GB2222621A - Underreamer for making piles - Google Patents

Abstract

A tool for enlarging a portion of an underground shaft is disclosed. The tool comprises a generally cylindrical body portion 32 the axis of which defines an axis of rotation and which has at least one slot 23, 24 or opening in its side. At least one cutting member 25, 26 is pivotally connected to the body portion so that in one configuration it can protrude through the slot to perform a cutting action on surrounding ground material and, in another configuration, can retract within the slot. Each cutting member 25, 26 includes an upper blade 27 and a lower blade 28, the blades being arranged in relation to each other and in relation to the body portion so that the lower blade 28 is inclined upwardly and outwardly with respect to the axis of rotation when the cutting member protrudes through the slot in the side of the cylindrical body portion. <IMAGE>

Description

IMPROVEMENTS RELATING TO PILES This invention relates to piles and, more particularly, is concerned with the construction of piles using an underreamer.

The process of underreaming piles is long established. Where the ground is stable, for example in stiff clays, a pile shaft is usually bored to a given designed depth and then a tool is inserted which is used to form the underream or enlarged base of the pile. This underreaming tool is conventionally cylindrical in form with two long open slots in its sides which are in diametrically opposed positions. Within each slot is a cutting arm, which in currently available apparatus is almost universally hinged at the top. Some prior designs are known, however, where the cutting arms are hinged at the bottom. In both cases, the cutting arms are connected by a linkage to the drilling or Kelly bar of a rotary boring machine so that when the bar is moved downwards and the base of the reaming tool rests on the bottom of the hole, the arms are forced outwardly.On retraction of the drilling bar, the arms are also retracted. While the arms are extended from the underreamer body and are pressing against the surrounding soil, the underreamer is rotated by the drilling bar so that a soil cutting action is performed. retraction of the cutting arms draws soil into the body or centre part of the tool and from time to time the tool is withdrawn from the hole in the ground where the cut soil is removed.

Currently, underreaming tools are used almost exclusively in holes which are of a size sufficient to allow access for a worker to the base of the hole. With such man-access, it is possible to inspect the base of the pile shaft directly, and to clean the pile base if necessary. Typically, an underreamer is raised from the hole during its use several times in order to cut the required size of base enlargement. In general, underreams are cut to final diameters which may be up to three times the diameter of the main part of the pile shaft. Manual inspection and cleaning of the bases of pile shafts is generally impossible in bore holes of less than 750mm diameter since human entry into such holes is not practical nor is it generally permitted under local safety regulations.As a result, the conventional underreaming process tends to be limited to use with piles which are 750mm in diameter or greater.

Underreaming has been carried out in bore holes of 600mm diameter or thereabouts in the past, but without direct inspection and with indifferent performance; as a result the underreaming of such narrow bore holes appears to have ceased in commercial practice.

Underreaming is carried out, for example, in forming ground anchors in clay where the objective is to apply loads to the anchor which tend to withdraw it from the ground, so that the process of cleaning the bottom of the shaft is unimportant and does not affect the performance of the anchor. Typically, holes of up to 300mm diameter are used for ground anchors. In contrast, where a pile is to be constructed, the downward load carried by the pile is transmitted to the ground through the base of the pile shaft, and consequently we believe that base cleaning of such pile shafts is critical in assuring satisfactory and consistant performance in piles.

From the summary given above, it will be appreciated that there is a particlar need for underreaming apparatus capable of constructing an umderreamed pile shaft of less than 750mm diameter, as well as a general need for underreaming apparatus which produces a cleanly cut underreamed shaft without requiring human access and manual cleaning of the base of the shaft.

according to one aspect of the present invention, there is provided a tool for enlarging a portion of an underground shaft, which tool comprises: (a) a generally cylindrical body portion the axis of which defines an axis of rotation; (b) at least one slot or opening in the side of said body portion; and (c) a cutting member pivotally connected to said body portion so as to be able, in one configuration, to protrude through said slot or opening to perform a cutting action on surrounding ground material when the tool is rotated about said axis of rotation and, in another configuration, to retract within said slot or opening; characterised in that: (1) the cutting member includes an upper blade and a lower blade; and (2) said upper and lower blades are arranged in relation to each other and in relation to said body portion such that, when the cutting member protrudes through said slot or opening to its maximum possible extent, said lower blade is inclined upwardly and outwardly with respect to said axis of rotation.

