GB2222191A

GB2222191A - Forming underground walls

Info

Publication number: GB2222191A
Application number: GB8919258A
Authority: GB
Inventors: Roger Alfred Bullivant
Original assignee: Roxbury Ltd
Current assignee: Roxbury Ltd
Priority date: 1988-08-25
Filing date: 1989-08-24
Publication date: 1990-02-28
Also published as: GB8919258D0

Abstract

A method of forming an underground wall comprising driving a member S1 into the ground to form a cavity, driving a further member S2 adjacent the first member to form a further cavity, removing the first member from the cavity and simultaneously providing a filling through the member S1 to the cavity, and repeating these operations until the wall is completed. In a modification one member can be driven, filled with wail forming material, removed then re-driven alongside the recently driven and filled cavity. <IMAGE>

Description

Improved Method and Apparatus of Land Improvement The present invention concerns an improved method and apparatus of land improvement, especially but not exclusively the improvement of land which has been infilled with waste and refuse.

Land, for example pits, depressions and quarries which has been infilled with refuse is often difficult to further utilise not only because of the unstable nature of the infilled land but also due to the production of explosive gases on decomposition or chemical change of the fill material.

The problem of poor ground stability can be overcome by a mechanical compaction and/or by the use of piles driven through the infill to a sufficiently good load bearing stratum. There remains the problem, however, of gas collection and dispersal. To efficiently collect and disperse gas the in fill must be contained within a gas impervious structure so that escaping gases can be contained and safely exhausted.

Many methods have been attempted to achieve the containment of gas including pumping a cementitious mixture into the fill to consolidate it and contain the gas. To an extent this has proved satisfactory bt it can never be completely relied upon as, for example, the changes in the nature of the fill can result in the previously impervious grout and fill structure becoming pervious through the passage of time. Furthermore there can never be certainty that the grout passes into all the areas which it is intended that it should occupy.

Further methods of containing an area in fill have involved excavating a trench in which a diaphragm wall is constructed from concrete in situ. Owing to the poor structural qualities of most infills when a trench is excavated according to this method it is necessary to temporarily fill the trench immediately after the removal of fill by, for example, bentonite which holds back the trench walls against collapse and is subsequently displaced when the concrete is poured to form the partition wall. Bentonite is a difficult substance to work with and consequently forming infill containment walls of this nature is not a popular operation.

A further proposal has been to enclose the fill area with a continuous metal structure formed from trench sheets. Trench sheets are elongate metal members having lateral interconnecting means which are driven by hammering or vibration from above into the ground, one sheet at a time, a subsequent sheet being driven with its interconnecting means engaging with and sliding through the interconnecting means of a previously driven sheet so that eventually a continuous wall, formed from the plurality of interconnected sheets, is provided. In the main the method of providing such a wall is satisfactory but its disadvantage lies in its cost as steel trench sheets are expensive.

It is an object of the present invention to obviate and mitigate these disadvantages.

A further difficulty encountered has been the controlled removal of escaping gases. Various attempts have been made to obtain a controlled gas removal, for example by positioning gas pervious pipes in the infill but many difficulties have been encountered with such proposals. Obviously the pipes cannot be placed at the optimum positions unless they are arranged when the in fill is being placed and this, clearly, is unpractical.

Subsequent placing of pipes is difficult and to obtain satisfactorily complete gas removal numerous pipes are required. This is obviously expensive. It is a further object of the present invention to obviate or mitigate this disadvantage.

According to the present invention there is provided a method of forming an underground wall comprising the steps of successively forming a plurality of contiguous wall sections by driving a member into the ground to a predetermined depth to form a cavity providing a filling of wall forming material to the cavity, removing the member from the cavity and repeating these operations until the wall is completed.

Preferably the lower end of the member is closed during driving and desirably said end is open when the member is being removed from the cavity.

Preferably the internal filling is inserted into the cavity as the member forming the said cavity is removed, the filling may be inserted through the member.

Alternatively, the internal filling may be inserted whilst the member is being driven. As a further alternative in good ground the filling may be inserted after removal of the member.

When the filling is inserted whilst the member is being driven, the member is preferably hollow with openings in its side walls and is driven through a hopper arranged at ground level into which the filling is supplied to pass through the openings into the member.

The internal filling is preferably a fluent material and may be cementitious with or without reinforcement or a pervious material such as pea gravel.

A subsequent cavity may be formed before the first driven member is removed. Alternatively the same member may be used to form the next adjacent cavity.

Where the same member is used to form a subsequent cavity, the member is guided during driving such that its longitudinal axis is parallel to that of the adjacent pre-formed cavity.

Also according to the present invention there is provided a method of forming a lateral impervious member around a volume of ground according to any of the preceding seven paragraphs.

Still further according to the present invention there is provided a method of forming a gas pervious underground wall according to any of said eight preceding paragraphs.

