GB2411909A - Tubular foundation element - Google Patents

Abstract

A foundation element 500 comprises a hollow-section tube 501 adapted to connect longitudinally with similar tubes, and at least one radially extending projection 502, 503 adapted to distribute axial loads. The projection preferably projects both outwards and inwards from the exterior and interior of the tube respectively. The projections may comprise a helical vane, possibly comprising a helix. The vane may extend normal to the side of the tube. Also claimed is a method of forming a foundation with a foundation element which has a radially extending projection and which is not retracted, wherein a load-bearing mounting platform is secured thereto. A further method is claimed wherein a pilot bore-hole is drilled and subsequently is reamed by a rotating foundation element.

Description

. .e Be: I: - . .

A FOUNDATION ELEMENT

The present invention relates generally to forming foundations. Foundations formed according to the invention may have applications in many industries, for example: railways, S highways, airports, civil structures etc. The foundations may be for a variety of superstructures, such as lighting columns, telecommunications masts, gantries, barriers, or other structures.

Conventionally, railway signalling posts have been secured to a concrete plinth set within the ground adjacent to the railway tracks. A foundation hole once drilled is filled with concrete and this is capped-off with the concrete plinth. Once the concrete (or grout) has dried and hardened (usually after about 2 weeks) steel bolts which are set within the plinth are able to receive a base platform of the signalling post (or other such structure).

T he problem with the above method is that it is a distinct three-stage process; the particular section of railway track must be closed to traffic on three separate occasions: when undertaking preliminary site investigation works, when drilling the foundation, and when pouring the concrete plinth. This is often a disruptive and highly costly process.

Consequently, it is desirable to have a method of erecting railway signalling posts and the like, in a single stage such that track closure is minimised but signalling post stability and integrity are maintained.

One such method is disclosed in WO-A-03/038198. This system works welt although the foundations formed by this method are limited by the magnitude of the tension and compression loads that can be borne.

In accordance with an aspect of the present invention, there is provided a foundation element comprising a hollow-section tube adapted to connect longitudinally with other hollow-section tubs, and at least one radially extending projection adapted to distribute axial loads. ..

eë ee - 2 The projection may be on the exterior surface of the tube and project outwards, and/or on the interior surface and project inwards. Thus, in some embodiments, both inwardly and outwardly extending projections may be used.

In accordance with another aspect of the present invention, there is provided a method of forming a foundation including the steps of: drilling a pilot bore-hole to a required depth; reaming the pilot bore- hole with a rotating foundation element, which includes a radially extending projection adapted to distribute axial loads, and which is not retracted and remains in the ground, and securing a load-bearing mounting platform to the end of the tube.

In accordance with a further aspect of the present invention, there is provided a method of forming a foundation, comprising the steps of rotating a hollow-section foundation element, which includes a radially extending projection adapted to distribute axial loads, into the ground to form a support, and securing a load-bearing mounting platform to the end of the tube.

Preferably, the projection comprises a substantially helical vane.

Thnge most preferably subtends an angle of 360 or less. That is, it is formed as mingle hollow disc, cut radially, and the resulting ends pulled in a respectively opposite direction perpendicular to the nominal plane of the disc to form a single-turn helical vane.

In other embodiments a helix subtending more than 360 may be used.

The vane may be disposed on an outer circumferential surface or an inner circumferential surface of the hollow-section tube.

Alternatively, the foundation element may include a vane on both the inner and outer circumferential surfaces of the hollow-section tube.

8 8 8 8. . a 8 8 8' 8 8 8 8 8 8 e 8 c 8 8.8 c 8 8 8 8 8 8 8. 8 8. 8 - 3 According to the present invention in a further aspect, there is provided a foundation element comprising a hollow-section tube and at least one single-turn helical vane mounted to project externally and/or internally from the tube surface.

According to the present invention in a further aspect, there is provided an apparatus or method comprising any one or more of the novel features described herein.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: Figure 1 is a side view of a drilling rig; Figure 2 is a side view of the drilling rig of Figure I including a reaming tube; Figure 3 is a partially exploded view of the reaming tube, terminal tu8De section and mounting platform; Figure 4 is a plan view of a securing jig; Figure 5 is a sectional view of a signalling post in place after installation; Figure 6 is a schematic force diagram showing the lines of action on a reaming tube within the ground; Figure 7 is an elevation view of a displacing tube section; Figure 8 shows the displacing tube section in operation; Figure 9 shows a foundation element; Figure 10 is a sectional view of the foundation element of Figure 9 including an inner and art outer projection; Figure 1 OA is a plan view of the foundation element of Figure 10; Figure 11 is a sectional view of a foundation element including an outer projection only; Figure 1 1A is a plan view of the foundation element of Figure 1 1; Figure 12 is a sectional view of a foundation element including an inner projection only; and Figure 12A is a plan view ofthe foundation element of Figure 12.

