Precast Reinforced Concrete Foundation Piles and Method of Manufacture

Abstract

A method of manufacturing a steel reinforced concrete foundation 6 pile comprising slipforming concrete over a steel reinforcement and subsequently pressing a steel headband 8 onto at least a head end of the of pile before the concrete is fully cured. The slipformed piles may be sawn to a selected length before a headband is pressed onto the head end of each pile. The headband may be pressed onto the end of the pile when the concrete has a hardness of less than 35 N / mm2.

Description

FIELD OF THE INVENTION This invention relates to precast reinforced concrete piles and to a method of manufacture thereof by using a slipforming process. BACKGROUND OF THE INVENTION In construction, precast concrete foundation piles are often used to provide a stable foundation for a building or other structure. Precast steel reinforced concrete piles can be driven into the ground using impact or vibration hammers to a design depth or resistance. In general, precast concrete piles can withstand high-tensile as well as high compression loads. However, a problem with precast concrete foundation piles is that concrete is relatively brittle and therefore the head of the pile is prone to damage due to impacts during the driving process. To mitigate this problem it is known to provide reinforcement links or steel headbands around the head end of a precast concrete foundation pile. Precast concrete foundation piles are typically manufactured by a moulding process, wherein a steel reinforcement cage is formed and placed into a mould having the dimensions of the required pile. Concrete is then poured into the mould before being allowed to cure. The mould may be vibrated to improve the quality of the pile. A steel headband may be located in the mould, before the concrete is poured, to reinforce the head end of the pile and reduce the risk of damage during driving. The main drawback of this traditional method of making precast concrete foundation piles is that it is slow, with piles only ready the next day, and uses large quantities of cement. Furthermore only piles of a set cross-section and length can be formed in each mould, and different sized piles require moulds to be changed over. Firms often do not have all the necessary moulds . Precast piling companies have typically produced and stockpiled a large number of different piles sizes and lengths to allow new contracts to start without waiting for piles to be cast, requiring large amounts of storage space. Slip forming extruders are used to manufacture precast hollow-core elements in which the concrete mix is extruded by means of auger flights or moving vibratory formers. The extruder moves on rails on a long bed. The auger flights or vibratory formers are shaped to aid the compaction of the concrete. Slipforming is a quick and efficient method of making precast concrete structures of various shapes. Attempts have be made to use a slipforming process to manufacture steel reinforced concrete foundation piles. Slipforming has the advantage of producing piles of different dimensions by simply changing the cassette forming the desired product. Changing production from one element to another is a quick and simple operation and does not require the use of skilled labour. However, the manufacture of precast concrete piles using a slipforming technique has met with limited success because it has not been possible to incorporate steel headbands onto head end of the piles using the slipforming technique and therefore such piles are prone to damage during driving. Consequently piles formed by this method to date have only been driven to length for low loads in very soft soils SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a method of manufacturing a steel reinforced concrete foundation pile comprising slipforming concrete over a steel reinforcement and subsequently pressing a steel headband onto at least a head end of the of pile before the concrete is fully cured. In one embodiment a headband may be pressed onto each end of the pile. Preferably the or each steel headband has internal dimensions less that the external dimensions of the pile such that each headband removes concrete from the sides of the or each outer end of the pile as it is pressed onto the pile. In one embodiment the or each headband may be pressed onto an end of the pile when the concrete of the pile has hardness of less than 35 N / mm2 The or each headband may be pressed onto an end of the pile when the concrete of the pile of the pile has hardness of approximately 30 N / mm2. At least the head end of the pile may be finished using a vibratory finishing device following slipforming and prior to application of the steel headband to ensure the pile has the desired dimensions in at least said head end. In one embodiment both ends of the pile may finished using a vibratory finishing device to ensure dimensional consistency of the ends of the pile. The vibratory finishing device may comprises a series of beams or plates adapted to engage upper and lateral sides of the pile in the region of its ends while the pile rests on a manufacturing bed. The method may comprise sawing the slipformed piles to a selected length before a headband is pressed onto at least the head end of each pile. The steel reinforcement comprises a welded cage of reinforcing rods or an arrangement of pre-stressed reinforcing rods over which concrete is slipformed. According to a further aspect of the present invention there is provided a precast reinforced concrete foundation pile manufactured in accordance with the method of the first aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS A method of manufacturing a precast concrete foundation pile in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is an illustration of a slipformed pile section; Figure 2 is an illustration of a pile cut from the pile section of Figure 1; Figures 3 and 4 illustrate the pressing of a steel headband onto an end of the pile of Figure 2; and Figure 5 shows a finishing device for finishing the ends of the pile of Figure 2. DETAILED DESCRIPTION OF THE DRAWINGS A method of manufacturing a precast reinforced concrete foundation pile in accordance with an embodiment of the present invention will now be described with reference to the accompanying drawings. In a first step, reinforcement cages (not shown), formed from welded steel rods and / or wire, are located on a manufacturing bed along which a slipforming machine runs. The slipforming machine is of standard known construction and will not be described in more detail. In a second step the slipforming machine moves along the manufacturing bed and slipforms concrete, preferably comprising a relatively dry non-sag mix, over the reinforcement cages to form a plurality of parallel pile sections 2. The pile sections 2 may each having a length of approximately 126 metres. Once the pile sections 2 have been slipformed on the bed they may be marked at locations 4 corresponding to the desired pile section lengths. Pile sections 2 are preferably made in multiples of either 3 or 4 across each bed. The manufacturing bed may have a width of 1.2 metres. While the pile sections 2 are still wet and located on the manufacturing bed, a finishing device 10 may be used to ensure the dimensions of at least the end regions of each pile are as specified. As illustrated in Figure 5, this finishing device 10 may takes the form of a three sided vibratory unit having vibratory plates or beams 12,14,16 adapted to engage upper and lateral sides of the pile in the region of the ends of the pile as it rests on the manufacturing bed, wherein the plates or beams 12,14,16 can adjust the exact required pile cross sectional dimensions at what will become the ends of each pile, thus ensuring dimensional consistency of the ends of the pile. After at least partial curing, the pile sections 2 may be sawn at marked and gauged locations 4 to form piles 6 of the desired length, as illustrated in Figures 1 and 2. The piles 6 may have small variations in section size from the slip forming process but at least at their ends the finishing device will create the exact required size. This is important because, immediately after removal from the manufacturing bed and preferably while the piles 6 are stacked on removal bogies, the piles enter a process area where a tubular steel headband 8 is pressed over the gauged part of at least the head end, more preferably each end of each pile. In one embodiment a frame (not shown) may be positioned over each pile and a hydraulic press may be operated to engage a respective headband 8 on each end of the pile and push the headbands onto the ends of the pile, preferably from both ends. The headbands 8 scrape away the fresh concrete to form an interference fit, thus emulating the a cast-in place headband. The invention is not limited to the embodiment described herein but can be amended or modified without departing from the scope of the present invention.

