Apparatus for the dredging of sediments from the seabed

Abstract

A dredging apparatus for removing sediments from a bed of an expanse of water, includes: a suction apparatus including a) a submersible pump including: a housing body provided with an inlet mouth and with a discharge opening and an impeller rotatably supported in the body between the inlet mouth and the discharge opening and rotatably driven by a respective driving device; and b) a suction head associated to the inlet mouth of the housing body of the pump and provided at the bottom with a suction opening of the sediments; wherein the suction opening of the head has a value of the cross-section area dimensioned to achieve in the working range of the pump a suction speed capable of removing the sediments by means of the fluid dynamics removal action carried out by the water sucked into the head.

Claims

1. Dredging apparatus configured to remove sediments from a bed of an expanse of water in absence of any contact with the bed, comprising a suction apparatus including: a) a submersible pump including: a1) a housing body provided with an inlet mouth and with a discharge opening; a2) an impeller rotatably supported in said body between said inlet mouth and said discharge opening and rotatably driven by a driving device; b) a suction head associated to said inlet mouth of the housing body of the pump and provided at the bottom with a suction opening of the sediments; wherein the suction opening of the head has a value of the cross-section area dimensioned to achieve in a working range of the pump a suction speed capable of removing the sediments by means of the fluid dynamics removal action carried out by the water sucked into said head; wherein the dredging apparatus further comprises a separating device for separating a slurry of water and sediments discharged from the suction apparatus in a liquid phase and a solid phase including the sediments and a recirculation system to the suction head of at least a part of the liquid phase separated by said separating device; and wherein the suction head is provided with an inner hollow space defining a radially outer annular portion of the suction opening, said radially outer annular portion of the suction opening being in liquid communication with the recirculation system and being configured to feed the liquid phase separated by the separating device towards the suction opening and inside the suction head.

2. Dredging apparatus according to claim 1, wherein the suction opening of the head has a cross-section area smaller than the maximum cross-section area of the suction head.

3. Dredging apparatus according to claim 1, wherein the suction head comprises at least a first portion proximal to the suction opening having a progressively increasing cross-section area moving away from said opening and a second portion distal with respect to the suction opening having a substantially constant cross-section area.

4. Dredging apparatus according to claim 1, wherein the suction head comprises at least a first portion proximal to the suction opening having a progressively increasing cross-section area moving away from said opening and a second portion distal with respect to the suction opening having a progressively decreasing cross-section area moving away from said first portion.

5. Dredging apparatus according to claim 3, wherein the suction head comprises a pair of portions proximal to the suction opening having a progressively increasing cross-section area moving away from said opening and a different inclination with respect to a longitudinal axis of the suction opening.

6. Dredging apparatus according to claim 4, wherein the suction head further comprises an intermediate portion interposed between said first and second portion of the suction head.

7. Dredging apparatus according to claim 6, wherein said intermediate portion has a substantially constant cross-section area.

8. Dredging apparatus according to claim 6, wherein said intermediate portion comprises a lower portion proximal to the suction opening and having a progressively increasing cross-section area moving away from said opening and an upper portion distal with respect to the suction opening and having a progressively decreasing cross-section area moving away from said lower portion.

9. Dredging apparatus according to claim 6, wherein said first and/or second portion and/or intermediate portion of the suction head has a substantially frusto-conical shape.

10. Dredging apparatus according to claim 6, wherein the suction head comprises a perforated partition supported in said head downstream of said suction opening.

11. Dredging apparatus according to claim 10, wherein said perforated partition is supported in the suction head at said intermediate portion.

12. Dredging apparatus according to claim 1, comprising a plurality of flow deflecting elements associated to the suction head close to said suction opening.

13. Dredging apparatus according to claim 12, wherein said flow deflecting elements comprise a plurality of fins having a substantially rectilinear or curvilinear shape extending along a radial direction or along an inclined direction with respect to said radial direction.

14. Dredging apparatus according to claim 4, wherein said first portion of the suction head is provided with a jacket forming a double wall wherein said inner hollow space is defined.

15. Dredging apparatus according to claim 1, further comprising a plurality of flow deflecting elements arranged in said hollow space close to said suction opening.

16. Dredging apparatus according to claim 15, wherein said flow deflecting elements comprise a plurality of fins having a substantially rectilinear or curvilinear shape extending along a radial direction or along an inclined direction with respect to said radial direction.

17. Dredging apparatus according to claim 1, comprising a first shut-off valve mounted on a discharge duct extending downstream of said discharge opening of the housing body of the submersible pump.

