GB2094374A - Lifting subsided building structures - Google Patents

Abstract

A building structure (e.g. a house) having a floor slab (10) is lifted by forming a plurality of piles (14) through clearance holes (13) in the floor slab, supporting a first beam (16) on said piles to extend horizontally above said floor slab, disposing a second beam (17) above and parallel to said first beam, providing a plurality of tie members (18) each secured at its lower end to the slab (10) and extending freely up through aligned apertures (19, 20) in said first and second beams, providing stop means (21, 22) associated with each said tie rod above and below said second beam, lifting the floor slab (10) and its building structure by exerting a separating force (23) between the first and second beams, reaction being provided by the piles and the upper stop means, moving the lower stop means (22) to contact the first beam to hold the lifted structure, and securing the structure in the lifted position by cutting off the piles (14) at floor level and bonding them in the apertures (13). This method avoids any digging down beneath the structure, is quick and clean and gives the lifted structure piled support. <IMAGE>

Description

SPECIFICATION Lifting subsided building structures This invention relates to the lifting of subsided building structures, for example foundations or concrete floor slabs, beams or rafts. Remedial work on a subsided building structure is traditionally a very expensive and time-consuming task. Considerable expertise has been acquired, particularly in mining areas, but buildings in any area are liable to subsidence due to poor ground conditions, poorly filled sites, inadequate original foundations, growth or felling of trees, drought or flood and for many other reasons.

Traditionally, remedial work has involved digging down beneath the structure in order to construct new footings. Since the subsided structure is thus being undermined and further weakened the work can only proceed in stages, waiting at each stage for the previous section of new footing to acquire load-bearing strength. The work is also obviously dangerous, laborious and time-consuming. In many cases a survey has recommended that the most cost-effective course is to demolish the building and commence afresh.

An object of the present invention is to provide a method of lifting a subsided building structure which avoids any such digging down beneath the structure and which is also much quicker than traditional methods.

According to the present invention there is provided a method of lifting a building structure comprising forming a plurality of piles not bonded to said structure, supporting a first beam on said piles to extend above said structure, disposing a second beam above said first beam, providing a plurality of tie members each secured at its lower end to said structure and extending freely up through aligned apertures in said first and second beams, providing stop means associated with each said tie rod above and below said second beam, lifting said structure by exerting a separating force between said first and second beams, reaction being provided by the piles and the upper stop means on the tie members, moving said lower stop means to contact the first beam to hold the lifted structure, repeating the lifting and holding steps if desired, and securing the structure in the desired lifted position.

An embodiment of the invention will now be described, by way of example, with reference to the single Figure of the accompanying drawings.

The drawing is a vertical section through apparatus shown in position lifting a subsided building structure by a method according to the invention. A subsided concrete raft 10, e.g. a house floor, rests on a substrate of compacted hardcore 11 on subsoil 12. It is desired to lift the raft which, typically, has subsided a few inches at one side and less at the other.

The first step is to drill a pattern of apertures 13 through the raft 10. Pile holes are formed working through the apertures 13. The pile holes may be formed by a number of methods depending on ease of access and headroom and the nature of the subsoil. For example a self-propelled soil displacing mole may be used as disclosed in my published U.K. Patent Application No.

2 048 999 A and may be lined as disclosed in my Patent Application No. 8023589. Alternatively the hole may be formed by means of top driven steel tubes as disclosed in my Patent Application No.

8040772. These methods permit the formation of pile holes of 4 or 5 metres or more in depth working within the confined space and headroom of an average room of a house.

Piles 14 are formed in situ in the pile holes by filling the holes with concrete and introducing reinforcement as required. The piles are either lined or at least provided with sleeves at ground level so that each pile extends freely through its aperture 13 to stand proud of the raft 10 by 30 centimetres or so. In suitable cases the piles may be formed by the direct method of hammering reinforced concrete beams end-to-end down through the apertures 1 3.

The piles are capped with saddles 1 5 and a first beam 1 6 is supported on the pile saddles to extend above said structure. The saddles 1 5 are preferably arranged so that beam 1 6 extends horizontally even though the subsided raft may not be horizontal. The beam may be a steel I-beam. A second beam 1 7 is disposed above the first beam.

A plurality of steel tie rods 18 are each secured at their lower ends to the raft 10 and extend freely up through pre-formed aligned apertures 19, 20 in the two beams. The lower ends may conveniently be secured by mortaring them into pre-drilled bores in the raft with an epoxy mortar. Upper and lower stop means 21,22 are associated with each tie rod 18 above and below the second beam 17.

