GB2268951A

GB2268951A - Ground fill material

Info

Publication number: GB2268951A
Application number: GB9314602A
Authority: GB
Inventors: John James Patrick Brown
Original assignee: Kay Metzeler Ltd
Current assignee: Kay Metzeler Ltd
Priority date: 1992-07-14
Filing date: 1993-07-14
Publication date: 1994-01-26
Anticipated expiration: 2013-07-14
Also published as: GB2268951B; GB9314602D0

Abstract

Ground fill material for combating heave and settlement of ground in the construction of building foundations is in the form of bodies of expanded polystyrene 20, either in rectangular block form or with castellations on one surface. The polystyrene bodies have a semi-rigid, sheet material 24 bonded to one face; this may be a corrugated board of polyethylene. <IMAGE>

Description

GROUND FILL MATERIAL This invention relates to ground fill material intended for use particularly in building applications. The purpose of such ground fill material in ground beam applications is to absorb surge resulting from ground movement or to line trench walls of foundations in order to overcome cracking from heave or earth movement. The ground fill material will therefore occupy volume in foundation construction whilst allowing any subsequent movement of the ground to be absorbed by compression of the fill material rather than by cracking of the foundations.

It is known to use low density expanded polystyrene bodies for this purpose. Low density expanded polystyrene has sufficient resistance to crushing to enable it to support the weight of concrete poured over and around it, but will yield by compression if subsequent ground movement takes place after the concrete has set. This ground movement can be surge, ie upward ground movement which is an occurrence which is particularly to be guarded against when building on clay soils.

It is known to use low density expanded polystyrene bodies both in the form of rectangular blocks and in the form of "castellated" blocks. A castellated block has one surface from which a plurality of protrusions extend, and in use the surface with the protrusions is generally placed so that the protrusions face against the ground.

We have surprisingly now found that the performance of both block and castellated expanded polystyrene ground fill can be substantially improved by bonding a semi-rigid sheet of material to one surface of the body. When the body has castellations, then the sheet material is bonded to the face which is opposite to that from which the castellations or projections project.

Accordingly, the invention provides ground fill material comprising a body of expanded polystyrene which has one substantially flat surface and a semi-rigid sheet material bonded to the substantially flat surface.

The function of the semi-rigid sheet of material is to act as a load distribution platform across the polystyrene, and to this end the term "semi-rigid" is to be construed as meaning significantly more rigid than expanded polystyrene alone. The sheet material should not however crack when loaded and so should possess a significant degree of flexibility. Preferably the material should be capable of bending around a 600mm radius without cracking or breaking.

As a result of the presence of the semi-rigid sheet material, a load which is positioned at one point, for example above one of the castellation projections, does not act only on that projection but is distributed across a larger area or across a number of projections thus avoiding premature failure of the first mentioned of the projections.

Furthermore, should the polystyrene body fracture, the sheet material will not fracture but will remain as a continuous sheet to keep the body in its correct formation.

The semi-rigid sheet material is preferably a plastics material and can, for example, be a laminated and/or fluted polypropylene membrane. It is advantageous if the exposed surface of the sheet material is smooth to assist the flow of concrete over the ground fill body during the construction of foundations. If the sheet material has shape memory, it will try to return to its original form after bending, so that if a body is bent so that the polystyrene cracks, the memory of the sheet material will tend to restore the original form of the body. As a result, even sheets where the polystyrene has been damaged can still be used.

It is important that the sheet material should not degrade when buried in the ground, and in particular should not evolve methane gas on exposure to ground moisture.

The bonding of the sheet material to the polystyrene needs to be strong enough to hold the two together during transport, installation and during the pouring of concrete.

However once the concrete has been poured, the bonding has no further job to do.

