GB2205121A - Underpinning buildings by using, in situ, cast piles - Google Patents

Abstract

A method and apparatus for supporting an existing building structure comprises excavating a void (54 Fig. 4) or trench (72 Fig. 4) alongside the structure, forming a hole (16) in which a pile can subsequently be cast from the base of the void, forming a passage (20) into the strucure, placing a one limb (20) of an L-shaped structural member into the passage and the other (22 Fig. 2) into the hole and casting concrete into the said passage and hole to form a pile. Fig. 4 shows a modified method and apparatus for use in ground which is subjected to heave. <IMAGE>

Description

Improvements in or relating to Methods of and Apparatus for Supporting Building Structures The present invention concerns improvements in and apparatus for supporting building structures, especially but not exclusively existing building structures which have shallow corbelled brick foundations or structures which are built on ground which is liable to heave when, for example, the moisture content thereof changes.

There are existing methods of supporting subsiding building structures involving, for example underpinning but, especially in the case of buildings having corbelled brick foundations or buildings which are built on ground which is subjected to heave, traditional systems have disadvantages, for example, they require considerable excavation to expose the foundation and this increases the time, cost and dangers involved.

It is an object of the present invention to obviate or mitigate these disadvantages.

According to the present invention there is provided a method of supporting an existing building structure comprising forming a hole in which a concrete pile can be cast in situ alongside the building structure, forming a passage in the building structure, locating a member having two interconnected limbs with one limb in the said passage and the other limb in the top of the pile hole and forming a pile by pouring concrete in the hole and passage with the cap of the pile incorporating said members.

Further according to the present invention there is provided for a building structure a pile formed in situ from concrete and including a pile cap, into which is cast a structural member having two interconnected limbs with one limb of the member extending substantially horizontally into a passage which has been pref-ormed the structure to be supported and the other substantially vertically limb downwards towards the base of the pile.

Preferably said structural member includes a tubular steel section which forms the vertical member and an I-beam which forms a horizontal section.

Preferably the I-beam is fixed to the tubular member by bolting the end of the member remote from that part thereof which extends into the building structure to the end of the tube.

Further according to the present invention there is provided a method of supporting a building structure on ground which is liable to heave comprising forming a plurality of spaced passages In said structure in or above the foundation, forming a substantially vertical hole in which a concrete pile can be formed alongside the building in registry with each of said passages, excavating in the ground alongside the building a void in which a pile cap can be cast, laying a layer of a compressible material on the base of the void, locating a tube of a material having a low co-effiction of friction in the upper portion of said pile hole with the upper end thereof in said compressible layer, locating within said tube a structural member having two interconnected limbs, the downwardly directed limb of which is longer than said tube and the other limb of which is attached to the downwardly directed member and extends therefrom into said passage in the building structure, filling the pile hole, void and passage with a cementitious mixture which, after setting, forms a pile.

Preferably the void has a greater width at its top than at its base. Similarly the passage may have a greater width at its top than at its base.

Alternatively the void and/or passage may be rectangular in cross-section.

Each void is connected to its neighbour(s) by an interconnecting void which is sufficiently deep to accommodate on its base at least a layer of compressible lining material.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 shows diagrammaticaly a pile supporting a building structure with a corbelled brick foundation; Fig. 2 shows an end elevation of a structural member of the pile; Fig. 3 shows a cross-sectional plan on the line III-III of Fig. 2; and Fig. 4 is a diagrammatic elevation towards the wall of a structure supported on ground which is subjected to heave and a pile for supporting said structure.

Referring to the building structure with a corbelled brick foundation shown in Fig. 1, there is shown a wall 10 of the structure supported on its foundation 12, the internal floor of the structure being indicated generally by the floor level line 14.

To support the structure a hole 16, in which a concrete pile can be cast in situ, is formed to a calculated predetermined depth outside the building substantially alongside the outer face of the wall.

The hole may be formed by augering, by driving in hollow steel casings, or by any other suitable methods.

As shown in the drawings the hole may penetrate an edge of the foundation 12.

Prior to forming the hole 16 a void (not shown) is excavated in the ground 18 against the structure so that the structure can be broken into from the outside to form a substantially horizontal mutually spaced passage tq therethrough, leading from the void.

A pile with a specially designed pile cap can then be formed in the void and hole 16 by pouring concrete into the hole and void or shuttering erected within the void, the concrete flowing also into the passage t) to fill it.

Prior to the pouring of concrete a structural member is placed at the top of the pile. The structural member is of inverted L-shape and comprises a first horizontal limb member 20, which is conveniently an I-beam, and a second vertical member 22 which is of tubular steel. The diameter of the tube 22 is greater than the width across the flanges of the beam 20 and the beam is attached by one end over the top of the tube by two bolt and nut assemblies 24, the bolts of which are welded to the outer surface of the tube to project thereabove through suitably drilled holes in the lower flanges of the beam 20.

A V-shaped guide or guides 26 is welded to the inner surface of the tube near its upper end to locate and support one or more reinforcing rods 28 projecting downwardly into the pile.

On locating the structural member within the pile, void and passage concrete is poured to provide a capped pile as shown in Fig. 1. It will be realised therefore that on setting the pile provides a support from the structure.

A plurality of piles are provided at regularly spaced intervals, for example at one metre centres, around the periphery of the building.

In the modification shown in Fig. 4 there is shown a pile similar to the pile of Figs. 1 to 3 supporting a building 110 which is built on ground subjected to heave, that is movement due, for example, to changing moisture content within the ground.

