IE42271B1 - Apparatus and method for digging a trench below a submerged pileline or cable - Google Patents

Abstract

1492151 Sub sea trench excavators SAIPEM SpA 11 Feb 1976 [11 Feb 1975] 05468/76 Heading E1F Submersible apparatus 1 that is advanceable stepwise in either direction along a submerbed pipeline 49 or like elongate member to dig a trench beneath the member comprises at least two longitudinally extending support members 31; two hoods 5 carried at opposite end regions of the support members and each having an open downward facing region; two sleeves carried one on each hood and each being formable from two arcuate elements, e.g. sectors 2, 3, capable of undegoing relative movement between a first position in which the sleeve is completed and second position in which the arcuate elements do not obstruct entry of the elongate member into the downward facing region of the hood on the apparatus descending onto the elongate member; two annular members each carried by a sleeve and each being formable from two arcuate cutter-carrying members e.g. sectors 4, 7, corresponding to and capable of being carried by the two arcuate elements respectively; first means 8, 29 for causing relative movement of the arcuate elements and arcuate members to complete full sleeves; second means 30 for causing rotation of the completed annular members with respect to the completed sleeves; and at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate element 49 or to move along the element. As shown one of the sleeve-forming arcuate elements 2, 3 is rotatably mounted on the hood 5 and can be rotated through 180‹ around the hood whilst the other element 3 is longitudinally slidable of the hood and can be so moved by ram 8 to enter the jaws of the element 2, when the element is covering the downwardly directed opening of the hood 5, to complete the sleeve and circumferentially align the arcuate, cuttercarrying members 4, 7, which can then be rotated around the sleeve by a motor 30 and a pinion 64 and gear ring associated with the members 4, 7. In a second embodiment the members 4, 7, comprise two half sleeves pivoted together in a region atop the hood 5. Material cut out of the trench by cutters e.g. roller cutters 27, 28 carried by the members 4, 7 is removed from the trench by suction pipes 52.

Description

This invention relates to an apparatus for digging a trench beneath a submerged pipeline or other elongate element.

It is known that the digging of a subsea trench is necessary for protecting a pipeline on the sea bed from the detrimental effects of crushing and breakage which may be caused by the anchors of ships.

. According to the present invention there is provided an apparatus for digging a trench beneath a submerged pipeline, cable or other elongate element, which apparatus comprises: W at least two longitudinally-extending support members; two hoods carried at opposite end regions of the support members, the hoods having an open downward-facing region; two sleeves, one carried on each hood, each sleeve being formable from two arcuate elements capable of undergoing relative movement 15 between a first position in which the sleeve is completed and a second position in which the arcuate elements do not obstruct entry of an elongate element into the downward-facing region of the hood; 2. two annular members, one carried by each sleeve and each carrying bits, each annular member being formable from two arcuate members corresponding to, and capable of being carried by, the two arcuate elements respectively; first means for causing relative movement of the arcuate elements and arcuate members to complete full sleeves and full annular members surrounding an elongate element; second means for causing rotation of the completed annular members with respect to the completed sleeves; and at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate element or to move along the elongate element; the arrangement of the apparatus being such that, when an apparatus straddles an elongate element, the first means can be actuated to cause formation of the complete annular members, the second means can be actuated to cause rotation of the annular members with respect to the sleeves to effect digging, and the clamping devices can be actuated to permit the apparatus to travel in either direction along the elongate element to dig the trench below the elongate element.

The apparatus may be driven by engines having an independent power source or receiving power through cable from surface ships. The apparatus can follow the path of the digging to be carried out beneath a laid pipeline in that the supporting members for the bits which crush and disaggregate the kind of ground from which the sea bed is composed, completely surround the pipeline. The apparatus, furthermore, can be stabilized so as to maintain its transversal trim which may possibly have been varied during the advance of the apparatus. The apparatus is also equipped with two digging mechanisms each of which is provided with an annular member which 3. is rotated, either centrally or eccentrically, about the laid pipeline and may have cone or roller bits equipped with teeth which are adapted to abate any kind of minerals, even in rock form, which makes up the sea bed, which is encountered as the apparatus is advanced, and is, moreover, ; designed to perform the digging operation in either direction of advance of the apparatus in a direction parallel to the longitudinal axis of the laid pipeline. In addition the rotation of the bit-carrying annular member placed at either end of the apparatus is encouraged, in order to complete the digging, by the rotation in the opposite direction of the other bit-carrying annular member at the opposite end of the apparatus and the rotation of which in the opposite direction additionally cooperates towards stabilizing the apparatus on the plane transversal to the longitudinal axis of the laid pipeline.

