METHOD FOR FORMING A FOUNDATION IN THE GROUND

Abstract

A method of forming a foundation in the ground, comprising the steps of—forming a foot (11) in the ground (100); —forming a column (12) made from a load bearing material in the ground (100) on top of the foot (11); and —forming a pile (13) in the material column (12) such that the pile (13) extends down to the material foot (11) or into the material foot (11).

Description

TECHNICAL FIELD

This disclosure in general relates to a method for forming a foundation capable of bearing a load in the ground.

BACKGROUND

Rigid bodies, such as concrete piles may be used as foundations in the ground for any kind of structure when a load bearing capability of the ground is not high enough to support the structure on a shallow foundation. There is a need for a cost saving method for producing a foundation in the ground.

SUMMARY

One example relates to a method. The method includes forming a material foot in the ground, forming a material column on top of the material foot, and forming a pile inside the material column such that the pile extends down to the foot or into the foot.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples are explained below with reference to the drawings. The drawings serve to illustrate certain principles, so that only aspects necessary for understanding these principles are illustrated. The drawings are not to scale. In the drawings the same reference characters denote same features.

FIGS. 1A to 1C illustrate one example of a method for forming a foundation in the ground, wherein the foundation includes a pile and a bedding of the pile, wherein the bedding includes a material foot and a material column;

FIG. 2 illustrates one example of a depth vibrator in greater detail;

FIGS. 3A to 3C illustrate method steps for producing the material foot according to one example;

FIGS. 4A and 4B illustrate one example of a method for forming the pile of the foundation in the bedding;

FIGS. 5A and 5B illustrate another example of a method for forming the pile;

FIGS. 6A and 6B illustrate yet another example of a method for forming the pile;

FIG. 7 illustrates one example of a concrete pile manufactured in a conventional way using a so-called continuous flight auger method; and

FIG. 8 illustrates another example of a foundation, wherein this foundation has been formed without a material column.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings. The drawings form a part of the description and for the purpose of illustration show examples of how the invention may be used and implemented. It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise.

One way of forming a foundation capable of bearing a load includes ramming a precast rigid element, such as a concrete pile into the ground. As a load transfer from a pile into surrounding soil happens in part by friction along sidewalls of the pile but to a large part also by the load bearing on the bottom of the pile, a foundation based on piles often requires that the piles are long enough to reach a stable ground region, such as a stiff or dense soil layer or a rock region, capable of bearing large parts of the load provided by the structure through the bottom of the pile. When the pile hits an obstacle in the ground, such as a rock embedded in sand or clay, the prefabricated pile often has to be cut off along the ground surface and is “lost” for future load bearing.

Another way of forming a pile in the ground includes drilling a hole and filling the hole with concrete. This method, similar to driving a precast concrete pile into the ground, requires that the hole is drilled down to a stable ground region capable of bearing the load provided by a structure.

Concrete piles with an enlarged foot, for example so called Franki piles, may be used to form foundations even in a loose ground, such as loose sand or silt, when solid ground regions are too deep to be reached cost efficiently by ramming precast piles into the ground or by drilling holes. These Franki piles are formed by ramming a tube filled at the bottom with gravel or dry concrete into the ground and by driving, with a falling weight, the concrete or gravel from the tube into the ground after the tube has reached a desired depth. By driving the concrete or gravel in the ground a foot having a diameter larger than the diameter of the tube is formed. After installation of such foot, and while withdrawing the tube from the ground, the pile is completed by filling the hole formed by the tube with concrete down to the foot. This method, however, is slow and, therefore, expensive.

There is therefore a need for a method for forming foundation capable of bearing a load in the ground, wherein the method is inexpensive and suitable to produce the foundation in loose ground. One example of such method is illustrated in FIGS. 1A to 1C.

Referring to FIG. 1A, the method includes forming a foot 11 in the ground 100. More specifically, forming the foot 11 includes forming the foot 11 spaced apart from a ground surface 101. The foot 11 may be formed in various ways.

According to one example, illustrated in FIG. 1A, forming the foot 11 includes introducing material into the ground and forming the foot 11 using a vibrator arrangement 2. In this case, the foot 11, which may also be referred to as material foot, is formed such that a diameter d1 of the material foot 11 is larger than a diameter d2 of the vibrator arrangement 2. One example of a method for forming the material foot 11 using the vibrator arrangement 2 is explained in greater detail herein further below.

