GB2120304A

GB2120304A - Forming concrete piles

Info

Publication number: GB2120304A
Application number: GB08214698A
Authority: GB
Inventors: Joachim Berg; Gerd Chambosse
Original assignee: GKN Keller GmbH
Current assignee: GKN Keller GmbH
Priority date: 1982-05-20
Filing date: 1982-05-20
Publication date: 1983-11-30
Also published as: DE3318050C2; DE3348198C2; GB2120304B; DE3318050A1

Abstract

A method of forming a reinforced concrete pile 12 in the ground comprises the steps of forming a bore by means of a vibrator tool, filling the bore with concrete and then introducing an elongate reinforcement member 10 into the concrete from the top thereof before the concrete has set. The reinforcement member 10 may be untensioned or may be tensioned after the concrete has set to impart compressive loading to the concrete. <IMAGE>

Description

SPECIFICATION Method of forming a concrete pile This invention relates to a method of forming a concrete pile in the ground.

Various methods are already known to form a concrete pile. For example, a bore may be excavated in the ground and the side walls thereof shuttered to retain the earth whilst concrete is poured into the bore. In this method steel reinforcing fabric may be located within the shuttering before the concrete is poured to encase the reinforcement.

A known alternative quicker and more economic method of forming a concrete pile involves the use of a vibrator tool which imparts lateral oscillations from a motor-driven eccentric weight therein to allow the tool to bore into the ground under its own weight to displace the soil laterally without excavation. Concrete is then introduced into the void below the tool as the tool is withdrawn upwardly out of the bore.

However, such a method although offering advantages of efficiency over the more traditional excavation methods does not permit the introduction of reinforcement prior to the introduction of the concrete and it is an object of the present invention to provide a method of forming a concrete pile using a vibrator tool wherein reinforcement is present in the finished pile.

The method in accordance with the invention comprises forming a reinforced concrete pile in the ground wherein a bore is formed in the ground by a vibrator tool and the bore is filled with concrete characterised in that the reinforcement is introduced from the top into the concrete before the concrete has set.

The reinforcement conveniently comprises an elongate member of a length substantially identical with the depth of the pile and said member may be in the form of a steel rod, tube or cable. Alternatively, the reinforcement may comprise an elongate tension element together with a sleeve through which the tension element is freely movable, the sleeve and the tension element being introduced into the concrete before it has set with the tension element projecting beyond the bottom of the sleeve; the tension element having means associated therewith above the level of the concrete whereby, after the concrete has set, said means is operable to tension the tension element to apply compression to, at least a portion of the concrete. Said means conveniently comprises a nut rotatably mounted on a cooperating screw threaded part of the tension element above the level of the concrete.

The concrete may be further reinforced by fibres of steel, glass, carbon or plastics materials.

Other features of the invention will become apparent from the following description given herein solely by way of example with reference to the accompanying drawings wherein: Figure 1 is a somewhat diagrammatic longitudinal sectional view through a finished concrete pile produced with the aid of a vibrator tool and having a single reinforcement member extending centrally thereof; Figure 2 is a similar view to that of Figure 1 but wherein the reinforcement member comprises a tension element and a sleeve; Figure 3 and Figure 4 are diagrammatic plan view of apparatus for ensuring that the reinforcement member is introduced centrally of the concrete pile before the concrete has set.

In the method of forming the reinforced concrete pile in accordance with the invention a bore is first of all formed in the ground by means of a vibrator tool. Such a vibrator tool is known per se and forms no part of the present invention but generally such a tool comprises a torpedo like elongated body of circular plan form having internally thereof at its lower end an eccentrically mounted motor-driven weight for imparting lateral osciliations to the lower end of the tool. The tool is suspended from a crane or like device and is lowered into the ground at the position at which the pile is to be formed. When the motor is running the lateral oscillations imparted to the lower end of the tool allow it to bore into the ground under its own weight as it is lowered from the crane.

When the tool has bored into the ground to the required depth of the pile the tool is withdrawn upwardly out of the bore and concrete is introduced into the void below the tool as it is withdrawn. Conveniently this introduction of concrete may be achieved by means of a pipe extending inside or outside the tool body and terminating in a discharge orifice below the bottom of the tool. Thus the bore may be filled completely with concrete as the tool is withdrawn upwardly therefrom but, if the concrete is then allowed to set, the concrete pile so produced is not usually suitable for receiving horizontal forces and moments as the pile would break under fairly low loading.

Thus in accordance with the invention a reinforcement member is introduced into the poured concrete pile from the top thereof before the concrete has set. In the embodiment illustrated in Figure 1 the reinforcement comprises an elongate member 10 of a length substantially equal to the depth of the pile 12 and wherein the reinforcement is in the form of a steel rod or tube or cable. The reinforcement member 10 may be introduced into the concrete column either under its own weight or by a compression or impact or vibration force.

In the embodiment of Figure 2 the reinforcement comprises an elongate tension element in the form of a steel rod 14 again of a length substantially equal to the depth of the pile 12. As illustrated in Figure 2, the reinforcement also includes a sleeve 16 through which the rod 14 is freely movable, which sleeve 1 6 is also introduced into the concrete along with the rod 1 4 before the concrete has set in such manner that the rod projects beyond the bottom of the sleeve.