Furthermore, the advance of the apparatus in either direction is effected concurrently with the operation of stabilizing the apparatus. The'apparatus is initially moved, in the direction of the digging, by the thrust of, for example, two first hydraulic jacks, which are attached on one side to the support members of the apparatus and on the other side to a sliding bridge, which is attached to the support member by means of two sliders. The bridge supports, by means of a guideway, a first set of cl amps, is placed both, on the sides as Well as on the top Of the pipeline and is tightened by two hydraulic jacks and a torsion bar about the pipeline, a second set of clamps being first released. As soon as the two first jacks have finished, urging the two support members, and hence also the annular members, in the direction of digging whilst the first set of clamps were tightened about the pipeline, the second set of clamps is tightened about the pipeline and, immediately after the first set of clamps 4. is clear of the pipeline, the relative first thrust jacks begin the recovering stage. Then the second set of clamps is tightened about the pipeline, through the action of a hydraulic jack placed in the plane transverse to the pipeline and driven by a mechanism governed by a sensor which measures the deflection of the digging apparatus from its normal vertical position. By this means, the second set of clamps imposes, with a rotary movement transverse to the longitudinal axis of the pipeline, a rotational movement on a guide on the bridge, which is connected to the support members and hence the annular members. The guide is connected to the clamps which are tightened about the pipeline, until the bridge is disposed again, should it have been unbalanced, in the normal vertical position of advance. The apparatus for digging a trench according to the present invention thus acquires again its normal trim on the plane transversal to the pipeline, which stabilizing operation occurs during the entire advance of the apparatus along the path of the laid pipeline, whenever the trim has undergone a change.

When conversely, the direction of advance of the apparatus according to the present invention is reversed, the advance of the apparatus is carried out by the thrust of two additional hydraulic jacks which act, on one side, on the support member of the apparatus and, on the other side, via the bridge on the sliders and the guide of the second set of clamps which are tightened onto the pipeline and which, when the apparatus advanced in the opposite direction, were tightened about the pipeline by the agency of the transversal jack to stabilize the apparatus. In contrast, the second set of clamps is now intended only for the operation of advancing the pipeline in the direction opposite to the one described hereinbefore, with the first set of clamps being tightened around the pipeline by the transverse jack, and serving only for stabilizing the apparatus.

. The bridge pins, during the advance of the apparatus along the laid pipeline, have the function of eliminating any defective tightening of the clamps on the pipeline which has been laid whenever the pipeline follows a non-recti linear path, the result otherwise being a misalignment between the pipeline and the machine in the longitudinal direction.

According to one embodiment of the present invention, there is provided an apparatus for digging a trench beneath a submerged pipeline, cable or other elongate element, which apparatus comprises:at least two longitudinally-extending support members; two hoods carried at opposite end regions of the support members and each having a cross-section resembling an arc of a circle, the open portion of each hood being downward facing; two minor arcs of two sleeves, mounted on the hoods and capable of movement relative to the hoods in the longitudinal direction; two major arcs of the two Sleeves, mounted on the hoods and capable of movement relative to the hoods in a peripheral direction; two annular members each carrying digging bits and each formed or formable from a minor arc and a major arc, the minor and major arcs of the annular members corresponding to, and being capable of being carried by the minor, and major arcs of the sleeves; first means for causing movement of the two major arcs of the two sleeves around the periphery of the hoods; second means for causing movement of the two minor arcs of the two sleeves longitudinally along the hoods; third means for causing rotation of the annular members when assembled with respect to the sleeves when assembled; and 6. 2 2 71 at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate element or to move along the elongate element; the arrangement of the apparatus being such that, when the apparatus straddles an elongate element, the first means can be actuated to cause the major arcs of the sleeves conveying the major arcs of the annular members to move from generally above the hood to generally below the hood, the second means can be actuated to cause the minor arcs of the sleeves carrying the minor arcs of the annular members to move along the hoods to complete the sleeves and annular members, which now surround the elongate element, the third means can be actuated to cause the bit-carrying annular members to rotate with respect to the sleeves to effect digging, and the clamping devices can be actuated to permit the apparatus to travel in either direction along the elongate element to dig the trench below the elongate element.