Various materials or combinations of various materials may be used to form the material foot 11. According to one example, the material foot 11 is formed from concrete. According to another example, the material foot 11 is formed from a granular material, such gravel or sand. Optionally, the material foot 11 includes a granular material and grout. In the case of forming the material foot using a vibrator arrangement, grout may be injected from grouting nozzles (not shown) attached to the vibrator arrangement 2 at the same time as the granular material is introduced into the ground, wherein the grout provides for a bonding between the stones or grains of the granular material of the material foot 11.

Referring to FIG. 1B, the method further includes forming a material column 12 on top of the material foot 11. Referring to FIG. 1B, the material column 12 may extend from the material foot 11 to the ground surface 101. The material column may be formed from one or more different materials. These materials include, for example, gravel or sand. The gravel may include angular gravel or rounded river gravel. According to one example, the material column is formed from only one material, such as gravel or sand.

According to another example, the material column is formed from two or more different materials, such as gravel and sand. When forming the material column from two or more materials the column may be formed such that it includes two or more column sections, wherein each column section only includes one material, such as gravel or sand. The type of material and, optionally, the size of the material particles may be selected dependent on the type of soil in which the respective column section is formed. The ground may include different soil layers one above the other, wherein for each column section formed in a respective soil layer the column material can be selected independently. According to another example, the material column or at least one section of the material column is formed from a mixture of two or more different material, such as sand and gravel.

Referring to FIG. 1C, the method further includes forming a rigid pile 13 inside the gravel column 12 such that the rigid pile 13 extends down to the material foot 11 or, as illustrated in FIG. 1C, is partially embedded into the material foot 11.

A foundation of the type illustrated in FIG. 1C that includes a foot 11, a material column 12 on top of the material foot 11, and a rigid pile 13 inside the material column 12 provides an increased lateral support of adjustable magnitude over depth, as compared to a conventional foundation formed in the ground. This higher lateral support can be beneficial to increase the portion of the load to the pile 13 that is carried by a shaft of the pile 13 as compared to a bottom of the pile 13, wherein the bottom of the pile 13 is the section of the pile 13 that faces the foot 11. Higher lateral support can also be beneficial to reduce the moment load in the pile shaft when the pile is horizontally loaded or loaded by a moment on the pile head, wherein the pile head is a section of the pile facing away from the foot 11.

The vibrator arrangement 2 that may be used for forming the material foot 11 is only schematically illustrated in FIG. 1A. Vibrator arrangements for introducing material into the ground are known. Nevertheless, for a better understanding, one example of a vibrator arrangement 2 is briefly explained with reference to FIG. 2 in the following. Referring to FIG. 2, the vibrator arrangement 2 includes a silo tube 21, a vibrator 23, which may also be referred to as vibroflot, coupled to the silo tube 21 and including a tip 25. The tip 25 forms a lower end of the vibrator arrangement 2. The vibrator 23 may be coupled to the silo tube 21 by a damper element 22. Further, the vibrator arrangement 2 includes a pipe 24 connected to the silo tube 21 and extending from the silo tube 21 towards the lower end of the vibrator arrangement 2, wherein the pipe 24 has an outlet 26 at the lower end of the vibrator arrangement 2. At an upper end, which is not shown in FIG. 2, the vibrator arrangement 2 includes an inlet 27 (illustrated in FIG. 1A), wherein material can be fed into the silo tube 21 via the inlet 27. Material fed into the silo tube 21 can be introduced into the ground 100 via the outlet 26 of the pipe 24 connected to the silo tube 21. The silo tube 21 may include one or more locks in order to apply excess air pressure in the silo tube 21 to control material flow from the input 27 to the outlet 26 against the in-situ pressure in the soil. Such locks, however, are not illustrated in the drawings.

In operation, the tip 25 of the vibrator oscillates (repeatedly moves) in lateral directions, which are directions parallel to the ground surface 101 and perpendicular to a longitudinal direction of pipe. In this way, the vibrator 23 laterally compacts the ground and creates space for the vibrator arrangement 2 to move into the ground, just driven by its own weight.

The vibrator arrangement 2 illustrated in FIG. 2 includes one pipe 24 and one outlet 26. This, however, is only an example. According to another example (not illustrated) two or more pipes extend from the silo tube 21 along the vibrator 23 to the lower end of the vibrator arrangement 2.

