GB2163800A - Precast concrete piles - Google Patents

Abstract

A precast concrete pile is manufactured with a thin tubular shell 1 of helically seamed steel strip strengthened with annular or helical corrugations 2. The profile of both the seam and the corrugations is such that the tubular shell 1 has a smooth cylindrical outer profile surface free of projections. The shell is filled with concrete. One end of the tubular shell 1 may be closed by a metal plate 4, and the other end with an apertured plate to allow insertion of a hose for filling with concrete. The pile may also be provided with reinforcement 7. <IMAGE>

Description

SPECIFICATION Precast concrete pile This invention re!ates to piles for use in the building and construction industries and more specifically to drivèn piles in which the main structural element is a precast body pf concrete, which will normally be reinforced with steel.

Precast concrete piles have an established place in the market. As at present known, they are prepared, normally off site, in casting beds which provide moulds of certain standard cross-sections.

For lengths up to about 12 metres, they are normally cast in one piece; when greater lengths are required, expensive metal fittings are cast into the ends of the precast concrete sections to enable them to be coupled together, since concrete ends cannot be guaranteed sufficiently true to form reliable couplings.

These long heavy precast concrete piles present obvious transport problems, and they also require large and expensive pile drivers to place them, which may make use quite impossible on a restricted site, especially when overhead clearance is limited, for example in internal reconstruction of existing buildings, on sites under bridges or under airport flight paths. Furthermore, the smallest pile cross-section which can satisfactorily be made by current techniques has a load bearing capacity of about 70 tonnes.

There is therefore a need to develop precast concrete piles which are sufficiently true to be connected by simple inexpensive joints so that they can be economically driven in short sections when required and which can be made in much smaller cross-sections than hitherto, so opening up a new market sector in the support of relatively lightweight buildings (for example housing and single storey factory units) on sites that have hitherto been uneconomic to build on.

In accordance with the present invention, a precast concrete pile comprises a thin enclosing tubular shell formed from steel strip helically seamed and strengthened by corrugations, the profile of both seam and corrugations being such that the shell has a smooth cylindrical outer surface free of projections, the shell being filled with concrete (normally with reinforcement).

The helical seam could be welded, but we prefer an interlocked seam as this contributes to the strength of the shell and permits, if desired, the use of galvanised or otherwise coated steel strip for corrosion protection without requiring separate treatment of the seam.

Machines for making such helically seamed steel tubing are well know and readily available on the market and need not be described in detail.

Suitable corrugating equipment is also well known and freely available. The corrugations may be helical, with a pitch either the same as or different from the pitch of the seams, or it may be annular.

Preferably at least one end of the shell is closed by a metal plate, which may be secured by welding or mechanically, in order to define a true end After placing reinforcement (when required) liquid concrete can then be pumped in through a hose inserted from the other end and gradually withdrawn. An end cap, apertured to pass the hose, may be desirable at the other end, this is not essential at least if casting is performed with the pile in a vertical position. Small apertures for escape of air may be provided in or adjacent the closed end and if needed in other places.

The inside of the steel shell may if desired be coated with a protective medium when the pile is to be used in a corrosive soil and the concrete needs to be protected after the shell may have corroded away. An advantage over conventional precast piles is that the protective medium will remain in place during the driving of the pile. On the other hand, when the use environment is non-corrosive the shell may make a contribution to the strength of the pile.

Because the piles of the present invention are of circular cross-section, they can be moved in one direction by rolling, unlike conventional precast piles of square or hexagonal section, economising on the use of lifting plant; indeed, it may be possible to roll them from the casting site when the degree of cure of the concrete is insufficient for them to be lifted without risk of cracking. Moreover, there is no problem of orientation on site.

The tube forming plant is relatively compact and could be operated on site when the scale of the operation justifies it. For smaller jobs, the steel shells can be factory made, and being light and relatively short present few delivery problems.

Casting of the concrete requires only a standard concrete pump and a reasonably smooth and preferably gently sloping working area.

Shells ranging from about 50 to 500 mm or more in diameter can be made without difficulty from steel strip of the order of 0.5 to 1 mm thick.

Piles made in accordance with the invention, being straight and true-ended, can be jointed by a simple steel coupling sleeve with a central septum or internal flange to position it correctly on the joint.

Steel a little thicker than the shell of the piles is normally recommended, and corrosion protection will often be required.

This simple form of joint is clearly only suitable when the pile is loaded only in compression. A useful degree of tensile strength can be obtained by using piles in accordance with the invention in which the corrugations are helical and forming a matching helical rib on the interior of the joint sleeve so that the adjacent sections can be screwed together.

In frosty weather or when accelerated curing is desired, the temperature of the concrete may be raised during curing by electrically heating the shell by current directly passed through it or by means of electric heating cables suitably wound around it.

In order that the invention may be more readily understood, a description is now given, by way of example of the preferred precast concrete pile and a method of making such.

