Abstract:
A trench cutting apparatus comprises a main body portion, ground contacting conveying means on which the body portion is mounted and by which the apparatus can traverse the ground and at least one soil cutting device operable to cut a trench wherein the attitude of the soil cutting device is adjustable between a first use configuration configured for cutting a linear trench portion and a second use position configured for cutting a curved trench portion, said second use position being selected to minimise undercutting of a trench wall as said curved trench portion is formed.

Description:
[0001]    This invention relates to an apparatus and method for cutting a trench in the ground and more especially (but not exclusively) for cutting a trench in the bed of a body of water such as the bed of a lake or the sea bed. The invention relates in particular to apparatus and a method which avoids or reduces undercutting of the trench when executing a turn of the trench. 
       BACKGROUND 
       [0002]    The formation of trenches in the ground is a well known requirement and is typically needed for burying utility supply means such as gas and water pipes and electricity and telecommunications cables. In underwater environments, the cutting of a trench is typically required for burial of pipes and cables and requires specially constructed or adapted equipment configured for underwater conditions, such as the nature of the seabed. Herein “seabed” is used to refer to the bed of the sea or of a lake or even a river, unless the context requires otherwise. 
         [0003]    Various apparatus for constructing a trench are known in the art. These can include soil cutting devices in the form of ploughs, jetting apparatus (for underwater use) and chain cutters which form the desired trench. Typically the soil cutting device is mounted on a vehicle which moves over the ground (e.g. the seabed) either under its own power of by external means. For example, the trench cutting vehicle might be towed by a tractor vehicle or by a ship at the surface. Generally it is preferred that the trench cutting vehicle is self-powered. Typically the trench cutting vehicle is mounted on endless articulated tracks. 
         [0004]    An issue encountered by trench forming vehicles of this type is when the course of the trench executes a turn, in particular a turn of small turning radius. In this situation, it is possible for the soil cutting device (more especially where the soil cutting device is a chain cutter or jetting device) to undercut the trench wall on the outer side of the curved portion of the trench. This has the effect of de-stabilising the trench wall. Also, it is possible for the soil cutting device such as a chain cutter to become wedged or jammed with respect to the trench wall 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0005]    The present invention seeks to ameliorate or overcome the above problem. In particular, the present invention seeks to provide trench cutting apparatus and a method of trench cutting which reduces, minimises or avoids the undercutting of the trench wall as a turn in the trench is executed. The wall of the trench is formed at a desired angle, most preferably substantially vertical. 
         [0006]    In accordance with the a first aspect of the present invention there is provided a trench cutting apparatus comprising a main body portion, ground contacting conveying means on which the body portion is mounted and by which the apparatus can traverse the ground and at least one soil cutting device operable to cut a trench wherein the attitude of the soil cutting device is adjustable between a first use configuration configured for cutting a linear trench portion and a second use position configured for cutting a curved trench portion, said second use position being selected to minimise undercutting of a trench wall as said curved trench portion is formed. 
         [0007]    In preferred embodiments the soil cutting device is a chain cutter or a jetting cutter. 
         [0008]    In preferred embodiments the apparatus further comprises a control device wherein the attitude of the soil cutting device is adjustable under the control of the control device. 
         [0009]    In some preferred embodiments the attitude of the soil cutting device is automatically adjusted by the control device in dependence on the radius of curvature required for the trench being formed. 
         [0010]    In some preferred embodiments the soil cutting device is a chain cutter comprising a plurality of soil cutting teeth mounted for movement in an endless loop, the chain cutter having, in an operational position, a lower end at which the soil cutting teeth cut the soil to form the trench and a upper end at which the teeth are spaced apart from the soil, said lower end having an outer edge and an inner edge which respectively define opposed boundaries of the trench being cut, and wherein the adjustment in the attitude of the chain cutter is such that at least a portion of said outer edge is displaced towards the direction of curvature of the trench. 
         [0011]    Preferably in these embodiments the attitude of the chain cutter is adjusted by rotating the chain cutter about a nominally horizontal axis. Said horizontal axis is preferably at least approximately parallel to the direction of motion of the trench cutting axis at any given time. 