The hoods partially surround the pipeline as the apparatus settles astride the pipeline. The ends of the hoods can be partially closed by shields which tend to prevent the entrance of digging debris between the hood and the elongate element, this operation being facilitated by a set of ejectors which surround the shields, the latter being equipped with wheels which accompany the longitudinal motion of the apparatus as the latter is pushed by the jacks along the pipeline during the sea bottom digging operation. The major arc is also initially inverted and, once the apparatus has gone astride the pipeline, undergoes half a revolution, by the agency of the first means which may be a hydraulic motor, arranged on the fixed hood and equipped with a pin meshing with a hook arranged on the major arc. Thus the major arc now has its open region uppermost, the circle being immediately completed by a minor arc sliding on longitudinal 7. guides of dovetail cross-section arranged on the fixed hood, which minor arc is caused to move by the thrust of the second means which may be a jack, longitudinally on the fixed hood. By so doing, there is formed a sleeve describing a complete circle which remains stationary relative to the hood during the advance of the apparatus in digging, and which supports the annular member rotatable thereon, which describes a complete circle and which was initially split up, before the thrust of the jack placed longitudinally on the fixed hood, into a major and a minor arc which were fastened respectively on the major and the minor arc of the sleeve.

The bit-carrying annular member thus formed rotates, during the advance of the apparatus, on circumferential guides preferably with a dovetail cross-section on the sleeve and receives its drive from the third means which may be'a hydraulical motor arranged on the minor arc of the sleeve.

According to an alternative embodiment of the present invention there is provided an apparatus for digging a trench beneath a submerged pipeline, cable or other elongate element, which apparatus comprises:at least two longitudinally-extending support members; two hoods carried at opposite end regions of the support members, the hoods having an open downward-facing region; two sleeves one carried on each hood, each sleeve being formable from two half-sleeves pivotted together in a region atop the hood; two annular members, one carried by each sleeve and each carrying bits, each annular member being formable from two half-annular members pivotted together and carried by the two half-sleeves; 8. 2271 first means for causing pivotal movement of the halfsleeves and half-annular members to complete full sleeves and full annular members surrounding an elongate element; second means for causing rotation of the completed annular members with respect to the completed sleeves; and at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate element or to move along the elongate element; the arrangement of the apparatus being such that, when an apparatus straddles an elongate element, the first means can be actuated to cause formation of the complete annular members, the second means can be actuated to cause rotation of the annular members with respect to the sleeves to effect digging, and the clamping device can be actuated to permit the apparatus to travel in either direction along the elongate element to dig the trench below the elongate element.

Conveniently each of the clamping devices comprises an arcuate bridge mounted on silders which can travel in either direction on the supporting members, and an arcuate guide which is rotatable with respect to the arcuate bridge by hyraulic means and which supports an upper clamp and side clamps.

According to a further feature of the invention, one of the two groups of clamps, which is tightened about the pipeline, serves as a thrust base for the jack which imparts the motion, through the support members, to the digging apparatus. The other group of clamps which is freed during the motion of the first group of Clamps, is then tightened about the pipeline as the first groups of clamps is released and serves to restore, at the end of every stroke of the thrust jack, the transverse trim of the apparatus. 9.

These functions are performed by the two sets of clamps, which may be operated hydraulically when the digging apparatus is moved in one of the two possible directions of motion along the laid pipeline; when the apparatus, on completion of the first digging pass, reverses its direction of motion to start the second digging pass, the functions of the clamps are reversed. Each set of clamps is arranged, to provide a reliable tightening, along with the best distribution of forces about the pipes, so that the outer lining of the pipes does not suffer any damage. For this reason four clamps are arranged pair-wise beneath each support member and are actuated by means of double acting pistons.

Conveniently the upper clamp of each clamping device is designed to distribute over a wide surface of the elongate element that upward vertical component of force produced by the side clamps.

According to another feature of the invention, the digging of 15 a trench is generally carried out in several passes, a pass being intended to mean the entire length of the trench to be dug beneath the pipes at a depth governed by the height of the bit-carrying annular member.

Preferably the apparatus also includes torsion bars connected to the upper clamp which urges rolling wheels downwardly to about an elongate element when present.

