Methods for providing piled foundations for constructions, piled foundations and a balloon for providing an enlarged footing

Field of the invention The present invention relates to a method for providing a single piled foundation for constructions and a method for providing a multi piled foundation for constructions.

The present invention relates to a single piled foundation and a multi piled foundation and to a balloon for providing an enlarged footing of said foundations

Background of the Invention When founding large constructions such as e.g. houses, walls, tower elements, and similar building structures, a foundation supported by a number of foundation piles is typically used, where the piles are placed in the ground for supporting the foundation and for absorbing the compressive and tensile forces caused by wind loads and the dead weight of the constructions.

For absorbing the compressive forces, typically smooth foundation piles are used that are driven down into the earth until they hit a firm substratum. This implies that in some places, many metres of foundation pile are required before the bottom of the foundation pile reaches a firm bed. Therefore, it may be a very expensive method of founding a building construction.

For founding in areas where geological analyses show that there is a long distance down to a firm bed, another type of foundation pile is used, where the foundation pile is provided at its lower end with a footing element having a diameter larger than the diameter of the foundation pile itself. This means that the foundation pile is provided with a large area over which the pressure is distributed, and the footing element makes it more difficult for the pressure caused by the dead weight of the building structures to press the foundation pile further down into the ground.

Since it is not possible to drive down a foundation pile having an enlarged footing element or to press such a foundation pile down through a pre-drilled hole, different solutions have been proposed for placing a foundation pile in the desired position before the enlarged reinforcement unit is provided.

JP-A2-01017924 describes how an enlarged footing for a pile is provided with an inflatable bag where the pile is positioned and connected to the bag, which is positioned in a cavity and filled with a solidifying fluid.

SE-C2-515 997 describes a method for placing an inflatable bag at the lower end of a hole for a concrete material pile and then filling the bag with concrete, hence creating an enlarged footing for the concrete pile.

US-A-4,661,021 describes an expansion body for constructions like piles or anchorages located in the ground. The expansion body is adapted to be inserted in a compact shape and then expand when positioned.

A disadvantage of using such expansion members as enlarged footing is that these expansion members only can be used once and they have no internal reinforcement.

Aspects of the invention It is therefore the purpose of the present invention to provide a method for providing a new type of piled foundations, where the piled foundations are provided by an easy process in-situ and have a better stability and a higher strength against compressive and tensile forces caused by wind loads and the dead weight of the constructions.

Furthermore it is the purpose of the present invention to provide methods for providing piled foundations where it is possible to reuse the expanding member, hence reducing the cost of a piled foundation.

This is achieved either by a method being inventive in that a hole for a foundation pipe is drilled with a first worm auger, and a foundation pipe is positioned in said hole, a further section below the lower end part of the positioned foundation pipe is drilled, a cavity is provided in said section by means of a scraper and water pressure, the loose material from said cavity is removed with said first worm auger, a tool implement pipe is lowered down through said foundation pipe into the lower part of said section, and said tool implement pipe comprises a second worm auger and a resilient balloon surrounding a lower part of said second worm auger, said balloon is pressurised and a casting material is injected into the walls of said cavity, upon which any displaced material is removed with said second worm auger. After said casting material has hardened, said balloon is deflated and removed through said foundation pipe, a reinforcement unit is lowered down through said foundation pipe, a concrete material is poured down through said foundation pipe, said cavity is filled, and said reinforcement unit is embedded in said concrete providing an enlarged footing for said foundation pipe, or by a method being special in that a hole for a foundation pipe is drilled with a first worm auger, and a foundation pipe is positioned in said hole, a further section below the lower end part of the positioned foundation pipe is drilled, a cavity is provided in said section by means of a scraper and water pressure, the loose material from said cavity is removed with said first worm auger, a tool implement pipe is lowered down through said foundation pipe into the lower part of said section and said tool implement pipe comprises a second worm auger and a resilient balloon surrounding a lower part of said second worm auger, said balloon is pressurised and a casting material is injected into the walls of said cavity, upon which any displaced material is removed with said second worm auger. After said casting material has hardened, said balloon is deflated and removed through said foundation pipe, a number of holes are drilled into an upper part of said cavity, where each of said holes is adapted to receive a further foundation pile with a number of reinforcement units protruding into said cavity, a reinforcement unit is lowered down through said foundation pipe, a concrete material is poured down through said foundation pipes, and said cavity is filled and said reinforcement units are embedded in said concrete providing an enlarged footing for said foundation pipes.

