FONDATION STRUCTURE AND RECTION OF TOWERS BACKGROUND OF THE INVENTION This invention relates generally to the erection of a tower and more particularly is concerned with a foundation structure for a tower. The invention is described hereinafter with particular reference to a tower which is suitable for use in a cellular communications network, but this is only by way of example, and the scope of the invention is not limited to this application.

A tower for use in a cellular network is, to the applicant's knowledge, normally erected on a massive reinforced concrete slab which is cast in a suitable hole formed in the ground.

The amount of concrete required is substantial and a time penalty is incurred while the concrete sets to a hardness which is sufficient to allow the erection of a tower on the slab.

SUMMARY OF THE INVENTION The invention provides a foundation structure for a tower which inclues a plurality of piles, each pile including a passage which extends into the ground and which is filled with a settable material and at least one anchor located in the passage and embedded in the settable material, and a base which is secured to the anchor.

The settable material is preferably concrete.

Each anchor may have a respective fastener secured to it and the fastener may be used to secure the base to the respective anchor.

The base may be made of any suitable material and in any appropriate way but, preferably, inclues opposed spaced lower and upper steel plates with a plurality of ribs or similar reinforcing or bracing members between opposing surfaces of the plates.

Fixing means may extend from an upper surface of the upper steel plate and the fixing means may be secured to a leg of a tower.

In an alternative form of the invention the base is made from concrete, which is precast or cast in situ, and the concrete is reinforced. Fixing means may extend from the concrete base.

The anchor may be a rod or a cable or any appropriate elongate member which possesses adequate properties of strength. Where use is made of a cable the cable may have a ground engaging member secured to it. The ground engaging member may provide an initial anchor to the ground and the cable may thereafter be embedded in concrete (ie. the settable material), in the manner described.

The invention also extends to a tower which has at least three legs, each leg being fixed to a foundation structure of the kind described hereinbefore.

In one form of the invention a container or housing is straddled by the legs of the tower.

In a different form of the invention the tower legs extend from within a container or housing. Preferably the legs are an integral part of the housing.

The housing may contain communications apparatus of any suitable kind used for making the tower operational.

Thus, in a preferred arrangement, the invention provides a communication structure which includes a housing which contains communication equipment, at least three tower legs which are an integral part of the housing, at least three foundation structures, each structure being of the aforementioned kind, each tower leg being fixed to a respective foundation structure, and a tower which is supported by the said legs.

The invention also extends to a method of forming a foundation structure for a tower which inclues the step of forming an elongate passage into the ground, locating at least one anchor in the passage, embedding the anchor in a settable material which is placed in the passage, and securing a base to a protruding upper end of the anchor.

Preferably a plurality of substantially parallel or relatively incline passages are formed into the ground with each passage having a respective anchor located therein, embedded in the settable material.

Preferably the base comprises a concrete slab which may be pre-cast, under controlled factory conditions.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described by way of examples with reference to the accompanying drawings in which: Figure 1 is a view in perspective of a foundation structure according to one form of the invention, Figure 2 is a side view of the structure of Figure 1 illustrating the manner in which a leg of a tower is attached to the structure, Figure 3 is a view similar to Figure 2 of an alternative arrangement according to the invention, Figure 4 is a plan view, somewhat simplified, of foundation structures for legs of a tower, Figure 5 shows a different foundation structure according to the invention, Figure 6 is a perspective plan view of a housing or container used in the erection of a communication structure, Figure 7 is a perspective view of a communication structure according to the invention, and Figure 8 shows a different view of a communication structure according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 of the accompanying drawings illustrates a foundation structure 10 according to the invention which is particularly suited for the erection of a tower in a cellular network.

The use of the invention is however not confined to this particularly application.

At a selected site four holes 12A, 12B, 12C and 12D respectively are drilled into the

ground to a desired depth which depends on prevailing geological conditions and which, by way of example, may be of the order of 8 metres. Each hole is circular in cross section and, by way of example, may have a diameter of the order of 250mm.

Steel rods 14 of appropriate dimensions are located in the respective holes 12 and a settable material of any suitable kind eg. a resin but preferably concrete 16 of an appropriate mix is then placed in the holes thereby embedding the rods in the concrete.

If necessary use may be made of spacers or positioning devices to ensure that the rods are correctly located more or less centrally inside the holes.