Also provided may be passageways, drilled on the other circumference of the bit-carrying annular members, which passageways serve for the flow of debris resulting from the crushing of the material on the sea bed, towards the mouths of the suction pipes equipped with the ejectors as dis25 closed in the British Patent No. 1 399 892.

According to one embodiment of the present invention the digging bits each have a conical shape and are mounted freely rotatably along two concentric circles adjacent the periphery of each annular member, with the . digging bits on the outermost circle having their axis inclined towards the axis of the annular member in a region beyond the annular member.

Conveniently the digging bits on the innermost circle have their axis disposed radially with respect to the axis of the annular members.

Furthermore the mounting of the apparatus according to the present invention astride the pipeline, followed by the operations for completing the sleeves and the bit-carrying annular members, can be carried out either by directly positioning at the out-set, the digging apparatus on the pipeline the trim of which is maintained by a compressed air and arranged atop the apparatus and then by reservoir having balancing compartments drawing in, through the suction pipes, the sludge and sand which form the material of the sea bed so as to provide the space which is required for setting up the sleeves and the complete annular members; or by lifting the pipeline off the rocky sea bed by means of a mechanism as already disclosed in Patent No. 39038 and then placing the digging apparatus astride the thus lifted pipeline, and setting up the sleeves and the bitcarrying annular members before beginning to move the apparatus machine in the desired direction and starting the rotation of the bit-carrying annular members.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:Figures la, 2a and 3a are side views of an apparatus according to the present invention, being arranged on a submerged pipeline; Figures lb, 2b and 3b are corresponding views towards one end of the apparatus shown in Figures la, 2a and 3a; Figure 4 is a view from above of the same apparatus. 11.

Figure 5 is a side elevation of one half of the same apparatus, the other half being a mirror image of the illustrated half; Figure 6 is mainly a vertical section through one end region of the apparatus, showing a hood, a sleeve and an annular member; Figure 7 is a view from above of either end of the apparatus, but with the bits on the annular member omitted for clarity, during positioning of the annular member; Figure 8 is a side view, partly in section, of the hood at either end of the pipe, and part of the sleeve prior to positioning of the annular member; Figure 9 is a cross-sectional view taken along the line A-A of Figure 6; Figure 10 is a cross-sectional view taken along the line B-B of Figure 6; Figure li shows diagrammatically the eccentric mounting of the annular member on the pipe, together with a shield with ejectors and guiding wheels; Figure 12 is an end view towards the major and minor sectors of the bit-carrying annular member; Figure 13 shows a view towards one end of the completed annular member; Figures 14 and 15, which are radial sectional views, show two different types of bits to be mounted on the annular member; Figure 16 shows di agrairmati cally the relative orientation of the two bits; Figure 17 is a side view of a portion of a top clamp to which a guide is welded, abutting a pipe; 12. 42371 Figure 18 is a front view of the arrangement shown in Figure 17; Figure 19 is a view from above of the arrangement shown in Figure 17; Figure 20 is a longitudinal sectional view of the top clamp and the guide of Figure 17; Figure 21 is a side view, looking parallel to the axis of the pipe, of one of two bridges, pivotally mounted on two support members; Figure 22 is a longitudinal sectional view of a bridge in engagement with a guide welded to a top clamp; Figure 23 is a side view of a side clamp and a portion of a top clamp; Figure 24 is a cross-sectional view taken along the line C-C of Figure 23 and shows the side clamp together with the clamp to which it is matched for tightening the apparatus on the pipe; Figure 25 is a top view of the arrangement shown in Figure 24; and Figure 26 is a side elevation view of the torsion bar for lifting the top clamp of the arrangement of Figures 23 to 25.

Referring firstly to Figures la to 3b, there is shown the apparatus generally indicated by the reference numeral 1 and its relationship to a pipe 49. The apparatus 1 includes a buoyancy tank 56 for adjusting the trim and buoyancy of the apparatus, and two clamps 61 and 62, each with two jaws for clamping the apparatus 1 to the pipe 49. Also provided are four tubes 52 for sucking in material from the sea bed 57. Shown in Figure 3b is a bit-carrying annular member 12 but in Figures lb and 2b only a major sector 7 of the annular member 12 is shown. Also included is a container 54 which houses electric motors (not shown) which receive power 13. via a cable 60 coming from a surface vessel. The annular members 12 are. powered by hydraulic motive means (not shown) which in turn are driven by the electric motors.

