(19)
(11)EP 2 422 020 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
22.05.2019 Bulletin 2019/21

(21)Application number: 10725366.8

(22)Date of filing:  20.04.2010
(51)International Patent Classification (IPC): 
E02F 5/10(2006.01)
E02F 5/00(2006.01)
F16L 1/16(2006.01)
(86)International application number:
PCT/IB2010/000871
(87)International publication number:
WO 2010/122395 (28.10.2010 Gazette  2010/43)

(54)

GROUP AND METHOD FOR LAYING AND BURYING PIPELINES AT THE SEAFLOOR

EINHEIT UND VERFAHREN ZUM VERLEGEN UND VERGRABEN VON ROHRLEITUNGEN AUF DEM MEERESBODEN

GROUPE ET PROCÉDÉ POUR POSER ET ENFOUIR DES OLÉODUCS SUR LE FOND MARIN


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK SM TR

(30)Priority: 23.04.2009 IT MI20090689

(43)Date of publication of application:
29.02.2012 Bulletin 2012/09

(73)Proprietor: Saipem S.p.A.
20097 San Donato Milanese (Milano) (IT)

(72)Inventors:
  • LAZZARIN, Diego
    I-31100 Treviso (TV) (IT)
  • FORMENTI, Massimiliano
    I-30034 Mira (VE) (IT)

(74)Representative: Eccetto, Mauro et al
Studio Torta S.p.A. Via Viotti, 9
10121 Torino
10121 Torino (IT)


(56)References cited: : 
EP-A2- 1 985 766
JP-A- 2003 336 765
US-A- 4 149 326
US-A- 4 516 880
US-B1- 6 196 766
DE-A1- 3 045 901
US-A- 2 731 800
US-A- 4 436 450
US-A1- 2004 031 174
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention relates to a group and method for laying and burying pipelines at the seafloor.

    [0002] In laying pipelines at the seafloor it is also desirable to bury them in order to protect them from specific local factors such as fishing, navigation, streams, wave-motion, natural events and so forth.

    [0003] On the basis of these factors and depending on the morphology and bathymetry of the seafloor, in addition to deciding upon the necessity of burying a partial tract or the whole length of a pipeline, the characteristics of the cavity, i.e. the digging depth, the entity and gradation of the covering, are also established.

    [0004] In recent years, compatibly with the economical aspect implied in the burying operations of pipelines at the seafloor, this operation has become standard in sub-coastline tracts, also due to the imposition of regulations.

    [0005] There are, in particular, three methods for laying and burying pipelines in the seafloor:
    • pre-trenching, i.e. the preliminary digging and treatment of the trench destined for receiving the pipeline, before the laying operation of the same;
    • co-trenching during the launching and laying of the pipeline; and
    • post-trenching after the laying of the pipeline, i.e. burying the pipeline by removing the underlying material, after being launched, hauled or placed in the desired position.


    [0006] The pre-trenching methods are preferably applied in the case of compact seafloors, consisting of cemented sediments or lithifications or rocks. The co-trenching and post-trenching methods, on the contrary, are particularly suitable for seafloors covered by a mantle of sediments having a thickness greater than the depth required for the excavation, or consisting of non-lithified or non-cemented materials or easily breakable materials.

    [0007] The pre-trenching methods require a much larger excavation than the pipeline dimension, as the latter is laid subsequently, or a particularly precise laying technique, called guided laying.

    [0008] The co-trenching methods require the concurrence of two types of equipment, launching and digging equipment, and the synchronism of the two operations making the procedure difficult to effect.

    [0009] The post-trenching methods can be effected after laying the pipeline, as they do not require the contemporaneous presence of two different naval means.

    [0010] The co-trenching and post-trenching methods have the disadvantage of a possible deformation or damage to the pipes during the digging phase, as shown in fig. 1.

    [0011] During the digging, in fact, the pipelines are in a so-called "span" configuration, i.e. suspended between the area of the seafloor already excavated and the portion of seafloor not yet emptied, in particular in correspondence with the immediate position of the trenching machine.