FIGS. 3A to 3C illustrate, in greater detail, one example of a method for forming the foot 11 in the ground 100 using a vibrator arrangement. Referring to FIG. 3A, this method includes introducing the vibrator arrangement 2 to a predefined depth into the ground 100. The vibrator arrangement 2 may be held by a suitable device, such as an excavator arm, and may be lowered or lifted by this device. For introducing the vibrator arrangement 2 into the ground 100, however, no external force is required. The vibrator arrangement 2 penetrates into the ground 100 just supported by its own weight and vibrations of the vibrator 23, wherein these vibrations of vibrator 23 create a space at the lower end of the vibrator arrangement 2 that enables the vibrator arrangement 2 to penetrate deeper into the ground 100. When the vibrator arrangement has reached the predefined depths, the device holding the vibrator arrangement 2 may stop lowering the vibrator arrangement 2 so that the vibrator arrangement 2 stops penetrating deeper into the ground 100. Referring to FIG. 3B, the method further includes lifting the vibrator arrangement 2 and introducing material 11′ into a space below the lower end of the vibrator arrangement 2, wherein this space has been created by the vibrator arrangement 2. According to one example, the silo tube 21 has been filled with material before, so that automatically when the vibrator arrangement 2 is lifted the material 11′ is introduced into the ground via the silo tube 21 and the pipe 26.

Referring to FIG. 3C, the method further includes lowering the vibrator arrangement 2 into the material 11′. In this way, the material 11′ is compacted and driven mainly radially into the ground surrounding the space into which the material 11′ had been introduced.

Forming the material foot 11 may include repeating the method steps illustrated in FIGS. 3A to 3C several times, that is, (a) lifting the vibrator arrangement 2 in order to introduce material 11′ into the ground 11, and (b) penetrating into the introduced material 11′ by the vibrator arrangement 2 in order to compact the material 11′ and drive the material into ground regions surrounding the material. A size of the material foot 11, that is, a height of the material foot 11 in a direction perpendicular to the ground surface 101, and a width or diameter d1 of the material foot 11 in directions parallel to the ground surface 101 are dependent on an amount of material that is introduced into the ground 100. The amount of material increases as the number of repetitions of the method steps illustrated in FIGS. 3A to 3C increases.

According to one example, the material 11′ introduced into the ground 100 and forming the material foot 11 may be concrete. This concrete is introduced into the ground in liquid form, wherein the concrete cures (hardens) after being introduced into the ground 100.

According to another example, the material 11′ introduced into the ground 100 in order to form the material foot 11 is gravel, wherein the gravel is compacted by a method step of the type illustrated in FIG. 3C. Optionally, liquid grout may be introduced into the gravel by the vibrator arrangement 2 either from time to time in the process of forming the material foot 11 or after the gravel forming the material foot 11 has been introduced. The liquid grout flows between the gravel and finally cures so that a solid material foot 11 is formed.

Referring to the above, the material foot 11 is formed such that the diameter d1 of the material foot 11 is greater than a diameter d2 of the vibrator arrangement 2. The diameter d2 of the vibrator arrangement 2 essentially equals the diameter of a hole the vibrator arrangement 2 forms when penetrating into the ground 100. Due to irregularities in the ground and variations in the manufacturing process of the material foot 11 the material foot 11 might not have the same diameter along its entire height. According to one example, as used herein “the diameter d1 of the material foot 11” is an average diameter of the material foot 11.

According to one example, the diameter d1 of the material foot 11 is at least two times the diameter d2 of the vibrator arrangement 2, d1≥2*d2. According to one example, the diameter d1 of the material foot 11 is between two times and five times the diameter d2 of the vibrator arrangement 2, 2*d2≤d1 5*d1. According to one example, the diameter d1 of the material foot 11 is between 0.5 meters (m) and 2 meters.

According to an example, the diameter d1 of the material foot 11 is controlled by controlling or monitoring at least one operating parameter of the vibrator arrangement. According to one example, the at least one operating parameter is a power consumption of the vibrator 23 when the vibrator arrangement 2 (by its weight and vibrations of the vibrator 23) is driven into the material of the material foot 11. Depending on the type of motor drive used in the vibrator arrangement 2, the power consumption may be measured by measuring an electric power consumption of a motor of the vibrator arrangement 2 or by measuring a hydraulic pressure in a motor of the vibrator arrangement 2. The power consumption of the vibrator 23 required to penetrate into the introduced material is a function of the stiffness/density of the material and also the soil that surrounds the material into which the vibrator arrangement 2 penetrates. In other words: The stiffer or denser the material, the higher is the power consumption and the higher is also the lateral confinement between the installed column 12 and the surrounding soil. According to one example, in order to achieve a material foot 11 with a desired stability, the power consumption is measured and the method steps of lifting and lowering the vibrator arrangement 2 is repeated until the power consumption reaches a predefined threshold. Basically, the weaker the ground, the greater the diameter of the material column 12 will be before a desired power consumption threshold is reached.

