Abstract:
A strand-like material laying device for an appliance for laying any kind of strand-like material into the ground is disclosed. The strand-like material laying device is designed to lay a more rigid strand-like material such as steel pipes into the ground, and assures that the strand-like material to be laid can smoothly be fed into a trench formed in the ground without risking that a bending radius thereof falls below a minimum allowable bending radius which depends on the type of the strand-like material to be laid. The strand-like material laying device can also be immersed into the ground to form a subterranean trench while being moved in a longitudinal direction.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a strand-like material laying device for appliances for laying strand-like material of endless length, such as steel pipes, conduits, cables, etc., into a trench formed in the ground. 
     BACKGROUND OF THE INVENTION 
     Various appliances have been suggested which include a device for forming a trench having substantially vertical side walls in the ground, and for laying strand-like material of endless length, such as conduits, pipes and cables, into the trench. It should be noted that “endless length” designates a material which is very long in comparison with the length of the device laying the material, and does not require that the material be of infinite length. Such appliances are described e.g. in WO 86/00536 A1, U.S. Pat. No. 3,747,357, U.S. Pat. No. 3,486,344, U.S. Pat. No. 3,486,344, U.S. Pat. No. 3,429,134, DE 1 189 602 A1, DE 32 45 625 A1, DE 25 29 285 A1, DE 28 06 379 A1 or DE 491 887 B1 and typically comprise a support vehicle, a blade connected to and supported by the support vehicle for lifting and lowering, and a feeding means mounted in connection with the blade for pivotal movement about a horizontal axis and feeding the strand-like material from a storage reel rotatably mounted on the support vehicle, through an internal guide channel into a subterranean trench formed by the blade immersed into the ground when moving the support vehicle. With such appliances, in a single step a vertical trench can be formed in the ground and a strand-like material can be fed into the trench and laid onto the base of the trench while the support vehicle is moved forwardly. 
     The above mentioned appliances are designed for laying a strand-like material of relative high flexibility, such as cables, wound on a storage reel. However, such appliances are not appropriate in cases where strand-like material of relatively low flexibility and of “endless” length, such as more rigid steel pipes like gas pipes, oil pipes, etc., are to be laid. Normally, strand-like material of the latter mentioned more rigid or less flexible type is not fed from a storage reel but rests on the ground surface prior to being laid into the ground and is picked up, fed along a curved path into a trench formed in the ground by the appliance. In order to reduce a risk of being damaged or broken due to failing below a minimum allowable bending radius of the strand-like material of the more rigid or less flexible type to be laid, the curved path must be set so as to assure a sufficiently large radius of curvature, so that the length of the known appliances becomes very large if more rigid strand-like material is to be laid into the trench. 
     SUMMARY OF THE INVENTION 
     The present invention provides a strand-like material laying device for an appliance for laying any kind of strand-like material into the ground. A strand-like material laying device according to the present invention is designed to lay a more rigid strand-like material such as steel pipes into the ground. A strand-like material laying device according to the present invention assures that a strand-like material to be laid can smoothly be fed into a trench formed in the ground without risking that a bending radius thereof falls below a minimum allowable bending radius which depends on the type of the strand-like material to be laid. 
     The present invention provides a strand-like material laying device for immersing into the ground to form a subterranean trench while being moved in a longitudinal direction. To this end the strand-like material laying device comprises a first unit for cutting the ground to form said trench and guiding said strand-like material into said trench, said first unit having a plurality of first elements which are connected in series like a flexible chain. Each of the plurality of first elements has at its front end a cutting edge wherein the cutting edges of two successive ones of the plurality of first elements are offset with respect to each other in depth direction of the strand-like material laying device so that a cutting depth of the strand-like material laying device increases in a direction opposed to the direction of movement thereof. Two successive ones of the plurality of first elements are coupled with each other for pivotal movement about an axis being substantially parallel to the depth direction of the strand-like material laying device, which corresponds to the vertical direction when using the strand-like material device. 
