GB2241525A

GB2241525A - Piling

Info

Publication number: GB2241525A
Application number: GB9001074A
Authority: GB
Inventors: Robert Michael Sloma; Michael Francis Forni; Marcus Paul Andrews
Original assignee: MACROPILING Ltd
Current assignee: MACROPILING Ltd
Priority date: 1990-01-17
Filing date: 1990-01-17
Publication date: 1991-09-04
Anticipated expiration: 2010-01-17
Also published as: GB9001074D0; GB2241525B

Abstract

The upper region of a pile bore 10 formed in the ground is sleeved to provide heave relief by a device 15 including a tube 14 and a ring 17, supported by elements 16, 18 and inflated once the tube has been inserted in the bore. Inflation forces elements 18 into the side of the bore to resist upward motion of the device. Alternatively, resilient fingers, restrained on insertion, resist the motion. Further restraint, if the tube rises, is provided by rod 30 engaging the tube, abutting a transverse element 28 of the reinforcing cage, secured in the lower region of the pile. Heave is accommodated by void 13, which may be filled eg with sand. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO PILING A problem of increasing concern associated with piling is so-called "heave", this being the lift effect upon a pile by the ground material 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 by the pile) at a value of 40kN/mg 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.

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

According to a first aspect of this invention there is provided heave relief apparatus for the upper region of a pile bore formed in ground material (e.g. soil, clay or the like), said apparatus comprising: a generally tubular device including a generally tubular member; engagement means having a first, extended condition in which to effect interengagement between the generally tubular member and the wall of the upper region of said pile bore and a second, non-extended condition in which it permits unfettered entry of the generally tubular device into the upper region of the pile bore; and means to resist upwards motion of the device out of the pile bore (prior to setting of the piles's settable composition), the resistance being manifested as a mechanical reaction force.

It will be appreciated that as the bore is in use filled with the settable composition for the intended pile, the generally tubular device will tend to float upwards on the settable composition as the latter rises within the bore, this upwards motion being resisted by the last-mentioned said means.

Preferably the engagement means comprises an expansible element. The expansible element may comprise a resilient flexible walled chamber encompassing the cylindrical tubular member, the chamber being in use charged with fluid under pressure to change from said non-extended to said extended condition.

Alternatively the expansible element may comprise outwardly movable fingers - the free ends of which provide said means to resist upwards motion - said fingers being retained in said non-extended condition by retainer means, e.g. a collar slidable longitudinally of the cylindrical tubular member.

According to a second aspect of the present invention there is provided heave relief apparatus for the upper region of a pile bore formed in ground material (e.g. soil, clay, or the like), said apparatus comprising a tubular device including a cylindrical tubular member and, externally and at least adjacent one (in use lower) end of the tubular member, expansible means comprising a chamber to be in use supplied with fluid under pressure, the chamber being formed with a resiliently flexible membrane such that when in use pressurised as aforesaid it is of substantially toroidal form, said apparatus being characterised by means to restrain the expansible means against travel along the tubular member in a direction away from said one end, and being further characterised by means to be deflected outwards into engagement of the pile bore upon pressurisation of the chamber and, by such engagement, to restrain the tubular member against withdrawal from the pile bore.

The means to be deflected outwards may comprise one or more plate-like members which engage the bore wall by digging into its surface. By this means, any tendency to upwards motion of the device will be resisted and produce a mechanical reaction force in the plate-like member(s), this mechanical reaction force being additional to any frictional force between the flexible membrane and the wall of the pile bore's upper region.

Advantageously the chamber is pneumatically inflatable with air. Alternatively the chamber is hydraulically expansible with oil.

After pile formation, i.e. after the concrete (or other settable composition) has set to a self-supporting state, the tubular device may be left in situ whereby the pile's upper region is spaced from the ground material by the tubular device and can therefore accomodate heave induced movement of the ground material.

According to a third aspect of this invention there is provided heave relief apparatus for the upper region of a pile bore formed in ground material (e.g. soil, clay or the like), said apparatus comprising: a generally tubular device including a generally tubular member; engagement means disposed externally and at least adjacent one (in use lower) end of the generally tubular member to effect inter-engagement between said device and the wall of the bore's upper region and to space said one end of the generally tubular member from the said wall; means to space the distal region of the generally tubular member from the said wall and to render the axis of the generally tubular member substantially vertical; and an abutment member to extend across the said distal region for engagement of the underside of a transverse element of a pile reinforcement assembly that in use extends downwardly in the pile bore to be embedded in the settable composition of the intended pile.