         [0012]    In other preferred embodiments the soil cutting device is a jetting cutter having, in an operational position, a first portion from which cutting fluid is expelled along a line of action to cut the soil to form the trench and a second portion which is in fluid communication with a supply of cutting fluid and wherein the adjustment in the attitude of the jetting cutter is such that said line of action of the cutting fluid is displaced towards the direction of curvature of the trench. 
         [0013]    Preferably in these other preferred embodiments the attitude of the jetting cutter is adjusted by rotating the jetting cutter about a nominally horizontal axis. Said horizontal axis is preferably at least approximately parallel to the direction of motion of the trench cutting axis at any given time. 
         [0014]    In preferred embodiments the apparatus further comprises actuators coupled to the soil cutting device and configured to adjust the attitude of the soil cutting device by rotating the soil cutting device about said horizontal axis. 
         [0015]    Preferably the change in attitude of the soil cutting device is effected by a change in attitude of the body portion, the attitude of the soil cutting device being maintained in fixed relation to the body portion. 
         [0016]    Preferably the attitude of the body portion is adjustable by adjustment of the spacing of one or both of the ground contacting conveying means with respect to the body portion. 
         [0017]    According to a second aspect of the present invention there is provided a method of cutting a trench comprising providing a trench cutting apparatus having an soil cutting device which is adjustable between first and second attitudes and prior to cutting a curved portion of the trench, adjusting the attitude of the soil cutting device to an attitude in which undercutting of the trench wall of said curved portion is minimised. 
         [0018]    In preferred embodiments of the second aspect of the invention the attitude of the soil cutting device is adjusted in dependence on the radius of curvature of the trench being formed 
         [0019]    Preferably the adjustment in the attitude of the soil cutting device comprises rotating the soil cutting device about a nominally horizontal axis. Said horizontal axis is preferably at least approximately parallel to the direction of motion of the trench cutting axis at any given time. 
         [0020]    Preferably the trench cutting apparatus comprises a main body portion to which the soil cutting device is attached and the adjustment in the attitude of the soil cutting device comprises adjusting the attitude of the main body portion. 
         [0021]    In particularly preferred embodiments the trench cutting apparatus is an apparatus as defined in the first aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  is a representation of a typical trench cutting apparatus; 
           [0024]      FIG. 2   a  shows schematically a plan view of a trench and a cutting part of a trench cutting apparatus according to the prior art indicating the potential for undercutting of the trench wall; 
           [0025]      FIG. 2   b  is similar to  FIG. 2   a  and illustrates the reduction in the undercutting of the trench wall achieved by the apparatus and method of the invention; 
           [0026]      FIG. 3   a  is a view of the outline of a trench cutting device viewed from the front and illustrating the degree of undercutting of the trench wall which can occur with trench cutting arrangements of the prior art; 
           [0027]      FIG. 3   b  is similar to  FIG. 3   a  and shows the outline of a trench cutting device when the attitude thereof is adjusted according to the present invention and illustrating the reduction in the degree of undercutting which is achieved; 
           [0028]      FIG. 4   a  is a plan view of a typical trench cutting device according to the present invention; 
           [0029]      FIG. 4   b  is a side view of the trench cutting device of  FIG. 4   a ; and 
           [0030]      FIG. 4   c  is a perspective view of the trench cutting device of  FIGS. 4   a  and  4   b.    
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Referring now to the drawings, the present invention addresses the problem of the formation of undercuts in a trench side wall in curved portions of a trench when the trench is formed using apparatus of the prior art. Undercuts are formed with prior art apparatus in the outer trench wall, that is, the wall in a curved section of trench having a greater radius of curvature than an opposed inner trench wall. 