18. Dredging apparatus according to claim 1, comprising a second shut-off valve mounted on a recirculation duct of the liquid phase separated by the separating device to the suction opening of the suction head.

19. Dredging apparatus according to claim 1, further comprising a unit for chemically treating the liquid phase separated by said separating device.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Additional features and advantages of the present invention will become more readily apparent from the following detailed description of some preferred embodiments of a dredging apparatus according to the invention, made hereafter by way of explanation and not of limitation with reference to the attached drawings. In the drawings:

(2) FIG. 1 is a schematic view of a preferred embodiment of a dredging apparatus according to the invention;

(3) FIG. 2 is a schematic view showing some details of the dredging apparatus of FIG. 1 in an operative condition thereof;

(4) FIG. 3 is a schematic axonometric view partially in cross section of the suction apparatus of the dredging apparatus of FIG. 1;

(5) FIG. 4 is a schematic axonometric view partially in cross section and in enlarged scale of some details of the suction apparatus of the dredging apparatus of FIG. 1;

(6) FIG. 5 is a schematic axonometric view in enlarged scale and with some parts removed of some details of a suction apparatus of a further preferred embodiment of the dredging apparatus according to the invention;

(7) FIG. 6 is a schematic axonometric view in enlarged scale and with some parts detached of some details of a suction apparatus of a further preferred embodiment of the dredging apparatus according to the invention;

(8) FIG. 7 is a schematic axonometric view of a suction apparatus of a further preferred embodiment of the dredging apparatus according to the invention;

(9) FIGS. 8-10 are as many schematic axonometric views partially in cross section of respective suction apparatuses of further preferred embodiments of the dredging apparatus according to the invention;

(10) FIGS. 11 and 12 are as many schematic axonometric views partially in cross section and in enlarged scale of suction heads of respective suction apparatuses of further preferred embodiments of the dredging apparatus according to the invention;

(11) FIG. 13 is a schematic view that illustrates some details of an alternative preferred embodiment of the suction apparatus of the dredging apparatus according to the invention in an operating condition thereof.

DETAILED DESCRIPTION OF THE CURRENTLY PREFERRED EMBODIMENTS

(12) With reference to FIGS. 1-5, a dredging apparatus according to a first preferred embodiment of the invention, for example a dredging apparatus of the so-called sucking-discharging type for removing sediments from a bed F of an expanse of water S like for example a sea bed, river bed, lake bed, marsh bed, etc, is generally indicated at 1.

(13) The dredging apparatus 1 comprises a hull 2, preferably constituted by a plurality of modular bridge units (not illustrated in greater detail), conventionally supporting a driving station 3, inside which a driving panel is positioned to drive all of the displacement operations of the hull and actual dredging operations by means of suitable driving devices, a power station 4 for operating a submerged suction apparatus 5 and a lifting frame 6 for moving the suction apparatus 5.

(14) The power station 4 comprises in turn an endothermic engine (for example a diesel engine) and a hydraulic or electric control unit, not better shown in FIG. 1, to hydraulically or electrically operate the submerged suction apparatus 5 as will become clearer hereinafter.

(15) The dredging apparatus 1 also comprises one or more tanks of a suitable fuel of the endothermic engine and one or more devices for moving the hull 2, both of the conventional type and not shown.

(16) The hull 2 also conventionally supports a work station 7 comprising: a separating device 8 for the separation of a slurry of water and sediments coming from the suction apparatus 5, for example a separating device of the diaphragm type (see FIG. 2), for separating a slurry of water and sediments discharged from the suction apparatus 5 in a liquid phase and a solid phase including the sediments; a recirculation system 10 to a suction head 9 of the suction apparatus 5 of at least a part of the liquid phase separated by the separating device 8, comprising a tank 11 for collecting the liquid phase separated by the separating device 8 and at least one recirculation duct 12 to the suction head 9 of the separated liquid phase; a unit 13 for chemically treating the liquid phase separated by the separating device 8, for example including a tank 14 for neutralizing the pollutants in fluid communication with the tank 11 of the recirculation system 10 by means of a pair of ducts 15, 16 for feeding the liquid phase to the tank 14 and for returning the neutralized liquid phase to the tank 11.

(17) The suction apparatus 5 includes, as better illustrated in FIGS. 2-4:

(18) a) a submersible pump 18 including: a housing body 17 provided with an inlet mouth 19 and with a discharge opening 20; an impeller 21 rotatably supported in the body 17 between the inlet mouth 19 and the discharge opening 20 and rotatably driven by a respective driving device 22, in particular a motor operated by the control unit of the power station 4; and

(19) b) the aforementioned suction head 9, which is associated to the inlet mouth 19 of the housing body 17 of the pump 18 and provided at the bottom with a suction opening 23 of the sediments.

