GB2178462A

GB2178462A - In situ piling

Info

Publication number: GB2178462A
Application number: GB08614459A
Authority: GB
Inventors: Lewis Stansfield
Original assignee: STENT FOUNDATIONS Ltd
Current assignee: STENT FOUNDATIONS Ltd
Priority date: 1985-06-13
Filing date: 1986-06-13
Publication date: 1987-02-11
Also published as: GB2178462B; GB8614459D0; GB8514945D0

Abstract

A hole (2) is driven downwardly into the ground and is filled with a mixture (3) of bentonite and water and a rigid pipe (4) is introduced into the filled hole, which pipe, at its lowermost end (5) is open and, at its uppermost end (6), opens into a mixing chamber (7). The mixture of bentonite and water is caused to flow up the pipe (4) into the mixing chamber (7) and cement and pulverised fuel ash are introduced into the mixing chamber (7), the upper end of the pipe and the mixing chamber being of such shapes that the cement, pulverised fuel ash and mixture of bentonite and water are mixed into a cement slurry (12) which flows downwardly into the hole (2) through the open lowermost end (8) of the mixing chamber (7). After the hole (2) has been substantially filled with cement slurry (12), the pipe (4) is removed from the hole and the cement slurry is permitted to set. The method avoids mixing of the cement slurry at a position remote from the location of the pile. <IMAGE>

Description

SPECIFICATION Piling This invention relates to piling and is particularly concerned with a method of forming in situ a pile of a cement slurry or other cement mix of low strength.

According to the invention we provide an improved method of forming in situ a pile of a cement slurry or other cement mix of low strength, which method comprises driving or otherwise forming a hole downwardly into the ground and substantially filling the hole with bentonite and/or other clay-like material mixed with water; introducing into the filled hole a substantially rigid pipe which, at its lowermost end, is open and, at its uppermost end, opens into a mixing chamber whose lowermost end opens into the hole; causing bentonite and/or other clay like material mixed with water to flow up the pipe into the mixing chamber and introducing cement into the mixing chamber, the upper end of the rigid pipe and/or the mixing chamber being of such a shape that the cement and bentonite and/or other clay-like material mixed with water are mixed into a cement slurry which flows downwardly into the hole through the open lowermost end of the mixing chamber; continuing to cause bentonite and/or other clay-like material mixed with water to flow up the pipe into the mixing chamber until substantially all the mixture of bentonite and/or other clay-like material and water has been caused to flow into the mixing chamber and is mixed with cement and until the hole is substantially filled with a cement slurry; and withdrawing the rigid pipe from the hole and permitting the cement slurry to set.

Preferably, pulverised fuel ash or other cement replacement product and/or sand is or are also introduced into the mixing chamber with the cement.

Preferably, the mixture of bentonite andlor other clay-like material and water is caused to flow up the pipe into the mixing chamber by injecting air into the rigid pipe at a position intermediate of its ends through a flexible tube connected to the pipe and extending out of the hole. Air is preferably injected into the pipe through the flexible tube by means of a compressor.

Alternatively, in some circumstances, the mixture of bentonite and/or other clay-like material and water may be sucked up the rigid pipe by means of a pump which is interconnected in the rigid pipe and from which the discharge is fed into the mixing chamber with the other constituents of the slurry to be formed.

To facilitate mixing of the constituents of the cement slurry, preferably an upper end part of the rigid pipe protruding into the mixing chamber is bent radially outwardly and, near its extreme end, is bent so that it extends circumferentially to encourage the mixture of bentonite and/or other clay-like material and water emerging from the rigid pipe to flow around the mixing chamber.

The mixing chamber carried at the upper end of the rigid pipe preferably has a shape approximating to the frustum of a cone and, to assist mixing of the constituents of the cement slurry, the side wall of the mixing chamber may carry a plurality of circumferentially spaced fins.

Where the hole is unlined as it is driven or otherwise formed in the ground, the hole may be filled with a mixture of bentonite and/or other clay-like material and water as the hole is being driven or otherwise formed in order to maintain the hole open. Where the hole is lined with a metal wall, the mixture of bentonite and/or other clay-like material and water will not be introduced into the hole until driving of the hole has been completed.

The invention also includes a pile formed in situ of a cement slurry or other cement mix of low strength by the improved method hereinbefore described.

The improved method of the invention has the important advantage that mixing of the constituents of the cement slurry is effected immediately above the hole into which the cement slurry is to be introduced thereby avoiding mixing of the cement slurry at a position remote from the location of the pile and conveying the mixed cement slurry from this remote position to the location of the pile.

The improved method of the invention is especially, but not exclusively, suitable for use in forming a retaining wall, e.g. by the method forming the subject of our co-pending Patent Application No: 86/ filed on 0 June 1986.

The invention is further illustrated by a description, by way of example, of the preferred method of forming in situ a pile of a cement slurry with reference to the accompanying diagrammatic drawing which illustrates a sectional side view of the pile during its formation.

