The present invention relates to machines and apparatus for making trenches and to methods of making trenches using the machines or apparatus of the invention. The invention is particularly, but not exclusively, concerned with making sub-sea trenches, that is, trenches in the seabed, in particular for locating pipelines, cables, umbilicals or the like therein. Pipelines, cables, umbilicals and the like will hereinafter be referred to as “elongate workpieces”.
It is well known to cut trenches in the seabed and to locate elongate workpieces in the trench. After laying an elongate workpiece, the trench can be back-filled to provide mechanical protection for the elongate workpiece against damage from objects crossing the seabed, such as fishing gear, anchors and so on. Burying a pipeline can also provide insulation to improve the passage of pipeline contents.
Methods of trenching use trenching machines which fall into one of three broad categories: towed machines such as ploughs or jetting machines, free swimming ROVs (remotely operated vehicles) and tractors. The tractors are usually mounted on continuous (endless) articulated tracks and are moveable under their own power, in a similar manner to earth moving vehicles used on land. The present invention is particularly, but not exclusively, directed towards trench cutting machines in the form of tractors, and in particular tractors constructed for operation on the seabed.
In a typical trenching operation, an elongate workpiece is laid on the seabed and a trenching apparatus is placed over the elongate workpiece. The trenching apparatus is used to cut a trench, typically alongside the elongate workpiece, and the elongate workpiece is then manoeuvred into the trench. Various cutting arrangements are known, including ploughs, jetting arrangements and chain cutters. The present invention is particularly concerned with trenching machines employing chain cutters.
Chain cutters as such are known. A typical prior art trenching machine employs at least a pair of chain cutters arranged at an angle (for example 60° to the vertical) to cut a V-shaped trench. Cutting a V-shaped trench is inefficient in that, for a given depth of cut, the amount of spoil which must be removed is high. This generates large piles of spoil on either side of the trench which may interfere with subsequent operations. Also when using angled cutters, there is a strong tendency for soil to remain in the trench which reduces the effective burial of the elongate workpiece which can be achieved. In conventional trenching machines there is a significant danger of interference between the cutters and the elongate workpiece which can cause substantial damage to the elongate workpiece. This is particularly so at the time when the trenching machine is being located in its position of use, and as the elongate workpiece is being mounted to pass through the trenching machine.
WO 99/54556 describes a trenching machine in the form of a tractor, which includes a single chain cutter unit. The chain cutter is mounted on an arm which is pivoted at an upper part of the tractor. By pivoting the arm, the chain cutter can be moved from a use position to a stowed position in which the cutter is raised. In the stowed position, the elongate workpiece can be mounted on the trenching machine without interference from the cutter.
According to a first aspect of the present invention there is provided a trenching machine comprising:
In a first preferred embodiment of the invention, when the arms are in the first position, the cutter units are spaced apart and when the arms are in the use position the cutter units are relatively closer together.
Preferably in this embodiment when the arms are in the first position the cutter units are spaced apart to an extent sufficient to allow passage therebetween of the an elongate workpiece to be trenched.
In a second preferred embodiment preferably the trenching machine further comprises lifting means for raising an elongate workpiece between the cutter units to a position above the cutter units, when the cutter units are in the stowed position.
In another preferred embodiment when the arms are in the first position, the cutter units are in a relatively higher position and when the arms are in the use position the cutter units are in a relatively lower position.
Most preferably, the first and second arms are pivotally mounted on the body portion.
In preferred embodiments the pivot axes of the respective arms are arranged to be generally parallel to the longitudinal axis of a work piece to be disposed in the trench.
In further preferred embodiments, when the arms are in a use position, the cutter units are selectively moveable relative to the arms to adopt any of a desired range of trenching conditions. Preferably, the cutter units are moveable relative to the arms by rotation of the cutter units about an axis.
Preferably said axis of rotation of the cutter units is orthogonal to the pivot axes of the respective arms.
In preferred embodiments the cutter units are chain cutter units.
In still further preferred embodiments in one or more use positions of the arms, the cutter units are juxtaposed.
Preferably the trenching machine further comprises securing means operable to join the first and second cutter units together.
Preferably in one or more use positions of the arms the cutter units are in spaced apart relation.
In still further preferred embodiments, in their trenching condition, the cutter units are arranged substantially vertically. That is, the cutter units are arranged substantially parallel to a vertical plane. Preferably the cutter units are spaced equidistantly from a plane passing through the elongate workpiece in use. More specifically, in preferred arrangements the line of action of the cutter units lies in a substantially vertical plane.
In preferred embodiments the trenching machine includes supporting means configured to support the workpiece on passing through the body of the machine substantially without deformation of the workpiece from a generally linear condition, with respect to a nominally horizontal plane.
According to a second aspect of the invention there is provided a method of laying an elongate workpiece in a trench, comprising the steps of:
providing a trenching machine as defined in the first aspect of the invention; arranging the trenching machine over the elongate workpiece; moving the first and second arms to their first position, if not already in said first position; moving the elongate workpiece to a supported position within the machine; and moving the arms to a use position in which the cutter units adopt a trenching condition.
