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1. WO2020001798 - SLIPFORM CONCRETE STRUCTURE AND METHOD FOR SLIPFORMING

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

SLIPFORM CONCRETE STRUCTURE AND METHOD FOR SLIPFORMING

Technical Field

The invention relates to a slipform structure, and a method of operating a slipform apparatus for constructing a slipform structure.

Background

It is known to form a vertical building or structure using slipforming, which is a construction method whereby concrete is poured into a continuously moving form to provide a cast-in-situ concrete structure. The continuously moving form is provided by a platform on an inside and an outside of the concrete structure. A workforce stands on the platforms and can place steel reinforcing rods into the concrete as required. The platforms are raised by means of hydraulic jacks that lift on steel jack rods that are cast into the concrete. Generally, the slipform concrete structure rises at a rate which permits the concrete to set and hold its own structure and weight by the time it emerges from the bottom of the form. The rate of climb is determined by the platform operator to ensure the quality of the concrete structure.

A problem with the above known slipforming technique is that the concrete structure uses a platform on both the inside and the outside thereof, which is not possible when the concrete structure is required to be installed in a vertical shaft such as a hole in the ground where access is only available from one side thereof in the vertical shaft. Such an operational limitation means that scaffolding is typically required within the shaft to construct the concrete structure. Whereas it is known from KR101218185 to provide a

single-sided slipforming platform, such an arrangement must form the concrete structure structure from a base to a top of the vertical shaft in the ground. Such arrangements create operational disadvantages and limit the installation options for the concrete structure.

When installing a concrete structure in a vertical shaft in the ground it is also known to use precast concrete segments to create a concrete tube that is then pushed down into the ground. Such a construction method has limitations because the diameter of the shaft can only be up to the maximum diameter of the concrete segments, which are currently provided up to 25m in diameter. The relatively small diameter of 25m may require a relatively deeper concrete structure. For example, if a larger volume for the concrete structure is required then the shaft must be deeper, but if the shaft is deeper the ground conditions may be relatively worse, which increases the cost of the construction. A relatively deeper concrete shaft also requires a larger foundation structure (i.e. concrete slab) at a base thereof to prevent water from welling upwards into the shaft. Overall a deeper shaft is relatively more expensive to construct.

A further problem when using the precast concrete segments is the requirement to lift them into position using a crane prior to pushing them into the ground. In general, the lifting of large and heavy items on a construction site requires additional safety procedures, which may increase cost. Furthermore, lifting such large and heavy items can only be performed when the wind speed on the construction site is below a safe operating level. If the wind speed is above the safe operating level the construction process may be required to be stopped, which can delay schedules and increase costs.

It is also known to install a concrete structure in a vertical shaft in the ground from scaffolding within the shaft using formwork mounted on the scaffolding. Sections of the concrete structure are formed on top of each other by pouring concrete into the formwork and then waiting for the concrete to set. After one section of concrete has been completed the formwork is stripped off and placed higher up the scaffolding to form the next section of concrete. A problem with this technique is that the formwork is required to be stripped off and re-located higher up the scaffolding to form the next concrete section. Such an arrangement is labour intensive, and may also present a safety challenge because the formwork is required to be removed and re-fitted over an increasing height as the concrete structure is formed in the shaft. Furthermore, the use of scaffolding and formwork requires a lot of crane time, which may not be able to be operated if the wind speed is above the safe operating level. Overall the requirement for a crane may add cost and time to the construction process.

When installing a retaining wall for a basement, or a foundation for a building, it is also known to use piling such as secant piling. The piling may be constructed by boring a hole into the ground following inserting steel rebar into the hole and then pouring concrete. A problem with such piling is that it can be complex and expensive to install. Furthermore, the boring of the holes for the piling may create unwanted noise and vibration.

It is broadly an object of the present invention to address one or more of the above mentioned disadvantages of the previously known slipforming method and apparatus.

Summary

What is required is an apparatus and method which may reduce or minimise at least some of the above-mentioned problems.

According to a first aspect of the invention, there is provided a method of operating a slipform apparatus for constructing a slipform structure, the slipform apparatus comprising a platform and a lift device, the method including:

performing a concrete slipform operation comprising pouring concrete and raising the platform using the lift device to construct the slipform structure; and

performing an excavation operation comprising removing material from underneath or one side of the slipform structure so that the slipform structure lowers under the action of gravity.

Such a method provides the advantage that the slipform structure can be formed above ground, or at ground level, and then lowered into the ground under its own weight by digging underneath it, or to one side thereof, in an uninterrupted manner and as a continuous process. Accordingly, such arrangements permit the slipform structure to be formed in the ground (e.g. within a vertical shaft) as the region adjacent to or underneath the slipform structure is removed (i.e. dug out). It will be understood that the excavation operation is performed only after the concrete at a base of the slipform structure has set. Using the method of the invention avoids the need to lift pre-cast concrete forms above ground and then push them into the ground as per the prior art. Accordingly, the method of the invention be safer than the prior art because there is no need to precast concrete forms to be raised above ground, and the method of the invention is not required to be stopped for safety reasons when there is a high wind speed.

