GB2293850A

GB2293850A - Cast in situ piles

Info

Publication number: GB2293850A
Application number: GB9520404A
Authority: GB
Inventors: Roger Alfred Bullivant
Original assignee: Roxbury Ltd
Current assignee: Roxbury Ltd
Priority date: 1994-10-08
Filing date: 1995-10-06
Publication date: 1996-04-10
Anticipated expiration: 2015-10-06
Also published as: GB9520404D0; GB2293850B

Abstract

A method and apparatus for forming finned piles in situ comprises forming a frusto-conical recess, preferably by augering, at ground level, placing a top casing 18 in the recess corresponding to the shape thereof, placing a pile former comprising a finned casing 16 with fins projecting radially therefrom in the top casing 18, driving the finned casing 16 through the base of the top casing 18 to a pre-determined depth, thereafter removing the finned casing 16 from the hole it has formed in the ground while filling the void behind the retreating finned casing 16 with a cementitious material and removing the top casing 18 and 16 finned casing from the hole. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO PILES The present invention concerns improvements in or relating to piles, especially but not exclusively to piles which have been formed in the ground mainly by a soil displacement method.

Our co-pending European Patent Application 9090^4877.9 discloses a method of forming a pile using a pile former, the method comprising forcing cylindrical pile forming casing having radially projecting fins at its lower end into the ground to form a hole in the ground and having a cross-section corresponding to the cross-section of the finned end of the pile and as the finned casing is withdrawn from the hole pumping cementitious material into the void left behind the withdrawn finned casing to form a pile with a cross-section comprising a circular centre with radially projecting fins.

Piles of this nature utilise a relatively small amount of concrete but provide a relatively large surface area and consquently have good load-bearing characteristics.

In certain circumstances such prior piles have exhibited certain disadvantages, for example, guidance of the pile has been relatively difficult and the cross-sectional area of the pile top has been relatively small presenting problems when the pile top has to support, for example, a stanchion oF the structure of a steel framed building.

An object of the present invention is to obviate or mitigate these disadvantages.

According to the present invention there is provided a method of forming a pile comprising forming from ground level a recess, placing a top casing in the recess corresponding to the shape thereof, placing a pile former comprising a finned casing with three or less fins projecting radially therefrom in the top casing, driving the finned casing through the base of the top casing to a pre-determined depth, thereafter removing the finned casing from the hole it has formed in the ground while filling the void behind the retreating finned casing with a cementitious material and removing the top casing and finned casing from the hole.

Preferably the top casing is removably fixed to the bottom region of the finned casing and is positioned in the pre-formed recess by downward movement of the finned casing. Preferably the downward movement is a vibratory movement.

Preferably, the recess is formed as a downwardly converging recess.

Preferably after the top casing has been placed its fixing to the finned casing is removed prior to the finned casing forming the pile hole.

Preferably after forming the pile hole and on removal from the pile hole, the finned casing is re-fixed to the top casing to remove it from the top hole as the recess is being filled with concrete.

Preferably the top casing guides the finned casing as it forms the pile hole.

Preferably the finned casing is passed through guide means in the form of a plate having an aperture therethrough corresponding to the cross-section of the finned casing at its fins is provided at at least base of the top casing to guide the finned casing. The finned casing is passed through an additional guide plate which may be provided at the top of the top casing.

Further according to the present invention there is provided pile forming apparatus comprising a top casing for fitment in a recess formed in the ground above where a pile is to be formed, a pile former comprising a casing with fins projecting radially therefrom projecting through the casing, means for driving the casing into the ground to a predetermined depth, means for removing the finned and top casing and for filling the hole left behind the casings as they are removed with a cementitious material.

Preferably the apparatus includes means for fixing the top casing to the end of the finned casing which the assembly of casings is forced into the ground to form the said recess.

Preferably the means for driving the finned casing into the ground is a vibrator.

Preferably the top casing converges downwardly.

Preferably guide means in the form of a plate having an aperture therethrough corresponding to the cross-section of the finned casing at its fins is provided at at least the base of the casing.

Preferably an additional guide plate is formed at the top of the casing.

In a first embodiment the leading end of the finned casing has a front plate whose dimensions are greater than the dimensions of at least the fins.

In the first embodiment the finned casing has parallel sides. In a second embodiment the finned casing converges downwardly.

In the first embodiment, the finned casing has three fins. In the second embodiment, the finned casing has two fins which are preferably diametrically opposed on the casing.

