GB2351516A

GB2351516A - Pile formed from stack of tubular segments

Info

Publication number: GB2351516A
Application number: GB9913457A
Authority: GB
Inventors: Paul Kiss
Original assignee: ABBEY PYNFORD CONTRACTS PLC
Current assignee: ABBEY PYNFORD CONTRACTS PLC
Priority date: 1999-06-09
Filing date: 1999-06-09
Publication date: 2001-01-03
Anticipated expiration: 2019-06-09
Also published as: GB2351516B; GB9913457D0

Abstract

A pile includes tubular segments forming an axial passage (5) through the pile, each segment having an upper cylindrical portion (2) with a larger diameter than that of a lower cylindrical portion (3) where the upper and lower portions are joined by an intermediate step(4), the ends of the segments are provided with complementary formations (6, 7) and the upper and lower segments are dimensioned such that their height and diameter satisfy certain mathematical relationships. The segments may be threaded on to a wire (13, Figure 4) extending through the axial passage and additional reinforcement may be inserted through the axial passage. Also grout may be poured or injected into the passage. The pile may further comprise an alignment unit (12, Figure 6) extending from within the lower end of one segment to the within the upper end of an adjacent lower segment and slip membranes (18, Figure 4; 30, 31, 32 Figures 5a and b) around the upper segments of the pile. A nose unit (12, Figures 4, 5a and b) may be located at the lower end of the stack.

Description

2351516 Improvements Relating to Piles GB-A-2299360 discloses a novel

friction pile, of the kind which may be used for supporting a foundation or an underpinning beam in the repair of a subsided building, the pile comprising a stack of tubular segments which together create an axial passage down through the pile, the segments being arranged during driving of the pile to be added successively to the top of the pile, and wherein the bottom of each pile segment has a smaller peripheral diameter than the top of the next lower segment.

The significance of the different peripheral diameters at the top and bottom of each segment is that, as the pile is successively lengthened and driven down into the ground, the lower portions of the segment, which are of smaller diameter than the hole created by the larger upper portions of the segments below, are spaced from the wall of the hole by an annulus, thereby significantly reducing the friction during the driving. After a period of time, which depends upon the composition of the ground, the ground squeezes in on the smaller diameter portion of each segment, thereby increasing the load required to mobilise the pile. In cases in which the ground squeezes in significantly during pile driving, the longitudinally spaced larger diameter portions repeatedly reopen the annulus. In certain soils, the annulus remains open and the load is increased by filing the annulus with grout.

our development work has established that the dimensions of each pile segment are critical for two reasons. A first important criterion is that, at any stage during pile driving, the annulus surrounding the lower portion of each segment is of appropriate radial and axial dimensions to ensure the maximum strength and adequate reopening of the annulus at typical pile driving speed. A second criterion is that it has been found desirable for the pile segments to be constructed f rom concrete by either the wet or dry casting method and the shape and dimensions 2 of the segment have had to be carefully selected for reliable mass production techniques.

In our earlier application we suggested that each pile segment could have a peripheral shape presenting an upper substantially cylindrical portion, merging through an intermediate frusto conical chamfer into a lower substantially cylindrical portion of smaller diameter. We still f ind this shape to be preferred and in order to satisfy the criteria mentioned above, and in accordance with the primary aspect of the present invention, a pile comprises a stack of tubular segments which together create an axial passage down through the pile, the segments being arranged during driving of the pile to be added successively to the top of the pile, and wherein each segment has an upper substantially cylindrical portion, having a diameter DL and an axial length HL, joined by an intermediate step to a lower substantially cylindrical portion, having a diameter Ds and an axial length Hs, and, at the ends of the segment, complementary formations which, when like segments are engaged end to end, provide keying against relative lateral movement, wherein the following relationships are satisfied:

D)5 -<0.9 DV DV-DA>l 6mm Hp 0. 1<-<O. 5 H The complementary keying formations formed at each end of the segment may be mating male and female formations, to 3 inhibit mutual lateral movement. Thus the upper face of each segment may include a socket, f ormed by recessing the upper f ace within an annular raised lip, in which the lower end of a like segment can be nested during pile driving.

The diameter DL of the upper substantially cylindrical portion may be between 120 and 80Omm, preferably 140mm, and the diameter Ds of the lower substantially cylindrical portion may be between 100 and 40Omm, preferably 120mm.