     Due to its flexibility in lateral direction by the chain-like series connection of the plurality of first elements for pivotal movement about a substantially vertical axis the strand-like material laying device allows for a compensation of changing lateral forces acting on the cutting and inserting elements when cutting and ploughing the ground. Lateral forces acting on the cutting and inserting elements when cutting and ploughing the ground may change between left and right sides as well as between front and rear sides of the strand-like material laying device i.e. in lateral and longitudinal direction of the strand-like material laying device, due to variations of ground conditions as regards the ground constitution (gravel, sand, clay, etc.), the existence of obstacles (stones, root systems, etc.) included in the ground, as well as atmospheric conditions within the ground (frost and frost-free ground sections). 
     Offsetting the cutting edges of respective two successive elements of the plurality of first elements in depth direction so that a working depth of the two successive elements increases in a direction opposed to the direction of movement of the strand-like material laying device enables the division of the overall longitudinal force acting on the strand-like material laying device when being moved forward, into a plurality of longitudinal force components each acting on a respective one of the cutting and inserting elements. Thus a risk for the strand-like material laying device when being moved in the longitudinal direction to experience a torque causing the strand-like material laying device to tilt about a front end thereof is reduced. 
     A pivotal movement of said two successive ones of the plurality of first elements may be limited to a predetermined maximum angle of pivotal movement. This maximum angle of pivotal movement of said two successive ones of the plurality of first elements may be adjustably set on the basis of the type of strand-like material to be laid into the trench formed in the ground. In most cases it may be sufficient if said angle of pivotal movement is limited to be within a range of 1 and 3 degrees. 
     Furthermore, different cutting edges may be exchangeably mounted to each element of the plurality of first elements, so as to be able to adapt these first elements to any prevailing ground conditions. 
     In order to generate downwardly directed reaction forces, the cutting edges may be inclined slightly downward from a horizontal level so as to terminate at a bottom end of the respective element and form a blade nose projecting in the direction of movement of the strand-like material laying device. 
     At least one of the plurality of first elements may have as means for controlling the working depth thereof, a fin-like shoe coupled to said nose for pivotal movement about an axis which is substantially perpendicular with respect to the depth direction and direction of movement of the strand-like material laying device. Preferably, a pivotal movement of said fin-like shoe is limited to a predetermined angle of pivotal movement. Furthermore, preferably, said fin-like shoe is exchangeably mountable to the at least one of the plurality of first elements. 
     Said fin-like shoe may comprise at its front end an exchangeably mounted cutting tip projecting in the direction of movement of the strand-like material laying device. Different cutting tips can be inserted in the shoe, for adaptation of the cutting and inserting elements to various different prevailing ground conditions. 
     Furthermore, at least one of the plurality of first elements, preferrably the first two of the plurality of first elements, may have at its blade nose an exchangeably mounted cutting tip projecting in the direction of movement of the strand-like material laying device. Different cutting tips can be inserted in the blade nose, for adaptation of the cutting and inserting elements to various different prevailing ground conditions. 
     The strand-like material laying device may further comprise a second unit for guiding said strand-like material into said trench and laying it at a bottom of said trench, which second unit is coupled to the first unit of first unit having said plurality of first elements, for pivotal movement about an axis which is substantially parallel to the depth direction of the strand-like material laying device. This second unit may comprise a plurality of second elements which are connected in series like a flexible chain, and wherein two successive ones of said plurality of second elements are coupled with each other for pivotal movement about an axis being substantially parallel to a depth direction of the strand-like material laying device, i.e. a substantially vertical axis, to allow for a compensation of lateral forces acting on the strand-like material laying device when ploughing the ground. This second unit is primarily for supporting the strand-like material laying device and serves to smoothly lay the strand-like material into the trench formed by the plurality of first elements. 
     The two successive ones of said plurality of second elements may further be coupled with each other at their bottom ends for pivotal movement about an axis which is substantially parallel to a width direction of the strand-like material laying device, to allow for an adaptation of the strand-like material laying device as a whole when crossing a hill or the like. 
     Preferably, a bottom end of said second unit is aligned with a bottom end of a trailing one of the first group of plurality of first elements in depth direction of the strand-like material laying device to form a substantially continuous sole (i.e., external bottom surface) for sliding on the base of the trench. 
     Furthermore, the strand-like material laying device according to the present invention may comprise an internal guiding channel extending continuously over the overall length of the strand-like material laying device from an inlet opening at a front end thereof towards an outlet opening at a rear end thereof, for guiding a strand-like material through the strand-like material laying device into a trench formed by the strand-like material laying device. 