The head 18 of the rod 14 is arranged to extend above the level of the poured concrete and is formed with a screw threaded part for cooperation with a nut 20 whereby, after the concrete has set, the nut may be tightened to apply tension to that part of the rod which is embedded in the concrete, i.e. that part 22 of the rod 14 which extends below the sleeve 1 6. The application of this tension to the rod results in a compressive load being applied to the concrete outside the sleeve 1 6.

In both of the embodiments described with reference to Figures 1 and 2 the concrete itself may be further reinforced by being mixed with fibres of steel, glass, carbon or plastics materials.

Thus in accordance with the invention there is provided a method of forming a reinforced concrete pile utilizing a vibrator tool wherein, when the concrete has set around the reinforcement, the reinforced pile has a much greater bearing capacity against horizontal forces and moments than is the case with an unreinforced concrete pile.

Figures 3 and 4 of the drawings are diagrammatic plan views of a simple apparatus for ensuring that the reinforcement is introduced accurately and centrally of the concrete pile before the concrete has set. Referring to Figure 3, there is illustrated a turn-table 24 mounted for rotation about a vertical axis 26 and carrying at one edge thereof a guide tube 28 extending in a vertical direction through which the reinforcement member may be lowered into the concrete of the pile before it has set. The position of this guide tube 28 is angularly displaced by angle A from the rod datum centre line 30 of the turn-table 24. A marker rod 32 is attached to the edge of the turntable at the other side of the centre line 30 which rod is of a length subtending a similar angle A to the off-set of the guide tube 28 from the centre line.

In use, the centre line 30 of the turn-table 24 is aligned with the position at which the bore is produced by the vibrator tool and an indicator 34 is affixed into the ground at one end 36 of the marker rod 32. After the bore has been formed by the vibrator tool and has subsequently been filled with concrete, the turn-table 24 is rotated to the position shown in Figure 4 to bring the other end 38 of the marker rod 32 to the indicator 34. This movement ensures that the turn-table 24 will have been rotated through angle A thereby bringing the reinforcement member guide tube 28 accurately over the centre of the unset concrete in the bore at which time the reinforcement member may be lowered through the guide tube into the concrete before it has set in the manner hereinbefore described with reference to Figures 1 and 2.

A reinforced concrete pile produced by means of a vibrator tool as hereinbefore described offers various advantages over the known shuttered poured concrete construction of pile as follows:- 1. The vibrator tool, during its penetration into the ground, will automatically densify the soil around and below the foot of the concrete. Thus the foundations of the pile foot are always in well compacted and uniform ground thus leading to only extremely small and uniform subsequent settlement.

2. Frequently it is possible to make the concrete pile of the invention shorter than known piles due to the provision of the well densified soil below the foot of the pile thus giving a positive economic advantage.

3. The vibrator tool can be utilised to form an enlarged foot to the pile by lifting and lowering the tool at the base of the bore. The resulting pile can thus have an extremely high bearing capacity relative to its diameter.

Claims

1. A method of forming a reinforced concrete pile in the ground wherein a bore is formed in the ground by a vibrator tool and the bore is filled with concrete characterised in that the reinforcement is introduced from the top into the concrete before the concrete has set.

2. A method according to Claim 1 wherein the reinforcement comprises an elongate member of a length substantially identical with the depth of the pile.

3. A method according to either one of Claims 1 or 2 wherein the reinforcement comprises an elongate member in the form of a rod, tube or cable.

4. A method according to either one of Claims 1 or 2 wherein the reinforcement comprises an elongate tension element.

5. A method according to Claim 4 wherein the reinforcement comprises a tension element and a sleeve through which the tension element is freely movable, the sleeve and the tension element being introduced into the concrete before it has set with the tension element projecting beyond the bottom of the sleeve; the tension element having means associated therewith above the level of the concrete whereby, after the concrete has set, said means is operable to tension the tension element to apply compression to at least a portion of the concrete.

6. A method according to Claim 5 wherein said means comprises a nut rotatably mounted on a cooperating screw threaded part of the tension element.

7. A method according to any one of Claims 4 to 6 wherein the tension element comprises a steel rod of a length substantially identical with the depth of the pile.

8. A method according to any one of the preceding Claims wherein the concrete is reinforced by fibres of steel, glass, carbon or plastics materials.

9. A method of forming a reinforced concrete pile in the ground substantially as hereinbefore described with reference to the accompanying drawings.

10. A method according to any one of the preceding Claims including the further steps of centering the reinforcement over the bore before the reinforcement is introduced into the concrete by means of a turn-table having a guide for the reinforcement off-set at a predetermined angle from a datum line of the turn-table and a marker rod subtending the same predetermined angle at the turn-table axis of rotation; aligning the datum line with the centre of the bore, placing an indicator in the ground at one end of the marker rod and subsequently rotating the turn-table through the predetermined angle to bring the other end of the marker rod to the indicator and hence centre the guide over the bore.

11. A reinforced concrete pile in the ground whenever produced by the method according to any one of Claims 1 to 9.