EP2093332B1

EP2093332B1 - Method for constructing a foundation

Info

Publication number: EP2093332B1
Application number: EP20090153179
Authority: EP
Inventors: Johan Willem Van Der Pol
Original assignee: Dura Vermeer Business Development BV; Unidek Group BV
Current assignee: Dura Vermeer Business Development BV; Unidek Group BV
Priority date: 2008-02-19
Filing date: 2009-02-19
Publication date: 2012-12-12
Anticipated expiration: 2029-02-19
Also published as: EP2093332A1; NL2001295C2

Description

The invention relates to a method for constructing a foundation for a structure, which foundation is laid on an unstable surface. Within the framework of the present invention, the term "structure" is understood to mean all that which is placed on a foundation in practice, for example an earth structure or a building. The invention in particular relates to the construction of a foundation for sports fields, such as soccer or hockey fields or tennis courts, as well as other light structures, such as lawns, grass strips and footpaths, without the invention being limited thereto. Within the framework of the present invention, the term "unstable surface" is understood to mean a surface which lacks the load bearing capacity, or sufficient load bearing capacity, to support a foundation and a structure to be placed thereon, such as an earth structure, without additional measures being required. Peaty ground is such a weak surface, for example.
With reference to figure 3 thereof British patent publication no. 2,174,441 discloses an earth structure including alternate layers of soil and filler elements of expanded polystyrene, whereas the stability of said structure is improved by steel strips extending in the soil layers and anchored to prefabricated slabs of concrete. The entire structure is about 8 meter high and is sunk by about 80 cm relative to the surrounding ground.
Such a method is generally known, especially from GB 2174441A .
In another known method, an artificial lawn is constructed on a lava foundation, for example, which lava foundation is supported in particular on sand that has been pre-loaded for a prolonged period of time. It has been found in practice that an artificial lawn constructed in this way will invariably exhibit bumps and hollows or other damage after some time. Said bumps and hollows result from local unevennesses caused by settlement and/or subsidence of the ground, for example at the location of filled-in ditches.
A method according to the preamble of claim 1 is furthermore known from WO 2007030013A .
The object of the invention is to improve the prior art, i.e. to ensure that local unevennesses caused by settlement and/or subsidence of the unstable ground cannot cause damage to the foundation and the structure to be placed thereon.
In order to accomplish that object, the invention provides a method for constructing a foundation for a structure, said method comprising the steps of

forming the foundation by a floating base;
laying the foundation on an unstable surface, so that the foundation floats on a water-containing layer, characterised in that the floating base is made up of
at least two floating layers, each comprising several elongated blocks made of expanded polystyrene (EPS), which abut each other along their long sides, wherein the blocks of the first layer are arranged in crosswise fashion relative to the blocks of the second layer, the blocks of the first layer being arranged so that they are staggered relative to the blocks of the second layer; and
at least one stiffening web, which is provided on at least one outer side of each of the floating layers.

Thus, a "sandwich structure" is provided. The stiffening web functions to impart sufficient rigidity to the foundation, in particular to prevent the floating layers of EPS blocks from deforming upon being locally subjected to a specific load in use. The invention is in particular based on the realisation of a state of equilibrium, in which the foundation and the structure to be placed thereon float on a water-containing layer (for example a water-saturated layer of soil in the condition of use, i.e. in the loaded condition, making use of the upward force of the water ("Archimedes' law"). The water, in combination with the floating base, will compensate for unevennesses caused by settlement and/or subsidence of the unstable ground that may occur, for example at the location of filled-in ditches. Preferably, the stiffening web is also provided on an inner side of one or more floating layers. The present invention more in particular provides the following advantages:

1. it is now possible to build on unstable surfaces in an efficient and economical manner, which - in view of the instability of the surface - was so far considered to be problematic or impossible;
2. there is no need for costly and lengthy preloading of sand, a pile base or a state of equilibrium as in the prior art;
3. the floating foundation that is now provided has hardly any limitations as regards load bearing capacity and is low-maintenance, whilst it is perfectly level for placing in particular light structures thereon.

In a preferred embodiment of a method according to the invention, the stiffening web is provided on both sides of at least one of the floating layers. The stiffening web is in particular provided in blocks or in layers on at least one side of one of the floating layers.
In another preferred embodiment of a method according to the invention, the blocks of each floating layer are attached, preferably glued, together along their long sides. Preferably, several floating bases are formed, which are joined together, for example by mechanical means.
In another preferred embodiment of a method according to the invention, the stiffening web is made of at least one material selected from the group consisting of metal, plastic, carbon and glass. More in particular, a mesh of metal, plastic, carbon or glass is used. If a mesh of plastic material is used, the stiffening web is made of at least one material selected from the group consisting of polypropylene, polyester, polyethylene, nylon and glass fibre.
In another preferred embodiment of a method according to the invention, a top layer is laid on the floating base. The top layer in particular comprises a layer of poured concrete, which may or may not be reinforced. The concrete is for example selected to comprise closed or open cells (so-called "cellular concrete"). In another preferred variant, the top layer is for example made up of a granulate layer. This has a positive effect on the distribution of forces, in particular the damping of vibrations, as well as on the drainage of rain water, for example.
In a preferred embodiment of a method according to the invention, the unstable ground is dug off to below the ground water level, with the floating base floating on a layer of ground water. By partially digging off the unstable ground, a layer of ground water on which the foundation can float is automatically created. The groundwater is stable by nature, so that unacceptable fluctuations, for example caused by undulation, cannot occur. In another preferred variant, the floating base, in a condition of use thereof, floats on a water layer provided between the floating base and the unstable ground.
In another preferred embodiment of a method according to the invention, the layer of (ground) water has a thickness of at least 5 cm. Experiments have shown that this thin water layer is quite capable of compensating for unevennesses caused by settlement and/or subsidence of the unstable ground.
In another preferred embodiment of a method according to the invention, the thickness of the water layer is maintained by pump means. Preferably, the water layer is also refreshed - periodically or non-periodically - by said pump means. This furthermore makes it possible to store or buffer water.
The invention will now be explained in more detail with reference to figures illustrated in a drawing, in which:

Figure 1 is a schematic side view of a soccer field built in accordance with a preferred variant of the invention;
Figure 2 is a schematic, perspective view of the composition of a foundation as used in the football field of figure 1; and
Figures 3 and 4 show further preferred variants of the foundation according to the invention.

