GB2067623A - Method for supporting buildings - Google Patents

Abstract

Pairs of piles (25, 26) are formed adjacent a subsided wall (10, 11). Pile cap members (24), which may be integral arms of a concrete ring beam (23), extend across the top of the piles of each pair to support the wall. A horizontal line of weakness (30) is cut along the wall above the cap members and hydraulic expansion devices are inserted in openings (31) along the line. The wall is lifted by means of the devices and is retained by steel rods in the lifted position. This method of underpinning and lifting has the advantage over conventional methods of avoiding undermining of the existing footings. <IMAGE>

Description

SPECIFICATION Method for supporting buildings This invention relates to the supporting and lifting of subsided building structures.

Conventionally, structure underpinning is effected by digging down to good ground below the level of the existing subsided footings, forming new and massive concrete foottings beneath the existing footings, and working thus in short sections around the building. After allowing the new concrete time to gain strength, jacks can be arranged to act between the old and new concrete footings to raise subsided portions of the building, the gap then being mortared.

This procedure is difficult, time-consuming and labour intensive in view of the need to dig down well below existing footing level in each section around the building.

My British Patent Application No. 7916657, the disclosure of which is incorporated herein by reference, discloses a method of constructing a pile in situ comprising: forming a hole in the subsoii by allowing an elongate self-propelled soil displacing mole to descend through the subsoil; withdrawing the mole; filling the hole with concrete; allowing such mole to descend within the filled hole before the concrete sets to produce a bulbous pile footing and to displace concrete into the hole wall; withdrawing such mole; and refilling the hole with concrete and allowing the concrete to set to form an in situ pile with an integral footing.

Figures 5 and 6 and the related description in the Application No. 7916657 disclose a procedure for supporting pre-existing walls by the use of a pair of such in situ piles and a horizontal pile cap member extending across the tops of the piles and into an aperture in the wall to support the wall. This procedure can stabilize the wall to prevent further subsidence and avoids the disadvantages of conventional underpinning noted above. A problem arises however when it is desired to lift the subsided portion of the wall back to its proper level.

According to the present invention there is provided a method of supporting a pre-existing wall comprising: forming a plurality of pairs of piles in situ adjacent to the wall; forming pile cap members each extending across the top of the piles of a said pair to support said wall; creating a generally horizontal line of weakness along the wall above the cap members; inserting a plurality of hydraulic expansion devices in openings formed in said line of weakness: lifting the wall above said line by means of said devices; and retaining said wall in said lifted position to permit removal of said devices.

The invention also provides a wall lifted and supported by a method as set out in the immediately preceding paragraph.

This method still avoids the above noted disadvantages of conventional underpinning while succeeding in solving the problem of lifting the wall. In addition this method has a major technical advantage over conventional underpinning in that it is not necessary to disturb or undermine the existing footings. The existing footings therefore continue to serve to give substantial support to the building. Moreover the hydraulic expansion devices, during lifting, react downwardly against both the existing footings and against the new piles. The existing footings can usually withstand such short term loading alone, subsidence being a slow movement, and thus this step can be effected without waiting for the new piles to gain full strength. The whole operation can thereby be effected in a much shorter time period than conventional underpinning.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a vertical section through a wall showing the first steps in a support method according to the invention; and Figure 2 in a front elevation of a portion of the wall showing subsequent steps in the method.

Referring to the drawings there is shown a typical modern house cavity wall comprising inner and outer brick skins 10, 11 supported on a concrete footing 1 2. As required the cavity is filled with concrete 13 to a level 1 4 above ground level 1 5. A portion of the interior concrete floor slab 16 is shown on a hard core base 17. It is assumed that the wall has subsided, typically at a corner or at one side of the house.

A first step in practising a support method according to this invention is to dig a shallow (e.g.

18 inches deep) perimeter trench 1 8 around the house. At suitable intervals, e.g. at 3 foot centres, apertures 1 9 are formed through the wall to penetrate both brick skins 10, 11 and the infill 13.

The apertures may be 12 inches square.

Reinforcement rods are laid both peripherally of the house (20) and transversely (21) to extend into the apertures 19, and are tied together at their intersections. Expanded metal sleeves 22, e.g. of 4 inches diameter, are incorporated into and tied to the reinforcement rods. The sleeves are located in spaced pairs, each pair being aligned with a respective aperture 1 9. The inner sleeve of a pair may be centred about 1 foot or less and the outer sleeve about 2 foot or more from the house wall.

Concrete is then poured to form a reinforced ring beam 23 around the house with integral arms 24 extending into the apertures 19. The concrete is not poured into the sleeves 22 but it extrudes slightly through the expanded metal mesh to give a roughened hole.

When the concrete has gained strength all the subsequent steps in the method can be effected working on and from the so-formed clean concrete working platform extending around the house. A plurality of pairs of piles 25, 26 are now formed in situ, one pile created by working down through each sleeve 22. The piles are formed by a method as discussed in my British Patent Application No.