Preferably, both the upper and lower blades are linear. One or other of the blades may, alternatively, be slightly arcuate. If an arcuate configuration is adopted, the lower cutting blade should be outwardly convex, so that the sloping surface cut by that blade when the tool is in use will have a concave profile.

Conveniently, the upper and lower blades may be in the form of metal struts hinged at their inboard ends directly or indirectly to said cylindrical body portion.

Advantageously, the upper and lower blades are hinged together at their outward ends, so that in the extended condition the cutting member is more or less "V"-shaped.

Preferably the angle enclosed between the upper and lower blades at maximum extension is not less than 450.

Advantageously, the upper and lower blades are caused to move by a mechanical linkage arrangement wnen the tool is in use. Alternatively, a hydraulic operating system may be employed, e.g. a hydraulically-linked piston and a pair of rams, one acting on each of two cutting members.

Conveniently, the or each slot through which a cutting member protrudes is arranged with its major axis parallel to the axis of rotation. Other arrangements, i.e. in which the slot is arranged obliquely with respect to the axis of rotation, are also possible.

Preferably, the tool has two opposed slots each containing a similar cutting member. The upper part of the cylindrical body portion will generally include a coupling connection for a drilling (Kelly) bar of a rotary boring machine.

In a particularly preferred embodiment of the invention, the tool also includes a hollow container attached to or forming part of said cylindrical body portion, and disposed below the cutting member or members. In this way, when the tool is in use, the blades of the cutting member(s) sweep cut material into the container. Preferably, the volume of the container is such that all of the spoil generated in forming a desired underream can be accommodated within the container. In this way, the desired expanded region of the underground shaft can be formed in a single step, without requiring repeated raising and lowering of the rotary drilling equipment and without requiring any cleaning of the pile base.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 illustrates a conventional "top-hinged" underreaming tool of the type widely used currently in commercial practice; Figure 2 illustrates a known design of "bottom-hinged" underreaming tool which has not found favour in commercial practice for many years; and Figure 3 illustrates a preferred embodiment of the present invention.

Referring first to Figure 1, the underreaming tool 1 is secured to a drilling bar 2 located within a shaft 3. The tool 1 comprises a pair of opposed blades 4 and 5 pivotally connected to a generally cylindrical body 8 by hinges 6 and 7, respectively which are located at the top of each blade. Pivoting linkages 9 and 10 are connected to blades 4 and 5 at the points 11 and 12 respectively, and are connected to the base of cylindrical body portion 8 at points 13 and 14, respectively. In use, such an underreaming tool is first lowered into pre-formed shaft 3; in this condition, linkages 9 and 10 adopt a more or less vertical orientation, and the wing-like blades 4 and 5 are retracted into the hollow interior of cylindrical body 8.When the tool 1 reaches the base of the shaft, the drilling bar 2 is pushed downwardly, thus urging blades 4 and 5 to pivot outwardly, this movement coupled with rotational movement resulting in scraping away of ground material from the sides of the shaft in contact with blades 4 and 5. At the end of the reaming operation, the base of the shaft is enlarged to a frustoconical shape.

Referring next to Figure 2, a "bottom-hinged" underreamer (now generally regarded as obsolete) is.

depicted. The same reference numerals as were used in Figure 1 are used here to denote similar components.

