WO1988003197A1

WO1988003197A1 - Cutting device

Info

Publication number: WO1988003197A1
Application number: PCT/GB1987/000765
Authority: WO
Inventors: Anthony Walby Wakefield
Original assignee: Wakefield Anthony W
Priority date: 1986-10-28
Filing date: 1987-10-28
Publication date: 1988-05-05
Also published as: AU8105487A; GB8625749D0

Abstract

A cutting device comprising a drum (1) which is rotatable about a longitudinal axis and which carries on its outer surface a plurality of spaced teeth (2) arranged on at least one helical path over the surface of the drum and at least one drive motor mounted within the drum. The cutting device may be used in connection with underwater piling and suction dredgers etc.

Description

CUTTING DEVICE

This invention relates to a cutting device, particularly for use in excavation.

Under sea technology frequently demands that cables and pipelines should be buried In the sea bed. For maintenance, inspection and repair of such pipelines and cables it is sometimes necessary to erect a coffer dam around the section in question in order that the trench containing the cable or pipeline can be unfilled. Such coffer dams are generally constructed of sheet piling and can, be erected, in principle, using single piles, pre-assembled panels or as a complete unit. Whatever the method of erection, however, the bottoms of the piles must, of course, be buried in the sea bed.

Conventional methods of pile driving are not suitable for submarine use and currently, the method used to introduce the bottoms of the piles below the surface of the sea bed has been to use water jets to fluidise the sea bed material so that the pile sinks under its own weight below the surface. This works quite well, in free- running granular material such as sand but becomes less satisfactory when the sea bed material is variable or cohesive or contains boulders. It is unworkable In boulder clay which is a common sea bed material around the coasts of the U.K.

According to the invention a cutting device which may be used for excavating trenches for introducing piling in the erection of coffer dams and for other under water and terrestrial operations has now been developed.

The cutting device of the Invention comprises a drum which is rotatable about a longitudal axis and which carries on its outer surface a plurality of spaced teeth, preferably arranged on at least one helical path over the surface of the drum. The drum at its ends has support means whereby it can be mounted with its longitudal axis parallel to the surface which is to be excavated and preferably it also has at least one drive motor located within the drum.

For use in the construction of a coffer dam at least one cutter device according to the invention is arranged along the bottom end of each pile to be used In the construction with Its longitudinal axis perpendicular to the longitudinal axis of the pile and parallel to the plane of the pile. On operation of the motor to rotate the drum, the teeth in the drum cut into the bed material to form a trench into which the pile drops, following the cutter. The helical flight of the teeth tends to move bed material both up the sides of the pile and longitudinally so that the bed material is cleared out of the way as the rotation continues and the drum, carrying its pile, continues to penetrate the bed.

If after completion of the operation for which the coffer dam is required it is desired to move the coffer dam, rotation of the drum in the opposite direction to that for insertion of the pile will tend to cause it to climb up the walls of Its trench thereby aiding removal of the pile.

A sideways force is applied to the pile by the rotation of the drum. This can be minimised by providing on each pile a plurality of drums adjacent pairs of which carry flights of teeth of different hand and are rotated in opposite directions. Although in this case, excavated material tends to accumulate between adjacent drums because of the lateral movement of material this can be cleared easily by means of a jet pump or suction means or the like.

The cutter of the invention is also of use in suction dredging operations to break up the material to be dredged so that the spoil can be fed at the optimum concentration for efficient operation of the dredge pump.

For acceptable maintenance levels and stability in operation dredging spoil must be fed to traditional centrifugal pumps at a low solids concentration. To this end in conventional dredgers the cutter is generally of an an open crown or open cylindrical form and the suction inlet leading to the dredge pump is located within the cutter. The cutter disengages the dredging spoil which passes up through the cutter and is sucked together with large quantities of water into the dredge pump. Recent developments in dredge pumping equipment have led to pumps that can handle spoil at far higher solids concentration and for this purpose it is desirable to have a cutting device that directs the spoil directly into the dredge pump inlet so that the amount of water that is sucked in with the spoil can be controlled more easily to achieve optimum operating conditions for the dredge pump.

