A PILE AND METHOD OF CONSTRUCTING THE SAME

The present invention relates to a pile, a method of constructing the same, and to apparatus for constructing a pile.

It is known to construct a cast in situ pile foundations by forming a bore in the ground to a required depth and filling the bore with uncast, or wet, concrete so that on hardening a cast concrete pile is formed. Typically, a rotary auger forms the bore in the ground. The auger can be withdrawn from the bore prior to concrete filling or the auger may comprise a central conduit for concrete so that the bore can be filled with concrete as the auger is withdrawn.

The term cast concrete pile, or cast in-situ pile, means that the concrete is cast in the bore and not pre-cast prior to insertion in the bore.

Over the course of time a site that has been previously developed may be reused for the construction of subsequent buildings, for instance for redevelopment. It is preferable when an existing building is demolished that piles used as the foundation of the existing building are re-used for subsequent buildings. However, the condition of concrete piles may decrease over time and if piles are to be re-used, then it is important that thejr condition can be tested to ensure they can withstand the required loading. Piles are tested by extracting samples of the pile along its length and analysing the condition of the samples. Preferably, samples are taken of the ground adjacent the piles at various depths to check for consolidation and loading capacity.

Hereto, it has not been practical to test cast concrete piles in situ and therefore it is normal practice to remove existing piles or construct additional piles prior to building construction.

The present invention provides a method of constructing a pile, the method comprising: forming a bore in the ground to a required depth; disposing a longitudinal cavity forming means in the bore; filling the bore with uncast concrete so that, on hardening, a cast concrete pile is formed in the bore, the pile having a longitudinal cavity permitting access to the pile along at least a portion of its length.

The present invention also provides a bored cast concrete pile, comprising concrete cast in situ and having a longitudinal cavity which extends substantially along a longitudinal extent of the pile to allow access to the pile along at least a portion of its length.

The present invention also provides apparatus for forming a pile with a substantially longitudinal cavity, the apparatus comprising boring means for forming a bore in the ground to a required depth; and a longitudinal cavity forming means for insertion in the bore; wherein when the bore is filled with uncast concrete, on hardening, a cast concrete pile is formed in the bore, the pile having a longitudinal cavity which permits access to the pile along at least a portion of its length.

Additionally, the present invention provides a method of increasing loading capacity of a pile, the method comprising: extending a depth of the pile after said pile is constructed by forming an extended bore with increased depth and/or width underneath said pile; and at least partially filling said extended bore with uncast concrete.

Further, the present invention provides a method of controlling environmental conditions in a building of which a pile forms a foundation, wherein an environmental control fluid which is used for controlling environmental conditions in said building is circulated within said longitudinal cavity so that the ambient conditions in said cavity affect a condition of said control fluid.

In order that the present invention is well understood, an embodiment thereof, which is given by way of example only, will now be explained with reference to the accompanying drawings, in which:

Figure 1 shows a bore formed in the ground for a pile;

Figure 2 shows the bore with concrete at the bottom;

Figure 3 shows the bore, a longitudinal cavity forming means and reinforcement members; and

Figure 4 shows the bore filled with concrete.

The Figures show one example of the method steps involved in constructing a pile and the apparatus required for performing those steps.

Referring to the Figure 1 , a bore 10 is formed in the ground to a required depth by suitable boring equipment. An auger can be used for this purpose. The shape, width and depth of the bore are calculated according to the loading characteristics which the pile must sustain. As shown the bore is generally cylindrical, but other shapes are possible. For instance, a bore with triangular, square or octagonal cross-section may be formed. Further, an underream (not shown) may be formed under the bore.

Depending on the characteristics of the soil, the walls of the bore may require reinforcement to prevent the surrounding earth from collapsing into the bore. If reinforcement is required, it can be removed prior to introduction of concrete or left in situ. A bentonite slurry can be used to fill the bore to prevent collapse. A wet clay soil on the other hand may not require reinforcement as the soil particles are sufficiently cohesive to prevent collapsing.

