A METHOD AND APPARATUS FOR FORMING FOUNDATIONS

Abstract: A method of forming a foundation with a hollow-section reaming tube (100). The method includes drilling a pilot bore-hole to a required depth and reaming the pilot borehole by rotating the hollow section reaming tube which is subsequently not retracted. The hollow section reaming tube (100) comprises at least one tube section (103) adapted to connect with another tube section (102) via corresponding screw threads (104).

Description: A METHOD AND APPARATUS FOR FORMING FOUNDATIONS The present invention relates generally to forming foundations, and more particularly, but not exclusively, to the formation of foundations for the purpose of mounting railway signalling posts and the like thereto. Foundations formed according to the invention may, however, be used for many purposes, not just limited to railway applications, but also applications in many other industries, for example, highways, airports, civil structures. 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). The 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. In accordance with an 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 hollow-section tube which is not retracted and remains in the ground; and securing a load-bearing mounting platform to the end of the tube. The method preferably includes the steps of: reaming the pilot bore-hole with a hollow-section steel tube, comprising a plurality of tube sections which are interconnected via mutually mating screw threads; and mounting a signalling post to the load-bearing mounting platform. In accordance with another aspect of the present invention, there is provided a foundation forming apparatus including: a hollow section reaming tube comprising at least one tube section adapted to connect with other tube sections via corresponding screw threads; a displacing tube section with an end shaped to displace material; a rotary mechanism for providing a torque to an end of the reaming tube distal from the displacing tube section; and a terminal tube section. The terminal tube section preferably includes, or is adapted to receive, a load- bearing mounting platform. The present invention further provides a method of forming a foundation, comprising the steps of rotating a hollow-section tube into the ground to form a support, and securing a load-bearing mounting platform to the end of the tube. 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 1 including a reaming tube; Figure 3 is a partially exploded view of the reaming tube, terminal tube 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; and Figure 8 shows the displacing tube section in operation. 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. In an embodiment of the present invention, the reaming tube consists of several tubular steel sections of lm 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. In one non-limiting example, a pilot bore-hole of diameter 185mm 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 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 110 (the diameter of which is less than the diameter of the reaming tube) by displacing the outer section 125 until the tube 100 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 cork-screw fashion has the advantage over the conventional technique of pile-driving (ie hammering), that the same plant equipment, ie rig 110, 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. 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 110 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 110. 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 of tube 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 lm 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 terminal tube section 140 is screwed into the exposed open end of the 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 maybe 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 of the 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. 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 105. 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 advantages of the present invention can be summarised as follows: 1. The auger and steel reaming tube sections are preferably in easily manoeuvrable sections eg, but not necessarily, in the range of 250mm to in excess of 3m, preferably lm in length, to restrict the overall height of the operation. 2. It is an all dry process therefore no curing time is required since there is no concrete or grout. 3. Limited spoil to dispose of. 4. Rapid installation. 5. Manoeuvrable rig for sites and locations with restricted access. 6. Permanent support to the ground during installation which prevents side collapse of the hole and possible vertical displacement at surface. 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. 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. h a variation, a plurality of tubes can be installed over an area, to support a common superstructure (ie several tubes support a single load-bearing 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.

Claims: CLATMS 1. A method of forming a foundation including the steps of: forming a bore-hole to a required depth; reaming the pilot bore-hole with a rotating hollow-section tube which is not retracted and remains in the ground; and securing a load-bearing mounting platform to the end of the tube. 2. A method as claimed in Claim 1, wherein the hollow-section tube is rotated into the ground. 3. A method of forming a foundation as claimed in Claim 1 or 2, wherein the method includes the step of reaming the pilot bore-hole with a hollow-section tube. 4. A method of forming a foundation as claimed in Claim 1 , 2 or 3, wherein the hollow-section tube comprises a plurality of tube sections connected longitudinally. 5. A method as claimed in Claim 4, wherein the plurality of tube sections are interconnected via mutually mating screw threads. 6. A method of forming a foundation as claimed in any preceding claim, wherein the hollow-section tube is steel tube. 7. A method of forming a foundation as claimed in any preceding claim, wherein a structure is mounted to the load-bearing mounting platform. 8. A method of forming a foundation as claimed in Claim 7, wherein the structure is a signalling post. 9. A method of forming a foundation as claimed in any preceding claim, wherein the hollow-section tube includes an end shaped to displace material. 10. A method of forming a foundation as claimed in any preceding claim, wherein the pilot borerhole is drilled using a mobile rig that includes an auger, and wherein the auger is removed prior to reaming and replaced by the hollow-section tube once the desired pilot hole depth has been reached. 11. A method of forming a foundation as claimed in any Claim 1 to 9, wherein the pilot bore-hole drilling directly precedes reaming by the hollow-section tube in a continuous operation, and wherein no intermediate auger replacement occurs. 12. A method of forming a foundation as claimed in any preceding claim, wherein a jig is secured over the pilot hole to facilitate firm and secure rotation of the hollow-section tube. 13. A method of forming a foundation as claimed in any of Claims 5 to 11, wherein an adhesive is used to aid connection of tube portions. 14. A method as claimed in any preceding claim, wherein the bore hole is formed by the action of rotating the hollow section tube into the ground. 15. A method of forming a foundation, comprising the steps of rotating a hollow- section tube into the ground to form a support, and securing a load-bearing mounting platform to the end of the tube. 16. A foundation forming apparatus including: a hollow section tube comprising at least one tube section adapted to connect longitudinally with other tube sections; a displacing tube section with an end shaped to displace material; a rotary mechanism for providing a torque to an end of the reaming tube distal from the displacing tube section; and a terminal tube section. 17. A foundation forming apparatus as claimed in Claim 15, wherein the terminal tube section includes, or is adapted to receive, a load-bearing mounting platform. 18. A foundation forming apparatus as claimed in Claim 16 or 17, wherein the displacing tube section flares from a diameter equal to. the diameter of the reaming tube to a diameter greater, and then tapers to a diameter less than the diameter of the reaming tube. 19 A foundation forming apparatus as claimed in any of Claims 15 to 18, wherein the apparatus further includes a mobile jig including an auger, the auger being removable for replacement with the hollow section reaming tube prior to reaming, and wherein the mobile ig is adapted to operate in locations with restricted access such as railway track-side locations or highways.

Inventors: GORDON CLARK, GORDON, CLARK
Applicants: ASPIN FOUNDATIONS LTD, GORDON CLARK, ASPIN FOUNDATIONS LIMITED, GORDON, CLARK
Application year: 2001
Main classification: E02D27
IPC codes: E02D7, E02D27