Preferably three supplementary fins are provided projecting radially from the casing in line with the said fins, spaced upwardly from the said fins.

Preferably the said fins converge upwards.

Preferably a sacrificial cap is fitted over the end of the finned casing during its downward movement and remains down the hole on retraction of the finned casing so that cementitious poured through the finned casing can pass its end.

In the second embodiment, the finned casing may be formed of a central and an outer tube. The finned casing preferably comprises a leading end region in which the central and outer tubes may taper outwardly from the leading end of the finned casing. A central region of the finned casing may extend rearwardly from the leading end region and in which the outer tube may taper outwardly from the said leading end region of the finned casing. The finned casing may also comprise a rear end region extending rearwardly of said central region.

Preferably, the outer tube is of a constant cross-section along said rear end region. The central tube may extend rearwardly of the rear end region and may be of constant cross-section, preferably along substantially its length to the leading end region. The central tube may taper inwardly at said leading end region.

A plurality of radially extending ribs may extend from the central tube to the outer tube. The diametrically opposed fins on the finned casing may constitute extension of a pair of said ribs.

The outer tube of the finned casing may be octagonal, hexagonal or circular in configuration.

In this embodiment the aperture forming the guide means in top casing, may be so configured as to conform to the shape of the outer skin of the finned casing.

Preferably, the top casing is provided with a pair of passages arranged to correspond with a pair of apertures on the finned casing. A pair of pins may be provided for insertion through said passages and apertures, when said apertures are in register with said passages, to secure the finned casing to the top casing.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figs. la to lg illustrate various stages of a pile forming operation of a first embodiment; Figs. 2a,b and c show respectively end elevations, top and bottom plan views of a top casing of the first embodiment; Figs. 3a and b show respectively front and side elevations of a finned casing of the first embodiment, Figs. 3c and d show views of the finned casing of the first embodiment from below and above respectively, Fig. 3e shows a longitudinal cross-section of the tip of the finned casing of the first embodiment with the fins removed.

Figs. 4a to 49 illustrate various stages of a pile forming operation of a second embodiment, Fig. 5 is a sectional side elevation of a finned casing of a second embodiment, Fig. 6 is a view along the lines VI-VI of Fig. 5, Fig. 7 is a sectional side view of an alternative pile casing to that shown in Fig. 5, Fig. 8 is a view along the lines VIII-VIII of Fig.

7, Fig. 9 is a view along the lines IX-IX of Fig. 7, Fig. 10 is a top plan view of a top casing of the second embodiment, and Fig. 11 is a part sectional view of the top casing shown in Fig. 10.

Fig. la shows the first stage of a first embodiment the process of forming a pile involving a mainly soil displacement method where the pile former is driven into the ground and as the pile former is removed a concrete pile is formed behind it by pumping concrete into the void left by the retreating casing.

The first step of the operation involves, from ground level 10 and utilising a conical rotated auger 12, forming a downwardly converging recess 14.

An assembly comprising a finned pile casing 16 carrying at its lower end a downwardly converging frusto-conical top casing 18 is then presented to the recess 14 with the top casing 18 temporarily fixed to the lower end of the finned casing 16 which, at its upper end, is attached to vibratory pile driving rig (not shown). The top casing 18 is vibrated into the augered recess 14 until the top of the casing 18 is at or near ground level 10 at which stage a locking mechanism attaching finned casing 16 to the top casing 18 is released and the finned casing 16 continues in a downward direction through and guided by the top casing 18 to form a pile hole below the top casing 18 by displacing soil, the pile hole having a cross-section corresponding to the cross-section of the leading end of the finned casing 16, details of which will be given below.This preliminary pile hole-forming step is illustrated in Fig. 1c and Fig.

1d shows that the pile hole forming step is continued until the desired depth is achieved by the finned casing 16.

As shown in Fig. 1e, the finned casing is then withdrawn from the hole leaving behind it an end cap 20 thereby unblocking the end of the cylindrical tube 22 forming the finned casing and allowing cementitious material to be pumped from the top of the tube 22 through the finned casing to fill the void in the ground left behind the retreating finned casing, the void having a cross-section which corresponds to the cross-section of the leading end of the finned casing.Fig. 1 shows that retraction continues until the leading end of the finned casing enters the top casing 18 where, once again, the top casing 18 is attached the finned casing and the assembly of finned and top casing 16,18 is removed from the hole which is then topped up with concrete material to provide a finned pile having a top, the diameter of which is greater than the maximum diameter of the finned pile so that it can readily accept, for example, a stanchion of a steel framed building structure to be erected on the pile and the plurality of neighbouring piles formed by a similar technique. Reinforcement can be placed in the pile hole and recess before the concrete therein sets.

