GB2284843A

GB2284843A - Cast in situ piles

Info

Publication number: GB2284843A
Application number: GB9323287A
Authority: GB
Inventors: Roy Henry King
Original assignee: Keller Ltd
Current assignee: Keller Ltd
Priority date: 1993-11-11
Filing date: 1993-11-11
Publication date: 1995-06-21
Anticipated expiration: 2013-11-11
Also published as: GB9323287D0; GB2284843B

Abstract

Cast insitu piles are formed by driving a capped conventional hollow steel tube 5 into the ground, filling the internal space with wet concrete and metal reinforcement 12 and then withdrawing the tube 5 (leaving the cap or shoe 8 behind) so that the concrete slumps to fill the driven hole, sets, and hardens. A surrounding member 6, orificed at 7 and preferably conical, is placed at ground level around the tube 5 and forced into the ground by the weight of the leaders so that when the tube 5 is removed the upper end of the cast pile is (e.g.) conically formed. This gives an installation of piles over a given area better support characteristics for an overlying concrete raft. <IMAGE>

Description

IMPROVEMENTS IN DRIVEN CAST INSITU PILING This application relates to the equipment and techniques of driven cast insitu piling.

Driven cast insitu piling involves percussive driving into the ground of a hollow steel tube closed by a detachable metal end shoe, to a distance which can be widely variable but is typically some 8-25 metres; thereafter filling the driven hollow tube with concrete and reinforcement members: and extracting the hollow tube (leaving behind the detachable end shoe) so that the concrete within the hollow tube flows into the hole remaining and bonds to the wall of this hole. The tube is usually circular in cross section, but could be of other profile e.g. square. The process is typically repeated at intervals, for example over an area to be supplied with a concrete raft, (i.e. a thick concrete layer, supported essentially by the set and hardened concrete piles) or with a frame support at the upper ends of the piles.

Such pile-supported concrete raft or the like is often subject to considerable load, and is essentially supported only at the cross sectional areas of the concrete piles. The raft should itself be suitably dimensioned, shaped and reinforced and the underlying piles should be spaced so that cracks do not appear in the concrete raft between the points of support when the raft is under its designed load. It is not possible to generalise as to the exact spacing, but typically the piles will be of some 30 to 48 cm diameter and will be spaced at between 2 - 4 metres.

The present invention sets out to improve the equipment and techniques used in cast insitu driven piling so that the piles can be more widely spaced for a given load, or conversely be more supportive at conventional spacings.

The invention consists in equipment for the installation of driven cast insitu piling, comprising a set of drive leaders with a base structure extending outwards from the leaders at its lower end, and a percussive member guided by the leaders to fall by gravity onto the upper end of a hollow drive tube passing through the base member, in order to drive the hollow drive tube into a supporting ground layer and provide a vertically extending orifice within which concrete can be cast and from which the hollow drive tube can be removed after such casting: in which there is further provided a member located beneath the base structure and orificed at its centre to permit passage of the driven tube, the weight of the leaders being such that the said member is forced into the surface thereby, so as to provide a depression around the hollow tube into which the concrete may eventually flow.

Typically, the orificed member is, at its outer surface, downwardly and inwardly directed. Preferably, it is a hollow steel cone with a suitably dimensioned orifice at the downwardly pointing apex. The weight of the leaders, acting upon the base structure, will force such a cone into the ground so that the hollow tube is essentially driven through the base of a depression.

When the hollow tube is thereafter filled with reinforcement members and with concrete, and then removed, the concrete slumps to fill not only the driven hole but also the conical depression. The cone can be of a range of included angle but from 60 to 120 i.e.

90 angle (45 semiangle) is preferred.

In another aspect the invention consists in a method of providing driven cast insitu piles comprising the essential steps of percussively driving into the ground a hollow steel tube to define the eventual piling location, filling said tube with concrete and optionally with suitable reinforcement members and withdrawing the hollow steel tube so that the concrete fills the hole remaining; in which the additional step of depressing the surface of the ground, preferably in a downwardly and inwardly directed configuration, around the end of the pile is also incorporated and the concrete is also caused to fill the depression so caused.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically and from one side the essential features of equipment for driving a hollow steel tube within which concrete is poured, in accordance with the present invention, to form cast insitu piles as the hollow steel tube is removed.

Figure 2 shows diagrammatically certain operative members at the ground level of such equipment, and Figures 3a, 3b, 3c and 3d show progressively the stages of driving and casting insitu a concrete pile.

