Perimeter walls

Abstract

The present application describes methods and apparatus for installing a load bearing pile 1 which is installed in the line of a perimeter wall, in particular to a perimeter wall consisting of a series of diaphragm wall panels. In this way substantial concentrated vertical loads can be carried in the line of a perimeter or retaining wall, in particular

Description

[0001] The present invention relates to methods of forming a foundation structure and, in particular, to the construction of perimeter or retaining walls.

[0002] Most perimeter walls are designed essentially to act as earth or soil retaining structures, e.g. basement structures, storm water tanks and traffic underpasses etc. Often the retaining walls comprise a series of piles (such as bored, CFA or secant piles), diaphragm walls, sheet pile walls or ‘post & plank’ schemes.

[0003] In many instances the perimeter wall is also required to support vertical loads from the superstructure. Often the loads are relatively small and can therefore be carried on a single wall element. Alternatively, the loads can be accommodated by installing a relatively small capping beam, which serves to distribute the load over several wall elements (piles, panels, etc.).

[0004] In many instances there is a need to support heavy concentrated loads and in these circumstances it is usually necessary to: i) extend the depth of the perimeter walls; and/or ii) install a deep capping beam to distribute the load to several elements.

[0005] However, both of these approaches suffer from a number of disadvantages. Extending the depth of the perimeter wall is labour intensive and obviously requires a larger quantity of concrete, therefore adding considerable cost to the overall foundation construction. Installing a deep capping beam which serves to distribute the load to a number of elements requires considerable skill and can be difficult and time consuming. Furthermore, it may be necessary to support local structures in order to excavate for a deep capping beam.

[0006] Preferred embodiments of the present invention seek to provide a method whereby substantial concentrated vertical loads can be carried in the line of a perimeter or retaining wall which, advantageously, do not require the use of a capping beam or spreader beam to distribute the vertical loads onto several wall elements. Advantageously, the depth of the retaining wall can therefore be reduced. Additionally, in some circumstances, it may be possible to reduce the thickness of the retaining wall element.

[0007] The present invention therefore seeks to provide a method in which a load bearing pile is installed in the line of a perimeter wall. The method of the present invention is particularly applicable to a perimeter wall consisting of a series of diaphragm wall panels.

[0008] According to one aspect of the present invention there is provided a foundation structure comprising a load bearing element positioned between adjacent elements of a perimeter wall.

[0009] According to a second aspect of the present invention there is provided a method of constructing a perimeter wall, the method comprising the formation of at least one load bearing element in the ground between adjacent elements of the perimeter wall.

[0010] In one embodiment of the present invention diaphragm wall panels are constructed either side of the load bearing element. However, the present invention may also be applied to periemter walls constructed from a driven sheet wall or a secant pile wall formed from complementary “male” and “female” piles.

[0011] A steel reinforcement section provided along a longitudinal axis of the load bearing element serves to transmit the load of an above ground structure down to the toe of the load bearing element.

[0012] The foundation structure of the present invention is generally constructed by forming the load bearing element first and then constructing the adjacent elements of the perimeter wall either side.

[0013] Formation of the load bearing element may be by forming a hole in the ground to a depth below that of the proposed perimeter wall. The hole is then partially filled with concrete to a level just below the toe of the proposed perimeter wall and a reinforcement section is plunged into the concrete before it has hardened. Alternatively the section may be positioned within the hole and the concrete placed around the lower end thereof, within the lower part of the bore hole. Preferably, a suitable embedment length is used in order to accommodate the load to be transferred by the reinforcement section to the base of the pile.

[0014] Positioning of the reinforcement section is advantageously achieved by employing the use of a positioning frame having a means to adjust the plan position of the section at an upper and lower level.

[0015] The reinforcement section may comprise steel, pre-cast reinforced concrete, or a combination of steel and concrete. For perimeter walls which are to be constructed from diaphragm wall panels, an “I” shaped section has advantages since the width of the panels may complement either side of the I shape.

[0016] When the reinforcement section has been positioned, the bore is filled above the low level cast concrete with a backfill mixture of sand/cement, bentonite, mortar/grout. After the backfill has gained adequate strength (usually after 1 to 2 days), guide walls are constructed to define the proposed perimeter wall in the conventional manner.

[0017] The perimeter wall elements are then constructed on either side of the column section. The column section will preferably be slightly wider than the perimeter wall element excavating tool, and the tool will excavate any material in the ‘belly’ of the section.

[0018] In accordance with the present invention it is possible to install a load-bearing element (e.g. a column section) into a perimeter wall, which can support a concentrated load of 20,000 kN. In practice, with a suitably designed embedment detail, loads of 40,000 kN and even greater can be accommodated.

[0019] Conventionally perimeter walls are designed to span vertically, whether as a cantilever or between horizontal supports such as floor slabs. The thickness of the wall element depends on the soil properties and the length of vertical span.

[0020] An important advantage of the present invention is that it is possible to economise the design of the perimeter wall by the provision of a load bearing element in the line of the wall. For example, where the cantilever height, or distance between supports, is large, the wall elements between adjacent (main) piles can be designed to span horizontally. This reduces the stresses, and a thinner, more economical, wall can be designed.

[0021] In a similar manner, where the wall elements themselves are reinforced concrete piles, sheet piles or other discrete vertical elements, the horizontal support can be accommodated by, for example, a steel walling beam spanning between the vertical load-bearing elements.

[0022] The individual load bearing elements and the embedded sections can be designed to resist the external soil forces, and at the same time support substantial vertical loads as described herein.

