GB2394727A

GB2394727A - Elements for forming a void in a foundation

Info

Publication number: GB2394727A
Application number: GB0225440A
Authority: GB
Inventors: Mohammad Yunas
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-11-01
Filing date: 2002-11-01
Publication date: 2004-05-05
Also published as: GB0225440D0

Abstract

An element (1) comprises a generally C shaped channel which in use may be put in a trench (20) so that the side walls (8, 12) of channel support the base (10) of the channel away from the floor (24) of the trench. The channel may be provided with feet (28) or rest on bricks to prevent the channel from penetrating the ground. A further invention discloses a void forming element (201, 202, Figure 4) of substantially non-compressible material and having at least one flat face. Two of said elements may be used to support a plastics coated panel (42, Figure 4) upon which a structure (44, Figure 4) can be built. A method of using said elements in a trench is also disclosed.

Description

VOIDED FOUNDATION

DESCRIPTION

5 This invention relates to a voided foundation and especially, but not exclusively, to such a voided foundation for use in the erection of both permanent and temporary structures.

10 It is well known in the construction industry that the type of foundation used during building depends on the type of structure being built. For example, there will be differences between the foundations of a house and the foundations of a 15 temporary stage.

The type of foundation used will also, however, depend on other factors, such as the type of soil on which the structure is being built or otherwise 20 erected and the weather conditions during building.

Building on some soils, and in particular clay type soils, is difficult because clay has several undesirable characteristics. These characteristics 25 cause technical problems which need to be overcome to build successfully on this type of soil.

Soils, and in particular clay, can be very absorbent, acting much like a sponge soaking up 30 groundwater and/or rainwater. When, for example, clay absorbs water, it swells and moves. This movement is known as "heave" and can cause damage,

for example, cracking walls or unequal subsidence, a structure built thereon.

l This damage is caused by the force of the s heaving soil pushing on the foundations of the structures. These forces, generated by the heave of the soil, can be very large and any way of preventing them from acting on the structure is desirable.

10 The most effective way of limiting the damage caused by heave, is the formation of a void beneath the structure itself. This void allows for the soil to expand beneath the structure, therefore eliminating, or at least substantially reducing, any 15 force which would otherwise have been exerted on the structure if the soil heaved directly beneath it.

Traditionally, permanent structures have been built with voided foundations for this reason. These 20 voided foundations are generally formed in one of two main ways, either as a strip foundation or a raft foundation. In both cases, concrete beams are supported on piles which are driven deep into the ground. The walls of the structures are built upon 25 the beams, although the weight of the structure is actually supported by the piles.

If the beams were placed directly on to the soil, either at ground level or on the base of a 30 trench dug in the soil, any heave in the soil would cause an upward movement of the beam and corresponding movement of a wall or other structural

-3 member erected thereon. Building directly on soil is therefore very undesirable for this reason.

As stated above, a void beneath the beam will 5 provide room for the soil to heave, meaning that no upward force will be placed on the beam.

Voids have been formed under beams in two ways in the past, both methods involving placing expanded 10 polystyrene fillers in a trench prior to the formation of the beam within the trench.

These voids have been formed by first digging a trench and then preparing the base of the trench such 15 that it is generally flat. Expanded polystyrene, in the form of blocks or in the form of weaved masses, is then placed within the dug trench along its length. The top surface of the expanded polystyrene forms a substantially flat surface on to which a 20 suitably folded sheet of polypropylene is placed, such that it covers the inside of the dug trench above the expanded polystyrene filler, to form an impermeable trench within the dug trench. The concrete beam can then be formed in this 25 polypropylene-coated trench in the normal manner by placing a steel fabric cage within the impermeable trough and pouring in wet concrete.

These traditional voids are therefore not 30 actually true voids as they are filled substantially with expanded polystyrene. The expanded polystyrene does have a similar effect to a void due to its

-4 compressible and/or collapsible properties but it is not actually a true void.

