TECHNICAL FIELD

The present invention relates to a digging machine for burying a continuous elongated member in the bed of a body of water.

BACKGROUND ART

Burying a continuous elongated member in the bed of a body of water normally comprises laying the continuous elongated member along a given path on the bed of the body of water; breaking up a mass of the bed to a given depth along the- path; digging a trench or generally removing the broken-up bed mass, normally at the same time it is broken up; and possibly covering over the continuous elongated member.

More specifically, currently used known techniques comprise removing the broken-up bed mass to form a trench in the bed of the body of water; and lowering the continuous elongated member into the trench. The removed bed mass may subsequently be used as backfill to fill the trench and bury the continuous elongated member.

Continuous elongated members are routinely buried, either completely or partly, for various reasons : to protect them from damage by blunt objects, such as anchors or nets, close to shore approaches or in relatively shallow water; and at times to avoid severe stress by natural elements, such as wave motion and current. In the case of continuous elongated members in the form of rigid pipelines laid on the bed of the body of water, the pipeline may have unsupported tracts spanning two supporting points, i.e. in which it is detached from the bed; in which case, it is particularly exposed to, and vulnerable to movement induced by, wave motion and current. At times, burying is necessary to protect pipelines from deformation (upheaval/lateral buckling) caused by thermal instability; or to protect continuous elongated members from the bed-scouring action of ice in very shallow water.

To protect it from damage, a continuous elongated member very often need simply be laid in the bottom of a suitably deep trench dug either before (pre-trenching) or, more usually, after the continuous elongated member is laid on the bed of the body of water (post- trenching) . At times, the protection afforded by the trench and by natural backfilling is not enough, and the continuous elongated member must be buried using the broken-up bed mass removed from the trench, or any available bed mass alongside the trench.

Post-trenching is advantageously performed using digging machines for which the continuous elongated member laid on the bed of the body of water acts as a guide. In other words, the continuous elongated member acts as a guide and grip rail to which the drive force to move the digging machine forward is applied.

Digging machines of this type are extremely advantageous when working with continuous elongated members in the form of rigid pipelines with a constant, regular-shaped cross section, but are limited, for example, when the continuous elongated member comprises a main pipeline, and an auxiliary, so-called piggyback' pipeline, the position of which with respect to the main pipeline may change over time. For practical reasons, the auxiliary pipeline is normally strapped to the main pipeline, but the straps fail to provide for a permanently rigid, stable connection. In fact, the main and auxiliary pipelines together form an irregularly- shaped continuous elongated member, the shape of which varies over time along its length, with the result that digging machines of the type described above pose a serious threat to the integrity of the auxiliary pipeline .

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a digging machine for burying continuous elongated members in the bed of a body of water effectively and without damaging the continuous elongated member, even when this is of variable, irregular shape.

According to the present invention, there is provided a digging machine for burying a continuous elongated member in the bed of a body of water, the digging machine comprising a frame extending along a longitudinal axis; at least two guide assemblies, which are arranged successively along the longitudinal axis, are fitted to the frame to move crosswise to the

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longitudinal axis, and are designed to engage and move along the continuous elongated member; and a control device designed to adjust the position of the guide assemblies with respect to the frame and the continuous elongated member according to the conformation of the continuous elongated member.

This way, contact between the guide assemblies and the continuous elongated .member can be controlled to avoid damaging the continuous elongated member.

Preferably, each guide assembly is connected to the frame by a sliding coupling which slides along a preferably arc-shaped trajectory.

This way, the contact area between each guide assembly and the continuous elongated member can be adjusted about the continuous elongated member.

In a preferred embodiment of the present invention, each guide assembly is movable with respect to the frame along a respective plane perpendicular to the longitudinal axis.

The digging machine extends mainly along the longitudinal axis, and is positioned over the continuous elongated member, with the longitudinal axis substantially parallel to the continuous elongated member. Moving each guide assembly along a respective plane perpendicular to the longitudinal axis enables the guide assembly to move substantially around the continuous elongated member.

