Dredging apparatus and method of dredging

Abstract

A dredging head assembly for deploying on the bed of a body of water, is provided, the assembly comprising a cutter housing having a cutting opening for extending over a section of the bed from which material is to be removed; a cutting assembly disposed within the cutter housing, the cutting assembly operable through the cutting opening in the cutter housing to loosen material from the bed; and an outlet opening in the cutter housing for removing water and entrained material from within the cutter housing under suction; wherein the cutter housing comprises a plurality of holes therein, in use water being drawn into the cutter housing through the holes under the action of reduced fluid pressure within the cutter housing. A dredging assembly comprising the dredging head assembly and a method of dredging are also provided.

Claims

1-57. (canceled)

58. A dredging head assembly for deploying on the bed of a body of water, the assembly comprising: a cutter housing having a cutting opening for extending over a section of the bed from which material is to be removed; a cutting assembly disposed within the cutter housing, the cutting assembly operable through the cutting opening in the cutter housing to loosen material from the bed; and an outlet opening in the cutter housing for removing water and entrained material from within the cutter housing under suction; wherein the cutter housing comprises a plurality of holes therein, in use water being drawn into the cutter housing through the holes under the action of reduced fluid pressure within the cutter housing.

59. The dredging head assembly according to claim 58, wherein the cutter housing has a floor, the cutting opening being formed in the floor.

60. The dredging head assembly according to claim 58, wherein the cutter housing has a front portion, a rear portion, an upper portion and a lower portion, the front portion of the lower portion of the cutter housing having a first depth and the rear portion of the lower portion of the cutter housing having a second depth, with the first depth being less than the second depth.

61. The dredging head assembly according to claim 60, wherein the change in depth from the front portion to the rear portion is continuous.

62. The dredging head assembly according to claim 58, wherein the plurality of holes in the cutter housing is arranged in an upper portion of the cutter housing.

63. The dredging head assembly according to claim 58, wherein the holes in the cutter housing are arranged in a plurality of lines extending across the cutter housing.

64. The dredging head assembly according to claim 63, wherein the lines of holes in the cutter housing extend from the front of the cutter housing to the rear of the cutter housing.

65. The dredging head assembly according to claim 58, wherein the cutting assembly comprises a rotary cutter.

66. The dredging head assembly according to claim 58, comprising a first cutting assembly and a second cutting assembly.

67. The dredging head assembly according to claim 66, wherein the first cutting assembly is disposed at a first height within the cutter housing and the second cutting assembly is disposed at a second height within the cutter housing, the first height being greater than the second height.

68. The dredging head assembly according to claim 66, wherein the cutter housing comprises a first compartment therein containing the first cutting assembly and a second compartment therein containing the second cutting assembly.

69. The dredging head assembly according to claim 68, wherein the cutter housing is provided with a first outlet opening communicating with the first compartment and a second outlet opening communicating with the second compartment.

70. The dredging head assembly according to claim 58, further comprising a stabilizer assembly extending from the cutter housing.

71. A dredging assembly comprising: a dredging head assembly comprising: a cutter housing having a cutting opening for extending across a section of the bed from which material is to be removed; a cutting assembly disposed within the cutter housing, the cutting assembly operable through the cutting opening in the cutter housing to loosen material from the bed; an outlet opening in the cutter housing; and a suction tube connected to the outlet opening for removing water and entrained material from within the cutter housing under suction through the opening; wherein the cutter housing comprises a plurality of holes therein, in use water being drawn into the cutter housing through the holes under the action of reduced fluid pressure within the cutter housing.

72. A method for dredging material from the bed of a body of water, the method comprising: providing a cutter housing, the cutter housing having a cutting opening extending across a portion of the bed; conducting a cutting operation within the cutter housing through the cutting opening loosen material from the portion of the bed; reducing the pressure of fluid within the cutter housing relative to the surrounding water pressure by applying suction to the interior of the cutter housing through an outlet opening in the cutter housing, material from within the cutter housing leaving through the outlet opening; and allowing water to flow into the cutter housing through a plurality of holes in the cutter housing under the action of the pressure differential between the fluid at reduced pressure within the cutter housing and the pressure of the surrounding water.

73. The method according to claim 72, wherein the cutter housing has a floor, the cutting opening being formed in the floor.

74. The method according to claim 72, wherein the cutter housing has a front portion, a rear portion, an upper portion and a lower portion, the front portion of the lower portion of the cutter housing having a first depth and the rear portion of the lower portion of the cutter housing having a second depth, with the first depth being less than the second depth.

75. The method according to claim 72, wherein the cutter housing has an upper portion, with the outlet opening being formed in the upper portion, material being removed from the upper portion of the cutter housing.