A further purpose of the present invention is to provide piled foundations which have a very high strength against compressive and tensile forces caused by wind loads and the dead weight of the constructions.

This is achieved by either a single piled foundation wherein said enlarged footing comprises an outer layer of a casting material and a core of concrete wherein a reinforcement unit is embedded, and where said reinforcement unit is connected via a number of connecting means to said construction or by a multi piled foundation wherein said enlarged footing comprises an outer layer of a casting material and a core of concrete wherein a number of reinforcement units are embedded, and where each of said reinforcement units is connected with said construction by connecting means extending through either said first or said further foundation pipes.

A further purpose of the present invention is to provide a balloon for providing a sufficiently enlarged footing of said foundations. This is achieved by a balloon wherein said balloon on an outer surface is provided with a number of injection channels.

Summary of the invention In the following piled foundations for founding a wind turbine are described that have footing elements reinforced by a number of reinforcement units, and a method is described for providing such piled foundations. However, the piled foundations and methods described in the present invention may also be used for providing foundations for other kinds of tower elements, e.g. chimneys, large flagpoles, columns, power pylons and antennae. Besides, the foundation pile may also be used for providing foundations under houses, bridges, offshore platforms and the like.

To provide a single piled foundation for the aforementioned construction in-situ, the method comprises the following steps:

i) a hole for a foundation pipe is drilled with a first worm auger, and a foundation pipe is positioned in said hole,

ii) a further section below the lower end part of the positioned foundation pipe is drilled,

iii) a cavity is provided in said section by means of a scraper and water pressure,

iv) the loose material from said cavity is removed with said first worm auger, v) a tool implement pipe is lowered down through said foundation pipe into the lower part of said section, and said tool implement pipe comprises a second worm auger and a resilient balloon surrounding a lower part of said second worm auger,

vi) said balloon is pressurised, and a casting material is injected into the walls of said cavity, upon which any displaced material is removed with said second worm auger,

vii) after said casting material has hardened, said balloon is deflated and removed through said foundation pipe,

viii) a reinforcement unit is lowered down through said foundation pipe,

iv) a concrete material is poured down through said foundation pipe, said cavity is filled and said reinforcement unit is embedded in said concrete providing an enlarged footing for said foundation pipe.

Alternatively the hole can be provided with other kinds of ground working tools, e.g. a propelling nozzle.

In one embodiment of the invention the worm member is provided with a slightly re¬ entrant angle, hence the loosened material will always be lead inwards in the worm auger and be removed by the worm member.

The foundation pile is a circular tube that allows the implement pipe with working tools and balloon, casting material, reinforcement units, connecting means, and concrete to be passed though the foundation pile.

To be able to easily provide an enlarged footing at the lower part of the positioned foundation pipe, it is necessary to drill the hole a section below the lower part of the positioned foundation pipe. To provide the cavity a compressed scraper member is brought down the foundation pile and is unfolded in the section below the lower part of the positioned foundation pipe and rotated, whereby surrounding material will be loosened and the cavity will be circular.

To be able to remove the loosened material the foundation pipe and the underlying hole are filled with water and put under pressure. It will then be easier to rotate the scraper, and the loosened material will form a clayey paste which can be removed by the first worm auger.

The first worm auger is positioned in the foundation pile after the scraper is removed upon which the clayey paste is removed.

The form of the cavity is determined by the form of the scraper and by the form of the inflatable balloon. Right after the positioning of the tool implement pipe, the balloon is inflated with air at a pressure of preferably 1-5 bar, hence the balloon will expand and form the cavity.

The expansion of the balloon redistributes the ground material around the cavity so that the loosened material will be forced downwards to the second worm auger and then removed.

The size of the cavity is determined by the size and form of the balloon. For inflating the balloon e.g. either air or water is used. Hence it is possible to exactly provide a cavity of the wanted size and form by controlling the amount of water or air entering the balloon.

