GB2261009A - Improvements in or relating to piling - Google Patents

Abstract

Heave relief apparatus 20; 40 for the mouth-adjacent region of a pile bore 15 formed in ground material, said apparatus including a generally tubular device 20; 40 which comprises an extruded plastics material tube 10 composed of two substantially co-axial skins integral with a plurality of longitudinally extending membranes that interconnect the two skins and define a plurality of longitudinally extending cavities between them. In use, after forming a pile bore in ground material, the generally tubular device 10 is located within a mouth-adjacent region of the pile bore (i.e. adjacent the surface of the ground material), and a settable composition is poured into the tube to form at least part of the pile with a diameter commensurate with that of the said inner skin. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO PILING DESCRIPTION A problem of increasing concern associated with piling is so-called "heave", this being the lift effect upon a pile by the ground material (e.g. soil, clay, or the like) around the pile. Such "heave" tendencies are generally of greatest concern where the ground material is at least mainly of clay and the site has been cleared of trees, shrubs and other flora. It is thought to be due in such circumstances to the tendency of the substantially desiccated clay in the uppermost regions of the ground material to regain its natural moisture content and, in so doing, to expand in volume thereby raising the ground level. It has been found virtually impossible to predict accurately the heave forces likely to be encountered in any practical situation.For example, in one particular case one "expert" put the expected heave force (to be resisted 2 by the pile) at a value of 40kN/m2 and another "expert" in the same case put it at a value of 100kN/m2.

With regard to the effect on a pile of the heave forces arising in the ground material, much depends upon the estimated c-value, i.e. cohesion value, indicative of the cohesive force likely to arise between the ground material and the pile. Accordingly, in attempting to ensure an adequate factor of safety in pile construction, it has become customary to require substantially high tensile strength for the piles. This has necessitated incorporating in concrete piles, steel tensioning wires in greater number and/or thickness than warranted if potential heave forces could be accurately predicted or even discounted totally, and also in increasing the depth of the pile to provide sufficient anchorage for the steel wires. The precautionary use of excess steel in, and increased depth of, the piles dramatically increases the cost of piling.

It is therefore considered desirable to provide a method and apparatus for piling which can overcome the aforementioned and/or other difficulties and disadvantages of piling procedures prevalent heretofore.

It is known from UK Patent No. 2 178 460 to provide for a pile heave relieving means comprising a first surface for engagement by encompassing ground material, the first surface being readily deformable by heave of the ground material thereby to accommodate heave induced strain, and a second surface disposed within and in spaced relation to the first surface and for encompassing engagement of the pile.

A piling method has also been proposed in UK Patent Publication No. 2 195 688 in which pile top spacer means is provided in the upper region of the pile bore, said pile top spacer means comprising a tubular device including a tube and one or more expansible elements externally of the tube, and in which the or each of the said element(s) is expanded against the wall of the bore's upper region so as frictionally to retain the tube within said upper region in spaced relation to the bore wall, the pile itself being constructed by insertion of pile constituents (i.e. a settable composition, such as concrete or the like, with a reinforcement assembly embedded therein) through the said tube and to form the upper portion of the pile with an external contour conforming to the interior of the said tube.

UK Patent Publication No. 2 241 525 proposes employing, as heave relief apparatus, a generally tubular device and means to resist upwards motion of the device out of the pile bore (prior to setting of the pile's settable composition), the resistance being manifested as a mechanical reaction force.

The present invention is concerned with improvements to these prior art arrangements.

According to a first aspect of this invention there is provided a piling method comprising the steps of: forming a pile bore in ground material, locating a generally tubular device within a mouthadjacent region of the pile bore (i.e. adjacent the surface of the ground material), the generally tubular device comprising an extruded plastics material tube composed of two substantially co-axial skins integral with a plurality of longitudinally extending membranes that interconnect the two skins and define a plurality of longitudinally extending cavities between them, and pouring a settable composition into the tube to form at least part of the pile with a diameter commensurate with that of the said inner skin.

It is envisaged that, once the composition has set, the tube's cavities will in use enhance the radial compressibility of the tube and thereby permit it to accommodate some of the potential ground heave, it being considered that most of such heave will be accommodated by slippage of the ground material relative to the tube.