         [0032]      FIG. 1  shows on example of a prior art trenching apparatus  100 , in this particular case configured for forming a trench  102  in the seabed  104  and simultaneously burying a pipeline  106  in the trench  102 . For the avoidance of doubt, the apparatus according to the present invention may usefully be equipped with means both for trench forming and for simultaneous burying of a pipeline, but pipe burying means are not per se an essential feature of the apparatus of the invention. The prior art apparatus  100  includes a main body  108  and ground contacting conveying means  110  in the form of endless articulated tracks on which the main body  108  is mounted and by means of which the apparatus  100  moves over the seabed  104  in the direction of arrow A. The prior art trenching apparatus  100  as illustrated in  FIG. 1  includes primary and secondary soil cutting devices  112 ,  114 , it being noted for the avoidance of doubt that there is no requirement for the apparatus according to the present invention to include both primary and secondary soil cutting devices, although useful embodiments may do so. In  FIG. 1 , the primary soil cutting device  112  is a chain cutter and the secondary soil cutting device  114  is a jetting cutter. The chain cutter  112  comprises an endless belt  116  carrying a plurality of soil cutting teeth  118 . The belt  116  is driven by suitable drive means so that the soil cutting teeth move in an endless loop during the course of which the teeth  118  contact, and displace, soil so to form the trench  102 . The chain cutter  112  is mounted to pivot about horizontal axis  120  in order to adjust the depth of cut of the trench. Horizontal axis  120  passes transversely with respect to the body  108 , that is, perpendicular with respect to the direction of travel A of the apparatus  100 . Jetting cutter  114  comprises a plurality of outlets or nozzles from which fluid (typically water) is expelled under high pressure to displace soil. 
         [0033]      FIGS. 2   a  and  3   a  and  FIGS. 2   b  and  3   b  respectively illustrate the formation of an undercut using prior art apparatus and the avoidance of undercut formation using the apparatus of the invention. In  FIGS. 2   a  and  2   b  the trench is illustrated schematically at  202 A and  202 B respectively. The centre lines of the trenches are shown at  240 A and  240 B. In the right hand portions of  FIGS. 2A and 2B , the trenches  202 A and  202 B are substantially linear and the problem of undercutting of the trench walls does not arise. Thus, the orientation of the trench walls is about vertical, generally in alignment with the side edges of the soil cutting devices  200 A and  200 B. If in any particular case the soil cutting device is set an angle to the vertical (e.g. when cutting a V-shaped trench) then the trench walls follow the orientation of the soil cutting device. 
         [0034]    At about points  230 A and  230 B respectively the trenches  202 A and  202 B begin to curve or turn, in the illustrated case to the left. In  FIG. 2   a  the illustrated positions of soil cutting devices  200 A and  200 AA in the left portion of the Figure indicate the degree of undercutting of the trench wall which can occur, it being noted that portions of the soil cutting devices  200 A  200 AA extend beyond the indicated boundaries of the trench. In  FIG. 2   a  (and in  FIG. 3   a ) according to the prior art method, the soil cutting device  200   a ,  200 AA is maintained in a vertical orientation. In contrast, in  FIG. 2B  which illustrates an adjustment of the attitude of the trench cutting device  200 B,  200 BB according to the invention, the undercuts are avoided, as can be noted at  232 B and  234 B, and substantially vertical trench walls are achieved. 
         [0035]    The same effect is illustrated in  FIGS. 3   a  and  3   b . In  FIG. 3   a , the soil cutting device  200 A (shown schematically) produces an undercut  232 A when executing a turn (because of the essentially vertical orientation of the soil cutting device  200 A) whereas in  FIG. 3   b , the soil cutting device  200 B according to the invention produces no such undercut, as can be noted at  232 B. 
         [0036]      FIGS. 4   a  to  4   c  show a typical arrangement of a trench cutting apparatus  400  according to the invention, the apparatus  400  including a main body portion  408  (shown schematically) on which is mounted a soil cutting device  412 . The main body portion  408  is mounted on ground contacting conveying means (not illustrated) of any suitable type such as endless tracks of the kind illustrated at  110  in  FIG. 1 . 
         [0037]    The soil cutting device as illustrated in  FIGS. 4   a  to  4   c  is a chain cutter device which includes a plurality of teeth (not specifically illustrated) mounted to process around an endless path in the same manner as discussed in relation to chain cutter  112  in  FIG. 1 . The chain cutter  412  is mounted to the main body  408  at a pivot  420 . The inclination of the chain cutter  412  is controlled by means of an actuator  452 , such as a hydraulic actuator, mounted on an arm  450  by means of which the orientation of the chain cutter  412  about the pivot  420  can be adjusted in order to determine the depth of the trench being cut. 