In Figures la and lb the jaws of the clamps 61 and 62 5 are wide open and the major sectors 7 of the annular members 12 each have their open region pointing downwards. The apparatus 1 is lowered onto the pipe 49 with the jaws straddling the pipe 49. The jaws of the clamps 61 and 62 close in on the pipe 49, and the tubes 52 are used to suck in the material of the sea bed 57, which may be sandy or muddy, to provide the space required to complete the annular members T2. Then with the annular members 12 completed, the latter can commence digging to form the trench 58 shown in Figures 3a and 3b.

The buoyancy tank 56 stabilizes the apparatus 1 during the lowering of the apparatus from a surface vessel and during the advance15 ment of the apparatus along the pipe: > As is shown in Figure 5, the apparatus 1 includes two support members 31 (only one of which is shown) which are parallel and spaced-apart in the same horizontal plane. These support members 31 are connected at their opposite ends to the mechanism for carrying out the digging, and support in a central region the mechanism for stabilizing the apparatus and advancing the same along the pipe.

Part of the digging machinery is most clearly shown in Figures 5 to 10.

Carried by the two support members 31 are two fixed hoods 5, one at each end of the apparatus. Each hood 5 has a crosssection resembling an arc of a circle and has the open portion directed downwardly. 14.

Each hood 5 is provided with two outwardly directed ' circumferential male guides 16 of generally dovetailed shape, and each hood 5 carries a sleeve 11 formed of a major sector 2 and a minor sector 3.

The major sector 2 has two inwardly directed circumferential female guides of generally dovetailed shape in which are accommodated the male guides of the hood. The hood 5 carries a hydraulic motor 29 having a pinion 6 which engages a ring gear integral with the major sector 2 of the sleeve 11, to enable the major sector 2 to be rotated about the hood 5.

Along the top of each hood 5 are two longitudinally10 extending female guides 9 of generally dovetailed shape, and the minor Sector 3 of each sleeve 11 is provided with two corresponding male guides, to enable the minor sector 3 to be moved longitudinally with respect to the hood 5.

Carried on the top of each hood 5 is a ram 8 having a 15 piston rod connected to the minor section 3 of the sleeve 11, to effect longitudinal movement of the minor sector 3.

The annular member 12 is formed of a minor sector 4 and the major sector 7 corresponding respectively to the minor sector 3 and the major sector 2 of the sleeve 11. The sleeve 11 is formed with two concentric, dovetail-shaped, female guides on its outer end face in which are located two corresponding male guides 22 (shown in Figure 6) carried by the annular member 12, to permit rotation of the latter relative to the sleeve 11.

Additionally each hood 5 is fixed to a shield 17 (shown in Figure 6) provided with a set of wheels 19 to assist movement of the apparatus 1 along the pipe 49.

The major sector 2 of sleeve 11 can rotate about the hood from an initial position in which the opening of the major sector 2 faces downwards to a position in which that opening faces upwards. In this latter . 42371 position the major sector 2 can be locked against further rotation by means of a pin 23 extending between major sector 2 and hood 5, as shown in Figure 5.

The major sector 2 of the sleeve 11 can be locked 5 relative to the major sector 7 of the annular member 12 by means of a pin . Similarly the minor sector 4 of the annular member 12 can be locked relative to the minor sector 3 of the sleeve 11 by means of a pin 26.

Mounted on the minor sector 3 is a hydraulic motor 30 provided with a pinion 64 which engages a ring gear carried by the annular member 12, so that when pins 25 and 26 are not in the locking position, the motor 30 can cause rotation of the annular member 12.

Also shown in Figure 5 are various passageways 59 in the annular member 12 to allow debris to be removed from the cutting area; and a shield 63 carried by the annular members 12 for protecting the pipe 49 from debris. Figure 5 also shows two of the bits mounted on the annular member, bit 28 being one of six bits mounted on an inner circle and bit 27 being one of six bits mounted on an inner circle and bit 27 being one of six bits mounted on an outer concentric circle, the disposition of these bits being more clearly shown in Figures 12 and 13.

In addition Figure 5 shows one of four ejectors 53 for sucking up material via the pipe 52 and for discharging the material through outlets 55. The materials loosened by the bits 27 and 28, are drawn via the passageways 59 to the tubes 52 and from there via the ejectors 53 to the outlets 55.