The structure 50 rests on a footing or foundation 52 and alongside the outer face 50 there is excavated a series of inverted trapezoidal voids 54 that is voids having a wider top than base, neighbouring voids being interconnected by a shallower channel or void 56. A hole 58 for a pile to be cast in situ is formed, normally by augering, from the base of the void 54 in a manner similar to that described with reference to Fig.

1 and an inverted L-shaped structural member 60 which is similar to the member described with reference to Figs. 2 to 3 but has a longer tubular vertical section is inserted into the top of the pile and into a passage 62 formed in the wall 50 after the insertion into the hole 58, outside the member 60 and spaced therefrom, of a plastics material tube 64 whose length is just less than the length of the tubular section of the structural member 60, the upper end of the tube projecting slightly above the top of the hole 58.

Before concrete is poured into the passage 52, the void 54 and the hole 58 to form in situ a capped pile, a continuous layer of clayboard 66 is laid on the lower surfaces of the deep and shallow voids 54, 56.

Clayboard is a compressible material which, when a load has been removed therefrom, returns substantially to its original shape, and it will be observed from Fig. 4 that if a series of voids and piles are provided around the periphery of the building the pile caps will be isolated from the ground, which up till then was supporting the building and which was subjected to heave, by the compressible clayboard. As the parts of the piles below the end of the tubular plastics sections 64 are in intimate contact with ground at a level lower than that which is subjected to heave (normally only the first two or three metres are subjected to heave) the structure will be supported by piles anchored in stable ground, the clayboard layer and plastics tubes 64 allowing movement of the heaving layer without effecting the stability of the building.

In practice, when supporting a structure alternate piles are driven, that is piles 1, 3, 5, etc. After the piles have been fully formed and the concrete set piles 2, 4, 6, etc. can be formed thereby ensuring the stability of the structure during the piling operation.

It is preferable that a layer of clayboard is provided on the upstanding side of the void 54, that is, the side of the void facing the surface of the wall. The location of this layer is shown by the chain dotted line 70 in Fig. 1. It will be realised that in the Fig. 1 embodiment a clayboard layer in this location is not necessary, it is shown in Fig. 1 merely for convenience.

Various modifications can be made without departing from the scope of the invention, for example, the structural member can take a number of different forms provided that it projects into the wall from the side and downwards into the top of the pile.

In practice it is often difficult to excavate a trapezoidal void and form correspondingly shaped passages through the brick-work building structure 50.

In these circumstances a flat bottomed trench, having a base represented by the chain dotted line 72 (Fig.

4), can be formed around the outside of the structure with alternate pile holes 58, (the piles being spaced at approximately one metre centres), being formed from the base of the trench. In this modification the clayboard layer 74 is again continuous but effectively horizontal. A rectangular shaped passage can be formed through the brick-work in this modification.

Claims (16)

1. A method of supporting an existing building structure comprising forming a hole in which a concrete pile can be cast in situ alongside the building structure, forming a passage in the building structure, locating a member having two interconnected limbs with one limb in the said passage and the other limb in the top of the pile hole and forming a pile by pouring concrete in the hole and passage with the cap of the pile incorporating said members.

2. A pile for a building structure formed in situ from concrete and including a pile cap, into which is cast a structural member having two interconnected limbs with one limb of the member extending substantially horizontally into a passage which has been preformed the structure to be supported and the other substantially vertically limb downwards towards the base of the pile.

3. A pile as claimed in claim 2, in which said structural member includes a tubular steel section which forms the vertical member and an I-beam which forms a horizontal section.

4. A pile as claimed in claim 3, in which the I-beam is fixed to the tubular member by bolting the end of the member remote from that part thereof which extends into the building structure to the end of the tube.

5. A method of supporting a building structure on ground which is liable to heave comprising forming a plurality of spaced passages in said structure in or above the foundation, forming a substantially vertical hole in which a concrete pile can be formed alongside the building in registry with each of said passages, excavating in the ground alongside the building a void in which a pile cap can be cast, laying a layer of a compressible material on the base of the void, locating a tube of a material having a low co-effiction of friction in the upper portion of said pile hole with the upper end thereof in said compressible layer, locating within said tube a structural member having two interconnected limbs, the downwardly directed limb of which is longer than said tube and the other limb of which is attached to the downwardly directed member and extends therefrom into said passage in the building structure, filling the pile hole, void and passage with a cementitious mixture which, after setting, forms a pile.

6. A method as claimed in claim 5, in which the void has a greater width at its top than at its base.

7. A method as claimed in claim 5 or claim 6, in which the passage has a greater width at its top than at its base.

8. A method as claimed in claim 5, in which the void and/or passage are rectangular in cross-section.

9. A method as claimed in any one of claims 5 to 8, in which each void is connected to its neighbour(s) by an interconnecting void which is sufficiently deep to accommodate on its base at least a layer of compressible lining material.

10. A method as claimed in any one of claims 5 to 9, in which said tube is manufactured from plastics material.

11. A method as claimed in claim 5, in which said void is continuous and extends alongside the wall.

12. A method as claimed in any one of claims 5 to 11, in which the side of the void facing the wall is lined with a compressible material.

13. A method of supporting an existing building structure substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

14. A pile substantially as hereinbefore described with reference to Figs. 1 to 3 or Fig. 4 of the accompanying drawings.

15. A method of supporting an existing structure substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

16. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.