(20) In a way known per se, the discharge opening 20 of the housing body 17 of the pump 18 is in fluid communication with the separating device 8 by means of a duct 24 (shown with a dashed line in FIG. 3) for sending the slurry of water and sediments discharged by the suction apparatus 5, said duct being connected to the body 17 by means of a flanged pipe fitting 25.

(21) The suction opening 23 of the head 9 has a cross-section area dimensioned to achieve, in the working range of the pump 18, a suction speed capable of removing the sediments by means of the fluid dynamics removal action carried out by the water sucked into the head 9.

(22) In the preferred embodiment illustrated, the suction opening 23 of the head 9 has a cross-section area smaller than the maximum cross-section area of the suction head 9.

(23) In this way, it is advantageously possible to create, in the suction head 9, a calibrated section that generates a strong depression and a consequent high suction speed of the water or of the water/sediment slurry.

(24) Preferably, the average suction speed, measured at the suction opening 23 of the head 9, varies between 0.3 m/s and 30 m/s essentially according to the particle size and cohesion characteristics of the sediments.

(25) In the preferred embodiment illustrated, the suction head 9 comprises a first portion 9a proximal to the suction opening 23 having a progressively increasing cross-section area moving away from the opening 23 and a second portion 9b distal with respect to the suction opening 23 having a progressively decreasing cross-section area moving away from the first portion 9a.

(26) In the preferred embodiment illustrated, the suction head 9 comprises, inside the same, a perforated partition 26 supported in the head 9 downstream of the suction opening 23 and adapted to hold solid material having a size exceeding the passage section of holes 27 made in the partition 26.

(27) In the preferred embodiment illustrated, the holes 27 are uniformly distributed in the part of the partition 26 crossed by the liquid, they are preferably circular in shape and they preferably have a diameter comprised between 15 mm and 300 mm, so as to define a cross-section passage area preferably comprised between 175 and about 75000 mm.sup.2.

(28) Advantageously, by positioning the perforated partition 26 within the suction head 9 it possible to achieve the following advantages with respect to known dredging apparatuses: greater operating flexibility of the dredging apparatus 1 since any solid residues of large size are no longer capable of interfering with the operation of the suction head, and possibility of separating the solid material having a particle size exceeding the passage section of the holes 27 from the rest of the sediments, by holding such material during the dredging operations in the area of the head 9 upstream of the perforated partition 26 for subsequent recovery and removal thanks to the depression conditions generated within the head 9.

(29) Since the suction opening 23 of the head 9 has a cross-section area smaller than the maximum cross-section area of the suction head 9, the following important advantageous technical effects are also achieved: limiting the mechanical stresses on the perforated partition 26; limiting the wearing phenomena due to impacts on the perforated partition 26; allowing a sufficient autonomy of operation between one cleaning operation of the area upstream of the perforated partition 26 and the next one; carrying out a prior particle size classification of the sucked sediments so as to optimise the subsequent steps of separation and/or decontamination; and washing the sediments held by the perforated partition 26, an operation that is particularly important in dredging operations of contaminated sites.

(30) Thanks to the aforementioned geometric configuration of the portion 9a of the head 9, it is advantageously possible to progressively slow down the speed of the water/sediment slurry sucked into the head 9 and facilitate the emptying of the suction head 9 from the debris held upstream of the perforated partition 26 present in the head 9.

(31) In this way, it is thus advantageously possible to optimise from the geometric and fluid-dynamic point of view the area of the suction head 9 proximal to the suction opening 23 upstream of the perforated partition 26.

(32) Preferably, the suction head 9 comprises, in the aforementioned first portion 9a proximal to the suction opening 23, a lower wall 28 having an inclination with respect to a longitudinal axis X-X of the suction opening 23 comprised in the range of numerical values indicated above.

(33) In this way, it is thus advantageously possible to optimise from the geometric and fluid-dynamic point of view the area of the suction head 9 proximal to the suction opening 23 upstream of the perforated partition 26.

(34) Preferably, the suction head 9 comprises, in the aforementioned second portion 9b distal with respect to the suction opening 23, an upper wall 29 having an inclination with respect to the longitudinal axis X-X of the suction opening 23 comprised in the range of numerical values indicated above.

