GB2218722A

GB2218722A - Pile pressing

Info

Publication number: GB2218722A
Application number: GB8811877A
Authority: GB
Inventors: Basil Green
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-05-19
Filing date: 1988-05-19
Publication date: 1989-11-22
Also published as: GB8811877D0

Abstract

A piling system uses a piling tube 10, a shoe 12 and a mandrel 14, which enables a piling machine to apply forces Fm and Ft alternately to the mandrel and the piling tube to work against the end resistance Fe on the shoe 12 and the frictional side resistances Ff on the piling tube 10 substantially independently of each other. <IMAGE>

Description

PILE PRESSING This invention relates to pile pressing.

Background of the Invention Pile driving or pressing involves the forcing of a member into the ground for use in support of, for example, a building, roadway or other structure. In order to force the pile member into the ground, it is necessary to overcome the end resistance applied by the ground at the lower end of the member, and also to overcome the frictional resistance applied by the ground along the length of the member. The end resistance arises due to the necessity to displace the ground generally sideways to make room for the member, and the frictional resistance along the member arises due to any existing compressive forces in the ground and further the compressive forces created due to displacement of the ground to make way for the pile member.

One conventional way of forcing a pile into the ground involves driving it with a hammering action. Hammer driving a pile is inefficient, and typically only about 60% of the applied energy is effectively employed. The remaining energy is dissipated as ground shock waves or vibration, pile vibration, hammer vibration and temporary compressions, and in causing physical damage to the pile. Furthermore, it is not immediately apparent when the lower end of the pile encounters difficult conditions, such as boulders, and thus the pile may be unduly driven and damaged due to overstressing. A further problem with hammered piles, is that the load-bearing capacity of the pile cannot be directly established from the hammering action used to drive the pile, and therefore large factors of safety need to be employed, often resulting in unnecessary lengths of pile being driven.

Many of the problems of hammer driven piling have been overcome by the jacked piling method. In the jacked piling method, the pile member is pressed into the ground, for example using a hydraulic piling machine.

This method is substantially silent, and vibrationless and is far more energy efficient than the hammer driven method. Furthermore, the resistance to penetration of the pile can be determined far more accurately and simply, and it is thus unnecessary to adopt such high factors of safety as with hammered piling. However, since jacked piling relies upon the application of a steady force, rather than hammer blows, it is necessary to use a heavy piling machine, or to anchor the piling machine to the ground, in order to provide sufficient pressing force to the pile. Obviously, as the weight of the piling machine is increased, the machine becomes more expensive and is more difficult to transport from one site to another and move around the construction site.

Summary of the Invention The problem with which the present invention is concerned is how to increase the placing capacity of a pile jacking machine and reduce costs.

In accordance with one aspect of the present invention there is provided a pile pressing system which enables a piling machine to work against the end resistance on a pile assembly and the frictional side resistance along the pile assembly substantially independently of each other. Thus, in an example case where the end resistance and frictional side resistance are equal, by working against the end resistance and the frictional side resistance alternately, it is possible to press the pile assembly with half of the force required in a conventional system where end resistance and frictional side resistances have to be overcome simultaneously. In addition, during the pressing operation, the end resistance and frictional side resistances can be measured independently and simply while pressing is in progress.

If an obstruction is encountered, then it will be immediately apparent from a rise in the end resistance and remedial action can be taken before any damage is caused. By adopting the system of this invention, the pile member can be of lighter construction compared with those used in hammer driven piling systems.

In accordance with a further aspect of the present invention, there is provided a piling assembly comprising a shoe having a sole portion for penetrating the ground, a piling tube adapted to mate telescopically with the shoe, and a mandrel extending through the piling tube and resting on the shoe for pressing the shoe into the ground. Thus, the shoe can be advanced downwardly by pressing on the mandrel to overcome end resistance. Then, the piling tube can be pressed downwardly, whilst the shoe remains stationary, against only the frictional side resistance along the piling tube.