Each concrete filled hole with its embedded steel rod thus forms a robust pile to act as a support and foundation for a tower leg.

A preformed base 18 is then placed over the rods. The base has a lower plate 20, an upper plate 22, and a number of strengthening ribs 24 which extend between opposing inner surfaces of the upper and lower plates. The plates are formed with holes 26 and the upper ends of the rods, which are threaded, pass through the holes. Nuts 28 are engaged with the threaded upper ends of the rods thereby to secure the base to the concrete foundations.

Figure 2 illustrates the structure of Figure 1 from the side, and a lower end of a leg 30 of a tower, not shown, which has a plate 32 fixed to it. The plate has holes 34 and bolts 36 are passed through the holes and registering holes 38 in the upper plate thereby to fix the leg to base. As an alternative to this arrangement the bolts 36 can be extended, as is

indicated by means of a dotted line 40 so that, in each case, the bolt extends through the upper plate and the lower plate.

The foundation structure of the invention has a number of advantages over a conventional approach. It is formed rapidly and the amount of concrete which is used is substantially less than in a conventional approach. Once the base has been bolted to the foundation structure the tower can be erected. Substantial time is saved therefor in the erection of the tower.

Figure 3 illustrates a variation of the invention. In this case a foundation structure 10A is formed, as is the case with Figure 1, with a plurality of concrete filled passages. In this instance only one passage designated 50 is shown. As is the case with the arrangement shown in Figure 1 a hole 12 is initially bored into the ground to a desired depth. A steel cable 52, as opposed to a rod 14, is then placed in the hole. At its lower end the cable has a wedge shaped ground engaging member 54 which is pivotally attached at a point 56 to the cable. The member 54 can pivot in a way which allows the lower end of the cable to move under gravity action into the hole. When an upwards force is exerted on the cable the member 54 pivots about the point 56 and digs into the wall of the hole. The anchoring force which is exerted in this way can be substantial and can be immediately tested. The cable 52 is therefore stressed immediately and its upper end 58 is secured with a wedge- type locking arrangement 60 to the base 18 which is similar to the base shown in Figure 1. Concrete 16 is then placed in the hole 12 to embed the cable in the concrete. The approach shown in Figure 3 is twofold in that a positive anchoring force is immediately provided without the use of concrete. The magnitude of the force is determined by means

of a stressing arrangement engaged with an upper end of the cable. In addition once concrete is placed in the hole the cable is embedded in position and the arrangement is therefore similar to what has been described in connection with Figure 1.

The Figure 3 arrangement further shortens the time which is required before a tower can be erected. With the Figure 3 arrangement a tower can be erected immediately even though the concrete has not set for the restraining forces which are exerted by the stressed cables are accurately known.

Figure 4 illustrates, in plan, three foundation structures 10A, 10B and 10C respectively which are positioned at apices of an equilateral triangle. Each foundation structure is formed in the way which has been described in connection with Figures 1 and 2, or Figure 3. A respective base 18A, 18B and 18C is positioned at, and engaged with, each foundation structure. Legs, not shown, generally of the type shown in Figure 2, extend upwardly from each base and support a centrally positioned tower (not shown).

The invention is not limited to the precise constructional details shown in the attached drawings and described hereinbefore. Details of the foundation structure can be varied without departing from the scope of the inventive principles. Thus the number of holes drilled in the ground can be varied and the cross sectional size, length and inclination of each hole can be changed. The nature of the base plate can also be varied according to requirement.

Figure 5 illustrates in perspective and partly cut away a foundation structure 70 according

to another form of the invention. The steel base 18 shown in Figure 1 is dispensed with and is replace by a concrete base 72. The concrete base is cast in situ or, preferably, is precast under factory conditions. The base is suitable reinforced by means of a lattice 74 of reinforcing rods.

The base is anchored to the ground in the same way as what has been described in connection with Figure 1 although, in this case, only two holes 12E and 12F are drilled into the ground inclined to the vertical. The holes are filled with concrete and steel rods 14A are embedded in the concrete and extend through passages in the concrete slab 72.

Protruding upper ends of the steel rods are threaded and nuts, not shown, are engaged with the upper ends of the rods and are tightened to secure the slab to the rods.

The slab is fairly massive and typically has a mass of between 1000kg and 2000kg.

