GB2447622A - Method of excavating a non-circular shaft - Google Patents

Abstract

Method of excavating a non-circular lift shaft comprising the steps of: <SL> <LI>a) excavating a leading shaft section 16 of substantially circular cross-section; <LI>b) introducing a cutting apparatus 20 into an upper portion of said leading shaft section; <LI>c) orientating said cutting apparatus Into a desired position; <LI>d) excavating said upper portion using said cutting apparatus to convert said upper portion from having a substantially circular cross-section to having a non-circular cross-section; <LI>e) installing a sectional supporting element 9 of non-circular cross-section into said converted upper portion; <LI>f) repeating steps b) - e) until a non-circular shaft of desired depth has been excavated. </SL> Also disclosed are a cutting apparatus and a sectional support for use in the above method.

Description

METHOD OF EXCAVATING A NON-CIRCULAR SHAFT

This invention relates to the a method for sinking or excavating a non-circular shaft into the ground, in particular but not exclusively for the purpose of creating a lift shaft in low headroom and restricted access conditions, and to apparatus for implementing such a method.

Lift shafts are commonly rectangular, and this invention is particularly beneficial for, but not exclusive to, the construction of shafts having a generally square or rectangular cross-section in locations having restricted headroom and/or a confined working space.

Shaft sinking is conventionally carried out by one of four techniques, each of which is described in turn below.

1. Diaphragm Walling Under Support Fluid Diaphragm walling is an excavation technique in which the walls of a structure are excavated directly in the ground using mechanical excavation techniques, under a support fluid, (usually bentonite mud or polymer fluid).

The hydraulic pressure of the support fluid acts against the surrounding ground to support the ground during excavation. On completion of the excavation, steel reinforcement is inserted into excavation and the support fluid is replaced with fluid concrete, which then sets to form a solid structure in reinforced concrete. The internal area to the completed structure may then be excavated to form a shaft.

Diaphragm walling is very intensive in terms of labour and plant and also comparatively slow and, for this reason, the market price is higher than other methods. The items of plant generally used are comparatively large, and this method of forming shafts is more suited to large underground structures where the created wall thickness is at least 600mm and where restricted headroom is not an issue.

2. Piled Cofferdam Piled cofferdams are formed by the installation of individual vertical piles, either as sheet piles or as bored piles, which then act to support the ground by spanning in a vertical direction between fixed support points. They often require an internal horizontal bracing system to provide additional support.

After the piled cofferdam is installed, the internal space is excavated, and the shaft structure constructed within the contained space.

This system has the disadvantage of requiring a support system to be installed, prior to the installation of the completed structure. The method is expensive and time-consuming. The method usually employs large items of plant, and is best suited where large structures are required. It is not likely to be cost effective for the construction of smaller lift shafts in low headroom or restricted access conditions.

3. Caisson sinking Caissons are formed by constructing a sectional element of the overall structure above the ground, then sinking the element into the ground by excavating underneath it and applying a vertical force to push the sectional element into the ground.

Frictional resistance between the sectional element and the adjacent ground is usually overcome by the introduction of a lubricating support fluid (usually bentonite mud or polymer) in the space between the structure and the surrounding ground.

As the sectional element is sunk into the ground, further sectional elements are constructed at ground level above the element being sunk, and these are used to extend the structure as the structure is sunk. This method of construction is most suited to large structures, where mechanical equipment can be easily used within the caisson being sunk.

4. Segmental Shaft Construction Segmental shafts are formed by excavating the ground below the shaft structure in incremental lengths, and then forming the incremental length of shaft, either by the use of shutters and by pouring in fluid concrete, or more commonly, by utilizing pre-cast concrete segments which are connected together in each excavated incremental length of shaft.

This type of shaft construction is more typically used for small diameter shafts, but commonly involves hand excavation of the shaft, and hand fixing of the segments, and accordingly is very labour intensive, and potentially more dangerous for operatives who have to work at the base of a deep shaft.

Segmental shaft construction is easier with circular sections, as earth pressure forces are accommodated with compressive hoop stress. Rectangular section shafts constructed in segments are more difficult to construct.