Preferably said engagement means comprises an expansible element, e.g. comprising outwardly movable fingers or comprising a fluid chargeable, resiliently and flexibly walled chamber) According to a fourth aspect of this invention there is provided a piling method employing heave relief apparatus according to said third aspect of the invention, said method including the steps of: (a) providing a pile bore in the ground material (e.g.

soil, clay or the like); (b) inserting said generally tubular device into an upper region of the pile bore; (c) actuating said engagement means to effect interengagement between the said device and the wall of the bore's upper region; (d) placing said distal region spacing means around the generally tubular member at the mouth of the pile bore to render the axis of the generally tubular member substantially vertical (preferably substantially coaxial with the pile bore); (e) inserting into the pile bore a pile reinforcement assembly having a transverse element to be located in the vicinity of said distal region; (f) providing for said abutment member to extend across the generally tubular member at a location immediately beneath said transverse reinforcement element such that the latter is engageable by the abutment member if the generally tubular member rises; and (g) pouring the settable composition of the intended pile through the generally tubular member into the pile bore to embed therein the pile reinforcement assembly.

Any tendency for the generally tubular device to float upwards on the settable composition as the latter fills the bore will be restrained by abutment of the abutment member against the underside of the transverse element of the reinforcement assembly, the assembly itself being held by its lower end embedded in the high viscosity settable composition. Such abutment will produce a reaction force in the abutment member and consequently in the generally tubular device with which it is engaged.

Preferably said distal region spacing means comprises an annular member to fit around the exterior of the said generally tubular member, the annular member having an outer diameter in use greater than the diameter of the pile bore and having a generally frusto-conical lower surface to engage the mouth of the pile bore.

Advantageously the distal region spacing means has an upper surface (preferably horizontal in use) to support the said abutment member.

Preferably the distal region of the generally tubular member is apertured to permit the passage therethrough of said abutment member. Advantageously the apertures are provided by diametrically opposite vertical slots or circular holes.

By way of non-limiting example, two embodiments of heave relief apparatus according to the present invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a schematic longitudinal sectional view through the first said embodiment in situ about a pile in a pile bore, Figure 2 is a similar view to that of Fig. 1 but through the second said embodiment, Figure 3 is a schematic sectional view of part of the apparatus of Fig. 2, the portions thereof when in engaged condition being shown in broken outline, Figure 4 shows schematically, and to a larger scale, part of the apparatus shown in Fig 2 when in the engaged condition, and Figures 5a and 5b are schematic cross-sectional views, to a greatly enlarged scale, of two modifications of portions of the apparatus shown in Fig. 3.

In Fig. 1, the apparatus according to the first embodiment of the invention is shown schematically in longitudnal section, in situ about a pile in a pile bore 10 which has been drilled into soil or clay ground material 12 to a depth H. The open bore 10 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. The length of the upper part of the finished pile that is to be sleeved (to provide for heave relief) is designated 1.

The exemplary apparatus is formed and used as follows: After completing the drilling of bore 10, tubular device 15 of the apparatus is inserted into the upper region of the bore. The device 15 comprises a central cylindrical tube 14 of length t, and a generally toroidal ring 17 of resiliently flexible material (e.g. rubber) encompassing the exterior of tube 14 at its bottom end. An air line 19, of length somewhat greater than t and with a valve at its upper end, extends from the toroidal ring 17 and in use feeds a supply of compressed air to it. Initially the tubular device is inserted into the bore with the toroidal ring 17 uninflated so that it can pass relatively unencumbered down the bore 10. Compressed air from the supply is then fed down air line 19 to inflate the toroidal ring and urge it into gripping contact of the wall 11 of the bore's upper region.

Inflation is continued to ensure such gripping contact with a force sufficient frictionally to retain the tubular device 15 in position with its tube 14 in spaced relation of the ground material 12, i.e. with an air gap or void 13 between the tube 14 (above ring 17) and the wall 11.