7916657 referred to above. A reinforced rod or rods is or are inserted into the hole subsequent to last withdrawing the mole and before the step of refilling with concrete. The roughened interior of the sleeve holes binds the piles to the ring beam 23 so that the integral arms 24 become pile cap members.

It will now be appreciated that the wall has been given support independently of and in addition to that given by the original footing 12.

The downward loading of the wall on the inward end of a pile cap member 24, which functions as a lever, is borne by an upward compressive force by the inner pile 25 and a downward tensile force by the outer pile 26 of each pair. The pile 26 opposes the upward tensile force by skin friction along its length and around its bulbous foot. Pile 25 opposes the compressive force by skin friction and usually also by end loading on a firm substratum of ground.

With the house now supported and stabilized against further subsidence, the wall can be lifted back, typically an inch or so, to nearer its original level. A line of weakness 30 is created along at least the subsided portion of the wall, suitably along the mortar course about two brick courses above the ring beam 23 but at least one brick course below ground-level. The line may be formed quickly and simply by nailing a timber guide along the wall and running the disc of a motor-driven disc cutter along the mortar course adjacent the guide.

A plurality of openings 31 are then formed along the line 30. The openings are suitably 3 inch diameter drilled holes and extend through the full thickness of the wall. For a typical phase of a lifting operation at a corner, six openings 31 may be drilled, three at 3 foot centres along each wall away from the corner. Hydraulic expansion devices are inserted in the openings, suitable devices being those commercialiy available as rock bursters.

Such a rock burster may be a steel cylinder about 3 inches in diameter and 1 foot long and provided with a plurality of pins that move out laterally in response to hydraulic pressure. Six such bursters are easily capable of controlled lifting of a corner of a house, the line of weakness 30 opening up in a controlled manner to form a tapered gap 32 as the lifting proceeds. A lift of about 1 inch can be effected in about 1 hour. It will be appreciated that the upward lifting force exerted by the rock bursters is countered both by the existing footings 12 and by the new piled support.

It is however not usually necessary to wait for the new piles to gain full strength because the existing footings can usually withstand the temporary additional loading due to the lifting. This is because the existing footings have not been undermined in practice of this invention and continue to perform a supporting function for the house.

The wail is now retained in the lifted position.

This is suitably accomplished by drilling a closely spaced series of 14 inch diameter holes along the line 31 and forcing standard 1 + inch diameter steel bars as a tight fit into the holes. This is quicker than trying to fit shims to a tapered gap 32. The rock bursters can now be depressurized and removed. If necessary a further phase of lifting can be effected by repeating the steps of forming openings 31 and using the rock bursters. Finally the gap is filled by injection of epoxy mortar and the gap and line pointed over with fresh mortar.

In a modification of the described method one pile of each pair is formed within the house, e.g. by working down through a hole formed through the ground floor slab, and the other pile if formed outside. The pile cap members will then extend through the wall so that the wall load is supported by both piles in compression.

Claims (9)

1. A method of supporting a pre-existing wall comprising: forming a plurality of pair of piles in situ adjacent to the wall; forming pile cap members each extending across the top of the piles of a said pair to support said wall; creating a generally horizontal line of weakness along the wall above the cap members; inserting a plurality of hydraulic expansion devices in openings formed in said line of weakness; lifting the wall above said line by means of said devices; and retaining said wall in said lifted position to permit removal of said devices.

2. A method as claimed in claim 1 wherein both piles of each said pair are disposed adjacent the same side of said wall, one pile being further away from the wall than the other, whereby the associated said pile cap member functions as a lever and the downward loading of the wall is borne by an upward compressive force by the nearer pile and a downward tensile force by the outer pile.

3. A method as claimed in claim 1 wherein the piles of each said pair are disposed one at each side of the wall, whereby the associated pile cap member extends through the wall and the wall loading is supported by both piles of said pair in compression.

4. A method as claimed in any one of claims 1 to 3 wherein prior to forming said piles a horizontal concrete beam is formed extending along the wall with integral arms extending into apertures in said wall, and wherein said pairs of piles are then formed adjacently respective said arms so that said arms serve as said pile cap members.

5. A method as claimed in claim 4 wherein said beam, said arms and said piles are formed of reinforced concrete.

6. A method as claimed in claim 4 or claim 5 wherein said beam is constructed by allowing concrete to set around tubular members disposed in the desired pile head positions, and wherein said piles are formed by working down through the respective tubular members.

7. A method as claimed in any one of claims 1 to 6 wherein said step of lifting the wall is effected before the piles have gained their full strength.

8. A method of supporting a pre-existing wall substantially as described herein with reference to the accompanying drawings.

9. A wall lifted and supported by a method as claimed in any one of claims 1 to 8.