The expanded polystyrene works because it 5 collapses and/or compresses when/if the soil beneath it heaves upwardly towards the beam. However up until the time when, the weaved block collapses or during the compression of the solid block, almost all of the force acting on the polystyrene due to the 10 heave of the underlying soil, is transferred to the beam. The fact that the void is not a true void is undesirable for several reasons and expanded 15 polystyrene itself has disadvantages as a material for use In certain conditions, as discussed below.

A major disadvantage with the current system of void formation is the expense involved, both from the 20 need to prepare a flat bottomed trench and from the cost of the expanded polystyrene. Also, work cannot be carried out in bad weather conditions due to the buoyancy of expanded polystyrene which will float in a waterlogged trench and also my be carried by high 25 winds out of the trenches, or generally around the site, stopping any progress.

Also, in the construction of temporary structures such as stages, or any structure which 30 needs to be raised off the ground, it is common to form a foundation structure of some sort, having a

-5 void beneath. These voids are often formed using expensive scaffolding structures.

Any method of improving the formation of voided S foundations for temporary structures, permanent structures or structures which require a raised ground level is therefore desirable.

Accordingly it is an object of the present 10 invention to overcome, or at least substantially reduce, the disadvantages associated with known types of voided foundations, such as those discussed above.

Accordingly, a first aspect of the invention 15 provides a construction element for forming a void in a foundation of a permanent or temporary structure, the element comprising at least three walls which define a void therewithin, such that, in use, the element is placeable on a surface, for example, a 20 ground surface, to form a support upon which a permanent or temporary structure can be erected.

Preferably, the construction element is arranged to be positioned within a trench dug in the ground.

The at least three walls are preferably in the form of a channel which is most preferably elongate and positionable along the length of a trench, in use. In use, at least one wall, preferably a substantially flat wall, of the element may be

-6 supported in spaced relationship from a base of any trench by the remaining walls, to form the void between the uppermost wall and the base of the trench. s The construction element may comprise any non-

compressible material, for example, a metal, mineral and/or plastics material, but preferably comprises a fabric or a lattice and most preferably a metal 10 fabric, such as one made of steel.

Also, the element may further comprise resistance means which, in use, can be used to control the depth of penetration of the element into 15 the base of any trench. The resistance means may comprise one of many forms, for example, a body may be placed on the base of the trench, such that, during use, the underside surface of a substantially flat wall of the element can rest.

The body may be, for example, any commonly available brick or indeed a number of bricks which may be placed in the trench into which the element can be placed, in use. Even more preferably, the 25 resistance means may, alternatively or additionally, comprise one or more feet which are attached to the element and which may contact soil surrounding the trench, in use, and, as a result, prevent the element from penetrating the ground too far.

A second aspect of the invention provides a temporary construction element for forming a void in

-7 a foundation and being formed from a non-compressible material, the element having at least one substantially flat wall which, in use, is uppermost and upon which a permanent or temporary structure can s be erected.

The non-compressible material preferably comprises a natural material, for example, soil or unbaked clay. The element may comprise a block of 10 said non-compressible material and, also, preferably further comprises a degradable plastics coating.

In use of a construction element in accordance with the second aspect of the invention, preferably 15 at least two such elements are used in spaced relationship in a trench. Preferably also, a generally planar member, such as a panel, may then be placed over and upon the at least two elements. Such a member may comprise a plastics coated plasterboard 20 panel, to provide a substantially flat surface on which a structure can then be erected.

A third aspect of the invention provides a method of producing a voided foundation for a 25 temporary or permanent structure, comprising the steps of: providing a construction element made of a non-

compressible material; locating the element upon a surface, such that, a wall of the element is uppermost; and

-8 erecting a temporary or permanent structure upon the so-located element.

s Preferably, the surface is the base of a trench and the construction element has at least three walls which may form of a channel and which, in use, may run the length of the trench.

10 One wall, which is preferably flat, may be supported in spaced relationship from the base of the trench by the remaining walls of the element, such that a void is formed between that one wall and the base of the trench.

The construction element may be constructed from any suitable noncompressible material, for example metal, mineral and/or a plastics material.