A plurality of rigid plate-like elements 16 are provided above ring 17 in ecompassing fixed relation about the tube 14. These fixed elements are directed outwardly and downwardly of the tube 14 and serve to restrain the inflated ring 17 against travel upwardly of the tube 14. Below the ring 17, the tube 14 is encompassed by a plurality of rigid plate-like elements 18 that are directed outwardly and upwardly of the tube 14. The rigid elements 18 are deflectable outwards (i.e. their included "cone angle" is increased) by inflation of the ring 17 and until the free ends of the elements 18 dig into the bore's wall 19.

A collar 25 of inverted frusto-conical shape is provided around the upper end of tube 14 at the mouth of the pile bore to locate the upper end of the tube 14 centrally of the bore with its axis substantially vertical, and coaxial with the pile bore, and to maintain the spatial relationship between the said upper end and the bore's wall 11.

A pile reinforcement cage or like assembly 26 is then inserted into the pile bore in the usual way. The reinforcement assembly 26 has a plurality of interconnected logitudinal and transverse steel reinforcement elements 27 and plastics spacer rings 29 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 14, is identified by the reference numeral 28, and optionally this 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 30 is pushed through the wall of tube 14 to extend across the tube at a location immediately beneath the transverse reinforcement element 28, preferably at right-angles to two opposed parts of the element 28. The abutment member may extend through a pair of diametrically opposite circular holes or vertical slots cut downwardly from the top edge of the tube 14. The position of such holes or slots is such that the abutment member 30 can rest upon the upper horizontal surface of collar 25 and such that the underside of element 28 is engageable by the abutment member 30 if the tube 14 should rise in the bore 10 carrying the abutment member 30 upwardly therewith.This is a possibility because there may be a tendency for the device 15 to float upwards upon the concrete (or other settable composition) of the intended pile as the concrete (or other settable composition) is poured through the tube 14 into the pile bore 10 to embed therein the pile reinforcement assembly 26.

(A removable funnel 32 may be provided as an aid to the pouring of said settable composition).

It will be appreciated that any tendency for the tube 14 to float upwards on the settable composition as the latter fills the bore will be restrained by abutment of the abutment member 30 against the underside of the transverse element 28 of the reinforcement cage assembly 26, 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 30 and consequently in the tube 14 with which it is engaged.

A restraint to such upwards movement of the tube 14 is also provided by the plate-like elements 18 which engage the bore wall 11 by digging into its surface. The restraint provided by these elements 18 is likewise manifested as a mechanical reaction force in the said elements 18, this mechanical reaction force being additional to any frictional force between the inflated ring 17 and the wall 11 of the pile bore's upper region.

In an alternative method, the reinforcement cage 26 with element 28 can be located in the bore 10 before the tubular device 15 is placed in position.

In the embodiment of Figs 2 to 4, a tubular device 115 is inserted into the upper region of the bore 10. The device 115 comprises a central cylindrical tube 114 of length L (substantially less than the height H of the bore 10), a skirt-like generally bell-shaped member 118 encompassing the lower end of the tubular member (see Fig 3). The skirt-like generally bell-shaped member 118 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 118. The fingers 120 are all of equal length and are resiliently attached to the upper main body 119 of member 118, e.g. by being moulded integrally therewith of plastics material - high impact polystyrene being considered particularly suitable.They are formed such as to extend, when unconstrained, downwardly and outwardly away from the tube 114 (as shown by broken lines in Fig 3).

For example, for use with a bore 10 of nominal 400mum diameter, the tube 114 may be of approximately 28Omm diameter, and the member 118 may be molded of high impact polystyrene with a thickness of approximately 3 mm. The overall height of the member 118 may be approximately 200mum, composed of the solid or un-apertured uppermost main body 119 of approximately 75mm and integral with 23 depending fingers 120 each approximately 125mm in length and approximately 40mm wide. These fingers 120 may be formed with one or two longitudinal ribs 126 to increase their stiffness (see Figs 5a and 5b). 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 10 approximately 80mm from the tube 114.The member 118 is positioned towards the bottom of tube 114 and is spaced upwardly from the tube's lower edge by approximately 50mm.