    [0012] In this configuration, if the difference in level between the unexcavated and excavated portion is considerable, the pipelines are subjected to stress which could cause the deformation or even collapse of the same.

    [0013] Consequently, the post-trenching, and co-trenching excavations are currently effected with successive small-depth passages in order to reduce the span which is created between the digging machine and the seafloor already excavated, to the minimum.

    [0014] The necessity of various digging passages in any case causes a lengthening of the overall operating period necessary in the co-trenching and post-trenching methods.

    [0015] Document US 6,196,766 describes a subsea movement apparatus comprising a mining head connected to a pipeline for discharge and conveyance of sediments toward a station. In particular, in the embodiment illustrated in figure 11 of such document, the discharge pipeline comprises some floating elements therein.

    [0016] Examples of post-trenching method are disclosed in US 4,149,236 and EP 1,985,766. In particular, document US 4,149,236 discloses the technical features of the preamble of claim 1.

    [0017] An objective of the present invention is to overcome the drawbacks mentioned above and in particular to identify a group and method for the laying and burying of pipelines on seafloors which allows the positioning of pipes in situ in short times, at the same time maintaining the stress suffered by- said pipelines within tolerance limits.

    [0018] Another objective of the present invention is to provide a group and method for the laying and burying of pipelines on seafloors, which is capable of effecting the excavation of the seafloor during or after the laying of the pipes, reducing the risks of deformation or collapse of the same.

    [0019] A further objective of the present invention is to provide a group and method for the laying and burying of pipelines on seafloors, which is capable of effecting deep excavations of the seafloor in a reduced number of passages, without damaging the pipes to be laid and buried.

    [0020] These and other objects according to the present invention are achieved by providing a group and method for the laying and burying of pipelines on seafloors as specified in the independent claims.

    [0021] Further characteristics of the group and method for the laying and burying of pipelines on seafloors are subject of the dependent claims.

    [0022] The characteristics and advantages of a group and method for the laying and burying of pipelines on seafloors according to the present invention, will appear more evident from the following illustrative and non-limiting description, referring to the enclosed schematic drawings in which:
    • figure 1 is a schematic configuration of the possible effects caused by the laying and burying of pipelines according to the methods currently used;
    • figures 2a-2c show the sequence of operating phases implemented by the method for the laying and burying of pipelines on the seafloor, according to the present invention;
    • figure 3 is a partial perspective view of the laying and burying group of pipelines on the seafloor according to the present invention;
    • figure 4 is a perspective view of two floating elements used in the laying and burying group of pipelines on the seafloor, according to the present invention;
    • figure 5 is a raised side view of the two floating elements of figure 4;
    • figure 6 is a raised front view of a floating element used in the laying and burying group of pipelines on the seafloor, according to the present invention;
    • figure 7 is a sectional view along the line A-A of figure 5;
    • figure 8 is a block scheme of the method for the laying and burying of pipelines on the seafloor, according to the present invention.


    [0023] With reference to the figures, these illustrate a laying and burying group of pipelines on the seafloor, indicated as a whole with 10.

    [0024] The group for the laying and burying of pipelines 10 comprises a digging device in the form of a trenching machine with cutting means 16 of the seafloor 20, such as milling cutters, toothed wheels and/or diamond-disks, and sediment suction and removal means 13, such as draining pumps and/or suction pumps which suck the debris of the excavation and discharge it at the side of the same, forming rims and spurs on the edges of the trench produced by the digging device 11.

    [0025] In order to effect the excavation of the seafloor 20, during or after the laying of the pipelines 15, the digging device 11 is equipped with hooking means to a pipeline 15 and means for sliding on the same, such as, for example, gripping and hauling clamps and/or rubberized rollers.

    [0026] In this way, it is possible to both maintain the relative position between the pipeline 15 and the digging device 11 to prevent the movement of the milling cutters and mechanical cutting organs 16 from accidentally damaging the coating, generally of cementitious material, which covers it externally, and also to slide along the pipeline 15 in the advancing phase.