With the Figure 2 arrangement, hinges 6 and 7 are located at the bottom end of blades 4 and 5, while linkages 9 and 10 are disposed upwardly of hinges 6 and 7. AS with the Figure 1 arrangement, the blades 4 and 5 nest inwardly (with linkages 9 and 10 substantially vertical) when the tool is lowered into shaft 3. Kotation of the tool when it is at the base of the shaft after blades 4 and 5 have moved outwardly under downward pressure from drilling bar 2 results in excavation of a sector of a sphere which is conical in section.

With tools of the type shown in Figures 1 and 2, it is necessary to make repeated cutting operations between each of which spoil generated by the previous cutting stage is removed from the base of the shaft.

This is an inconvenient and potentially hazardous operation, generally requiring a worker to descend to the base of the shaft to clear debris manually or to supervise the operation of debris removing equipment.

Referring now to Figure 3, a tool in accordance with this invention comprises a cylindrical body portion 21 having at its top end a coupling connector 22 adapted to receive drilling bar 20. Body 21 includes two opposed slots 23 and 24 through which cutting members 25 and 26 are able to protrude. Each cutting member comprises an upper blade 27 and a lower blade 28. Each blade is in the former of a linear strut hinged at the inboard end to a plate 36 which is able to move upwardly and downwardly within body 21. The upper hinges are denoted by reference 29, and the lower hinges by -reference 30. The limit of downward movement of plate 36 is determined by a stop member 38.The limit of upward movement of plate 36 is determined by a second stop member 39, although in an alternative arrangement the inner surface of the end face 37 of body 21 can act as a stop member instead of item 39. Each blade 27 is pivotally connected to its companion blade 28 by a hinge 31. Thus in the configuration illustrated, the two cutting members adopt a "V"-shaped form. Each stop member 38 and 39 may take the form of two steel blocks (one on each side diametrically of the interior of body 21) welded to the inner side wall of body 21. Alternatively, each stop member 38 and 39 may take the form of a cross bar extending across the interior of body 21.

Stop member 38 is positioned so that when cutting members 25 and 26 are extended to their maximum, the slope of lower blades 28 is kept at an angle which allows cut spoil to roll down into the interior of container 32.

Typically this angle will be about 300 The lower part of body 21 is constructed as a spoil container 32. The base 33 of container 32 is releasably secured by means 34 and 35 to the cylindrical side wall of container 32. Typical dimensions of the tool are as shown in the drawing.

In use, the tool is first lowered into a pre-formed shaft, during which the cutting members 25 and 26 are retracted into the interior of body portion 21.

Stop member 39 is located so that, with the cutting members retracted, hinge joint 31 is just outside the line joining points 29 and 30 so that when the action of moving cutting members 25 and 26 begins there is always a tendency for blades 27 and 28 to move outwardly. When the soil container 32 reaches the base of the shaft, drilling bar 20 is rotated while under downward pressure, this serving to force cutting members 25 and 26 to protrude through slots 23 and 24 and to cut away the surrounding ground material. As material is cut, the rotational sweeping of the cutting members together with the inclined lower floor of the enlarged shaft section encourages spoil to enter the container 32. When the maximum extension of cutting members 25 and 26 is reached, the configuration shown in Figure 3 results.

The capacity of container 32 is such that all of the ground material cut in generating the enlarged shaft portion is contained within the container (allowing for bulking), so that a single reaming operation is all that is required. At the end of this operation, rotation of drilling bar 20 is stopped, and bar 20 and the tool to which it is attached are raised. Initially, this results in cutting members 25 and 26 retracting into the body 21, as blade 36 moves upwardly towards stop member 39. When parts 36 and 39 meet, blades 27 and 28 are within slots 23 and 24, but are not quite co-linear. This prevents any tendency for hinge joint 31 to move inwardly instead of outwardly when the next reaming operation is commenced. Once members 25 and 26 are within slots 23 and 24, respectively, further lifting action applied will result in the tool being raised to the surface.

