GB2306536A - Steel piles - Google Patents

Abstract

A steel pile for use in construction work in ground which is underlain by rock is provided at its forward end with a square cut hard pin 7 which is preferably set in a reinforced section including plates 8, 9. The pile may have an underlying H section structure 1, 2, 3 and have reinforcing side plates 5.

Description

STEEL PILES This invention relates to steel piles.

In the construction of buildings, a fundamental requirement to ensure the stability of the building is to provide an adequate foundation. For relatively low or lightweight buildings, this may take the form of a unitary foundation structure which distributes the load of the weight of the building satisfactorily so that the bearing capacity of the ground on which the building stands is not exceeded. The heavier or taller the building, the more necessary it is to ensure that the foundations are adequate, and for centuries a known technique has been to introduce into the ground, to form the lower-most part of the building structure, a set of vertical elongated members known as piles.

Originally, piles were simply wooden stakes with a pointed end which were driven into the ground until the flat top reached the desired level. Over the centuries, piles have been refined and wooden piles are now rarely used save for certain marine structures. Instead, steel or concrete piles are used.

Steel piles are particularly useful if the structure of the ground on which the building is to be constructed becomes progressively harder, for example relatively soft ground near the surface, underlain by harder stratum for example of sand, gravel or rock. Underlying rock obviously provides a particularly firm foundation so long as the piles can be driven into it to an adequate extent, and this is accordingly a particularly preferred type of piling for large buildings.

Although a pile being driven downwards through the ground by impacts on its exposed upper end can be expected to stay straight, problems can arise if, at some level below the ground, a relatively penetrable stratum is underlain by rock. While it is sometimes the case that the upper surface of the rock will be generally horizontal, all too often it is found that across part or the whole of the site the upper surface of the rock is not horizontal.

While small deviations from horizontal may not make very much difference, if the upper surface of the rock is substantially inclined to the horizontal, the bottom of the pile, instead of penetrating into the rock, shifts sideways and can even, in certain circumstances, finish up running across, but not penetrating, a sloping rock surface. On the other hand, the corner of the pile toe that impacts with the bedrock would suffer stress concentration. The impact loading would produce uneven compressive stress as well as bending movement at the pile toe, hence damaging the pile. The above situation is undesirable as the load bearing capacity both of the individual pile and of the entire assembly of piles is reduced.

According to the present invention there is provided a steel pile consisting of a box section having at one end a central protruding square cut hard material pin. The square cut end of the pin constitutes the leading portion of the pile as it is driven downwards and accordingly it is the first portion of the pile to meet the rock face.

The edge of the pin appears to interact with the surface of the rock in such a way as to form a lead zone of weakness and subsequent impacts on the upper end of the pile cause the pin to enter the rock followed by the remainder of the pile, impacts being continued until the top of the pile has reached the desired level. We have found that constructing a pile in this way gives much improved performance in practice.

The square cut pin must of course be secured very firmly into the leading end of the pile. It should of course be made of very hard material but since the pin may be relatively short and need not be very wide, it is economic to use high grade engineering materials.

Although conceivably exotic materials might be used, it is found that very strong, very hard grades of special steel function satisfactorily.

The particular shape and size of the pin and its crosssection, may vary. Since the material of the pin is difficult to work, however, a round section is preferred generally of diameter 50 to 100 mm and of length 200 to 400 mm.

In a preferred form of the invention, the end of the pile in which the pin is set is reinforced, for example by additional high tensile steel plates welded into position and shaped to form a pin receiving seating.

The main length of the pile may be a box section or an H section steel pile of conventional construction. A particularly preferred construction, however, is a double box section formed by welding steel stiffener plates to cover the channels on either side of an H section pile.

For particularly strong piles, angle section steel may be welded into the internal corners of the H section.

The overall length of the pile may vary depending upon the site conditions.

A typical pile constructed in accordance with the present invention is illustrated in the accompanying drawings, in which: Figure 1 is a schematic side view of a pile constructed in accordance with the invention; Figure 2 is a diagrammatic cross section on an enlarged scale along the lines 2-2 in Figure 1, and Figure 3 is a like cross section of the pile along the lines 3-3 in Figure 1.

Referring to the drawings, the pile consists basically of a steel H-section member running from top to bottom, the central connecting web being denoted 1 and the two side portions of the H section being denoted 2 and 3 in the Figures. At its upper end, the pile simply consists of this H section, but for the majority of its length, which may be for example 20 to 25 m, it consists of the box section shown in Figure 2 which is formed by welding 50 x 50 x 8 mm equal angle sections 4 into the interior angles of the H section, and butt welding 15 mm thick stiffeners 5 spanning the edges of sections 2 and 3.

At the lower end of the pile, the H section has been cut off to form a broadly angled point and the centre portion of the web 1 then cut to form a slot for the receipt of a square cut pin 7. The pin is round in section and is held firmly in position by welding it into the central web with the addition of four plates of high tensile steel 8. In addition to those plates 8, the pin 7 is held even more firmly in position by a pair of welded-on high tensile steel plates 9 which lie in a plane perpendicular to web 1 of the H section. Plates 8 and 9 are, in the specific pile illustrated, 15 mm thick and of high tensile steel, for example grade 50B or 43A ex.

British Steel.

The pin is an 85 mm diameter section of rod, 300 mm long and of grade 460 steel ex. McCall.

Plates 5 are of grade 43A steel in the embodiment illustrated while the H pile section itself is of grade 55C (BS4360) steel, ex. British Steel Corporation.

Claims (7)

1. A steel pile comprising an elongate member having at one end a square-cut pin of hard material protruding therefrom, the pin constituting the leading portion of the pile in use.

2. A steel pile according to Claim 1 wherein the pin is set in and protrudes from a reinforced section of the member.

3. A steel pile according to Claim 2 wherein the reinforced section comprises steel plates welded to one end of the member, the plates being shaped to form a pin-receiving seating.

4. A steel pile according to any preceding claim wherein the member is at least partially has a of double box section structure.

5. A steel pile according to any preceding claim wherein the pin has a circular cross section.

6. A steel pile according to any preceding claim wherein the pin is composed of a strong and hard grade of steel.

7. A steel pile according to any one of the preceding claims and as substantially hereinbefore described with reference to the accompanying drawings.