Alternatively or in addition to monitoring the power consumption of the vibrator arrangement 2 an acceleration or a velocity of the vibrator arrangement 2 may be monitored. This may be achieved by placing one or more accelerometers or velocity sensors at the vibrator arrangement 2. The measured acceleration or velocity, similar to a power measurement, can be correlated with the confinement generated by the vibrator arrangement 2 while building the foot 11.

Operating parameter control during installation of the material foot 11 can lead to a better quality of such material foot 11 since the foot's lateral confinement with the in-situ soil can be controlled by controlling the Operating parameter. In a very loose soil, for example, the foot 11 would have to be built bigger to reach the same power consumption in the motor than this would be the case in a less loose soil. Thereby building the foot 11 power controlled will give a better control over the effort spent versus the result obtained.

There may be soils, such as sandy soils, in which an operating parameter controlled formation of the foot 11 will not achieve a satisfying result. Thus, according to another example, forming the material foot 11 using a vibrator arrangement includes introducing a predefined amount of material into the ground 100 and compacting the material using the vibrator arrangement 2.

Referring to the above, forming the material foot 11 using a deep vibrator 23 is only one of several different examples for forming the material foot 11. According to another example, the material foot is formed in accordance with forming the material foot in the Franki pile method explained above. In this case, forming the material foot includes: ramming a tube filled at the bottom with gravel or dry concrete into the ground; and driving, with a falling weight, the concrete or gravel from the tube into the ground. By driving the concrete or gravel in the ground a foot having a diameter larger than the diameter of the tube is formed. The foot 11 has a diameter larger than a diameter of the tube. The diameter of the material foot 11 may be between two times and five times the diameter of the tube. According to one example, the diameter d1 of the material foot 11 is between 0.5 meters (m) and 2 meters.

According to yet another example, forming the material foot 11 includes: ramming a tube having a lock at its lower end into the ground until the tube reaches a desired depth; partially filling the tube with gravel or dry concrete; withdrawing the tube and opening the lock so that the filling material is introduced into a hole below the tube; closing the lock and driving the tube into the material at least once. The tube may be lifted and driven into the material several times. The lock may be implemented in such a way that it automatically opens when the tube is lifted and closes when the tube is driven into the material. The foot 11 has a diameter larger than a diameter of the tube. The diameter of the material foot 11 may be between two times and five times the diameter of the tube. According to one example, the diameter d1 of the material foot 11 is between 0.5 meters (m) and 2 meters.

Again, forming the foot 11 using one of the methods explained above are just examples. Other examples include: forming the foot using any type of top driven mandrel with or without a lock; forming the foot 11 using a rotary bottom feed stone column technique; forming the foot 11 using a top feed technique, wet or maybe even dry; or the like.

Referring to the above, the vibrator arrangement 2 may penetrate into the ground 100 just supported by its own weight and vibrations of the vibrator 23. Further, referring to FIGS. 3A-3C, the ground may include different soil layers 110-140, wherein one or more of these soil layers may be too stable for the vibrator arrangement 2 to penetrate through. In this case, the hole at the bottom of which the material foot 11 is formed by the vibrator arrangement 2 is at least partially predrilled. That is, a hole is formed by a drilling device such that the hole extends through soil layers impenetrable by the vibrator arrangement 2. After removing the drilling device, the vibrator arrangement is lowered into the predrilled hole in order to form the material foot 11 as explained above. A depth of the predrilled hole may correspond to the desired depth of the hole at the bottom of which the material foot is to be produced. Alternatively, the predrilled hole is less deep as desired and the vibrator arrangement 2 is used to extend the hole to the desired depth. A diameter of the predrilled hole may be less than the diameter of the vibrator arrangement 2. The drilling device is an auger, for example.

At least partially pre-drilling the hole is not restricted to a method in which the material foot 11 is produced using a vibrator arrangement. The hole may also be pre-drilled when forming the material foot 11 in accordance with any one of the other methods explained above.

In the examples explained above, foot 11 is a material foot that is formed by introducing material into the ground. This, however, is only an example. According to another example, forming the foot 11 includes compacting ground material. A foot 11 formed in this way may be referred to as in-situ foot. Forming an in-situ foot may include using a vibrator arrangement 2 of the type explained above, introducing the vibrator arrangement 2 to a predefined depth, and repeatedly lifting and lowering the vibrator arrangement. The foot 11 may be formed in this way in a sandy soil layer, for example, wherein each time the vibrator arrangement 2 is lifted ground material flows into the space below the vibrator tip 25 and is compacted when the vibrator arrangement is lowered. The vibrator arrangement 2 may be implemented without a tube in this example. In the case that a cavity is formed above the foot 11 due to material flow, this cavity is filled by the material column 12 formed later in the process.