When using the method of the invention it is possible to form a tubular slipform structure with a relatively larger diameter, for example, up to 30m to 40m or more in diameter. Such a larger diameter means that the slipform structure is not required to be as deep as a concrete structure with a relatively smaller diameter as per the prior art, and means that the construction process is less expensive. Such arrangements provide a high degree of operational efficiency with a reduced construction time, and may lead to cost savings when compared to the prior art. The improved operational efficiency may also permit the slipform structure to be made with a more uniformed structure. Furthermore, when using the method of the invention it is also possible to perform slipforming from one or both sides of the slipform structure (i.e. one or two-sided slipforming) because the slipform is created above ground, or at ground level, which avoids the need for single-sided slipforming within the shaft.

The method of the invention avoids the need for scaffolding and formwork mounted thereon, and the need to strip off and re-fit the formwork over an increasing height as the slipform structure is formed in the shaft. Accordingly, the requirement for a crane to move the scaffolding and formwork is also avoided. Furthermore, the platform of the invention can be fully enclosed during the full construction process and provides an improvement in safety. In addition, when constructing a retaining wall for a basement, or a foundation for a building, such an arrangement avoids the need for piling such as secant piling, and the slipform structure may be used an alternative to such piling.

In one embodiment the method further includes performing the concrete slipform operation at the same time as performing the excavation operation. Such an arrangement provides for the pouring of concrete and the excavation of material in parallel.

In one embodiment the method further includes stopping the concrete slipform operation, waiting until the concrete of a section of the slipform structure has set, and then performing the excavation operation. Such an arrangement provides for the pouring of concrete and the excavation of material in sequence one after the other, which may produce a more uniformed structure. It will be appreciated that in this embodiment the platform may lower as the slipform structure lowers.

In one embodiment the method further includes repeating the concrete slipform operation on top of the section of the slipform structure, and repeating the excavation operation. Such a method provides for forming another section of the slipform structure on top of a first slipform structure.

Preferably the platform has at least one work level around a perimeter of the platform that surrounds a central space through the at least one work level, the method further including:

said excavation operation comprising removing material via an open mouth of the slipform structure.

Such a method provides the advantage of providing ready access to the ground within the slipform structure to perform the excavation operation.

Preferably the method further includes providing the slipform structure with a cutting edge at a base thereof prior to performing the concrete slipform operation on top thereof Such a cutting edge assists with the lowering of the slipform structure under the action of gravity.

Preferably the method further includes providing the cutting edge as a taper on one side of the slipform structure to push material to one side thereof as it lowers under the action of gravity. Preferably the method further includes providing the taper so that the material is pushed radially inward of the central space. Such an arrangement provides the advantage that the slipform structure cuts a vertical path through the ground at an outer surface of the slipform structure as it moves downwards under gravity, and at the same time also pushes the material (e.g. the soil) to one side of the slipform structure, and radially inwards of the slipform structure when it has a central space.

Preferably the method further includes providing the slipform structure with a capping structure adjacent thereto prior to performing the concrete slipform operation, wherein the platform is above the capping structure and has a part thereof for preventing the platform from moving below the capping structure. The capping structure acts as a safety feature because the platform cannot move below it due to the part of the platform, and provides a fail-safe arrangement for the platform.

Preferably the method further includes forming the capping structure of concrete. Preferably the method further includes placing the cutting edge with the capping structure adjacent thereto prior to performing the concrete slipform operation. Such an arrangement provide an advantageous way to form the components of the slipform structure.

Preferably the method further includes providing the slipform structure with a support adjacent thereto prior to performing the concrete slipform operation. Preferably the method further includes forming the support of concrete. The support provides the advantage of a firm surface on which operatives can work to construct the platform.

Preferably the method further includes forming the support with the capping structure prior to performing the concrete slipform operation. Such an arrangement provide an advantageous way to form the components of the slipform structure.

Preferably the method further includes forming the capping structure so that it is outermost of the slipform structure, and forming the support so that it is innermost of the concrete structure, wherein the cutting edge is placed between the capping structure and the support. It will be understood that such arrangements are provide when there is a central space of the slipform structure.

Preferably the method further includes separating the cutting edge from the capping structure and the support using shuttering during forming thereof. Such an arrangement permits the cutting edge and the slipform structure thereon to slip past the capping structure when performing the excavation operation.

Preferably the method further includes removing the support when performing the excavation operation. Such an arrangement provides ready access to the material from underneath or one side of the slipform structure when performing the excavation operation.

Preferably the method further including performing a lift device installation operation comprising:

installing one or more jack rods into the slipform structure , the lift device comprising one or more jacks that operate on the one or more jack rods to raise the platform; or

installing one or more cables and winches for the lift device suitable for raising or lowering the platform.

Such arrangements provide a convenient way to install the lift device and may provide a fail-safe mechanism for the slipform apparatus.

Preferably said performing the rebar installation operation comprises raising the platform using the lift device and installing the at least one rebar cage. The rebar installation operation may be performed as part of the concrete slipform operation.