A plug 12 of concrete is deposited at the bottom of the bore as shown in Figure 2 so that the concrete occupies substantially the entire bottom of the bore. Although concrete is shown for this purpose, other material may be used provided it is substantially impermeable to liquid. The purpose of the plug 12 is described in more detail below.

Referring to Figures 3 and 4, a longitudinal cavity forming means, such as a tube or cylinder 14, is inserted into the bore 10 with a suitable jig. The tube 14 is positioned generally co-axially with the bore and extends substantially along a longitudinal extent of the pile. The jig can be retained in position to fix the tube- during concrete filling. Alternatively, as shown, the tube 14 extends into plug 12 and/or into the earth at the bottom of the bore to provide stability to the tube and fix it in relation to the bore when the bore is filled with uncast concrete. Plug 12 can be cast at one longitudinal end of the tube prior to inserting the tube into the bore, or the tube can be inserted into the bore containing an uncast concrete plug, which is then allowed to hydrate fixing it to the end of the tube.

The longitudinal cavity forming means forms a longitudinal cavity 16 in the cast concrete pile as shown in Figure 4 when the uncast concrete has hydrated. The longitudinal cavity forming means can take a variety of forms, although tube 14 is the

currently preferred form, whilst still allowing access to the pile after construction. For instance and without limitation, the longitudinal cavity forming means may comprise a tube with a non-circular cross-section such as triangular square or octagonal. The longitudinal cavity forming means may comprise a diaphragm or other flexible member which is arranged to create a longitudinal cavity in the finished pile. For instance, the diaphragm can be positioned in the bore and inflated with a fluid to the required shape. The longitudinal cavity forming means may consist solely of a diaphragm or one portion of an otherwise solid structure can be replaced with a diaphragm. This latter arrangement may be desirable if an irregular shaped cavity is required.

The longitudinal cavity forming means may be arranged to form a cavity which extends downwardly from bore 10 as shown into an underream or other formation. The simplest arrangement comprises a longitudinal cavity forming means which extends downwardly from the bore for extending the longitudinal cavity into the underream. Alternatively, the longitudinal cavity forming means is designed to provide a cavity which expands outwardly in a downwardly direction to follow the wal of the underream. A diaphragm can be used for this latter purpose.

Tube 14 may be made from metal, such as steel, plastics or cardboard or any other suitable material. A strong material such as steel is desirable if the tube is to be retained in situ and contribute to the overall strength and loading characteristics of the finished pile. If a weaker material such as cardboard is used, the lower end of the tube is preferably fitted with a shoe (not shown) to assist penetration of the tube into the earth at the bottom of the bore.

The longitudinal cavity forming means provides a boundary so that uncast concrete can be filled between the longitudinal cavity forming means and the ground in which the bore is formed in order to shape the concrete and produce a pile with the required internal dimensions. In this regard, the longitudinal cavity is sufficiently wide to allow a testing tool access to the longitudinal cavity so that cast concrete can be tested at a time after construction. Preferably, the longitudinal cavity is sufficiently wide to allow a person access to the longitudinal cavity so that cast concrete can be tested at a time after construction.

The longitudinal cavity forming means as shown is open at an upper end thereof. However, if desired the longitudinal cavity forming means may be closed at one or both ends. If the longitudinal cavity forming means is closed at an upper end and the longitudinal cavity forming means is left in situ in the finished pile, the closure is preferably such that that end can be readily opened to permit access to the cavity. It is preferable that the longitudinal cavity forming means is open at an upper end to permit the cavity to be filled, as described in further detail below.

Reinforcing members 18 are provided in the space between the tube 14 and bore wall for reinforcing the cast concrete of the pile. The reinforcing members may comprise fibres or steel. Reinforcing members are not always required in piles, since an unreinforced concrete pile may be adequate to achieve the necessary performance characteristics. If reinforcing members 18 are provided they can be fixed to tube 14 to facilitate insertion in the bore. Alternatively, the reinforcing members can be inserted separately.