In each case, the material column 12 is formed in the hole above the foot 11, wherein this hole is formed by the vibrator arrangement 2 when penetrating into the ground (see FIG. 1B), or by any other kind of tube used in the manufacturing process of the foot 11. Forming the material column 12 may include simply filling the hole with material.

Filling the hole with material may be achieved by feeding the column material via the tube 26 of the vibrator arrangement 2 or via any other kind of tube into the hole when the vibrator arrangement 2 or the tube is withdrawn from the hole. Alternatively, the vibrator arrangement 2 or tube is withdrawn from the hole and gravel is filled into the hole after the vibrator arrangement 2 has been withdrawn. The latter may be applied when the ground is stable enough that the hole formed by the vibrator arrangement 2 remains open after the vibrator arrangement 2 or the tube has been withdrawn from the ground.

According to another example, the material column 12 is formed using a wet top feed method. This method uses a deep vibrator that does not have a material pipe attached to it. Instead, the material forming the material column 12 is fed in an annular space around the vibrator, wherein the space is kept open by flushing water from the vibrator tip.

Referring to the above, the material column may include two or more column sections formed from different materials or material combinations. A material column of this type may be achieved by introducing different materials or different material combinations into the hole at different times of the filling process.

According to another example, forming the material column 12 includes forming the material column 12 using a vibrator arrangement and using the same kind of method steps explained with reference to FIGS. 3A to 3C, that is, lifting the vibrator arrangement 2 and introducing material into a space below the lower end of the vibrator arrangement 2 and causing the vibrator arrangement 2 to penetrate into the introduced material in order to compact the material and laterally drive the material into the ground. The vibrator arrangement may be the same vibrator arrangement used to form the material foot 11 or a different vibrator arrangement. Forming the material column may include forming several column segments (column sections) one above the other. According to one example, a diameter of the material column 12 is lower than the diameter d1 of the material foot 11. This may be achieved by forming the material columnl2 such that in each segment of the gravel column 12 having essentially the same height as the material foot 11 the number of repetitions is lower than the number of repetitions used to form the material foot 11. The diameter d1 of the material column 12 is larger than the diameter d2 of the vibrator arrangement 2 (d1>d2). According to one example, the diameter of the material column is between the diameter d2 of the vibrator arrangement 2 and 1.5 times the diameter d2 of the vibrator arrangement 2 (d2<d1<1.5*d2).

According to one example, which may result in a particularly high bearing capacity of the rigid body, the number of repetitions when forming the gravel column is controlled dependent on at least one operating parameter, such a power consumption, an acceleration, a velocity, etc of the vibrator 23. The power consumption may be measured by measuring an electric power consumption of a motor of the vibrator arrangement 2 or by measuring a hydraulic pressure in a motor of the vibrator arrangement 2, depending on the type of motor drive used. The acceleration and the velocity may be measured using suitable sensors.

The power consumption, the acceleration, or the velocity of the vibrator 23 required to penetrate into the introduced material is a function of the stiffness/density of the material and also the soil that surrounds the material into which the vibrator arrangement 2 penetrates. In other words: The stiffer or denser the material, the higher is the power consumption, the lower is the acceleration and the velocity, and the higher is also the lateral confinement between the installed column 12 and the surrounding soil. According to one example, in order to achieve a material column 12 with a desired stability, at least one operating parameter is measured and the method steps of lifting and lowering the vibrator arrangement 2 is repeated until the operating parameter in each installation depth interval reaches a respective predefined threshold. The vibrator arrangement 2 is then lifted to a greater extent and forming a new segment of the gravel column 12 starts, wherein forming each segment includes lowering the vibrator arrangement 2 into the introduced material at least once. Dependent on the stiffness/density of the surrounding ground 100 the diameter of the material column 12 may vary along its length. Basically, the weaker the ground, the greater the diameter of the material column 12 will be before a desired operating parameter threshold is reached.

A load transfer between the concrete pile 13 and the soil surrounding the material column 12 happens at least in part by shaft friction between the material column 12 and soil. Based on this, it may generally be beneficial to increase such shaft friction also in weak layers by raising the lateral stress in such layers by means of the power consumption-controlled installation of the gravel column 12.

