EP0020820B1

EP0020820B1 - Anchor pile hoisting device

Info

Publication number: EP0020820B1
Application number: EP79200351A
Authority: EP
Inventors: Thomas Jacobus Ruyter
Original assignee: Amsterdamse Ballast Bagger En Grond (Amsterdam Ballast Dredging) BV; Scheepswerf en Machinefabriek De Liesbosch BV; Ballast Nedam Groep NV
Current assignee: Ballast Nedam NV; Amsterdamse Ballast Bagger En Grond (Amsterdam Ballast Dredging) BV; Scheepswerf en Machinefabriek De Liesbosch BV
Priority date: 1979-06-29
Filing date: 1979-06-29
Publication date: 1983-05-11
Also published as: EP0020820A1; DE2965356D1

Description

The invention relates to an anchor pile hoisting device comprising at least one hoisting cable, a supporting ring attached to the lower end of said cable or cables, said ring having a passage adapted for slidably receiving a pile, said ring at least substantially surrounding said passage, at least one wire loop connected at each end to said supporting ring, the or each wire loop in use frictionally engaging the pile surface and forming an acute angle (a) with a plane extending perpendicularly to the sliding direction of said ring.
Such a device is known. The loop ends each engage a pin fixed to the ring. With the known type of anchor pile hoisting device hoisting or withdrawal of the anchor pile requires the extraction force to be transferrable to the pile. This is achieved by causing the wire loop to engage the pile wall with adequate frictional force. An extraction force in the hoisting cable equal to the sum of the adhesive force of the pile in the ground and the weight of the pile brings about an orthogonal force of the wire loop on the pile jacket which produces a lighter friction between the wire loop and the pile wall as the angle between the wire loop and the plane at right angles to the pile becomes larger. With given dimensions and a given weight of the anchor pile and its adhesive force are thus associated a fixed length and section of the wire and the wire loop angle. If the wire length increases, for example, due to elongation of the wire loop, the wire loop angle will also increase so that less friction will be produced and the wire loop may slip.
The known device of the kind set forth comprises a wire loop which is pre-tensioned in order to avoid elongation so that with the wire loop load to be expected the resultant lengthening of the wire loop and hence the wire loop angle can be kept within permissible limits. However, in the rough dredging operations the wire will nevertheless lengthen after prolonged use. Therefore, in order to avoid catastrophes the known wire loops are replaced at regular intervals.
The invention has for its object to enhance the lifetime of the wire loop, whilst the length of the wire loop and hence the wire loop angle are kept within the predetermined narrow limits. To this end the anchor pile hoisting device according to the invention is characterized by adjustment means acting between the supporting ring and wire loop to set the effective length of the or each wire loop.
US-A-1 501 888 discloses a hoisting device for handling concrete pipes mainly consisting of a sling surrounding the pipe to be handled. Said sling is constituted by a ring part, which in combination with a hoisting chain part constitutes a closed loop, having a non-predetermined length. Due to the non-predetermined length, the acute angle between the loop and the plane extending perpendicularly to the pipe is not predetermined resulting in a non-predetermined tension in the loop and a non-predetermined friction.
The loops of the hoisting devices of FR-A-932 467, US-A-2 819 923 and US-A-1 912 244 also each have a non-predetermined length.
The adjustment means of a preferred embodiment of an anchor pile hoisting device according to the invention comprise tensioning means which may consist of a simple screw.
In a further development of the anchor pile hoisting device according to the invention the wire loop has a smaller structural height, because the wire loop only partly surrounds the pile.
In order to permit of carrying out the post- adjustment operations in due time, a further development of the anchor pile hoisting device according to the invention comprises an angle feeler arranged on the supporting ring and measuring the wire loop angle.
In a still further developed embodiment of the anchor pile hoisting device according to the invention the tensioning device comprises a leverage for adjusting the effective length during the hoisting operation.
The above mentioned and further features of the invention will be described more fully hereinafter with reference to a drawing.
The drawing shows schematically in:

Figures 1 to 3 each a play of forces for a wire loop engaging around a pile,
Figure 4 part of a suction dredger with an anchor pile hoisting device in accordance with the invention,
Figure 5 on an enlarged scale a detail V of Figure 4,
Figures 6, 7, 9, 10, 11 and 12 each a variant of the detail V of Figure 4 and
Figure 8 a side elevation of detail VIII of Figure 7.