In the accompanying drawings: Figure 1 shows a tubular shell for use in making a pile in accordance with the invention; Figure 2 shows in end elevation, a group of such shells laid out on a sloping site against a line of supporting stakes; Figure 3 shows in plan view, a group of such shells as shown in Figure 2; Figure 4 shows the first section of a pile in course of being driven into the ground; Figures 5 and 5a illustrate the use of a simple sleeve joint to connecttwo piles in accordance with the invention for compressive loading; Figures6 and 6a illustrate an alternative screw joint for use when tensile loading may be encountered; and Figure 7 illustrates an alternative method of completing manufacture of the pile shown in Figure 6A.

The shell 1 shown in Figure 1 of the drawings is of circular cross-section and formed from helically interlocking seamed mild steel strip about 0.7 mm thick (22 gauge) and has an outside diameter of 180 mm. The shell 1 is formed with annular corrugations 2 of flat bottomed vee-profiled crosssection, preserving the smooth cylindrical outer shape, in contrast with the sinusoidally corrugated shells used on some cast-in-situ piles. The end 3 of the shell 1 is closed by a steel plate 4 which is 8 mm thick and which is secured by welding to define á true end.

The above described tubular shells 1, are manufactured on site using one of the conventional machines for making helically seamed steel tubing.

Once formed the tubularshells 1 are laid out on a sloping site against a line of supporting stakes 5, so that there is a gentle upward slope from end 3 to end 6 of each shell and from the shell nearest the support stakes 5 to that furthest away, as shown in Figures 2 and 3 in which four tubular shells are shown resting against the stake & Oncethetubular shells 1 have been laid out, two high yield steel reinforcement rods 7, each 15 mm in diameter, are inserted into each tubular shell and the end 6 of each tubular shell is blocked with an end cap 8 having an aperture 9. A hose connected to the outlet of a standard concrete pump can now be inserted through the aperture 9 into the tubular shell 1 and until it reaches position near to the closed end 3 of the tubular shell.

Liquid concrete of grade 50N is then pumped into the tubular shell via the hose and the hose is gradually withdrawn as the tubular shell is filled. Air displaced by the concrete is allowed to escape from the tubular shell by small apertures 10 provided adjacent the closed end 3 and adjacent the apertured end 6 of the tubular shell and the concrete 11 is allowed to cure to form a pile section.

The pile section (when sufficiently cured) is transported to the piling site, and driven into the ground using a conventional driving hammer until most of the pile is buried, as shown in Figure 4. A second pile section is then lifted into position, and jointed to the first pile, as shown in Figures 5 and 5a, by a simple steel coupling sleeve 12 with a central septum 13, to position it correctly on the joint. The coupling sleeve 12 is made from 1 mm thick steel.

The form of joint shown in Figure 3 is only suitable when the pile is loaded only in compression. Where a tensile loading may be applied, we prefer, as shown in Figures 6 and 6a, to use pile sections in which the corrugations 2 in the tubular shell 1 are helical and to form a matching helical rib 14 on the interior of the coupling sleeve 12 so that adjacent piles can be screwed together.

Where the tubular shells of adjacent pile sections are permanently jointed to one another, for example by a coupling sleeve 12 as shown in Figure 6A, the last pile section may be cast in situ. This is carried out by attaching a tubular shell 15 to the uppermost pile section 17 by a coupling sleeve 12 and inserting a mandrel 16 into the tubular shell so that it rests against the uppermost pile section. The driving hammer is caused to act against the mandrel 16, the tubular shell 15 being pulled into the ground as the pile is driven.

Once the pile has been driven to the required depth, the mandrel is withdrawn and the final pile section formed by introduction into the shell 15 of appropriate reinforcement and concrete.

Any part of the tubular shell 15 protruding above ground level is cut away and may be used on another pile.

Claims (8)

1. A precast concrete pile comprising a thin enclosing tubular shell formed from steel strip helically seamed and strengthened by corrugations, the profile of both seam and corrugations being such that the shell has a smooth cylindrical outer surface free of projections, the shell being filled with concrete.

2. A precast concrete pile comprising a thin enclosing tubular shell formed from steel strip helically seamed and strengthened by corrugations, the profile of both seam and corrugations being such that the shell has a smooth cylindrical outer surface free of projections, the shell being filled with reinforced concrete.

3. A precast concrete pile as claimed in Claim 1 or Claim 2, in which the helical seam is an interlocked seam.

4. A precast concrete pile as claimed in any one of the preceding Claims, in which at least one end of the shell is closed at one end by a metal plate in order to define a true end.

5. A precast concrete section pile substantially as hereinbefore described and substantially as shown in Figure 4 or Figure 6 of the drawings.

6. Ajointed precast concrete pile substantially as hereinbefore described and substantially as shown in Figure 5a or Figure 6a of-the drawings.

7. A method of manufacturing a precast concrete pile substantially as hereinbefore described with reference to Figures 1 to 6A of the drawings.

8. A method of manufacturing a precast concrete pile substantially as hereinbefore described with reference Figure 7 of the drawings.