For a better understanding of the invention and to show how the same may be carried into effect, reference will be made, by way of example only, to the following drawings, in which:
Referring now to the drawings, trenching machine 10 comprises a body portion 12 which, in the illustrated machine, is defined by a plurality of frame members such as 14a, 14b, 14c, 14d. The body portion 12 is carried on ground engaging means 16 which allow for forward and reverse motion of the machine over the seabed and, where required, for steering of the machine 10. In the illustrated example, and in preferred embodiments, the ground engaging means 16 comprise endless articulated tracks 16a, 16b of known type. The trenching machine 10 is most preferably moveable under its own power by movement of tracks 16a, 16b, in the manner of a land-based tracked vehicle.
The trenching machine 10 includes a path along which the elongate workpiece 18 is supported within or on the machine during trenching operations. The path is such that (as can be seen from
The trenching machine 10 further comprises first and second arms 20, 22 which are pivotally attached at pivot points 24a, 24b respectively to a portion of the body such as 14a. The arms are arranged to pivot about an axis nominally parallel to frame members 14c, 14d, that is, nominally parallel to the longitudinal axis of the elongate workpiece 18 and also nominally parallel to the normal straight line movement of the trenching machine 10. A chain cutter unit 26a, 26b is attached to each respective arm 20, 22 distal from the pivots 24a, 24b. Means 28 are provided for moving the arms 20, 22 between raised and use positions. Preferred means 28 are hydraulic actuators such as piston and cylinder arrangements 30. Each chain cutter unit 26a, 26b is pivotally mounted on its respective arm 20, 22 for movement about an axis 26c which is orthogonal to the axis of the pivots at 24a, 24b and to the direction of forward movement of the trenching machine 10. Thus the chain cutter units 26a, 26b can be raised and lowered between lower trenching positions in which the chain cutter units 26a, 26b can engage the seabed and raised positions in which the chain cutter units 26a, 26b are spaced from the seabed. Means such as a hydraulic actuator (e.g. piston and cylinder arrangement) 32 are provided for moving the chain cutter units 26a, 26b about axis 26c.
Various configurations of the arms 20, 22 and chain cutter units 26a, 26b are illustrated in particular in
It is also possible, in particular when cutting a narrow trench, to employ only a single chain cutter unit 26a or 26b. In such a case, the respective arm 20 or 22 carrying the chain cutter unit 26a or 26b to be used is lowered, and the chain cutter unit 26a or 26b is moved about axis 26c to its operational position. The other chain cutter unit 26b or 26a is maintained in a position in which the seabed is not engaged. For example, the chain cutter unit 26b or 26a may be in its upper position with respect to rotation about axis 26c and the arm 22 or 20 may be raised. It is therefore apparent that the arms 20, 22 and chain cutter units 26a, 26b may be operated independently when required.
The chain cutter units 26a, 26b preferably each comprise a single chain cutter, but each unit 26a, 26b may possibly include a plurality of chain cutters. Each chain cutter unit 26a, 26b is provided with its own drive motor. A typical chain cutter unit 26a, 26b is about 0.5 m wide, giving a total width of trench of about 1 m. Wider or narrow cutter units 26a, 26b may be used as appropriate, for example depending on the desired trench width and the soil conditions. The provision of a motor on each cutter unit 26a, 26b is advantageous over using a single cutter, in that the available torque is increased which increases cutting efficiency, in particular in difficult soil conditions. In some preferred embodiments, engagement means are provided on the respective chain cutter units 26a, 26b, by which the units 26a, 26b may be joined, so that they support each other. In other preferred embodiments, the drives of the respective chain cutter units 26a, 26b may be linked to increase torque availability at any given point.
The provision of two symmetrical chain cutter units 26a, 26b also results in increased stiffness, which is enhanced by joining the cutters together. Increased stiffness of mechanical cutters is an important consideration, for example in ensuring more effective torque availability.
At the end of trenching operations, the chain cutter units 26a, 26b are returned by piston and cylinder arrangement 32 to their raised state as seen in
Aspects of the loading of the elongate workpiece 18 onto the trenching machine 10 are illustrated in
By using a pair of chain cutter units 26a, 26b which are oriented substantially vertically the trenching machine 10 of the invention maximises the efficiency of the trenching operation by disturbing the minimum amount of seabed and ensuring that the trench which is cut has the smallest cross-sectional area for a given depth. In contrast, trenching machines which rely on angled cutters define trenches with inclined side walls and necessarily must remove more soil and rock to achieve a given depth of trench. This reduces work rates.
A particular advantage of the trenching machine 10 according to the invention is that the chain cutter units 26a, 26b can be mounted in the middle of the track centre of steering. This is advantageous in enabling the tractor (trenching machine 10) to steer about the chain cutter units 26a, 26b, allowing the cutter units 26a, 26b to be more rigidly mounted within the body of the trenching machine 10 and so improving their structural connection and rigidity. This enhances the ability of the trenching machine 10 to cut through rock and poor soil conditions, improving both the work rate and the quality and uniformity of the resulting trench.
Although the present invention has principally been described in relation to its application to a sub-sea tractor, the skilled person will appreciated that the invention is susceptible to being adapted for use with a plough, ROV or other sub-sea trenching apparatus.
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.
Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.
Number | Date | Country | Kind |
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0701719.7 | Jan 2007 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB08/00200 | 1/21/2008 | WO | 00 | 7/30/2009 |