Methods and Systems for Dredging

Abstract

The invention relates to a dredging method for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel. The method comprises performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel. The method also comprises, in a step different from said performing agitation dredging, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel.

Claims

1-30. (canceled)

31. A method for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the method comprising performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel, in a step different from said performing agitation dredging, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel.

32. A method according to claim 31, wherein said displacing the mobilized sediment is performed by water injection.

33. A method according to claim 31, wherein said displacing the mobilized sediment is performed by plough dredging.

34. A method according to claim 31, wherein, prior to said agitation dredging, the method comprises forming the trench in the navigation channel.

35. A method according to claim 31, wherein said performing agitation comprises agitation dredging through water injection dredging using a water injection dredger or wherein said performing agitation comprises agitation dredging through water injection dredging using a plough dredger.

36. A method according to claim 31, wherein said performing agitation comprises using a water injection system installed at or near the nautical bottom.

37. A method according to claim 36, wherein said performing agitation comprises performing agitation through a water injection system being at least partly integrated in mats for scour protecting or mats forming the wall of the collector.

38. A method according to claim 31, wherein said removing sediment from the collector comprises removing sediment with a jumbo hopper dredger.

39. A method according to claim 31, wherein said removing sediment from the collector comprises removing sediment by pumping through a stationary or mobile pumping system.

40. A method according to claim 31, wherein the method comprises, prior to said performing agitation for mobilizing sediment, determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer.

41. A method according to claim 31, wherein the method comprises predicting when the sediment needs to be moved to the collector.

42. A method according to claim 31, wherein the method comprises predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical depth.

43. A method according to claim 31, wherein the method comprises predicting when the sediment needs to be removed from the collector.

44. A method for assisting according to claim 43, wherein said predicting is based on an estimate of the amount of mobilized sediment collected in the collector or the degree of consolidation of the sediment in the collector.

45. A water injection platform for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the platform comprising an agitation system for performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel.

46. A water injection platform according to claim 45, the platform further comprising the collector for collecting the mobilized mud and/or comprising the platform comprising a dredging pumping system for pumping the liquefied sediment and/or wherein the collector is a trench made in the seabed of the navigation channel and/or wherein the agitation system is based on a floating platform or vessel.

47. A water injection platform according to claim 45, wherein the water injection system comprises a submersed system with mounted or integrated nozzles and/or comprises one or more mats where injectors are integrated and connected with a water injection pump and/or wherein the mat is a mat suitable for scour protection or as surface or wall to shape a collector and/or wherein the collector is formed and shaped in the soil or in the mud and/or wherein the collector is made out of material like concrete or steel.

48. A water injection platform according to claim 45, wherein the water injection platform furthermore comprises a monitor system for measuring soil strength and density for determining the dredging power, the dredging effort in hours and the water injection volume to erode, liquefy and mobilise an underwater sediment layer and/or wherein the water injection platform comprises a monitor system for predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical bottom level and/or wherein the water injection platform comprises a pumping station on a dredging ship for pumping the sediment from the collector towards a dredging ship or a stationary pumping station for pumping the sediment from the collector towards a pipe line to relocate the sediment to a dumping or treatment site where the sediment is permanently stored or where it is re-suspended and carried away from the area temporally or permanently.

49. A monitor system for assisting a dredging process in a navigation channel, the dredging process comprising a step of performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel and a separate step of, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel, the monitoring system being adapted for determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer, and/or for predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical bottom level.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 illustrates an example of an water injection dredger as can be used in embodiments of the present invention.

[0074] FIG. 2 shows a T-bar with injection nozzles as can be used in embodiments of the present invention.

[0075] FIG. 3 shows the injection dredging principle where sediment is injected, liquefied, mobilized and displaced, according to an embodiment of the present invention.

[0076] FIG. 4 shows the water injection principle in combination with a trench. The trench is cut out of the seabed. The water injection dredging technique is used to erode and mobilize sediment from around the trench into the trench, according to an embodiment of the present invention.

[0077] FIG. 5 show a cross section of a navigation channel where the seabed soil underwater is depicted, before applying a method according to an embodiment of the present invention.

[0078] FIG. 6 shows a navigation channel where in the middle of the channel a trench is made, according to an embodiment of the present invention.

[0079] FIG. 7 shows a figure where the sediment in the navigation channel is mobilized from the side into the trench, according to an embodiment of the present invention.

[0080] FIG. 8 illustrates the working procedure according to an embodiment of the present invention, wherein the erosion is done in steps starting from close to the trench going to the other sides. While mobilizing the sediment a small slope is introduced.

[0081] FIG. 9 shows a filled trench with water sediment emulsion as can be obtained using a method according to an embodiment of the present invention. The trench is used to consolidate the sediment.

[0082] FIG. 10. Illustrates features and principles as can be used for determining the liquid delivery system parameters in mats usable in embodiments of the present invention.