A further pin shown in Figure 5 is that numbered 24 which locks the minor sector 3 of the sleeve 11 to the hood 5 when the minor sector 3 has travelled sufficiently to bring the minor sector 4 into line with the major sector 7. 16. 43271 Before describing the remaining components shown in Figure 5, the method of completing the annular member will now be described. Assume that the minor sector 3 is in the position shown in Figure 7 with the piston retracted inside the ram. Assume also that the major sector 7 of the annular member 12 has the opening downwards as shown in Figure lb. The apparatus 1 is lowered as shown in Figures la, lb, 2a and 2b over the pipe 49. The motor 29 is then actuated to cause rotation of the major portion 2 of the sleeve 11 and hence rotation of the major portion 7 of the annular member, through 180°. The major portion 2 of the sleeve is then locked in position relative to the hood 5 by means of the pin 23. The ram 8 is then actuated to cause the minor sector 3 and hence the minor sector 4 to move to the right until the minor sector 4 is in line with the major sector 7, whereupon the pin 24 is moved to lock the minor sector 3 relative to the hood 5. At this point the pins 25 and 26 can be withdrawn from their locking positions to leave the annular member 12 free to rotate. During longitudinal movement of the minor sector 4, dovetailshaped male guides 13 entered corresponding female guides in the major sector 7 and come to rest against the blind ends of these female guides, to form securely the annular member 12. When the motor 30 is actuated, the annular member 12 is caused to rotate about the sleeve 11, The pins 23, 24, 25 and 26 can be controlled automatically from a remote position, such as a surface vessel, by means not shown.

Before describing the remaining components in Figure 5, which correspond to the components shown in Figures 17 to 25 inclusive, the components in Figures 11 to 15 will be described.

Figure 11 shows diagrammatically the eccentric mounting of the annular member 12 on the pipe 49, the former having its axis at the 17. 42371 point 51 and the latter having its axis at the point 50. Also shown is the shield 17 with three wheels 19. Also shown are ten ejectors 18, one of which is shown in Figure 6, for preventing the digging debris from entering the inner region of the hood 5 (shown in Figure 6 but not in Figure 11).

Figure 12 shows the minor sector 4 and major sector 7 of the anhular member 12 in exploded form. The minor sector 4 carries these bits, in fact one bit 27 and two bits 28; and the major sector 7 carries nine bits, in fact five bits 27 and four bits 28. The bits 28 lie on a circle and the bits 27 lie on a larger concentric circle, as is more clearly shown in Figure 13 which shows the annular member 12 in assembled form. Also shown in Figures 12 and 13 are the passageways 59 to allow debris from the digging to pass to the tubes 52. Figure 14 shows the mounting of one bit 28 relative to the shield 63, and Figure 15 shows the mounting of-the other type of bit 27, the relative mounting positions of the two bits being as shown in Figure 16.

Turning now to the remaining components shown in Figure 5, the two support members 31 each support a slider 32 capable of sliding longitudinally with respect to the support member 31. Spanning the pipe 49 is a bridge 34 pivotally mounted at its ends in the sliders 32 by means of pins 33 (shown in Figure 21). Linked to the bridge 34 is a top clamp 39 on which are mounted arms 42 bearing side clamps 41, two on each side of the pipe 49. The top clamp 39 is strengthened by a longitudinally extending stiffening ridge 38. Also included is a jack 48, the cylinder end of which is secured to one support member 31 and the piston rod of which is secured to the bridge 34 in a manner such as to permit longitudinal displacement of the bridge 34 and sliders 32 relative to the support members 31. 18. 43271 The clamps 41 can be urged towards the side regions of the pipe 49 by the arms 42, and the clamp 39 is also urged towards the pipe 49 under these conditions. Otherwise the combination of wheels 45 and torsion bars 46 tends to keep the top clamp 39 just clear of the pi pe 49.

Also provided is a jack 40 which extends between one support member 31 and a guide 35 (not shown in Figure 5, but shown in Figures 17, 18, 19 and 20) welded to the top clamp 39, which jack 40 can be driven by a sensor (not shown) responsive to any departure from the vertical (in cross-section of the apparatus 1) of the bridge 34, to ensure that the majority of the apparatus 1 can assume the vertical even if the clamps 39 and 41 are displaced from that position in which the top clamp 39 is exactly at the top.