Optionally the said device may comprise another tube, in encompassing relation to the first-mentioned tube. This other tube may be of like construction to the firstmentioned tube (but increased diameter), or may alternatively be a simple sleeve of flexible sheet material, e.g. converted from a tube wrapping of polythene or other suitable plastics material.

It will be appreciated that, due to the plastics material, the (or each) tube may be light in weight, water or moisture resistant, resistant to degradation and/or corrosion, and less expensive than the (primarily) cardboard tubular devices of the above-stated prior art.

Preferably said pile bore is directed downwardly and the said mouth-adjacent region is the upper region of the pile bore.

Advantageously the said device is located substantially coaxially with the bore axis.

According to a second aspect of this invention there is provided heave relief apparatus for the mouth-adjacent region of a pile bore formed in ground material, said apparatus including a generally tubular device which comprises an extruded plastics material tube composed of two substantially co-axial skins integral with a plurality of longitudinally extending membranes that interconnect the two skins and define a plurality of longitudinally extending cavities between them.

According to a third aspect of the present invention there is provided a pile constructed by a method according to said first aspect of this invention and/or incorporating heave relief apparatus according to said second aspect of this invention.

Preferably, a portion of the tube adjacent the bore's mouth is bonded to a membrane of impervious material (e.g. a suitable plastics material) that is to form a damproof course for a building or other structure imparting a loading - directly or indirectly - on the said pile.

Advantageously the tube is crimped to bond together its two skins prior to bonding of the tube to the membrane.

By way of example embodiments of this invention will now be described with reference to the accompanying drawings of which: Figure 1A is a diagrammatic cross-section through tubing incorporated in the heave relief apparatus of the embodiments described below with reference to Figs 2-5, Fig 6, Fig 7 and Fig 8, Figure 1B is an enlarged detail of the cross-sectional view of Fig 1, Figure 2 is a schematic longitudinal sectional view through the first embodiment in situ about a pile in a pile bore, Figure 3 is a schematic sectional view of part bf the apparatus of Fig 2, the portion thereof when in engaged condition being shown in broken outline, Figure 4 is a schematic sectional view of part of the apparatus of Fig 2 in non-engaged condition, Figures Sa and 5 are schematic cross-sectional views, to an enlarged scale, of two modifications of portions of the apparatus shown in Fig 3, Figure 6 is a schematic longitudinal sectional view through the second embodiment in situ about a pile in a pile bore, and Figure 7 is a schematic cross-sectional view of an application of the first or second embodiment.

The heave relief apparatus of each embodiment described herein comprises - as an essential element - a length of extruded plastics material 'twin-wall' tubing 10 (Fig 1).

This twin-wall' tubing 10 is composed of concentric inner and outer substantially cylindrical skins 11,12 integral with a plurality of longitudinally extending membranes 13 that interconnect the two skins 11,12 and define a corresponding number of longitudinal cavities between them.

The plastics material may be based upon propylene/ethylene copolymer. Preferably the plastics material is polypropylene. The plastics material is preferably extruded such that the tube's outer skin 12 is wholly smooth and its inner skin 11 has a longitudinal indentation of shallow cusp-like cross-section at each location where that inner skin 11 adjoins a membrane 13. The resultant appearance is somewhat like a tube formed of corrugated cardboard.

Advantageously, in a particularly preferred embodiment, the outer skin 12 has a thickness of the order of 0.63 mm, the inner skin 11 has a thickness of the order of 0.30 mm, and each cross-rib or membrane 13 has a thickness of the order of 0.30 mm.

The first embodiment of Figs 2 to 5, illustrates heave relief apparatus incorporating a generally tubular device 20 (shown schematically in longitudinal section) in situ about the upper region L of a pile 14 in a pile bore 15 which has been drilled into soil or clay ground material 16 to a depth H (substantially greater than length L). The open bore 15 is of uniform cross-section throughout and may be formed by a drilling rig according to UK Patent No.

2108185 or to UK Patent No. 2159553 or by any other suitable method. If required, a temporary steel casing or lining (not shown), of length somewhat less than L, may be provided in the bore 15 adjacent its mouth to prevent soil or clay caving into the bore.