The stop means 21,22 are suitably nuts, and preferably washers, and the tie rods are threaded so that the nuts can be spun to any desired position along the rod and remain in position to transfer axial loading to and from the tie rod. Any functionally similar device may be employed as the stop means, for example collars, clamps, ratchets or pegs, and in some of these cases the tie rods need not be threaded or otherwise specifically formed.

Lifting devices 23, for example hydraulic jacks or air cushions, are inserted between the beams and are actuated to lift the raft 10 by exerting a separating force between the first and second beams 16, 17. It will be appreciated that the reaction forces are provided by the piles 14 reacting upwardly against the lower beam, and the upper stop means 21 reacts downwardly against the upper beam. A plurality of piles, tie rods and lifting devices are provided along each beam pair, and a number of parallel beam pairs may be provided across a raft. Control of the lift provided by each device 23 permits the raft to be lifted without undue localized strain back to a true horizontal position.

The travel of a typical jack may be 2 or 3 centimetres. After the first lift, the lower stop means 22 are moved to contact the upper surface of the first beam 1 6. The lifted raft is thereby suspended from the first beam 1 6. The jacks are retracted, the second beam 17 lowered and the upper stop means 22 moved down the tie rods 18 again to contact the beam 1 7. A second increment of lifting may then be undertaken. The process is repeated as necessary to lift the raft to its desired position. The lifted slab is then retained in its lifted position suitably by injecting concrete grout through further apertures drilled through the raft into the space opened up beneath the raft. When set, the beam apparatus is removed, the tie rods cut off, the piles cut back to floor level and their heads bonded to the raised slab around apertures 13 to provide enduring piled support to the raft.

It will be seen that the above method avoids any digging beneath the raft. The method can be effected in a matter of days as opposed to weeks or months, and is carried out entirely within the building so that work can continue in bad weather.

The method can be carried out in situations where the traditional recommendation would have been to demolish, and finally the result is a raised building structure given enduring piled support.

Claims (13)

1. A method of lifting a building structure comprising the steps of: forming a plurality of piles not bonded to said structure; supporting a first beam on said piles to extend substantially horizontally above said structure; disposing a second beam above and substantially parallel to said first beam; providing a plurality of tie members each secured at its lower end to said building structure and each extending freely up through a pair of substantially vertically aligned apertures in said first and second beams; providing stop means associated with each said tie rod above and below said second beam; lifting said building structure by exerting a separating force between said first and second beams, reaction being provided by said piles and by said upper stop means on the tie members; moving said lower stop means to contact the first beam to hold the lifted building structure;; repeating said lifting and holding steps if desired; and securing the building structure in the desired lifted position.

2. A method according to claim 1 wherein said step of forming a plurality of piles comprises forming a plurality of apertures through the building structure, forming a plurality of pile holes by working down through respective said apertures, and forming the plurality of piles in situ in the respective said pile holes.

3. A method according to claim 2 wherein said step of forming a plurality of piles further includes lining each said pile hole, and forming said plurality of piles in situ so that each said pile extends freely up through the respective said aperture to stand proud of the building structure.

4. A method according to claim 2 wherein said step of forming a plurality of pile holes comprises forming each said pile hole by means of a string of top driven steel tubes, the lower end of the lowest tube being closed.

5. A method according to claim 2 wherein said step of forming a plurality of pile holes comprises forming each said pile hole by means of a selfpropelled soil displacing mole.

6. A method according to claim 1 wherein said step of forming a plurality of piles comprises forming a plurality of apertures through the building structure, and hammering a plurality of reinforced concrete beams end-to-end down through each said aperture.

7. A method according to any one of claims 1 to 6 including the step of capping each said pile with a saddle to support said first beam.

8. A method according to any one of claims 1 to 7 wherein said lower end of each said tie member is secured to said building structure by providing bores in said building structure and mortaring each said lower end into a respective said bore.

9. A method according to any one of claims 1 to 8 wherein each said tie member is threaded, wherein each said lower and each said upper stop means comprises a nut threadedly received on the respective said threaded tie member, and wherein said step of moving said lower stop means comprises rotating the respective said nuts.

10. A method according to any one of claims 1 to 9 wherein said step of lifting the building structure comprises inserting a plurality of hydraulic jacks between said first and second beams, and actuating said jacks to exert a separating force between said first and second beams.

11. A method according to any one of claims 1 to 10 wherein said step of securing the building structure in the desired lifted position includes bonding said lifted building structure to said piles.

12. A method according to any one of claims 1 to 11 wherein said step of securing the building structure in the desired lifted position includes injecting concrete grout beneath the lifted building structure and allowing said grout to set.

13. A method of lifting a building structure substantially as described herein with reference to the accompanying drawings.