GB2484431A

GB2484431A - A detachable base for an under - reamer

Info

Publication number: GB2484431A
Application number: GB1200441.2A
Authority: GB
Inventors: Ronald Peter Payne
Original assignee: Cementation Skanska Ltd
Current assignee: Cementation Skanska Ltd
Priority date: 2008-03-05
Filing date: 2008-03-05
Publication date: 2012-04-11
Anticipated expiration: 2028-03-05
Also published as: GB2458140B; GB2458140A; GB201200441D0; GB2484431B; GB0804136D0

Abstract

A detachable base 12 for a soil working tool includes an upper surface having an attachment member comprising a surface formation 16. The surface formation 16 may be in the form of a tapered pin having an annular recess (20, fig 4). The pin may be used to engage with a clamping tool to allow the base 12 to be recovered from a bore hole.

Description

DEVICE FOR RECOVERING DETACHABLE BASE FROM BORE HOLE

The present invention relates to a device for recovering a detachable base of a soil working tool, such as a soil boring apparatus for use in under-reaming or enlarging the base of a bore hole formed in the ground.

Under-ream tools generally comprise a cutting means operable to enlarge the lower portion, or bottom of a bore hole. The cutting means is usually in the form of a pair of digging arms which are pivotally connected to an upper portion of a main body of the tool. In use, the tool is lowered to the bottom of a bore hole and a downward force is applied to the cutting means thereby causing the digging arms to pivot outwardly. A rotational force is applied to the central shaft to thereby sheer material from the side of the bore hole. A bucket is often provided at the base of the tool which serves to collect spoil which is cut from the walls of the bore hole. Such a tool may be used in order to progressively enlarge the bottom of the bore hole. Concrete may be poured into the resultant bore hole to form an enlarged base foundation element in the ground.

Under-ream tools are usefully employed in both cast-in-situ and pre-cast operations.

For example, it is possible to form the enlarged base of a pile in-situ, and then to position/drive a pre-cast pile into the ground above the base. The enlarged base, which may be generally conical or frusto-conical in shape once formed, advantageously enhances the load bearing capacity of the eventual foundation element, by providing an enlarged cross-sectional footing at the base of a pile.

When constructing a pile with an under-reamed base one of the major difficulties is to maintain the bottom of the bore hole at the desired depth. Most under-ream tools have a cutting blade on the base, the purpose of which is to remove any debris from the bottom of the bore hole that has fallen from the tool as it is removed at each digging increment. When the tool is repositioned in the bore hole, the tool is rotated to remove the debris. However, it is very difficult to maintain the depth identical to the previous cut. The consequence of this is that the bore hole shelf formed at the bottom of the bore hole could be cut to a greater or lesser depth with the inherent danger of forming remoulded material on the cut shelf. IRemoulded material on the shelf should be avoided since it is known to have a detrimental effect on the behaviour of an eventual pile installed in the bore hole. To alleviate this problem, it is known in the art for under-ream tools to be provided with a base in the form of a base plate which serves to limit the downward excavation of the tool. Preferably, when using the base plate, the bottom of the bore hold should be substantially clean and flat. The base plate is usually positioned at the bottom of the bore hold at the beginning of a cutting operation, and is left in the bore hole when the concrete is poured in to form the pile or pile foundation.

If a finished under-reamed bore hole has to be left overnight or is failed by an inspector, it may be necessary to re-drill and re-ream the bore hole. This can only be achieved successfully if the base plate can be removed from the bore hole. The present invention seeks to address this problem.

According to a first aspect of the present invention, there is provided a device for recovering a detachable base of a soil working tool from the bottom of a hole, the device comprising a releasable clamping tool which is adapted to engage a predetermined portion of the base when the clamping tool is lowered onto the base.

The clamping tool may engage the base automatically as it is lowered on to it. The clamping tool may engage a portion of the base which is used to attach the base to the soil working tool. The said portion may be the central portion of the base. For example, it may engage an upstanding pin formed centrally on the base. The pin may be tapered.