Preferably the platform has a plurality of work levels, the method further including using one level to perform one operation, and using another level to perform another operation. Preferably said rebar installation operation further includes using one of the plurality of work levels to install vertical reinforcing bars, and another of the plurality of work levels to install horizontal reinforcing bars. Preferably said concrete slipform operation further includes using one of the plurality of work levels for pouring of the concrete, and another of the plurality of work levels to finish the set concrete. Preferably said lift device installation operation further includes using one of the plurality of work levels to install one or more jack rods, and another of the plurality of work levels to install the at least one rebar cage.

The plurality of work levels around a perimeter of the platform can be used to perform multiple tasks on the primary slipform structure at the same time. Such arrangements help to reduce the time to construct the slipform structure because a larger workforce can operate on the platform at a given time. The plurality of work levels permit different teams to perform different tasks thereon, which may be more efficient. Such an arrangement may also improve the operational flexibility of the platform, which may reduce the construction time and reduce costs.

Preferably the method further includes assembling the platform above ground prior to operation thereof. In other words, the platform is assembled at ground level prior to the installation of rebar, or the performing of slipforming, or the performing of excavation.

Preferably the method further includes installing a foundation underneath the slipform structure after completion thereof.

Preferably the method further includes performing a reinforcement operation of the slip form structure comprising:

performing a rebar installation operation of the slipform structure comprising installing at least one rebar cage; and/or

using fibre concrete for the concrete slipform operation.

It will be appreciated that the rebar installation operation may be performed with the concrete slipform operation.

Preferably the method further includes using a slurry agent to assist with lowering of the slipform structure under the action of gravity.

Preferably said rebar installation operation further includes installing more than one rebar cage.

According to a second aspect of the invention, there is provided a slipform structure produced using the method of claims 1 to 23.

According to a third aspect of the invention, there is provided a slipform structure comprising a cutting edge at a base thereof, the cutting edge having a taper on one side of the slipform structure for pushing material to one side thereof as it lowers under the action of gravity.

Such an arrangement provides the slipform structure with the advantage of being able to cut a vertical path through the ground at an outer surface of the slipform structure as it moves downwards under gravity under its own weight, and at the same time also pushes the material (e.g. the soil) to one side of the slipform structure, and radially inwards of the slipform structure when it has a central space, which assists with excavation.

Preferably the slipform structure further includes a capping structure adjacent thereto, wherein a platform to form the slipform structure is above the capping structure and has a part thereof for preventing the platform from moving below the capping structure. The capping structure acts as a safety feature because the platform cannot move below it due to the part of the platform, and provides a fail-safe arrangement for the platform.

Preferably the slipform structure further includes a support adjacent thereto, wherein the capping structure is outermost of the slipform structure, the support is innermost of the concrete structure, and the cutting edge is between the capping structure and the support. It will be understood that such arrangements are provide when there is a central space of the slipform structure.

According to an alternative characterisation of the invention there is provided a method of operating a slipform apparatus for constructing a slipform structure, the slipform apparatus comprising a platform, the method including:

performing a concrete slipform operation of the at least one rebar cage comprising pouring concrete to construct the slipform structure; and

performing an excavation operation comprising removing material from underneath or one side of the slipform structure so that the slipform structure lowers under its own weight due to the action of gravity.

According to another alternative characterisation of the invention there is provided a method of operating a slipform apparatus for constructing a slipform structure having a central space thereof, the slipform apparatus comprising a platform and a lift device, the method including:

performing a concrete slipform operation comprising pouring concrete and raising the platform using the lift device to construct the slipform structure; and

performing an excavation operation comprising digging material from underneath or from one side of the slipform structure, and removing it via an open mouth of the slipform structure so that the slipform structure lowers under its own weight due to the action of gravity, said excavation operation being performed after at least a lower part of the concrete has set so that the slipform structure can support its own weight.

Any preferred or optional features of one aspect or characterisation of the invention may be a preferred or optional feature of other aspects or characterisations of the invention.

Brief Description of the Drawings

Other features of the invention will be apparent from the following description of preferred embodiments shown by way of example only with reference to the accompanying drawings, in which;

Figure 1 shows a perspective view of the placement of a concrete cutting ring prior to the commencement of slipforming according to an embodiment of the invention;

Figure 2 shows a perspective view of formwork and walers assembled onto the concrete base shown in Figure 1 ;

Figure 3 shows a perspective view of a framework for a platform assembled onto the formwork and walers shown in Figure 2;

Figure 4 shows a perspective view of the platform with decking and cladding assembled onto the framework shown in Figure 3;

Figure 5 shows a perspective cross sectional view of the platform of Figure 4 at the start of slipforming;

Figure 6 shows a perspective cross sectional view of a concrete structure at l5m above the concrete base;

Figure 7 shows a perspective cross sectional view of the concrete structure at 5m above the concrete base and lOm below the concrete base;

Figure 8 shows a perspective cross sectional view of the concrete structure at 0m above the concrete base and l5m below the concrete base;

Figure 9 shows a perspective cross sectional view of the concrete structure at l5m above the concrete base and l5m below the concrete base;

Figure 10 shows a perspective cross sectional view of the concrete structure at

0m above the concrete base and 30m below the concrete base;

Figure 11 shows a perspective cross sectional view of the concrete structure at l5m above the concrete base and 30m below the concrete base;

Figure 12 shows a perspective cross sectional view of the concrete structure at 0m above the concrete base and 45m below the concrete base;

Figure 13 shows a perspective cross sectional view of the concrete structure at l5m above the concrete base and 45m below the concrete base;

Figure 14 shows a perspective cross sectional view of the concrete structure at

0m above the concrete base and 60m below the concrete base;

Figure 15 shows a perspective view of the completed concrete structure with underpinning and with the platform removed; and

Figure 16 shows steps of a method according to an embodiment of the invention.