Figure 17 shows clearly a side view of a portion of the top clamp 39 above the pipe 49. Welded to the top clamp 39 is the guide 35 which is provided with two opposing inwardly directed flanges 37 (see Figure 20) of arcuate configuration. These flanges 37 are located in two grooves 36 on the opposite faces of the bridge 34, thus permitting oscillatory motion between the bridge 34 and guide 35.

The arms 42 are pivotally mounted by pins 43, shown in Figures 22 and 24, extending through opposite end regions of the guide 35 and are pivotally linked to a jack 44 shown in Figures 24, 24 and 25 which upon expansion causes the clamps 41 to seize the pipe 49 and upon retraction causes the clamps 41 to withdraw well clear of the pipe 49.

The bridge and clamping arrangement shown in Part of Figure 5 and in Figures 17 to 26 can be regarded as the clamp 62 shown in Figure la; it will be appreciated that there is also present in the apparatus 19. 42371 a further similar bridging and clamping arrangement as shown by clamp 61 in Figure la.

It will be appreciated that with clamp 61 firmly gripping the pipe 49, the other clamp 62 and the rest of the apparatus 1 can be advanced along the pipe 49, after which with clamp 62 now gripping the pipe 49 the first clamp 61 can be released and moved towards the clamp 62.

With the jack 44 retracted the clamps 41 are clear of the pipe 49, and the torsion bar 46 urges the wheel 45 through a slot in the clamp 39 to urge the latter away from the pipe 49. Actuation of the jack 48 then causes the bridge 34, sliders 32 and clamps 39 and 41 to be moved relative to the support members 31. Then the jack 44 can be expanded to lock the clamps 39 and 41 to the pipe 49. Then, with the clamps of the other bridging and clamping arrangement free of the pipe 49, the jack 48 can be retracted to cause the support members 31 and the majority of the apparatus to be moved to the right in Figure 5. After which all the clamps can be moved to grip the pipe 49, to enable drilling to occur in the new positions.

Should the apparatus adopt a position other than vertical, the jacks 40 can be actuated to bring the apparatus back to the vertical position.

Claims (21)

1. An apparatus for digging a trench beneath a submerged pipeline, cable or other elongate element, which apparatus comprises: 25 at least two longitudinally-extending support members; two hoods carried at opposite end regions of the support members, the hoods having an open downward-facing region; 20. 42371 two sleeves, one carried on each hood, each sleeve being formable from two arcuate elements capable of undergoing relative movement between a first position in which the sleeve is completed and a second position in which the arcuate elements do not obstruct entry of an elongate element into the downward-facing region of the hood; two annular members, one carried by each sleeve and each carrying bits, each annular member being formable from two arcuate members corresponding to, and capable of being carried by, the two arcuate elements respectively; first means for causing relative movement of the arcuate elements and arcuate members to complete full sleeves and full annular members surrounding an elongate element; second means for causing rotation of the completed annular members with respect to the completed sleeves; and at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate element or to move along the elongate element; the arrangement of the apparatus being such that, when an apparatus straddles an elongate element, the first means can be actuated to cause formation of the complete annular members, the second means can be actuated to cause rotation of the annular members with respect to the sleeves to effect digging, and the clamping devices can be actuated to permit theapparatus to travel in either direction along the elongate element to dig the trench below the elongate element.

2. An apparatus for digging a trench beneath a submerged pipeline, cable or other elongate element, which apparatus comprises:at least two longitudinally-extending support members; 21, two hoods carried at opposite end regions of the support members and each having a cross-section resembling an arc of a circle, the open portion of each hood being downward facing; two minor arcs of two sleeves, mounted on the hoods and 5 capable of movement relative to the hoods in the longitudinal direction; two major arcs of the two sleeves, mounted on the hoods and capable of movement relative to the hoods in a peripheral direction; two annular members each carrying digging bits and each formed or formable from a minor arc and a major arc, the minor and major arcs 10 of the annular members corresponding to, and being capable of being carried by, the minor and major arcs of the sleeves; first means for causing movement of the two major arcs of the two sleeves around the periphery of the hoods; second means for causing movement of the two minor arcs of 15 the two sleeves longitudinally along the hoods; third means for causing rotation of the annular members when assembled with respect to the sleeves when assembled; and at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate 20 element or to move along the elongate element; the arrangement of the apparatus being such that, when the apparatus straddles an elongate element, the first means can be actuated to cause the major arcs of the sleeves conveying the major arcs of the annular members to move from generally above the hood to generally below the hood, 25 the second means can be actuated to cause the minor arcs of the sleeves carrying the minor arcs of the annular members to move along the hoods to complete the sleeves and annular members, which now surround the elongate 22. 43271 element, the third means can be actuated to cause the bit-carrying annular members to rotate with respect to the sleeves to effect digging, and the clamping devices can be actuated to permit the apparatus to travel in either direction along the elongate element to dig the trench below the elongate element.