In a preferred embodiment of the present invention, the control device comprises a control unit designed to set each guide assembly, with respect to the frame, to a plurality of positions about the continuous elongated member .

In other words , the digging machine has an automatic system for precisely adjusting the positions of the guide assemblies.

Preferably, each guide assembly comprises a runner fitted slidably to the frame; and at least two setting members fitted to the runner and designed to be positioned contacting and astride the continuous elongated member.

In other words, each guide assembly can be positioned contacting two separate, spaced-apart areas of the continuous elongated member, to enhance the stability of the digging machine and distribute the mass of the digging machine over the continuous elongated member .

Preferably, each setting member is hinged to the runner and movable selectively between a work position and a rest position.

This way, each guide assembly can be positioned contacting the continuous elongated member at one contact point, two contact points, or with both setting members detached a given distance from the continuous elongated member. Individual adjustment of the setting members makes it possible to overcome any obstacles along the continuous elongated member.

In a preferred embodiment, the control device comprises at least one sensor for detecting signals relating to the conformation of the continuous elongated member close to a guide assembly.

In other words, the control device adjusts the guide assemblies according to the detected, appropriately processed signal. The types of sensors used comprise transponder detectors connected beforehand to the continuous elongated member; feelers; and any type of sensor capable of supplying a reliable signal in a body of water with large amounts of suspended inert material thrown up by the digging machine .

Preferably, the control device comprises at least two sensors for detecting signals relating to the conformation of the continuous elongated member close to at least two respective guide assemblies.

In other words, precision adjustment of the guide assemblies is greatly enhanced by providing a sensor close to each guide assembly.

In a preferred embodiment of the present invention, the digging machine comprises a drive assembly between two guide assemblies.

The guide and drive functions are separate.

Preferably, the drive assembly is connected rigidly to the frame, and is a push-pull type. .

Preferably, the drive assembly comprises a first pair of clamps for selectively clamping the continuous elongated member; and a second pair of clamps for selectively clamping the continuous elongated member and movable along the longitudinal axis with respect to the frame; one of the first and second pairs of clamps engaging the continuous elongated member at all times.

This way, the digging machine is secured to the continuous elongated member by both the guide assemblies and the drive assembly. The drive assembly prevents the digging machine from rotating about the continuous elongated member, while the guide assemblies define the supporting points on the continuous elongated member.

Preferably, the drive assembly comprises gripping portions designed to grip the underside of the continuous elongated member.

The continuous elongated member normally comprises a main pipeline, and an auxiliary pipeline connected to the top of the main pipeline. Locating the gripping portions beneath the continuous elongated member avoids any interference with the auxiliary pipeline.

In a preferred embodiment of the present invention, the digging machine comprises a digging assembly in turn comprising at least two digging members located on opposite sides of the frame and tilted to dig out a mass of the bed from beneath the continuous elongated member.

To some extent, the digging assembly thus provides for further supporting and stabilizing the digging machine .

The present invention also relates to a method of advancing the digging machine along, and without damaging, irregular-shaped continuous elongated members.

According to the present invention, there is provided a method of advancing a digging machine for burying a continuous elongated member in the bed of a body of water, the method comprising the steps of guiding a digging machine along a continuous elongated member, laid on the bed of a body of water, by means of at least two guide assemblies fitted to the continuous elongated member and arranged successively along a longitudinal axis of the digging machine; acquiring signals relating to the conformation of the continuous elongated member; and adjusting the position of the guide assemblies according to the conformation of the continuous elongated member.

The digging machine is thus able to take into account the irregular shape of the continuous elongated member, to adapt the position of the guide assemblies accordingly.

Preferably, the step of adjusting the position of the guide assemblies comprises the step of rotating each guide assembly about the continuous elongated member along a respective plane perpendicular to the longitudinal axis, according to the conformation of the continuous elongated member.

One of the main irregularities and unknowns of the continuous elongated member is the position of the auxiliary pipeline with respect to the main pipeline. The precise function of rotating each guide assembly is to ensure it only contacts the main pipeline.

Preferably, the step of adjusting the position of the guide assemblies comprises the step of setting each guide assembly to a work position contacting the continuous elongated member, and to a rest position a given distance from the continuous elongated member.

