GB2248082A

GB2248082A - Pile driving

Info

Publication number: GB2248082A
Application number: GB9024708A
Authority: GB
Inventors: Sin Seng Kong; Say Kiat Ong
Original assignee: CONCILINK
Current assignee: CONCILINK
Priority date: 1990-09-18
Filing date: 1990-11-14
Publication date: 1992-03-25
Anticipated expiration: 2010-11-14
Also published as: GB2248082B; GB9024708D0

Abstract

A method of and apparatus for placing piles in the ground, in which a hollow sleeve (22) is forced into the ground. under the action of a substantially continuous force to form a shaft, the sleeve (22) is withdrawn from the ground and material for forming a pile is introduced into the shaft before, during or after the removal of the sleeve (22) from the ground. The end of the sleeve (22) which is forced into the ground may be open or may be capped by a pile shoe. if the end is open, soil which enters the sleeve (22) as it penetrates the ground is retained in the sleeve (22). The sleeve (22) is then withdrawn at intervals to remove the soil. <IMAGE>

Description

PILE DRIVING This invention relates to a method of and apparatus for placing piles in the ground.

Conventionally, two main piling methods are used.

In one method, precast or preformed piles are driven into the ground by the action of a hammer striking the upper end of the pile.

In a second method a shaft is excavated by means of drilling or augering and then concrete is backfilled into the shaft as the drill bit or auger is withdrawn from the shaft.

These known piling methods are adequate for placing large diameter piles. However, where micropiles or smaller diameter piles (i.e. piles with a working bearing capacity of under approximately 20 tonnes) are required, the excavation piling system proves slow and expensive.

Where the ground to be piled is very hard the driven pile method simply cannot be used beyond a certain depth using conventional precast piles, since the resistance to the downward progression of the pile is such that the pile starts to disintegrate under the action of the pile driving hammer. The speed of piling is also severely reduced.

According to a first aspect of the present invention there is provided a method of placing piles in the ground characterized in that a hollow sleeve is forced into the ground under the action of a substantially continuous force to form a shaft, the sleeve is withdrawn from the ground and material for forming a pile is introduced into the shaft before, during or after the removal of the sleeve from the ground.

According to a second aspect of the present invention there is provided apparatus for placing piles in the ground characterized in that an actuator is provided, which propels a hollow sleeve into the ground with a substantially continuous force to form a shaft for a pile, the direction of force applied by the actuator being reversible so that the hollow sleeve can be extracted from the shaft.

Using the method according to the present invention piles can be placed quickly and reliably even in very hard ground. A further benefit of the present invention is that the bearing capacity of the pile is known accurately, since the bearing capacity will be equal to the final load applied to the hollow sleeve during the jacking process. This load may be calculated directly from the hydraulic pressure exerted by the hydraulic rams which are used to apply the jacking force tithe hollow sleeve.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a side view of-the pile placing apparatus according to the invention; Figure 2 is a plan view of the apparatus of Figure 1; Figure 3 is a detailed plan view on an enlarged scale of the shaft gripping device and hydraulic actuator of the apparatus of Figures 1 and 2; Figure 4 is a side view of the shaft gripping device and hydraulic actuator shown in Figure 3; Figure 5(a) is a section through the hollow sleeve taken on the line D-D in Figure 6(a); Figure 5(b) is a section through the hollow sleeve, in the region of the grip joint taken on the line A-A in Figure 6(b); Figure 6(a) is a view on the line C-C in Figure 5(a); Figure 6(b) is a view on the line B-B in Figure 5(b);; Figure 7 is an enlarged plan view of the shaft gripping device; Figure 8 is a section on the line A-A in Figure 7; Figure 9 is a longitudinal section through a hollow sleeve particularly for use in hard ground; Figure 10 is a longitudinal section through the end of a hollow sleeve fitted with a pile shoe; Figure ll(a) to (g) shows the major steps involved in carrying out the invention; and Figure 12 is a side view of pile placing apparatus according to a second embodiment of the invention in which two hydraulic actuators are provided to force the hollow sleeve into and out of the ground.

Referring to the drawings, Figure 1 shows a side view of one embodiment of the piling apparatus of the present invention.

The apparatus is supported on a base frame 2 which has rollers 4 resting on steel pipe rollers 6. Timber runners 8 support the steel pipe rollers 6 above the ground G.