Further according to the present invention there is provided apparatus for forming an underground wall comprising a hollow member having means for closing its lower end during the driving of the member into the ground, means for guiding the member relative to a previously driven member and means for allowing the passage of material supplied to the interior of the member into the cavity formed in the ground by the member.

Preferably the member is of rectangular cross-section.

Preferably said guide means are interconnecting means provided on the member for meeting with corresponding means on previously driven similar member.

Alternatively said guide means are vanes on at least the lower end of the member adapted to engage the surrounding ground to guide the member.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 shows a plan view of three trench sheets utilised in the method of the present invention, Fig. 2 shows a plan view of modified trench sheets, Fig. 3A and B show a schematic plan of and a cross-section through an infill site having pervious and impervious walls according to the present invention, Figs. 4, A, B, C & D illustrate diagrammatically a method of providing pervious or impervious walls, and Fig. 5 shows a perspective view of a further modified trench sheet.

A first aspect of the invention provides a method of forming a lateral peripheral impervious wall W (Fig.3) around a volume of ground which has been infilled. Prior to the forming of the impervious wall an impervious lower layer L is provided under the infill by injecting a cementitious or any other suitable grouting material through the infill to form a continuous layer across the base of the volume which has been filled. After carrying out the method of the present invention the contained ground can be capped with an impervious cover C utilising any existing convenient civil engineering means, which may include means for landscaping the cover, carrying off drainage water and trapping and venting off gas produced by the infill.

The first aspect of the invention concerns itself with providing a continuous surrounding wall W extending between the gas impervious base L and the impervious cover C as described in the preceding paragraph.

Fig. 1 shows three trench sheets S each of which is identical to its neighbours. Each trench sheet is hollow and comprises a pair of side members 10 spaced apart by 100 mm and connected at their ends by end members 12 of any suitable shape. Each end member carries continuous interconnecting means 14 which are adapted to interfit with the interconnecting means on a neighbouring sheet in a manner which permits relative movement in the longitudinal direction of the sheets but prevents.

transverse movements. Conveniently the interconnecting means comprise complimentary channel members. A closure, not shown, is provided at the leading end of each sheet.

The closure closes off the forward end of the sheet during driving but opens if the sheet is moved in a direction opposite to the driving direction.

According to the method of the present invention illustrated in Fig. 4 first trench sheet S1 having its end closure closed is driven by any suitable pile driving technique, for example, hammering or vibration, through the infill until its lower end reaches the impervious layer already provided. Obviously, the sheet is driven as close to the peripheral edge of the infilled area as convenient. A second similar sheet section S2 is then connected with the first section at their mutual interconnecting means and driven down to the desired depth. Once again the leading end of the trench sheet is closed by a closure means so that its interior remains empty.When the second sheet 52 has been driven a third sheet and optionally further sheets 53 - 55 may be driven and the first driven sheet section 51 is removed by a suitable jacking assembly pulling it upwards (Fig.4C).

As it is pulled upwards its closed lower end is opened to enable a fluent impervious wall forming medium to be introduced through the sheet as it is removed to occupy the area once occupied by the sheet. The removed section can then be taken to the side of the previously driven third or fifth section and re-utilised at S6. Clearly by following this continuous operation a wall around the infill can be completed. As shown in Fig. 4D the subsequent voids created by sections 52, 53 etc. can be filled from the side, i.e. by way of a previously formed void.

As the wall must be continuous the interconnecting means 14 at the edges of each sheet are so designed that they themselves displace infill so that the void formed by driving the sheets is continuous.

Various modifications can be made without departing from the scope of the invention, for example, any form of sheet can be provided and Fig. 2 shows such a modification. The sheet comprises a pair of parallel facing plates 20 and transverse end plates 22, the plates 20 having inwardly directed enlargements 24 at each end.

One end of each plate 20 is located in a channel 28 of an H section member 26 with the other channel being open to receive the enlargement 24 of the next-to-be driven section. Clearly one of the end plates 22 is attached to the member 26, the other to the plates 20 at a location suitably spaced from the end of the section.

It is important to note that only a small number of metal sheets are required (relative to the length of the wall to be provided) thereby keeping material costs to a minimum. In good ground it is possible to remove the sheets prior to filling the cavity formed by the sheets.

Any suitable impervious wall forming material can be provided with or without reinforcement and it may set to a hard final form or remain flexible.

To facilitate the collection of gas generated as a result of decomposition of the infill a similar wall forming technique can be utilised to provide a grid of pervious membrane walls P extending throughout the infill.

The apparatus shown in Figs. 1 and 2 and the method illustrated in Figs. 4A to 4D can be utilised again but in this instance rather than filling the voids left by removed sections S with an impervious grout a pervious material can be provided. A suitable material is pea gravel. This means that throughout the infill there are walls extending from the impervious layer to the covering offering relatively unrestricted passage for escaping gases so that gases are collected and pass upwards through the pervious walls to be collected at the surface by a suitable pipework arrangement and lead, for example, to a gas flare stack F where the gases can be burned off.