Preferably, the material is in the form of a fabric 20 or a lattice, for example, steel fabric.

The support structure may also further comprise resistance means which, in use, may control the depth of penetration of the support structure in the base 25 of any trench. The resistance means may comprise one of several forms, such as at least one body, for example a brick, placed on the base of the trough such that any substantially flat wall of the element rests, in use. Additionally or alternatively, the 30 resistance means may comprise feet which contact soil around the trough and are attached to the element.

Alternatively, the non-compressible material may comprises a natural material, for example unbaked soil or clay. When the support structure is in this form, it may comprise a block of said non 5 compressible material and, preferably, further comprises a degradable plastics coating.

In use of this embodiment of element, preferably at least two such elements are placed in a spaced 10 relationship along a trench. A panel, for example, plastics coated plasterboard, may then be placed upon the at least two construction elements, to provide a substantially flat surface upon which a structure can be erected.

In order that the various aspects of the invention can be more fully understood, preferred embodiments thereof will now be described by way of example only and with reference to the following 20 drawings in which: Figure l is an elevation in partial section of a first embodiment of construction element in accordance with the first aspect of the invention; Figure 2 is a plan view of the first embodiment shown in Figure It Figure 3 is an elevation in partial section of a 30 second embodiment of construction element in accordance with the first aspect of the invention;

- lo -

Figure 4 is an elevation in partial section of an embodiment in accordance with the second aspect of the invention; and S Figure 5 is a side elevation of a third embodiment in accordance with the first aspect of the invention. Referring firstly to Figure 1, a voided 10 foundation, comprises a construction element, indicated generally at 1, in accordance with the first aspect of the invention, for forming a void 2 In the foundation, indicated generally at 4, for a permanent or temporary structure (not shown). The 15 element 1 comprises three walls 8, 10, 12, which define the void 2, such that the element 1 is placed on a ground surface 24 to form a support on top of which a steel reinforced concrete beam 16 is provided and beneath which the void 2 is located. The element 20 1 is positioned within a trench 20 dug in the ground 22. The walls 8, 10, 12 of the element 1 are in the form of a channel, as shown in Figure 2, which 25 extends along the length of the trench 20.

The construction element 1 has the flat uppermost wall 10 which is parallel to the base 24 of the trench 20.

The wall 10 is supported in spaced relationship with respect to the base 24 of the trench 20 by the

two remaining walls 8, 12, to form the void 2 between the wall 10 and the base 29 of the trench 20.

The construction element 1 is constructed from a 5 shaped length of steel fabric, indicated at 26 in Figure 1, such that the three walls 8, 10, 12 are continuous. The element 1 also has resistance means 28 which 10 controls the depth of penetration of the element 1 in the base 24 of the trench 20. The resistance means 28 in this first embodiment shown in Figure 1 comprises feet which are attached at 6 to the element 1, to prevent the element 1 from penetrating too far Is in the ground.

A second form of resistance means is shown in Figure 2 in the form of bricks 30 located on the base 24 of the trough 20 on which the underside surface of 20 the uppermost wall 10 rests.

A second embodiment is shown in Figure 3 wherein a second construction element 101 is positioned at the side of a steel reinforced concrete beam 18, to 25 produce a second void 102. This beneficially prevents heave pressures from acting upon the sides of the beam 18.

Figure 4 shows an embodiment in accordance 30 with the second aspect of the invention.

-12 A temporary arrangement for forming a void 34 in a foundation, indicated generally at 36, comprises one or more construction elements 201 formed of a natural non-compressible material for example, soil s or unbaked clay. Each element 201 has one uppermost flat wall 40 and also a degradable plastics coating (not shown).

In use, two construction elements 201 are lo arranged in a spaced relationship along a trench, much like the resistance means 30 shown in Figure 2.

A piece of plastics coated plasterboard 42 is placed upon the elements 201, to provide a substantially flat surface on which a beam 44 can then be 15 constructed or otherwise erected.