A reaction column 10 is fixed rigidly to the base frame 2 at right angles to the ground G. The reaction column 10 supports a hydraulic actuator 12 and a sleeve gripping device 14. The hydraulic actuator 12 is fixed rigidly to the reaction column 1 by means of a bracket 16. A piston ram 18 of the hydraulic actuator 12 is mounted on a pair of shear plates 20 which are connected to a hollow sleeve 22 by means of the sleeve gripping device 14.

The hollow sleeve 22 passes through the base frame 2 into the ground G and is held substantially vertically by the reaction column 10.

A Kentledge 26 is mounted on the base frame 2 around the base of the reaction column 10.

Figure 2 shows the disposition of the pipe rollers 6 and the timber runners 8 beneath the piling apparatus.

With the hollow sleeve 22 raised out of the ground G, the apparatus may be moved into position for piling, by rotation of the pipe rollers 6 over the timber runners 8 in a first direction and by rotation of the rollers 4 along the pipe rollers 6 in a second direction, perpendicular to the first direction.

The relationship between the sleeve gripping device 14 and the hydraulic actuator 12 can be seen in more detail in Figures 3 and 4. As mentioned above, the piston ram 18 of the hydraulic actuator 12 is mounted on a pair of shear plates 20. The shear plates 20 project at right angles from a first face of a force transmission plate 28 which slides along the web 30 of the substantially I shaped reaction column 10. A second pair of parallel shear plates 32 project at right angles from the opposite face of the force transmission plate 28 through longitudinal slots 34 in the web 30 of the reaction column 10. The shaft gripping device 14 is fixed to the second shear plates 32 at right angles to the reaction column 10. Thus, movement of the piston ram 18 causes movement of the shaft gripping device 14 along the reaction column 10.

A runner 34 is fixed to the inner face of the shaft gripping device 14 (i.e. that face which is directed towards the reaction column 10). The runner 34 comprises a flat plate which abuts the web 30 of the reaction column 10. The leading and trailing ends 36 of the plate (i.e. the upper and lower ends as viewed in Figure 4) are curved away from the web 30 to facilitate smooth movement of the runner 34 up and down the reaction column 10.

Each hollow sleeve 22 is provided with circumferential recesses 38 at regular intervals along its length. Figures 5 and 6 show how these recesses 38 are provided.

The hollow sleeve 22 generally comprises a hollow, steel walled tube 40 of regular cross section anndof regular wall thickness. At a position where a recess 38 is required, the steel tube 40 is terminated and an inner, steel sleeve 42 is inserted into the open end of the steel tube 40. The outside diameter of the inner sleeve 42 is selected so that the inner sleeve 42 is a push fit into the steel tube 40. A further section of steel tube 40 is then pushed over the free end of the inner sleeve 42. The overlap of each section of steel tube 40 over the inner sleeve 42 is adjusted until a predetermined separation is provided between the ends of the steel tubes 40 in order to produce the required recess 38. The inner sleeve 42 is then welded to the steel tubes 40 through longitudinal slots 44 cut at equal intervals around the circumference of the steel tubes 40.

In the embodiment illustrated, the inner sleeve 42 is not of uniform wall thickness. In the region of the recess 38, the outside surface of the inner sleeve 42 has been milled to reduce the wall thickness locally and hence to increase the depth of the recess 38.

However, in an embodiment in which the wall thickness of the steel tubes 40 is large, no reduction of the wall thickness of the inner sleeve 42 will be necessary in order to provide a recess of sufficient depth to accommodate the sleeve gripping device 14.

Figures 7 and 8 show the sleeve gripping device 14 in detail. The device 14 comprises a pair of thick steel plates 46 provided with central circular orifices 48. Two pairs of lugs 50, which project at right angles from the plates 46, are disposed around the orifices 48, between the plates 46. Each pair of lugs 50 supports a shaft 52. Two C-shaped sleeve clamping jaws 54, 55 are slideably mounted on the shafts 52 and are biased towards each other by compression springs 56 which are retained on the shafts 52, between the lugs 50.

Steel cables 58 and 60 are connected to the centre portions of first and second clamping jaws 54, 55, respectively.

