GB2037349A

GB2037349A - An Improved Method of Filling a Void Beneath the Ground

Info

Publication number: GB2037349A
Application number: GB7943103A
Authority: GB
Original assignee: Balfour Beatty Ltd
Current assignee: Balfour Beatty Group Ltd
Priority date: 1978-12-14
Filing date: 1979-12-14
Publication date: 1980-07-09

Abstract

In a method of filling a void beneath the ground a hole 11 is drilled downwardly through the ground and into the void and aggregate is introduced into the void through the hole using a rotatable injector device 14 which directs the aggregate outwardly to the peripheral extremity of the void, the void being gradually filled with aggregate inwardly from its periphery. Interstices between the aggregate and any remaining space in the void is filled with a hardenable mixture of cold setting synthetic resin in a liquid or semi-liquid state and a filler. <IMAGE>

Description

SPECIFICATION An Improved Method of Filling a Void Beneath the Ground This invention relates to a method of filling a void beneath the ground and is especially, but not exclusively, concerned with a method of filling a void beneath a body or bodies of concrete constituting the load-bearing component or components of a road, airfield runway, car racing track, path, heavy machinery foundation or other similar construction.

It is an object of the invention to provide an improved method of substantially filling a void beneath the ground, which method can be effected in substantially less time than methods hitherto proposed and used, is substantially more economical in materials than such methods and is therefore substantially cheaper.

According to the invention the method comprises drilling or otherwise forming at least one hole downwardly through the ground and into the void; introducing into the void through said hole or holes an aggregate or other multiplicity of separate small bodies in such a way that the aggregate is directed outwardly to the peripheral extremity of the void and the void is gradually at least partially, and preferably substantially, filled with aggregate inwardly from the periphery of the void: substantially filling interstices between the aggregate and any remaining space in the void with a hardenable mixture of cold setting synthetic resin in a liquid or semi-liquid state and a filler; and permitting the hardenable mixture to set and bond firmly to the surfaces of the aggregate.

Since the void is at least partially and preferably substantially filled with aggregate, the amount of hardenable mixture required to fill said interstices and any remaining space in the void is substantially less than the amount of hardenable mixture that would otherwise have been required to fill the void; the saving in cost of material can therefore be substantial. Furthermore, the hardenable mixture of cold setting synthetic resin and filler effects a very strong bond with the aggregate and will harden to a sufficient extent for the ground to support traffic or to permit construction work to commence in a few hours only.

Preferably, the or each downwardly extending hole is formed at or near a central portion of the void and the aggregate is introduced through the hole into the void by means of a rotatable injector device which extends through the hole into the void and which is of such a form that, when rotatably driven about a substantially vertical axis, it directs aggregate to the peripheral extremity of the void by centrifugal force.

A preferred rotatable injector device for this purpose comprises a tube having in its bore two passages, one for introduction of aggregate and one for introduction of air under pressure, and, rotatably mounted on one end of the tube, a separately formed spout which is curved both radially outwardly and partially circumferentially.

In use the injector device is inserted into the hole to such an extent that the rotatable spout at least partially protrudes into the void and, when air under pressure and aggregate are fed into the passages of the tube, the spout is rotatably driven about the tube to propel aggregate from the spout to the peripheral extremity of the void. When the void is substantially filled with aggregate or has been filled to the required extent, the injector device is removed before the hardenable mixture is introduced.

To ensure that the hardenable mixture not only substantially filis the interstices between the aggregate but also enters cracks, pores and other voids in the surfaces of the separate bodies constituting the aggregate, and thereby when it sets will effect a very strong bond with the aggregate, preferably after the void has been at least partially filled with aggregate, a flexible fluid-impermeable covering is sealed to the surface of the ground around the underlying void to form a substantially fluid-tight enclosure incorporating the void; air and any other fluid is evacuated from the fluid-tight enclosure; said hardenable mixture is allowed to enter the evacuated enclosure until hardenable mixture substantially fills the interstices between the aggregate and any remaining space in the void; and the hardenable mixture is permitted to set.

Other operating steps that may be employed in introducing the hardenable mixture of cold setting synthetic resin and filler into the void using the aforesaid vacuum impregnation technique are described and claimed in the Complete Specifications of our Patents Nos 1399510, 1479020, 148718, 1490101 and 1490102 and of our co-pending Patent Application No.

33933/77 (Serial N. ).

To eliminate any risk that air will be introduced into the evacuated enclosure in the hardenable mixture, when preparing the mixture, the synthetic resin and filler may be mixed together under vacuum.

A preferred aggregate is gravel because of its flow properties but, in some circumstances, stone or granite chippings may be employed. In all cases, preferably the aggregate is clean and is so graded that, in size, it is no greater than 8mm and no smaller than 4mm.

It is preferred to use, as the cold setting synthetic resin, polyester or acrylic resin because each has a very short setting time, usually one or two hours, but in some circumstances where a short setting time is not of first priority, epoxy resin is preferred because there is less risk of cracks forming in the resin due to shrinkage of the resin as it hardens; also in wet conditions epoxy resin shows better water tolerance.

One preferred hardenable mixture comprises a synthetic resin/filler mixture in the proportion 1:1 to 2:1, by weight. A preferred hardenable mixture consists of 1 part by weight polyester resin and 1 part by weight calcite. Other fillers that may be employed include granular bauxite and atmosphere, a material consisting of tiny hollow spheres of glass which are an extract of pulverised fuel ash.