Detailed Description

Figures 1 to 4 show the stages of constructing a slipform apparatus comprising a platform 10 that is suitable for forming a concrete slipform structure 12 from the top down as shown in Figures 5 to 16. Also shown in Figures 1 to 15 is a vertical section of ground 14 where the concrete slipform structure 12 is installed. In Figures 1 to 15 like features are shown with like reference numerals. The platform 10 of the slipform apparatus is constructed substantially at ground level 13, and the concrete slipform structure 12 is formed downwards into the vertical section of ground 14 as discussed below with reference to Figures 5 to 16 which show stages of operating the slipforming apparatus according to an embodiment of the invention to form the concrete slipform structure 12, which may be alternatively termed a single face concrete liner or a concrete internal wall. The concrete slipform structure 12 is shown to be substantially cylindrical although other shapes may be formed using the slipforming apparatus. The concrete slipform structure 12 may be termed a slipform structure or a concrete structure.

Figure 1 shows a perspective view of the placement of a concrete cutting ring 16 prior to the commencement of slipforming according to an embodiment of the invention. |Reinforced concrete or steel piles 18 are driven or cut into the ground 14 (e.g. up to 6m deep) and act as shuttering. A surface of the ground is also prepare with the required profile before a concrete base 20 is poured and subsequently allowed to set. The concrete base 20 comprises three parts which are the cutting ring 16 at a central annulus, an inner ring 22 at an inner annulus, and an outer ring 24 at an outer annulus. The cutting ring 16 is a known item of steel and is placed in the base 20. The cutting ring 16 may be termed a cutting shoe. The outer ring 24 may be termed a capping structure or capping beam. The arrangement of the cutting ring 16, the inner ring 22 and the outer ring 24 is also shown in Figures 5 to 15 in cross section. As shown in those Figures the cutting ring 16 moves downwards past the inner ring 22 and the outer ring 24 along the dashed lines 28 shown in Figure 1 as the concrete structure 12 is formed onto the cutting ring 16. The cutting ring 16 is separated from the inner ring 22 and the outer ring 24 by shuttering (i.e. sheets or boards) provided at the dashed lines 28 to permit the movement of the cutting ring 16 and the concrete structure 12 past the inner ring 22 and the outer ring 24. Such an arrangement separates the middle annulus from each of the inner annulus and outer annulus when the concrete base 20 is poured. The cutting ring 16 is the leading edge of the concrete structure 12 as it is driven into the ground 14 under the action of gravity. It will be appreciated that whereas the top surface of the base 20 is flat as shown in Figures 1 to 4 the underside thereof is profiled as the cutting ring 16, the inner ring 22 and the outer ring 24 are formed as shown in Figures 5 to 15.

Figure 2 shows a perspective view of formwork 30, 32 and walers 34, 36 assembled onto the concrete base 20 shown in Figure 1. The formwork 30, 32 comprises inner and outer vertical shuttering that is part of the platform 10 used to form the concrete structure 12. The formwork 30, 32 is held in place by the walers 34, 36, which are steel bands. The inner ring 22 and the outer ring 24 of the base 20 provide a firm surface on which operatives can work and install the formwork 30, 32 and walers 34, 36.

Figure 3 shows a perspective view of a framework 38 for the platform 10 assembled over the formwork 30, 32 and walers 34, 36 shown in Figure 2. In the embodiment shown the framework 38 comprises a plurality of sections, for example up to forty sections, for a concrete structure 12 of about 40m in diameter. The sections may be termed yokes. The framework 38 straddles the formwork 30, 32 and walers 34, 36 so that feet of each section of the framework 38 stand on the inner ring 22 and the outer ring 24 of the base 20. The inner ring 22 may be termed a support. Each level of the platform 10 is supported by a plurality of deck beams 39, which extend in a radial direction of the platform 10 and are spaced around the perimeter of the platform 10. Only the top deck beam 39 for the top level is shown, but it will be understood that middle deck beams are provided for the middle level of the platform 10, and lower deck beams are provided for the lower level of the platform 10. The cladding 44, 46, 47, 49, 50 (shown in Figure 6) is hung on posts 39 which are connected to a respective deck beam 39.

The formwork 30, 32 is also shown below the middle level so that the concrete structure 12 can be formed when concrete is poured at the middle level. In the embodiment shown the formwork 30, 32 depends from the middle level of the platform 10. The formwork 30, 32 may be any suitable panel or shuttering to contain the poured concrete until it has set. Vertical beams 43 are also shown between adjacent deck beams 39 of the levels.