Because the main pipeline and the auxiliary pipeline are connected by strap assemblies equally spaced along the continuous elongated member, and the auxiliary pipeline is smaller in diameter than the main pipeline, the strap assemblies constitute localized obstacles to the guide assemblies. To avoid damaging the straps, it is therefore best to set the guide assemblies to the rest position when travelling over the straps.

Preferably, each guide assembly comprises a runner,- and at least two setting members, which are hinged to the runner and can be set selectively to a work position contacting and astride the continuous elongated member, and to a rest position at a given distance from the continuous elongated member.

This enables sole movement of the setting members, and allows each setting member to be moved selectively into the work position or rest position, according to the conformation of the continuous elongated member.

In a preferred embodiment of the present invention, the frame comprises at least two supports for respectively supporting the guide assemblies and having respective preferably arc-shaped guides; the method comprising the step of moving each guide assembly along a respective guide into a plurality of positions.

This therefore permits fine adjustment of the guide assemblies along the respective guides.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the attached drawings , in which :

Figure 1 shows a view in perspective, with parts removed for clarity, of a digging machine in accordance with the present invention and connected to a continuous elongated member laid on the bed of a body of water;

Figure 2 shows a larger-scale view in perspective, with parts removed for clarity, of the continuous elongated member in Figure 1;

Figures 3 to 7 show larger- scale elevations, with parts removed for clarity, of the Figure 1 machine in different operating positions, according to the conformation of the continuous elongated member;

Figure 8 shows a view in perspective, with parts removed for clarity, of the Figure 1 machine;

Figure 9 shows a view in perspective, with parts removed for clarity, of a component part of the Figure 1 machine .

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figure 1 indicates a digging machine connected to a continuous elongated member 2 lying on the bed 3 of a body of water 4.

For the purpose of the present description, the term body of water' is intended to mean any expanse of water, such as a sea, ocean, lake, etc., and the term ^bed' is intended to mean the concave layer of the earth's crust containing the body of water.

In the example shown, continuous elongated member 2 comprises a main pipeline 5 of axis A2 ; and an auxiliary or service pipeline 6 fitted to and smaller in diameter than main pipeline 5.

With reference to Figure 2, continuous elongated member 2 comprises straps 7 for binding auxiliary pipeline 6 to main pipeline 5. Straps 7 are arranged in groups spaced, possibly equally spaced, along continuous elongated member 2. Continuous elongated member 2 preferably comprises spacers 8 between main pipeline 5 and auxiliary pipeline 6. Straps 7 being unable to secure auxiliary pipeline 6 in a fixed position with respect to main pipeline 5, i.e. to prevent auxiliary pipeline 6 from rotating about main pipeline 5, it is impossible to predict the position of auxiliary pipeline 6.

Digging machine 1 shown in Figure 1 comprises a frame 9, four guide assemblies 10, a drive assembly 11, a control device 12, and a digging assembly 13. Frame 9 extends along an axis Al substantially parallel to continuous elongated member 2, and supports in succession two guide assemblies 10, drive assembly 11, digging assembly 13, and two guide assemblies 10.

Control device 12 is shown schematically and comprises a control unit 14 ; and at least two sensors 15 designed to determine the configuration of continuous elongated member 2. In other words, control device 12 supplies reliable information concerning the instantaneous positions of auxiliary pipeline 6 and straps 7 (Figure 2) . As shown in Figure 2, each group of straps 7 is preferably associated with a transponder 16 located in a given position, and which serves to clearly indicate the position of auxiliary pipeline 6 and the bulk of straps 7 at a given point. The spacing of groups of straps 7 is relatively constant and sufficient to interpolate and predict the position of auxiliary pipeline 6 between two consecutive groups of straps 7.

With reference to Figures 3 to 7, the position of each guide assembly 10 is adjustable with respect to frame 9 and continuous elongated member 2 according to the instantaneous conformation of continuous elongated member 2. In other words, control unit 14 controls adjustment of each guide assembly 10.