[0023] For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0024] FIGS. 1A to 1D illustrate the stages involved in a method of constructing a perimeter wall, according to an embodiment of the present invention;

[0025] FIG. 2 shows the formation of a load bearing column according to embodiments of the present invention;

[0026] FIG. 3 shows the construction of a perimeter wall element on a first side of the load bearing column depicted in FIG. 2;

[0027] FIG. 4 shows the construction of a perimeter wall element on the other side of the load bearing column depicted in FIG. 2;

[0028] FIGS. 5A and 5B illustrate the stages involved in a method of constructing a perimeter wall, according to a further embodiment of the present invention; and

[0029] FIGS. 6A to 6C illustrate the stages involved in a method of constructing a perimeter wall, according to a further embodiment of the present invention.

[0030] FIG. 1A illustrates the first stage in the construction of a perimeter wall embodying the present invention and shows a plan view of a large diameter bored pile 1, having a reinforcement element 2 in the form of a steel I section column, positioned along its central longitudinal axis. The areas 3 and 4 either side of the pile column 1 indicate the line of the proposed perimeter wall. The dimensions of the I section are advantageously chosen to complement the thickness of the future perimeter wall elements.

[0031] FIG. 2 shows in more detail the construction of the pile column shown in FIG. 1A. A hole of appropriate size is formed in the ground and concrete 5 is pumped or poured into the bore up to a level 7 just below the lower level 8 of the proposed perimeter wall. The section 2 is plunged into the wet concrete to a predetermined depth and the plan position of the column is adjusted at an upper and lower level using a positioning frame having an upper and lower steering module. The bore is then filled with a mortar grout 6 up to a level at or near ground level. The resultant column will serve to carry a load 10, from an above ground structure, down into the base of the pile 5.

[0032] FIG. 1B shows the next stage of the construction in which guide walls 11 and 12 have been formed at an appropriate distance apart and above the load bearing column.

[0033] In FIG. 1C, area 4 between the guide walls 11 and 12 has been excavated so as to provide a cavity in the ground into which a cementious fluid will be pumped or poured in order to form a diaphragm wall panel. A stop end 13 (shown in FIG. 1D) is positioned within the cavity so as to comprise the end of the diaphragm wall panel. A reinforcing cage 14 is usually placed within the excavated area before filling with concrete to form the panel 15 (shown in FIG. 1D).

[0034] The construction of the first diaphragm wall panel is also illustrated by FIG. 3. The mortar grout substance which was used to form the upper part of the load bearing column has been excavated so that the concrete may be placed right up to the I section which is intended to protrude above the upper level of the perimeter wall.

[0035] In FIG. 1D and FIG. 4 the diaphragm wall panel 16 constructed on the other side of the load bearing column is shown. The resultant structure thus comprises a load bearing column which extends between two adjacent diaphragm wall panels and serves to transmit a load 10 down into the base of the pile in the ground.

[0036] FIGS. 5A and 5E illustrate the construction of a perimeter wall according to a further embodiment of the present invention. The load bearing element 20 is constructed as previously described, however the perimeter wall element comprises a sheet pile wall 21. The sheet piles, which may be interlocking or may be discrete elements in suitable ground conditions, will extend to the same level 8 to which the diaphragm wall 16 extended in FIG. 4.

[0037] After installation of the load bearing element 20, a pitching frame is erected along the proposed line of the sheet pile wall 21, and the sheet piles are then driven or vibrated to the required depth in the conventional manner. In suitable soil conditions it may be possible to install discrete sheet pile, i.e. without the need to inter-lock adjacent sheets.

[0038] FIGS. 6A, 6B and 6C illustrate the stages in the construction of a perimeter wall embodying the present invention in which a secant pile wall, comprising complementary male 26 and female 28 piles, is constructed either side of the load bearing element 23. Prior to the installation of the secant piles, guide walls 24 and 25 are formed and the mortar grout column of the load bearing element itself is partially excavated so as to complement adjacent secant pile 26a and 26b. The secant piles will extend to the same level 8 to which the diaphragm wall 16 extends in FIG. 4.

[0039] After installation of the load-bearing element 23, a secant pile wall is constructed in the conventional manner: a sequence of primary (or “male”) piles 26 and secondary (or “female”) piles 28 are formed which are counter-bored into the mortar grout column of the load bearing element 23.

Claims

1. A foundation structure comprising a load bearing element positioned between adjacent elements of a perimeter wall.

2. A foundation element as claimed in claim 1, wherein the load bearing element extends from a level above that of the perimeter wall to a level below that of the perimeter wall.

3. A foundation element as claimed in claim 1 or 2, wherein the load bearing element comprises a concrete column having a reinforcement section provided along a longitudinal axis thereof.

4. A foundation element as claim in claim 3, wherein the reinforcement section comprises a steel “I” section.

6. A foundation element as claimed in claim 1 or 2, wherein the elements of the perimeter wall comprise diaphragm wall panels.

7. A foundation element as claimed in claim 1 or 2, wherein the elements of the perimeter wall comprise sheet piles.

8. A foundation element as claimed in claim 7, wherein the sheet piles may be inter-locking or discrete elements.

9. A foundation element as claimed in claim 1 or 2, wherein the elements of the perimeter wall comprise complementary male and female piles.

10. A method of constructing a perimeter wall, the method comprising the formation of at least one load bearing element in the ground between adjacent elements of the perimeter wall.

11. A method as claimed in claim 10, wherein the method comprises the steps of:

i) forming the load bearing element in the plane of the proposed perimeter wall; and

ii) forming perimeter wall elements either side of the load bearing element.

12. A method as claimed in claim 10 or 11, wherein the load bearing element extends from a level above that of the perimeter wall to a level below that of the perimeter wall.

13. A method as claimed in any one of claims 10 or 11, wherein the load bearing element comprises a concrete column having a reinforcement section provided along a longitudinal axis thereof.