GB2250048A

GB2250048A - Piling

Info

Publication number: GB2250048A
Application number: GB9124566A
Authority: GB
Inventors: David Frederick Adams
Original assignee: Cementation Piling and Foundations Ltd
Current assignee: Cementation Skanska Ltd
Priority date: 1990-11-20
Filing date: 1991-11-20
Publication date: 1992-05-27
Anticipated expiration: 2011-11-20
Also published as: GB9025245D0; GB2250048B; GB9124566D0

Abstract

A quasi-continuous method of forming a series of cast in situ driven piles is disclosed, which comprises: (a) driving a piling tube (1) containing a pile reinforcement into the ground to the desired depth; (b) pumping concrete into the interior of the piling tube; (c) locating a second pile reinforcement above said piling tube; (d) withdrawing said piling tube so that it engages said second pile reinforcement; and (e) moving the piling tube with said second pile reinforcement therein to a location at which the next of the series of piles is to be constructed. <IMAGE>

Description

PILING This invention relates to piling and, more particularly, is concerned with the installation of cast in situ driven piles.

Conventionally, cast in situ driven piles are constructed in a series of steps. First, a piling tube fitted with a pile shoe is driven into the ground to the required depth. Next, a reinforcement (e.g. a metal cage or bar) is placed in the interior of the piling tube.

With the pile reinforcement in place, the interior of the piling tube is filled with concrete. Next, the piling tube is extracted (leaving behind the pile shoe) and additional concrete is put in place, if required, leaving behind the pile reinforcement embedded in concrete. The pile tube is usually tamped or vibrated during extraction.

The conventional procedure as described above has been used for many years and, under proper operating conditions, leads to the construction of piles with acceptable physical characteristics, for example of uniform cross-section, without voids or "necking", and with adequate compressive strength. The procedure is, however, relatively slow.

We have now found, surprisingly, that considerable savings in time can be made without prejudicing the desired structural characteristics of the piles. More particularly, in accordance with the present invention, there is provided a method of forming a series of cast in situ driven piles, which comprises: (a) driving a piling tube containing a pile reinforcement into the ground to the desired depth; (b) pumping concrete into the interior of the piling tube; (c) locating a second pile reinforcement above said piling tube; (d) withdrawing said piling tube so that it engages said second pile reinforcement; and (e) moving the piling tube with said second pile reinforcement therein to a location at which the next of the series of piles is to be constructed.

Preferably, the pile reinforcement is in the form of a bar or a plurality of bars, with or without a 'cage' or reticulate structure in the upper region of the pile. It is not preferred to use a cage extending the full length of the pile. It is also preferable to subject the piling tube to vibration or tamping during its withdrawal, and optionally during the stage of locating the second pile reinforcement above the piling tube.

During extraction of the pile tube, the rate of withdrawal of the tube is preferably controlled. It is generally advantageous to adopt a slow rate of extraction initially. It is also preferred to tamp or vibrate the piling tube throughout the extraction phase.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which illustrate seven stages in the production of a cast in situ driven pile in accordance with the present invention.

As shown in the drawings, a piling tube 1 has an enlarged head section 2 which is provided with a concrete inlet 3. A pile reinforcement, in this instance a metal cage 4, is located within the interior of piling tube 1 below the level of head section 2. An expendable pile shoe 5 is located at the foot of piling tube 1 and rests on the surface 6 of the ground at the location where one of a series of piles is to be formed.

Piling tube 1 is driven into the ground by hammer 7 which strikes the top of the head section 2 of piling tube 1. In Stage 1, the piling tube and pile reinforcement are ready to be driven into the ground.

During driving of the piling tube, concrete 8 is pumped via inlet 3 into the interior of piling tuber. This is illustrated in Stage 2. As the piling tube approaches its final driven depth, the interior of the piling tube is almost completely filled with concrete (see Stage 3).

By the time the required depth is reached (Stage 4), the tube 1 is substantially filled with concrete 8; hammer 7 is lifted clear of the tube head 2, and a second pile reinforcement in the form of metal cage 4' is positioned over the partially formed pile. At this stage, an extractor/vibrator 9 comes into use. The extractor/ vibrator is in the form of an annular collar which is clamped to the region of the piling tube 1 where tube head 2 joins the main body of the piling tube.

Extractor/vibrator 9 is supported by steel cables 10.

While the pile cage 4' is being located above the existing pile, extractor/vibrator 9 is operated to cause piling tube 1 to vibrate. This assists in causing the concrete in the tube to flow so as to fill the hole completely and to compact in the hole in the ground which forms as the tube is extracted. Next, as illustrated in Stage 5, the extractor/vibrator 9 is lifted by means of cables 10 (or by other means, if desired) thereby extracting piling tube 1, leaving behind metal cage 4 and pile shoe 5. The initial extraction (over the first metre of the pile length) is performed relatively slowly.

If, after the tube has been filled with concrete (Stage 4), additional concrete is required to complete the pile, this is added during the extraction of the pile tube (Stage 5). Extractor/vibrator 9 continues to vibrate throughout the extraction phase until the piling tube 1 is near to, or clear of ground surface 6. This is illustrated in Stage 6. Next, the assembly comprising piling tube 1, pile reinforcement 4' and extractor/vibrator 9 is moved to a new location where the next of the series of piles is to be formed. A new pile shoe 5' is located on the surface 6' where the new pile is to be formed, and the procedure described above in relation to Stages 1-6 is repeated.

By means of the present invention, the production of a series of piles can be achieved in a considerably shorter time than is possible using conventional techniques. Since concrete is supplied to the interior of the piling tube as the piling tube is being driven into the ground (and also during tube extraction, if required), and since the pile reinforcement for a second pile is received into the piling tube during its extraction from the first pile, the entire process is quasi-continuous.

Claims

CLAIMS:

1. A method of forming a series of cast in situ driven piles, which comprises: (a) driving a piling tube containing a pile reinforcement into the ground to the desired depth; (b) pumping concrete into the interior of the piling tube; (c) locating a second pile reinforcement above said piling tube; (d) withdrawing said piling tube so that it engages said second pile reinforcement; and (e) moving the piling tube with said second pile reinforcement therein to a location at which the next of the series of piles is to be constructed.

2. A method according to claim 1, wherein the piling tube is subjected to vibration or tamping during its withdrawal.

3. A method according to claim 1 or 2, wherein concrete is pumped into the interior of said piling tube while said piling tube is being driven into the ground.

4. A method according to claim 1, 2 or 3, wherein concrete is pumped into the interior of said piling tube while said piling tube is being withdrawn from the ground.

5. A method according to claim 1, 2, 3 or 4, wherein the upper region of said pile reinforcement has a reticular structure.

6. A method according to any preceding claim, wherein said pile reinforcement comprises one or more bars.

7. A method according to any preceding claim, wherein withdrawal of said piling tube is effected by means of an initial, relatively slow withdrawal stage and a subsequent, relatively fast withdrawal stage.