         [0038]    As noted above, in accordance with the present invention, the attitude of the soil cutting device is adjustable in order to minimise or prevent the formation of undercuts in the walls of the trench being formed in cases where the trench is other than linear. The problem of forming undercuts in the trench walls is particularly acute with prior art apparatus when it is necessary to form curves or turns in the trench of small radius. In its broadest sense, the attitude of the soil cutting device  412  is changed by adjusting the lower end  412   a  of the soil cutting device by displacement of at least a part or portion thereof in the direction of curvature of the trench. That is, if the trench curves to the left (with respect to the direction of trench cutting), then the lower end portion  412   a  of the soil cutting device  412  is also adjusted to the left and, likewise if the trench curves to the right (with respect to the direction of trench cutting), then the lower end portion  412   a  of the soil cutting device  412  is also adjusted to the right. 
         [0039]    In preferred embodiments, for the adjustment of the attitude of the soil cutting device  412 , the soil cutting device  412  is rotated about a horizontal axis such as axis  454  illustrated in  FIGS. 4   b  and  4   c , such that a lower part  412   a  of the trench cutting device  412  is moved away from the outer trench wall. Axis  454  preferably is substantially parallel to the direction of travel of the apparatus  400  and will generally pass through the soil cutting device  412 . Rotation of the soil cutting device  412  about axis  454  is indicated by arrows  454   t  (no particular significance being given to the direction of the arrows in the Figures). In preferred operational orientations of the soil cutting device  412 , where a turn is to be made to the right, the soil cutting device  412  is rotated about axis  454  in an anti-clockwise (counter-clockwise) sense and, similarly where a turn is to be made to the left, the soil cutting device  412  is rotated about axis  454  in a clockwise sense. 
         [0040]    The apparatus  400  according to the invention is provided with suitable actuating means for adjusting the attitude of the soil cutting device  412 , these actuating means being shown generally at  456  in  FIG. 4   a . Suitable actuating means include hydraulic actuators. 
         [0041]    The apparatus  400  according to the invention most preferably further includes a control device, such as an electronic controller, which controls the adjustment of the attitude of the soil cutting device  412  (via actuators  456 ). Such control device may rely on the manual inputs of an operator, but in more preferred arrangements the control device determines the required attitude of the soil cutting devices  412  at least partially automatically. For example, the control device may determine the attitude of the soil cutting device  412  on the basis of positional data relating to the steering system of the apparatus  400  and/or reference data relating to the required curvature of the trench. 
         [0042]    In a further alternative construction, the attitude of the soil cutting device  412  may be adjusted by adjusting the attitude of the main body  408  of the apparatus on which the soil cutting device  412  is mounted. This may be achieved by providing adjustment of the height of the ground contacting conveying means (e.g. endless articulated tracks) with respect to the body portion. In other words, the distance of the respective conveying means, primarily in the vertical plane, is adjusted so that the conveying means at one side of the main body  408  is at a greater displacement from the main body  408  than the conveying means at the opposite side of the body. The body  408  must thus adopt an inclined attitude with respect to the horizontal and the soil cutting device  412  is correspondingly inclined. In practical terms, for cutting of a trench which curves to the left, the right hand side of the main body is made relatively higher and the left hand side is made relatively lower, and vice versa for cutting a trench which curves to the right. 
         [0043]    The details of the present invention have been described primarily herein in relation to the use of a chain cutter as the soil cutting device. It is noted that the principles of the invention are applicable also to the use of jetting tools (jetting cutters) as the soil cutting device. Jetting cutters expel one or more jets of high pressure cutting fluid—normally water)—in order to displace soil and form the trench. The line of action of the jets of cutting fluid (i.e. the direction in which the cutting fluid is expelled) is determined by the orientation of the one or more nozzles from which the cutting fluid is expelled. Typically the (or each) nozzle is mounted at an end of an arm. The present invention contemplates the adjustment of the attitude of such an arm in order to adjust the line of action of the (or each) jet of cutting fluid, the line of action being adjusted at least generally in the direction in which the trench is to turn or curve. 
         [0044]    Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. 
         [0045]    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. 
         [0046]    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. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 
         [0047]    The reader&#39;s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.