. c c.

c c c c * c c c c c c c. c c c c c c Referring to Figures 1 and 2, a drilling rig 10 includes a mast 20 and a platform 15 with a ram 30 connected therebetween. The rig is most preferably self-propelled.

Attached to the mast 20 is a rotary drive means in the form of a motor 60 for providing rotary power to an auger 70.

The rig 10 can be manoeuvred via caterpillar tracks 40 and control means 50. An operator controls the rig through manipulation of control levers 51. The control means 50 can be mounted on the rig 10 as shown, or it may be independent and remote from the rig but connected to the rig via a suitable control line.

The motor 60 is slidably supported on a jib element 21 which is adapted to traverse up and down the mast 20, thus giving control over drilling depths. Again, movement of the jib 21 is controlled via the control means 50 and the levers 51.

In a foundation installing operation, the rig 10 is manoeuvred into place until the auger 70 is positioned over the desired spot. A pilot hole 110 is then bored out to a desired depth (shown as 115 for convenience). Drilling a pilot hole enables investigation of the type and parameters of the material surrounding the location of the foundation site. The depth of the pilot hole depends on these parameters, and these are determined on site.

The auger 70 is withdrawn from the pilot hole, detached from the motor 60 and replaced with a reaming tube 100. The reaming tube 100 is coupled to a screw thread 80 disposed on a lower portion of the motor. For clarity, the tube 100 is depicted as a single unit, whereas it will in general consist of a plurality of tube sections as shown in Figure 3.

The reaming tube consists of several tubular steel sections of Im in length. Each tubular section has an external diameter of 220mm, the internal diameter is dictated by the thickness of the outer wall of the tube; wall thickness will be determined by the strength of the tube required and corrosion rate analysis in a given application.

. ee. ce: A: . . ë e ë ee - 5 In one example, a pilot bore-hole of diameter 1 85mm will be sunk to the required depth. The reaming operation will then extend the diameter of the hole to 220mm.

Each reaming tube section 101 to 103 has an outer screw thread 104 which mates with an internal screw thread 105 of an adjoining section. Alternatively, the tube segments can be joined by other means, such as clips, bolts, welds or others.

In operation, a displacing tube section 106 will act to displace the surrounding soil l O as it travels down the pilot bore-hole, see Figure 8.

The reaming tube 100 is rotated downwards into the soil 200, consequently reaming the pilot hole 1 10 (the diameter of which is less than the diameter of the reaming tube) by displacing the outer section 1 25 until the tube 1 00 reaches a desired depth 115. At this stage (the diagram is not to scale for simplicity) the proximal end of tube section 103 will be at a particular specified level (eg ground level).

Rotating ("spinning") the reaming tube 100 into the ground in a corkscrew fashion has the advantage over the conventional technique of piledriving (ie hammering), that the same plant equipment, ie rig 1 10, is used for both pilot bore-hole drilling and the implanting of the foundation itself, namely, the reaming tube 100.

To prepare a given foundation, only the rig and the relevant number of reaming tube sections are required; no pile-driving or concrete pouring equipment is needed. The tube 100 itself provides the foundation, no concrete, grout or other filler is necessary.

During operation, the rotary drive means 60 rotates the reaming tube 100 in a sense that tends to tighten the connection between the tube sections 101-103. Furthermore, usually (but not always) a structural glue will be used to aid adhesion between adjacent tubes sections. A typical structural glue is an epoxy adhesive, an example of which is made by FEB Limited.

c c c c c c c c. c .c c c c c c c c c c c c c c c c - 6 Lateral loads to the tube are resisted during insertion into the ground due to the rotation applied in the reaming process.

During rotation of the reaming tube, the displacing tube section 104 displaces the ground 200 surrounding the bore hole. There are no restrictions to the depth to which the tube may be sunk, or to the diameter of the tube itself.

During operation, as shown in Figure 8, the displacing tube section 106 (bit 106) enlarges the pilot bore-hole 1 10 to the larger diameter hole 120. The displacing tube section includes an outer screw thread 107 for mating with thread sections 104. Section 106 flares from a diameter equal to the diameter of the reaming tube to a diameter greater, and then tapers to a diameter which is less than the diameter of the pilot bore-hole 1 10.

This profile assists in displacing the soil surrounding the pilot hole.