As shown in Figure 4 construction elements 202 can be positioned along the side of the beam 44 to prevent heave forces acting thereon.

The method of producing the voided foundations shown in Figures 1 to 3, and in accordance with the third aspect of the invention, comprises the steps of digging the trench 20 and then shaping the element 1, 25 in the form of a channel, from a steel fabric 26.

The element 1 is then positioned within the trench 20, such that the walls 8 and 12 support the uppermost wall 10 in spaced relationship from the 30 base 24 of the trench 20. A void 2 is thus defined between the wall 10 the trench base 24.

-13 A polypropylene sheet 32 is then placed in the trench 20 on top of the wall 10 of the element 1 in a U-shape, to form a second trough in which the steel reinforced concrete beam 16, 18 Is formed. These 5 beams 16, 18 are supported at each end by piles 34 which support the weight of any structure (not shown) built or otherwise erected upon the beams 16, 18.

The construction element 1 described with 10 reference to the voided foundation of Figure 1 and in accordance with the first aspect of the invention, could also be used in foundations above ground level.

Such elements 1 could provide a base on which a temporary structure, such as a stage, could be 15 erected, such an embodiment being shown in Figure 5.

The method of producing the voided foundation 500 shown in Figure 5 comprises the steps of providing at least an element 501 from steel fabric 20 and in the form of a channel, each having a flat uppermost wall 510 and arranged upon the ground surface 522. A temporary structure 552 can then be erected on the elements 501.

25 The construction elements discussed above all provide voided foundations in a manner which improves greatly on the traditional voided foundations using expanded polystyrene.

30 The arrangements discussed above in relation to Figures 1, 2 and 3 provide voided foundations having real voids.

-14 If the soil beneath the concrete beam 16, 18 heaves, then the soil will tend to fill the void 2 defined by the element 1. Because the element 1 is S not load bearing, it needs to remain in position only for the length of time it takes to form the concrete beam 16, 18. After this time, it does not matter if the element 1 sinks further into the soil or remains in the same position, because the perforated nature lo of the element 1 means that the soil can expand through the holes in its fabric 26.

The exception to this is when the element is required to produce a solid foundation, for example, IS in the temporary staging structure shown in Figure 5.

In this case, the resistance to sinking can be increased by using efficient resistance means 528.

The embodiment described with reference to 20 Figure 4 is a temporary arrangement which is very environmentally friendly. The elements 201, 202 in this case are constructed from naturally occurring materials, for example, clay, lime or chalk.

25 These elements 201, 202 are strong enough to provide a surface on which the concrete beam 44 can be provided but then slowly begin to degrade and collapse over time, due to the action of, say, water on them. In time, both the elements 201, 202 and the 30 plastics coated plasterboard 42, which rests on the elements 201, will collapse to produce a larger void 34 into which the underlying soil can expand.

-15 These construction elements 201, 202 can be constructed in a range of sizes and/or shapes to suit the end use. Materials may additionally be combined 5 with the natural material to retard or enhance their moisture absorption characteristics and are preferably coated with a degradable plastic, so that they do not collapse too quickly.

Claims

-16 CLAIMS

1. A construction element for forming a void in a 5 foundation of a permanent or temporary structure, the element comprising at least three walls which define a void therewithin, such that, in use, the element is placeable on a surface to form a support upon which a permanent or temporary structure can be erected.

2. A construction element according to claim l, wherein the construction element is arranged to be positioned within a trench dug in the ground.

15 3. A construction element according to claim l or 2, wherein the at least three walls are in the form of a channel which is elongate and positionable along the length of a or the trench, in use.

20 4. A construction element according to claim l, 2 or 3, wherein, in use, -at-- least one substantially flat wall of the element is supported in spaced relationship from a base of any trench by the remaining walls, to form the void between the 25 uppermost wall and the base of the trench.

5. A construction element according to any preceding claim comprising a non-compressible material. A..... a: À:e A. À.. À..

À.. À. À

À.......