Figure 4 shows a perspective view of the platform 10 with decking 40, 42 and cladding 44, 46, 49, 50 assembled onto the framework 38 shown in Figure 3. As shown in Figure

4, the decking comprises upper decking 40, middle decking 41, and lower decking 42. The cladding comprises upper inner cladding 44, middle inner cladding 46, upper outer cladding 49, and middle outer cladding 50. The platform 10 has three working levels around a perimeter thereof which surround a central space generally shown at 48. The central space 48 is a through hole in the three working levels. In other words the platform 10 is shown to be ring-shaped or annular such that each working level is ring-shaped or annular whereby each working level is a walkway around the outer perimeter of the slipform apparatus 10. In the arrangement shown in Figure 4 the platform 10 is shown to be circular, such that the overall platform 10 with the working levels is tubular. The platform 10 is also provided with stairs (not shown) to allow the workforce to gain access between the working levels. Whereas three working levels are shown it will be appreciated that more or less than three work levels may be provided.

A plurality of hydraulic jacks (not shown) are also installed onto the platform 10. The hydraulic jacks operate on steel jack rods that are cast into the concrete structure 12 according to known arrangements. The hydraulic jacks comprise a lift device, and may be termed strand jacks. In an alternative arrangement an alternative lift device is used to raise the platform 10 such as a plurality of cranes at ground level 13 comprising respective winches and cables (not shown) whereby each cable is connected to the platform 10. A

control module (not shown) is also installed to ensure that the lift device (i.e. jacks or winches) are operated at the same time to raise the platform 10. It will be understood that the any suitable lifting device may be used such as winches/cables or strand jacks with the proviso that the lifting device has a sufficient lifting capacity to raise the platform 10.

It will be understood that the platform 10 must always have a lift device wherein the platform is raised by the lift device during the pouring of concrete, followed by excavation underneath the concrete structure when at least a lower part of the concrete structure sets so that it can support the weight of the concrete structure.

Figure 5 shows a perspective cross sectional view of the platform 10 of Figure 4 at the start of slipforming of the concrete structure 12. As shown in Figure 5 the platform 10 is just above the base 20 after slipforming has commenced whereby the concrete structure 12 is formed directly onto the steel cutting ring 16. It will be appreciated that the concrete is poured from the surface 13 via a pipe (not shown). During or shortly before pouring of the concrete the jack rods are installed as discussed above. One or more rebar cages (not shown) are also installed, for example an outer rebar cage and an inner rebar cage with a middle rebar cage therebetween. Each rebar cage may comprise an outer layer of steel reinforcing bar, which may comprise three vertical layers of reinforcing bar that are close together, and which are tied together with pre-bent horizontal bars known as lacers. The outer rebar cage may be termed an outer layer, the inner rebar cage may be termed an inner layer, and the middle rebar cage may be termed a middle layer. The middle layer may be installed with the inner rebar cage and may comprise links between the outer rebar cage and the inner rebar cage. It will be understood that the number and density of the

one or more rebar cages that are installed depends on the required structural strength of the finished concrete structure 12. The one or more rebar cages are installed during the same pass of the platform 10 when slipforming upwards. It will also be appreciated that due to the multiple levels of the platform 10 it is possible to assemble the one or more rebar cages during slip forming of the concrete structure 12.

Also shown in Figure 5 is a pointed leading edge 52 of the cutting ring 16. The outside face of the cutting ring 16 down to the leading edge 52 is vertical. The inside face of the cutting ring 16 down to the leading edge 52 tapers radially inwards. In the embodiment shown the angle of the taper is substantially 70 degrees from the vertical, and it is envisaged that the angle of the taper could also be between 40 to 80 degrees from the vertical and still provide the required effect. The pointed leading edge 52 provides the advantage that the concrete structure 12 cuts a vertical shaft (i.e. path) through the ground 14 at an outer surface of the concrete structure 12 as it moves downwards under gravity, and at the same time also pushes the soil radially inwards of the concrete structure 12.

Figure 6 shows a perspective cross sectional view of the concrete structure 12 at l5m above the concrete base 20. Also shown is that the lower decking 44 is provided with lower cladding 47 as the slipform apparatus 10 rises with the concrete structure 12 as shown by the arrow 54. Accordingly, each level of the platform 10 has an internal safety wall to fully enclose the work force at each level so that they are separated from the central space 48. The cladding 44, 46, 47, 49, 50 comprises vertical panelling or fencing between each level of the platform 10 and the central space 48. Such an arrangement provides an improved safety for the work force on the levels. It will be understood that each level

comprises a substantially horizontal walkway, which may be of any suitable material such a wood.