Construction-wise, each guide assembly 10 comprises a runner 17 connected slidably to frame 9; and two setting members 18 - in the example shown, wheels - designed to be positioned . contacting continuous elongated member 2. Each setting member 18 is hinged to runner 17 and movable between a work position shown in Figure 3, and a rest position shown in Figure 4. Each setting member 18 is operated independently of the other setting member 18 by a respective actuator 18A. In the Figure 3 work position, setting members 18 are positioned contacting continuous elongated member 2 - more specifically, only contacting main pipeline 5. In the work position, setting members 18 are tilted and converge towards axis A2 of main pipeline 5. In the Figure 4 rest position, setting members 18 are raised a given safety distance off continuous elongated member 2.

Setting members 18 are selectively set to the rest position to avoid interfering with straps 7, spacers 8 and auxiliary pipeline 6.

With reference to Figures 5, 6 and 7, each guide assembly 10 can rotate, preferably along a given arc, about continuous elongated member 2. More specifically, guide assembly 10 substantially rotates about axis A2 of main pipeline 5 and along a plane perpendicular to longitudinal axis Al of frame 9.

To move it this way, guide assembly 10 is connected movably to frame 9. In other words, runner 17 engages a guide 19 on frame 9.

With reference to Figure 1, frame 9 comprises a longitudinal beam 20 parallel to longitudinal axis Al; and four supports 21 crosswise to longitudinal axis Al and connected rigidly to beam 20. Each support 21 supports a respective guide assembly 10 in sliding manner . With reference to Figure 7, runner 17 is moved selectively along guide 19 by an actuating system 22 preferably comprising a rack 23 and pinion 24 mechanism operated by a rotary actuator 25.

In the example shown in the attached drawings, two adjacent guide assemblies 10 are operated by the same actuating system 22, and so perform the same movements.

This solution is made possible by the adjacent guide assemblies 10 being located close together.

When setting members 18 are in the work position resting on main pipeline 5, guide 19 - preferably arc- shaped -is substantially centred about axis A2 of main pipeline 5.

Guide assembly 10 can thus be set to a plurality of work positions about continuous elongated member 2, depending on the conformation of continuous elongated member 2 and as shown in Figures 5 to 8. More specifically, Figure 8 shows the position of guide assemblies 10 according to the position of auxiliary pipeline 6 around main pipeline 5.

With reference to Figure 9, drive assembly 11 is a so-called ^x push-pull' type, and comprises two opposite flanges 26, 27 connectable rigidly to beam 20 (Figure 1); guides 28 connecting flanges 26 and 27; a carriage 29 movable selectively along guides 28; two clamps 30 hinged to flange 26; and two clamps 31 hinged to carriage 29. Carriage 29 is movable back and forth along guides 28, and is operated by an actuator 32.

Clamps 30 and 31 are each operated by a respective actuator 33, to move between a grip position (clamps 30) and a release position (clamps 31) .

Clamps 30 and 31 each comprise a gripping portion

34.

With reference to Figure 1, clamps 30 and 31 are designed to position gripping portions 34 on the underside of continuous elongated member 2, where auxiliary pipeline 6 is very unlikely to be.

Digging assembly 13 comprises two digging members 35 fitted to frame 9 and operated by actuators not shown in the drawings. Digging members 35 are tilted so as to penetrate, break up, and remove a mass of bed 3 beneath continuous elongated member 2.

In actual use, digging machine 1 is moved in travelling direction Dl by drive assembly 11, and rests on continuous elongated member 2 by means of guide assemblies 10. As it moves along, digging assembly 13 breaks up and removes the mass of bed 3 beneath continuous elongated member 2 so as to sink it.

Control device 12 determines the configuration of continuous elongated member 2, controls the orientation of guide assemblies 10 with respect to frame 9 and continuous elongated member 2, and selectively sets each setting member 10 to the work or rest position.

Clearly, changes may be made to the embodiment described of the present invention without, however, departing from the protective scope defined in the accompanying Claims .

More specifically, the control device may be equipped with feelers, so there is no need for transponders; and the drive assembly may be a continuous type, in the form of a guide assembly with drive wheels.