After completing drilling of the bore 15 (and insertion of any temporarily required steel casing or lining), the tubular device 20 of the apparatus is inserted into the upper region of the bore. The device 20 comprises a length L of the said tubing 10, and a pair of oppositely directed skirt-like, generally bell-shaped members 17,18 encompassing the lower end of the tubular member (see Fig 3). Each skirt-like, generally bell-shaped member 17,18 is provided with a plurality of individual equi-angularly spaced depending fingers 120 formed by slots 121 extending upwards from the lower periphery of member 18 and downwardly from the upper periphery of member 17.The fingers 120 are all of equal length and are resiliently attached to a common cylindrical main body 19 disposed inbetween the two members 17 and 18, e.g. by being moulded integrally therewith of plastics material - high impact polystyrene being considered particularly suitable. These fingers 120 are formed such that they, when unconstrained, extend curvingly and outwardly away from the tube 10 (as shown by broken lines in Fig 3).

For example, for use with a bore 15 of nominal 400mm diameter, the tube 10 may be of approximately 280mm diameter, and the members 17,18 may be molded of high impact polystyrene with a thickness of approximately 3 mm.

The overall height of the members 17,18 may be approximately 350mm, composed of the solid or un-apertured main body 19 of approximately 100mm and integral with twenty-three upstanding and twenty-three depending fingers 120 each approximately 125mm in length and approximately 40mm wide. These fingers 120 may be formed with one or two longitudinal ribs 26 to increase their stiffness (see Figs 5a and sub). The length of the fingers 120 is such as to render them capable of bowing (as shown) and still reach to the wall of the bore 15 approximately 80mm from the tube 10. The bottom of member 18 is spaced upwardly from the bottom of tube 10 by approximately 50mm. The length L of tube 10 will depend upon individual pile requirements but may be up to 5m.

Retaining means comprising a collar 22 (Fig 4) slidably surrounds the fingers 120 and constrains them inwardly towards the tube 10, e.g. into surfacial abutment therewith. With the fingers 120 thus constrained, the tubular device 20 can be freely inserted into the bore 15.

After the device 20 is inserted into bore 15 to the required depth (approximately L), collar 22 is pushed downwardly into the bore, i.e. from off the fingers 120, e.g. by a stick or other implement (not shown). The fingers 120 can thus spring outwards under their inherent resiliency until the free ends 125 of the fingers engage the wall of bore 10. The fingers 120 thus serve to centralise the lower end of tube 10 within the bore, and their free ends 25 tend to dig into the soil of the bore's wall and resist upwards motion of the device 20 by engendering a mechanical reaction force in the fingers 120 of the generally bell-shaped members 17,18.

Optionally two collars such as 22 may be provided, one for each of the bell-shaped members 17 and 18, the lower one being pushed into the bore (and lost) and the upper one being pulled out of the bore, e.g. in like manner to that disclosed in GB 2241525, so as to be available for re-use in another heave relief apparatus. Alternatively both such collars may be pulled out of the bore (or pushed into the bore).

It is considered that, notwithstanding a possible tendency for the poured concrete or other settable composition to rise in the bore 15 and pass through the slots 121 in members 17,18 (which slots are somewhat wedge-shaped when the fingers are bowed outwards in their extended or splayed condition), such a tendency will be minimised (if not wholly obviated) by the fingers 120. resisting such passage.

This resistance arises in consequence of the upward pressure on the fingers 120 of lower member 18 causing their free ends 25 to dig still further into, and/or engage even more tightly against, the wall of the bore 15 thereby increasing the mechanical reaction force resisting upwards motion of the tubular device 20.

After withdrawal of any temporary mouth-adjacent casing or lining from the bore 15, a collar 125 of inverted frustoconical shape is provided around the upper end of tube 10 at the mouth of the pile bore to locate the upper end of the tube centrally of the bore 15 with its axis substantially vertical, and coaxial with the pile bore, and to maintain the spatial relationship between the said upper end and the wall of the bore.