The invention also provides a method of constructing a building foundation, the method comprising the steps of excavating a trench, lining at least one wall of the trench with expanded polystyrene which has semi-rigid sheet material bonded to one substantially flat face, such that the semi-rigid sheet material faces into the trench, and pouring concrete into the trench.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a section through a building constructed on foundations which include a compressible fill in accordance with the invention; Figures 2, 3 and 4 show alternative foundation constructions in accordance with the invention; Figure 5 shows a detail through a foundation trench with a compressible fill in accordance with a first embodiment of the invention; Figure 6 is a perspective, exploded view of a body of ground fill material in accordance with a second embodiment of the invention; Figure 7 is a view corresponding to Figure 5 but showing a trench in which ground fill material in accordance with both the first and second embodiments of the invention is in use; and Figure 8 illustrates how ground fill material in accordance with the invention can be used at corners of a trench.

Figure 1 shows a building 10 which is constructed on a site where a mature tree (indicated in dotted lines 12) has been removed. The removal of the tree and the associated change in moisture retention in the area surrounding the roots will lead to potential instability of the ground and the foundations 14, 16 and 18 are therefore constructed as trenches which are lined on one side with a compressible fill 20 and are then filled with concrete. The walls of the house and the floor slab 22 are then supported on these foundations.

It is well known to use expanded polystyrene sheets as the compressible fill 20. However this material is difficult to handle without breaking and, particularly in thinner sheets (for example 15mm or less) it is liable to break during handling and during securing to the side of the trench.

This can result in loose pieces of polystyrene entering the trench and if this happens then the desired resistance to clay heave, surge or other ground movement is not achieved.

In order to avoid this problem, sheets of expanded polystyrene 20 are provide with a facing 24 of a relatively stiff corrugated plastics material which is bonded to one complete face of each polystyrene slab. The application of a corrugated plastics sheet provides sufficient rigidity to prevent the known problems of breaking of the polystyrene sheets without increasing the weight of the sheets to any substantial degree. Furthermore the corrugated sheet is reasonably compressible in a direction perpendicular to the plane of the sheet so that it does not adversely affect the compressible characteristics of the material for which the fill is being used.

In use, a trench 26 is dug as shown in Figure 5. A sheet 20 of compressible fill formed predominantly by a sheet of expanded polystyrene 28 but with a facing of corrugated plastics sheet material 24 on one side, is laid in the trench, along one vertical wall of the trench and with the corrugated plastics sheet material 24 exposed to the interior of the trench. The compressible fill is anchored to the wall of the trench by earth bolts 30 which pass right through both layers of the fill 20. The sheet material 24 helps to hold the heads of the earth bolts.

The remaining open space of the trench is then filled with concrete 18 to produce a structure as shown in any one of Figures 1 to 4. Because of the smooth outer surface of the sheet material 24, the concrete can flow smoothly along the trench so that air voids are avoided.

In the embodiment of Figure 6, the ground fill material comprises a body 128 of expanded polystyrene. This body has a platform 129 from which a plurality of castellations or projections 130 depend. The projections 130 can be regular in shape as shown, or they can take any alternative shape, as suitable for manufacturing convenience and to achieve the necessary load bearing performance.

The upper surface of the platform 129 is flat, and a semirigid sheet material 124 is bonded to this flat surface.

Any suitable bonding method can be used, but the most likely method is some form of adhesive.

The sheet material 24, 124 can be bonded to, or laminated with the polystyrene 28, 128 by using a suitable adhesive or possibly by heating the adjacent surfaces of the two materials so that they fuse together.

The construction of the sheet material 24, 124 can take a number of forms, but one likely construction would be a laminated and fluted board such as that sold under the Trade Mark Twins lute by Twinplast Limited. It is important that the rigidity of the sheet material should be significantly greater than that of the polystyrene, so that when a load is applied to the outer surface, ie to the sheet material, the load will be distributed over the body. In the embodiment of Figure 6, the load will be distributed over several of the projections 130.

In use, the ground fill body will be supplied in sections of a convenient size in accordance with the site requirements.

Typical sizes might be 500mm square by 150mm thick, and would include the bonded sheet material 24, 124 permanently attached to the upper surface of the platform area 29.

Where a large area of ground fill body is required, several such members can be placed adjacent to one another in a foundation trench before concrete is poured over the whole assembly. It may be appropriate to lay polyethylene sheeting over such an assembly to prevent concrete penetration between the ground fill members.