In accordance with another aspect of the invention, there is provided a method of placing a pile in the ground, comprising the steps of pressing a shoe into the ground to form a passageway, pressing a piling tube into the passageway, inserting a mandrel through the piling tube into contact with the shoe, and repeating the steps of pressing the shoe further into the ground through the agency of the mandrel, and pressing the piling tube further into the ground.

There follows a description by way of example of specific embodiments of the present invention, reference being made to the accompanying drawings.

Brief Desciption of Drawings Figures 1A to 1C schematically show the various stages in the pressing of a pile assembly.

Figures 2A and 2B show completed piles.

Figures 3A to 3D show different stages in a pile pressing method.

Figures 4A to 4D show various stages in a further pile pressing method.

Figure 4E shows the complete piles.

Figure 4F is a cross-sectional view taken along the line 4F-4F in Figure 4C.

Figures 5 and 6 show alternative forms of shoe for the piling assembly.

Specific Description of the Embodiments Referring to Figure lA, a pile assembly comprises a cylindrical piling tube 10, a shoe 12 and a mandrel 14. As shown in Figure 1A, the piling tube 10 has been jacked part way into the ground 16. The shoe 12 has a lower portion 18 of approximately the same diameter as that of the piling tube 10, and an upstanding spigot 20, which projects into the lower end of the piling tube 10 and can slide relative thereto. The mandrel 14 is a sliding fit in the piling tube 10 and is longer than the piling tube 10.

In order to press the piling assembly further into the ground, a force Fm is applied to the upper end of the mandrel 14, as shown in Figure 1B. The applied force Fm (and the weight Wm of the mandrel 14) are reacted mainly by the end resistance Fe on the bottom surface of the shoe 12, although there will also be a small frictional resistance on the sides of the shoe exposed to the ground. Once the shoe has been advanced downwardly by a required distance h, the force Fm is removed. Then, as shown in Figure 1C a downward force Ft is applied to the upper end of the piling tube 10.

This force Fp (together with the weight of the piling tube 10) is resisted mainly by the frictional forces Ff arising along the piling tube 10 due to the compressive forces Fc of the ground on the piling tube 10. There may of course be a relatively much smaller end resistance against the narrow lower edge of the piling tube 10. Once the piling tube 10 has been pressed down through the distance h so that the lower end of the piling tube contacts or is closely adjacent the shoulder 24 formed around the spigot on the shoe 12, the pressing force Ft is removed from the piling tube.

It will be appreciated from the above that the piling tube 10 and shoe 12 together can resist a total force applied to the piling tube of Fm + Ft, and yet in order to press the pile, the piling tube has been required to apply a pressing force of whichever is the greater Fm and Ft, rather than the total of the forces Fm + Ft.

The steps of applying a force Fm to the mandrel to advance the shoe 12 and then applying a force Ft to the piling tube to advance the tube are repeated until the tube 10 and shoe 12 have been sunk into the ground to enable a desired resistance to be obtained. The mandrel 14 is then removed, any excess piling tube projecting above the ground is cut. off, and the remaining piling tube 10 is filled with concrete to provide a core 26 as shown in Figure 2A, or is sealed with a steel plate 27 as shown in Figure 2B.

Referring to Figures 3A to 3D, there is shown an example of how a piling machine may be used to press the piling tube and mandrel into the ground.

Referring specifically to Figure 3A, firstly two screw threaded anchors are screwed into the ground. Then, referring specifically to Figure 3B, a piling machine 30 having a hydraulic jack 32 is suspended above the anchors 28 and is attached to each anchor by a tether 34. An assembly of piling tube 10, mandrel 14 and shoe 12 is disposed beneath the hydraulic jack 32.

The piston 36 of the hydraulic jack 32 has a diameter which is less than the internal diameter of the piling tube 10, so that the piston can be advanced inside the tube 10 to press the mandrel 14. However, a cap 38 is also provided, which has a diameter at least as great as the external diameter of the piling tube 10, so that with the cap 38 placed between the piston 36 and the piling tube 10, the piston can be used to press the piling tube 10 alone, or the piling tube 10 and the mandrel 14 together.