The axial length HL of the upper substantially cylindrical portion may be between 50 and 10Omm, preferably 70mm, and the axial length Hs of the lower substantially cylindrical portion may be between 100 and 100Omm, preferably 21Omm.

The intermediate step may be formed by a right angular step or by a frustoconical chamf er. This may have an axial length of between 10 and 30mm, preferably 20mm, and a conical half angle of between 300 and 600, preferably 450.

The raised lip on the upper face of the segment may have an axial length of between 2 and 6mm, preferably 4 mn.

The pile segments may be threaded on to a wire, such as a galvanised steel wire, which is fixed to the lower end of the pile and extends up to ground level through the central axial passage. Alternatively or additionally to being galvanised, the wire may be protected against corrosion by filling the passage down through the pile with grout, after the pile has been driven, in order to encapsulate the wire. The wire may then be post or pretensioned and will act to reinforce the pile.

Alternatively or additionally a reinforcing bar may be used.

A further alternative is that additional reinforcement is introduced to the pile once it has been driven, f or example, steel rods may be inserted through the central axial passage and the subsequent introduction of grout to the central passage will fix the additional reinforcement in place.

4 Grout may be poured or injected into the central axial passage either after completion of driving all segments or during the course of adding each segment depending upon ground conditions. For example, to prevent water entering the central passage grout is added as the water table is approached. The grout may be added under pressure.

Depending upon ground conditions it may be desirable to provide additional keying between adjacent pile segments to prevent their mutual misalignment in the lateral direction. Such keying could be provided by an alignment unit which may be a tube, a square boxed section or a metal frame extending from within the lower end of one segment to within the upper end of an adjacent lower segment. The alignment unit could be made from steel and may be is galvanised or made of a soft non corrosive material. such as aluminium or an aluminium alloy or plastics material, its lack of inherent strength being compensated by the subsequent grouting up of the internal passage, and hence the filling of the tube with grout. 20 Slip membranes may be provided around the upper segments of the pile to allow the ground to flow over this section of the pile when the ground is subject to the effects of heave. According to a second aspect of the present invention, there is provided a driven friction pile assembly comprising: a stack of tubular segments wherein the bottom of each pile segment has a smaller peripheral diameter than the top of the next lower segment; 30 a nose unit at the lower end of the stack of tubular segments, the nose unit having a diameter greater than the maximum diameter of the tubular segments; and a slip membrane disposed at the upper end of the assembly around one or more of the tubular segments and having a first set of tubular elements having an outer diameter equal to or less than the diameter of the nose unit and an inner diameter equal to or greater than the diameter of the top diameter of the segment and a second set of tubular elements disposed around the bottom of each segment and having an outer diameter substantially the same as that of the top diameter of the segments and an inner diameter substantially the same as that of the bottom of the segment.

The slip membranes may comprise a number of concentric lining tubes surrounding the upper segments of the pile. The slip membranes may comprise an outer liner, which may be made from a plastics material and which surrounds an intermediate liner tube, which may be formed from either plastics material or cardboard, which, in turn, surrounds the pile segment. Additionally, a polythene coated cardboard tube may be fitted around the smaller diameter section of the pile segment.

Ducts may extend from the central axial passage to the periphery of the pile through which ducts grout may in use be injected from the passage to the external surface of the pile.

The grout may be injected through the ducts during pile driving so as to provide a lubricant between the external surface of the pile and the surrounding ground, to reduce the resistance to driving, the grout subsequently setting to provide good frictional engagement between the pile and surrounding earth. Alternatively, the grout may be injected after completion of pile driving, essentially to fill any voids between the peripheral surface of the pile and surrounding earth.

The ducts may be grooves located in the lower face of the segment, i.e. the smaller diameter end, as this gives a greater overall resistance to crushing and reduces the likelihood of blockages.

Alternatively or additionally the ducts may be substantially cylindrical passages through the segment and be axially located between the chamfered shoulder section and the lower face of the segment.

6 The grout may be injected into the central axial passage by means of a grout lance which is placed in the driven pile and comprises an elongate tube having an expanded injection end which sealingly engages with the central axial passage to prevent grout rising up the central passage. As the grout is injected from the tube, it is forced through the ducts which extend from the central axial passage to the periphery of the pile. This forces any air or water from the periphery of the pile into the central axial passage above the sealed portion of the lance and, subsequently, expels the air or water at ground level. This ensures that grout fully surrounds each pile segment.