There is a need for an apparatus and method for shaft construction which can be used in low headroom and restricted access conditions and is capable of, but not exclusively, for the construction of rectangular shafts, or of any other shape.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the invention there is provided a method of excavating a non-circular shaft comprising the steps of: a) excavating a leading shaft section of substantially circular cross-section; b) introducing a cutting apparatus into an upper portion of said leading shaft section; c) orientating said cutting apparatus into a desired position; d) excavating said upper portion using said cutting apparatus to convert said upper portion from having a substantially circular cross-section to having a non-circular cross-section; e) installing a sectional supporting element of non-circular cross-section into said converted upper portion; f) repeating steps b) -e) until a non-circular shaft of desired depth has been excavated.

According to a second aspect of the invention there is provided apparatus for performing the method of the preceding paragraph including cutting apparatus comprising: a frame of a size capable of being raised and lowered through the central aperture of said sectional supporting element; cutters attached to said frame and moveable with respect thereto in at least two directions in a single plane.

According to a third aspect of the invention there is provided a sectional supporting element for use in the method described above comprising a frame cast in concrete, the frame comprising: a plurality of tubular posts having machined engagement means at the top and bottom thereof for engagement with tubular posts of vertically adjacent sectional supporting elements.

Preferred features of the invention are defined in the appended c'aims.

BRIEF DESCRIPTiON OF THE DRAWINGS

Preferred embodiments of the present invention will now be more particularly described, by way of example only, with reference to the accompanying drawings wherein: Figure 1 shows four corner posts which are part of the sectional element's frame; Figure 2 shows the internal threaded bar which is located inside each corner post; Figure 3 shows the four corner posts of Figure 1 with internal threaded bars therein; Figure 4 shows a sectional element's frame; Figure 5 shows a sectional element having the frame of Figure 4 cast in concrete; Figure 6 partly in cross-section, shows how two sectional elements locate one on top of the other; Figure 7 partly in cross-section, shows the interface between the two sectional elements of Figure 6 drawn to a larger scale; Figure 8 shows how two sectional elements locate one on top of the other; Figure 9 shows a cutting shoe for use in the construction of a shaft structure using the sectional elements; Figure 10 shows schematically a shaft structure comprising a plurality of sectional elements, a cutting shoe and a piling rig for excavating a circular hole; Figure 11 is a perspective view of the cutting rig; Figure 12 is a perspective view of the underside of the cutting rig; Figure 13 shows the underside of the cutting rig having its cutters in a position suitable for excavating at the periphery of the circular hole; Figures 14-16 show the cutting rig having its cutters in different positions suitable for excavating the non-circular hole; Figure 17, shown partly in cross-section, shows how the corner posts are used to attach two sectional elements together; Figure 18, drawn to a larger scale, shows the corner posts in more detail; Figure 19, shown partly in cross-section, shows how the intermediate posts are used to attached two sectional elements together; Figure 20, shown partly in cross-section, shows reinforcing bars in the interior of the intermediate posts; Figure 21 shows schematically a shaft structure comprising a plurality of sectional elements; and Figure 22 is an exploded view of two sectional elements and the cutting shoe.

DETAILED DESCRIPTION

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Throughout the present application the terms vertical", "horizontal", "lower", "lowermost", "upper" and "uppermost" are relative to the orientation of the longitudinal axis of the shaft. The lowermost end of the shaft is therefore the end nearest the bottom of the shaft and the uppermost end is the end nearest to the top of the shaft. The terms "shaft sinking" and "shaft construction" can be used interchangeably.

The terms "square", "rectangular", "circular" and "non-circular" are not intended to be mathematically exact and should be construed purposively. The terms "circular hole" and "cylindrical shaft" could be used interchangeably.

The term "lift shaft" is used in the following description of a preferred embodiment but it will be understood that the invention could be used equally in the creation of structures other than lift or elevator shafts.

An improved apparatus and method for creating a lift shaft of square or rectangular cross-section is provided in which a lift shaft is formed using a plurality of engineered pre-cast sectional elements mounted vertically, one on top of the other, as will be described in more detail below.

The structure of the sectional elements will be described first.

Referring to Figure 1, four corner posts 1A, 1 B, IC, ID are provided, each having a generally cylindrical tubular shape. The uppermost end of each corner post is provided with a spigot 2A, 2B, 2C, 2D. The lowermost end of each corner post is provided with a socket 3A, 3B, 3C, 3D (not shown in Fig 1) of suitable size and shape to receive a spigot of another corner post. Bearing surfaces 2A', 3A' etc are provided around each of the spigots and sockets.

Each corner post, its spigot, socket and bearing surfaces, are machined to precise tolerances, for example to within 0.25mm, so that they can be used to accurately locate one sectional element relative to another in the finished structure.