    [0027] The functioning of the excavation device 11 during the progression and excavation is normally operated by remote control and controlled by an umbilical cable (not shown) consisting of a bundle of connections which supply on the one hand the hydraulic and electric feeding, and on the other the driving commands of the various functions and sensors installed on the digging device 11 itself.

    [0028] According to the present invention, the laying and burying group of pipelines 10 comprises a plurality of float devices 14 connected to the digging device 11 and constrainable to the pipeline 15.

    [0029] In particular, a first float device 14 is connected by specific first connection means 12, such as cables for example, behind the digging device 11 with respect to the advance direction of the same, and in particular behind the sediment suction and removal means 13.

    [0030] The subsequent float devices 14 are suitably connected to the immediately previous floating device, with respect to the advance direction of the digging device 11. In this way, a so-called series or train of float devices 14 is formed, which, during the digging phase, becomes gradually constrained to the pipeline 15 in order to support is when it is in the span configuration between the excavation front and front of the trench.

    [0031] The number of float devices 14 used in subsequent phases in the group for the laying and burying of pipelines 10 according to the present invention, for supporting the pipeline, varies according to the depth and development of the trench effected by means of the relative device 11, in addition to the characteristics of the pipeline 15.

    [0032] The overall number of float devices 14 used during the whole laying and burying procedure is determined in relation to the physical characteristics of the pipeline 15 and burying depth.

    [0033] The physical characteristics of the pipeline 15 which effect the determination of the overall number of float devices 14 necessary are:
    • the weight, linked to the thickness of the tubular body of the pipe 15, generally made of steel, and its outer coating of cementitious material; and
    • the rigidity - also linked to the thickness of the steel body - which causes the lay back of the pipe and, together with the type of material used, its free span resistance limit.
    The float devices 14 used in the group 10 for laying and burying pipelines according to the present invention preferably comprise a rigid structure 17, made of steel for example, having an elongated conformation with a longitudinal development, to which at least one floating element 18 preferably made of a material having a lower density with respect to the density of the water, such as polyethylene shells for example, is integrally constrained.

    [0034] In the preferred conformation illustrated, the rigid structure 17 and the at least one floating element 18 form a sandwich structure in which the rigid structure 17 comprises two end walls 17a with respect to its longitudinal development, between which the at least one floating element 18 is interposed.

    [0035] Hooking means 19 to a pipeline 15 are envisaged in a peripheral position of the float device 14, which form a tubular seat which extends for the whole longitudinal development of the float device 14.

    [0036] Said hooking means 19 are preferably composed of a plurality of pairs of sickle-shaped arms 19a, 19b hinged to the rigid structure 17 and distributed along the whole longitudinal extension of the same 17, so as to form a tubular jaw structure.

    [0037] The opening and closing of the jaw structure 19a, 19b is piloted by means of hydraulic actuators or oil-dynamic pistons, such as for example hydraulic jacks, driven by the umbilical cable.

    [0038] In the interior of the tubular structure, the pairs of arms 19a, 19b preferably support a plurality of sliding blocks 21 having an elongated conformation and arranged parallel to each other, along the longitudinal extension of the rigid structure 17.

    [0039] Once the float device 14 has been hooked to the pipeline 15, it rests on the parallel sliding blocks 21 which allow it to slide with respect to the float device 14.

    [0040] The sliding surface of the sliding blocks 21 which is in contact with the pipeline 15 is preferably made of a low-friction material such as polytetrafluoroethylene (PTFE) or a wear-resistant steel. The float devices 14 also preferably comprise hooking means 22 to a caged transport structure 30 used for the positioning of each float device 14 hooked to the pipeline 15.

    [0041] The float devices 14 are removed, by means of the transport structure 30, from a storage base, for example situated on a supporting vessel (not illustrated), transported in correspondence with the pipeline 15 in the implementation phase and guided during the hooking phase to the pipeline 15 and to the float device 14 previously installed. In order to maintain a minimum reciprocal distance between two successive float devices 14, said float devices 14 comprise at least one rigid spacing means 23 protruding from the end walls 17a of the rigid structure 17.

