GB2200156A

GB2200156A - Fluid ejection apparatus

Info

Publication number: GB2200156A
Application number: GB08727061A
Authority: GB
Inventors: Graham Kenneth Smithard
Original assignee: Cementation Piling and Foundations Ltd
Current assignee: Cementation Skanska Ltd
Priority date: 1984-12-06
Filing date: 1987-11-19
Publication date: 1988-07-27
Also published as: GB8727061D0; GB2200156B

Abstract

Apparatus for use in fabricating an underground concrete (or other cementitious) structure is disclosed. The apparatus is generally in the form of a pipe having at its lower end a suitable outlet arrangement, e.g. a generally horizontal cross- member or a tubular pipe provided with outlets. Fluid may be ejected into the cementitious structure from the pipe during the fabrication process. The apparatus is used in the method disclosed in application 2168099. <IMAGE>

Description

IMPROVEMENTS RELATING TO UNDERGROUND CONCRETE STRUCTURES" This invention relates to constructing underground concrete (or other cementitious) structures, for example piles and diaphragm walls.

In many circumstances, it is desired to fabricate a concrete structure extending some depth into the ground and terminating at its upper end some distance below ground level. With cast in situ concrete piles, for example, it is often necessary to construct a concrete column several metres in length which terminates, at its upper end, one metre or more below ground level. For practical reasons, it is not feasible to fabricate the concrete structure so that it terminates at the desired upper level, and no higher; for instance, where a concrete pile is being cast in non-cohesive soil where the water table is high, it is necessary to form a concrete column whose height is sufficient to counteract the hydraulic uplift caused by the water table.It is also necessary to ensure in some cases that the column of concrete is cast so that it reaches to the ground level since otherwise expensive protective measures are required to prevent ingress of soil material into the upper parts of the concrete column before it has set with consequent weakening of the upper regions of the pile.

These and similar considerations give rise to the conventional practice of fabricating a concrete column or similar underground structure to a level which is considerably above the desired final level.

Subsequently, after the concrete column has set, the upper, unwanted mass of concrete is removed down to the so-called cut-off level. This trimming operation is itself problematical, since it is difficult to ensure that the cut-off level is accurately achieved. The trimming operation must be carried out with care in order not to cause damage to the concrete at a deeper level.

The operation is noisy and time-consuming, as well as introducing an additional cost element in the overall construction program. For these reasons, there has been a need for a method of construction of underground concrete structures which facilitates the trimming operation described above.

According to the present invention, there is provided apparatus for fabricating an underground concrete or other cementitious structure, substantially as described herein with reference to the accompanying drawings.

The non-cementitious material can be a fluid which serves to cause segregation of the concrete in the region above the cut-off level. Alternatively, a granular solid may be used for the weakened zone. A third embodiment utilises substances which react together on contact to form an interstitial material (e.g. granules of a plastics material) which gives rise to the weakened zone. It is presently preferred to use a fluid as the non-cementitious material, and the invention will be described hereinafter with reference to this embodiment.

Preferably, water is used as the fluid and is injected into the concrete by means, for example, of a pipe having at its lower end a suitable outlet arrangement. Such a pipe is lowered through the still fluid concrete to a point just above the desired cut-off level, and the water pressure is then applied. The pipe is then raised gradually through the standing concrete until it is free, whereupon water pressure is cut off.

The water pressure may alternatively be applied throughout the lowering and raising action. The injection of a fluid in this way into the unset concrete causes segregation of the concrete, so that after the main body of the structure has set hard, the material above the desired cut-off level has little or no strength and cohesion. This makes it easy to remove the excess material after the main structure has set hard, while protecting the structure from ingress of surrounding soil material and from hydraulic uplift during the time taken for the concrete to set hard. In practice, the segregation of the concrete material above the desired cut-off level may be such that immediately above the cut-off level there is a thin layer of relatively soft concrete, above which is a layer of ballast and finally a layer of sand.It will be appreciated that, in other embodiments of the invention, sufficient weakening of the concrete may be achieved by introducing a gas or granular solids, either alone or in conjunction with a liquid through the delivery tube at an appropriate level.

The pressure at which the fluid is injected into the concrete, and the quantity of fluid employed, will depend upon a number of factors including the nature of the concrete, the depth of the desired cut-off point and the properties of the fluid itself. In all cases, the object is to ensure weakening, e.g. by segregation, of the concrete in the vicinity of the embedded injector outlets.

The present invention may be used to achieve segregation over substantially the full cross-section of a pile, but it may also be used to achieve segregation of only the core of the pile. In general, complete segregation of the major part of the pile cross-section is desirable.

The present invention may be practiced with any concrete or cementitious material which can be segregated in the manner described above before it sets hard; it may, for example, be used with a sand grout.

The design and the number of the outlets for delivering the segregating fluid will be varied according to the cross-sectional area and the nature of the material to be segregated. It will be appreciated, however, that more than one pipe may be required for the treatment of large piles or other concrete sections in order to encourage effective segregation over most of the concrete section. For this reason a number o pipes may be used simultaneously, or a single pipe system may be employed repeatedly after the concrete material has been cast. Alternatively the pressure of fluid injection may be varied so as to segregate a larger volume of cementitious material in a single pass of the pipe.

The accompanying drawings show three embodiments of apparatus of this invention, Figures la, 2a and 3a being schematic side elevations and Figures lb, 2b and 3b being diagrammatic plan views of the apparatus of Figures la, 2a and 3a respectively. In each case, the apparatus comprises a tube 1 having at its upper end a hose connector 2. At the lower end of tube 1 there is an outlet structure 3. In the embodiment of Figure 1, structure 3 comprises a linear tube open at both ends.

As shown, the outlets are directed slightly upwardly with respect to the horizontal. In the embodiment of Figure 2, the outlet structure 3 is in the form of a tubular ring provided with a plurality of outwardly directed apertures 4. In the embodiment of Figure 3, the outlet structure 3 is in the form of a linear tube provided with a plurality of upwardly directed outlets and also with generally horizontally directed outlets at the ends of the tubes.

Claims

CLAIMS 1. Apparatus substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 or Figure 3 of the accompanying drawings. 2. Apparatus substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompnaying drawings. Amendments to the claims have been filed as follows Claims.

1. Apparatus for use in fabricating an underground concrete or other cementitious structure, which apparatus comprises a rigid, elongate tube having a hose connector at its upper end and having an outlet arrangement at its lower end, said outlet arrangement including at least one outlet vent which is d-isposed so that, in use, a fluid supplied to the apparatus through said hose connector will issue therefrom in an upward direction or in a direction which includes an upward component when resolved vectorially.

2. Apparatus as claimed in claim 1, wherein said outlet arrangement comprises a bar at the foot of said tube.

3. Apparatus as claimed in claim 1, wherein said outlet arrangement comprises a ring member having a plurality of outwardly directed vents and being attached to said tube so that the tube axis intersects the plane of the ring member.

4. Apparatus as claimed in claim 1, and substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 or Figure 3 of the accompanying drawings.

5. Apparatus as claimed in claim 1, and substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompanying drawings.