Initially, the piling tube 10 and mandrel 14 are pressed together until the force applied by the piston 36 is slightly less than the total uplift resistance of the two anchors 28, combined with the weight of the piling machine.

The example described so far may be performed in stages, with the piston 36 being retracted and the tethers 34 being adjusted between the stages.

As an example, the uplift resistance of each anchor 28 may be 50 tons, the weight of the piling machine 30 may be 10 tons, and the piling tube 10, shoe 12 and mandrel 14 may be pressed into the ground with a force approaching 110 tons fi.e. (2x50) +10.-).

Figure 3B shows the arrangement after the piling tube 10, shoe 12 and mandrel 14 have been pressed a substantial distance into the ground. Once no further advance can be made by the method described above, then the cap 38 is removed, and the piston 36 is used to press the shoe 12, via the mandrel 14, into the ground. Therefore, the hydraulic jack 32 needs to work against only the end resistance applied against the shoe 12. Once the shoe 12 and mandrel 14 have been advanced a distance slightly shorter than the range of telescopic movement between the shoe 12 and the piling tube 10, the piston 36 is retracted and the cap 38 is replaced. As shown in Figure 3D, the piston 36 can then be used to press solely the piling tube 10 through the same distance by which the mandrel 14 and shoe 12 were pressed in the previous stage.

During the present stage, the hydraulic jack 32 has to work solely against the frictional side resistance along the length of the piling tube.

The last two stages are repeated, firstly pressing the mandrel 14 and shoe 12 against the end resistance, and then pressing the piling tube 10 against the frictional side resistances, until either the total of the end resistance and the frictional side resistance is equal to a desired value, or until it is not possible to apply sufficient force to advance the piling tube 10, or the mandrel 14 and shoe 12 any further. It will be noted, however, that the piling tube 10 and the mandrel 14/shoe 12 can each be independently pressed with a force equal to the weight of the piling machine 30 and the total uplift of the anchors 28. Therefore, with the example figures given above, the piling tube 10 alone maybe pressed with a force of up to 110 tons, and the mandrel 14/shoe 12 may also be pressed with a force of up to 110 tons.

Once the piling tube has been sunk to the required resistance, the piling machine 30 is removed, the mandrel 14 is extracted, any excess material is cut away from the top of the piling tube 10, and the tube is filled with concrete or sealed with a steel plate.

Both of the screw anchors 28 may be removed, or alternatively only one may be removed, and the remaining anchor may be used in the pressing operation for the next pile.

Referring to Figures 4A to 4F, there is shown a modified method of pressing piles. Referring specifically to Figure 4A, two steel sections 40, 42 are pressed by a piling machine into the ground to the position shown in Figure 4B. As an example, in the case of a piling machine and kentledge weighing 20 tons, each of the sections 40, 42 may be pressed to provide a frictional resistance of, say, 18 tons.

Referring to Figure 4C, the piling machine is then clamped to the sections 40, 42, and a piling assembly 44 similar to that shown in Figures 1A to 1C is pressed by the piling machine into the ground. The maximum force against which the piling tube or the mandrel/shoe of the piling assembly 44 may be pressed is equal to the combined frictional resistances of the sections 40, 42 and the weight of the piling machine and kentledge, that is 56 tons. The piling machine is then clamped to the piling tube of the assembly 44, and firstly section 40, and then section 42 are pressed further into the ground against the frictional resistance along the piling tube and the weight of the machine and kentledge. Assuming that the frictional resistance against the piling tube is 56 tons, then the sections 40, 42 can each be pressed against a frictional resistance of 76 tons.The piling machine is then clamped to the sections 40, 42, and the piling tube and the the mandrel/shoe are alternately and repeatedly pressed against a resistance of 76 + 76 + 20 = 172 tons. Thus, a maximum frictional size resistance or a maximum end bearing resistance of 172 tons can be achieved. The mandrel is then withdrawn from the piling assembly 44. Figure 4F is a cross-sectional view along the section line 4F - 4F shown in Figure 4C showing the tube 10 of the piling assembly and the sections 40, 42, which are both T-shaped in cross-section.