    [0042] Furthermore, in order to control the position of the train of float devices 14 with respect to the digging device 11, at least the first float device 14 is equipped with braking means, consisting for example of a sliding block pressed onto the pipeline 15 overcoming the resistance of a spring. The activation of said braking means can be hydraulic.

    [0043] The activation of the braking means has the purpose for example of preventing the train of float devices 14 from coming too close to the cutting means 16 of the digging device 11.

    [0044] In order to establish the pipe supporting action from case to case, the float devices 14 are optionally equipped with ballasts 24 having a weight adequate for calibrating the force exerted by the float devices 14 on the pipeline 15.

    [0045] The functioning 100 of the group for laying and burying pipelines 10 is the following.

    [0046] Through the digging device 11 begins to create a trench at the sea bottom 20 in correspondence with the laying position of the pipeline 15 (phase 110).

    [0047] The first digging phase proceeds without any further interventions until the pipeline 15 is close to a "critical span" configuration, i.e. when the distance between the two rest points of the pipeline 15 is such as to create stress on the same 15 which could cause its collapse or deformation.

    [0048] Close to this critical span configuration, a first float device 14 is taken from a storage base and transported in correspondence with the pipeline 15 (phase 120).

    [0049] The first float device 14 is then constrained to the pipeline 15 in a rear position with respect to the digging device 11 and is connected to the same 11 (phase 130). As the portion of pipeline, which is in a suspended configuration, increases as the digging proceeds, further float devices 14 are taken in succession from the storage base and transported in correspondence with the pipeline 15 (phase 140).

    [0050] The successive float devices 14 are constrained to the pipeline and connected to the float device 14 previously installed (phase 150). A train of float devices 14 connected to the digging device 11 and constrained to the pipeline 15 is therefore gradually created in order to sustain it in its span configuration during the digging procedure on the part of the digging device 11. As the digging device 11 advances, the train of float devices 14 slides along the pipeline 15 in order to keep constant the reciprocal positioning between the digging device 11 and the first float device 14 situated in direct connection with the same 11.

    [0051] The group and method for the laying and burying of pipelines at the sea bottom according to the present invention therefore allow pipelines to be positioned in situ, with the subsequent and contemporaneous excavation of the sea bottom in order to bury them without them being subjected to stress due to the in span layout which is created as a result of the difference in level between the rest points of the pipeline created by the excavations. It is therefore possible to effect the excavations in a single passage or in a reduced number of passages at a great depth, thus reducing the overall implementation and burying times of the pipelines at the sea bottom.

    [0052] Finally, the group for the laying and burying of pipelines thus conceived can obviously undergo numerous modifications and variants, all included in the invention; furthermore, all the details can be substituted by technically equivalent elements. In practice, the materials used, as also the dimensions, can vary according to the technical demands.


    Claims

    1. A group for laying and burying pipelines at the seafloor, the group (10) comprising a trenching machine (11) provided at least with means for cutting into the seafloor (20), sediment suction and removal means (13) and with means for hooking onto a pipeline (15) and for sliding over it (15) in an advance direction; and a first float device (14), which comprises a rigid structure (17) extending in a longitudinal direction, the group being characterized in that the first float device (14) comprises at least one floating element (18) fixedly connected to the rigid structure (17) and configured to be fixed to said pipeline (15) to support it in span through the means for hooking to said pipeline (15) arranged at the peripheral portion of said first float device (14); wherein the first float device is directly connected to the back of the trenching machine (11) with respect to the advance direction through first connection means (12), the group comprising second float devices (14), which are connected to a float device (14) arranged in a position directly preceding in the advance direction of movement of said trenching machine so as to form a train of float devices (14).
     
    2. The group as claimed in claim 1, wherein the rigid structure (17) and the at least one floating element (18) form a sandwich structure, said rigid structure (17) comprising two end walls (17a) with respect to its longitudinal extension between which said at least one floating element (18) is arranged.
     