The invention also includes a pile segment for use, when stacked with like segments, to form a pile according to the primary aspect of the invention, the segment comprising an upper substantially cylindrical portion, having a diameter DL and an axial length HL and joined by an intermediate step to a lower substantially cylindrical portion having a diameter Ds and an axial length Hs; a central axial passage extending through the pile segment; and, at the ends of the segment, complementary formations which, when like segments are engaged end to end, provide keying against relative lateral movement, wherein the following relationships are satisfied:

-5 <O. 9 DV DV-DA>l6MM H7 0.1<-<0.5 H, In the accompanying drawings:

7 Figure 1 is a plan of a pile segment, f or use in constructing a pile, and according to the present invention; Figure 2 is a perspective view of the pile segment from above and one side; Figure 3 is a side elevation of the pile segment; Figure 4 is a diagrammatic side elevation of a driven pile according to the present invention; Figures Sa and 5b are axial sections through a pile showing the use of slip membranes; Figure 6 is an axial section through a nose unit; Figure 7 is an axial section through a pile showing the use of a grout lance; Figures 8 (a) to (d) are progressive stages in a construction of the pile cap; and Figure 9 is a side elevation of a completed pile cap.

The pile segment illustrated in Figures 1 to 3 is a concrete casting having an upper substantially cylindrical portion 2 and a lower substantially cylindrical portion 3. The upper and lower portions are joined by an intermediate frustoconical chamfer 4 having a preferred axial length of 20 mm and a preferred conical half angle of 450. The upper portion 2 has an axial length denoted by HL, typically 70 nm, and a diameter denoted by DL, typically 140 mm. The lower portion 3 has an axial height denoted by Hs, typically 210 mm, and a diameter denoted by Ds, typically 12 0 mm.

A central passage 5 extends from one end to the other end axially through the segment. The upper face 6 of the segment is recessed within an upstanding rim 7, to form a socket in which the lower end of a like segment can be nested during pile driving.

A diametrical groove 8 is formed in the lower face 9 of the segment and, when the lower face 9 of one segment is abutted against the upper face 6 of a like segment, provides a duct through which grout can be injected from 8 the central passage 5 to the periphery of the pile segment. When in use, the upper limit of the groove 8 in the lower face of one segment should extend beyond the upper limit of the rim 7 of the segment below so that any grout injected into the central passage can exit the groove 8. If, at any particular junction between adjacent segments, such channels are not required, then the groove 8 can be filled before the next segment is placed on top.

Instead of, or in addition to the groove 8, one or more ducts 8a, e.g. of 10-30 mm diameter, may be formed through the portion 3 from the central passage 5 to the periphery.

Depending upon ground conditions, the grout may be poured or injected under pressure after the installation of each segment, or after all of the segments have been installed, to fill the central passage 5 and, via the grooves 8, the annulus surrounding the segment.

Figure 4 shows a driven pile 10. The first segment 11 to be installed is fitted with a nose unit 12. If the pile is being installed in an area susceptible to the affects of heave then a galvanised cable 13, typically 11 mm in diameter, may be attached to nose unit of the first segment. If a cable is not used in ground susceptible to heave, additional reinforcement is added once the pile has been driven. If the ground is not susceptible to heave then a cable may not be needed, but a reinforcing bar may be installed after the pile has been driven.

The f irst segment 11 is jacked into the ground by pushing against the existing foundation 17. A second segment 14 is then threaded over the cable 13, if used, and its lower face nested into a socket in the upper face of the first segment. The second segment is then also jacked into the ground.

Difficult or obstructed ground may deflect piling units, in which case alignment units 15 are installed. Aligranent units. 15 are generally installed between the first three segments as a precaution.

9 Further segments are added and pressed into the ground as before until the pile achieves the necessary length.

Then two pile caps are added above the final segment and beneath the existing foundations to complete the pile.

When the pile is driven into ground which is susceptible to the ef f ects of heave, the upper segments are provided with an anti-slip membrane 18, e.g. a polythene coated cardboard tube, which surrounds the reduced diameter body portion 5 and which allows the ground to flow over this section of the pile.

An alternative arrangement of the slip membranes can be seen in Figures 5a and 5b. The outer liners 30 are driven together with the nose cone and the first few pile segments. These initial sections are driven to the required depth for the outer liners, which corresponds to the depth of the desiccated or other unsuitable ground in which heave is expected to take place. Once the outer-liners have reached the required depth, the remaining pile segments are driven through the outer liners so forcing the nose cone and the initial pile sections through the bottom of the outer liners 30 such that, once the pile has been completed, the ground may squeeze in on the lower pile segments to increase the load required to mobilise the pile. The intermediate liners 31 may be inserted at the same time as the outer liners jO or alternatively may be inserted when the final pile segments are driven. An inner polythene coated cardboard tube 32 is fitted around the smaller diameter sections of those pile segments which, when the pile is fully driven, will coincide with the outer liners 30.