The cable 58 is attached to a second hydraulic actuator 61 via pulleys 62, 64, 66, 68 and 70. The cable 60 is attached to the second hydraulic actuator 61 via pulleys 72, 68 and 70. The disposition of the cable over the pulleys is such that as the piston ram 73 of the second hydraulic actuator 61 is withdrawn the clamping jaws 54, 55 are pulled apart so that a hollow sleeve 22 can be inserted into the orifice 48. When a recess 38 of the hollow sleeve 22 aligns with the clamping jaws 54, 55 the piston ram 73 is advanced, so releasing the tension in the cables 58 and 60 and allowing the clamping jaws 54, 55 to close around the inner sleeve 42 of the hollow sleeve 22 under the action of the compression springs 56. By varying the size and curvature of the clamping jaws 54, 55 a variety of shapes and size of hollow sleeve 22 can be accommodated in the gripping device 14.

Figures 9 and 10 show the types of hollow sleeve 22 which may be used with the present invention.

For boring into hard ground there is used a hollow sleeve 22 comprising a steel tube 40 having a curved blade 75 arranged around its open lower end. The steel tube 40 is provided with a removable liner 76 which is also open'at its lower end.

The upper end of the steel tube 40 is provided with an internal thread which receives a removable connecting adapter 78. A further steel tube 40, which is provided with an internal thread at both ends and has no curved blade 75, may be screwed onto the protruding threaded portion 80 of the connecting adapter 78 to lengthen the hollow sleeve 22. By using a series of steel tubes 40 joined by connecting adapters 78 a hollow sleeve 22 of any desired length may be produced.

For boring into soft ground, there may be used a simpler hollow sleeve 22 comprising at least one steel tube 40, the lower end of which is capped by a detachable pile shoe 82 shown in Figure 10. The hollow sleeve may be lengthened by addition of further steel tubes 40 joined by connecting adaptors 78, as before.

Figures 9(a) to 9(g) illustrate the method of placing piles according to the present invention.

9(a) - the piling apparatus is moved into position ready for piling and its orientation is adjusted so that the reaction column is substantially vertical.

9(b) - a hollow sleeve 22 is inserted into the piling apparatus and is held by the gripping device 14 as described above. The hydraulic actuator 12 is then operated so that the piston ram 18 advances to its maximum extent, driving the gipping device 14 and hollow sleeve 22 downwards into the ground.

9(c) - the clamping jaws 54, 55 of the gripping device 14 are retracted and the pistol ram 18 of the hydraulic actuator 12 is withdrawn until the gripping device 14 aligns with the next recess 38 on the hollow sleeve 22.

9(d) - steps 9(b) and 9(c) are repeated until the required penetration and/or bearing capacity is achieved. The bearing capacity may be calculated from the pressure exerted by the hydraulic actuator 12 on the hollow sleeve 22.

9(e) - steel reinforcement bars are placed into the hollow sleeve and is then liquid concrete is poured over them. Vibrators are applied to both the reinforcement and the hollow sleeve 22 itself, to ensure adequate compaction of the concrete.

9(f) - the hydraulic actuator 12 is operated so that the piston ram 18 retracts to its maximum extent, so lifting the hollow sleeve 22 out of the ground.

Steps 9(c) and 9(d) are repeated, in reverse, until the hollow sleeve is lifted out of the ground completely.

The pile shoe 82 is left at the bottom of the hole to provide a solid base for the pile.

Vibration continues as the hollow sleeve 22 is withdrawn from the hole. Vibration of the hollow sleeve 22 helps to reduce the frictional resistance to removal of the hollow sleeve 22.

9(g) - the hollow sleeve 22 is completely retracted so that the piling apparatus can move to the next piling site.

In the above method, where a 5 or 6 inch diameter concrete pile is required to carry a working load of approximately 15 tonnes in soft ground, then a pile depth of approximately 45 ft will typically be necessary.

To achieve the required working load, a hollow sleeve 22 approximately 50 ft in length (constructed from a series of steel tubes 40, joined end to end) must be jacked into the ground to approximately twice the working load. A Kentledge 26 of at least 30 tonnes will be required to achieve the necessary force on the sleeve.

When piling in very hard or compacted ground the above method is modified slightly and the special steel tube 40 shown in Figure 7-is used.

Steps 9(a) to 9(c) are repeated as before until the resistance to penetration of the hollow sleeve becomes excessively high. The hollow sleeve 22 is then withdrawn from the ground by reverse operation of the hydraulic actuator 12, the hollow sleeve 22 again being sequentially gripped by the gripping device 14 in successive recesses 38.