Basically, by controlling at least one operating parameter the column 12 can be produced in such a way that the lateral confinement stress caused by the column 12 is essentially the same at each longitudinal position of the material column 12. This, however, is only an example. In general, monitoring at least one operating parameter makes it possible to control the lateral confinement stress, wherein it may be desirable to vary the lateral confinement stress according to soil mechanical requirements of the particular pile 13 that is embedded in such column 12.

In cases where the pile 13 has to carry high horizontal loads it could for example be beneficial to concentrate a larger effort into building a strong gravel column 12 in the uppermost part of such column 12 so that the horizontal bedding to transport such horizontal loads from the pile 13, via the gravel column 12 into the soil is highest. In cases where for example an upper sand fill is placed on a soft clay and below the soft clay is the load bearing stratum for the pile, it could be beneficial to have a very low bedding in the sand layer to minimize added loading onto the pile 13 from what is well known as the so called negative skin friction acting from the sand via the gravel column onto the pile shaft and hence unwanted increasing its load. In such particular scenario the gravel column 12 could in the sand layer be replaced by a material that has very low friction (clay slurry for example).

In order to be able to control formation of the material column 12 the ground may be analyzed beforehand. Analyzing the ground may include any kind of analytical processes that provides information on stability, thickness, etc. of individual ground layers. One method of analyzing the ground 100 includes measuring a power consumption of a vibrator arrangement when it penetrates into the ground in the process of forming the material foot 11 and/or the material column 12.

The pile 13 inside the gravel column 12 may include various kinds of materials and may be formed in various ways. According to one example illustrated in FIGS. 4A and 4B, the method includes forming the pile 13 as a concrete pile using a vibrator arrangement 30. This vibrator arrangement 30 may have a lower diameter than the vibrator arrangement 2 used to form the material foot 11. This however, is only an example. The diameter of the vibrator arrangement may also be larger than the diameter of the material column 12. Referring to FIG. 4A, forming the concrete pile 13 includes forming a hole in the gravel column 12 by the vibrator arrangement 30 such that the hole in the gravel column 12 extends down to the material foot 11 or into the material foot 11. According to one example, the hole extends into the material foot 11 such that a depth of the hole in the material foot 11 is between 0.3 times and 0.5 times the height of the material foot 11.

Referring to FIG. 4B, forming the pile 13 includes withdrawing the vibrator arrangement 30 from the ground 100 and introducing liquid concrete into the hole formed by the vibrator arrangement 30. Forming the pile 13 in this way may be referred to as cast in place piling. The concrete may be introduced into the hole via the vibrator arrangement while withdrawing the vibrator arrangement 30 from the hole. In addition to concrete the pile 13 may include a reinforcement cage. The hole is filled with concrete, either via the vibrator arrangement 30 or after withdrawing the vibrator arrangement 30 from the hole, and the reinforcement cage is inserted after filling the hole with concrete. Inserting the reinforcement cage may include using a vibrator or any other kind of device capable of driving the reinforcement cage into the liquid concrete.

Forming the pile 13 by cast in place piling may result in a high friction between the concrete pile 13 after curing and the material column 12, wherein the friction is particularly high when the material column is at least partially formed from angular gravel.

According to another example, forming the pile 13 includes forming the concrete pile 13 from gravel and grout, wherein both grout and gravel are introduced into the hole via the vibrator arrangement 30. Gravel and grout may be introduced into the hole at the same time. Alternatively, gravel and grout are alternatingly introduced into the hole while withdrawing the vibrator arrangement 30 from the hole, wherein the grout flows into the gravel and fills spaces between gravel stones so that, finally and after curing, the concrete pile 13 is formed. The grout also flows into spaces of the material column surrounding the hole, so that a high friction between the concrete pile 13 and the material column can be achieved.

According to yet another example (not illustrated), an auger is used to drill a hole into the material column 12 and the pile 13 is formed as a concrete pile in the drilled hole. Forming the concrete pile may withdraw the auger from the ground and may include the same method steps explained above with regard to forming the concrete pile after entirely withdrawing the vibrator arrangement 2 from the ground 100. Alternatively, the hole is filled with concrete when withdrawing the auger from the ground 100, wherein a reinforcement cage 14 may be inserted after withdrawing the auger from the ground 100.

The pile 13 may be formed such that it essentially has the same diameter along its length. This, however, is only an example. According to another example, the pile 13 has a varying diameter. According to one example, the pile diameter increases towards the ground surface 101.