.......CLME: -17 6. A construction element according to claim 5, wherein the non- compressible material is a metal, mineral and/or plastics material.

s 7. A construction element according to claim 5 or 6 comprising a fabric, a lattice or a metal fabric, such as one made of steel.

8. A construction element according to any lo preceding claim further comprising resistance means which, in use, can be used to control the depth of penetration of the element into the base of any trench. IS 9. A construction element according to claim 8, wherein said resistance means comprises a body placed on the base of any trench, such that, during use, the underside surface of a substantially flat wall of the element can rest.

10. A construction element according to claim 8 or 9, wherein said resistance means comprises one or more feet which are attached to the element and which may contact soil surrounding any trench, in use, and, 25 as a result, prevent the element from penetrating the ground too far.

11. A construction element according to claim 8, 9 or 10, wherein the body is any commonly-available 30 brick or a number of bricks which can be placed in the trench into which the element is placeable, in use. A-.e À..:e À....

:::::..

:.. A. À..:.:.:..

12. A construction element for forming a void in a foundation, the element being formed from a non-

compressible material and having at least one 5 substantially flat wall which, in use, is uppermost and upon which a permanent or temporary structure can be erected.

13. A construction element according to claim 12, lo wherein the noncompressible material comprises a natural material, such as, soil or unbaked clay.

14. A construction element according to claim 12 or 13 comprising a block of the non-compressible 15 material and a degradable plastics coating.

15. A construction element according to claim 12, 13 or 14, wherein, in use, at least two such elements are used in spaced relationship in a trench.

16. A construction element according to claim 15, wherein said at least two elements have a plastics coated plasterboard panel placed thereover and thereupon, to provide a substantially flat surface on 25 which a structure can be erected.

17. A method of producing a voided foundation for a temporary or permanent structure, comprising the steps of: providing a construction element made of a non-

compressible material; .... e:e ':e..

., ,. ::.:.::: 2'..:..

-19 locating the element upon a surface, such that, a wall of the element is uppermost; and 5 erecting a temporary or permanent structure upon the so-located element.

18. A method according to claim 17, wherein the surface is the base of a trench and the construction lo element has at least three walls.

19. A method according to claim 18, wherein the at least three walls of the element form a channel.

15 20. A method according to claim 19, wherein the channel, in use, runs the length of the trench.

21. A method according to any of claims 17 to 20, wherein one wall of the element is supported in 20 spaced relationship from the base of the trench by the remaining walls of the element, such that a void is formed between that one wall and the base of the trench. 25 22. A method according to any of claims 17 to 21, wherein the construction element is constructed from a non-compressible material.

23. A method according to claim 22, wherein the non 30 compressible material is a mineral and/or a plastics material. A....'..:e ':..

A::::::

:e e.. À.e:e:e:..

-20 24. A method according to claim 22 or 23, wherein the noncompressible material is formed as a fabric or a lattice, such as a steel fabric.

s 25. A method according to any of claims 17 to 24, wherein the construction element is provided with resistance means which, in use, controls the depth of penetration of the support structure in the base of any trench.

26. A method according to claim 25, wherein said resistance means is provided by a body, such as a brick placed on the base of the trench, such that any substantially flat wall of the element rests, in use.

27. A method according to claim 25 of 26, wherein said resistance means comprises feet which contact soil around the trench and are attached to the element. 28. A method according to any of claims 22 to 27, wherein the non-compressible material comprises a natural material, such as unbaked soil or clay.

25 29. A method according to claim 28, wherein the non-

compressible material comprises a block of such material and a degradable plastics coating.

30. A method according to any of claims 17 to 29, 30 wherein at least two elements are placed in a space relationship along a trench.

a'- be,.'. ':' ':'.'.

. .....

, ... . ....

-21 31. A method according to claim 30, wherein a panel, such as a plastics coated plasterboard, is placed upon the at least two construction elements, to provide a substantially flat surface upon which the 5 structure can be erected.

32. A construction element substantially as hereinbefore described with reference to the accompanying drawings.

33. A method of producing a voided foundation for a temporary or permanent structure, substantially as hereinbefore described.

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