Abstract:
A device for transmitting and distributing vibration and stress exerted by a vibrator on objects to be driven into the ground includes a supporting plate of repartition of vibrations bolted on a sole plate of the vibrator having dimensions lower to that of the supporting plate. A “I” shaped profiled rail is on its entire length on the supporting movable plate supporting movable hydraulic clamps.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a device for the transmission and distribution of the vibration and stress exerted by a vibrator on objects such as stakes, tubes or sheet piles, with a view to driving them home, with a horizontal cross-section of dimensions exceeding those of the vibrator. 
     2. Description of the Prior Art 
     We know that the vibrators commonly used for this type of application are huge machines comprising at least one couple of offset rotary weights rotated in opposite directions and at a same speed by a motorization. 
     By way of these arrangements, the centrifugal forces generated by the rotation of the weights add up in a direction defining an axis of work. The centrifugal forces compensate one another in the other directions to cancel one another out in a direction perpendicular to the axis of work. 
     Usually, the vibrator is suspended at the end of the cable of a crane or similar mechanism, via a device (lifting eye) enabling the vibrator to be displaced vertically. 
     In the case of the cross-section of the object to be driven into the ground being greater than that of the vibrator, the transmission and distribution of the stress between the vibrator and the object to be driven into the ground are usually performed by a transmission and distribution chamber made of welded sheet steel which is fastened on one side, e.g. by bolting, to the underside of the vibrator (usually a fastening sole plate) and which bears, on the other side, a fastening device that can be adapted to the dimensions of the object to be driven into the ground. This chamber can, e.g., be constituted by two braced parallel plates by a partitioning forming crossbars as represented in U.S. Pat. No. 3,224,514. 
     When tubular stakes are involved, this device comprises a multiplex device, e.g. a so-called “quadriplex” device, made up of four rail sections or four “T”s bolted to the chambers and a hydraulic clamp mounted slidably with a locking facility on each of the sections or “T”s. 
     Experience has shown that, due to the intense stress to which it is subjected, the transmission and distribution chamber tends to deteriorate rapidly and must be frequently reloaded or replaced. 
     Detailed examination of the used chambers reveals that the deteriorations materialised in the form of cracks located along the welding seams and at the base of the protruding portions of the vibrodriver sole plate are due both to the quality of the chamber welding seams and to the heterogeneity in the mechanical behaviour of the chamber at the level of the welding seams. It so happens that this heterogeneity is particularly significant due to the distribution of the reverse bendings at the frequency of the vibrations generated by the vibrator. 
     OBJECT OF THE INVENTION 
     The aim of the invention is therefore more particularly to remedy these drawbacks. 
     To this end, the invention proposes a vibrator of type comprising at inside of a case at least one pair of eccentric-rotary weights driven in rotation, in the opposed direction, at a same speed, by a motorization and least one hydraulic clamp mounted sliding on a profiled rail integral with the lower part of said case. 
     SUMMARY OF THE INVENTION 
     According the invention, this vibrator is characterized in that: 
     the underside of the case is formed by a sole plate whose dimensions sensibly correspond to those of a cross section of the vibrator and on which is assembled by bolting a supporting plate of repartition of vibration and stress whose dimensions are selected so as to exceed the dimensions of said sole plate, and 
     the said profiled rail presents a “I” shaped cross section and is bolted on said plate. 
     In cases where it is possible to limit the number of fastening points to two, the rail can be rectilinear and bear two hydraulic clamps. 
     Conversely, in cases where the object to be driven into the ground is of tubular shape and requires more than two fastening points, the vibration and stress transmission and distribution device can comprise at least one cross-piece made with profiled rails of “I”-shaped cross-section, and assembled by bolting thereof to the supporting plate, each of the branches of this cross-piece bearing a hydraulic clamp. One can readily envisage six rail sections each bearing a clamp when required by virtue of the force to be transmitted. 
     The device embodying the invention does not therefore require any welding (only the branches of the cross-piece need be welded together where they meet). 
     Furthermore, the invention derives benefit from the “I”-shaped structure both in terms of the transmission of stress and the bending behaviour. 
     Likewise, the elastic deformation of the cross-piece adapts excellently to that of the supporting plate and fastening sole plate of the vibrator. 
     The life span of the device is therefore considerably extended. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will be described hereunder, by way of a non-limiting example, in reference to the corresponding accompanying drawings in which: 
     FIGS. 1 and 2 are frontal and side views of a vibrator equipped with a transmission and distribution device according to the invention; 
     FIGS. 3 and 4 are respectively views from underneath (FIG. 3) and the side (FIG. 4) of the transmission and distribution device of the vibrator represented in FIGS. 1 and 2; 
     FIG. 5 is a partial view on a larger scale of the vibrator represented in FIG. 1, this view enabling a more accurate description to be provided of the location of the bolts fastening the rail sections to the supporting plate; 
     FIGS. 6 and 7 are axial (FIG. 6) and transversal (FIG. 7) cutaway views, on a larger scale, of a hydraulic clamp; 
     FIG. 8 is a view from beneath of a transmission and distribution device equipped with six rail sections. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In these examples, the vibrator  1  is comprised of a substantially parallelepiped case  2  in which are rotatably mounted three series of weights M 1  to M 4 , M′ 1  to M′ 4 , M″ 1  to M″ 4  each comprising four weight/pinion assemblies meshing with one another. 