(35) Thanks to the aforementioned geometric configuration of the portion 9b of the head 9, it is advantageously possible to optimise from the geometric and fluid-dynamic point of view the area of the suction head 9 distal with respect to the suction opening 23 downstream of the perforated partition 26 in particular improving the fluid-dynamic efficiency of the head 9 close to the inlet mouth 19 in the body 17 of the pump 18, thereby optimising the operation thereof.

(36) In the preferred embodiment illustrated, the suction head 9 consists of two or more structurally independent portions, in this case consisting of the portion 9a proximal to the suction opening 23 and of the second portion 9b distal with respect to such an opening, removably associated to one another by means of a plurality of bolts (not shown) inserted in respective through holes 30a, 30b formed in respective radially outer fins 31a, 31b extending from a peripheral edge of the portions 9a and 9b.

(37) Preferably, the suction head 9 further comprises an intermediate portion 9e comprising a lower portion proximal to the suction opening 23 and having a progressively increasing cross-section area moving away from said opening and an upper portion distal with respect to the suction opening 23 and having a progressively decreasing cross-section area moving away from the lower portion (see FIG. 4).

(38) In this case, the intermediate portion 9e is thus preferably formed of two mutually adjacent end portions of the portions 9a, 9b of the suction head 9 and having a lower inclination with respect to the longitudinal axis of the suction opening 23 with respect to the remaining part of the first portion 9a and, respectively, of the second portion 9b.

(39) Preferably, the lower portion of the intermediate portion 9e has an inclination with respect to the longitudinal axis of the suction opening comprised in the range of numerical values indicated above.

(40) Preferably, the upper portion of the intermediate portion 9e has an inclination with respect to the longitudinal axis of the suction opening comprised in the range of numerical values indicated above.

(41) In this preferred embodiment, the perforated partition 26 is also provided with corresponding radial fins 32 perforated so as to be able to be mounted between the portions 9a and 9b of the suction head 9 preferably at a transversal mid-plane of the intermediate portion 9e of the head 9.

(42) In this preferred configuration, it is advantageously possible to dismount the suction head 9 and the perforated partition 26, facilitating the cleaning and maintenance operations thereof.

(43) Moreover, thanks to the configuration with a double inclination of the intermediate portion 9e of the suction head 9 it is possible to achieve the following advantageous technical effects: preventing the solid material having a size smaller than the passage section of the holes 27 formed in the perforated partition 26 from being trapped between the lower wall 28 of the head 9 and the partition 26 and thus not passing beyond the same; preventing the solid material having a size greater than the passage section of the holes 27 made in the partition 26 from being trapped between the lower wall 28 of the head 9 and the partition 26 thus making it difficult to carry out the operation of emptying the area of the head upstream of the partition 26 (the portion proximal to the suction opening 23); and preventing solid material having a size smaller than the passage section of the holes 27 formed in the partition 26 from being trapped between the upper wall 29 of the head 9 and the partition 26 and not drawn by the pump 18.

(44) In the preferred embodiment illustrated, the lower wall 28 of the portion 9a proximal to the suction opening 23 and the upper wall 29 of the second portion 9b distal with respect to such an opening (including the adjacent end portions forming the intermediate portion 9e of the head 9) are faceted and comprise a plurality of planar segments 9c, 9d inclined with respect to the longitudinal axis X-X of the suction opening and connected side-by-side.

(45) In this case, there is advantageously a simplification of the manufacturing operations of the head 9 with a reduction of the relative costs.

(46) In this way a polygonal-shaped suction opening 23 is thus defined.

(47) In the preferred embodiment illustrated, the suction head 9 is provided with an inner hollow space 34 defining an outer annular portion of the suction opening 23 and in liquid communication with the recirculation system 10 for feeding the liquid phase separated by the separating device 8 towards the suction opening 23 and within the suction head 9.

(48) Preferably, the first portion 9a of the suction head 9 is provided with a jacket 33 forming a portion 9a provided with an inner and outer double wall, wherein the aforementioned hollow space 34 is defined that is thus located within the suction head 9.

(49) In this preferred embodiment, therefore, the jacket 33 defines the outermost wall of the lower part of the first portion 9a of the suction head as well as the outermost perimeter of the suction opening 23 of the head 9.

(50) In the preferred embodiment illustrated and depending on the structural characteristics of the head 9, the suction opening 23 is thus polygonal in shape, in particular with 9 sides and it circumscribes a circle having a diameter comprised between 100 mm and 1500 mm thus generating a cross-section area comprised between 0.008 and 1.76 m.sup.2.

(51) Preferably, the cross-section area of the opening defined by the inner wall 28 of the first portion 9a of the suction head 9 is in this case comprised between 0.004 and 0.90 m.sup.2 so as to take into account the section of the recirculation hollow space 34.