As previously indicated, the method of the present invention is especially, but not exclusively, applicable to filling a void underlying a road or other ground construction made wholly or in part of concrete. Where, in a road fabricated from separately formed slabs of concrete, due to the presence of a void beneath a concrete slab the slab cracks and a part of the slab sinks below the normal running surface of the road, before the void is filled with aggregate and hardenable mixture by the method as hereinbefore described, it is preferred to raise the sunken slab so that its running surface is substantially level with the adjacent slab or slabs. Raising of a sunken concrete slab is preferably effected by means of expendable claws which are introduced into a plurality of holes drilled at spaced positions and each of which is attached to a jack, winch or other lifting means.

The invention is further illustrated by a description, by way of example, of a preferred method of filling the aggregate and a synthetic resin a void underlying a concrete road, with reference to the accompanying drawing which shows a fragmental cross-sectional view of the road.

Referring in the drawing, in a length 1 of concrete road comprising adjacent slabs 3 and 4, the slab 3 has a crack 2 extending transversely across the road, the slab having cracked as a result of a void 5 that developed beneath the road between the road and an underlying layer 6 of clinker.

In order to fill the void 5, the slab 3 having been raised of necessary to bring its running surface level with that of the or each adjacent slab,, at least one hole 11 is drilled through the concrete at a position judged to be above the centre of the void 5 and an injector device 12 is inserted into the hole until a rotatable spout 14 at its lower end protrudes into the void. The injector device 12 comprises a venturi tube 1 5 with an aggregate injection tube 1 6 opening into tube 1 5 as shown and with the spout 14 rotatably mounted at the lower end of the tube 1 5. The spout 14 has a tubular outlet which is curved both radially outwardly and partially circumferentially.

Air under pressure is fed into the tube 1 5 and aggregate is fed into the tube 1 6. Expulsion of air and aggregate from the outlet of the spout 14 rotatably drives the spout relative to the tubes and propels aggregate to the peripheral extremity of the void 5, as shown. Introduction of air and aggregate continues until aggregate prevents rotation of the spout 14. The device 12 is then removed and the remaining space in the void 5 and in the hole 11 is topped up with aggregate.

The interstices between the separate bodies of the aggregate and any remaining space in the void 5 and hole 11 are then substantially filled with a filled sythetic resin using the vacuum filling technique described and claimed in the Complete Specification of any one or more than one of the aforementioned patents and co-pending patent application.

Claims

1. A method of substantially filling a void beneath the ground which comprises drilling or otherwise forming at least one hole downwardly throught the ground and into the void; introducing into the void through said hole or holes an aggregate or other multiplicity of separate small bodies in such a way that the aggregate is directed outwardly to the peripheral extremity of the void and the void is gradually at least partiallly filled with aggregate inwardly from the periphery of the void; substantially filling interstices between the aggregate and any remaining space in the void with a hardenable mixture of cold setting synthetic resin in a liquid or semi-liquid state and a filler; and permitting the hardenable mixture to set and bond firmly to the surfaces of the aggregate.

2. A method as claimed in Claim 1, wherein the void is gradually substantially filled with aggregate inwardly from the periphery of the void.

3. A method as claimed in Claim 1 or 2, wherein the or each downwardly extending hole is formed at or near a central portion of the void and the aggregate is intoduced through the hole into the void by means of a rotatable injector device which extends through the hole into the void and which is of such a form that, when rotatably driven about a substantially vertical axis, it directs aggregate to the peripheral extremity of the void by centrifugal force.

4. A method as claimed in Claim 3, wherein the rotatable injector device comprises a tube having in its bore two passages, one for introduction of aggregate and one for introduction of air under pressure, and, rotatably mounted on one end of the tube, a separately formed spout which is curved both radially outwardly and partially circumferentially, and wherein the injector device is inserted into the hole to such an extent that the rotatable spout at least partially protrudes into the void and, when air under pressure and aggregate are fed into the passages of the tube, the spout is rotatably driven about the tube to propel aggregate from the spout to the peripheral extremity of the void.

5. A method as claimed in any one of the preceding Claims, wherein, after the void has been at least partially filled with aggregate, a flexible fluid-impermeable covering is sealed to the surface of the ground around the underlying void to form a substantially fluid-tight enclosure incorporating the void; air and any other fluid is evacuated from the fluid-tight enclosure; said hardenable mixture is allowed to enter the evacuated enclosure until hardenable mixture substantially fills the interstices between the aggregate and any remaining space in the void; and the hardenable mixture is permitted to set.

6. A method as claimed in any one of the preceding Claims, wherein, during preparation, the synthetic resin and filler are mixed together under vacuum.

7. A method as claimed in any one of the preceding Claims, wherein the aggregate is gravel.

8. A method as claimed in any one of Claims 1 to 6, wherein the aggregate is stone or granite chippings.

9. A method as claimed in any one of the preceding Claims, wherein the synthetic resin is polyester or acrylic resin.

10. A method as claimed in any one of Claims 1 to 8, wherein the synthetic resin is epoxy resin.

11. For use in the method of substantially filling a void beneath the ground as claimed in any one of the preceding Claims, a rotatable injector device comprising a tube having in its bore two passages, one for introduction of aggregate and one for introduction of air under pressure, and, rotatably mounted on one end of the tube, a separately formed spout which is curved both radially outwardly and partially circumferentially.

12. A method of substantially filling a void underlying a concrete road substantially as hereinbefore described with reference to the accompanying drawing.