     These series of weights are rotatably driven by means of at least one hydraulic motor (in this instance four hydraulic motors of which two, MH 1  and MH 2  are visible). 
     The hoisting of the vibrator by means of a lifting device such as a a crane is performed via a lifting eye  3  equipped with a means for damping the vibrations, this assembly being mounted on the upper part of the vibrator  1 . 
     As previously stated, the transmission and distribution of the vibrations, generated by the vibrator, to the objects to be driven into the ground (stakes, sheet piles) are ensured by a vibration and stress distribution device  4  which is secured by bolting to a sole plate  5  constituting the underside of the vibrator  1  and whose dimensions correspond substantially to those of a horizontal cross-section of the vibrator. 
     In the example represented in FIGS. 1 to  3 , this device  4  uses a supporting plate  6  whose dimensions exceed those of the sole plate and to which a cross-piece  7  is fastened by bolting, each of the branches B 1  to B 4  of said cross-piece consisting of a profiled rail R of “I”-shaped cross-section. 
     The cross-piece  7  is bolted to the supporting plate  6  by means of bolts which pass through a plurality of through holes P respectively opening out at the level of the transversal wings  8  on either side of the vertical web of the “T”. 
     This fastening is further completed, in each end of the rail section R by a series of bolts (5 in this instance) which pass through the supporting plate  6  and which come and screw into the respective threaded holes P′ made in the transversal wing  8 , these holes having their axis in the longitudinal mid-plane of symmetry of the rail section R. 
     These boltings enable the transversal wings  8  of the rails R (preferably larger than the transversal wings  9 ) to be fastened efficiently to the supporting plate  6  while ensuring good mechanical symmetry. 
     By way of these arrangements, the mechanical properties of the “I”-shaped structures are put to best advantage both in terms of bending and in terms of the transmission of stress (vibrations) between the supporting plate  6  and the hydraulic clamps PH mounted slidably on the rails at the level of the transversal wings  9 . 
     In the example illustrated in FIGS. 6 and 7, the clamps PH are each composed of a massive body comprising, on one side, a profiled groove G of “T”-shaped cross-section substantially complementary to that of the lower part of a rail (web A+transversal wing  9 ) into which it can fit and slide. 
     The lower part of the body is, in a plane perpendicular to the profiled groove G, of a form having a substantially “U”-shaped cross-section with relatively thick wings A 1 , A 2  constituting the jaws of the clamp. These wings A 1 , A 2  delimit a cavity C into which is fitted the edge of the object to be driven into the ground, e.g. the edge of the tube constituting a stake. 
     To the inner wall of the wing A 1  is bolted a block  11  whose outer side is striated so as to have good surface roughness. 
     As for the wing A 2 , it comprises a transversal bore  12  (perpendicular to the axis of the “U”-shaped cavity) which opens out into its inner wall, at right angles to the block. This bore  12  constitutes the cylinder of a jack of which the piston  13  can enter the cavity C, under the effect of the pressure exerted by a hydraulic fluid, to grip the upper edge of the part to be driven into the ground. 
     The axial locking of the clamp PH onto the profiled rail R is ensured by five small hydraulic jacks V 1  to V 5  oriented vertically, arranged in a housing L of the body opening out into the lower (horizontal) wall of the groove G. 
     These jacks V 1  to V 5  act on a mobile sole plate S guided by the upper edges of the housing L and which, under the effect of the pressure exerted, come to bear against the lower side of the rail R while axially locking the clamp PH to the latter. 
     These arrangements enable the vibrator to be adapted very easily to objects of different shapes and dimensions. 
     The locking of the clamp onto these objects is further facilitated by a flaring E of the cavity extended by deflectors D extending obliquely in relation to the vertical line. 
     The invention is not, of course, limited to the embodiment described above. 
     In fact, the stress transmission and distribution device could comprise a much larger number of rail sections. 
     Thus, this (multiplex) device could comprise six rail sections T 1  to T 6  arranged in the shape of a star as represented in FIG.  8 . 
     In this example, the rail sections T 1  to T 6  are arranged according to two diametrically opposite sets of three sections T 1  to T 3  and T 4  to T 6 , angled at 45° to one another. 
     The hydraulic clamps PH 1  to PH 3  borne by the set of rail sections T 1  to T 3  are arranged so as to clamp a cylindrical part of maximum diameter, whereas the clamps PH 4  to PH 6  borne by the set of rail sections T 4  to T 6  are arranged so as to clamp a part of minimum diameter.