Such a driving device may be a vibrating device, in which eccentrically rotating weights generate vibration. An object can be inserted into the ground by attaching such a vibrating device to said object, so that said object is inserted into the ground, either under the influence of its own weight or by exerting an additional downward force thereon, while being vibrated. While the term inserting an object into the ground is used herein, the same technique can be used for removing said object from the ground, and consequently it applies to both operations. When an object is being removed, an upward force rather than a downward force is exerted on the object during said vibration.

It is known to engage an object clampingly so as to attache a vibrating device to said object, for example by moving two clamping members together, so that part of the object is clampingly engaged therebetween. Since the clamping operation must meet stringent requirements, especially in the case of larger and/or heavier objects, that is, no relative movement must take place, not even in the case of very large, varying forces, such clamping means are voluminous and complicated. When an elongated object is to be inserted into the ground, the available space is not always sufficient to accommodate voluminous clamping means, especially when such an object is to be inserted entirely or nearly entirely into the ground, so

that the clamping means must reach below the ground surface.

The object of the invention is to make it possible to use clamping means which can be designed to have limited dimensions, which operate reliably and which are capable of inserting an elongated object entirely into the ground.

In accordance with the method for inserting an elongated objected into the ground, the object is to that end engaged by clamping means, wherein said clamping means extend into a recess formed in the end of said object and clampingly engage the object on the wall of the recess.

Preferably, an object whose circumferential shape is substantially constant along its length, such as a pipe, is inserted into the ground.

When the object is engaged, a number of clamping members are moved outwardly in radial direction with respect to the elongated object, until said clamping members abut against the wall of the recess. Since the clamping members move outwardly relative to each other thereby, said movement can be effected by having the clamping members push off against each another. A conical mandrel can thereby be moved between the clamping members in longitudinal direction with respect to the object, causing the clamping members to move in radial direction.

This enables a simple construction of the clamping means of limited dimension, whilst it is nevertheless possible to exert large clamping forces. Preferably, three or four, or even more clamping members are used.

In one preferred embodiment, convexly curved engaging surfaces are present on the clamping members, which engaging surfaces clampingly engage the cylindrical inner wall of the recess in circumferentially spaced-apart places. By engaging the inner wall of the recess in

several places, preferably six, or more preferably eight or more places, the object is prevented from being subjected to an excessive local force, which force may deform the object. In one preferred embodiment, each clamping member comprises two engaging surfaces, so that a total of eight engaging surfaces clampingly engage the inner wall of the recess when four clamping members are provided.

Preferably, the clamping means are also provided with a stop surface, which abuts against a transversely extending surface on the end of the elongated object.

Preferably, the elongated object is a pipe, and said stop surface is annular, so that it is capable of abutment against the circular edge of the pipe.

A good clamping action both of the stop surface and of the clamping members can be obtained by moving the clamping members not only radially outwards upon clamping, but also towards the stop surface. As a result of this obliquely upward movement, also the stop surface of the clamping means is pressed firmly against the end of the object.

Preferably, the driving device is a vibrating device, in which eccentrically rotating weights generate vibration.

The invention furthermore relates to a driving device for inserting an elongated object into the ground, which device comprises means which are capable of engaging the object in a recess present at the end of said object, wherein the clamping members clampingly engage against the inner wall of said recess.

In one preferred embodiment, the device comprises a narrow portion, which extends between said clamping members and the part of the device which generates the driving movement, which narrow portion has a transverse

dimension which is substantially equal to, or smaller than, the transverse dimension of the object to be inserted into the ground. When the object to be inserted into the ground is a pipe, and the clamping means are provided with an annular stop surface which abuts against the circular edge of the pipe, the narrow portion has a transverse dimension which is smaller than the outside diameter of the pipe, so that the pipe can be inserted entirely into the ground, whilst the driving device will remain above the ground, of course. Preferably, the length of the narrow portion is larger than the transverse dimension thereof, preferably it is at least twice as large. In one preferred embodiment, said narrow portion has a length of more than one metre, so that the object can readily be moved to a position below the ground surface.

Further aspects of the invention and of the method, which can be used separately as well as in combination with each other, will be described by means of an embodiment and be defined in the claims.

In order to explain the invention more fully, an embodiment of clamping means which are capable of clampingly engaging a pipe will now be described.

Figure 1 is a longitudinal sectional view of the clamping means; and Figure 2 is a cross-sectional view along line II-II of Figure 1.

The figures are merely schematic representations of the device, wherein only relevant parts are shown.

Figure 1 shows a pipe 1 in longitudinal view, which pipe is engaged by clamping means at its end. Said clamping means comprise clamping members 2, which can be moved outwardly into abutment against the inner wall 3 of pipe

1. To that end, each clamping member 2 comprises an oblique sliding surface 4, which abuts against a sliding surface 5 formed on an annular pushing member 6.

Clamping members 2 are movably provided on disc 7, which can be moved in vertical direction, from the top to the bottom in Figure 1, and vice versa, in order to move the clamping members 2 with their sliding surfaces 6 over the sliding surfaces 5 of annular pushing member 6. It will be apparent that upward movement of disc 7 will cause clamping members 2 to move outwardly.

The clamping means are furthermore provided with a radial flange 8, by which the clamping means are supported on the end of pipe 1. Flange 8 is thereby provided with an annular stop surface, which abuts against the circular edge of pipe 1.

Disc 7 is connected by means of a piston rod 9 to piston 10, which can move within a cylinder, wherein a cylinder space 11 is present above piston 10 and a cylinder space 12 is present under piston 10, which cylinder space 12 extends round piston rod 9. The supply and discharge of fluid to and from cylinder space 11 takes place via a pipe 13, and the supply and discharge of fluid to and from cylinder space 12 takes place via through-flow opening 14. It will be apparent that piston 10, and thus disc 7, can be moved up by supplying fluid to cylinder space 12, and down by supplying fluid to cylinder space 11. This movement causes the clamping members 2 to move obliquely outwards/upwards, until they clampingly engage the inner wall 3 of pipe 1.

The clamping means are placed on pipe 1 when piston 10 has been moved downwards to such an extent that the clamping members 2 have moved inwards, that is, towards each other. When flange 8 abuts against pipe 1, hydraulic fluid is supplied to cylinder space 12 via through-flow

opening 14, so that piston 10, and thus disc 7, will move in upward direction. Fluid is thereby discharged from cylinder space 11 via pipe 13. Disc 7 is moved upwards until clamping members 2 clampingly abut against the inner wall 3 of pipe 1. Following that, the vibrating device (not shown), which is positioned above the clamping means in Figure 1, can drive pipe 1 while vibrating said pipe, so that it can be inserted into the ground.

Figure 1 is a cross-sectional view along line II-II of Figure 1. Figure 2 shows the piston rod 9 surrounded by an annular cylinder space 12, which is enclosed by cylinder wall 15. Surrounding cylinder wall 15 is annular pushing member 6, which pushing member 6 is provided with four sliding surfaces 5, against which clamping members 2 abut. Each clamping member 2 is provided with two convexly curved engaging surfaces 16, so that the inner wall 3 of pipe 1 is engaged in eight, circumferentially spaced-apart places. Figure 2 furthermore shows disc 7 in elevation.