 7b and traction cable 70b) of cutter suction dredger 1 and back, wherein cutter suction dredger 1 rotates around an anchor point in the bottom 9 created by spud pole 12a. A port side spud pole 12b shown in figure 1 is in raised and unanchored position. This latter is used when the cutter suction dredger must be repositioned. The hauling speed of cutting device 10 over the underwater bottom can for instance amount to 5-50 m/min, wherein a hauling speed (sweeping speed) of 20-30 m/min is recommended. The rotation speed of cutting device 10 about its rotation axis 102 can for instance amount to 2-30 rpm, wherein a rotation speed of 5-15 rpm is recommended.

[0039] Referring to figures 3A and 3B, cutting device 10 comprises in the shown embodiment according to the invention a cylindrical revolving body 106 which can be rotated by means of drive means (not shown) around a rotation axis 102 running substantially perpendicularly of a longitudinal direction 21 of ladder 2. The visible diameter 113 of revolving body 106 can be selected as desired, but preferably lies between 0.5 and 15 m, and amounts for instance to 3 m.

[0040] Revolving body 106 is set into rotation in figures 3A and 3B in the indicated counterclockwise direction R. Cutting device 10 is attached to ladder 2 by means of a mounting structure 103. Mounting structure 103 has for this purpose on the end a cylindrical end piece 101 which does not co-rotate and in which is received the revolving body 106 with a reduced diameter. With mounting structure 103 the cutting device 10 is connected directly to a drive shaft 22 of cutter suction dredger 1 available for a known cutter head. Drive shaft 22 of cutter suction dredger 1 is generally rotated around an axis which runs parallel to the longitudinal axis 21 of ladder 2 as indicated in figure 3 with the arrow S. The drive means for cutting device 10 present in mounting structure 103, and more specifically in the cylindrical end piece 101 thereof, comprise in a practical embodiment a mechanical converter (not shown) configured to convert the rotation S of the cutter suction dredger shaft 22 to a rotation R of revolving body 106.

[0041] Revolving body 106 of the cutting device 10 shown in figures 3A and 3B is symmetrical relative to a plane 104 running perpendicularly of rotation axis 102 and comprises elongate members 105 with a free outer end. Members 105 extend outward from an outer surface of revolving body 106, each in a direction 107 away from rotation axis 102. Members 105 are provided on both sides of plane 104 on revolving body 106. Revolving body 106 is further provided on both end faces with guide fins 108 extending substantially spirally over the surface of an end face.

[0042] The (visible) diameter 113 of revolving body 106 can be selected within broad limits, wherein the ground properties are for instance taken into account. The width 114 of revolving body 106 can also be selected within broad limits. In the embodiment of figures 3A and 3B the width/diameter ratio amounts approximately to 1. The width 114a over which the cylindrical end piece 101, provided for the purpose of the suspension of revolving body 106 on mounting structure 103, extends is generally not provided with members 105 because this part does not rotate.

[0043] The length 111 of elongate members 105 is preferably adapted to the diameter of 113 of revolving body 106. In the shown embodiment this length/diameter ratio amounts to about 0.50, so that the length 111 of members 105 amounts to approximately 1.5 m.

[0044] The shown embodiment of cutting device 10 further comprises a scraper blade 109 which is configured to remove dislodged ground portions from between mutually adjacent elongate members 105 and from the outer surface of revolving body 106 in order to prevent clogging and jamming.

[0045] Elongate members 105 are distributed regularly in the rotation direction R over the outer surface of revolving body 106. The intermediate distance 110 between bases of two successive members 105 in the rotation direction R can be selected within broad limits and in the shown embodiment amounts to about 0.5 times the length 111 of members 105. A number of the elongate members 105 further extends parallel to the plane 104 running perpendicularly of the rotation axis. In addition, a number of elongate members 105 make an angle other than zero with the plane 104, this angle preferably lying between 5 and 25 degrees.

[0046] Members 105 can further be provided with cutting tools 115. Cutting tools 115 extend with a longitudinal axis substantially perpendicularly of the longitudinal direction 107 of elongate members 105. When revolving body 106 rotates, the longitudinal direction of cutting tools 115 runs substantially tangentially to the rotation direction of revolving body 106, wherein members 105 hold the cutting tools 115 at a distance from the outer surface.

[0047] In order to further increase the efficiency of cutting device 10 the elongate members 105 are 'twisted' at an angle in their longitudinal direction. Cutting tools 115 must after all preferably move at an ideal cutting angle through the underwater bottom at each cutting point. This angle is determined by the lateral speed, the rotation speed of the revolving body and the distance between this cutting point and the rotation axis.

