GB2226347A

GB2226347A - Under-pinning buildings

Info

Publication number: GB2226347A
Application number: GB8928630A
Authority: GB
Inventors: Ronald James Soutar; Craig Milloy
Original assignee: Pynford Ltd
Current assignee: Pynford Ltd
Priority date: 1988-12-20
Filing date: 1989-12-19
Publication date: 1990-06-27
Also published as: GB8829623D0; GB8928630D0

Abstract

A method of under-pinning the wall of a building in which at least one pile (11) is put down offset from the wall (10) and a rigid member (19), which is capable of transmitting the load from the wall to the pile, is mounted on top of the pile and projects in cantilever fashion beneath the wall. At least one jack is interposed between the rigid member and the wall and is extended to prestress the pile in bending prior to fixing the wall relatively to the rigid member by packing (31). <IMAGE>

Description

DESCRIPTION UNDER-PTNNTNG BUILDINGS One method of under-pinning a wall of a building, the existing foundation of which has been subjected to subsidence, is to replace the foundation by one or more piles, which are put down offset from! usually outside! the wall. The load of the wall is then transferred to each new pile via a member which is mounted on top of the pile and projects in cantilever fashion beneath the wall. When the full load is developed, the offset load of the wall tends to put the pile into beding so that in practice some further lowering of the wall may have to take place before the full load bearing reaction is developed.

In accordance with the present invention, in a method of under-pinning the wall of the building, in which at least one pile is put down offset from the wall and a rigid member, which is capable of transmitting the load of the wall to the pile, is mounted on top of the pile and projects in cantilever fashion beneath the wall; at least one jack is interposed between the rigid member and the wall and is extended to prestress the pile in bending prior to fixing the wall relatively to the rigid member.

With this arrangement the pile can be prestressed to for example up to one half of the pile design load.

The jack or jacks which are used are preferably recoverable prior to encapsulating the rigid member in! for example! a concrete pile head, which may be integrated with a low level beam extending along within the plane of the wall.

The fixing of the wall relatively to the rigid member, while the jacking is operational! may be achieved by interposing packing! such as wedges or earth damp mortar between the bottom of the wall, or a plate abutting the bottom of the wall, and the rigid member. Alternatively, the rigid member may be in two parts which are vertically separated as the jacking is carried out! and are then held spaced apart by lock nuts or earth damp mortar or otherwise to maintain the prestressing.

In one example the rigid member is a metal beam, such as an I beam, which is welded, bolted or otherwise rigidly fixed to the top of a pile or pile cap. A cover plate! which is arranged to abut directly or indirectly a lower surface of the wall, is located on top of the cantilevered end of the beam, and may have skirts overlapping the sides, or sides and end, of the beam for guidance. At least one r and preferably two, studs project down from the cover plate through a top plate of the beam. For jacking one or more jacks are placed within the beam to act between a bottom plate of the beam and the lower ends of the studs. When the jacks are extended the studs and cover plate are forced upwards to develop the reaction between the wall and rigid member and hence pile.When an adequate prestressing has developed cover plate is pinned up from the top surface of the top plate of the beam, whereupon the jacks can be retracted and removed prior to any final concrete placement around the beam.

The invention is illustrated by way of example in the accompanying drawings in which: Figure 1 is a vertical section transverse to a wall; Figure 2 is a section taken on the line II-II in Figure 1; Figure 3 is a pile head elevation; Figure 4 is a plan of the parts shown in Figure 3; Figure 5 is a section taken on the line V-V in Figure 3; Figure 6 is a view similar to Figure 1 but of an alternative example; Figure 7 is a diagrammatic plan of the second example; and! Figure 8 is an elevation of a pile cap of the second example.

Figure 1 shows a cavity wall 10! which is to under-pinned by one or more offset piles 11! to replace an existing insecure foundation 12. As shown in Figure 2, each pile 11 is a composite structure of an outer steel sleeve 13 containing an I beam 14 and filled with concrete 15. As shown more clearly in Figure 3, the upper end of the shell 13 is secured by a fillet weld 15 to a plate 16, which in turn is welded at 17 to the lower flanges 18 of an I beam 19 having a vertical web 20, one or more transverse strengthening webs 20A, and upper flanges 21.The right hand end of the beam 19, as seen in Figures 1 and 3, is cantilevered from the pile 11 beneath the wall 10 where it carries a cover plate 22 provided with side skirts 23 and end skirt 24 overlapping the sides and end of the beam 19 for guidance purposes.

Two studs 25 project down from the underside of the cover plate 22 and extend through holes in the upper flanges 21 of the beam 19. In the Figures 3 to 5 example, nuts 26 are fitted on the studs above the flanges 21 and below the flanges in the Figure 1 example.

After placement of the piles and initial assembly of the beam 19 with the cover plate 22 abutting a precast concrete plate 27 which in turn engages the lower raw surface of the wall 10 via a grouting layer 28, jacks 29 are inserted one on each side of the web 20 beneath respective ones of the studs 25 and are extended by oil provided by hand pumps through hoses 30. This causes the cover plate 22 to be raised relatively to the beam 19 and hence a load to be developed between the wall and pile and for the pile to be restressed in bending. This separation is then maintained by packing earth and mortar 31 between the cover plate 22 and upper flanges 21r as shown in Figure 1, or by screwing down the nuts 26 as shown in Figure 4. In the Figure 1 example the nut 26 prevents excessive extension of the cover plate 22 relatively to the beam 19 and a similar nut may be provided on the lower ends of the studs 25 in the Figures 3 to 5 example as well if necessary. The jacks may then be retracted and then removed and the beam 19 encapsulated within a concrete pile head 32, which may be integral with a low level beam extending along beneath the wall 10.

The example of Figures 6 to 8 differs essentially only in that the beam 19 is bolted to a plate 33 which is fixed to, and supported by a gusset plate 34 from, a tubular pile cap 35 which is fitted over the top of the pile 11. The cap 35 is lined with resin 36.

Claims

1. A method of under-pinning the wall of the building in which at least one pile is put down offset from the wall and a rigid member, which is capable of transmitting the load of the wall to the pile, is mounted on top of the pile and projects in cantilever fashion beneath the wall; wherein at least one jack is interposed between the rigid member and the wall and is extended to prestress the pile in bending prior to fixing the wall relatively to the rigid member.

2. A method according to claim 1, wherein the jack or jacks which is or are used is or are recovered prior to encapsulating the rigid member in a concrete pile head.

3. A method according to claim 3, wherein the pile head is integrated with a low level beam extending along within the plane of the wall.

4. A method according to any one of the preceding claims! wherein the fixing of the wall relatively to the rigid member, while the jacking is operational, is achieved by interposing packing between the bottom of the wall, or a plate abutting the bottom of the wall, and the rigid member.

5. A method according to any one of claims 1 to 3, wherein the rigid member is in two parts which are vertically separated as the jacking is carried out, and are then held spaced apart to maintain the prestressing.

6. A method according to any one of the preceding claims, wherein the rigid member is a metal beam which is rigidly fixed to the top of a pile or pile cap.

7. A method according to claim 6, wherein a cover plates which abuts directly or indirectly a lower surface of the wall, is located on top of the cantilevered end of the beam, and has skirt overlapping the sides, or sides and end, of the beam for guidance.

8. A method of under-pinning the wall of a building substantially as described with reference to the accompanying drawings.