The platform 10 is shown to be straddling the concrete structure 12 so that there are two levels on the outside thereof and three levels on an inside thereof. The concrete structure

12 is formed and rises at a rate which permits the concrete to set and hold its own structure and weight by the time it emerges from the bottom of the formwork 32, 34. The rate of climb is determined by the operator of the platform 10 to ensure the quality of the concrete structure 12. When the concrete structure 12 is at l5m above the concrete base 20 the slipforming is stopped. The portion of the ground shown at 56 is then removed by excavation. The inner ring 22 of the concrete base 20 is also removed. The ground 56 and the inner ring 22 are removed via the central space 48 and the open mouth of the concrete structure 12. During excavation the concrete structure 12 moves downwards under the action of gravity as shown by arrow 58 in Figure 7. It will be understood that the excavation operation is performed only after the concrete at a lowermost point (i.e. a base or foot) of the slipform structure 12 has set, or at least when the concrete structure 12 has set sufficiently to carry its own weight.

Also shown in Figure 6 is that the inner ring 22 is relatively thin, and the outer ring 24 is relatively thick. The reason for such an arrangement is that the inner ring 22 is a temporary formation to permit the construction of the platform 10 thereon, whereas the outer ring 24 remains in place after the concrete structure 12 has been completed and acts as a capping around a top thereof as shown in Figure 15. The outer ring 24 also acts as a safety feature because the platform 12 cannot move below it due to the framework 38 wherein an outer periphery thereof rests on the outer ring 24 as shown in Figure 8.

Figure 7 shows a perspective cross sectional view of the concrete structure 12 at 5m above the concrete base 20, and lOm below the concrete base 20. In Figure 7 the slipforming remains stopped, and the excavation of material is still in progress as the concrete structure 12 moves downwards under the action of gravity, as shown by arrow 58. The shuttering between the cutting ring 16 and the outer ring 24 of the base allows the concrete structure 12 to move downwards. In other words the concrete structure 12 is formed above the ground level 13 and then it slides downwards under its own weight as the material under the walls of the concrete structure 12 is dug out. An internal face of the diaphragm wall (i.e. the internal face of the concrete structure 12) is prepared/finished from the lowest work level (i.e. from the lower decking 42) of the platform 10. An external face of the diaphragm wall (i.e. the external face of the concrete structure) is prepared/finished at ground level by way of access from the external capping beam (i.e. the outer ring 24) of the base 20. After preparation/finishing of the internal face of the concrete structure 12 the lowest work level is removed from the internal face to allow the concrete structure 12 to sink further prior to recommencing slipforming. However, the internal wall of the ground 14 adjacent to the concrete structure 12 does not require any other preparation.

Figure 8 shows a perspective cross sectional view of the concrete structure at 0m above the concrete base 20, and l5m below the concrete base 20. In Figure 8 the excavation of material is stopped, and the platform 12 is ready to commence slipforming of the concrete structure 12 again.

Figure 9 shows a perspective cross sectional view of the concrete structure 12 at l5m above the concrete base 20, and l5m below the concrete base 20. When the concrete structure 12 is at l5m above the concrete base 20 the slipforming is stopped, and the next portion of ground 62 is ready to be excavated.

Figure 10 shows a perspective cross sectional view of the concrete structure 12 at 0m above the concrete base 20, and 30m below the concrete base 20. In Figure 10 the portion of ground 62 shown in Figure 9 has been removed so that the concrete structure 12 moves down under the action of gravity to the position shown in Figure 10 with the concrete structure at 30m below the concrete base 20.

Figure 11 shows a perspective cross sectional view of the concrete structure 12 at l5m above the concrete base 20, and 30m below the concrete base 20. When the concrete structure 12 is at l5m above the concrete base 20 the slipforming is stopped, and the next portion of ground 64 is ready to be excavated.

Figure 12 shows a perspective cross sectional view of the concrete structure at 0m above the concrete base 20, and 45m below the concrete base 20. In Figure 12 the portion of ground 64 shown in Figure 11 has been removed so that the concrete structure 12 moves down under the action of gravity to the position shown in Figure 12 with the concrete structure at 45m below the concrete base 20.

Figure 13 shows a perspective cross sectional view of the concrete structure at l5m above the concrete base 20, and 45m below the concrete base 20. When the concrete structure 12 is at l5m above the concrete base 20 the slip forming is stopped, and the next portion of ground 66 is ready to be excavated.

Figure 14 shows a perspective cross sectional view of the concrete structure at 0m above the concrete base 20, and 60m below the concrete base 20. In Figure 14 the portion of ground 66 shown in Figure 13 has been removed so that the concrete structure 12 moves down under the action of gravity to the position shown in Figure 14 with the concrete structure 12 at 60m below the concrete base 20.

Figure 15 shows a perspective view of the completed concrete structure 12 with underpinning 68 and with the platform 10 removed. The underpinning 68 is installed underneath the concrete structure 12 after slipforming of the concrete structure 12 has been completed. The concrete cutting ring 16 is removed prior to installing the underpinning 68. The underpinning 68 forms a lower base for the concrete structure 12 and comprises a foundation so that the concrete structure 12 does not move downward any further. As shown in Figure 15 the concrete structure 12 is formed in a vertical shaft within the ground 14 which is 60m below the concrete base 20. The outer ring 24 also acts as capping beam for the concrete structure 12.

Figure 16 shows steps of a method according to an embodiment of the invention, generally designated 70. It will be appreciated that the steps may be performed in a different order, and may not necessarily be performed in the order shown in Figure 16.