[0048] Cutting device 10 according to the invention is particularly suitable for use in a method in which cutting device 10, in a situation where it is attached to ladder 2 of cutter suction dredger 1, is moved in a lateral sweeping movement 13 of ladder 2. The cutting device is rotated here around rotation axis 102. This axis 102 runs substantially perpendicularly of the longitudinal direction 21 of ladder 2. During this process the elongate members 105 make contact with the bottom and penetrate therein along a significant part of their length under the weight of ladder 2 and the cutting device 2 itself. The underwater bottom 9 is hereby dislodged. According to an aspect of the invention, the dislodged ground portions 19 are preferably not suctioned up with water through a suction conduit or the like, but brought to the surface by means of an excavator 30 and stored in relatively dry state in a dumping zone.

[0049] A suitable excavator is shown with reference to figure 4, although other excavators such as a backhoe dredger or dragline can also be used, optionally in combination with the grab crane (of a grab dredger) shown in figure 4. Grab crane 30 comprises a pontoon 31 which if desired is anchored with spud poles in the underwater bottom 9. A crane housing 32 is connected rotatably to pontoon 31 via a slewing ring 33 and further comprises a crane boom 37. A top cable 320 can luff the crane boom 37 in and out relative to the work deck of pontoon 31 using winch 34. A grab 38 is suspended from the hoisting cable 36 controllable with winch 35. By paying out the hoisting cable 36 the grab 38 can be carried into the dislodged bottom 19 (see broken line) and be filled with dislodged ground portions. The relatively dry content of grab 38 is then deposited into a floating storage container 42 and discharged to a storage zone. A control cable 40 for grab 38 can be operated using a control winch 39.

[0050] The above described combination of a cutter suction dredger equipped with the cutting device according to the invention and an excavator, in particular a grab crane, is able to dredge an underwater bottom with an improved efficiency and without creating much turbidity. The relatively high efficiency is achieved, among other reasons, because the cutting device is able to dig deeply into an underwater bottom, this increasing production in that the dislodged ground portions can be taken up in relatively dry state and in simple manner and in that the size of the grab of a grab crane can be chosen such that it can cope with the depth of the dislodged bottom and can be adapted thereto.

Claims

1. Device for dredging an underwater bottom, comprising the combination of a cutter suction dredger for dislodging the underwater bottom and an excavator for discharging the dislodged ground portions, wherein the cutter suction dredger is provided with a cutting device which comprises attaching means for attachment to a ladder of the cutter suction dredger and in attached state is moved through the underwater bottom in a lateral sweeping movement of the ladder, wherein the cutting device comprises a revolving body which is rotatable around a rotation axis running substantially perpendicularly of a longitudinal direction of the ladder, wherein the cutting device comprises elongate members with a free outer end extending outward from an outer surface of the revolving body, and the members are provided with one or more cutting tools.

2. Device as claimed in claim 1, wherein elongate members extend at an angle other than zero to a plane running perpendicularly of the rotation axis, wherein the angle lies between 5 and 25 degrees.

3. Device as claimed in claim 1 or 2, wherein the elongate members are twisted over an angle in their longitudinal direction.

4. Device as claimed in any of the foregoing claims, wherein the revolving body has a diameter and a width in the direction of the rotation axis, and the width/diameter ratio lies between 0.5 and 2.

5. Device as claimed in any of the foregoing claims, wherein a cutting tool has a longitudinal axis and the cutting tool extends substantially perpendicularly of the elongate members.

6. Device as claimed in any of the foregoing claims, wherein an elongate member has a length and the revolving body a diameter, and the length/diameter ratio lies between 0.3 and 0.8.

7. Device as claimed in any of the foregoing claims, wherein a diameter of the revolving body lies between 0.5 and 15 m.

8. Device as claimed in any of the foregoing claims, comprising drive means for the rotation of the revolving body.

9. Device as claimed in claim 8, wherein the drive means comprise a mechanical converter configured to convert a rotation of a cutter suction dredger shaft to a rotation of the revolving body.

10. Device as claimed in any of the foregoing claims, wherein the revolving body is provided on an end face with guide fins.

11. Device as claimed in any of the foregoing claims, comprising a scraper blade configured to remove ground portions dislodged by the cutting device from the outer surface of the revolving body.

12. Device as claimed in any of the foregoing claims, comprising a guide device configured to carry ground portions dislodged by the cutting device a distance away from the revolving body.

13. Device as claimed in claim 12, wherein the guide device comprises a conveyor belt or screw conveyor.

14. Device as claimed in any of the foregoing claims, wherein the excavator comprises a backhoe dredger, a dragline or a grab crane, or a combination thereof.

15. Method for dredging an underwater bottom, wherein a device as claimed in any of the claims 1-14 is provided, wherein the cutting device, in a situation where it is attached to a ladder of the cutter suction dredger, is moved through the underwater bottom in a lateral sweeping movement of the ladder, wherein the cutting device is rotated around a rotation axis running substantially perpendicularly of a longitudinal direction of the ladder, wherein the elongate members make contact with the ground and penetrate at least partially therein under the weight of the ladder and the cutting device, whereby the underwater bottom is dislodged, and wherein the dislodged ground portions are not suctioned up by a suction conduit but are carried by means of the excavator to the surface.

Drawing