Figs. 2a to 2c show that the top casing 18 comprises a frusto-conical steel skin 22 having a top plate 24 across its top and a bottom plate 26 across its base. An aperture 28, having a cross-section corr-esponding to the leading end of the finned casing 16, is provided at the top plate 24 and the base plate 26 has a similar aperture 30 aligned with the top plate aperture 28. Steel sheets 34 deformed to correspond to the periphery of the aperature 28, 30 extend between the top and bottom plates 24,26 to define a passage 36 through the top casing 18 by which the finned casing can be guided through the top casing. Means (not shown in Fig. 2) are provided for locking the top casing 18 to the bottom of the finned casing which is illustrated in Figs.

3a to 3e.

Fig. 3a shows an end elevation of the end portion of the finned casing which can be seen to comprise a tubular steel member 22 provided at its lower end with three equispaced, radially extending steel fins 40. A plate 42 (Fig. 3c) is welded to the end of the tube 22 and has transverse dimensions greater than the thicknesses of the fins 40 and the diameter of the tube 22 respectively. A circular opening 44 is provided through the end plate 42 and this opening can be closed off by the sacrificial end cap 20 (Fig.1).

The three supplementary fins 46 are fixed to the tube 22 above the fins 40 in corresponding positions to the fins 40. They are of dimensions smaller than the fins 40.

It will be realised, therefore, that as the finned casing is vibrating downwardly into the ground, the plate 42 forms a three finned, star-shaped hole having a substantially circular central region. As the finned casings descent continues the fins 40 and 46 keep the three relatively thin grooves formed in the ground by the end plate 42 open and the central region is similarly kept open by the descending tube 22. The fins and plate form the same function as the finned casing is withdrawn and any debris falling from the sides of the hole tend to be drawn up on the upper face of the plate 42 thereby keeping the star shaped hole open as it is filled by concrete which is pumped into the top of the tube 22 by suitable pumping machinery and descends down through the tube and out of the aperture 34 to fill the void in the ground left by the ascending finned casing.

Various modifications can be made without departing from the scope of the invention, for example, only two fins can be provided or, alternatively, four fins can be provided but it has been found from experimentation that three fins is the most preferable configuration as this leaves behind a hole corresponding to the cross-section of the finned casing at its lower end and does not tend to separate and remove soil between the fins.

In a further modification the pile can be hammered into the ground but this is less desirable. The top casing can be designed to have differing depths depending upon circumstances of use, and, of course, if a deep pile cap is not required then the casing need not descend fully into the aperture 14 formed by augering but only partly into the relatively shallow aperture. It is important, however, that the casing is located in the ground as it forms a guide for the descending finned casing.

Figs. 4a to 49, and 5 to 11 show a second embodiment of the invention. Referring to Figs. 5 to 9, there is shown a finned casing 110. The finned casing 110 comprises a leading end region 112, a central region 114 extending rearwardly from the leading end region 112, and a rear end region 116 extending rearwardly from the central region 114. The finned casing 110 comprises an outer tube 118 of a hexagonal cross-section, but it will be appreciated that the outer tube 118 can be of any other appropriate cross-sectional profile, for example octagonal or circular. The outer tube 118 has a constant cross-sectional area along the rear end region 116.

The outer tube 118 tapers inwardly along the central region 114 from the rear end region 116 to the leading end region 112, as shown in Fig. 5. The outer tube 118 further tapers inwardly along the leading end region 112. Extending co-axially inside the outer tube 118 there is a central tube 120. The central tube 120 (as shown in Fig. 7) is of constant cross-section along the rear and central regions of the finned casing, and tapers inwardly, as shown in Fig. 7 along the leading end region 112. The central tube 120 extends rearwardly from the rear end region of the finned casing.

A pair of diametrically opposed fins, 122,124 extend radially outwardly from the central tube 120 in the central region 114. The fins 122,124 extend outwardly from the central tube 120 through the outer tube 118 in the central section 114, as shown in Fig. 5.

The outside edges of the fins 122,124 are substantially coterminous with the outside edge of the rear region 116.

The fins 122,124 are provided at their leading edges, 122a,124a with apertures 126,128 to enable the finned casing 110 to be attached to a top casing, as will be described below.

