Casings are generally cylindrical sections, or pipes, which are used in the foundation industry to temporarily support the soil when a pile bore is constructed. Sections or segments of casing will vary in size and are typically between 1 metre and 4 metres in length but could be longer.

Casings are usually made of steel and, as such, are very heavy and cumbersome. Consequently, it is usual for individual sections of casing to be joined together to form a segmental casing of appropriate length to support the bore.

Two known types of casings are in general use. The first type of casing is formed of a. single cylindrical wall whilst the second is of doubled walled construction. The present invention is relevant to both types of casing.

In use, a section of casing may be installed in the ground by means of a rotary piling rig equipped with a kelly bar, or by means of an oscillator attached to a piling rig. A typical construction sequence using a rotary rig equipped with a kelly bar to install a cylindrical casing is shown in Fig. 1 and generally comprises: installing a first section of casing 1 in the ground. This is facilitated by means of a piling rig which is operable, by means of a kelly bar 2 and an adapter 3, to alternately rotate or

oscillate the casing such that it penetrates the ground; removing the soil therein by means of a boring tool such as an auger 4 or a boring bucket; and applying a downward force to the casing. A second section of casing 5 is positioned above the first section and then coupled thereto by means of a joint. The process of rotating or oscillating the casing, removing the soil from the ground and applying a downward force is repeated in this manner, coupling additional sections of casing, until the desired length of casing has been installed.

Once the desired length of casing has been installed, the boring tool is usually caused to bore below the lower level of the casing to the required depth 6. Some means of reinforcement, usually in the form of a reinforcing cage 7, may then be installed, concrete 8 placed to fill the bore, and the segmental casing withdrawn. During the withdrawal operation, as the sections of casing are drawn above ground, each is disconnected and stored for future use.

The joints which are operable to couple adjacent sections of casing together are advantageously required to perform several functions, for example :- to allow the rotational, oscillatory or downward forces imparted by the rig to be transmitted to all sections of casing in the string ; to ensure that the vertical upward force required to withdraw the casing from the ground is transmitted to all of the sections of casing in the string; and to provide a level of water-tightness between sections. Various methods and techniques are known for achieving these'objectives.

Figs. 2-4 show typical details of the known joints which essentially comprise two complimentary joint portions,

often known as male/female joints or socket-type joints.

During installation it is usual for the male part 12 of the joint to be at the so-called driving end 12 of the casing, i. e. the upper most end of the casing. The female part 13 of the joint of the next section of casing is presented to the male part 12, and the two joint portions generally cooperate in a complimentary fashion. Before the female part is presented, it is usual for a flexible (e. g. rubber) O-ring 14 to be fitted in the groove 15 provided. The purpose to the 0-ring is to provide a level of water- tightness across the joint. It is possible for one or more 0-ring seals to. be fitted. The mechanical connection between the complementary joint portions 12 and 13 may be by plug screws 16 or any other suitable method. It is common for the kelly-applied torque to be transmitted from one section of casing to the next by an arrangement of keyways 17. One type of keyway is shown, but others may be used. The length of the joint is typically 200-300 mm.

To enable the heavy sections of casing to be assembled and coupled together, it is necessary for there to be an annular clearance gap 19 between the complimentary parts of the joint. Typically the difference between the internal diameter of the female joint, and the outer diameter of the male joint is 5-6 mm or greater. This clearance can cause misalignment of the casing at the joints and, moreover, allows sections of casing to flex at the joint during installation or use. As a result of misalignment of adjacent casings and/or the flexing of casings at the joint, it can be difficult to achieve and/or maintain verticality along the whole length of casing. In addition, any misalignment and/or flexing may adversely affect the ability of the 0-ring to provide a water seal at the joint.

There is therefore a need to alleviate the problems which are potentially caused by the clearance gap required between the complimentary portions of a two-part joint used to couple together adjacent sections of steel casing.

Preferred embodiments of the present invention seek to provide a means of improving the axial alignment of adjacent sections of a bore casing, and to reduce the flexing at the joint.

According to an embodiment of a first aspect of the present invention there is provided a casing for supporting the wall of a bore formed in the ground, the casing comprising a substantially hollow body having a longitudinal axis and having a joint portion at one end thereof, wherein the joint portion is provided with a plurality of discrete elements spaced apart on the inner or outer surface thereof.

According to an embodiment of a second aspect of the present invention there is provided a segmental casing for supporting the wall of a bore formed in the ground, the segmental casing comprising at least two sections of casing coupled together by means of first and second complimentary joint portions, each section of casing comprising a substantially hollow body and having one of said first and second complementary joint portions at an end thereof, wherein one or both of said first and second complementary joint portions is provided with a plurality of discrete elements which are spaced apart on the inner or outer surface of the joint portion.