     Taking account of maintaining a minimum allowable bending radius of the strand-like material to be laid the guiding channel is preferably formed along a curve having a radius of curvature which is set depending on a minimum allowable bending radius of the strand-like material to be laid in the trench. 
     Moreover, preferably, the inlet opening opens in a substantially horizontal direction for receiving a strand-like material lying on the ground ahead of the strand-like material laying device, and the outlet opening opens in a substantially horizontal direction on a level with the base of a trench formed by the strand-like material laying device. To enable a smooth feeding of the strand-like material through the internal guiding channel, the strand-like material laying device may have at its front end and rear end supporting rolls for supporting the strand like material fed into the inlet opening and out of the outlet opening, respectively. 
     Furthermore, a leading one of the first group of a plurality of first elements may comprise at its front end a towing eye for connecting to a towing rope, the towing eye being located beneath the inlet opening of the guiding channel. Therefore, according to an embodiment of the present invention the strand-like material laying device is pulled by means of the towing rope. Furthermore, according to an embodiment of the present invention, the towing eye may be located beneath the inlet opening of the guiding channel in order to cause a traction force transmitted by the towing rope to act directly at the strand-like material laying device at a position close to the ground. 
     Furthermore, another embodiment of the present invention provides an appliance for the subterranean laying of strand-like material, comprising a strand-like material laying device as above mentioned, and an off-road steerable chassis frame supporting the strand-like material laying device by straddling it between a pair of left wheels and the pair of right wheels and enabling to vertically lift and lower the strand-like material laying device from and towards the ground, respectively. 
     The chassis frame may be of the articulated frame type having a central structural framework which is supported on four wheels by means of an articulating linkage assembly associated with each wheel and the framework. 
     Preferably, the strand-like material laying device is connected at its front end side to the central structural framework for pivotal movement about an axis being substantially parallel to a width direction of the strand-like material laying device, and is coupled at its rear end side to means for vertically lifting and lowering the strand-like material laying device, which means is vertically slidably supported by the central structural framework. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate a preferred embodiment of the invention. 
         FIG. 1  is a side view schematically showing an appliance carrying a strand-like material laying device according to an embodiment of the present invention. 
         FIG. 2  is a side view schematically showing the appliance of  FIG. 1  in a state where the strand-like material laying device according to an embodiment of the present invention is immersed into the ground. 
         FIG. 3  is a top view schematically showing the appliance of  FIG. 1 . 
         FIGS. 4   a  and  4   b  are side views showing the strand-like material laying device according to an embodiment of the present invention. 
         FIGS. 5   a  and  5   b  are top views showing the strand-like material laying device according to an embodiment of the present invention. 
         FIG. 6   a  is a side view schematically picking out a single element of the strand-like material laying device according to an embodiment of the present invention. 
         FIG. 6   b  is a cross-sectional side view schematically showing a coupling portion of two elements of the strand-like material laying device along a dashed line A-A in  FIG. 5   b.    
         FIG. 6   c  is a cross-sectional top view schematically showing an upper hinge of the coupling portion shown in  FIG. 6   b.    
         FIGS. 7   a  and  7   b  are top and partial side views schematically showing a lower portion of a single element of the strand-like material laying device. 
         FIGS. 8   a  and  8   b  are top and partial side views schematically showing a fin-like shoe to be attached to a lower portion of another single element of the strand-like material laying device. 
         FIGS. 8   c  and  8   d  are top cross-sectional and partial side views schematically showing the fin-like shoe of  FIGS. 8   a  and  8   b  in a state attached to a lower portion of the another single element of the strand-like material laying device. 
         FIGS. 9   a ,  9   b ,  9   c ,  10   a  and  10   b  illustrate guiding means on an internal guiding channel in order to obtain a smooth guidance of the strand-like material through the internal guiding channel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made with  FIGS. 1 to 10  to the structure and effects of preferred embodiments of the invention. 
