GB2178461A

GB2178461A - Retaining walls

Info

Publication number: GB2178461A
Application number: GB08614041A
Authority: GB
Inventors: Lewis Stansfield
Original assignee: STENT FOUNDATIONS Ltd
Current assignee: STENT FOUNDATIONS Ltd
Priority date: 1985-06-11
Filing date: 1986-06-10
Publication date: 1987-02-11
Also published as: GB2178461B; GB8514710D0; GB8614041D0

Abstract

In a quick and inexpensive method of installing a concrete retaining wall by secant piling, a plurality of female piles (1) of a cement slurry are formed in situ side by side in such a way that adjacent female piles are spaced apart by a distance less than the diameter of a male pile which is to be formed and, after the piles have set, a male pile (2) of strong concrete is formed in situ between each adjacent pair of female piles. The portions of female piles (1) of cement slurry remaining between adjacent male piles (2) when the male piles have set effectively constitute water-tight seals. The surface of the retaining wall (3) exposed when the excavation in the ground which the retaining wall is to bound is excavated may be lined with a layer (4) of concrete. <IMAGE>

Description

SPECIFICATION Retaining walls This invention relates to retaining walls of concrete cast in situ and is especially, but not exclusively, concerned with retaining walls of this kind suitable for forming the walls of an excavation in the ground.

In one known method of installing a concrete retaining wall which is cast in situ, which method is generally and, for convenience, will hereinafter be referred to as secant piling, a plurality of concrete piles, hereinafter referred to as female piles, are formedin situ side by side in such a way that adjacent female piles are spaced apart by a distance less than the diameter of a female pile and, after the female pile have set, a concrete pile, hereinafter referred to as a male pile, is formed in situ between each adjacent pair of female piles. After the male piles have set, the excavation in the ground to be bounded by the retaining wall is excavated and in some instances the exposed face of the line of piles is lined with a layer of concrete.This method of installing a concrete retaining wall has the major disadvantage that heavy and expensive equipment must be used to out away portions of adjacent female piles when forming each male pile and, as a result forming of the male piles is both expensive and time consuming.

It has been proposed to so space adjacent female piles apart that only a small portion of each female pile must be cut away when the male pile is formed but this results in a reduction in the thickness of concrete at the interface between adjoining female and male piles, thereby rendering the joint between adjacent female and male piles less water-tight and the provision of a water-tight lining of concrete of substantial thickness on the exposed surface of the line of piles virtually essential.

It is an object of the present invention to provide an improved method of installing a concrete retaining wall be secant piling, which method is quicker and less expensive than methods of secant piling hitherto employed to install a concrete retaining wall of comparable size.

According to the invention, the method comprises forming in situ side by side a plurality of female piles of a cement slurry or other cement mix of low strength in such a way that adjacent female piles are spaced apart by a distance substantially less than the diameter of a male pile which is to be formed and, after the female piles have set, forming in situ between each adjacent pair of female piles, a male pile of concrete substantially stronger than the cement slurry or other low strength cement mix of the female piles, the portions of female piles of cement slurry or other low strength cement mix remaining between adjacent male piles when the male piles have set effectively constituting substantially water-tight seals.

Since the female piles are of a cement slurry or other cement mix of low strength, heavy equipment is not required when forming a male pile between an adjacent pair of female piles and, as a consequence, the improved method of secant piling is less expensive and less time consuming than methods of secant piling hitherto employed. Moreover, since the female piles are spaced apart by a distance substantially less than the diameter of a male pile, large portions of adjacent females piles are cut away when a male pile is formed in situ with the result that the retaining wall is effectively formed of male piles of concrete of high strength, the joint between adjacent male piles being rendered substantially water-tight by seals of cement slurry or other cement mix of low strength constituted by the remaining portions of the female piles.

Preferably, the cement slurry of which the female piles are formed is a mixture of cement, bentonite, pulverised fuel ash and water. In some instances, the cement slurry may include sand.

Preferably, also, the distance between adjacent male piles is substantially less than the radius of a male pile, e.g. d/4 where d is the diameter of a male pile.

For aesthetic reasons, the surface of the retaining wall which is exposed when the excavation in the ground which the retaining wall is to bound is excavated may be lined with a layer of concrete but, since the seals of cement slurry or other cement mix of low strength are substantially water-tight the thickness of this layer may be substantially less than would otherwise have been necessary to render the retaining wall substantially water-tight.

Preferably, the female and male piles are of substantially the same diameter as one another. The axes of the female and male piles may lie in a straight line or on a curved line or on any other line determined by the shape of the retaining wall that is required. Alternatively, the female and male piles may be slightly off set from each other whilst still following any desired line.

The invention also includes a concrete retaining wall made by the improved method hereinbefore described.

The invention is further illustrated by a description, by way of example, of the preferred method of installing a concrete retaining wall be secant piling with reference to the accompanying drawing which shows, on a greatly reduced scale, a fragmental cross-section of the concrete retaining wall.

Referring to the drawing, a plurality of female piles 1 of a cement slurry comprising a mixture of cement, bentonite, pulverised fuel ash and water are formed in situ side by side in such a way that adjacent female piles are spaced apart by a distance approximately equal to one quarter of the diameter of a female pile.

After the female piles 1 have set, a male pile 2 of concrete substantially stronger than the cement slurry of the female piles is formed in situ between each adjacent pair of female piles, large portions of the adjacent female piles being readily cut away when the male pile is formed using inexpensive equipment. The distance between adjacent male piles is approximately equal to one quarter of the diameter of a male pile.

After the male piles 2 have set, the retaining wall 3 is effectively formed of male piles 2 of concrete of high strength, the joints between adjacent male piles being rendered substantially water-tight by seals of cement slurry, constituted by the remaining portions of the female piles 1.

If desired, a thin lining 4 of concrete may be applied to that surface of the retaining wall 3 which is exposed when the excavation in the ground which the retaining wall is to bound is excavated.

Claims

1. A method of installing a concrete retaining wall by secant pilling, which method comprises forming in situ side by side a plurality of female piles of a cement slurry or other cement mix of low strength in such a way that adjacent female piles are spaced apart by a distance substantially less than the diameter of a female pile and, after the female piles have set, forming in situ between each adjacent pair of female piles, a male pile of concrete substantially stronger than the cement slurry or other low strength cement mix of the female piles, the portions of female piles of cement slurry or other low strength cement mix remaining between adjacent male piles when the male piles have set effectively constituting substantially water-tight seals.

2. A method as claimed in Claim 1, wherein the distance between adjacent male piles is substantially less than the radius of of a male pile.

3. A method as claimed in Claim 2, wherein the distance between adjacent male piles is d/4, where d is the diameter of a male pile.

4. A method as claimed in any one of the preceding Claims, wherein the surface of the retaining wall which is exposed when the excavation in the ground which the retaining wall is to bound is excavated is lined with a layer of concrete.

5. A method as claimed in any one of the preceding Claims, wherein the female and male piles are of substantally the same diameter as one another.

6. A method as claimed in any one of the preceding Claims, wherein the female and male piles are slightly offset from each other.

7. A method as claimed in any one of the preceding Claims, wherein the cement slurry of which the female piles are formed is a mixture of cement, bentonite, pulveried fuel ash and water.

8. A method as claimed in Claim 7, wherein the cement slurry of which the female piles are formed also includes sand.

9. A method of installing a concrete retaining wall by secant piling substantially as hereinbefore described with reference to the accompanying drawing.

10. A concrete retaining wall made by the method claimed in any one of the preceding Claims.