According to another example illustrated in FIGS. 5A and 5B, forming the pile 13 includes driving a pile 13 into the material column 12. Driving the pile 13 into the material column 12 may include using a conventional ramming or hammering device 5, which is only schematically illustrated in FIGS. 5A and 5B, or may include any other kind of device that is suitable to drive a precast pile into the ground, such as a top vibrator. In this example, the pile 13 may be comprised of any kind of rigid materials, such as concrete, steel, timber, or combinations thereof. According to one example, the pile 13 is a precast concrete pile that includes a steel reinforcement cage.

The foundation of the type explained above with a material foot 11 spaced apart from the ground surface 101, a material column 12 on top of the material foot, and a pile 13 in the material column may form a part of a solid foundation for any kind of structure. By virtue of the wide material foot 11 the arrangement is capable of bearing high loads even when the material foot 11 is formed in an initially relatively weak ground, such as compactable sand. In particular, when forming the material column 12 using a vibrator arrangement, vibrator 23 (horizontally vibrating depth vibrator) arrangement compacts the ground layers by vibrations inducing horizontally polarized shear waves and by displacement, while other displacement tools and/or vertically vibrating tools can only compact with limited effect by displacement only.

The load bearing capability of the rigid body is, inter alia, dependent on a friction between the material column and the surrounding soil and a load bearing capability of the material foot 11. The load bearing capability of the material foot 11 is dependent on the diameter of the material foot 11 and the load bearing capability of the soil region in which the material foot 11 rests. There may be scenarios in which a high friction between the material column 12 and the surrounding soil is difficult to achieve or technically not wanted, for example, because of unstable soil layers. In this case, the material column 12 may be formed from a material providing a low friction, such as sand or round (river) gravel. Using this type of material may result in an easier manufacturing of the concrete pile 13, either because the vibrator arrangement 30 can penetrate into the material column 12 more easily, or because a precast concrete pile can be rammed into the material column 12 more easily.

When forming the pile 13 using a vibrator arrangement or when ramming the pile 13 into the material column (and the material foot 11) may further increase the lateral confinement stress in the material column 12 and the material foot 11, and may further increase the diameter of the material column 11 and the material foot 11.

FIGS. 6A and 6B illustrate another example of a method for forming the concrete pile 13 in the material column. Referring to FIG. 6A, the method includes driving a hollow tube 71 that is closed at a bottom end by a shoe 72 into the material column 12. Driving the tube 71 into the material column may include using a vibrator (not shown). Further, referring to FIG. 6B, the method further includes filling the tube 71 with liquid concrete or with gravel and grout, and removing the tube from the ground, thereby forming the concrete pile 13. The shoe 72 remains in the material column 12 of the foot 11 after removing the tube (lost shoe). Optionally, a reinforcement cage is installed in the tube 71 before filling the tube 71 or after filling and withdrawing the tube 71.

In each of the examples explained above, the pile may be formed in such a way that it extends to the ground surface 101. This, however, is only an example. According to another example, the pile 13 is formed in such a way that its upper end is spaced apart from the ground surface, wherein a distance between the upper end and the ground surface 101 is between 0.5 and 1.5 meters, for example. A so called load transfer platform may be formed between the upper end of the pile 13 and the ground surface. The load transfer platform may include compacted crushed gravel with layers of reinforcement (geogrids and the like).

In the method explained above, the material column 12 which is produced prior to forming the concrete pile 13 (and which may be installed with variable diameter, i.e. a stronger diameter in a weak soil layer 130 as compared to a smaller diameter in stiffer/denser soil layers 140) stabilizes the ground before forming the concrete pile 13. This stabilizing of the ground 100 is more intense in weak layers than in stronger soil layers. Forming the material layer 12 pre-stresses the surrounding soil laterally, wherein by such pre-stressing it can be prevented that liquid concrete of the concrete pile expands in such weak layers under its self-weight, which would lead to the well-known bottlenecking effect as shown in FIG. 7 (see 61). Thus, unlike in a conventional method, bottle necks in the concrete pile can be avoided. This is explained with reference to FIG. 7 in greater detail.