A plurality of ribs 130 extend outwardly from the central tube 120 to the outer tube 118 at the apices of the outer tube 118. It will be appreciated that the fins 122,124 constitute extensions of the diametrically opposed ribs 130 externally of the outer tube 118 in the central region.

Referring to Figs. 10 and 11, there is shown a top casing 150 which is similar to the top casing 18, having a frusto-conical shape and top and bottom plates 152,154.

An aperture 156 is provided in the top plate 152 which is of a corresponding shape and size to the shape and size of the rear region 116 of the finned casing 110. The bottom plate 154 defines a bottom aperture 158 which is of the same size and shape as the top aperture 156.

Steel sheets 160 are arranged between the top and bottom apertures to define a passage of the same size and shape as the rear region 116 of the outer tube 118 of the finned casing 110 to allow the finned casing 110 to pass therethrough.

The steel sheets 160 extend above the steel plate 152 to define said top aperture 156. A pair of guides, 162,164 extend on opposite sides of the aperture 156.

The guide 162 defines passages 166 in an adjacent pair of steel sheets 160. Similarly, the guide 164 defines passages 168 in the opposite pair of steel sheets 160.

The guides 162,164 and the passages 166,168 are so shaped and configured to receive pins, one of which is shown at 170 to secure the leading ends 122a,124a of the fins 122,124 to the top casing 150 by insertion through the passages 166,168 and the apertures 126,128.

The method by which the pile casing 110 is driven into the ground is shown in Figs. 4a to 49. Referring to Fig. 4a, an auger 210 is first used to drill from ground level 10 a downwardly converging recess 212. An assembly comprising the finned casing 110, and the top casing 150 is then presented to the recess 212, and the top casing 150 is vibrated into the augered recess 210 until it reaches the position as shown in Fig. 4b. The finned casing 110 is attached to the top casing 150 by pins 170 as described above. The pins 170 are then removed, as shown in Fig. 4c to enable the finned casing 110 to be driven downwardly through the bottom aperture 158 into the ground. Fig. 4d shows the finned casing 110 after it has been driven part way into the ground. Fig. 4e shows the finned casing after it has been driven fully into the ground to the desired depth.A cementitious material is then pumped or gravity fed via the central tube 120 and out of the aperture 121 at the end, as shown by the arrows A. As the cementitious material is pumped into the central tube 120, the finned casing 110 is withdrawn from the void created thereby, as shown in Fig. 4f. The cementitious material 214 fills the void in the ground left behind the retreating finned casing 112. The void has a cross-section which corresponds to the cross-section of the leading end of the finned casing.

Withdrawal of the finned casing 110 continues until the apertures 126, 128 are aligned with the guides 162,164 and their corresponding passages 166,168. At this position, the pins 170 can be inserted back through the apertures 124,126 in the end region of the fins 122,124 via the passages 166,168 to secure the finned casing 110 to the top casing 150. This allows the top casing 150 to be withdrawn from the recess 212 on further withdrawal of the finned casing 110.

Fig. 49 shows the pile remaining after the finned casing 110 and the top casing 150 have been removed.

Claims

Claims:

1. A method of forming a pile comprising forming from ground level a recess placing a top casing in the recess corresponding to the shape thereof, placing a pile former comprising a finned casing with fins projecting radially therefrom in the top casing, driving the finned casing through the base of the top casing to a pre-determined depth, thereafter removing the finned casing from the hole it has formed in the ground while filling the void behind the retreating finned casing with a cementitious material and removing the top casing and finned casing from the hole.

2. A method as claimed in claim 1, in which the top casing is removably fixed to the bottom region of the finned casing and is positioned in the pre-formed recess by downward movement of the finned casing.

3. A method as claimed in claim 2, in which, the downward movement is a vibratory movement.

4. A method as claimed in any of claim 1 to 3, in which the recess is formed as a downwardly converging recess.

5. A method as claimed in any one of the preceding claims, in which after the top casing has been placed its fixing to the finned casing is removed prior to the finned casing forming the pile hole.

6. A method as claimed in any one of the preceding claims, in which after forming the pile hole and on removal from the pile hole, the finned casing is re-fixed to the top casing to remove it from the top hole as the recess is being filled with concrete.

7. A method as claimed in any one of the preceding claims, in which the top casing guides the finned casing as it forms the pile hole.

8. A method as claimed in any one of the preceding claims, in which the finned casing is passed through guide means in the form of a plate having an aperture therethrough corresponding to the cross-section of the finned casing at its fins provided at at least base of the top casing.