The clamping tool may comprise a receiving opening into which the pin engages. The receiving opening may comprise at least one clamping jaw. The jaw may engage in a recess formed in the pin. The jaw may comprise a latch hinged to the clamping tool, the free end of the latch engaging in the recess formed on the pin. The jaw may be adapted to drop into engagement with the pin under the action of gravity alone. In alternative embodiments, the jaw may be biased into engagement with the pin by biasing means such as a resilient element or a spring. There may be pair of opposing latches which engage from opposite sides of the pin. The recess on the pin may be annular and extend around the full circumference of the pin.

In a preferred embodiment, the clamping tool is adapted to be releasably connected to a Kelly bar.

The clamping tool may be provided with a stabilising frame which engages the base, as the pin engages in the receiving opening.

The base may comprise a base plate, which may be circular and/or substantially planar.

The use of a detachable base is particularly advantageous when applied to an earth working tool comprising an under-ream tool, because the base provides a depth stop, so that cutting arms of the tool are constrained to cut an under-ream on the same cutting arc at each cut increment as the under-ream is gradually enlarged. Should there be, on examination, any remoulded material on the cut shelf, the detachable base would not allow the tool to cut beyond this depth. It is therefore desirable that the detachable base is adapted to allow it to be removed easily and safely from the bore hole.

According to a second aspect of the present invention there is provided a detachable base of a soil working tool comprising a main body having a substantially planar lower surface and an upper surface having a surface formation. The surface formation may be a pin. The pin may be tapered and may have a recess or projection. The recess or projection may be annular. The recess may extend around the full circumference of the pin.

A particular advantage of the present invention is that the surface formation on the detachable base, which is used to connect the detachable base to a soil working tool, is also used as the point of attachment of a clamping tool which is used to withdrawn the detachable base from a bore hole.

The detachable base may be lowered to the bottom of the bore hole using the earth working tool. According to one embodiment, the base is fitted to the bottom of the tool or a cleaning bucket of the tool and is held in place by one or more sheer pins which allow the plate to be lifted and lowered to the bottom of the hole. When at the bottom of the hole, the base may be pushed into the ground under the weight of the tool. The sheer pin(s) which attach the base to the tool, may be formed of plastic or nylon and are adapted to break when subjected to a sheer force of sufficient magnitude. Thus, in order to detach the base once it has been properly positioned at the bottom of the hole, the tool can be rotated, thereby imparting a sheer force to the pin(s) to leave the base positioned at the bottom of the hole.

The base may be provided with one or more projections on the underside thereof in order to hold the base in position on the bottom of the hole even during rotational movement of the tool. The projection may be provided on the central underside of the base. The projection(s) may, for example, be conical in shape or may be in the form of a stud or lug.

According to another aspect of the present invention, there is provided a method of operating a soil working tool comprising: a) attaching a detachable base to the bottom of the tool; b) lowering the tool to the bottom of a pre-formed hole; c) operating the tool to work soil surrounding the tool; d) detaching the base from the tool; e) withdrawing the tool from the hole leaving the detachable base in-situ; f) repeating steps b), c) and e) until the soil working operation is complete; g) lowering a releasable clamping tool down the hole onto the detachable base; h) gripping the detachable base with the clamping tool; i) withdrawing the clamping tool and detachable base from the hole; and j) detaching the base from the clamping tool.

The step d) may take place as the step c) commences.

The clamping tool may grip the detachable base automatically, when the clamping tool and base come into contact.

The base may comprise a tapered pin to serve as a means to locate the tool centrally in the hole, illustrated by step g) above and to provide a means of attachment to the clamping tool.

For a better understanding of the present 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 1A illustrates an earth boring tool with digging blades retracted; Figure lB illustrates an earth boring tool with digging blades extended; Figure 2 shows features of a detachable base assembly; Figure 3 shows a clamping tool for recovering the detachable base assembly from a bore hole; and Figure 4 shows an enlarged portion of the base assembly and clamping tool.