As shown in figure 1, the ground is peaty ground, from which peat has first been dug off so as to obtain a deepened area 1. Subsequently, a foundation in the form of a floating base 2 has been laid on (ground) water 3 in the deepened area 1. On said floating base 2, a soccer field 4 has been built. A pump (not shown) can pump water from the surface water 5 into the deepened area 1 in the direction indicated by the arrow 6 (for example when the water is high and water needs to be stored under the floating base 2) and also from the deepened area 1 to the surface water 5. In this way it is possible to control the water level in the deepened area 1 (i.e. under the floating base 2). If desired, the pump can pump out all the water from under the floating base 2 (so that the floating base 2 will rest on the bottom of the deepened area 1) when the soccer field is not being used for playing. The thin water layer under the floating base 2 is quite capable of compensating for unevennesses caused by settlement and/or subsidence of the unstable peaty ground.
Figure 2 shows how the floating base 2 is made up of three floating layers 7, 8, 9 of expanded polystyrene (EPS) and stiffening layers 10 of geotextile provided, possibly glued, on one side thereof. In this way a sandwich structure is obtained. The stiffening layers 10 function to impart sufficient rigidity to the floating base, in particular to prevent the floating layers 7,8,9 from sagging too much upon being subjected to a specific (local) load of, for example, 250 kg/m² (2.5 kN/m²). The floating layers 7, 8, 9 are for example made of elongated blocks of EPS of about 200 mm, whilst the stiffening layer 10 is made of geotextile. Instead of using a sandwich structure, it is also possible to use two floating layers 7,8, which are provided with a stiffening layer 10 on one side. In said preferred variant, the floating layer 7 is about 100 mm thick and the floating layer 8 is about 400 mm thick.
As figure 2 shows, the elongated EPS blocks of neighbouring layers 7,8,9 are arranged in a crosswise, staggered pattern.
Figures 3 and 4 show other preferred variants of the floating base 2, in which parts corresponding to each other are indicated by the same numerals. In figures 3 and 4, four layers 7,8,9,11 or EPS blocks arranged in a crosswise, staggered pattern are shown. In figure 3, the layers 7, 8, 9, 11 are provided with a carbon or glass fabric 10 on one side, for example, whilst in figure 4 the layers 7,8,9,11 are provided with such a fabric on both sides. In both figures 3 and 4, a top layer 12 of concrete or a granulate is provided.
The invention is not limited to the embodiment (s) as shown, but it also extends to other preferred variants that fall within the range of the appended claims.

Claims

A method for constructing a foundation for a structure, said method comprising the steps of
- forming the foundation by a floating base (2);

- laying the foundation on an unstable surface, so that the foundation floats on a water-containing layer, characterised in that the floating base (2) is made up of

- at least two floating layers (7, 8, 9, 11), each comprising several elongated blocks made of expanded polystyrene (EPS), which abut each other along their long sides, wherein the blocks of the first layer are arranged in crosswise fashion relative to the blocks of the second layer, the blocks of the first layer being arranged so that they are staggered relative to the blocks of the second layer; and

- at least one stiffening web (10), which is provided on at least one outer side of each of the floating layers (7, 8, 9, 11).
A method according to claim 1, wherein the stiffening web (10) is provided on both sides at least one of the floating layers (7, 8, 9, 11).
A method according to claim 1 or 2, wherein the stiffening web (10) is provided in blocks or in layers on at least one side of one of the floating layers (7, 8, 9, 11).
A method according to claim 1, 2 or 3, wherein the blocks of each floating layer (7, 8, 9, 11) are attached, preferably glued, together along their long sides.
A method according to any one of the preceding claims 1-4, wherein at least two floating bases (2) are formed, which floating bases (2) are joined together.
A method according to any one of the preceding claims 1-5, wherein the stiffening web (10) is made of at least one material selected from the group consisting of metal, plastic, carbon and glass.
A method according to claim 6, wherein said stiffening material is a mesh of metal, plastic, carbon or glass.
A method according to claim 6 or 7, wherein the stiffening web (10) is made of at least one material selected from the group consisting of polypropylene, polyester, polyethylene, nylon and glass fibre.
A method according to any one of the preceding claims 1-8, wherein a top layer (12) is laid on said floating base (2).
A method according to claim 9, wherein the top layer (12) is a layer of concrete, which may or may not be reinforced.
A method according to claim 10, wherein concrete comprising closed or open cells is selected.
A method according to claim 9, wherein the top layer (12) comprises a granulate layer.
A method according to any one of the preceding claims 1-12, wherein the unstable ground is dug off to below the ground water level, with the floating base (2) floating on a layer of ground water.
A method according to any one of the preceding claims 1-12, wherein the floating base (2) floats on a water layer provided between the floating base (2) and the unstable ground.
A method according to any one of the preceding claims 1-12, wherein water forms the unstable surface.