Moreover, with conventional pump dredging equipment it is necessary to have a certain amount of water to provide the necessary dilution of the spoil for passage to the dredge pump before the dredging operation can commence. A certain level of water is normally also needed in order to be able to float the dredge. By using a cutter according to the invention instead of a conventional cutter it is possible to commence dredging on an almost dry site.

In use in a dredging installation the cutter is mounted transverse to the axis of the dredging ladder and just outside the suction inlet of the dredge pump. It is preferably arranged to be adjustable in level to suit the angle of the dredge ladder at any particular time. The cutter comprises either a single drum in which the helical flights of the teeth are of different hand on different sides of the centre line or two separate drums with helical flights of teeth of different hand. Whichever arrangement is used the excavated material passes longitudinally along the drum towards the centre line and is removed by the action of the dredge pump. When two separate drums are used the axies of the two drums are preferably each inclined towards the suction inlet of the dredge pump. By making the length of the cutter equal to the width of the dredging barge it is possible that dredging can commence with a minumum of water. A channel can be cut of sufficient width to receive the dredging barge without the need for swinging or slewing of the dredging ladder, which can be very difficult when the dredging barge is not actually afloat. If the material to be dredged is of a suitable consistency it is quite feasible to dredge out a channel of rectangular cross section which currently cannot be achieved with conventional dredging equipment or can be achieved only with great difficulty and very accurate manoeuvεring of the dredging barge. Simple alteration of the speed of rotation of the cutting drum will ensure that the average production rate of the dredge is very close to the maximum or Ideal production rate for the particular dredge pump used and the unit cost of the spoil that can be removed is greatly reduced.

The invention will now be described in greater detail by way of example with reference to the drawings in which Fig 1 is a diagrammatic side view of one form of cutter according to the invention; Fig.2 is an end view of the cutter shown in Fig.1; Fig.3 is a diagrammatic view of a coffer dam showing cutters according to Figs.1. and 2 in position for operation and Fig.4. is a diagrammatic view of a dredging barge embodying a cutter according to the invention.

Referring to Figs. 1 and 2 the cutting device according to the invention comprises a hollow drum 1 carrying on its outer surface a plurality of spaced teeth 2. The teeth 2 are arranged in at least one helical path on the surface of the drum. In the case of the drum shown in Fig.1. the teeth are arranged on two flights shown in dotted lines as 3a and 3b. A hydraulic drive motor 4 is arranged inside the drum to drive the drum in both clockwise and anticlockwise directions. The drum Fig.l is mounted for rotation on stub axles 5 carried on support yokes 6. The hydraulic fluid for driving motor 4 is passed to the motor through pipe 7 which passes through one of the stub axles 5 and it's associated yoke 6. The drum 1 is sealed against intrusion of water or other environment in which it is operated. The yokes 6 also carry water jets for local disintegration of the sea-bed material.

Although as described the motor 4 is a hydraulic motor any suitable motor drive can be used with the feed lines to the motor being protected by passage through the stub axles 5 and yokes 6. If necessary or desired two motors 4 can be provided one at each end of the drum 1.

As shown in Fig.3. a coffer dam 9 is constructed from sides 10 and ends 11 of prefabricated piling units to form a rectangular structure. The ends 11 have central cut out portions 12 to allow the coffer dam 9 to pass over an electric cable or pipe on the sea bed. Around the bottom edge of the coffer dam are arranged a plurality of cutting devices of the type shown in Figs.1 and 2. The drums 1 of these devices are arranged with their longitudinal axes perpendicular to the longitudinal axes of the piles and parallel to the length of the prefabricated piling structures 10 and 11. Adjacent cutters are arranged with the flight of their teeth 2 of opposite hand and are arranged to be driven for rotation in opposite directions. This arrangement minimises the lateral load on the piling caused by rotation of the drums. The drums 1 are mounted to the piles by means of the yokes 6.