As shown in Figure 2, threaded reinforcing bars 10 are provided which are designed to locate within the interior of the corner posts. The threaded bars may be externally threaded over substantially their whole length, or only part thereof. In the illustrated example, the threaded bar 10 has a threaded portion at its top end. At its bottom end, the bar is provided with an internally-threaded coupler 31, suitable for receiving the threaded top end of another threaded bar 10.

As shown in Figure 3, a reinforcing bar 10 is placed within each of the corner posts so that at least a small part of the reinforcing bar protrudes from the top and bottom of each corner post.

Referring to Figure 4, between each of the corner posts are provided a plurality of intermediate posts, preferably arranged in approximately equispaced pairs 4, 5. The intermediate posts are vertically orientated cylindrical tubes. The vertically orientated corner posts and intermediate posts are braced with inner and outer horizontal bracing 6 so as to provide a strong frame 7 as shown in Figure 4.

The sectional element 9 is completed by casting concrete 8 over the frame 7 as shown in Figure 5. The concrete is cast to a level below that of the bearing surfaces 2A', 2B, 2C', 2D' of the corner posts so that the spigots 2A-2D, sockets 3A-3D and their respective bearing surfaces are free of concrete and protruding upwards and downwards respectively (for example by 5mm) in relation to the concrete surfaces of the sectional element 9. The reinforcing bars 10 also protrude upwards and downwards, free of concrete, as illustrated in Figure 5. This enables the fit between adjacent sectional elements in the constructed shaft structure to be defined by the spigots, sockets and bearing surfaces, not by the mating of concrete surfaces. The casting bed for the sectional element has machined surfaces which precisely define the positions of the four corner posts and the intermediate posts, resulting in a sectional element having precise dimensions so that the fit between adjacent sectional elements in the constructed shaft structure is optimised.

As an example, the sectional element 9 could have dimensions of 2.3m x 2.5m with a depth of I.Om and a 300mm thick wall.

Figures 6-8 show how two sectional elements 9 can be stacked one on top of the other.

The corner posts are aligned such that the spigots of the lowemiost sectional element are located in the respective sockets of the uppermost sectional element. In a typical example, fifteen sectional elements could be stacked to form a continuous shaft of 15m depth.

As shown in Figure 7, the spigot 2A of the lowermost sectional element is aligned with the socket 3A of the uppermost sectional element so that, when the two sectional elements come together (as shown in Figure 8), their alignment is precisely defined by the spigots, sockets and beanng surfaces. Note that the bearing surface 2A' of the lowermost sectional element stand proud of the concrete so that the load between the two sectional elements is transmitted via the bearing surfaces, not via mating concrete surfaces.

The tubular intermediate posts 4, 5 are also aligned from one sectional element to the next. A reinforcing bar can be inserted into one or more of the intermediate posts 4, 5 so as to bridge the interface between the posts 4, 5 of adjacent sectional elements 9.

This will be described and illustrated in more detail below.

A method of constructing a shaft structure will now be more particularly described, by way of example only. The method is particularly applicable in soil/ground conditions which are generally cohesive or stable in nature and which allow at least a degree of excavation to take place in an unsupported condition without collapse. London clay is a typical example of such conditions. In other soil/ground conditions, for example where there are unstable granular or water-bearing soils overlying a cohesive stable ground, additional known techniques (for example those described in the introduction of this patent application) may need to be employed to initially create a stabilised zone through the upper unstable ground.

Before installing any of the sectional elements, a number of reaction piles (for example four) are installed at the site in order to provide a reactive force against which a sectional element can be jacked into the ground. The first sectional element to be installed is placed on the ground at the site and is connected to a reaction beam system via shear connectors cast into the side of the sectional element (not illustrated). Hydraulic jacks attached to the reaction piles can, when required, apply a force to the sectional element which is capable of jacking the sectional element down into the ground, or holding it in a desired fixed position.

When the first sectional element to be installed is placed on the ground at the site, it is placed on top of a cuthng shoe 11, such as that illustrated in Figure 9 Figure 9 shows a cutting shoe 11 made from metal, for example steel, having the same general shape as the sectional element 9 but having slightly larger dimensions so that its peripheral upstanding flange I IA sits against the exterior surface of the first sectional element.