(52) In this preferred embodiment, the dredging apparatus allows to achieve the following technical advantages: increasing the erosion action of the sediments and therefore the efficiency of the dredging operations thanks to a highly-directed feeding of the liquid phase separated by the separating device 8 towards the suction opening 23 of the head 9; effectively confining the suction area of the sediments with a block of any potential water turbidity phenomena. possibility of maintaining the sucked water in a substantially closed circuit, said circuit being optionally sealable at the end of the dredging operations, which is a particularly useful option in the case of polluted sites where it is not possible or desirable to discharge the liquid phase separated on land or in the sea.

(53) In the preferred embodiment illustrated, the dredging apparatus comprises a plurality of flow deflecting elements associated to the suction head 9 close to the suction opening 23 (FIG. 5).

(54) In this preferred embodiment, the aforementioned flow deflecting elements are positioned in the hollow space 34 close to the suction opening 23 and consist of a corresponding plurality of substantially rectilinear fins 35 extending along an inclined direction with respect to the radial direction.

(55) Thanks to the presence of these flow deflecting elements, the dredging apparatus 1 achieves the advantageous technical effect of imparting to the flow of liquid phase fed towards the suction opening 23 a highly-directed substantially rotary movement of the centrifugal type which increases the efficiency of the fluid-dynamic removal action of the sediments.

(56) With reference to the dredging apparatus 1 described above and to FIGS. 1-5, a dredging method for removing sediments from the bed F of the expanse of water S will now be described.

(57) In a first step, the method provides for positioning the suction apparatus 5 including the submersible pump 18 described above close to the water bed F.

(58) Thereafter, a triggering step is carried out in which with the motor 22 of the pump 18 at start-up speed, the suction head 9 is brought close to the bed F by the lifting frame 6 up to a distance such that by actuating the submersible pump 18 the water drawn from the outside is forced to lap on the outer periphery of the lower portion 9a proximal to the suction opening 23 of the head 9 and then to discharge its kinetic energy on the bed F, eroding the same.

(59) The erosion of the water bed F therefore starts from the periphery of the suction opening 23 and reaches the centre up to the longitudinal axis X-X by successive yielding.

(60) As soon as the head 9 has penetrated the water bed, the submersible pump 18 is operated so as to achieve, in the working range of the pump, a suction speed capable of removing the sediments by means of the fluid dynamics removal action carried out by the water sucked into the head 9.

(61) In this way, the dredging apparatus enters into a steady-state operating condition in which the strong depression generated at the suction opening 23 and in the areas immediately upstream thereof possesses a preferential direction axial to the head 9 and continues to draw water from the outside with a progressive erosion and removal of the sediments.

(62) At this point it is possible to distinguish two movements of the dredging front at any vertical movement of the head 9: a front movement, which takes place in the same way as the triggering step; and a peripheral movement, which takes place by virtue of the fact that the layers of material lying over the sucked layer close to the head 9 constitute unstable fronts and consequently slip downwards.

(63) The Applicant observed that such a mechanism, once triggered, is capable of self-feeding making the dredging operations very efficient and free from any interruptions.

(64) In an experimental test carried out according to this preferred embodiment of the dredging method of the invention, it was found that there was a suction speed comprised between 1.1 and 3.4 m/s with a particle size of the sediments of 60-80 mm, whereas the suction flow rate was equal to about 2400 m.sup.3/h.

(65) In this preferred embodiment, the dredging method also provides the step of reducing the average speed of the water/sediment slurry sucked into the suction head 9 downstream of the suction opening 23 carried out by means of the aforementioned increase of the cross-section area of the lower portion 9a of the suction head 9 proximal to the suction opening 23.

(66) Advantageously, such a preferred step allows to adequately slowing down the sucked solid material (sediments but also broken stone, or various kinds of debris).

(67) In this preferred embodiment, the average speed of the slurry at the maximum cross-section area of the intermediate portion 9e of the suction head 9 (where the perforated partition 26 is mounted) is comprised between 0.3 m/s and 0.9 m/s.

(68) In this preferred embodiment, the dredging method also comprises the step of carrying out a particle size classification within the suction head 9 of the sediments incorporated in the water/sediment slurry sucked into said head 9.

(69) Preferably, this step is carried out by means of the perforated partition 26 described above.

(70) Advantageously and as outlined above, it is possible in this case to achieve, with respect to known dredging apparatuses, not only a greater operating flexibility of the dredging method, since any solid residues of large size are no longer capable of interfering with the operation of the suction head 9, but also the possibility of separating solid material having a large particle size from the finer sediments, holding such material in the area of the head 9 upstream of the partition 26 for subsequent recovery and removal.