A tool of the type illustrated in Figure 3 has a number of important advantages compared to the prior art tools of Figures 1 and 2. These are: (a) The underreaming process is carried out in a single journey of the tool into and out of the shaft bore and the tool is able to remove the complete volume of a ream as cut soil in the single journey and operation.

(b) The tool cuts both top and bottom of the underream simultaneously, thereby considerably speeding operation.

(c) The tool produces a sloping floor to the underream as cut, so that the base of the ream is self-cleaning - the combined slope and rotation serving to propel cut earth into the cylindrical body of the soil container in the bottom section of the tool.

It will be appreciated that provision of the soil container 32 requires the underream to be cut at an appropriate level above the base of the borehole. The necessary distance between the ream and the base of the bore will depend upon the maximum shaft enlargement which is required. Typically, an enlargement up to a maximum of twice the bore diameter will be adopted, and the slope of the floor of the ream is about 300 to the horizontal.

It is, of course, possible to adopt any desired values for bore enlargement and inclination of the lower cutting blade at maximum extension.

When a pile is formed in an underreamed pile shaft produced with a tool in accordance with the present invention, pressure at the bottom of each pile ream may be expected to increase lateral stress on the soil beneath when a pile is loaded, thus increasing friction.

Furthermore, the pile will have a useful tension capacity when required.

Compared to the production of piles in straight shafts, there is a considerable potential saving in operating time and costs by using a tool of this invention to form an underreamed pile shaft. Thus in constructing a pile 600 millimetres in diameter in ground formed of London clay, use of a tool as illustrated in Figure 3 to produce an underream with a diameter of 1.2m will require a soil container 32 1.5m in length (allowing for bulking up of excavated material), which in turn means that an underreamed pile shaft will generate the same friction capacity as a linear shaft of the same diameter but approximately 8 metres deeper. The vertical extent of the ream will be 0.4 metres1 and the cost of generating this underream will be significantly less than that of the extra 8 metres shaft extension which would otherwise be required to give the same pile friction.

Claims (10)

1. A tool for enlarging a portion of an underground shaft, which tool comprises: (a) a generally cylindrical body portion the axis of which defines an axis of rotation; (b) at least one slot or opening in the side of said body portion; and (c) a cutting member pivotally connected to said body portion so as to be able, in one configuration, to protrude through said slot or opening to perform a cutting action on surrounding ground material when the tool is rotated about said axis of rotation and, in another configuration, to retract within said slot or opening; characterised in that: (1) the cutting member includes an upper blade and a lower blade; and (2) said upper and lower blades are arranged in relation to each other and in relation to said body portion such that, when the cutting member protrudes through said slot or opening to its maximum possible extent, said lower blade is inclined upwardly and outwardly with respect to said axis of rotation.

2. A tool as claimed in claim 1, wherein said upper and lower blades are linear.

3. A tool as claimed in claim 1, wherein said lower blade is outwardly convex.

4. A tool as claimed in claim 1, 2 or 3, wherein said upper and lower blades are in the form of metal struts hinged at their inboard ends directly or indirectly to said cylindrical body portion.

5. A tool as claimed in claim 1, 2, 3 or 4, wherein said upper and lower blades are hinged together at their outward ends. A tool as claimed in any preceding claim, wherein the angle enclosed between the upper and lower blades at maximum extension is not less than 450.

6. A tool as claimed in any preceding claim, wherein the or each slot or opening through which a cutting member protrudes is arranged with its major axis parallel to the axis of rotation.

7. A tool as claimed in any preceding claim, wherein the tool has two opposed slots each containing a similar cutting member.

8. A tool as claimed in any preceding claim, which further includes a hollow cylinder attached to or forming part of said cylindrical body portion, and disposed below the cutting member or members.

9. A tool as claimed in claim 8, wherein the volume of said hollow container is such that all of the spoil generated in forming a desired undeream can be accommodated within the container.

10. A tool for enlarging a portion of an underground shaft substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.