The essentials of the equipment are shown diagrammatically in Figure 1. A tracked crane 1 with lifting arm 2 serves to transport and hold upright a vertical framework 3, known in the art as leaders, which are capable of resting upon the ground at support plate 4. The crane also controls the movement up and down the leaders 3 of a driving weight W which is lifted by the crane and falls by gravity. The vertical leaders 3, when in use, guide a hollow steel drive tube 5. The base support plate 4 is suitably shaped at spaced arms 4a, 4b to let the tube 5 pass.

The operation of the above conventional features will be self-evident. The crane 1 transports the whole- of the equipment to the required location, the vertical leaders are erected to rest upon the base plate 4, and the tube 5 is driven percussively into the ground by the repeatedly falling weight W.

The present invention provides beneath the base plate 4 a surface-shaping member 6 which is conical in the example shown. In other embodiments it could be part-spherical or flared. This surface-shaping member is at its apex provided with an orifice 7 sufficiently large to permit the passage of the tube 5.

The arrangement therefore is as shown in Figure 2, with the tube 5 passing beneath the two arms 4a, 4b of the base plate 4 and through the orifice 7 in the conical member 6. Because of the weight of the vertical leaders 3, and the relative softness of the top soil, the conical member is pressed into the ground so that the tube 5 is subsequently driven through the base of a conical depression.

Figures 3a - 3d shows the different stages of pile driving and filling using such equipment. A man skilled in the art will appreciate that these are essentially conventional except for the incorporation of the surface-shaping conical member 6 where shown.

Figure 3a shows the hollow steel tube 5 being driven. It is conventionally capped at its lower end by a removable steel shoe 8, and is percussively forced through different layers of ground 9, 10, 11 in the manner shown. The pile can in theory be of a wide range of transverse dimensions, but is typically one of a relatively small number of standard sizes such as 340, 380, 430 and 480mm transverse dimension. Similarly, the pile can be of different transverse cross sections but is usually circular.

When the drive tube 5 has reached its desired depth, that is to say when it is securely founded in the resistant layer 11, reinforcement members 12, in the form of straight steel rods projecting above ground level, and interconnected by hoops or helices of reinforcement rod, are fed into the hollow steel tube 5. Then concrete is poured into the hollow steel tube, (Fig. 3b) to a level above ground level. Thereafter the drive tube 5 is progressively removed, (Fig.3c) typically with tamping vibration to assist movement and to assist moreover in the flow of concrete into the space left behind. The reactive force to such extraction bears on the base support plate 4, and thus holds the conical member 6 firmly in position against the movement of the pile. Eventually this member itself is freed and can be removed e.g. by being attached to the base foot. The predetermined head of concrete poured into the hollow tube before removal is such that in normal practice the cast pile terminates at ground level (Fig. 3d).

Figure 3d thus shows the completed pile, with the concrete from the excess, originally within the tube, having flowed to fill not only the vertical portion but also the shaped conical-surface portion of the cast pile. This conical portion can be provided with reinforcements, to unify its structure and ensure effective connection with the upper part of the cast pile.

Claims

CLAIMS:

1. Equipment for the installation of driven cast insitu piling, comprising a set of drive leaders with a base structure extending outwards from the leaders at its lower end, and a percussive member guided by the leaders to fall by gravity onto the upper end of a hollow drive tube passing through the base member, in order to drive the hollow drive tube into a supporting ground layer and provide a vertically extending orifice within which concrete can be cast and from which the hollow drive tube can be removed after such casting: in which there is further provided a member located beneath the base structure and orificed at its centre to permit passage of the driven tube, the weight of the leaders being such that the said member is forced into the surface thereby, so as to provide a depression around the hollow tube into which the concrete may eventually flow.

2. Equipment as claimed in claim 1 in which the orificed member is downwardly and inwardly directed at its outer surface.

3. Equipment as claimed in claim 2 in which the orificed member is a hollow steel cone.

4. Equipment as claimed in claim 3 in which the cone has an included angle of 60 to 120*.

5. A method of providing driven cast insitu piles comprising the essential steps of percussively driving into the ground a hollow steel tube to define the eventual piling location, filling said tube with concrete and optionally with suitable reinforcement members and withdrawing the hollow steel tube so that the concrete fills the hole remaining; in which the additional step of depressing the surface of the ground, preferably in a downwardly and inwardly directed configuration, around the end of the pile is also incorporated and the concrete is also caused to fill the depression so caused.