A nose unit for driving with the first pile segment is shown in Figure 6. The nose unit 12 is formed f rom concrete and comprises a substantially cylindrical body portion 21 having, at its lower end, an substantially conical section 22 which is joined to the body portion via a shoulder 23. An engagement portion 24 is provided in the other end of the body portion f or locating the central axial passage 5 of the first pile segment. A reinforcing cable 13 (see fig 4) may be fixed into the nose unit during casting.

A grout lance 40 for injecting grout into a driven pile is shown in Figure 7. The grout lance 40 comprises an injecting tube 41 having an expanded end portion 42 which seals the central axial passage 5 and ensures that grout is forced through the ducts SA. As the grout 43 is injected to the pile segments, air and water is forced upwardly at the periphery of the pile and is urged through ducts 8a above the level of the grout. The air and water 45 can be expelled upwards through the central axial passage 5 as shown by arrows 44. As the level of the grout 43 rises around the periphery of the pile, the lance 40 is withdrawn a short distance so that grout is injected through the next uppermost duct SA. This process is repeated until the whole pile has been grouted.

Successive stages in the preferred construction of the pile cap are shown in figures 8 (a) to (d). once piling has been completed, the pile is pressure grouted. Any required reinforcement is then added and the top pile units are placed. A precast pile cap 50 is fitted to the uppermost pile segment 51 beneath the foundations 52. The uppermost pile segment 51 is placed in an inverted position so that a seal 59 can be formed between the upper two segments (see f ig 9). The pile cap has a grout hole 53 which is in f luid communication with the central axial passage 5 in the upper pile segment. A precast load jack 54 is placed between the f oundation and the top of the pile cap and the pile is then reloaded. Wedges 55 are then installed between the loaded pile and the foundation. The jack 54 is removed and replaced by a grout bag 56 which is subsequently filled, via a hose 57, with grout 58 and pressurised. When the grout dries, it f orms a solid top section to the pile.

Finally grout is added under pressure through the. grout hole 53 to ensure that the central passage 5 is completely filled. Figure 9 shows a completed pile cap.

Claims

1. A pile comprising a stack of tubular segments which together create an axial passage down through the pile, the segments being arranged during driving of the pile to be added successively to the top of the pile, and wherein each segment has an upper substantially cylindrical portion, having a diameter DL and an axial length HLI joined by an intermediate step to a lower substantially cylindrical portion, having a diameter Ds and an axial length Hs, and, at the ends of the segment, complementary formations which, when like segments are engaged end to end, provide keying against relative lateral movement, wherein the following relationships are satisfied:

is D, < 0.9 DL D, - Ds > 16mm 0.1 < HL < 0.5 Hs

2. A pile according to claim 1, wherein the complementary keying formations formed at each end of the segment are mating male and female formations.

3. A pile according to either claim 1 or claim 2, wherein an upper face of each segment includes a socket, formed by recessing the upper face within an annular raised lip, in which the lower end of a like segment can be nested during pile driving.

12

4. A pile according to any one of the preceding claims, wherein the diameter DL of the upper substantially cylindrical portion is between 120 and 80Omm.

5. A pile according to any one of the preceding claims, wherein the diameter Ds of the lower substantially cylindrical portion is between 100 and 40Omm.

6. A pile according to any one of the preceding claims, wherein the axial length HL of the upper substantially cylindrical portion is between 50 and 10Omm.

7. A pile according to any one of the preceding claims, wherein the axial length Hs of the lower substantially is cylindrical portion is between 100 and 100Omm.

8. A pile according to any one of the preceding claims, wherein the intermediate step is formed by a right angular step or by a frustoconical chamfer.

9. A pile according to claim 8, wherein the intermediate step has an axial length of between 10 and 30mm, preferably 20mm.

10. A pile according to either claim 8 or claim 9, wherein the intermediate step has a conical half angle of between 30' and 600.

11. A pile according to any of claims 3 to 10, wherein the raised lip on the upper face of the segment has an axial length of between 2 and 6mm.

12. A pile according to any one of the preceding claims, wherein the pile segments are threaded on to a wire which is f ixed to the lower end of the pile and extends up to ground level through the central axial passage.