[0083] FIG. 11 to FIG. 14 illustrate features and principles as can be used in methods and systems for monitoring or assisting in dredging methods according to embodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0084] In the following detailed description, specific details are set forth in order to provide a thorough understanding of the invention and how it may be practiced in particular embodiments. However it will be understood that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures and techniques have not been described in detail, so as not to obscure the present invention. While the present invention will be described with respect to particular embodiments and with reference to certain drawings, the reference is not limited hereto. The drawings included and described herein are schematic and are not limiting the scope of the invention. It is also noted that in the drawings, the size of some elements may be exaggerated and, therefore, not drawn to scale for illustrative purposes.

[0085] Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0086] It is to be understood that the terms used in embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

[0087] It is to be understood that the term comprising should not be interpreted as being restricted to the steps or elements listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression a device comprising A and B should not be limited to devices consisting only of components A and B.

[0088] Where in embodiments according to the present invention reference is made to a waterway, reference is made to a navigable body of water, such as a river, channel, canal, sea, lake or ocean.

[0089] Where in embodiments according to the present invention reference is made to agitation dredging type identification, reference is made to water injection dredging of the soil based on injection of the top layer of the soil, eroding, liquefying and displacing the top layer of the soil consisting of sediment. This dredging technique can be combined with plough dredging to help moving mechanically the soft sediment.

[0090] Where in embodiments according to the present invention reference is made to nautical depth, reference is made to the depth where physical characteristics of the bottom of a waterway reach a critical limit beyond which normal navigation is not possible. The nautical bottom can be defined as the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship's keel influences the controllability and maneuverability. According to embodiments of the present invention, the nautical depth may be defined as in the report Navigation in muddy areas, Supplement to Bulletin no. 43, PTC2 report of WG 03-1983 issue, MarCom Working Group 03.

[0091] Where in embodiments according to the present invention reference is made to soil structure and soil type or soil type identification, reference is made to the classification of the soil type based on the physical parameters of the measured soil. Based on for example the density, shear stress, viscosity and other physical parameters a soil type can be identified.

[0092] Where in embodiments according to the present invention reference is made to a soil type identification, reference is made to the classification of the soil type based on the physical parameters of the measured soil.

[0093] In a first aspect, the present invention relates to a dredging method for displacing sediment in a navigation channel towards a deeper collector in order to keep the navigation channel on a sudden depth. According to embodiments of the present invention, a method is described for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel. The method comprises performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel. The method also may comprise, in a step different from said performing agitation dredging, removing sediment from the collector. Said displacing the mobilized sediment may be performed by water injection.

[0094] By way of illustration some standard and optional steps are described with reference to an exemplary method comprising several steps.

[0095] First step is the use of agitation dredging to mobilize sediment from one place to another. In FIG. 7 a navigation channel is depicted where via the method described in FIG. 3 the top of the soil consisting of deposited sediment is eroded, liquefied and displaced. The displacement is established by the injected water after it was eroded. The displacement can take place over several tens of meters.

[0096] The second step is to mobilize the sediment from the bed of a navigation channel towards a deeper positioned trench in the navigation channel. In FIG. 8 a deeper trench in the middle of a navigation channel is depicted. By eroding and liquefying the edges around the trench the loose sediment can be moved into the trench. By moving a portion of the sediment a slope for the sediment further away from the trench is created. During this process the water injection dredger can be assisted by a plough dredger.

[0097] The third step is to let the mobilized and liquefied sediment consolidate in the trench. The sediment in the trench is liquefied by the added water of the water injection dredger. By collecting the sediment and leave it untouched over time it will start to dewater and consolidate as depicted on FIG. 9.

[0098] The fourth step is a method to empty the collector. The emptying of the collector can happen via a pumping system. The pumping system can a stationary pump or a mobile pump or a jumbo hopper dredger.