An initial reamed area 125 is produced, of diameter roughly the same as the widest diameter of bit 106. This exists for a short period only. After a certain time the soil at the circumference of the hole 120 will 'relax' back to a position where the soil and the outer surface of the reaming tube 100 are in close contact. The close contact between tube and soil gives rise to the adhesion forces 215, as discussed above.

The displacing tube section 106 along with the entire reaming tube 100 remain buried in the soil.

In general, the number oftube sections 101 to 103 will depend on the nature and depth of the foundation required. An example might be to ream a 5m bore hole using five l m tube sections.

Once the desired depth of hole has been reached, the motor 60 is detached from the ultimate tube section by reversing the motor and thus undoing the final internal screw thread 105 from the thread 80.

a. . . e b e I e e e e I - 7 A terminal tube section 140 is screwed into the exposed open end ofthe embedded reaming tube 100; this will preferably have been pre-welded to a hollow, steel box section support platform 150. Alternatively, the support platform may be secured to the tube, once the tube is in place in the ground. To this platform many types of structural posts and supports may be secured. In particular (as shown in Figure 5), a track side railway signalling post 300 is bolted to the support platform 150. Many different types of supports or heads can be affixed to the tubes in site. One example is a levelling screw baseplate connection. Baseplates will usually be mounted at approximately ground level.

In practice, signalling posts and the like will be secured to the platform 150 via heavy gauge mounting bolts 160 which are threaded through the signalling post base 310 and are anchored to the platform 150.

Figure 6 shows a schematic diagram of the types of forces acting on the tube 100 in a typical foundation scenario.

The tube 100 is forced into the ground 200 by vertical load 230 assisted by an applied torque 225.

For simplicity, the ground in the vicinity of the foundation site is split into an upper strata 201 and a lower strata 202. These may be of different material, eg lower strata 202 may be generally clay-based, whereas upper strata 201 might be of lighter, sandy, material,

for example.

Shear forces 220 are resisted by the lateral support forces 250 provided by the surrounding soil in strata 201. Below this in strata 202 vertical load 230 (corresponding to the weight ofthe supported post) is resisted by adhesion forces 215 and end bearing forces 260.

Furthermore, bending moments 240 are resisted by the lateral forces 250 in addition to the mechanical resistance of the hollow steel tube 103.

. .: : - 8 Figure 6 includes the terminal tube section 140.

Applied bending moments to this section are prevented from causing a hinge failure to sections below the ground level by the mechanical integrity of the hollow steel tube 100 and the lateral support forces 250.

To facilitate firm and secure rotation of the topmost tube section during operation, a jig 400 is provided which sits above the pilot hole at ground level, see Figure 4.

The jig 400 comprises a base plate 410 which is bolted to the ground over the hole via bolts 420. The pilot hole 110 is surrounded by chuck-type jaws 425 whose inner most circumferential edge 430 delimits the reaming tube diameter 120.

As the successive sections 102 and 103 are inserted, the jig grips each section with sufficient pressure to allow the torque to be transferred downwards to the cutting end but also to prevent any slipping between thread 80 and section thread l OS.

In certain situations, it is envisaged that the pilot bore-hole and reaming operation will take place together with an auger preceding the reaming tube and then removed when the desired depth is reached, or alternatively the tube alone may be spun (rotated) into the ground without the necessity of a pre-bore.

instead of using a displacing type bit, having a widened (bulged) portion, as described above, a cutting bit may be used.

The tubes may be of any desired diameter and wall thickness.

Whilst the tubes are currently proposed to be of steel, or other metal, they may alternatively be of other materials, including, but not limited to, plastics materials, polymer, GRP, etc. , ce c:. ee:: ..

. . . Where they are made of possibly corrosible material, then corrosion analyses can be made for each tube and corrosion protection can be provided, eg by cathodic protection, galvanising or by the use of other protective techniques or paint applications, as will be known in the art.

In a variation, a plurality of tubes can be installed over an area, to support a common superstructure (ie several tubes support a single loadbearing platform).

Apparatus according to the invention may be connected to the hydraulic arm of a machine which is conventionally known as a road/railer machine, and which can then be used to make foundations according to embodiments of the invention.

In a modified apparatus, the reaming tube l O l and the bit 106 are replaced by a foundation element 500 as shown in Figures 9 to 12A.

The foundation element 500 comprises a hollow-section tube 501 and projecting vanes 502, 503. The hollow-section tube 501 is essentially the same as any of the reaming tubes described above, with the exception that the addition of a projecting vane modifies it into a foundation element. Both the inner and outer projecting vanes have a helical profile, and are attached by welding (or any other suitable joining process) to an inner circumferential surface and an outer circumferential surface ofthe tube 501 respectively.