Referring to Figure 4, bore 10 is filled with uncast or wet concrete 24 in the space between the bore wall and the tube 14. As described above referring to

Figure 2 the tube 14 is embedded in the bottom of the pile bore or in plug 12 to resist upward movement, or floating, of tube 14 during concreting. Floating occurs when there is insufficient friction generated between the wet concrete and the reinforcing 18 (if present) or tube 14. In an alternative method to avoid floating, the plug 12 acts to seal the bottom end of tube 14 so that the tube can be filled with a liquid such as water to provide a ballast.

Vibrators 20 are used to work or compact the concrete so that the wet concrete fully takes up the space between the tube 14 and the bore wall thereby reducing the occurrence of voids in the cast concrete. The vibrators may be positioned on an internal surface of the tube 14 or alternatively the tube as a whole can be vibrated from the surface.

As shown in Figure 4, the cast concrete 24 of the pile forms an annulus around a circumference of the longitudinal cavity thereby forming a hollow pile. The annulus is generally circular in lateral cross-section] The shape of the cast concrete is not restricted to a circular cross-section or to an annulus, provided it is shaped to permit access to the pile along at least a portion of Its length after the pile is constructed. For instance, an annulus may be triangular, square or octagonal in lateral cross-section. Although the cast concrete is preferably hollow, it is not required that the concrete fully surrounds the cavity[ The concrete may be open along a side and additionally provided with means tø prevent the ingress of earth into the cavity 16. Such means may comprise a plate farmed from steel or other material.

During or after concrete hydration additional lconcrete may be filled at the bottom portion of tube 14, as shown in Figure 4, to form a base formation 22. The

base formation 22 contributes to the loading capacity of the pile by providing full base capacity.

Although not currently preferred the bore may first be filled with wet concrete and the longitudinal cavity forming means inserted secondly.

In the finished pile, the concrete is open at its upper end, or can be opened, to permit access to the longitudinal cavity 16 and thereby access to the pile along its length. In accordance with building regulations in some countries, a void should not remain under the ground after construction to avoid damage by expanding gases etc. Accordingly, it is preferred that the pile is filled with a filling after construction and closed at the upper end portion thereof. The filling is any suitable material such as water or polystyrene foam. The filling may be the same liquid as that used for a ballast. The upper end portion of the pile is closed in any suitable manner such as by concrete or a steel plate. When it is required to test the pile, the closure and filling are removed to provide access to the pile. Such access enables testing of the concrete 24 of the pile, the surrounding earth or the reinforcing members 18 at a time after the pile is finished so that if it is desired to re-use a site for a subsequent building or structure the pile can be assessed. The longitudinal cavity 16 is sized to permit testing tools or a person to be lowered to test the condition of the concrete or surrounding soil.

Therefore, it is possible to re-use the pile rather than removing the pile and constructing another pile or constructing additional piles on the site. Accordingly, a pile as described with reference to the Figures reduces the cost and time required for re-using a site for subsequent building.

When a site is to be used for a subsequent building or structure, it may be found that the originally designed loading capacity of the pile is not sufficient for the subsequent structure. The pile described permits a method of increasing or modifying a loading capacity of the pile. Since the pile has a longitudinal cavity a depth of the pile can be extended after the pile is constructed by passing boring equipment down the cavity and forming an extended bore with increased depth and/or width underneath the pile and at least partially filling the extended bore with uncast concrete. Such a method provides a deeper pile with increased loading capacity.

Environmental conditions in a building may be controlled by use of the thermal mass of the ground under or in the vicinity of the building. Since the currently described pile provides a longitudinal cavity which extends into the ground, the pile can beneficially be used to control such environmental conditions in a building of which the pile forms a foundation. An environmental control fluid which is used for controlling environmental conditions in the building is circulated within the longitudinal cavity so that the ambient conditions in the cavity affect a condition, such as temperature, of the control fluid. If the ambient conditions in the cavity are cooler than in the building, for instance at night, an air conditioning system of the building can circulate a fluid which is cooled by circulation in the longitudinal cavity. If the ambient conditions in the cavity are warmer than in the building, for instance during daylight, a heating system of the building can circulate fluid which is heated in the longitudinal cavity.

As the longitudinal cavity is pre-formed in the pile, piping can readily be installed in the ground, avoiding the requirement to form additional bores in the ground for the piping.