3. An apparatus for digging a trench beneath a submerged pipeline, cable or other elongate element, which apparatus comprises; at least two longitudinally-extending support members; two hoods carried at opposite end regions of the support members, the hoods having an open downward-facing region; two sleeves, one carried on each hood, each sleeve being formable from two half sleeves pivoted together in a region atop the hood; two annular members, one carried by each sleeve and each carrying bits, each annular members pivoted together and carried by the two half-sleeves; first means for causing pivotal movement of the half-sleeves and half-annular members to complete full sleeves and full annular members surrounding an elongate element; second means for causing rotation of the completed annular members with respect to the completed sleeves; and at least two clamping devices carried by the supporting members and capable of causing the apparatus to clamp on to the elongate element or to move along the elongate element; the arrangement of the apparatus being such that, when an apparatus straddles an elongate element, the first means can be actuated to cause formation of the complete annular members, the second means can be actuated to cause rotation of the annular members with respect to the sleeves 23. 42371 to effect digging, and the clamping device can be actuated to permit the apparatus to travel in either direction along the elongate element to dig the trench below the elongate element.

4. An apparatus according to claim 2, wherein the first means is a hydraulic motor.

5. An apparatus according to any preceding claim, wherein the second means is a jack.

6. An apparatus according to claim 2, 4 or 5, wherein the third means is a hydraulic motor.

7. An apparatus according to any one of claims 2, 4, 5 and 6, wherein arcuate guides of dovetail cross-section permit movement between the hoods and the major arcs of the sleeves.

8. An apparatus according to any one of claims 2, 4, 5, 6 and 7, wherein longitudinal guides of dovetail cross-section permit movement between the hoods and the minor arcs of the sleeves.

9. An apparatus according to any preceding claim, wherein the digging bits each have a conical shape and are mounted freely rotatably along two concentric circles adjacent the periphery of each annular member, with the digging bits on the outermost circle having their axis inclined towards the axis of the annular member in a region beyond the annular member.

10. An apparatus according to claim 9, wherein the digging bits on the innermost circle have their axis disposed radially with respect to the axis of the annular member.

11. An apparatus according to any preceding claim, wherein the clamping devices are capable of being operated hydraulically.

12. An apparatus according to any preceding claim, wherein each of the clamping devices comprises an arcuate bridge mounted on sliders which can travel in either direction on the supporting members, and an arcuate 24. 4 2 271 guide which is rotatable with respect to the arcuate bridge by hydraulic means and which supports an upper clamp and side clamps.

13. An apparatus according to claim 12, wherein the side clamps are actuatable pairwise by means of double acting pistons.

14. An apparatus according to claim 12 or 13, which also includes torsion bars connected to the upper clamp which urge rolling wheels downwardly to abut an elongate element when present.

15. An apparatus according to claim 12, 13 or 14, wherein the upper clamp of each clamping device is designed to distribute over a wide surface of the elongate element that upward vertical component of force produced by the side clamps.

16. An apparatus according to any preceding claim, wherein at least one of the clamping devices is capable of serving as a thrust base for a jack which can impart relative longitudinal motion to the remainder of the apparatus.

17. An apparatus according to any preceding claim, wherein at least one of the clamping devices is capable of restoring the trim of the remainder of the apparatus.

18. An apparatus according to any preceding claim, wherein each annular member is provided with passageways to allow debris to flow towards the mouth of suction pipes for clearing the debris.

19. An apparatus according to any preceding claim, which includes shields arranged at the ends of the apparatus on the annular members, to prevent the entrance of digging debris between the hoods and the elongate element.

20. An apparatus according to any preceding claim, wherein the apparatus includes a compressed air reservoir, and means associated therewith for maintaining the apparatus at a desired level. 25. 4237 1

21. An apparatus according to claim I, substantially as hereinbefore described with reference to, and/or as illustrated in, the accompanying drawings.