    3. The group as claimed in claim 1 or 2, wherein the hooking means (19) comprise a plurality of pairs of sickle-shaped arms (19a, 19b) hinged to the rigid structure (17) and distributed along the longitudinal extension of the rigid structure (17) so as to form a tubular jaw structure.
     
    4. The group as claimed in claim 3, comprising a plurality of hydraulic actuators for opening and closing the tubular jaw structure (19a, 19b).
     
    5. The group as claimed in claim 2 or 3, wherein the pair of arms (19a, 19b) supports a plurality of sliding blocks (21), having elongated configuration and arranged parallel to each other and parallel to the longitudinal extension of said rigid structure (17), inside said tubular structure.
     
    6. The group as claimed in claim 5, wherein the sliding blocks (21) have a sliding surface made at least partially from polytetrafluoroethylene.
     
    7. The group as claimed in any one of the claims from 2 to 6, wherein the first float device (14) comprises at least one spacing means (23) projecting from said end walls (17a) of said rigid structure (17).
     
    8. The group as claimed in any one of the foregoing claims, wherein at least the first float device (14) comprises brake means suitable for stopping the first float device (14) from sliding on said pipeline (15).
     
    9. A method for laying and burying pipelines at the seafloor, the method (100) comprising the step of:

    - making an excavation (110) in the seafloor in an advance direction along a pipeline (15) through a trenching machine (11) equipped with seafloor cutting means (16), sediment suction and removal means (13) and with means for hooking onto a pipeline (15) and for sliding over it (15) in an advance direction; the method being characterized by comprising the steps of:

    - picking up (120) a first float device (14) from a storage base and transporting it to said pipeline (15);

    - attaching (130) said first float device (14) to the pipeline (15) behind said trenching machine (11) with respect to said advance direction and connecting said float device (14) to said trenching machine (11), when at least one portion of pipeline (15) is in suspended configuration;

    - as said portion of pipeline (15) that is in suspended configuration increases, picking up (140) a second float device (14); and

    - attaching (15) the second float device (14) to said pipeline (15) and connecting it (14) to the first float device (14).


     


    Ansprüche

    1. Gruppe zum Verlegen und Vergraben von Rohrleitungen am Meeresboden, wobei die Gruppe (10) eine Grabenfräse (11) umfasst, die mindestens mit Mitteln zum Einschneiden in den Meeresboden (20), Mitteln zum Absaugen und Entfernen von Sedimenten (13) und mit Mitteln zum Einhaken in eine Rohrleitung (15) und zum Gleiten darüber (15) in einer Vorschubrichtung versehen ist; und eine erste Schwimmervorrichtung (14), die eine starre Struktur (17) umfasst, die sich in Längsrichtung erstreckt, wobei die Gruppe dadurch gekennzeichnet ist, dass die erste Schwimmervorrichtung (14) mindestens ein schwimmendes Element (18) umfasst, das fest mit der starren Struktur (17) verbunden und konfiguriert ist, um an der Rohrleitung (15) befestigt zu werden, um sie in Spannweite durch die Mittel zum Einhängen in die Rohrleitung (15) zu halten, die am peripheren Abschnitt der ersten Schwimmervorrichtung (14) angeordnet sind; wobei die erste Schwimmvorrichtung direkt mit der Rückseite der Grabenfräse (11) in Bezug auf die Vorschubrichtung durch erste Verbindungsmittel (12) verbunden ist, wobei die Gruppe zweite Schwimmvorrichtungen (14) umfasst, die mit einer Schwimmvorrichtung (14) verbunden sind, die in einer Position angeordnet ist, die unmittelbar vor der Vorschubrichtung der Grabenfräse liegt, um einen Zug von Schwimmvorrichtungen (14) zu bilden.
     
    2. Die Gruppe nach Anspruch 1, worin die starre Struktur (17) und das mindestens eine schwimmende Element (18) eine Sandwichstruktur bilden, wobei die starre Struktur (17) zwei Stirnwände (17a) in Bezug auf ihre Längserstreckung umfasst, zwischen denen das mindestens eine schwimmende Element (18) angeordnet ist.
     