Figures 1A and lB show a soil working tool comprising an under-ream tool 10. The tool 10 comprises a central shaft 1 in the form of two I-beams and a cross head assembly 5 which is adapted to be coupled to a Kelly bar (not shown) of a piling rig.

The tool is provided with a pair of diametrically opposed digging arms 2, each having a series of cutting teeth (not shown) spaced along the length of the digging arm on a leading edge thereof. One end of the digging arm is provided with a cutting means in the form of a detachable scraper blade (not shown) and a paddle 4. The paddle 4 serves to direct material cut from the side of the bore hole by the associated cutting teeth into a bucket 11 at the base of the tool. Each digging arm is pivotally attached to the tool by means of a first pin 6a. The tool is also provided with a slide mechanism, comprising a sliding cross head 5, adapted to be connected to the Kelly bar and to be driven down the central shaft of the tool under the action of a downward force.

A support arm 3 provides a link connection between the digging arm and the tool, each support arm being connected to the sliding cross head 5. A downward force causes the cross head 5 to travel down along the shaft 1 of the tool so that the other end of the support arm, which is connected to the digging arm, is displaced outwardly to thereby cause the digging arm 2 to pivot radially. The maximum possible radial displacement of the digging arm 2 is therefore limited by the length of the support arm 3.

Figure 1A shows the tool 10 with the digging arms 2 in a retracted position whilst Figure 1 B show the tool 10 with the digging arms 2 displaced outwardly for performing a reaming action against the side of a bore hole.

Figure 2 is an enlarged view of the bottom of the tool 10, illustrating the mounting of a detachable base. The detachable base is in the form of a base plate 12 which is connected to the bottom of the collection bucket 11 by means of a centrally disposed pin 16 which projects at right angles from a substantially planar upper surface of the base plate 12 into a socket 14 formed in the bottom of the bucket 11. The pin 16 is secured to the collection bucket 11 by means of a sheer pin 17. In a preferred embodiment, the sheer pin 17 is formed from nylon, but any appropriate material is contemplated for the sheer pin 17.

The pin 16 is provided with an annular recess 20 which is adapted to be gripped by a releasable clamping tool 22. Referring to Figures 3 and 4, the releasable clamping tool comprises a central box section core 24 having a Kelly bar fitting 26 on its upper end and a clamping assembly 28 on its lower end.

The core 24 is stabilised by four outriggers comprising sections of round steel bar 30 interconnected by bracing bars 32 and fixed to the core 24 by four steel plates 34, which are equidistantly spaced around the circumference of the core 24.

In Figure 3, the clamping tool 22 is shown connected to the base plate 12 by engagement of the pin 16 of the base plate 12 in the clamping assembly 28. An enlarged view of the clamping assembly 28 and pin 16 is shown in Figure 4. The clamping assembly 28 is formed by short sidewall elements 36 interconnecting sidewalls 37 and 38 of the core 24 and forming a pin receiving opening 29. Pin receiving opening 29 is partially occluded jaws in the form of opposing latching plates 40, 42 which are hinged at one end to the sidewalls 37, 38. The free end of each latching plate 40, 42 opposite to the hinged end, is provided with a semicircular cut out 43, which is sized to fit the annular recess 20 of the pin 16.

In use, the under-ream tool 10 is attached to the Kelly bar (not shown) of a piling rig.

The base plate 12 is then fitted to the bottom of the bucket assembly 11 such that the pin 16 on the base plate 12 is located in the socket 14 formed in the bottom of the bucket assembly 11. The nylon sheer pin 17 is then passed through the pin 16 and sidewalls of the socket 14 from inside the bucket 11.