According to an embodiment of a third aspect of the present invention, there is provided a method of installing a longitudinal segmental casing in the ground, the method comprising the steps of: installing a first section of casing to a predetermined depth in the ground, the first section of casing comprising a substantially hollow body having a first joint portion at an upper end thereof; removing soil from within the first section of casing; and positioning a second section of casing above the first section of casing, wherein the second section of casing comprises a substantially hollow body having a second joint portion at a lower end thereof, the first and second joint portions being operable to be coupled together in a complementary fashion; coupling the second section of casing to the first section by means of first and second complementary joint portions, wherein one or both of said first and second complementary joint portions is provided with a plurality of discrete elements which are spaced apart on the inner or outer surface of the joint portion (s).

The effect of the plurality of discrete elements provided on the joint portion is that the clearance gap between the first and second portions of the gap is reduced. The advantage of this is two-fold. Firstly it allows the degree to which the joint may flex to be reduced and, furthermore, the alignment of the outer surface of adjacent sections of segmental casings can be improved. Advantageously, the water-tightness of the joint is also improved due to the reduced flexing which is achieved.

Preferably, the discrete elements are spaced apart on the joint portion, such that there exists an angular separation

between the elements with respect to a central longitudinal axis of the casing and so as to avoid the connection holes in the male and female joints. The discrete elements may preferably comprise longitudinal ribs which may advantageously extend substantially parallel to the longitudinal axis of the casing. Alternatively, the discrete elements may be non-elongate elements.

The discrete elements may be formed of any material suitable for preventing or minimising flexing of the joint.

In particular, the discrete elements may be formed of a hard metal, such as steel.

In the case of a joint comprising male and female portions as shown in Figures 2 to 5, it can be seen that the male portion i s an extension of the inner wall of the casing, and the female portion is an extension of the outer wall of the casing. The male and female joint portions are preferably similar in length. Thus, the outer perimeter of the male portion defines a smaller diameter, (or if the casing is non-cylindrical, a smaller maximum cross- sectional dimension), than the inner perimeter of the female portion. This allows the male joint portion to fit in a complementary fashion within the female joint portion.

According to preferred embodiments of the present invention, the discrete elements are provided on the outer surface of the male joint portion, i. e. such that they protrude outwardly towards the inner surface of the female joint portion when the sections are'coupled together.

However, it is also envisaged that the elements may alternatively, or additionally, be provided on the inner surface of the female joint portion. In this case the

elements will protrude towards the interior of the casing and towards the outer surface of the male joint portion when the sections are coupled together. Either way, the discrete elements advantageously serve to decrease the clearance gap between the male and female parts of the joint.

It should be appreciated that while the present description relates to casings having a generally circular cross section, other shapes of casing are envisaged such as oval, square, rectangular etc.

Segmental casings are often used in the construction of piles forming a secant pile wall, as shown in Figure 9. In this form of construction, alternate piles are first constructed, e. g. pile nos. 1,3, 5, etc. At a later stage the infill piles, e. g. pile nos. 2,4, etc are constructed by counter-boring between two existing piles. The extent of the so-called"cut-back"into existing piles is determined, in part, by the accuracy of maintaining verticality of each and every pile. Furthermore, the ability. to reduce the cut- back reduces construction time, and wear & tear on the equipment, thus reducing the overall cost of the piling operation.

Thus, preferred embodiments of the present invention are particularly useful during the construction of a secant pile wall, due to the noticeable improvements in achieved verticality of the resultant pile which allows the cut-back between adjacent piles to be reduced.

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: Figure 1 shows a typical construction sequence for installing a cylindrical casing in the ground ; Figures 2 to 5 show known complimentary joint for coupling together two sections of casing ; Figures 6 to 8 show a casing having a joint embodying the present invention ; and Figure 9 illustrates the construction of a secant pile wall.

Those features which are identical are denoted by the same reference numeral throughout.

Figure 6 shows both a sectional view and an elevational view of a male joint portion 12 embodying the present invention. The joint portion 12 is provided with a plurality of discrete elements which in this embodiment comprise a number of vertical ribs or spacers 21. The elements 21 are fitted to the outer surface of the joint portion 12 such that it resembles a splined shaft. In this embodiment, the ribs are slightly thinner than the annular gap between male and female joints, as can be seen more clearly in Figures 7 and 8. Figures 7 illustrate a cross- sectional slice through a portion of the male joint portion 12, shown in Figure 6, when coupled to a complementary female portion 13. Figure 7 shows an enlarged version of this to ore clearly illustrate the element 21 within the gap between the male portion 12 and the female portion 13.

In this embodiment, each of the ribs 21 has a chamfered leading edge 24 which facilitate assembly of two sections.

Furthermore, the ribs are arranged around the outer circumferential surface of the joint portion 12 such that there exists a substantially equal angular distance between them with respect to the central longitudinal axis of the casing.

The ribs effectively reduce the clearance between the male and female parts of the joint, and thus significantly reduce the possibility of misalignment of the casing at the joints. The possibility of flexing at the joint during use is also reduced. This significantly increases the ease with which the verticality of the casing can be maintained.

In addition, the improved alignment and reduced flexing at joints significantly improve the ability of the 0-ring 14 to provide a water seal at the joint. It should be noted that if the clearance were to be reduced over the complete perimeter, it is unlikely that the joint could be easily assembled, because of the practical difficulties with sections of this size, and the distortions that are generated during use.