In a modified wall forming method a single member 30 (Fig. 5) having approximately the same thickness as the sheet members of Figs. 1 and 2 but a width approximately three times as great is utilised. It is driven into the infill as before and, without driving a similar member alongside it, is withdrawn as pervious or impervious material is supplied to the void thus created, through the member. Accordingly the same member is used to form each section.

The member 30 has a rectangular cross section and its lower edge 32 is closed during driving and open when being pulled out of the ground. The edge 32 is downwardly inclined towards the adjacent previously formed void to direct displaced material away from this void to maintain the member against deflection from its intented direction during the driving operation, normally vertically downwards, two sets of guide vanes are provided thereon.

A first set 34 are effectively extensions of the members longer walls and are intended to project into the previously formed cavity to ensure that the member follows the line of this cavity. The vanes 34 may extend over the entire length of the member or may be located only at its lower end. A second pair of vanes 36 project laterally from the member at its lower end on each side thereof.

During driving they ensure that the inclined leading face of the member does not tend to move it transversely off to the side into the previously formed cavity.

In a further modification the member can be driven and simultaneously in filled using the method described in the Applicant's co-pending Patent Application No. 8914764.9. The member has openings in its side walls and is driven through a hopper situated at ground level.

The infilling is supplied into the hopper and passes through the openings into the member to fill the cavity as the member is being driven.

Claims

1. A method of forming an underground wall comprising the steps of successively forming a plurality of contiguous wall sections by driving a member into the ground to a predetermined depth to form a cavity, providing a filling of wall forming material to the cavity, removing the member from the cavity, and repeating these operations until the wall is completed.

2. A method according to claim 1, in which the lower end of the member is closed during driving.

3. A method according to claim 1 or claim 2, in which the lower end of the member is open when the member is being removed from the cavity.

4. A method according to any of claims 1 to 3, in which the internal filling is inserted into the cavity as the member forming the said cavity is removed.

5. A method according to any of claims 1 to 3, in which the internal filling is inserted whilst the member is being driven.

6. A method according to claim 5, in which the member is hollow with openings in its side walls and is driven through a hopper arranged at ground level into which the filling is supplied to pass through the openings into the member.

7. A method according to any of claims 4 to 6, in which the filling is inserted through the member.

8. A method according to any of claims 1 to 3, in which the filling is inserted after removal of the member.

9. A method according to any of the preceding claims, in which the internal filling is a fluent material.

10. A method according to claim 9, in which the filling is cementitious.

11. A method according to claim 9 or claim 10, in which the filling has reinforcement.

12. A method according to claim 9, in which the filling is a pervious material.

13. A method according to claim 12, in which the filling is pea gravel.

14. A method according to any of the preceding claims, in which one or more subsequent cavities are formed before the first driven member is removed.

15. A method according to claims 1 to 13, in which the same member is used to form the next adjacent cavity.

16. A method according to claim 15, in which the member is guided during driving such that its longitudinal axis is parallel to that of the adjacent pre-formed cavity.

17. A method according to claim 16, in which the next adjacent cavity is provided with its filling prior to the driving of the member for the subsequent cavity.

18. A method of forming a laterial impervious member around a volume of ground according to any of claims 14 to 17 when dependent on any of claims 9 to 11.

19. A method of forming a gas pervious underground wall according to any of claims 14 to 17 when dependent on claim 12 or claim 13.

20. Apparatus for forming an underground wall comprising a hollow member having means for closing its lower end during the driving of the member into the ground, means for guiding the member relative to a previously driven member and means for allowing the passage of material supplied to the interior of the member into the cavity formed in the ground by the member.

21. Apparatus as claimed in claim 20, in which the member is of rectangular cross-section.

22. Apparatus as claimed in claim 20 or 21, in which said guide means are interconnecting means provided on the member for meeting with corresponding means on a previously driven similar member.

23. Apparatus as claimed in claim 20 or 21, in which said guide means are vanes on at least the lower end of the member adapted to engage the surrounding ground to guide the member.

24. A method of forming an underground wall substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

25. A method of forming an underground wall substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

26. A method of forming an underground wall substantially as hereinbefore described with reference to Figs. 4A, B, C and D of the accompanying drawings.

27. A method of forming an underground wall substantially as hereinbefore described with reference to Fig. 5 of the accompanying drawings.

28. A method of land improvement substantially as hereinbefore described with reference to Figs. 3A and B of the accompanying drawings.

29. Apparatus for forming an underground wall, substantially as hereinbefore described with reference to any of Figs. 1, 2 or 5, of the accompanying drawings.

30. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.