(71) In other words, thanks to the presence of the perforated partition 26 it is possible to achieve: a selective withdrawal of the material according to its size; a greater precision in achieving the desired dredging depths.

(72) With respect to common dredging heads, in fact, the dredging apparatus and method of the invention allow to withdraw the foreign bodies and all the material which does not pass through the partition 26 from a certain location, keep them within the suction head 9 and then deposit the same in a different area so as to be able to continue excavating the water bed F in the same location.

(73) In common heads, on the contrary, the filter is positioned outside of the head and once it is saturated it is necessary to move the same with the consequence that the foreign bodies are deposited and thus it is not possible to continue the dredging operations in the same location.

(74) By carrying out also the aforementioned step of reducing the average speed of the water/sediment slurry downstream of the suction opening, this preferred embodiment of the method of the invention allows to achieve the additional important advantageous technical effects of: limiting the mechanical stresses on the perforated partition 26; limiting the wearing phenomena due to impacts on the perforated partition 26; allowing a sufficient autonomy of operation between one cleaning operation of the area upstream of the partition 26 and the next one; and carrying out a prior particle size classification of the sucked sediments so as to optimise the subsequent steps of separation and/or decontamination.

(75) In this preferred embodiment, the dredging method also comprises the step of separating the slurry of water and sediments discharged from the submersible pump 18 in a liquid phase and a solid phase including the sediments.

(76) In this way and as outlined above, it is advantageously possible both to recover the sediments for their subsequent treatment, storage or reuse, and to have a flow of water substantially free of sediments that is at least partially recirculated to the suction head 9 by means of the duct 12 of the recirculation system 10.

(77) This separation step is in particular preferably carried out by means of the separating device 8 described above.

(78) Advantageously, the step of recirculating at least a part of the liquid phase separated from the slurry is carried out in a passive manner, thanks to the depression which is created at and close to the suction opening 23 by the submersible pump 18.

(79) In this way, it is advantageously possible to recirculate at least a part of the liquid phase separated by the separating device 8 towards the suction opening 23 of the suction head 9 without any additional driving element, but simply by exploiting the action of the submersible pump 18 which is in any case already provided to suck the sediments in the dredging apparatus 1.

(80) In a preferred embodiment, the dredging method comprises the step of recirculating to the head 9 substantially all of the liquid phase separated from the slurry, with the exception of the losses of the liquid which impregnates the separated solid phase, said losses being compensated by withdrawing water from the surrounding environment, and the step of feeding the recirculated liquid phase towards the suction opening 23.

(81) In this way, the recirculated liquid phase has a speed substantially equal to the suction speed for which reason it is advantageously possible to ensure that the recirculated liquid phase is substantially confined in a closed hydraulic circuit without any substantial disturbing action of the sediments and without any undesired generation of turbulence capable of bringing the sediments in suspension.

(82) Moreover and as outlined above, it is advantageously possible to achieve the following technical effects: increasing the erosion action of the sediments and therefore the efficiency of the dredging operations thanks to the highly-directed feeding of the liquid phase separated by the separating device 8 towards the suction opening of the head 23; effectively confining the suction area of the sediments with a block of any possible water turbidity phenomena; possibility of keeping the sucked water within a substantially closed circuit.

(83) These steps are in particular carried out by means of the duct 12 of the recirculation system 10 and by the hollow space 34 defined within the suction head 9.

(84) In this preferred embodiment, the dredging method also comprises the steps of imparting to the recirculated liquid phase fed towards the suction opening 23 a highly-directed substantially rotary movement with respect to the suction opening 23 and of eroding the sediments from the water bed F by channelling the water present close to the suction opening 23 outside of the head 9 in a tangential direction towards the suction opening 23.

(85) These preferred steps are carried out in this case by means of the flow deflecting elements (fms 35) described above positioned within the hollow space 34 defined in the head 9.

(86) Advantageously and as outlined above, these steps allow to optimise the fluid-dynamics of the dredging operations thereby increasing their efficiency and reducing the times and costs thereof.

(87) In this preferred embodiment, the dredging method also comprises the step of chemically treating the liquid phase separated from the slurry of water and sediments in the separating device 8.

(88) This step is preferably carried out by means of the chemical treatment unit 13 and it allows to achieve the advantages outlined earlier.

(89) With reference to FIGS. 6-13 further preferred embodiments of the dredging apparatus 1 according to the invention will now be described.