13 13. A pile according to claim 12, wherein the wire is formed from galvanised steel wire.

14. A pile according to either claim 12 or claim 13, wherein the wire is protected against corrosion by filling the central axial passage with grout, after the pile has been driven, in order to encapsulate the wire.

15. A pile according to any one of claims 12 to 14, wherein the wire is post- or pre-tensioned.

16. A pile according to any one of the preceding claims, further comprising a reinforcing bar.

is

17. A pile according to any one of the preceding claims, wherein additional reinforcement is inserted through the central axial passage once the pile has been driven.

18. A pile according to any one of the preceding claims, wherein grout is poured or injected into the central axial passage either after completion of driving all segments or during the course of adding each segment depending upon ground conditions.

19. A pile according to claim 18, wherein the grout is added under pressure.

20. A pile according to any one of the preceding claims, further comprising an alignment unit which is one of the following: a tube, a square boxed section or a frame extending from within the lower end of one segment to within the upper end of an adjacent lower segment.

21. A pile according to claim 20, wherein the alignment unit is made from steel.

14

22. A pile according to claim 20, wherein the alignment unit is galvanised or made of a soft non corrosive material, such as aluminium or an aluminium alloy or plastics material.

23. A pile according to any one of the preceding claims, further comprising slip membranes around the upper segments of the pile.

24. A driven friction pile assembly comprising:

a stack of tubular segments wherein the bottom of each pile segment has a smaller peripheral diameter than the top of the next lower segment; a nose unit at the lower end of the stack of tubular is segments, the nose unit having a diameter greater than the maximum diameter of the tubular segments; and a slip membrane disposed at the upper end of the assembly around one or more of the tubular segments and having a f irst set of tubular elements having an outer diameter equal to or less than the diameter of the nose unit and an inner diameter equal to or greater than the diameter of the top diameter of the segment and a second set of tubular elements disposed around the bottom of each segment and having an outer diameter substantially the same as that of the top diameter of the segments and an inner diameter substantially the same as that of the bottom of the segment.

25. A pile assembly according to claim 24, wherein the slip membranes comprise a number of concentric lining tubes surrounding the upper segments of the pile.

26. A pile assembly according to either claim 24 or 25, wherein the slip membranes comprise an outer liner which surrounds an intermediate liner tube which, in turn, surrounds the pile segment.

is

27. A pile assembly according to claim 26, wherein the outer liner is made from a plastics material.

28. A pile assembly according to either claim 26 or claim 27, wherein the intermediate liner is formed from either plastics material or cardboard.

29. A pile assembly according to any one of claims 26 to 28, wherein a polythene coated cardboard tube is fitted 10 around the smaller diameter section of the pile segment.

30. A pile assembly according to any one of claims 24 to 29, wherein ducts extend from the central axial passage to the periphery of the pile through which ducts grout is, in is use, injected from the passage to the external surface of the pile.

31. A pile assembly according to claim 30, wherein the grout is injected through the ducts during pile driving so 20 as to provide a lubricant between the external surface of the pile and the surrounding ground.

32. A pile assembly according to either claim 30 or claim 31, wherein the grout is injected after completion of pile 25 driving.

33. A pile assembly according to any one of claims 30 to 32, wherein the ducts are grooves located in a lower face of the segment.

34. A pile assembly according to any one of claims 30 to 33, wherein the ducts are substantially cylindrical passages through the segment.

35. A pile assembly according to any one of claims 30 to 34, wherein the ducts are axially located between the 16 chamfered shoulder section and the lower face of the segment.

36. A pile assembly according to any one of claims 30 to 35, wherein the grout is injected into the central axial passage by means of a grout lance.

37. A pile assembly according to claim 36, wherein the grout lance comprises an elongate tube having an expanded injection and which sealingly engages with the central axis passage to present grout rising up the central passage.

38. A pile segment for use, when stacked with like segments, to form a pile or a pile assembly according to any one of claims 1 to 37, the segment comprising an upper substantially cylindrical portion, having a diameter DL and an axial length HL and joined by an intermediate step to a lower substantially cylindrical portion having a diameter Ds and an axial length Hs; a central axial passage extending through the pile segment; and, at the ends of the segment, complementary formations which, when like segments are engaged end to end, provide keying against relative lateral movement, wherein the following relationships are satisfied:

Ds < 0.9 DL DL - Ds > 16mm 0.1 < HL < 0.5 HS