[0099] Instead of applying a water injection dredger to erode and mobilize the sediment on the seabed of the navigation channel an anti-erosion mat with an internal water injection pumping system could be deployed. When sediment is on top of the mat, water can be injected through the mat so the sediment is liquefied and starts to mobilize. When the mat is under a sudden angle of repose the sediment will start to flow toward a lower point like a collector. Such a mat thus may comprise a fluid delivery system, such as for example integrated or mounted injectors for injecting water or a structure for diffusively providing water, whereby the fluid delivery system is adapted for mobilizing sediment that has formed on the mat. When injectors are used, such injectors can be integrated in the mat. Such injectors may be part of or integrated in a fluid channel system. The injectors may for example be positioned at one end of the channels of the fluidic channel system and the channels may be combined at the other end and form a water injection entrance. Such a water injection entrance may for example be interconnected with a pumping system for pumping water through the mats or may be for example be based on tidal flow. The injectors or water openings may be oriented in such a direction with respect to the mat surface, such that a displacement in a given direction can be enforced to the sediment. The mats used may be suitable for scour protection or may serve as a surface or wall to shape a collector. Design of the mats and the fluid delivery therein can be performed taking into account how consolidation of sediment can be prevented. By way of illustration, an illustration of considerations to be taken into account are described below. FIG. 10 depicts consolidation behaviors of 2 different substances. The evolution of the top of the mud in function of the time is depicted. When injecting water from below the volume of water injected must be at least equal to the volume of water drained from the system. The required volume of water must be equal or more than the worst case drain scenario over a time span of 1 tidal cycle, on average 12 h. Also consolidation speed depends on the mud layer thickness. In order to find the worst case requirements a sample must be taken in-situ, liquidized to the point where yield stress starts to form in the sediment, and a sedimentation column must be filled with sediment until the worst case thickness of the sediment layer that will lay upon the infrastructure. In FIG. 10, the modified mud1 consolidation was 20 cm during one tidal cycle, this would mean that a discharge from below of at least 0.2 m.sup.3/m per 12 hours must be done in order to let the sediment recover the drained water. Ideally, the discharge into the sediment layer is at least 2 times higher than the drained volume. The reason why it must be higher is that internal drain channels in the consolidating sediment will also partly drain the injected water and as such reduce the efficiency of the injection. It is expected that the consolidation curve described here is rapid and most sediments in ports will consolidate slower.

[0100] The injection of water into the sediment can be done diffuse or by injection nozzles, both systems have advantages and disadvantages. In general one could state that a violent discharge of water into the consolidating sediment will be the most efficient system, since it destroys all internal structures formed during the consolidation. Violent discharge will require nozzles and large volumes of water will need to be available, diffuse injection will require a low discharge rate, minimal water volumes but internal structures in the sediment will be preserved, resulting in a gradual efficiency decrease.

[0101] In one aspect, the present invention relates to a water injection platform for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the platform comprising an agitation system for performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel. The platform further may comprise the collector. The collector may be a trench in the navigation channel or may be an artificial collector having concrete or metal walls. Furthermore, a dredging pumping system for pumping the liquefied sediment also may be comprised. Other features may correspond with elements of the injection platform used for describing the above method or with means for performing method aspects of the method as described above.

[0102] Whereas the mat has been described above as part of an injection platform, the present invention also relates in another aspect to a mat as such, comprising standard and/or optional features as described above.

[0103] In yet another aspect the present invention relates to a measurement method for obtaining information regarding the preparation of the dredging method and the follow up of the dredged area and the collector. The present invention thus also relates to a method for assisting a dredging process in a navigation channel, the dredging process comprising a step of performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector in the navigation channel and a separate step of removing sediment from the collector. The method for assisting comprises determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer. Additionally or alternatively the method for assisting comprises predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical depth or a consolidation level or density level in the collector. Such predicting may be based on an estimate of the amount of mobilized sediment collected in the collector. For determining the parameters as described above, use can be made of a free fall penetrometer, such as for example a free fall penetrometer as known from literature. It is to be noticed that for determining the parameters and their use, information may be taken into account regarding the position, shape or other details of the collector in the navigation way. By way of illustration, embodiments of the present invention not being limited thereto, some further details and advantages may be illustrated with reference to FIGS. 11 to 14.

[0104] As depicted in FIG. 11 there is a relationship between the cutting depth of the injection nozzle of a WID dredger and the resistance of intrusion of a free fall penetrometer. By taking free fall penetrometer measurements of the sediment layers in the zone of interest, one can predict the cutting depth and the volume of sediment that will be influenced and agitated by the nozzle action.

[0105] The bulk density levels of the in-situ sediment determine the amount of water that need to be added in order to bring the sediment to the liquefaction point. As depicted on FIGS. 12, 13 and 14, out of the cutting depth and the density levels the number of times a sudden water injection dredger need to go over measured zone to liquefy and mobilize the measured sediment.

[0106] In one aspect, the present invention also relates to a monitoring system for performing a method as described above. Such a monitoring system may be a processing system performing the method steps of the method for assisting dredging as described above, and may include or be connectable to a free fall penetrometer or other parameter determination means for determining parameters. In some embodiments the processing system may also be wireless connectable to such devices for receiving parameter input.

[0107] In a further aspect, the present invention relates to a computer program product for, when executing on a computing device, executing the determining and/or deriving of information as described in the method according to the above aspects. The present invention also relates to a computer-readable data carrier storing a computer program product according to this further aspect, and to the transmission of such computer program product over a communication network. The present invention thus also includes a computer program product, e.g. an application program product also referred to as applet, which provides the functionality of any of the data processing steps of the methods according to the present invention when executed on a computing device. The computer program product can also be transmitted via a carrier wave in a network, such as a LAN, a WAN or the Internet. Transmission media can take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. Transmission media include coaxial cables, copper wire and fibre optics, including the wires that comprise a bus within a computer.

[0108] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

[0109] The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.