(90) In the following description and in such figures, the elements of the dredging apparatus which are structurally or functionally equivalent to those illustrated earlier with reference to FIGS. 1-5 will be indicated with the same reference numerals and will not be described any further.

(91) In the embodiment of FIG. 6, a variant of the suction head 9 is illustrated in which the flow deflecting elements positioned in the hollow space 34 consist of substantially curvilinear fins 35 inclined with respect to the radial direction so as to impart to the recirculated water flow a substantially rotary movement of the centripetal type which facilitates the water intake into the suction head 9 and effectively erodes the water bed F removing the sediments.

(92) In a further alternative preferred embodiment, not illustrated, the substantially curvilinear fins 35 can be oriented in the opposite direction with respect to the radial direction (in other words with the concavity to the left of the fins with reference to FIG. 6) so as to impart to the recirculated water flow a substantially rotary movement of the tangential type with respect to the suction opening 23, achieving also in, this case an effective erosion of the water bed F.

(93) FIG. 7 shows a variant of the suction apparatus 5 and of the suction head 9 in the case in which the dredging apparatus 1 lacks the recirculation system 10 of the water to the head 9.

(94) In this preferred embodiment, the suction head 9 comprises a plurality of flow deflecting elements, consisting of respective substantially rectilinear fins 35 extending along a direction inclined with respect to the radial direction, externally associated to the first portion 9a of the suction head 9 close to the suction opening 23.

(95) Thanks to the presence of these inclined fins 35, the dredging apparatus 1 achieves the advantageous technical effect of imparting to the liquid phase flow fed towards the suction opening 23 a substantially rotary movement of the centrifugal type which increases the efficiency of the fluid-dynamic removal action of the sediments.

(96) Consequently, the dredging method carried out by means of the aforementioned dredging apparatus 1 comprises the step of imparting to the water sucked into the head 9 a substantially rotary movement oriented towards the suction opening 23.

(97) In this preferred embodiment, the second portion 9b of the suction head 9 distal with respect to the suction opening 23 is provided with a plurality of inspection ports 36 which advantageously allow to inspect the inner space of the suction head 9 and to verify the need for a possible intervention to remove solid materials held by the perforated partition 26 and/or to carry out maintenance or repair interventions.

(98) Clearly, the aforementioned inspection ports 36 can also be provided on the other embodiments of the invention.

(99) FIG. 8 illustrates a further preferred embodiment of the suction apparatus 5 and of the suction head 9 in the case in which the dredging apparatus 1 lacks the recirculation system 10 of the water to the head 9.

(100) In this case, the suction head 9 is integrally formed as a single piece with the perforated partition 26, while the portions 9a and 9b of the suction head 9, respectively proximal and distal with respect to the suction opening 23, have a frustoconical shape, thereby achieving the advantageous technical effects described above in relation to the presence of this specific combination of features.

(101) FIG. 9 illustrates a further preferred embodiment of the suction apparatus 5 and of the suction head 9 in the case in which the dredging apparatus 1 lacks the recirculation system 10 of the water to the head 9.

(102) In this case, the suction head 9 is integrally formed as a single piece with the perforated partition 26 and its intermediate portion 9e interposed between the portions 9a and 9b has a substantially constant cross-section area.

(103) The portions 9a and 9b of the suction head 9, respectively proximal and distal with respect to the suction opening 23 have also in this case a frustoconical shape, thereby obtaining the advantageous technical effects described above in relation to the presence of this specific feature.

(104) In this case, the perforated partition 26 is supported in the suction head 9 at the intermediate portion 9e having a substantially constant cross section so as to achieve the advantageous technical effects illustrated above with reference to the embodiment of FIGS. 1-5.

(105) FIG. 10 illustrates a further preferred embodiment of the suction apparatus 5 and of the suction head 9 in the case in which the dredging apparatus 1 lacks the recirculation system 10 of the water to the head 9.

(106) In this case, the suction head 9 is integrally formed as a single piece with the perforated partition 26 and comprises a single cylinder-shaped portion having a substantially constant cross-section area.

(107) In this case, the suction opening 23 is centrally formed in a bottom wall 37 of the head 9 and similarly to the other preferred embodiments illustrated, it has a smaller cross-section area than the maximum cross-section area of the suction head 9 (in this case equal to the area of its cross section that is constant).

(108) FIG. 11 illustrates a further preferred embodiment of the suction apparatus 5 and of the suction head 9 in the case in which the dredging apparatus 1 lacks the recirculation system 10 of the water to the head 9.