A pile reinforcement cage or like assembly 126 is then inserted into the pile bore in the usual way. The reinforcement assembly 126 has a plurality of interconnected logitudinal and transverse steel reinforcement elements 127 and plastics spacer rings 129 as is generally conventional. One of the assembly's transverse elements that is to be located in the vicinity of the upper end of the tube 10, is identified in Fig 2 by the reference numeral 128, and optionally this element may take the form of a square or circular "ring" of steel lying in the horizontal plane.

An abutment member 30 in the form of a steel rod 130 is pushed through diametrically opposite holes in the wall of tube 10 to extend across the tube at a location immediately beneath the transverse reinforcement element 128, preferably at right-angles to two opposed parts of the element 128. Alternatively the abutment member 130 may extend through a pair of diametrically opposite vertical slots cut downwardly from the top edge of the tube 10. The position of the diametrically opposite holes or slots is such that the underside of element 128 is engageable by the abutment member 130 if the tube 10 should rise in the bore 15 carrying the abutment member 130 upwardly therewith.

It will be appreciated that any tendency for the tube 10 to float upwards on the settable composition as the latter fills the bore (a removable funnel may be provided as an aid to the pouring of said settable composition), will be restrained by abutment of the abutment member 130 against the underside of the transverse element 128 of the reinforcement cage assembly 126, the cage assembly itself being held by its lower end embedded in the high viscosity settable composition. Such abutment will produce a mechanical reaction force in the abutment member 130 and consequently in the tube 10 with which it is engaged.

In an alternative method, the reinforcement cage 126 with element 128 can be located in the bore 15 before the tubular device 20 is placed in position.

In the embodiment of Fig 6, heave relief apparatus 40 is provided in a pile bore 15 having a temporary. steel casing or lining 41 adjacent the mouth of the bore. The apparatus 40 differs from apparatus 20 described above in that it comprises two concentric 'twin-wall' tubes 10a,10b of similar construction but of different diameter. In other words, each of the tubes 10a,10k is composed of inner and outer skins 11,12 integral with a plurality of interconnecting membranes 13. The two tubes 10a,10b may be provided in a mutually telescoping arrangement or may be spaced apart a small distance. In either case, the two tubes are interconnected at their upper ends by releasable fastening means, e.g. clips, (not shown).The inner tube 10 is provided at its lower end either with a single skirt-like, generally bell-shaped member 48 such as that disclosed in GB 2241525, or with a pair of oppositely directed skirt-like members such as the members 17,18 described above. Prior to use, the or each generally bellshaped member is constrained to a substantially cylindrical shape by one or more collars (such as 22, Fig 4).

After insertion of the heave relief apparatus 40, the collar(s) encompassing the constrained skirt-like member(s) is/are removed to permit the fingers 120 of the member(s) to expand or extend outwards and dig into the bore's wall.

The apparatus is thus centralised at its lower end and restrained against movement (in at least one direction) in the pile bore 15. The pile's constituents (the settable composition and, if not already in situ, the reinforcement cage) are then inserted through the centre of the apparatus 40 into the bore 15, the settable composition being pored in through a removable funnel. Thereafter, the fastening means holding together the two tubes 10a,10 are released to permit upward sliding of the outer tube 101 relative to the inner tube 10a. Such motion can arise by the frictional forces engendered between the casing or lining 41.

The casing or lining 41 can then be removed without causing the inner tube 10 to slide upwardly out of the bore. This should apply even if some debris, loose soil and/or spilled concrete 42 has become frictionally jammed between the casing 41 and the outer tube lOb, (or has effected a bond between them) since removal of casing 41 will be then only likely to pull the outer tube 10b upwards out of the bore but leave the inner tube 10a in position. The inner tube 10a can thus function to accomodate ground heave forces in like manner to that described above in relation to the embodiment of Figs 2-5, and the outer tube lOb that has been thus frictionally (or bondingly) removed may be reused in another similar heave relief apparatus for another pile.

In yet another embodiment, illustrated in Fig 8, the double-skin or twin-wall tube 10 is supplied encased in a sealed wrapper of suitable sheet or tubular plastics material, e.g. polythene, that serves to protect the tube particularly the tube interior. For use on site, the two end portions of the wrapper 50 are cut off, e.g.

approximately 50mm from each end of tube 10, and the remaining ends of the wrapper are bound firmly to the wall of the tube 10 a short distance from the wrapper's ends, e.g. approximately 150mm from the ends of tube 10.