9. A method as claimed in claim 8, in which the finned casing is passed through on additional guide plate provided at the top of the top casing.

10. Pile forming apparatus comprising a top casing for fitment in a recess formed in the ground above where a pile is to be formed, a pile former comprising a casing with fins projecting radially therefrom projecting through the casing, means for driving the casing into the ground to a predetermined depth, means for removing the finned and top casing and for filling the hole left behind the casings as they are removed with a cementitious material.

11. Apparatus as claimed in claim 10, including means for fixing the top casing to the end of the finned casing while the assembly of casings is forced into the ground to form the said recess.

12. Apparatus as claimed in claim 10 or claim 11, in which the means for driving the finned casing into the ground is a vibrator.

13. Apparatus as claimed in any one of claims 10 to 12, in which the top casing converges downwardly.

14. Apparatus as claimed in any one of claims 10 to 13, in which guide means in the form of a plate having an aperture therethrough corresponding to the cross-section of the finned casing at its fins is provided at at least the base of the casing.

15. Apparatus as claimed in claim 14, in which an additional guide plate is formed at the top of the casing.

16. Apparatus as claimed in any one of claims 10 to 15 in which the leading end of the finned casing has a front plate whose dimensions are greater than the dimensions of at least the fins.

17. Apparatus as claimed in any one of claims 10 to 16, in which the finned casing has parallel sides.

18. Apparatus as claimed in any one of claims 10 to 15, in which the finned casing converges downwardly.

19. Apparatus as claimed in any one of claims 10 to 16, in which the finned casing has three fins.

20. Apparatus as claimed in claim 18, in which the finned casing has two fins which are diametrically opposed on the casing.

21. Apparatus as claimed in claim 19, in which three supplementary fins are provided projecting radially from the casing in line with the said fins, spaced upwardly from the said fins.

22. Apparatus as claimed in any one of claims 10 to 21, in which the said fins converge upwards.

23. Apparatus as claimed in any one of claims 10 to 22, in which a sacrificial cap is fitted over the end of the finned casing during its downward movement and remains down the hole on retraction of the finned casing so that cementitious material poured through the finned casing can pass its end.

24. Apparatus as claimed in any one of claims, lib,20, 22 and 23 when dependent upon claim 18 and 20, in which the finned casing is formed of a central and an outer tube.

25. Apparatus as claimed in claim 24, in which the finned casing comprises a leading end region in which the central and outer tubes may taper outwardly from the leading end of the finned casing.

26. Apparatus as claimed in claim 24 or claim 25, in which a central region of the finned casing extends rearwardly from the leading end region and in which the outer tube may taper outwardly from the said leading end region of the finned casing.

27. Apparatus as claimed in claim 26, in which the finned casing comprises a rear end region extending rearwardly of said central region, the outer tube being of a constant cross-section along said rear end region.

28. Apparatus as claimed in claim 26 or claim 27, in which the central tube extends rearwardly of the rear end region and is of constant cross-section along its length to the leading end region.

29. Apparatus as claimed in claim 26 or claim 27, in which the central tube tapers inwardly at said leading end region.

30. Apparatus as claimed in any one of claims 24 to 29, in which a plurality of radially extending ribs extend from the central tube to the outer tube.

31. Apparatus as claimed in claim 30, in which the diametrically opposed fins on the finned casing constitute extensions of a pair of said ribs.

32. Apparatus as claimed in any one of claims 24 to 31 , in which the outer tube of the finned casing is octagonal, hexangonal or circular in configuration.

33. Apparatus as claimed in claim 32, in which the aperture forming the guide means in the top casing is configured to conform to the shape of the outer skin of the finned casing.

34. Apparatus as claimed in any one of claims 10 to 33, in which the top casing is provided with a pair of passages arranged to correspond with a pair of apertures on the finned casing.

35. Apparatus as claimed in claim 34, in which a pair of pins are provided for insertion through said passages and apertures, when said apertures are in register with said passages, to secure the finned casing to the top casing.

36. A method substantially as hereinbefore described with reference to Figs. 1 to 3, 10 and 11, or Figs. 4 to 6 or Figs. 7 to 9 of the accompanying drawings.

37. Apparatus substantially as hereinbefore described with reference to Figs. 1 to 3, Figs, 4 to 6, Figs. 7 to 9 and Figs. 10 and 11 of the accompanying drawings.

38. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.