     Referring to  FIGS. 1 to 10 , the ground surface is denoted by GS, the ground is denoted by G, a trench formed by a strand-like material laying device according to the present invention is denoted by T, and a strand-like material laid in the trench T is denoted by M. Arrows L, D, and W denote a longitudinal direction (or direction of movement), a depth direction, and a width direction (or lateral direction), respectively, of the strand-like material laying device  10 . 
       FIGS. 1 to 10  show a strand-like material laying device  10  according to an embodiment of the present invention, which is carried by an off-road steerable, four-wheeled chassis frame  100  as seen from  FIGS. 1 to 3 . As it is illustrated in  FIG. 2 , the strand-like material laying device  10  carried by the chassis frame  100  is configured to substantially vertically immerse into the ground G when being moved or pulled in the longitudinal direction L, thereby to excavate or cut the ground G and form a trench T, to smoothly feed the strand-like material M, such as a steel pipe, cable, etc., from the ground G over its entire length into the thus formed trench T and to smoothly lay it onto a base B of the thus formed trench T. 
     The chassis frame  100  as depicted in  FIGS. 1 to 3  generally includes a central structural framework  102  which is supported on four wheels  104  by means of an articulating linkage assembly  106  associated with each wheel  104  and central structural framework  102 . The central structural framework  102  may serve as a support for a cabin  108  and/or power section  110  depicted in  FIGS. 1 to 3  and a control box not shown. Other items, such as body, driver&#39;s seat, etc. (not shown) may be supported on frame in a conventional manner. The articulating linkages  106  are configured to move the four wheels  104  independently from each other in both horizontal and vertical directions with respect to the chassis frame  100 . 
     An example of a possible chassis frame  100  is SpiderPlow used by SpiderPlow Services a specialized pipeline installation company, operating in western Canada and the United States, and engineered and manufactured in Germany by Walter Föckersperger GmbH. Technical details of the chassis frame  100  and linkages  106  can be obtained from SpiderPlow Services or Walter Föckersperger GmbH, Germany. 
     As it is seen from  FIGS. 1 ,  2  and  3 , the strand-like material laying device  10  is supported astraddle by the chassis frame  100  between the pair of left wheels and the pair of right wheels. More specifically, the strand-like material laying device  10  is attached to the chassis frame  100  via support bolts which extend in width direction W through support holes  11 ,  12 ,  13  provided at the strand-like material laying device  10 , as shown in  FIGS. 4   a  and  4   b , and are held at support portions  111 ,  112 ,  113  provided at the chassis frame  100 . As illustrated in  FIGS. 1 and 2  a first support portion  111  is provided at a front end side of the central structural framework  102 , while a second support portion  112  is provided at a blade means  114  which is supported at a rear end side of a longitudinal direction extension  103  of the central structural framework  102  by means of a hydraulically operated lifting equipment  116 . An additional third support portion  113  is provided at a front end side of the central structural framework  102  at a predetermined distance above the first support portion  111 . While the first and second support portions  111 ,  112  have the function to pivotally carry the strand-like material laying device  10  on the chassis frame  100 , the third support portion  113  is primarily for supporting the strand-like material  10  in width direction W in order to prevent the strand-like material laying device  10  from tilting with respect to the chassis frame  100  about a longitudinal axis. 
     By simultaneously operating the articulating linkages  106  and the lifting equipment  116  the strand-like material laying device  10  carried by the chassis frame  100  can be moved in the depth direction D, i.e., can be lowered to immerse into the ground G as shown in  FIG. 2 , or lifted out of the ground G as shown in  FIG. 1 . 
     While in operation, the strand-like material laying device  10  can be divided in longitudinal direction L in a front or first unit  20  and a rear or second unit  40  as shown in  FIG. 2 . Referring to  FIG. 2 , the first unit  20  has the primary function of cutting the ground G and forming the trench T having substantially vertical side walls and a base B in a predetermined depth defined by the depth of immersion of the strand-like material laying device  10 , and internally feeding the strand-like material M lying on the ground surface GS in front of the strand-like material laying device  10  into the trench T when being moved in the longitudinal direction L. The second unit  40  has the primary function of internally feeding and smoothly laying the strand-like material M onto the base B of the thus formed trench T. When being immersed into the ground G by means of lowering the central structural framework  102  and blade means  114 , and being moved in the longitudinal direction L both the first unit  20  and the second unit  40  will align themselves in a substantially vertical direction due to side forces laterally acting from the vertical side walls of the trench T onto the strand-like material laying device  10 . In summary, the first unit  20  and the second unit  40  of the strand-like material laying device  10  cooperate to form a substantially trench T in the ground G and to act like a chute to smoothly feed and lay a strand-like material M from the ground surface GS towards the base B of trench T. 