FIG. 7 schematically illustrates a concrete pile 6 that has been formed by drilling a hole in the ground and filling the hole with concrete. In this method, however, the hole needs to be drilled down to a solid region, such as bedrock 110, so that the hole must not end in a relatively loose region such as compactable sand region 120. Further, the weight of the concrete before curing provides a load to the ground surrounding the hole. This may result in an unwanted varying diameter of the concrete pile, wherein the weaker the surrounding material, the larger the diameter. Moreover, in the region of an interface between a weaker ground region 130, such as a soft clay region, and a more rigid region 140 above such weak region, such as a sand region a bottle neck may be formed such that the concrete pile 61 locally has a diameter that is smaller than the diameter of the hole formed before. In the worst case the pile would be interrupted at such a transition zone between strong soil 140 and weak soil 130 and no longer be contiguous over its full length.

The material column 12 explained above may be omitted. According to one example, forming a foundation without the material column may include forming the foot 11 in accordance with one of the methods explained above and forming the pile 13 in the hole that remains above the foot 11 after installing the foot 11. Forming the pile 13 may include any one of the pile forming methods explained above. A foundation formed in this way is illustrated in FIG. 8.

According to one example, the pile 13 is a precast pile in accordance with any of the examples explained above and has a diameter that is larger than a diameter of the hole remaining above the foot 11. The pile 13 is driven into the ground using any kind of driving device, wherein the hole provides a guidance for the precast pile 13.

Although various exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. It will be obvious to those reasonably skilled in the art that other components performing the same functions may be suitably substituted. It should be mentioned that features explained with reference to a specific figure may be combined with features of other figures, even in those cases in which this has not explicitly been mentioned. Such modifications to the inventive concept are intended to be covered by the appended claims.

With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.

Claims

1. A method comprising:

forming a foot in the ground;

forming a material column on top of the material foot; and

forming a pile in the material column such that the pile extends down to the material foot or into the material foot.

2. The method of claim 1, wherein forming the foot includes forming the material foot using a vibrator arrangement.

3. The method of claim 2, wherein the vibrator arrangement includes a laterally vibrating vibrator.

4. The method of claim 1,

wherein forming the foot includes introducing material into the ground.

5. The method of claim 4, wherein the material includes at least one of

a granular material;

grout; or

concrete.

6. The method of claim 1,

wherein forming the foot includes compacting ground material.

7. The method of claim 2,

wherein forming the material foot includes:

introducing the vibrator arrangement to a predefined depth into the ground; and

repeatedly lifting and lowering the vibrator arrangement,

wherein material is introduced in a space below the vibrator arrangement when the vibrator arrangement is lifted and the vibrator arrangement penetrates into the introduced material when the vibrator arrangement is lowered.

8. The method of claim 7, wherein introducing the vibrator arrangement into the ground includes predrilling a hole into which the vibrator arrangement is introduced.

9. The method of claim 1,

wherein an average diameter of the material foot, and wherein the diameter of the material foot is between 2 times and 5 times the diameter of the vibrator arrangement.

10. The method of claim 1,

wherein an average diameter of the material foot is between 0.5 meters and 2 meters.

11. The method of claim 1, wherein forming the pile includes:

introducing a vibrator arrangement into the material column (12) and forming the pile (13) using the vibrator arrangement.

12. The method of claim 11, wherein the pile includes at least one of concrete, gravel, and grout.

13. The method of claim 1, wherein forming the pile includes:

ramming with a ramming device a precast pile into the material column.

14. The method of claim 13,

wherein the pile includes at least one of concrete, steel, and timber.

15. The method of claim 1, wherein forming the pile includes:

drilling a hole into the material column and filling the hole with concrete.

16. The method of claim 1, wherein forming the pile includes:

installing a hollow tube in the material column;

filling the tube with concrete; and

removing the tube.

17. The method of claim 1,

wherein forming the pile (13) comprises forming the concrete pile (13) to include a reinforcement cage (14).

18. The method of claim 1, wherein forming the material column includes forming the material column to have a diameter that varies along a length of the material column.

19. The method of claim 1,

wherein forming the material column includes repeatedly lifting and lowering the vibrator arrangement at a plurality of different positions in the hole,

wherein material is introduced in a space below the vibrator arrangement when the vibrator arrangement is lifted and the vibrator arrangement penetrates into the introduced material when the vibrator arrangement is lowered.

20. The method of claim 19,

wherein repeatedly lifting and lowering the vibrator arrangement includes:

measuring an operating parameter of the vibrator arrangement when the vibrator arrangement is lowered, and

repeatedly lifting and lowering the vibrator arrangement until the measured operating parameter at each of the plurality of different positions has reached a predefined threshold.

21. The method of claim 20, wherein the at least one operating parameter is selected from the group consisting of:

a power consumption of the vibrator arrangement;

an acceleration of the vibrator arrangement; or

a velocity of the vibrator arrangement.