(109) In this case and similarly to the preferred embodiment illustrated in FIGS. 1-5, the portion 9a proximal to the suction opening 23 and the second portion 9b distal with respect to such an opening are structurally independent and are removably associated to one another in an analogous manner by means of a plurality of bolts (not shown).

(110) Also in this case, the perforated partition 26 is removably mounted between the portions 9a and 9b of the suction head 9 at the intermediate portion 9e and the walls of the head 9 are faceted and comprise a plurality of planar segments inclined with respect to the longitudinal axis X-X of the suction opening 23 and connected side-by-side to each other.

(111) In this way, a polygonal suction opening 23 is thus defined also in this case.

(112) In this case, the portion 9a proximal to the suction opening 23 differs from the previous ones in that it consists of a pair of portions 9a, 9a proximal to the suction opening 23 and having a progressively increasing cross-section area moving away from said opening and a different inclination with respect to the longitudinal axis X-X of the suction opening 23.

(113) More specifically, a first portion 28a of the lower wall 28 closest to the suction opening 23 has an inclination with respect to the longitudinal axis X-X comprised between 0 and 85 and, still more preferably, between 5 and 70 and a second portion 28b of the lower wall 28 has an inclination with respect to such a longitudinal axis X-X comprised between 5 and 85 and, still more preferably, between 25 and 70.

(114) In this way, it is advantageously possible to provide the suction head 9 with an element for reducing its cross section which, in the case of particularly cohesive sediments (e.g. compact clay), allows to achieve a cross-section area of the suction opening 23 that is adequately reduced so as to increase the suction speed and therefore the sediment removal capacity of the head 9.

(115) In the embodiment of FIG. 12, the suction head 9 is entirely similar to the head of FIG. 11 with the difference that the reducing elementconsisting of the portion 9a closest to the suction opening 23comprises a plurality of cut outs 38 formed at the peripheral edge of the suction opening 23 so as to avoid the triggering of possible cavitation phenomena in the case of accidental contact with the bed F.

(116) Finally, FIG. 13 illustrates a further preferred embodiment of the suction apparatus 5 and of the suction head 9 in the case in which the dredging apparatus 1 is provided with the recirculation system 10 of the water to the head 9 in a similar manner with respect to the previous embodiment of FIGS. 1-5.

(117) In this case, the dredging apparatus 1 comprises a first shut-off valve 40, for example a check valve of the swing type, mounted on the discharge duct 24 of the slurry of water and sediments sucked by the suction head 9 and extending downstream of the discharge opening 20 of the housing body 17 of the submersible pump 18.

(118) Preferably, the dredging apparatus 1 also comprises a second shut-off valve 41, for example a throttle valve, mounted on the recirculation duct 12 of the liquid phase separated by the separating device 8 to the suction opening 23 of the suction head 9.

(119) The presence of the shut-off valves 40, 41 is extremely advantageous in the case in which polluted sites are dredged, since it allows to: keeping the recirculated water in a substantially closed circuit, avoiding any type of reintroduction into the environment of pollutants present in the liquid phase, in case of failure of the submersible pump 18 or of other elements of the recirculation system or when the dredging operations are stopped; and preventing undesired back-flows of the slurry of water/sediments discharged by the impeller 21 of the submersible pump 18 in case of failure of the latter or when the dredging operations are stopped.

(120) From what has been outlined above, it is thus clear that the dredging apparatus and method of the invention achieve various advantageous technical effects and, more specifically: possibility of carrying out the dredging operations without any appreciable dispersion of the sediments which are eroded solely by means of the fluid dynamics removal action carried out by the water sucked into the head; possibility of carrying out the dredging operations without contact with the water bed by means of a fluid-dynamic suction/removal action of the sediments carried out by the water sucked by the suction head by means of the depression which is generated close to, in particular beneath and around, the suction opening of the head; possibility of sucking a water/sediment slurry having a high content of solids, up to a value equal to or greater than 40% by volume and, therefore, with the possibility of obtaining a high dredging efficiency in terms of hourly productivity; possibility of drastically reducing the environmental impact, so that the dredging apparatus and method may be used in SCI or SNI sites or in any case in areas where for environmental reasons it is not permitted to have any type of water turbidity and/or dispersion of polluting sediments in the water; possibility of recovering and, if needed, treating and/or exploiting, the dredged solid materials; possibility of reducing the times and costs of the interventions.

(121) Clearly, a man skilled in the art may introduce modifications and variants to the invention described hereinbefore in order to meet specific and contingent application requirements, variants and modifications which anyway fall within the scope of protection as defined in the attached claims.