Binding of the wrapper 50 to the tube 10 is effected (e.g.

by string or, as preferred, by adhesive tape) sufficiently tightly to.prevent the wrapper 50 riding up the tube 10 as the combined tube-and-wrapper is inserted into the bqre.

Nevertheless, the binding should not be so tight that it is not possible to slide the bound wrapper ends along the tube 10 by hard manual pressure.

When both wrapper ends have been bound to the tube 10, the combination is inserted into the borehole, and concrete for the pile is then poured in.

In use, the wrapping 50 forms a slip surface against the twin-wall plastics tube 10 and thereby reduces transmission of the upward heave forces that can be exerted on the pile by the ground.

Ideally the tubes 10, fully enclosed by their wrappers 20, should be stored in upright attitude, preferably vertically, to avoid becoming flattened due to superimposed loads (as occurs where such tubes are horizontally stacked). However, tubes 10 that have been deformed to slightly oval cross-section can usually still be fed into a circular bore and can usually still regain their circularity under even a small head of poured concrete.

Where the end of a tube 10 has become damaged, e.g. by inclined rather than vertical storage, the damaged end portion can be simply cut off with a sharp knife or scissors to leave a clean cut (preferably radial) end.

It will be appreciated that, in each of the illustrated embodiments, the pile diameter corresponds to that of the bore 15 over the major height (H-L) of the bore 15, but is of reduced diameter - corresponding to the internal diameter of tube 10 (or tube 10a) - over the length (L) of the pile's upper region. The air gap or void 13 between the upper pile region and the ground material serves in use to accomodate heave induced movement of the ground material and to reduce or wholly remove the likelihood of heave damage to the completed pile 14.

Accordingly it is considered that the heave relief apparatus of each of the above-described and illustrated embodiments permits of a reduction in the quantity and length of steel required in the reinforcement assembly 126 - so that the cost thereof can be less than that otherwise required - and yet permits of sufficient reinforcement of the pile to avoid, in conjunction with said heave relief apparatus, any major heave problem.

Additionally or in an alternative exemplary embodiment of the invention, after the concrete of a pile has set the void 13 may be filled with a substantially non-cohesive material, for example a granular material e.g. comprising silicate particles (preferably sand), which will obviate or at least minimise any heave induced drag on the concrete.

The non-cohesive fill material within the annular space 13 may then nevertheless permit the transmission of horizontal forces to the pile, and this may be appropriate where the pile is to be located near an existing structure.

In a particularly preferred application, the tube 10 (or 10a) encompassing the upper end of the pile 14 is bonded e.g. adhesively or by welding, or heat sealing - to a substantially horizontal membrane 45 of impervious material, e.g. a suitable plastics material, that is to form a damproof course (d.p.c.) for a building or other structure that is at least partially supported (directly or indirectly) by the pile 14.

Other modifications and embodiments of the invention will be readily apparent to those skilled in this art. All such modifications and embodiments are to be deemed within the ambit and scope of the invention, and the invention is not to be deemed limited to the particular embodiment(s) hereinbefore described which may be varied in construction and detail without departing from the scope of the patent monopoly hereby sought.

Claims (14)

1. A piling method comprising the steps of: forming a pile bore in ground material, locating a generally tubular device within a mouthadjacent region of the pile bore (i.e. adjacent the surface of the ground material), the generally tubular device comprising an extruded plastics material tube composed of two substantially co-axial skins integral with a plurality of longitudinally extending membranes that interconnect the two skins and define a plurality of longitudinally extending cavities between them, and pouring a settable composition into the tube to form at least part of the pile with a diameter commensurate with that of the said inner skin.

2. A piling method according to Claim 1, wherein said pile bore is directed downwardly and the said mouthadjacent region is the upper region of the pile bore.

3. A piling method according to Claim 1 or Claim 2, wherein the said device is located substantially coaxially with the bore axis.