76. The method according to claim 72, wherein the cutting operation is performed by a rotary cutter.

77. The method according to claim 72, comprising conducting a first cutting operation using a first cutting assembly and thereafter conducting a second cutting operation using a second cutting assembly.

78. The method according to claim 77, wherein the first cutting operation cuts to a first depth and the second cutting operation cuts to a second depth, wherein the first depth is greater than the second depth.

Description

[0063] Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which:

[0064] FIG. 1 is a diagrammatical representation of a dredging assembly and dredging head assembly of the present invention deployed in a body of water from a surface vessel;

[0065] FIG. 2 is a side view of one embodiment of a dredging head assembly of the present invention;

[0066] FIG. 3 is a bottom view of the dredging head assembly of FIG. 2 in the direction of arrow III;

[0067] FIG. 4 is a top view of the dredging head assembly of FIG. 2 in the direction of arrow IV;

[0068] FIG. 5 is a cross-sectional view of the dredging head assembly of FIG. 2 along the line V-V;

[0069] FIG. 6 is a top view of a dredging head assembly showing an alternative arrangement for the holes in the cutter housing; and

[0070] FIG. 7 is a cross-sectional view of a further alternative dredging head assembly employing a cutting assembly having a single rotary cutter.

[0071] Turning to FIG. 1, there is shown a body of water, generally indicated as 2, having a surface 4 and a bed 6. A dredging vessel 8 at the surface 4 of the body of water 2 has deployed therefrom a dredging assembly, generally indicated as 10, comprising a dredging head assembly 12 connected to the vessel 8 by a suction line 14. In operation, the vessel 8 and the dredging assembly 10 is moving from the left to the right as viewed in FIG. 1, with the portion 6a of the bed 6 to be dredged appearing at the right of the dredging head assembly 12 and the dredged portion 6b of the bed 6 extending to the left of the dredging head assembly 12.

[0072] One embodiment of a dredging head assembly is shown in FIGS. 2 to 5. The dredging head assembly, generally indicated as 102, is shown in FIG. 2 deployed on the bed 6 during a dredging operation. The dredging head assembly 102 comprises a cutter housing 104 having an upper housing portion 106 and a lower housing portion 108. In operation, the lower housing portion 106 extends below the level of the bed 6a to be dredged, as shown in FIG. 2.

[0073] The cutter housing 104 comprises opposing end walls 110, a front wall 112, a rear wall 114 and a top 116. The end walls 110, front wall 112 and rear wall 114 have a lower edge 120, which defines an opening 122 in the lower portion 108 of the cutter housing 104. As can be seen in FIG. 2, the rear wall 114 is deeper than the front wall 112 and each end wall 110 comprises an angled lower edge portion 120a that slopes forwards and upwards towards the front wall 112.

[0074] The cutter housing 104 comprises a partition wall 124 extending between the opposing end walls 110, which divides the interior of the cutter housing into a front portion 126a and a rear portion 126b.

[0075] The dredging head assembly 102 comprises a first cutting assembly in the form of a rotary cutter 130a disposed in the front portion 126a of the interior of the cutter housing 104. The rotary cutter 130a comprises a drum 132a rotatably mounted by a hub assembly 134a at each end to the respective end wall 110. A plurality of T-shaped cutting blades 136a extend from the drum 132a. As shown in the figures, the rotary cutters comprise four cutting blades. The number of cutting blades may be varied from that shown, for example providing the rotary cutters with fewer blades, such as 3 blades, or more blades, such as 5 or more.

[0076] A second cutting assembly in the form of a rotary cutter 130b is disposed in the rear portion 126b of the interior of the cutter housing 104 and is configured in an identical manner to the rotary cutter 130a of the first cutting assembly.

[0077] The rotary cutters 130a, 130b are arranged such that the ends of the blades 136a, 136b pass through a point level with the lower edge 120 of the cutter housing 104. In this way, the cutting action of the rotary cutters may be considered to be level with the lower edge 120 of the cutter housing 104.

[0078] The rotary cutters 130a, 130b are driven by a suitable motor or other drive means (not shown for clarity). The motor is preferably a hydraulic motor.

[0079] As shown in FIG. 4, the centre of the front rotary cutter 130a is higher than the centre of the second rotary cutter 130b. However, the centre of both rotary cutters 130a, 130b are at the same distance above the lower edge 120 of the cutter housing 104.

[0080] The top 116 of the cutter housing 104 is shown in FIG. 4. As can be seen, the top 116 is provided with a plurality of circular holes 140 connecting the interior of the cutter housing 104 with the surrounding water. The holes 104 are arranged in a plurality of rows 142, each row extending from the front wall 112 to the rear wall 114. The front wall 112 and the rear wall 114 are also each provided with a plurality of holes therein, in analogous manner to the holes in the top 116.