The method 70 is for operating a slip form apparatus for constructing a slip form structure 12, for example in a shaft, the slipform apparatus 10 comprising a platform 10 and a lift device, the method including: performing a concrete slipform operation comprising pouring concrete and raising the platform using the lift device to construct the slipform structure; and performing an excavation operation comprising removing material from underneath or one side of the slipform structure 12 so that the slipform structure lowers under the action of gravity, as shown at 72.

The method further includes performing the concrete slipform operation at the same time as performing the excavation operation, as shown at 74. The method further includes stopping the concrete slipform operation, waiting until the concrete has set, and then performing the excavation operation, as shown at 76. The method further includes repeating the concrete slipform operation on top of the section of the slipform structure, and repeating the excavation operation, as shown at 78.

The platform 10 has at least one work level around a perimeter of the platform 10 that surrounds a central space 48 through the at least one work level, the method further including: said excavation operation comprising removing material via an open mouth of the slipform structure 12, as shown at 80.

The method further includes providing the slipform structure with a cutting edge 16 at a base thereof prior to performing the concrete slipform operation on top thereof, as shown at 82. The method further includes providing the cutting edge 16 as a taper on one side of the slipform structure to push material to one side thereof as it lowers under the action of gravity, as shown at 84. The method further includes providing the taper so that the material is pushed radially inward of the central space 48, as shown at 84.

The method further including providing the slip form structure 12 with a capping structure 24 adjacent thereto prior to performing the concrete slip form operation, wherein the platform 10 is above the capping structure 24 and has a part thereof for preventing the platform 10 from moving below the capping structure 24, as shown at 86. The method further including placing the cutting edge 16 with the capping structure 24 adjacent thereto prior to performing the concrete slip form operation, as shown at 88.

The method further including providing the slip form structure 12 with a support 22 adjacent thereto prior to performing the concrete slipform operation, as shown at 90. The method further including forming the support 22 with the capping structure 24 prior to performing the concrete slipform operation, as shown at 91. The method further including forming the capping structure 24 so that it is outermost of the slipform structure 12, and forming the support 22 so that it is innermost of the concrete structure 24, wherein the cutting edge 16 is placed between the capping structure 24 and the support 22. The method further including separating the cutting edge 16 from the capping structure 24 and the support 22 using shuttering during forming thereof. The method further including removing the support 22 when performing the excavation operation.

The method further including performing a lift device installation operation, as shown at 92. The lift device installation operation 92 comprising installing one or more jack rods into the slipform structure, wherein the lift device comprising one or more jacks that operate on the one or more jack rods to raise the platform 10, or installing one or more cables and winches for the lift device suitable for raising or lowering the platform 10.

The method further includes performing a reinforcement operation of the slipform structure 12, as shown at 94. The reinforcement operation comprising: performing a rebar installation operation of the slipform structure 12 comprising installing at least one rebar cage; and/or using fibre concrete for the concrete slipform operation 12.

The platform 10 has a plurality of work levels, the method further including using one level to perform one operation, and using another level to perform another operation. The rebar installation operation further includes using one of the plurality of work levels to install vertical reinforcing bars, and another of the plurality of work levels to install horizontal reinforcing bars. The said concrete slipform operation further includes using one of the plurality of work levels for pouring of the concrete, and another of the plurality of work levels to finish the set concrete.

The method further includes assembling the platform 10 above ground prior to operation thereof. The method further includes using a slurry agent to assist with lowering of the slipform structure 12 under the action of gravity, as shown at 96. The method further includes installing a foundation 68 underneath the slipform structure 12 after completion thereof.

From the foregoing description it can be seen that the central space 48 of the platform 10 provides an advantage that the material from underneath the concrete structure 12 can be removed via the central space 48 and the open mouth of the concrete structure 12. Furthermore the three working levels of the platform 12 permit different teams of workers to install different parts of the rebar cages or jack rods as discussed above during pouring of the concrete. For example, one team on the upper level of the platform 12 may install vertical reinforcing bars, another team on the middle level may install pre-bent horizontal lacer bars, another team on the lower level may also install horizontal lacer bars, and another team on the middle level may pour the concrete. In another example, the concrete may be poured at the middle level by one team, and another team on the lower level may finish the set concrete surface by hand trowelling or brush finishing, and optionally another team on the upper level may install the rebar cage and jack rods. Each of the three working levels is about 3m in height such that the overall platform 10 is about 9m in height. Such an arrangement permits relatively long l2m vertical rebar to be used when installing the one or more rebar cages, which may help to reduce the time to construct them. Furthermore, since there are three working levels are larger workforce can operate on the platform 10 at a given time, which may further help to reduce the time of construction.

The above embodiments described herein provide a high degree of operational efficiency, which saves time and money to construct the concrete structure 12. Furthermore, the embodiments described herein permit the concrete placement to be completed in an uninterrupted manner from the ground level 13 downwards to the base thereof.