Referring to Figure 4D, the piling machine is then clamped to the sections 40, 42 and the piling tube 10 which has already been pressed, and a further piling assembly 46 is pressed into the ground, alternately pressing the piling tube and the mandrel/shoe of the assembly 46 until the total resistance for the assembly 46 reaches a required value, or no further penetration is possible. A further piling assemblies 47 may then be pressed into the ground, with the piling machine clamped to the piling tube and sections 40, 42 or to one of the other piling tubes which has been pressed into the ground. The sections 40, 42 are then removed, all of the mandrels are removed, excess material on the piling tubes is cut away, and concrete cores are formed in the piling tubes, as shown in Figure 4E.

As shown in Figures 1A to 1C and Figure 2, the shoe 12 may be formed from concrete having a spigot 20 which projects into the lower end of the piling tube 10. As an alternative, and as shown in Figure 5, the shoe may be formed from steel having a circular sole plate having a diameter at least as great as the external diameter of the piling tube 10, with a cylindrical spigot 50, which is welded to the sole plate 48 and is of slightly smaller diameter than the internal diamter of the piling tube 10. A further alternative shoe, as shown in Figures 3B to 3D and figure 6 has a circular sole plate 52 and a tubular portion 54 which is welded to the periphery of the sole plate and which has an internal diameter slight larger than the external diamter of the piling tube 10 so that the tubular portion fits around the lower end of the piling tube 10. Whilst the shoes shown in the drawings having flat sole plates, they, of course, be formed with domed or conical soles, if desired.

In the arrangements described above, the piling tubes and mandrels for each pile are not necessarily each formed from a single length of material. For example, the mandrel may be formed from sections, and further sections are added to the mandrel as pressing progresses. Similarly, the piling tube may be formed from sections. In the case of steel piling tubes, as each new section is added it is welded to the preceding sections. If concrete pile tube sections are used, they may be provided with annular steel ends, by which the sections may be welded together.

Claims

1. A pile pressing system which enables a piling machine to work against the end resistance on a pile assembly and the frictional side resistance along the pile assembly substantially independently of each other.

2. A piling assembly comprising a shoe having a sole suitable for penetrating the ground, a piling tube suitable for forming a pile casing and having one end adapted to mate telescopically with the shoe, and a mandrel capable of extending through the piling tube and engaging the shoe to transfer to the shoe a driving force exerted on the mandrel at the other end of the piling tube.

3. A piling assembly comprising the shoe having a sole portion for penetrating the ground, a piling tube end which mates telescopically with the shoe, and a mandrel extending through the piling tube and resting on the shoe for pressing the shoe into the ground.

4. An assembly as claimed in claim 3, wherein the shoe has a spigot which is a sliding fit inside the lower portion of the piling tube and a shoulder formed around the spigot for engaging the lower end of the piling tube.

5. An assembly as claimed in claim 3 or 4, wherein the shoe has a tubular portion which engages around the lower end of the piling tube, so that the shoe caps the lower end of the piling tube.

6. An assembly as claimed in any of claims 3 to 5, wherein the piling tube is formed from sections which are joined end-to-end.

7. An assembly as claimed in any of claims 3 to 6, wherein the mandrel is formed from sections which are joined end-to-end.

8. An assembly as claimed in any of claims 3 to 7 in combination with a piling machine having means to press the piling tube and the mandrel independently.

9. A combination as claimed in claim 8, wherein the piling machine includes a drive piston of a size such that the piston can be inserted into the upper end of the piling tube to press the mandrel, and a cap member for capping the upper end of the piling tube so that the piston can press the piling tube.