To be able to cast an enlarged footing without the cavity collapsing and deforming the enlarged footing during hardening of the concrete, it is necessary to cast an outer layer, which maintains the form of the cavity during the hardening of the concrete. On its outer surface the balloon is provided with a number of injection channels, wherefrom it is possible to inject a casting material into the surrounding ground of the cavity.

Li one embodiment of the present invention the injection of the casting material is performed while the balloon is pressurised in a pulsating manner, thereby ensuring that the casting material is pressed into the surrounding ground and evenly distributed and compacted, hence making the outer layer strong enough to prevent collapse while the concrete forming the enlarged footing is hardening.

When the balloon is pulsated and the casting material is injected, the surrounding ground will be compressed and the outer layer will be a compact shell. Furthermore an amount of the surrounding ground will be displaced, and therefore the tool implement pipe comprises a second worm auger that removes excess ground material and/or casting material.

Alternatively to pulsating the balloon for compressing the surrounding ground around the cavity sound waves can be used, e.g. sonar. Hence the ground will be compressed while at the same time it is possible to inject casting material into the surrounding ground around the cavity.

The balloon is made of a resilient material so it is possible to compress the balloon when it is led down though the foundation pile and to remove the balloon when the casting material is hardened.

To reinforce the enlarged footing a reinforcement unit is lowered down through said foundation pipe. This reinforcement unit can be a unit with a number of protruding elements which can enter into and connect with the concrete, hence making the enlarged footing stronger.

In a preferred embodiment the reinforcement unit is a unit as described in WO-Al- 03062539, where the reinforcement unit is provided with an expanding member for folding out a number of arms into the cavity whereby the enlarged footing is reinforced approximately evenly throughout the entire footing.

In one embodiment of the present invention, the reinforcement arms are formed by a network of rods and/or wires. This means that it is possible to make reinforcement members that are light and inexpensive, and which reinforces the footing element at several levels and not only in one plane.

In order to absorb the tensile forces in the foundation pile, according to the invention it is important that the foundation pile maintains its fastening to the reinforcement unit, and therefore the reinforcement unit is connected to the foundation pile with one or more connecting members.

The casting material which is pumped/pressed/injected into the surrounding ground for formation of the outer layer of the enlarged footing can be a cement mixture, cement gel, concrete, grout, slurry or a setting plastic material.

To ease the removal of the balloon from the outer layer, before use the outer surface is covered with oil, e.g. earth oil, which prevents the casting material to stick to the balloon.

To provide a multi piled foundation for the aforementioned constructions in-situ the method comprises the following steps:

i) a hole for a foundation pipe is drilled with a first worm auger, and a foundation pipe is positioned in said hole,

ii) a further section below the lower end part of the positioned foundation pipe is drilled,

iii) a cavity is provided in said section by means of a scraper and water pressure,

iv) the loose material from said cavity is removed with said first worm auger, v) a tool implement pipe is lowered down through said foundation pipe into the lower part of said section and said tool implement pipe comprises a second worm auger and a resilient balloon surrounding a lower part of said second worm auger,

vi) said balloon is pressurised and a casting material is injected into the walls of said cavity, upon which any displaced material is removed with said second worm auger,

vii) after the said casting material has hardened, said balloon is deflated and removed through said foundation pipe,

viii) a number of holes are formed into an upper part of said cavity, where each of said holes is adapted to receive a further foundation pile with a number of reinforcement units protruding into said cavity,

ix) a reinforcement unit is lowered down through said foundation pipe,

x) a concrete material is poured down through said foundation pipes, and said cavity is filled and said reinforcement units are embedded in said concrete providing an enlarged footing for said foundation pipes.

The only difference between providing a multi piled foundation and providing a single piled foundation is the aforementioned steps viii) - x), where the cast outer layer is provided with a number of holes, so it is possible to provide several foundation piles to the same enlarged footing. This will cause the piled foundations to be more stable and rigid because any force reacting on the multi piled foundation will be distributed on several foundation pipes and the earth volume above each enlarged footing will increase.