    3. Die Gruppe nach Anspruch 1 oder 2, worin die Einhängevorrichtung (19) eine Vielzahl von Paaren von sichelförmigen Armen (19a, 19b) umfasst, die an der starren Struktur (17) angelenkt und entlang der Längserstreckung der starren Struktur (17) verteilt sind, um eine rohrförmige Backenstruktur zu bilden.
     
    4. Die Gruppe nach Anspruch 3, umfassend eine Vielzahl von hydraulischen Stellgliedern zum Öffnen und Schließen der rohrförmigen Backenstruktur (19a, 19b).
     
    5. Die Gruppe nach Anspruch 2 oder 3, wobei das Armpaar (19a, 19b) eine Vielzahl von Gleitstücken (21) trägt, die eine längliche Konfiguration aufweisen und parallel zueinander und parallel zur Längserstreckung der starren Struktur (17) innerhalb der rohrförmigen Struktur angeordnet sind.
     
    6. Gruppe nach Anspruch 5, worin die Gleitstücke (21) eine Gleitfläche aufweisen, die zumindest teilweise aus Polytetrafluorethylen besteht.
     
    7. Die Gruppe, wie sie in einem der Ansprüche von 2 bis 6 beansprucht wird, worin die erste Schwimmervorrichtung (14) mindestens ein Abstandsmittel (23) umfasst, das von den Stirnwänden (17a) der starren Struktur (17) vorsteht.
     
    8. Die Gruppe, wie sie in einem der vorstehenden Ansprüche beansprucht wird, wobei mindestens die erste Schwimmervorrichtung (14) Bremsmittel zum Verhindern des Gleitens der ersten Schwimmervorrichtung (14) auf der Rohrleitung (15) umfasst.
     
    9. Verfahren zum Verlegen und Vergraben von Rohrleitungen auf dem Meeresboden, wobei das Verfahren (100) den Schritt umfasst von:

    - Ausführen einer Ausgrabung (110) im Meeresboden in einer Vortriebsrichtung entlang einer Rohrleitung (15) durch eine Grabenfräse (11), die mit einem Meeresbodenschneidemittel (16), einem Sedimentabsaugmittel und Sedimententnahmemittel (13) und mit Mitteln zum Einhaken in eine Rohrleitung (15) und zum Gleiten darüber in einer Vortriebsrichtung ausgestattet ist, wobei das Verfahren dadurch gekennzeichnet ist, dass es die folgenden Schritte umfasst:

    - Aufnehmen (120) einer ersten Schwimmervorrichtung (14) von einer Speicherbasis und Transportieren derselben zu der Rohrleitung (15);

    - Befestigen (130) der ersten Schwimmervorrichtung (14) an der Rohrleitung (15) hinter der Grabenfräse (11) in Bezug auf die Vorschubrichtung und Verbinden der Schwimmervorrichtung (14) mit der Grabenfräse (11), wenn mindestens ein Abschnitt der Rohrleitung (15) in einer schwebenden Konfiguration ist;

    - wenn der Abschnitt der Rohrleitung (15), der sich in schwebender Konfiguration befindet, zunimmt, Aufnehmen (140) einer zweiten Schwimmervorrichtung (14); und

    - Befestigen (15) der zweiten Schwimmervorrichtung (14) an der Rohrleitung (15) und Verbinden derselben (14) mit der ersten Schwimmervorrichtung (14).


     