10. A combination as claimed in-claim 8 or 9, further comprising means for anchoring the piling machine to the ground.

11. A method of placing a pile in the ground, comprising the steps of pressing a shoe into the ground to form a passageway, pressing a piling tube into the passageway, inserting a mandrel through the piling tube into contact with the shoe, and repeating the steps of pressing the shoe further into the ground through the agency of the mandrel, and pressing the piling tube further into the ground.

12. A method as claimed in claim 11, wherein a piling machine is used for pressing the tube and the mandrel, and further comprising the step of pressing a further member into the ground, and anchoring the piling machine to the further member.

13. A method as claimed in claim 11 or 12, wherein a piling machine is used for pressing the piling tube and the mandrel, and further comprising the steps, after pressing the piling tube into the ground, of anchoring the piling machine to the piling tube and placing a further pile in the ground by the method of claim 11 or 12.

14. A piling method substantially as described with reference to the drawings.

14. A method as claimed in any of claims 11 to 13, and including the further steps of adding piling tube sections to the piling tube and adding mandrel sections to the mandrel to increase the lengths thereof.

15. A method according to any of claims 11 to 14, and further comprising the step of monitoring the forces required to press the piling tube and required to press the shoe/mandrel, independently of each other.

16. A piling system substantially as described with reference to the drawings.

17. A piling method substantially as described with reference to the drawings.

Amendments to the claims have been filed as follows 1. A pile pressing assembly, comprising: a shoe having a sole suitable for penetrating the ground; a piling tube suitable for forming a pile casing and having a lower end which mates telescopically with the shoe; a mandrel extending through the piling tube and having a lower end engaging the shoe to transfer thereto a driving force exerted on the upper end of the mandrel; and an hydraulic piling machine operable to exert an hydraulically produced downward pressing force alternatingly on the mandrel and on the piling tube so that the shoe and piling tube are alternatingly pressed into the ground.

2. An assembly as claimed in claim 1, wherein the shoe has a spigot which is a sliding fit inside the lower portion of the piling tube and a shoulder formed around the spigot for engaging the lower end of the piling tube.

3. An assembly as claimed in claim 1 or 2, wherein the shoe has a tubular portion which engages around the lower end of the piling tube, so that the shoe caps the lower end of the piling tube.

4. An assembly as claimed in any preceding claim, wherein the piling tube is formed from sections which are joined end-to-end.

5. An assembly as claimed in any preceding claim, wherein the mandrel is formed from sections which are joined end-to-end.

6. An assembly as claimed in any preceding claim, wherein the piling machine includes a drive piston of a size such that the piston can be inserted into the upper end of the piling tube to press the mandrel, and a cap member for capping the upper end of the piling tube so that the piston can press the piling tube.

7. An assembly as claimed in any preceding claim, comprising means for anchoring the piling machine to the ground.

8. A method of placing a pile in the ground, comprising the steps of pressing a shoe into the ground to form a passageway, pressing a piling tube into the passageway, inserting a mandrel through the piling tube into contact with the shoe, and repeating the steps of hydraulically pressing the shoe further into the ground through the agency of the mandrel, and hydraulically pressing the piling tube further into the ground.

9. A method as claimed in claim 8, wherein an hydraulic piling machine is used for pressing the tube and the mandrel, and further comprising the step of pressing a further member into the ground, and anchoring the piling machine to the further member.

10. A method as claimed in claim 8 or 9, wherein a piling machine is used for pressing the piling tube and the mandrel, and further comprising the steps, after pressing the piling tube into the ground, of anchoring the piling machine to the piling tube and placing a further pile in the ground by the method of claim 8 or 9.

11. A method as clainied.in any of claims 8 to 10, and including the further steps of adding piling tube sections to the piling tube and adding mandrel sections to the mandrel to increase the lengths thereof.

12. A method according to any of claims 8 to 11, and further comprising the step of monitoring the forces required to press the piling tube and required to press the shoe/mandrel, independently of each other.

13. A pile pressing assembly substantially as described with reference to the drawings.