Claims

1. A method of manufacturing a steel reinforced concrete foundation pile comprising slipforming concrete over a steel reinforcement and subsequently pressing a steel headband onto at least a head end of the of pile before the concrete is fully cured.

2. A method as claimed in claim 1, wherein a headband is pressed onto each end of the pile.

3. A method as claimed in claim 1 or claim 2, wherein the or each steel headband has internal dimensions less that the external dimensions of the pile.

4. A method as claimed in any preceding claim, wherein the or each headband is pressed onto an end of the pile when the concrete of the pile has hardness of less than 35 N / mm25. A method as claimed in claim 4, wherein the or each headband is pressed onto an end of the pile when the concrete of the pile of the pile has hardness of approximately 30 N / mm2.

6. A method as claimed in any preceding claim wherein at least the head end of the pile is finished using a vibratory finishing device following slipforming and prior to application of the steel headband to ensure the pile has the desired dimensions in at least said head end.

7. A method as claimed in claim 6, where both ends of the pile are finished using a vibratory finishing device to ensure dimensional consistency of the ends of the pile.

8. A method as claimed in any preceding claim, wherein the slipformed piles are sawn to a selected length before a headband is pressed onto at least the head end of each pile.

9. A method as claimed in any preceding claim, wherein said steel reinforcement comprises a welded cage of reinforcing rods.

10. A method as claimed in any of claims 1 to 9, wherein said steel reinforcement5 comprises pre-stressed reinforcing rods over which concrete is slipformed.

11. A precast reinforced concrete foundation pile manufactured in accordance with the method of any of claims 1 to 10.

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