     As can be best seen from  FIGS. 4   a ,  4   b ,  5   a  and  5   b , the first unit  20  and the second unit  40  are each formed of a plurality of first elements, more specifically five first elements  21 ,  22 ,  23 ,  24 ,  25 , and a plurality of second elements, more specifically two second elements  41 ,  42 , respectively, which are connected to each other in series like a flexible chain. While the first elements  21 ,  22 ,  23 ,  24 ,  25  are pivotally coupled with each other about an axis which is substantially parallel to the depth direction D, the second elements  41 ,  42  are pivotally coupled with each other and with the last one  25  of the first elements  21 ,  22 ,  23 ,  24 ,  25  about an axis which is substantially parallel to the depth direction D and an axis which is substantially parallel to the width direction W. 
     Each of the plurality of first and second elements is formed of steel plates to have a hollow rigid configuration which is closed at the left and right side walls, at the bottom and top sides, and at the front and rear sides except where a later discussed internal guiding channel  70  enters and exits. A width of each of the plurality of first and second elements is set so that the internal guiding channel  70  can be formed to feed the strand-like material M internally through the strand-like material laying device  10  as illustrated in  FIGS. 2 ,  4   a  and  4   b.    
     The five elements  21 ,  22 ,  23 ,  24 ,  25  of the first unit  20  are each structured to have a depth directional lower front end portion  21   a ,  22   a ,  23   a ,  24   a ,  25   a  and a depth directional upper front end portion  21   b ,  22   b ,  23   b ,  24   b ,  25   b.    
     The lower front end portions  21   a ,  22   a ,  23   a ,  24   a ,  25   a  taper off in longitudinal direction L to define each a cutting edge  21   c ,  22   c ,  23   c ,  24   c ,  25   c  at their front ends as can be best seen from  FIGS. 5   a ,  5   b ,  7   a  and  8   c . As shown in  FIGS. 1 ,  2 ,  4   a  and  4   b , elements  21 ,  22 ,  23 ,  24 ,  25  are staggered with respect to each other in depth direction D of the strand-like material laying device  10  so that the lower front end portions  21   a ,  22   a ,  23   a ,  24   a ,  25   a  and thus the cutting edges  21   c ,  22   c ,  23   c ,  24   c ,  25   c  of respective two successive ones of the five elements  21 ,  22 ,  23 ,  24 ,  25 , i.e. cutting edges  21   c ,  22   c  of elements  21 ,  22 , cutting edges  22   c ,  23   c  of elements  22 ,  23 , cutting edges  23   c ,  24   c  of elements  23 ,  24 , and cutting edges  24   c ,  25   c  of elements  24 ,  25 , are offset with respect to each other in depth direction D of the strand-like material laying device  10 . Accordingly, a working depth of elements  21 ,  22 ,  23 ,  24 ,  25  increases in a direction opposed to the longitudinal direction L of the strand-like material laying device  10 . As it is seen from  FIGS. 4   a  and  4   b , the cutting edges  21   c ,  22   c ,  23   c ,  24   c ,  25   c  of elements  21 ,  22 ,  23 ,  24 ,  25  are formed so as to be inclined slightly downward from the horizontal direction, terminate at a front bottom end portion in a nose portion  21   d ,  22   d ,  23   d ,  24   d ,  25   d  and project forward in the longitudinal direction L. Cutting edges  21   c ,  22   c ,  23   c ,  24   c ,  25   c  may be fixed to the front ends of elements  21 ,  22 ,  23 ,  24 ,  25 , e.g. by welding. Alternatively, cutting edges  21   c ,  22   c ,  23   c ,  24   c ,  25   c  may be exchangeably mounted to the front ends of elements  21 ,  22 ,  23 ,  24 ,  25 , e.g. by way of positive locking and bolting. 