Upstanding locating pins 1 2A-1 2D shown in Figure 9 are provided for positioning a cutting rig, which will be described later. The central region of the cutting shoe 11 comprises a generally octagonal aperture 13 of sufficient diameter to allow the passage therethrough of an auger or other circular digging tool of known type. The underside of the cutting shoe II has a sharpened surface to facilitate the pushing or jacking in of the cutting shoe into the ground. The cutting shoe 11 is selectively detachable from the first sectional element.

Referring now to Figure 10, a piling rig 14 having an auger 15 or other circular digging tool of known type is used to excavate a circular hole 16, for example of 2m diameter, through the aperture 13 of the cutting shoe 11 and the aperture of the sectional element 9. Figure 10 actually shows several of the sectional elements one on top of the other, illustrating the position later in the process, but the circular hole 16 is needed before even the first sectional element 9 can be installed into the ground.

The circular hole 16 provides a leading section of circular excavation, from which the eventually desired non-circular (for example rectangular) shaft can be formed. Prior art methods of forming non-circular shafts require labour-intensive manual excavation because it is not possible to mechanically excavate a non-circular shaft without having the necessary space in which to collect the spoil which needs to be removed upwards from the shaft.

The method of the present invention has the advantage of excavating a leading section of circular hole, from which the non- circular shaft can be excavated and into which the spoil from the non-circular excavation can fall and be collected for removal.

Therefore, once the leading section of circular shaft has been excavated, the circular hole under the cutting shoe 11 and first sectional element 9 are excavated so that the hole has a rectangular section, creating a rectangular space into which the cutting shoe and first sectional element can be pushed or jacked downwardly.

Figures 11-16 illustrate a cutting rig 20 which can be used to automate the excavation of the non-circular shaft, thus making it much more cost-effective and efficient.

The cutting rig 20 comprises a generally rectangular frame 21 which has smaller external dimensions than the sectional elements 9 and cutting shoe 11, so that it is possible for the cutting rig 20 to move in and out of the central apertures of the cutting shoe and sectional element. The uppermost surface of the frame is provided with a plurality of wheels 22 which, in use, abut the internal surfaces of the sectional elements, thus facilitating the lifting and lowering of the cutting rig.

Referring to Figure 12, when the cutting rig 20 is lowered into position into an upper portion of the circular shaft, apertures 23 engage the upstanding locating pins 12A-12D on the cutting shoe 11 (see Figure 9). The underside of the cutting rig is provided with a fixed panel 24 fixed with respect to the frame 21, on which is located a bearing 25 and a rotary drive engagement 26. The drive engagement is capable of engaging with a rotary piling rig or the like so that the drive engagement can rotate with respect to the frame 21 and fixed panel 24.

Mounted to the drive engagement 26 are two telescopic hydraulically operated arms 27, 27. Rotary cutters 28 are mounted at the end of the telescopic arms 27, 27. The cutters 28 move, via a chain link, around an ellipse having a longitudinal axis L. The above-described components allow the cutters 28 to move in accordance with the rotary drive engagement (arrow A in Figure 13) and/or in accordance with the telescoping hydraulic arms (arrow B) and/or in accordance with the longitudinal axis L moving in relation to the nearest part of the frame 21 (arrow C). In this way, the cutters 28 can be orientated and positioned anywhere on the periphery of the already-drilled leading circular shaft or anywhere within the footprint of the part of the desired non-circular shaft which is yet to be cut. In this way, the cutters 28 are able to selectively excavate underneath the cutting shoe 11 so as to convert an upper portion of the leading circular shaft to having a non-circular cross-section so as to form a hole of rectangular (or other) shape.

Figure 13 shows the cutters 28 in their position nearest to the drive engagement 26 i.e. with the telescopic arms 27, 27' relatively short and with longitudinal axis L parallel to the nearest part of the frame 21. This position is necessary, initially, when starting to cut the periphery of the afready-drilled leading circular shaft.

Figures 14-16 show underside of the cutting shoe 11 so it can be seen how the cutters 28 can excavate at all positions beneath the cutting shoe, as desired. Note that in Figure 15, the hydraulic arms 27, 27' are extended so as to reach the corner of the desired rectangular excavation.

Once the rectangular hole has been formed, the cutting rig 20 can be withdrawn up to ground level so that the next stage can take place.

Hydraulic jacks (not illustrated) react against the reaction beam system described above which is connected to the first sectional element 9 in order to jack the cutting shoe and first sectional element into the ground.

As the first sectional element 9 is jacked into the excavated rectangular hole, the cutting shoe 11 cuts into an area of slightly larger dimensions than that of the sectional element.