In operation the coffer dam 9 is placed on the sea bed with the cut out portions 12 overlying a cable or pipe which it is desired to excavate. Rotation of the cutters is effected by means of the motors 4. As the drums 1 rotate the teeth 2 cut into the sea-bed material displacing material both upwards in the direction of rotation of the drums 1 and laterally of the drums 1 under the auger-action of the helical flights of teeth 2. Material that accumulates between adjacent drums 1 can be displaced by means of the fluid jets 8 carried by the yokes 6.

When the bottom ends of the piling 10 and 11 are sufficiently deeply buried in the sea-bed the rotation of the drums 1 is stopped.

On completion of the operation for which the coffer dam is required rotation of the drums 1 in a direction opposite to that used for their introduction tends to drive the drums and the associated piling up outwardly of the trench that they have made for themselves thereby greatly aiding the removal of the piling. Such rotation of the drums also creates turbulence which reduces suction between the bottom ends of the piling and the sea-bed material in which they are lying.

Fig 4 shows a dredging barge incorporating a cutter according to the invention. The dredging barge 21 has a dredging ladder 22. At its lower end the dredging ladder carries a jet pump 23 which is operated by means of fluid in pipe 24. Dredging spoil is sucked up in the dredging head 25 and passes along with the jet pump fluid along pipe 26. The cutting head 27 is as described in connection with Figs 1 and 2 except that the drum 1 carries helical flights of teeth 2 that are of opposite hand on each side of the central radial plane of the drum 1 so that on rotation of the drum 1 in an anticlockwise direction (as shown in the drawing material excavated by the cutter is fed towards the central radial plane of the drum 1. Moreover, in this arrangement the drum is supported by a single yoke 28 which engages the two ends of the drum for rotation on stub axles (not shown) The number of parallel flights or starts is governed by the relationship between the shear resistance of the cylinder of material and the axial reaction which each blade can exert on the material without excessive deformation of the material occurring and its leakage through the flight. Computer modelling has proved possible and to give good prediction.

The cutting device of the invention also allows of a handheld dredge pump that can be used by a diver. In this case a cutting device having a drum about 30 cms long and 10 cms in diameter can be fitted to a jet pump and can be controlled safely by the diver. The teeth on such a cutter can safely give a swept diameter of about 20 cms but should be rounded to aid in diver safety.

It may be convenient to split the drum into two, with a pump suction inlet in the gap between. Material is then conveyed into the gap whence it is removed. The auger will not in general run full, so that the suction inlet will be displaced off the centre line. It may then be convenient to angle the axes of the drums to minimise or eliminate the gap on one side of the circle, opening the gap to the size of the inlet on the other side. The drums may then require end covers which will advantageously be conical and equipped with blades to clearthe way for the advance of the otherwise dead projection ofthe drum ends. These blades will follow the general form of a centrifugal pump impeller, that is an approximate spiral, and may also be discontinuous or notched.

In addition, to use for sub-sea operations, the cutting device of the invention can also be used in certain terrestrial operations where, for example, conventional bucket excavators are used, for example in the winning of china clay or in open cast tin mining. The cutting device may be arranged relative to a conveyor device to remove spoil as it is disengaged by the cutting device. The cutter may be used successfully for the excavation of granular materials but is particularly suitabnle for cohesive materials having a shear strength of less than 300kN/m².

Claims

Claims.

1. A cutting device comprising a drum which is rotatable about a longitudinal axis and which carries on its outer surface a plurality of spaced teeth arranged on at least one helical path over the surface of the drum and at least one drive motor mounted within the drum.

2. A cutting device according to Claim 1, wherein the teeth of the cutter are inclined so that a plane passing through a tooth and the drum lies substantially parallel to the helical path on which the tooth lies.

3. A pile for under water use having on its lower end at least one cutter according to Claim 1 or Claim 2 arranged with its longitudinal axis perpendicular to the longitudinal axis of the pile and parallel to the plane of the pile.

4. A suction dredger including a cutting head comprising at least one cutting device according to Claim 1 or Claim 2.

5. A dredger according to Claim 4, wherein the cutting head comprises a single cutting device with the teeth at the two ends of the drum being arranged on helical paths of different hand.

6. A dredger according to Claim 4, which includes two cutting devices with the teeth on the two drums arranged on helical paths of different hand, the suction head of the dredger being located in a space between the two drums.