Figure 7 shows a trench 126 at the edges of which piles 127 have been sunk. Ground fill bodies 20, 120 are laid in this trench, between the piles 127. A framework or cage of reinforcing bars (not shown) will be laid in the trench, within the bodies 20, 120 and the trench will then be filled with poured concrete. This then provides stable footings with the ground fill bodies acting as a compressible material against upward surge.

Figure 8 shows how the presence of the semi-rigid sheet material 24 can be used in the area of a trench corner. By cutting away a triangular section of the polystyrene body 28, but not cutting the sheet material 24, it is possible to bend the ground fill body as shown to follow a right-angled (or any other angle) wall. This can particularly assist when the trench corner is broken away as shown at 32, because the ground fill can then restore the sharpness of the corner and avoid expensive remedial infilling.

The use of the bonded sheet material 24, 124 thus significantly enhances the ability of the ground fill material to do the work for which it is intended.

In use, the bonded sheet material assists in allowing ground heave/surge to take place due to expansion of the soil without affecting the ground beam formed by the poured concrete. Particularly when using castellated polystyrene, the polystyrene remains intact during pour as compression is eliminated from the base legs of the castellations thereby stopping possible fractures of the legs under the weight of the concrete pour.

By this principle the leg thickness is retained enabling the compressible fill castellated polystyrene to meet its designed purpose of combating anticipated earth surge.

Further advantages are also known in that less breakage on site is evident. Even when fractures of the polystyrene bodies take place it is still possible to use 'fractured' bodies due to the bonded sheet material which bends or flexes but does not fracture and which has the effect of keeping the broken parts together.

It will therefore be seen that by applying a semi-rigid sheet material to polystyrene bodies, their performance and usability as ground fill can be greatly increased.

Claims

1. Ground fill material comprising a body of expanded polystyrene which has one substantially flat surface and a semi-rigid sheet material bonded to the substantially flat surface.

2. Ground fill material as claimed in Claim 1, wherein the semi-rigid sheet material does not decompose when buried in the ground.

3. Ground fill material as claimed in Claim 1 or Claim 2, wherein the semi-rigid sheet material is capable of flexing without breaking.

4. Ground fill material as claimed in any preceding claim, wherein the semi-rigid sheet material can be bent around a 600mm radius without breaking.

5. Ground fill material as claimed in any preceding claim, wherein the semi-rigid sheet material has shape memory and tends to return to its original position after flexing.

6. Ground fill material as claimed in any preceding claim, wherein the semi-rigid sheet material is an extruded board having at least one flat face and an opposite face, with the space between the faces bridged by strengthening walls.

7. Ground fill material as claimed in Claim 6, wherein the board has two opposite flat faces.

8. Ground fill material as claimed in any preceding claim, wherein the semi-rigid sheet material is an extruded, fluted board made from polypropylene with two opposite flat faces supported spaced apart from one another by flutes between the faces.

9. Ground fill material as claimed in any preceding claim, wherein the semi-rigid sheet material has a thickness of between 2mm and 6mm.

10. Ground fill material as claimed in any preceding claim, wherein the semi-rigid sheet material is bonded to the flat face of the polystyrene body by adhesive.

11. Ground fill material as claimed in Claim 10, wherein the adhesive is a contact adhesive.

12. Ground fill material as claimed in any preceding claim, wherein the body of expanded polystyrene is a rectangular block.

13. Ground fill material as claimed in any one of Claims 1 to 11, wherein the body of expanded polystyrene has one substantially flat surface and an opposite castellated surface and the semi-rigid sheet material is bonded to the substantially flat surface.

14. A method of constructing a building foundation, the method comprising the steps of excavating a trench, lining at least one wall of the trench with expanded polystyrene which has semi-rigid sheet material bonded to one substantially flat face, such that the semi-rigid sheet material faces into the trench, and pouring concrete into the trench.

15. Ground fill material substantially as herein described with reference to any one embodiment shown in the accompanying drawings.

16. A method of constructing a building foundation, substantially as herein described with reference to the accompanying drawings.