[0081] The cutter housing 104 further comprises an outlet opening to allow connection to a suction line 14, as shown in FIG. 1, and through which water and material from the interior of the cutter housing 104 may be removed during operation.

[0082] The dredging head assembly 102 is provided with a front stabilizer assembly 150 extending from the front wall 112 and comprising a roller 152 bearing on the bed 6a to the front of the cutter housing 104. A rear stabilizer assembly 154 extends from the rear wall 114 and comprises a roller 152 bearing on the bed portion 6b to the rear of the cutter housing 104.

[0083] In operation, the dredging head assembly 102 is deployed on the bed of the body of water, for example from a surface vessel, as illustrated in FIG. 1. The cutter housing 104 is in contact with the bed. In particular, the edge 120 of the lower portion 108 of the cutter housing 104 is in contact with the bed and, in the case of a bed containing soft or loose material, such as mud or sand, can extend into the bed below the surface. In this way, the cutter housing 104, together with the bed, encloses the rotary cutters 130a, 130b. The rotary cutters 130a, 130b are rotated, causing the cutting blades 136a, 136b to loosen the portion of the bed exposed by the opening in the lower portion 108 of the cutter housing. Suction is applied to the interior of the cutter housing 104 by way of the suction tube 14, which draws water and loosened material from the bed to leave the interior of the cutter housing 104 through the outlet opening and along the suction tube 14. The water and material are recovered at the vessel 8, for storage, transport and/or disposal at a different location.

[0084] Under the action of the suction applied to the dredging head assembly 102 by means of the suction tube 14, the fluid pressure within the cutter housing 104 is lower than the surrounding pressure outside the cutter housing. Consequently, water is caused to flow into the cutter housing 104 through the holes 140. This inflow of water prevents material loosened from the bed due to the cutting action from leaving the cutter housing 104 and substantially prevents the formation of a plume in the water around the dredging head assembly.

[0085] The arrangement of the cutter housing 104 and the rotary cutters 130a, 130b loosens material from the bed in two stages. In a first stage, the front rotary cutter 130a loosens material to a first depth, corresponding to the depth of the front wall 112 of the cutter housing 104. In a second stage, the rear rotary cutter 130b loosens material to second depth, corresponding to the depth of the rear wall 114 of the cutter housing 104.

[0086] Turning to FIG. 6, there is shown a plan view of a dredging head assembly of an alternative embodiment of the present invention. The dredging head assembly, generally indicated as 202, has the same general configuration and arrangement as shown in FIGS. 1 to 5 and described above. The embodiment of FIG. 6 differs in respect of the shape and arrangement of the holes. As can be seen in FIG. 6, the cutter housing 104 is provided with holes in the form of slots 240 arranged in rows 242 in the upper portion of the cutter housing 104, in analogous manner to the circular holes of the embodiment of FIGS. 1 to 5.

[0087] It will be appreciated that the dredging head assembly 102 may comprise a single cutter assembly, such as a single rotary cutter 130 of the type shown and described above. An embodiment of this kind is shown in cross-section in FIG. 7.

[0088] The dredging head assembly, generally indicated as 302, comprises a cutter housing 304 having an upper housing portion 306 and a lower housing portion 308. In operation, the lower housing portion 306 extends below the level of the bed to be dredged, in an analogous manner to that shown in FIG. 2.

[0089] The cutter housing 304 comprises opposing end walls 310, a front wall 312, a rear wall 314 and a top 316. The end walls 310, front wall 312 and rear wall 314 have a lower edge 320, which defines an opening 322 in the lower portion 308 of the cutter housing 304. As can be seen in FIG. 7, the rear wall 314 is deeper than the front wall 312 and each end wall 310 comprises an angled lower edge portion 320a that slopes forwards and upwards towards the front wall 312.

[0090] The dredging head assembly 302 comprises a cutting assembly in the form of a rotary cutter 330 disposed in the interior of the cutter housing 304. The rotary cutter 330 comprises a drum 332 rotatably mounted by a hub assembly at each end to the respective end wall 310. A plurality of T-shaped cutting blades 336 extend from the drum 332.

[0091] The rotary cutter 330 is arranged such that the ends of the blades 336 pass through a point level with the lower edge 320 of the cutter housing 304. In this way, the cutting action of the rotary cutters may be considered to be level with the lower edge 320 of the cutter housing 304.

[0092] The rotary cutter 330 is driven by a suitable motor or other drive means (not shown for clarity). The motor is preferably a hydraulic motor.

[0093] In other respects, the arrangement and operation of the dredging head assembly of FIG. 7 is directly analogous to that of the dredging head assembly shown in FIGS. 1 to 5 and described above.