    Revendications

    1. Groupe destiné à poser et à enfouir des pipelines sur le fond océanique, le groupe (10) comprenant une machine de creusement de tranchées (11) pourvue au moins de moyens destinés à découper le fond océanique (20), des moyens d'aspiration et d'élimination de sédiment (13) et de moyens destinés à s'accrocher sur le pipeline (15) et à glisser sur celui-ci (15) suivant une direction d'avancement ; et un premier dispositif de flottaison (14) qui comprend une structure rigide (17) s'étendant suivant une direction longitudinale, le groupe étant caractérisé en ce que le premier dispositif de flottaison (14) comprend au moins un élément flottant (18) relié de manière fixe à la structure rigide (17) et configuré pour être fixé au dit pipeline (15) pour le supporter en longueur par l'intermédiaire des moyens destinés à s'accrocher au dit pipeline (15) disposé au niveau de la partie périphérique dudit dispositif de flottaison (14) ;
    dans lequel le premier dispositif de flottaison est relié directement à l'arrière de la machine de creusement de tranchées (11) par rapport à la direction d'avancement à travers les premiers moyens de connexion (12), le groupe comprenant des seconds dispositifs de flottaison (14), qui sont reliés à un dispositif de flottaison (14) disposé dans une position directement précédente dans la direction d'avancement de ladite machine de creusement de façon à former un train de dispositifs de flottaison (14).
     
    2. Groupe selon la revendication 1, dans lequel la structure rigide (17) et le ou les éléments flottants (18) forment une structure en sandwich, ladite structure rigide (17) comprenant deux parois d'extrémité (17a) par rapport à son prolongement longitudinal entre lesquelles ledit ou lesdits éléments flottants (18) sont disposés.
     
    3. Groupe selon la revendication 1 ou 2, dans lequel les moyens de fixation (19) comprennent une pluralité de paires de bras en forme de faucille (19a, 19b) articulés à la structure rigide (17) et répartis le long du prolongement longitudinal de la structure rigide (17) de façon à former une structure de mâchoire tubulaire.
     
    4. Groupe selon la revendication 3, comprenant une pluralité d'actionneurs hydrauliques pour ouvrir et fermer la structure de mâchoire tubulaire (19a, 19b).
     
    5. Groupe selon la revendication 2 ou 3, dans lequel la paire de bras (19a, 19b) supporte une pluralité de blocs coulissants (21) ayant une configuration allongée et disposés de manière parallèle les uns aux autres et parallèle au prolongement longitudinal de ladite structure rigide (17), à l'intérieur de ladite structure tubulaire.
     
    6. Groupe selon la revendication 5, dans lequel les blocs coulissants (21) ont une surface coulissante réalisée au moins en partie à partir de polytétrafluoroéthylène.
     
    7. Groupe selon l'une quelconque des revendications 2 à 6, dans lequel le premier dispositif de flottaison (14) comprend au moins un moyen d'espacement (23) faisant saillie à partir desdites parois d'extrémité (17a) de ladite structure rigide (17).
     
    8. Groupe selon l'une quelconque des revendications précédentes, dans lequel au moins le premier dispositif de flottaison (14) comprend des moyens de frein appropriés pour arrêter le premier dispositif de flottaison (14) de glisser sur ledit pipeline (15).
     
    9. Procédé pour poser et enfouir des pipelines sur le fond océanique le procédé (100) comprenant :

    - la réalisation d'un excavation (110) dans le fond océanique suivant une direction d'avancement le long du pipeline (15) par l'intermédiaire d'une machine de creusement de tranchées (11) équipée de moyens destinés à découper le fond océanique (16), de moyens d'aspiration et d'élimination de sédiment (13) et de moyens destinés à s'accrocher sur un pipeline (15) et à glisser sur celui-ci (15) suivant une direction d'avancement ; le procédé étant caractérisé par :

    - la saisie (120) d'un premier dispositif de flottaison (14) à partir d'une base de stockage et son transport vers ledit pipeline (15) ;

    - la fixation (130) dudit premier dispositif de flottaison (14) au pipeline (15) derrière ladite machine de creusement de tranchées (11) par rapport à ladite direction d'avancement et la connexion dudit dispositif de flottaison (14) à ladite machine de creusement de tranchées (11), quand au moins une partie du pipeline (15) est dans une configuration suspendue ;

    - au fur et à mesure que ladite partie de pipeline (15) qui est dans une configuration suspendue augmente, la saisie (140) d'un second dispositif de flottaison (14); et

    - la fixation (15) du second dispositif de flottaison (14) au dit pipeline (15) et sa connexion (14) au premier dispositif de flottaison (14).


     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description