Typically, the vanes are fabricated from the same material from which the tube has been constructed. However, in certain circumstances it may be necessary to fabricate the vanes from a harder material than the tube.

A foundation element may include an outer projecting vane 502, an inner projecting vane 503, or both. The combination of vanes included (as shown in the Figures) will be dependent upon the magnitude of the axial compression and tension loads of a particular situation. Also, the depth D' and D2, which represent the distance between the end of the tube and the outer and inner projecting vanes respectively, may be altered to suit the requirements of the particular foundation in question; the type of subsoil, ground conditions . ë: . :: . . . . - 10 and structure to be mounted will all have a bearing on the number and placement of the vanes.

In use, a reaming tube 100 including a foundation element 500 is rotated downwards into the soil 200 as described above. The foundation may be 'spun' into a smaller pre-bored pilot hole, or directly into undisturbed soil, as described above.

However, with the modified reaming tube, the outer projecting vane 502, due to the helical profile, will cut a spiral channel in the soil as the reaming tube descends into the earth.

Where the reaming tube is to be 'spun' into undisturbed soil (i.e. no pilot bore), the inner projecting vane 503 will cut an inner spiral channel in a similar fashion to that described above for the outer projecting vane 502. In the case where a pilot bore-hole already exists, the inner projecting vane 503 cuts into the subsoil at the desired depth 115.

As a consequence of the addition of the outer projecting vane 502, the axial compression load is distributed over a wider surface area, thus enabling the foundation to bare a greater load. Likewise, the inner projecting vane 503 also helps to disperse the load over a greater surface area.

Greater tension loads are also resisted since any upward force exerted on the foundation will be 'pulling' on a much wider surface area of subsoil, and therefore increasing the overall resistance to axial tension loads.

On-site testing of foundations using the modified foundation element has revealed that axial load carrying capacity can be increased by up to five times that of an unmodified foundation.

The vane most preferably subtends an angle of 360 or less. It may be formed from a single hollow disc, or annulus cut radially, and the resulting ends pulled in respectively opposite directions perpendicular to the nominal plane of the disc to form a single-turn helical vane. In other embodiments a helix subtending more than 360 may be used. The vane may alternatively be moulded or otherwise formed in its helical shape. - 11

Claims (16)

1. Claims 1. A foundation element comprising a hollow-section tube adapted to

   connect longitudinally with other hollow-section tubes, and at least one radially extending projection adapted to distribute axial loads.
2. 2. A foundation element as claimed in claim 1, wherein the projection is on the exterior surface of the tube and projects outwards.
3. 3. A foundation element as claimed in claim 1, wherein the projection is on the interior surface and projects inwards. . ë
4. 4. A foundation element as claimed in claim 1, wherein the foundation element . includes a projection on the outer surface projecting outward, and a further projection on 15 the interior surface projecting inwards. :e

   A'' .
5. 5. A foundation element as claimed in any preceding claim, wherein the or each projection comprises a substantially helical vane.
6. 6. A foundation element as claimed in claim 5, wherein the or each vane subtends an angle of 360 or less.
7. 7. A foundation element as claimed in claim 5, wherein the vane comprises an annulus, opposing ends of which are displaced in a direction perpendicular to the nominal plane of the annulus.
8. 8. A foundation element as claimed in claim 5, wherein the vane subtends an angle of more than 360 so as to form a helix having more than a single turn.
9. 9. A method of forming a foundation including the steps of: drilling a pilot bore-hole to a required depth; reaming the pilot bore-hole with a rotating foundation element, which includes a radially extending projection adapted to distribute axial loads, and which is not - 12 retracted and remains in the ground; and securing a load-bearing mounting platform to the end of the tube.
10. 10. A method of forming a foundation, comprising the steps of rotating a hollow section foundation element, which includes a radially extending projection adapted to distribute axial loads, into the ground to form a support, and securing a load-bearing mounting platform to the end of the tube.
11. 11. A method as claimed in claim 9 or 10, wherein the projection comprises a substantially helical vane.
12. 12. A method as claimed in claim 11, wherein the vane is disposed on an outer circumferential surface or an inner circumferential surface of the hollow-section tube.

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    l5
13. 13. A method as claimed in claim 11, wherein the foundation element includes a vane on both the inner and outer circumferential surfaces of the hollow- section tube.

    '..
14. 14. A foundation element comprising a hollow-section tube and at least one single-turn

    I

    helical vane mounted to project externally and/or internally from the tube surface.
15. 15. A foundation element substantially as hereinbefore described with reference to, and as illustrated by the accompanying drawings.
16. 16. A method of forming a foundation, substantially as hereinbefore described with reference to the accompanying drawings.