     Moreover, as it is seen from  FIGS. 4   a  and  4   b  the soles (i.e., the external bottom surfaces)  21   e ,  22   e ,  23   e ,  24   e  of each element  21 ,  22 ,  23 ,  24  are inclined in a rear-and-upward direction to define a clearance angle α between soles  21   e ,  22   e ,  23   e ,  24   e  and the longitudinal direction L when cutting the ground G. A sole  25   e  of element  25  extends in a direction substantially parallel with the longitudinal direction L to smoothly transition to a soles  41   e ,  42   e  of elements  41 ,  42  of the second unit  40 . 
     Elements  21 ,  22  each comprise, as means for controlling the working depth thereof, an exchangeably mounted chisel-like cutting tip  21   f ,  22   f  projecting in the direction of movement of the strand-like material laying device  10 . Cutting tips  21   f ,  22   f  are screwed onto noses  21   d ,  22   d  about a longitudinal direction thereof.  FIGS. 7   a  and  7   b  illustrate in more detail the cutting edge portion of element  22 . The structure of the cutting edge portion of element  21  may be similar to that of element  22 , so a further description thereof is omitted. 
     As opposed to elements  21 ,  22 , elements  23 ,  24 ,  25  each comprise, as means for controlling the working depth thereof, a fin-like shoe  30 ,  31 ,  32  coupled to respective noses  23   d ,  24   d ,  25   d  for pivotal movement about an axis being parallel with respect to the width direction W of the strand-like material laying device  10 .  FIGS. 8   a  and  8   b  illustrate in more detail the structure of the fin-like shoe  30 , while  FIGS. 8   c  and  8   d  illustrate in more detail the cutting edge portion of element  23  having the fin-like shoe  30 . As follows from  FIGS. 8   a ,  8   b  and  8   c , fin-like shoe  30  has a U-shaped structure comprising two rearwardly extending leg portions  30   c ,  30   d  that are disposed laterally outside the side walls of element  23  to partially embrace element  23 , and a cutting tip  30   b  exchangeably mounted to a front part of the U-shade structure as a means for controlling the working depth of element  23 . Cutting tip  30   b  is screwed onto the nose  23   d  about a longitudinal direction thereof. The fin-like shoe  30  is supported at nose portion  23   d  like a lever for pivotal movement about an axis  30   a  being substantially parallel with respect to the width direction W of the strand-like material laying device  10 . As it is illustrated in  FIG. 8   d  a relative angular position of the fin-like shoe  30  with respect to element  23  can be adjusted within a predetermined range of pivotal movement at various positions defined by bolt inserting holes  35  provided at the element  23 , by inserting a bolt  34  through bolt inserting holes  35  formed at a rear portion of leg portions  30   c ,  30   d  and an appropriate one of bolt inserting holes  35  formed at element  23 . A relative angular position of the fin-like shoe  30  with respect to the element  23  is set depending on the constitution of the ground. In a not shown alternative embodiment the rearward extending leg portions  30   c ,  30   d  may be hingedly coupled with a control mechanism (e.g., a hydraulically operated control mechanism) allowing to continuously pivot the fin-like shoe  30  within a predetermined range of pivotal movement during operation of the strand-like material laying device, Since the structure of the cutting edge portions of elements  24 ,  25  and fin-like shoes  31 ,  32  correspond to that of element  23  and fin-like shoe  30 , a further description thereof is not included. 
     A supporting mechanism  65  for the strand-like material M is attached, e.g. bolted, to the front end upper portion  21   b  of element  21 , as it is seen from  FIG. 4   a . The supporting mechanism  65  includes a housing  66  and a supporting roll  67  which is supported for rotation about an axis  68  being substantially parallel with respect to the width direction W, by the housing  66 . Moreover, as it is seen from  FIG. 3 , a row of three towing eyes  69  may be provided in width direction W at a front end of the supporting mechanism  65  for connecting the strand-like material laying device  10  to a towing rope (not shown). 