Once the lower steel tube 40 of the hollow sleeve 22 has been withdrawn from the ground, the soil filled liner 76 is removed from it and an empty liner 76 is put in its place. The hollow sleeve is then inserted into the hole once more and jacking continues until the resistance to penetration again becomes excessively high. This process of alternate jacking and soil removal is repeated until the desired bearing capacity and/or depth is achieved. The hollow sleeve 22 is then removed from the hole and the lower metal tube 40 is fitted with a pile shoe 82. Steps 9(d) and 9(f) are then repeated as before.

Figure 12 shows a second embodiment of the invention in which two hydraulic actuators 12 are used to force hollow sleeves 22 into the ground. Such an arrangement would be advisable where the ground is very hard.

In the previous embodiment a substantial moment is generated about the reaction column 10, since the hydraulic actuator 12 is on one side of the reaction column 10 and the gripping device 14 is on the other side. The symmetrical disposition of the two actuators 12 in the second embodiment causes the moments on the reaction column 10 to cancel.

Claims

1. A method of placing piles in the ground (G), characterized in that a hollow sleeve (22) is forced into the ground (G), under the action of a substantially continuous force to form a shaft, the sleeve (22) is withdrawn from the ground (G) and material for forming a pile is introduced into the shaft before, during or after the removal of the sleeve (22) from the ground (G).

2. A method as claimed in claim 1, in which the hollow sleeve (22) retains soil which enters through an open end of the sleeve (22) as the open end is forced into the ground (G).

3. A method as claimed in claim 2, in which the hollow sleeve (22) is withdrawn from the ground (G) at intervals so that the soil retained in the sleeve (22) can be removed.

4. A method as claimed in any one of the preceding claims, in which the end of the hollow sleeve (22) which is forced into the ground (G) is capped by a pile shoe (82) at least prior to final withdrawal of the hollow sleeve (22).

5. A method as claimed in claim 4, in'which the pile shoe (82) is left in the shaft made by the hollow sleeve (22) when the hollow sleeve (22) is withdrawn.

6. Apparatus for placing piles in the ground (G) characterized in that an actuator (12) is provided, which propels a hollow sleeve (22) into the ground (G) with a substantially continuous force to form a shaft for a pile, the direction of force applied by the actuator (12) being reversible so that the hollow sleeve (22) can be extracted from the shaft.

7. Apparatus as claimed in claim 6 in which the end of the sleeve (22) which is forced into the ground (G) is provided with a cutting edge (75).

8. Apparatus as claimed in claim 6 or 7, in which the hollow sleeve (22) is provided with a circumferential recess (38), the recess (38) being engaged by a gripping device (14) which transmits penetrating or withdrawing forces from the actuator (12) to the hollow sleeve (22).

9. Apparatus as claimed in claim 8, in which the gripping device (14) comprises a pair of spring loaded jaws (54, 55) which are adapted to engage the recess (38) in the hollow sleeve (22).

10. Apparatus for placing piles in the ground (G), as claimed in claim 8 or 9, in which a plurality of recesses (38) are provided at regular intervals along the hollow sleeve (22).

11. Apparatus as claimed in claim 10, in which the separation of the recess (38) is substantially equal to the distance between the limits of movement of the piston ram (18) of the actuator (12).

12. Apparatus as claimed in claim 10 or 11, in which the gripping device (14) sequentially engages successive recesses (38), the actuator (12) being operated to force the hollow sleeve (22) into the ground (G) or to withdraw the hollow sleeve (22) each time the gripping device (14) engages a recess (38).

13. Apparatus as claimed in any one of claims 8 to 12 in which the actuator (12) and gripping device (14) are mounted on a common frame (2).

14. Apparatus as claimed in claim 13 in which the frame (2) is provided with moving means (4, 6, 8) which enables it to be displaced relative to the ground (G).

15. Apparatus as claimed in claim 14 in which the moving means (4, 6, 8) comprises frame mounted rollers (4), tubular rollers (6) and runners (8), the frame being movable in a first direction by the rotation of the rollers (4) along the tubular rollers (6) and in a second direction which is substantially perpendicular to the first direction, by rotation of the tubular rollers (6) along the runners (8).

16. A method of placing piles in the ground (G) substantially as described herein, with reference to the accompanying drawings.

17. Apparatus for placing piles in the ground (G) substantially as described herein, with reference to, and as shown in, the accompanying drawings.