It should be noted that it is possible to provide a foundation to a construction, where the foundation comprises either a number of single piled foundations or a number of multi piled foundations or a mixture with a number of both kinds of piled foundations. The single piled foundation comprises an enlarged footing with an outer layer of a casting material and a core of concrete wherein a reinforcement unit is embedded, and where said reinforcement unit is connected via a number of connecting means to said construction. Hence the tensile forces can be transferred and distributed in the piled foundation.

The multi piled foundation comprises an enlarged footing with an outer layer of a casting material and a core of concrete wherein a number of reinforcement units are embedded, and where each of said reinforcement units is connected with said construction by connecting means extending through either said first or said further foundation pipes, hence any tensile and compressive forces can be transferred and distributed in the pile foundation.

By using a multi piled foundation with several foundation pipes connected into the enlarged footing it is possible, in theory, to obtain a very stable foundation for a construction because the construction due to e.g. wind will provide a pressure force on the foundation at one foundation pile, while at the same time, it will provide a tensile force of similar extent at the opposite foundation pile. Hence the pressure and tensile forces will equalize each other, and the actual accumulated force on the foundation will be very small.

The balloon is made of a resilient material to allow its being inflated and deflated. Furthermore on its outer surface, the balloon is provided with a number of injection channels which allow the injection of casting material into the surrounding ground when the balloon is inflated. These injection channels can be integrated in the balloon material or be external members, e.g. by means of an adhesive compound. For example, the hose to the injection channels on the balloon is brought down with the tool implement pipe.

As an alterative to having a central reinforcement unit in the form of a unit with expanding members and side reinforcement unit with rods protruding into the cavity, the side reinforcement units can be wires going down through a foundation pipe and up through an another foundation pipe. In this manner it is possible to provide a netting of wires in the cavity and below the first foundation pipe. To stretch out netting, the reinforcement unit provided in the first foundation pipe could either be formed with an end part gripping onto the wires and locking them in place or it could be formed with an end part which can push the netting down while the enlarged footing is being created.

As an alternative to using a balloon for providing the cavity, it is possible to use either - a sleeve, like e.g. a plastic sleeve for use in a sewage system, where the sleeve is made of layers of e.g. plastic and glass fibres and is kept in form by heating, or - a sleeve in combination with e.g. an inner rubber membrane for providing a shuttering around the cavity. - a sleeve or a net in combination with the injection of casting material into the surrounding ground whereby the sleeve will be cast into and reinforce and maintain the form of the outer layer when it is hardening into a shell around the cavity.

Brief description of the invention The invention is explained in the following with reference to the accompanying figures, where:

Figs. Ia-Ih show the process of constructing a single piled foundation, Figs. 2a-2j show the process of constructing a multi piled foundation, Fig. 3 shows the casting of a single piled foundation, Fig. 4 shows the casting of a multi piled foundation, Fig. 5 shows a foundation with both single piled and multi piled foundations, Fig. 6 shows a multi piled foundation, Fig. 7 shows a wind turbine arranged on a number of single piled foundations, Fig. 8a-8c shows a multi piled foundation with wires as reinforcement units. Detailed description of the invention Figs. Ia-Ih show the process of constructing a single piled foundation 1, where - a hole 2 for a foundation pipe 3 is drilled with a first worm auger 4, and the foundation pipe 3 is positioned in the hole 2, and a further section 5 below the lower end part 6 of the positioned foundation pipe 3 is drilled, - a cavity 7 is provided in the section 5 by means of a scraper 8 and water pressure, - the loose material from the cavity 7 is removed with the worm auger 4, - a tool implement pipe 9 is lowered down through the foundation pipe 3 into the lower part 10 of the section 5, the tool implement pipe 9 comprising a worm auger 11 and a resilient balloon 12 surrounding a lower part 13 of the worm auger 11, - the balloon 12 is pressurised and a casting material 14 is injected into the walls 15 of the cavity 7, upon which any displaced material is removed with the worm auger 11 through the tool implement pipe 9, after the casting material 14 has hardened, the balloon 12 is deflated and removed through the foundation pipe 3, - a reinforcement unit 16 is lowered down through the foundation pipe 3, - a concrete material 17 is poured down through the foundation pipe 3, and the cavity 7 is filled and the reinforcement unit 16 is embedded in the concrete 17 providing an enlarged footing 18 for the foundation pipe 3.