A ground dredger 32 as shown in Figure 4, for example, a cutter head dredger, turns during operation around an anchor pile 6 lowered into the soil 9 and being movable up and down in guides 28 with respect to a floating body 1 on the water 33. Lifting the anchor pile 6 is performed by means of an anchor pile hoisting device 31, comprising a lifting cylinder 2 standing on the floating body 1, a hoisting cable 3 passed around a pulley 4 supported by the piston rod of the lifting cylinder 2, a supporting ring 11 and a wire loop 5 wound twice around the anchor pile 6, said ring 11 being directly or indirectly attached to the hoisting cable 3. When the anchor pile 6 is lifted, the hoisting cable 3 draws the wire loop 5, which is thus drawn tightly around the anchor pile 6 and builds up a sufficient frictional resistance w in order to overcome by a lifting force G' the sum of the weight G of the anchor pile 6 and the ground resistance Gg Figures 1 to 3 illustrate this play of forces in a simplified manner.
Referring to Figure 1, the lifting force G' of the hoisting cable 3, which draws the wire loop 5 .surrounding the anchor pile 6, produces in said wire loop 5 a tensioning force K,, whilst an angle a₁ is formed between the wire loop 5 and the plane 7 extending perpendicularly to the axis 8 of the pile, and so perpendicularly to the sliding direction of said ring 11.
The component N normal to the pife axis 8 is G' cotan a. The frictional resistance w produced=f.N=f.G' cotan a.
Since the frictional resistance f between the wire loop 5 and the pile 6 is a constant, the cotan a and hence the angle a determine the lifting force G'.
From Figure 1 it will be apparent that in case of a small angle a₁ a heavy force N, is exerted, which results in a heavy frictional resistance w₁ so that a high lifting force G' is prevailing. With a small angle a₁, however, the tensioning force K, is found to be comparatively high so that the wire loop 5 must be made from a thick and hence expensive cable.
Referring to Figure 2 the angle a₂ appears to be chosen correctly, because it results in a reasonable tension force K₂, whilst because of G' being equal to f.N₂ a sufficient lifting force is obtained.
The angle a3 of Figure 3 is too large and results in an inadequate lifting force G'.
The anchor pile hoisting device of Figure 5 has a supporting ring 11 surrounding the pile 6 and suspended by means of a fastening pin 29 to the hoisting cable 3.
Figure 5 shows that the supporting ring 11 is arranged around the pile 6. One end 18 of the wire loop 5 is journalled by means of a wire fastener 12 as shown in Figure 11. The effective length of the wire loop 5 is adjusted by means of adjustment means which is fastened to the supporting ring 11.
Figure 5 shows a tensioning means 10, which automatically tensions the wire loop 5 by means of a lever 22 in accordance with the lifting force G'. The lever 22 is pivotally journalled on the support 11 by means of a pivot 57 and has a cam 23, to which is fastened an arcuate cable saddle 60. The end 36 of the wire loop 5 extends above the cable saddle 60 towards a fastening pin 61. The higher lever 22 turns upwards with a heavier force, the shorter becomes the effective length of the wire loop 5 and the smaller becomes the angle a.
Figures 7 to 10 illustrate a number of stretching devices adjustable in a different way.
The anchor pile hoisting device 31 according to the invention shown in Figure 7 comprises a tensioning device 40 comprising an eccentric 14 rotatably journalled in the supporting ring 11 and fixable by means of a pin 41 in a hole selected from a plurality of holes 42. By selecting the correct position among the plurality of eccentric positions the effective length of the wire loop 5 and hence the angle a can be adjusted to the required value. If due to elongation of the wire loop 5 the angle a becomes larger, the wire loop 5 comes into contact with the angle feeler 17, which indicates that the effective length of the wire loop has to be shortened by readjustment of the eccentric 14.
Referring to Figure 9 the anchor pile hoisting device according to the invention comprises as a tensioning device 40 a screw device 15 comprising a nut 45 bearing on a console 44 fastened to the ring 11 and received on a threaded rod 46, which is fastened to one end 36 of the wire loop 5, the other end 37 of which is fastened to a fixed pin (not shown) on the supporting ring 11.
Figure 10 differs from Figure 9 in that the screw device 15 is replaced by a pin 50 and a rod 48 having holes 49. The pin 50 is inserted into the console 44 and into a selected one of the holes 49.
Figure 11 shows an improved wire loop 5 made from a flat, for example, braided belt 18.
Figures 12 and 6 show each a wire loop structure of small height b. As shown in Figure 12 a single wire loop 20 partly surrounds the pile 6. Figure 6 shows a plurality of wire loops 20 journalled on a divided support ring 21, the two halves 51 of which are supported each by means of two hoisting cables 3. The wire loops 20 are held at a distance from the guide ring 21 by spring stretchers 24, which provide the required distance and hence the required lifting force G'. The effective length of the wire loop 20 is adjusted, as shown in Figures 12 and 6, by means of a hydraulic post-tensioner 56.

Claims

1. An anchor pile hoisting device (31) comprising at least one hoisting cable (3), a supporting ring (11, 21) attached to by the lower end of said cable (3) or cables, said ring (11,21) having a passage adapted for slidably receiving a pile (6), said ring (11, 21) at least substantially surrounding said passage, at least one wire loop (5, 20) connected at each end to said supporting ring (11, 21), the or each wire loop in use frictionally engaging the pile surface and forming an acute angle (1) with a plane extending perpendicularly to the sliding direction of said ring (11, 21), characterized by adjustment means (10, 40, 48, 50, 56) acting between the supporting ring (11, 21) and wire loop (5, 20) to set the effective length of the or each wire loop (5, 20).

2. A device as claimed in claim 1, characterized in that the adjustment means (10, 40, 48, 50) are journalled on said supporting ring 1).

3. A device as claimed in claim 1 or 2, characterized in that the adjusting means comprise a tensioning device (10, 40, 48, 50, 56).

4. A device as claimed in claim 3, characterized in that the adjustment means comprises at least one screw (24, 46).

5. A device as claimed in claim 1 characterized in that in order to reduce the structural height (b) of the wire loop (20) around the pile the at least one wire loop (20) surrounds the pile (6) only partly.

6. A device as claimed in claim 2 characterized in that the adjustment means comprises a leverage (22) for adjusting the effective length during the hoisting operation.

7. A device as claimed in any one of the preceding claims, characterized in that the at least one wire loop (5, 11) is constructed in the form of a flat belt (18).

8. A device as claimed in any one of the preceding claims, characterized in that an angle feeler (17) measuring the wire loop (5) is arranged on the supporting ring (11). ).