The above embodiments permit the concrete structure 12 to be made with a more uniform surface and with an increased water tightness due to the reduced number of joints when compared to the prior art technique of using precast concrete segments. Furthermore, the above embodiments permit the concrete structure 12 to be made with a reduced construction time, which reduces the cost of construction. The above embodiments also allow for larger diameter shafts to be constructed with a reduced depth, which reduces construction costs, in particularly when the ground is of poor quality.

In the above embodiments the concrete structure 12 is formed as a circular ring shape such that the concrete structure 12 supports the walls of the vertical shaft in the ground 14 and material is excavated from inside the ring shape. It will be appreciated that the concrete structure 12 may be formed with any cross section such as circular, square, rectangular hexagonal, etc with the proviso that there is a central space 48 (i.e. a through hole) within the cross section to allow access to the ground under the concrete structure 12 to permit excavation thereof. However it is also envisaged that the embodiments herein may be used where there is not necessarily a central space that is fully enclosed by the concrete structure 12, such as a part circle, or a single planar or curved wall, or any other shape. Furthermore, in the above embodiments reference is made to the concrete cutting ring 16. It will be appreciated that in the case of the concrete structure 12 not being ring-shaped then the cutting ring 16 may be termed a cutting edge.

The above embodiments relate to an apparatus and method to form the concrete structure 12 in a vertical shaft in the ground 14 where access is only available from one side thereof in the vertical shaft. In particular the apparatus and method relate to optionally lifting of the platform 10 during the installation of one or more rebar cages and pouring of the concrete, following by excavation of material (i.e. soil) underneath and within the

concrete structure 12 so that it moves down (i.e. sinks) under the action of gravity, and which also allows the internal concrete wall of the concrete structure 12 to be finished by, for example, brushing or hand-trowelling.

It will be understood from the foregoing that the installation of the one or more rebar cages and jack rods is performed either before slipforming, or during slipforming, or during the excavation stage, and the platform 10 may be stationary or moving. As such it will be understood that certain operations such as the installation of the one or more rebar cages and jack rods are performed in parallel (i.e. at the same time), whereas other operations such as the pouring of concrete and excavation of material are performed sequentially (i.e. one after the other). However, the pouring of concrete and the excavation of material may alternatively be performed in parallel (i.e. at the same time). Such arrangements provide for greater operational flexibility for the slip form apparatus 12 according to the embodiments described herein.

It will be understood from the foregoing that the platform 10 is assembled at ground level 13 prior to slip forming, and then the ground below the central space 48 is excavated so that the slipform structure 12 moves downwards under the action of gravity. The slip forming may include moving the platform upwards to create a section of the concrete structure 12 prior to excavation. Such arrangements permit the concrete structure 12 to be formed within a vertical shaft in the ground 14 as the central region is dug out. In a preferred arrangement there are distinct steps of slipforming upwards, then stopping slip forming, then excavating until the concreted structure 12 has moved downwards, then stopping excavation, and then recommencing slipforming upwards again to repeat the

process. Such distinct steps may provide for an improved quality of the concrete structure 12. In the above embodiments the concrete structure 12 is formed upwards in l5m sections before the excavation process commences. It will be understood that the concrete structure 12 may be formed upwards in sections that are more or less that l5m before the excavation process commences. It is envisaged that the time between successive slipforming stages might be one or two weeks or longer. Such a time between successive slipforming stages can be used by the workforce for excavation. However, it may not be necessary to stop slipforming prior to excavation, and the slipforming and the excavation steps may be performed at the same time or one after the other.

It is also envisaged that a relatively short concrete structure 12 of 15 to 20 meters is formed upwards and then the platform 12 is removed. After removal of the platform the excavation underneath the concrete structure 12 is completed to lower it into the ground 14.

The above arrangements permit the construction of a concrete structure 12 with a relatively larger diameter than the prior art. Such a larger diameter means that the concrete structure 12 is not required to be as deep as a concrete structure with a relatively smaller diameter, and means that the construction process is less expensive. For example, with the above embodiments the concrete structure 12 may have a diameter of 30m to 40m, and without the need to push pre-cast concrete forms into the ground as per the prior art. Such arrangements may lead to a cost saving of between 20 to 40% on a contract in the region of £lM, which is also safer and more efficient than the prior art.

Using the above method 70 and apparatus 10 it will be appreciated that the concrete structure 12 can be formed downwards using the platform 10, which may have one work level on one or both of the inside and outside of the concrete structure 12. The wall thickness and rebar density of the concrete structure 12 can be adjusted for particular applications of the concrete structure 12 as required.

In the above embodiments reference is made to pouring concrete to form the concrete structure 12. The concrete may be fibre concrete (i.e. concrete with steel or plastic fibres), which may remove the need to use rebar within the concrete structure 12 as described above. In one arrangement the fibre concrete may be used as well as the rebar to form the concrete structure 12.

In the above embodiments a slurry agent may be used to assist lowering of the concrete structure 12 into the ground under the action of gravity. The slurry agent may be any suitable liquid or semi-liquid (e.g. bentonite slurry or similar) that helps to lubricate the interface between the concrete structure 12 and the ground 14. The slurry agent may be pumped into the ground 14 at an external face of the concrete structure 12 where it comes into contact with the ground 14.