With the base plate 12 in place, the under-ream tool 10 is lowered to the bottom of a preformed bore hole, such that the weight of the tool 10 forces the anchoring fins 18 into the soil at the bottom of the hole. The tool 10 is then driven to rotate, but as the base plate 12 is prevented from rotating by the fins 18, the sheer pin 17 shears and the under-reaming operation proceeds with the tool 10 disconnected from the base plate 12, but supported on it as the tool 10 rotates in the bore hole. After the bucket 11 has been filled, the tool 10 is withdrawn from the bore hole, leaving the base plate 12 at the bottom of the bore hole. After the bucket has been emptied, the tool is lowered back on to the base plate 10, and the under-reaming operation is continued.

This process is repeated until the desired under-ream is achieved. It will be appreciated that the pin 16 on the base plate 12 serves to centre the tool 10 in the bore hole, by engagement in the socket 12 in the bucket 11.

With the tool 10 removed for the last time from the bore hole, it is disconnected from the Kelly bar assembly of the piling rig and replaced by the clamping tool 22, using the Kelly bar fitting 26 on the clamping tool 22 to secure it to the Kelly bar assembly.

As the clamping tool 22 is lowered into the bore hole, the stabiliser bars 30 keep the clamping tool centred in the bore hole until the pin 16 on the base plate 12 is received in the pin receiving opening 29 of the clamping assembly 28. As the pin 16 enters the clamping assembly 28, its tapered head assists alignment and pushes the free ends of the latching plates 40, 42 upwardly, so that the pin 16 can enter the clamping assembly 28 fully.

The Kelly bar assembly of the piling rig is then operated to withdraw the clamping tool 22 from the bore hole. As the clamping tool 22 lifts from the base plate 12, the free ends of the latching plates 40, 42 drop into the annular recess 20 on the pin 16, thereby jamming the pin 16 in the clamping assembly 28. The clamping tool 22 and base plate 12 are thereby withdrawn together from the bore hole.

When removed from the bore hole, the base plate 12 can be released from the clamping assembly 28 by lifting the base plate 12 relative to the clamping tool 22 and flipping the latching plates 40, 42 apart, as the pin 16 is withdrawn.

It will be appreciated that the connection of the central pin 16 of the base plate 12 to the clamping tool 22 allows the base plate 12 to be removed from the bore hole in a substantially horizontal orientation, so that dirt and debris on a upper surface of the base plate 12 remains on the base plate 12 and is withdrawn from the bore hole. This prevents such debris falling back into the bore hole and being remoulded on the bottom of the bore hole. As mentioned previously, remoulded materials on the bottom of the bore hole should be avoided, since it is known to have a detrimental effect on the behaviour and bearing capacity of the eventual pile installed in the bore hole.

The stability of the base plate 12, as it is withdrawn from the bore hole, is increased, if the steel bars 30 on the clamping tool 22 abut the base plate 12 when it is engaged with the clamping tool 22. This arrangement is illustrated in Figure 3.

In an embodiment (not illustrated), the latching plates 40, 42 may be biased towards one another, to ensure that they grip the pin 16 firmly when it is inserted into the clamping assembly 28. Biasing means may, for example, comprise an elastomeric element or spring acting on each latching plate 40, 42.

Claims

Claims 1. A detachable base of a soil working tool comprising a main body having a substantially planar lower surface and an upper surface having an attachment member comprising a surface formation.
2. A device as claimed in claim 1 in which the surface formation comprises a pin.
3. A device as claimed in claim 2 in which the pin is tapered.
4. A device as claimed in claim 3 or claim 3 in which the pin is provided with an annular recess.
5. A device as claimed in claim 2 in which a recess extends around the full circumference of the pin.
6. A device as claimed in any preceding claim in which the surface formation on the detachable base is configured for use in connecting the detachable base to a soil working tool, and is configured for use as the point of attachment of a clamping tool for withdrawing the detachable base from a bore hole.
7. A device as claimed in any preceding claim in which the base is provided with one or more projections on the underside thereof.
8. A device as claimed in claim 7 in which a projection is provided centrally on the underside of the base.
9. A device as claimed in claim 7 or claim 8 in which the or each projection is conical in shape or takes the form of a stud or lug.
10. A detachable base of a soil working tool, substantially as described herein, with reference to and as shown in the accompanying drawings.