Retaining means comprising a collar 122 (Fig 4) slidably surrounds the fingers 120 and constrains them inwardly towards the tube 114, e.g. into surfacial abutment therewith. With the fingers 120 thus constrained, the tubular device 115 can be freely inserted into the bore 10.

The bottom of the collar 122 is provided with a flange 123 directed outwardly by approximately 10 mm and with its extremity bent downwards. One or more, preferably three eqiangularly spaced, cords 124 are attached to the flange 123.

After the device 115 is inserted to the required depth (approximately L), the cord(s) 124 attached to collar's flange 123 is/are pulled upwardly to lift collar 122 from the fingers 120. The latter 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 114 within the bore, and their free ends 125 tend to dig into the soil of the bore's wall and resist upwards motion of the device 115 by engendering a mechanical reaction force in the fingers 120 of the generally belt shaped member 118.

In this regard it is considered that, notwithstanding a possible tendency for the poured concrete or other settable composition to rise in the bore 10 and pass through the slots 121 in member 118 (which slots are somewhat wedgeshaped when the fingers are bowed outwards in their extended condition), such a tendency will be minimised (if not wholly obviated) by the fingers 120 resisting such passage and, in consequence of the upwarad pressure thereon, causing their free ends 125 to dig still further into and/or engage even more tightly against the wall of the bore 10 thereby increasing the mechanical reaction force resisting upwards motion of the tubular device 115.

Optionally, as an additional safeguard, the device 115 of Figs 2 - 4 may be provided at its upper end not ohly with the locating collar 25 and a pile reinforcement cage or assembly 26 (including an upper transverse element 28), but additionally with abutment member 30 immediately beneath and skew to element 28 as shown in Fig 1. Just as for that embodiment, element 28 is to engage the abutment member 30 if the tube 114 should rise in the bore, e.g. due to flotation of the device on the poured concrete or other settable composition.

It will be seen from the drawings that, in each illustrated embodiment, the pile diameter corresponds to that of the bore 10 over the major height H-L of the bore 10, and is of reduced diameter (corresponding to the internal diameter of tube 14 or 114)) over the pile's upper region of length L.

If the bore 10 is without any exterior casing (at least in its upper region), then the tubular device 15 or 115 can be left in situ in the ground to tend to sustain the air gap or void 13 between the upper pile region and the ground material. This air gap or void 13 serves to accomodate heave induced movement of the ground material and reduce or wholly remove the likelihood of heave damage to the completed pile 20. Accordingly it is considered that the heave relief apparatus of each of the above-described and illustrated embodiments permit of a reduction in the quantity and length of steel required in the reinforcement assembly 26 - 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.

Advantageously the tube 14 of Fig 1, or 114 of Fig 2, is formed of cardboard. Optionally, this may be coated with plastics material although such a coating might be omitted on the tube's inner face if it is feared that the provision of such a coating could give rise to differential setting problems with the concrete (or other settable composition).

It will be appreciated that the present invention is not restricted to the illustrated exemplary embodiments described above and that modifications thereto (and, indeed, other embodiments) are countenanced by, and to be included within the scope of, the present invention. For example, in the embodiment of Fig 1, the ring 17 may be expanded hydraulically with oil instead of being inflated pneumatically. 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 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.

Claims

1. Heave relief apparatus for the upper region of a pile bore formed in ground material, said apparatus comprising: a generally tubular devise including a generally tubular member; engagement means having a first, extended condition in which to effect interengagement between the generally tubular member and the wall of the upper region of said pile bore and a second, non-extended condition in which it permits unfettered entry of the generally tubular device into the upper region of the pile bore; and either additional to or provided by said engagement means, means to resist upwards motion of the device out of the pile bore (prior to setting of the piles's settable composition), the resistance being manifested as a mechanical reaction force.

2. Heave relief apparatus according to Claim 1, wherein the engagement means comprises an expansible element.

3. Heave relief apparatus according to Claim 2, wherein the expansible element comprises a resilient flexible walled chamber encompassing the cylindrical tubular member, the chamber being in use charged with fluid under pressure to change from said non-extended to said extended condition.

4. Heave relief apparatus according to Claim 2, wherein the expansible element comprises outwardly movable fingers - the free ends of which provide said means to resist upwards motion - said fingers being retained in said non-extended condition by retainer means.