     The upper front end portions  22   b ,  23   b ,  24   b ,  25   b  of elements  22 ,  23 ,  24 ,  25  which are located behind the first or leading element  21  are each coupled with a rear end of a respectively preceding one of elements  21 ,  22 ,  23 ,  24  for a limited pivotal movement about an axis being substantially parallel with the depth direction D of the strand-like material laying device  10 . More specifically, as illustrated in  FIGS. 4   a  and  4   b  the rear end portions  21   g ,  22   g ,  23   g ,  24   g  of elements  21 ,  22 ,  23 ,  24  are each coupled with the upper front end portions of elements  22 ,  23 ,  24 ,  25  by a pair of upper and lower hinges  50 . As illustrated by  FIG. 6   a  these hinges  50  include each a pair of lugs  51  which extend rearwardly from a rear end portions  21   g ,  22   g ,  23   g ,  24   g  of elements  21 ,  22 ,  23 ,  24  and carry a bolt-like hinge pin  54  illustrated in  FIG. 6   b , extending substantially in the depth direction D of the strand-like material laying device  10 . The upper front end portions  22   b ,  23   b ,  24   b ,  25   b  of elements  22 ,  23 ,  24 ,  25  are each provided with upper and lower forwardly extending lugs  52  which are each sandwiched between a corresponding one of the pairs of rearwardly extending lugs  51  and have a hinge pin accommodating bore through which a corresponding one of the hinge pins  54  passes for a sliding motion. Each of the pairs of rearwardly extending lugs  52  includes a means of abutment  53  for a front end  52   a  of the forwardly extending lug  52  if a predetermined angle of pivotal movement β about an axis defined by hinge pin  54  is exceeded in clockwise or anti-clockwise direction. As for the structure of the hinges  50  it is referred to  FIGS. 6   b  and  6   c  showing a structure of hinges  50  for coupling elements  41  and  25 , which structure corresponds in principle to that of the hinges  50  for coupling elements  21 ,  22 ,  23 ,  24 ,  25 . The rearwardly extending lugs  51 , the hinge pins  54 , and the forwardly extending lugs  52  thus form hinges  50  between two successive ones of elements  21 ,  22 ,  23 ,  24 ,  25  (as well as between elements  41 ,  42 ) which allow a pivotal movement about an axis which is defined by hinge pin  54  to a limited extent, e.g. by ±1 degree. 
     A rear end upper portion  22   h  of element  22  and the front end upper portion  25   b  of element  25  are provided with support holes  11 ,  12  for pivotally attaching the strand-like material laying device  10  to the chassis frame  100 . Moreover, the rear end upper portion  22   h  of element  22  provides at a distance above the support hole  11  an elongated bore  13  for the accommodation of a front end portion of a not depicted sliding rod which is pivotally attached at its other end portion at the chassis frame  100 . To fix the strand-like material laying device  10  in the transport position shown in  FIG. 1  there is further provided a cross-hole  14  crossing the elongated bore  13  and positively engaging with a not depicted bolt provided at the chassis frame  100  in the transport position to prevent the strand-like material laying device  10  from laterally tilting with respect to the chassis frame  100 , during a transport thereof. 
     As can be best seen from  FIGS. 4   b  and  5   b , the second unit  40  is formed of elements  41 ,  42  which are connected to each other in series like a flexible chain. As opposed to the first elements  21 ,  22 ,  23 ,  24 ,  25  which are pivotally coupled with each other only about an axis which is substantially parallel to the depth direction D, the second elements  41 ,  42  are pivotally coupled with each other and with the last one  25  of the first elements  21 ,  22 ,  23 ,  24 ,  25  about both an axis which is substantially parallel to the depth direction D and an axis which is substantially parallel to the width direction W. Hinges  50  pivotally coupling elements  41 ,  42  with each other and element  41  with element  25  differ from hinges  50  between elements  21 ,  22 ,  23 ,  24 ,  25  only in the following feature. The upper forwardly extending lugs  52  of elements  41  and  42  comprise each instead of a round hinge pin accommodating bore an elongated hinge pin accommodating hole  52   b  extending in the longitudinal direction L as illustrated in  FIG. 6   b . Accordingly, the hinge pins  54  can slide within the hinge pin accommodating holes  52   b  provided at the upper forwardly extending lugs  52   b  of elements  41 ,  42  in longitudinal direction L. On the other hand, the lower forwardly extending lugs  52  of elements  41  and  42  comprise each a hinge pin accommodating bore similar to the upper and lower forwardly extending lugs  52  of elements  21 ,  22 ,  23 ,  24 ,  25 , in which the hinge pins  54  are accommodated with a small play only sufficient to enable the hinge pins  54  to slightly incline within the hinge pin accommodating bores. Therefore, an axis for a pivotal movement of elements  41 ,  42  with respect to elements  25 ,  41 , respectively, is provided at the interface of bottom ends of elements  41 ,  25  and  41 ,  42 , which is substantially parallel to the width direction W. Moreover, a pivotal movement of elements  41 ,  42  with respect to elements  21 ,  41 , respectively, is limited by the length of the elongated hinge pin accommodating hole  52   b  provided in the upper forwardly extending lugs  52   b  of elements  41 ,  42  to a predetermined angle of pivotal movement a which is e.g. 1 to 10 degrees. 