Referring to the drawing, a hole 2 is driven downwardly into the ground 1 and the hole is filled with a mixture 3 of bentonite and water. A rigid pipe 4 is introduced into the filled hole 2, the rigid pipe, at its lowermost end 5, being open and, at its uppermost end 6, opening into a mixing chamber 7 whose lowermost end 8 opens into the hole. By means of a compressor (not shown) air is injected through a flexible tube 9 into the rigid pipe 4 through a port 10 near the open lowermost end 5 of the pipe to cause the mixture of bentonite and water to flow up the pipe into the mixing chamber 7 through an upper end part 11 of the rigid pipe which is so bent that it extends radially outwardly and, near its extreme open end 6, circumferentially to encourage the mixture of bentonite and water emerging from the rigid pipe to flow around the mixing chamber.At the same time, cement, pulverised fuel ash and sand are introduced into the mixing chamber 7 so that the mixture 3 of bentonite and water and the cement pulverised fuel ash and sand are mixed into a cement slurry 12 which flows downwardly into the hole through the open lowermost end 8 of the mixing chamber. The mixture 3 of bentonite and water is caused to flow up the rigid pipe 4 into the mixing chamber 7 until substantially all the mixture of benotite and water has been caused to flow into the mixing chamber and is mixed with cement, pulverised fuel ash and sand and until the hole 2 is filled with the cement slurry 12. The rigid pipe 4 is then withdrawn from the hole 2 and the cement slurry 12 permitted to set.

By arranging for the constituents of the cement slurry to be mixed immediately above the hole into which the cement slurry is to be introduced, mixing of the cement slurry at a position remote from the location of the pile and conveying of the mixed cement slurry from this remote position to the location of the pile are avoided.

Claims

1. A method of forming in situ a pile of cement slurry or other cement mix of low strength, which method comprises driving or otherwise forming a hole downwardly into the ground and substantially filling the hole with bentonite and/or other clay-like material mixed with water; introducing into the filled hole a substantially rigid pipe which, at its lowermost end, is open and, at its uppermost end, opens into a mixing chamber whose lowermost end opens into the hole; causing bentonite and/or other clay-like material mixed with water to flow up the pipe into the mixing chamber, the upper end of the rigid pipe and/or the mixing chamber being of such a shape that the cement and bentonite and/or other clay-like material mixed with water are mixed into a cement slurry which flows downwardly into the hole through the open lowermost end of the mixing chamber; continuing to cause bentonite and/or other clay-like material mixed with water to flow up the pipe into the mixing chamber until substantially all the mixture of bentonite and/or other clay-like material and water has been caused to flow into the mixing chamber and is mixed with cement and until the hole is substantially filled with a cement slurry; and withdrawing the rigid pipe from the hole and permitting the cement slurry to set.

2. A method as claimed in Claim 1, wherein the mixture of bentonite and/or other clay-like material and water is caused to flow up the pipe into the mixing chamber by injecting air into the rigid pipe at a position intermediate of its ends through a flexible tube connected to the pipe and extending out of the hole.

3. A method as claimed in Claim 2, wherein air is injected into the pipe through the flexible tube by means of a compressor.

4. A method as claimed in Claim 1, wherein the mixture of bentonite and/or other clay-like material and water is sucked up the rigid pipe by means of a pump which is inter-connected in the rigid pipe and from which the discharge is fed into the mixing chamber with the other constituents of the slurry to be formed.

5. A method as claimed in any one of the preceding Claims, wherein an upper end part of the rigid pipe protrudes into the mixing chamber and is bent radially outwardly and, near its extreme end, is bent so that it extends circumferentially to encourage the mixture of bentonite and/or other clay-like material and water emerging from the rigid pipe to flow around the mixing chamber.

6. A method as claimed in any one of the preceding Claims, wherein the mixing chamber carried at the upper end of the rigid pipe has a shape approximating to the frustum of a cone.

7. A method as claimed in any one of the preceding Claims, wherein the side wall of the mixing chamber carries a plurality of circumferentially spaced fins.

8. A method as claimed in any one of the preceding Claims, wherein pulverised fuel ash or other cement replacement product and/or sand is or are also introduced into the mixing chamber with the cement.

9. A method as claimed in any one of the preceding Claims in which the hole is unlined as it is driven or otherwise formed in the ground, wherein the hole is filled with a mixture of bentonite and/or other clay-like material and water as the hole is being driven or otherwise formed to maintain the hole open.

10. A method as claimed in any one of Claims 1 to 8 in which the hole is lined with a metal wall, wherein the mixture of bentonite and/or other clay-like material and water is not introduced into the hole until driving of the hole has been completed.

11. A method of forming in situ a pile of a cement slurry or other cement mix of low strength substantially as hereinbefore described with reference to the accompanying drawing.

12. A pile formed in situ of a cement slurry or other cement mix of low strength by the method claimed in any one of the preceding Claims.