5. Heave relief apparatus according to Claim 4, wherein said retainer means comprises a collar slidable longitudinally of the cylindrical tubular member.

6. Heave relief apparatus for the upper region of a pile bore formed in ground material, said apparatus comprising: a generally tubular device including a generally tubular member; engagement means disposed externally and at least adjacent one (in use lower) end of the generally tubular member to effect inter-engagement between said device and the wall of the bore's upper region and to space said one end of the generally tubular member from the said wall; means to space the distal region of the generally tubular member from the said wall and to render the axis of the generally tubular member substantially vertical; and an abutment member to extend across the said distal region for engagement of the underside of a transverse element of a pile reinforcement assembly that in use extends downwardly in the pile bore to be embedded in the settable composition of the intended pile.

7. Heave relief apparatus according to Claim 6, wherein said engagement means comprises an expansible element.

8. Heave relief apparatus according to Claim 7, wherein said expansible element comprises outwardly movable fingers.

9. Heave relief apparatus according to Claim 7, wherein said expansible element comprises a fluid chargeable, resiliently and flexibly walled chamber.

10. Heave relief apparatus according to any one of Claims 6 to 9, wherein said distal region spacing means comprises an annular member to fit around the exterior of the said generally tubular member, the annular member having an outer diameter in use greater than the diameter of the pile bore and having a generally frusto-conical lower surface to engage the mouth of the pile bore.

1

11. Heave relief apparatus according to any one of Claims 6 to 10, wherein the distal region spacing means has an upper surface (preferably horizontal in use) to support the said abutment member.

12. Heave relief apparatus according to Claim 11, wherein said upper surface of the distal region spacing means is in use horizontal.

13. Heave relief apparatus according to any one of Claims 6 to 12, wherein the distal region of the generally tubular member is apertured to permit the passage therethrough of said abutment member.

14. Heave relief apparatus according to Claim 13, wherein the said apertures are provided by diametrically opposite vertical slots or circular holes.

15. Heave relief apparatus for the upper region of a pile bore formed in ground material, said apparatus comprising a tubular device including a cylindrical tubular member and, externally and at least adjacent one (in use lower) end of the tubular member, expansible means comprising a chamber to be in use supplied with fluid under pressure, the chamber being formed with a resiliently flexible membrane such that when in use pressurised as aforesaid it is of substantially toroidal form, said apparatus being characterised by means to restrain the expansible means against travel along the tubular member in a direction away from said one end, and being further characterised by means to be deflected outwards into engagement the pile bore upon pressurisation of the chamber and, by such engagement, to restrain-the tubular member against withdrawal from the pile bore.

16. Heave relief apparatus according to Claim 15 wherein the means to be deflected outwards comprises one or more plate-like members which engage the bore wall by digging into its surface.

17. Heave relief apparatus according to Claim 15 or Claim 16, wherein the chamber is pneumatically inflatable with air.

18. Heave relief apparatus according to Claim 15 or Claim 16, wherein the chamber is hydraulically expansible with oil.

19. A piling method employing heave relief apparatus according to any one of Claims 6 to 14, said method including the steps of: (a) providing a pile bore in the ground material; (b) inserting said generally tubular device into an upper region of the pile bore; (c) actuating said engagement means to effect interengagement between the said device and the wall of the bore's upper region; (d) placing said distal region spacing means around the generally tubular member at the mouth of the pile bore to render the axis of the generally tubular member substantially vertical (preferably substantially coaxial with the pile bore); (e) inserting into the pile bore a pile reinforcement assembly having a transverse element to be located in the vicinity of said distal region; ; (f) providing for said abutment member to extend across the generally tubular member at a location immediately beneath said transverse reinforcement element such that the latter is engageable by the abutment member if the generally tubular member rises; and (g) pouring the settable composition of the intended pile through the generally tubular member into the pile bore to embed therein the pile reinforcement assembly.

20. A piling method according to Claim 19 and substantially as herein described.

21. Heave relief apparatus substantially as herein described with reference to and/or as illustrated in Figure 1, or Figures 2 to 4, or Figures 2 to 4 with the modification of Figure 5a or Figure 5b.