     As can be seen from  FIGS. 4   a  and  4   b  elements  41  and  42  are aligned with each other and with respect to element  25  in depth direction D so that their bottom ends  41   e ,  42   e  are on substantially the same level with a bottom end of element  25 . 
     A supporting mechanism  60  for the strand-like material M is attached, e.g. bolted, to the rear end upper portion  42   g  of element  42  as it is seen from  FIG. 4   b . The supporting mechanism  60  includes a supporting housing  61  and a supporting wheel  62  which is supported for rotation about an axis  63  being substantially parallel with respect to the width direction W, by the supporting housing  61 . 
     Furthermore, the strand-like material laying device  10  comprises an internal guiding channel  70  which is constituted by guiding channel portions  70   a ,  70   b ,  70   c ,  70   d ,  70   e ,  70   f ,  70   g  each being provided in one of elements  21 ,  22 ,  23 ,  24 ,  25 ,  41 ,  42  so as to extend continuously over the overall length of the strand-like material laying device  10  from an inlet opening  71  at a front end of element  21 , which is located immediately above the supporting mechanism  65 , thereof towards an outlet opening  72  at a rear end of element  42 , which is located immediately below the supporting mechanism  60 , as seen from  FIGS. 4   a  and  4   b , for guiding the strand-like material M through the strand-like material laying device  10  into the trench T. Taking account of maintaining a minimum allowable bending radius of the strand-like material T the guiding channel  70  is formed through the strand-like material laying device  10  along a smoothly bent curve having a radius of curvature R which is set depending on a minimum allowable bending radius of the strand-like material T. 
     As it is seen from  FIG. 4  the inlet opening  71  is set so as to open in a substantially horizontal direction for receiving the strand-like material T laying on the ground G ahead of the strand-like material laying device  10 , and the outlet opening  72  opens in a substantially horizontal direction on a level with the base B of the trench T formed by the strand-like material laying device  10 . 
     Furthermore, in order to obtain a smooth guidance of the strand-like material M through the internal guiding channel  70  portions the internal guiding channel  70  expected to be in friction with the strand like material may be provided with guiding means  80  as shown in  FIGS. 9   a ,  9   b ,  9   c ,  10   a ,  10   b . Albeit such means are shown in combination with element  42  only, such means may be provided at any other friction portions as well, e.g. at any portions where the strand-like material M comes into contact with the sidewalls defining the internal guiding channel  70 . These guiding means  80  may include supporting members  81  which are attached via an elastically deformable material  81   b , e.g. a rubber material, at an upper side wall  71  of the internal guiding channel portions  70   a ,  70   b ,  70   c ,  70   d ,  70   e ,  70   f ,  70   g  of the corresponding one of elements  21 ,  22 ,  23 ,  24 ,  25 ,  41 ,  41 , and have a curved surface  81   a  which is provided with a low friction coating  82  to support the strand-like material M as illustrated in  FIG. 9   a . Alternatively, these guiding means  80  may include supporting rolls  85  which are each rotatably held by the corresponding one of elements  21 ,  22 ,  23 ,  24 ,  25 ,  41 ,  41 , and have a curved surface  85   a  which is provided with an elastic deformable coating  86  to support the strand-like material M as illustrated in  FIG. 10   b.    
     Although the present invention has been described in connection with a specific preferred embodiment for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.