Figs. 2a-2j show the process of constructing a multi piled foundation 20, where a hole 2 for a foundation pipe 3 is drilled with a first worm auger 4, and the foundation pipe 3 is positioned in the hole 2, and a further section 5 below the lower end part 6 of the positioned foundation pipe 3 is drilled, - a cavity 7 is provided in the section 5 by means of a scraper 8 and water pressure, - the loose material from the cavity 7 is removed with the worm auger 4, - a tool implement pipe 9 is lowered down through the foundation pipe 3 into the lower part 10 of the section 5, the tool implement pipe 9 comprising a worm auger 11 and a resilient balloon 12 surrounding a lower part 13 of the worm auger 11, - the balloon 12 is pressurised and a casting material 14 is injected into the walls 15 of the cavity 7, upon which any displaced material is removed with the worm auger 11 through the tool implement pipe 9, after the casting material 14 has hardened, the balloon 12 is deflated and removed through the foundation pipe 3, a number of holes 21 are drilled into an upper part 22 of said cavity 7, where each of said holes 21 are adapted to receive a further foundation pile 24 with a number of reinforcement units 23 protruding into said cavity 7, - a reinforcement unit 16 is lowered down through the foundation pipe 3 - a concrete material 17 is poured down through said foundation pipes 3,24, and said cavity 7 is filled and said reinforcement units 16,23, are embedded in said concrete 17 providing an enlarged footing 25 for said foundation pipes 3,24.

Fig. 3 shows the casting of a single piled foundation 1 , where the reinforcement unit 16 is in place at the bottom of the foundation pipes 3, and in the cavity 7. The cavity 7 has a precast outer layer 30. The concrete 17 is poured down through the foundation pipe 3. The reinforcement unit 16 is connected with a number of connecting means 31 extending through the foundation pipe 3.

Fig. 4 shows the casting of a multi piled foundation 20, where the reinforcement units 16,23 are in place at the bottom of the foundation pipe 3,24 and in the cavity 7. The cavity 7 has a precast outer layer 40. The concrete 17 is poured down through the foundation pipe 3. The reinforcement units 16,23 are connected with a number of connecting means 41 extending through the foundation pipes 3,24.

Fig. 5 shows a foundation 50 with both single piled foundations 1 and multi piled foundations 2, where the construction (not shown) is connected to the upper end of the foundation pipes 3,24.

Fig. 6 shows a multi piled foundation 2 with five foundation piles 3,24. According to an alternative embodiment of the invention, the five foundation piles 3,24 can be connected with a truss of reinforcement material, whereby the multi piled foundation 2 can be used as foundation for offshore constructions.

Fig. 7 shows a wind turbine 70 arranged on a number of single piled foundations 1, where the reinforcement units 16 are connected to the wind turbine's 70 second floor level by extending the connection means up through the foundation pipes and through the first floor level of the wind turbine tower.

The advantages of connecting the foundation to the second floor level are the following: - The theoretical force momentum on the tower construction is reduced significantly because the point of fixation of the tower is moved one floor level up, hence the flange connection between the foundation and the tower construction needs not transfer very large forces, and can therefore be dimensioned slightly smaller. - The tower construction can be allowed a smaller dimension because the risk of natural frequency of the towers is reduced as the lower part of the tower is calculated as a part of the foundation. - The flanges between the first and second floors are positioned inside the tower construction, thereby allowing easy connection of the connection means to the tower construction. Furthermore maintenance of the connection is reduced.

Figs. 8a-8c show a cavity 7, where the outer cast layer 80 is provided with holes for foundation piles 82,83,84. A wire 81 is provided down through foundation pile 82 and up through foundation pile 84, meanwhile a hold-down unit 85 is provided down through foundation pile 83. The hold-down unit 85 is stretching the wire 81 into the cavity 7, meanwhile a concrete material 86 is cast around the wire 81 and hold-down unit 85 for providing an enlarged footing 87.