As the first sectional element 9 is jacked into the ground, the next sectional element is placed on top thereof, Its weight may assist in inserting the first sectional element.

Once the first sectional element is fully installed in the rectangular hole, the cutting rig 20 can be reintroduced to cut the next region of rectangular hole under the culling shoe 11, and the process can be repeated. Further sectional elements continue to be added in this way until a shaft structure comprising the desired number of sectional elements has been installed, as illustrated in Figure 21.

Figures 17-20 illustrate how the second sectional element is attached to the first sectional element.

Figures 17 and 18 show how two sectional elements 9, 9' are attached together by their corner posts. The first sectional element 9 is attached to the cutting shoe 11 by an anchor 30 located inside each corner post IA. The anchor 30 is coupled to the threaded reinforcing bar 10 by a threaded tubular coupler 31. The top end of the reinforcing bar of the first sectional element protrudes about half way into another coupler 31'. The bottom end of the threaded reinforcing bar 10' of the second sectional element 9' fits into the coupler 31'. A temporary clamping cap 32 is provided at the top end of the reinforcing bar 10'. The clamping cap 32 can be screwed onto the reinforcing bar 10' and corner post 1A' to provide a clamping force throughout, such that any longitudinal forces can be transmitted from one reinforcing bar and corner post to the next. This clamping action assists during the drying of the epoxy resin (see below). The clamping cap 32 is used to temporarily clamp successive sectional elements together during the period while the epoxy resin sets. Once the resin is set, the clamping cap 32 can be removed to allow the next sectional element to be added.

Figures 19 and 20 illustrate how two sectional elements 9, 9' are attached together by their intermediate posts. This can be in addition to the attachment via the corner posts described above.

Figure 19 shows how, as the two sectional elements 9, 9' are brought together, their respective intermediate posts 4, 4' are aligned so that there is a continuous conduit through one intermediate post 4' to the next intermediate post 4 below it.

When the two sectional elements 9, 9' are together as shown in Figure 20, a reinforcing bar 33 is inserted into each of the intermediate posts 4. The reinforcing bars 33 are long enough to bridge the interface between intermediate posts 4, 4', perhaps extending halfway into the next intermediate post 4'. Epoxy resin or rapid-hardening cementitious grout or the like can be injected into the intermediate posts 4 to fill the gap between the reinforcing bar and the interior wall of the intermediate post. The epoxy resin can also migrate horizontally along the interface between the sectional elements 9, 9'. The epoxy resin secures the reinforcing bars into the intermediate posts 4, 5. These reinforcing bars bridge the interface between adjacent sectional elements, developing a tensile anchorage between the intermediate post and the reinforcing bar therein through the epoxy resin.

When the next (third) sectional element (not illustrated) is placed on top of the second sectional element 9', more reinforcing bars 33 are inserted into the intermediate posts so as to bridge the interface between the second and third sectional elements. Epoxy resin is inserted to fill the remainder of the intermediate posts 4' and the first half of the intermediate posts of the third sectional element.

Figure 22 shows again how the sectional elements 9 fit together. As mentioned above, the vertical spacing of the sectional elements is defined by the spigots, sockets and bearing surfaces, not by the concrete surfaces. Between the concrete surfaces is an epoxy resin reservoir defined by rubber seals 34 which sets to form a solid interface capable of transmitting load between adjacent sectional elements. The epoxy resin permits transmission of tensile, compressive and shear forces between adjacent sectional elements.

Claims (33)

1. Method of excavating a non-circular shaft comprising the steps of: a) excavating a leading shaft section of substantially circular cross-section; b) introducing a cutting apparatus into an upper portion of said leading shaft section; c) orientating said cutting apparatus into a desired position; d) excavating said upper portion using said culling apparatus to convert said upper portion from having a substantially circular cross-section to having a non-circular cross-section; e) installing a sectional supporting element of non-circular cross-section into said converted upper portion; f) repeating steps b) -e) until a non-circular shaft of desired depth has been excavated.

2. Method as claimed in claim 1 wherein said sectional supporting element comprises a frame cast within concrete and having a central aperture therethrough, the sectional supporting element preferably having a generally rectangular shape.

3. Method as claimed in claim 2 wherein said frame includes a tubular post.

4. Method as claimed in claim 3 further comprising the step of: g) inserting a reinforcing bar across an interface between one sectional supporting element and a second sectional supporting element installed on top thereof.