4. A piling method according to any preceding Claim, wherein a portion of the tube adjacent the bore's mouth is bonded to a membrane of impervious material that is to form a damproof course for a building or other structure imparting a loading - directly or indirectly - on the said pile.

5. A piling method according to Claim 4 wherein said tube-bonded membrane of impervious material that is to form a damproof course comprises a suitable plastics material.

6. A piling method according to Claim 4 or Claim 5, wherein the tube is crimped to bond together its two skins prior to bonding of the tube to the membrane.

7. A piling method according to Claim 1 and substantially as herein described with reference to the accompanying drawings.

8. Heave relief apparatus for the mouth-adjacent region of a pile bore formed in ground material, said apparatus including a generally tubular device which comprises an extruded plastics material tube composed of two substantially co-axial skins integral with a plurality of longitudinally extending membranes that interconnect the two skins and define a plurality of longitudinally extending cavities between them.

9. Heave relief apparatus according to Claim 8, wherein the said device may comprise another tube, in encompassing relation to the first-mentioned tube.

10. Heave relief apparatus according to Claim 9, wherein the said other tube is of like construction to the firstmentioned tube (but increased diameter).

11. Heave relief apparatus according to Claim 9, wherein the said other tube is a simple sleeve of flexible sheet material.

12. Heave relief apparatus according to Claim 10, wherein said flexible sleeve is derived from a generally tububular wrapping for the first-mentioned said tube.

13. Heave relief apparatus according to Claim 12, wherein said wrapping is of polythene or other suitable plastics material.

14. A pile constructed by a method according to any one of Claims 7 to 13 and/or incorporating heave relief apparatus according to any one of Claims 1 to 6.

14. Heave relief apparatus substantially as herein described with reference to and/or as illustrated in Figs 2-5, Fig 6, Fig 7, or Fig 8.

15. A pile constructed by a method according to any one of Claims 1 to 7 and/or incorporating heave relief apparatus according to any one of Claims 8 to 14.

Amendments to the claims have been filed as follows 1. Heave relief apparatus for the mouth-adjacent region of a pile bore formed in ground material, said apparatus including a generally tubular device which comprises: (a) an extruded plastics material tube composed of two substantially co-axial skins integral with a plurality of longitudinally extending membranes that interconnect the two skins and define a plurality of longitudinally extending cavities between them, and (b) another tube, in encompassing relation to the first mentioned tube.

2. Heave relief apparatus according to Claim 1, wherein the said other tube is of like construction to the firstmentioned tube (but increased diameter).

3. Heave relief apparatus according to Claim 1, wherein the said other tube is a sleeve of flexible sheet material.

4. Heave relief apparatus according to Claim 3, wherein the first-mentioned said tube is enclosed, prior to use, by a wrapping which, in use, provides said flexible sleeve.

5. Heave relief apparatus according to Claim 4, wherein said wrapping is of polythene or other suitable plastics material.

6. Heave relief apparatus substantially as herein described with reference to and/or as illustrated in Figs 2-5, Fig 6, Fig 7, or Fig 8.

7. A piling method comprising the steps of: forming a pile bore in ground material, locating, in a mouth-adjacent region thereof, heave relief apparatus according to any one of Claims 1 to 6, and pouring a settable composition into the tube to form at least part of the pile with a diameter commensurate with that of the said inner skin.

8. A piling method according to Claim 7, wherein said pile bore is directed downwardly and the said mouthadjacent region is the upper region of the pile bore.

9. A piling method according to Claim 7 or Claim 8, wherein the said device is located substantially coaxially with the bore axis.

10. A piling method according to any one of Claims 7 to 9, wherein a portion of the first-mentioned tube adjacent the bore's mouth is bonded to a membrane of impervious material that is to form a damproof course for a building or other structure imparting a loading - directly or indirectly - on the said pile.

11. A piling method according to Claim 10, wherein said tube-bonded membrane of impervious material that is to form a damproof course comprises a suitable plastics material.

12. A piling method according to Claim 10 or Claim 11, wherein the said first-mentioned tube is crimped to bond together its two skins prior to its being bonded to the membrane.

13. A piling method according to Claim 7 and substantially as herein described with reference to the accompanying drawings.