A plurality of bolts 74 are embedded in the concrete stab and extend upwardly at predetermined locations. A base plate 76 of a tower leg 78 is directly secured to the bolts by means of nuts 80 which are threadedly engaged with the bolts.

Although the arrangement shown in Figure 5 functions generally in the same way as the foundation structure shown in Figure 1 the former arrangement does possess a number of advantages. Firstly it has been found that, generally, it is only necessary to drill two holes 12E and 12F into the ground in order to anchor the foundation slab. The bolts 14A are sufficiently strong to give the tower which is erected over the foundation structure adequate resistance to bending forces. Secondly the concrete slab 72, which has a substantial ground-engaging area relatively to the base 18 shown in Figure 1, acts as a

load spreading component which reduces the effective pressure which is transmitted to the ground by the tower structure. As the concrete slab is fairly substantial its mass also acts as a stabilising factor.

It is of course possible to make use of cables of the type shown in Figure 3 to secure the concrete base 72 in position, instead of making use of bolts 14A, as is shown in Figure 5.

Figure 6 illustrates, in a perspective plan view, an interior of a container or housing 90 which is used with foundation structures of the type shown in Figure 1 or Figure 5 in the erection of a communication structure. The housing 90 is manufactured according to requirement or, if necessary, use may be made of a standardised shipping container. The container is filled with communication equipment under controlled conditions at a factory site. In this example the container is divided into two compartments 92 and 94 respectively and doors 96 and 98 are installed to provide access to the compartments. The compartment 92, in this example, has four substantial corner structures formed, in each case, by a lowermost component 100A, 100B, 100C and 100D respectively of legs of a tower which is shown in further detail in Figure 7. The components 100 are formed integrally with the side walls 102 of the container in that the side walls are attached to the components which, as noted, form respective corners of the compartment.

In Figure 6 a roof of the container 90 has been omitted to show its internal structure. It is to be understood that a secure roof is provided for the container in order to render the container weatherproof.

Figure 7 illustrates a communication structure 110 according to the invention which includes a mast or tower 112 erected over a container 90 of the type shown in Figure 6 which in turn is positioned over four foundation structures 70, each of the kind shown in Figure 5, although in Figure 7 only three of the foundation structures are visible.

The foundation structures 70 are constructed at predetermined positions in the manner which has been described in connection with Figure 5. Thereafter lowermost components 78 of tower legs are fixed to the respective foundation structures. The container 90 is positioned over the components 78 and the components are in turn bolted to the leg components 100A to 100D which are shown in Figure 6 and which, as noted, form an integral part of the container 90.

The tower 112 which is formed from a lattice arrangement of prefabricated sections is then erected above the housing 90 extending upwardly from the respective corners 100A to 100D of the container. The comers thus act as base portions or legs of the tower. In this example of the invention screens or bill boards 114 are attached to the tower 112 for advertising or display purposes.

The compartments 92 and 94 in the container are filled with communication equipment, standby electric generators and the like, according to requirement.

An end of the container which is remote from the compartment 92 is supported by means of concrete plinths 116 which are cast in situ depending on the terrain to ensure stability of the structure.

The arrangement shown in Figure 7 possesses a number of significant advantages. The container 90 is packed with the equipment which is necessary for erecting the tower 112 and with the communications equipment. The container, prepacked at a controlled factory site, is then transported to the erection site at which the foundation structures 70 are rapidly constructed using the techniques which have been described hereinbefore. Once the foundation structures have set the container is manoeuvred into position, as is shown in Figure 7, and is then fixed to the foundation structures and the plinths 116, whereafter the tower 112 is erected. Construction time is substantially reduced, compared to conventional construction techniques.

Figure 8 illustrates a further variation of the invention wherein a mast or tower 120 is erected directly over a framework 122 which is constructed on top of legs 124 which, in this example, are on an outer side of a container 126.

The legs extend from foundation structures 128 which may be of the type shown in Figure 1, Figure 3 or Figure 5. The container 126 houses communication equipment which can be accessed through a door 130.

The use of the container is of course optional although it is a preferred feature particularly for the erection of communication towers in remote areas. On the other hand if a relatively simple structure is required, eg. a standalone tower, then the tower can be constructed so that it extends directly upwardly from foundation structures of the type shown in Figure 1 or Figure 5 and under these conditions there may be no need for an intermediate container structure for housing electronic or other equipment.