5. Method as claimed in claim 4 wherein said reinforcing bar is located within said tubular post.

6. Method as claimed in any of the preceding claims wherein step a) is performed by a piling rig.

7. Method as claimed in any of the preceding claims wherein culling spoil from step d) is able to fall into said leading shaft section.

8. Method as claimed in any of the preceding claims wherein said culling apparatus can be selectively lifted and lowered into said leading shaft section.

9. Method as claimed in any of the preceding claims wherein rotary movement is provided to at least part of said cutting apparatus by a piling rig.

10. Method as claimed in any of the preceding claims wherein said cutting apparatus is capable of being orientated into a desired position anywhere between the periphery of said leading shaft section and a peripheral edge of said non-circular shaft.

11. Method as claimed in any of claims 3-10 further comprising the step of inserting epoxy resin, grout or the like into one or more of the tubular posts.

12. Method as claimed in any of the preceding claims further comprising the step of attaching a cutting shoe to the underside of the sectional supporting element before performing step e).

13. Method as claimed in any of the preceding claims further comprising the step of installing a plurality of reaction piles, against which the sectional supporting element can be hydraulically jacked downwardly during step e)

14. Method as claimed in any of claims 2-13 further comprising the step of placing said sectional supporting element on the ground and performing steps a)-d) through said central aperture.

15. Method of excavating a non-circular shaft substantially as described herein with reference to and as illustrated by any appropriate combination of the accompanying drawings.

16. Apparatus for performing the method of any of claims 1-15 including cutting apparatus comprising: a frame of a size capable of being raised and lowered through the central aperture of said sectional supporting element; cutters attached to said frame and moveable with respect thereto in at least two directions in a single plane.

17. Apparatus as claimed in claim 16 wherein said cutters are attached to said frame via one or more telescopic arms, for providing movement in one of said directions.

18. Apparatus as claimed in claim 16 or claim 17 wherein said cutters are attached to said frame via a rotary drive mechanism, one of said directions being rotary movement provided by said rotary drive mechanism.

19. Apparatus as claimed in claim 18 wherein said rotary movement is provided to said rotary drive mechanism by a piling rig.

20. Apparatus as claimed in any of claims 16-19 wherein said cutters are moveable with respect to said frame in a third direction comprising rotary movement between a position in which the cutters are substantially parallel to the nearest side of said frame and a position in which the cutters are substantially perpendicular to the nearest side of said frame.

21. Apparatus as claimed in any of claims 16-20 further comprising friction-reducing means, for example one or more wheels, attached to said frame, for facilitating raising and lowering of said frame through the central aperture of said sectional supporting element.

22. Apparatus for performing a method of excavating a non-circular shaft substantially as described herein with reference to and as illustrated by any appropriate combination of the accompanying drawings.

23. Sectional supporting element for use in the method of any of claims 1-15 comprising a frame cast in concrete, the frame comprising: a plurality of tubular posts having machined engagement means at the top and bottom thereof for engagement with tubular posts of vertically adjacent sectional supporting elements.

24. Sectional supporting element as claimed in claim 23 wherein said machined engagement means comprises a spigot and a socket.

25. Sectional supporting element as claimed in claim 24 wherein said engagement means comprises two bearing surfaces.

26. Sectional supporting element as claimed in claim 25 wherein said bearing surfaces are substantially free of concrete and define an interface between vertically adjacent sectional supporting elements.

27. Sectional supporting element as claimed in any of claims 23-26 wherein said engagement means are free from concrete.

28. Sectional supporting element as claimed in claim 23 wherein said frame is generally rectangular and said plurality of posts comprises four corner posts at the corners of the frame.

29. Sectional supporting element as claimed in claim 28 further comprising a plurality of intermediate posts intermediate said corner posts.

30. Sectional supporting element as claimed in claim 28 or claim 29 further comprising a reinforcing bar located inside one or more of the corner posts and/or intermediate posts, the reinforcing bar in use bridging the interface between two vertically adjacent sectional supporting elements.

31. Sectional supporting element as claimed in any of claims 28-30 wherein epoxy resin or grout or the like is placed inside said corner posts and/or said intermediate posts.

32. Sectional supporting element as claimed in claim 31 further comprising a clamping means for temporarily clamping two or more vertically adjacent sectional supporting elements together during a drying period for the epoxy resin or grout or the like.

33. Sectional supporting element substantially as described herein with reference to and as illustrated by any appropriate combination of the accompanying drawings.