There is often a need to interconnect sections of a wall of a member (for example a tank or other containment member) in a watertight manner. The materials from which the wall sections are made can however render it difficult to achieve a really watertight junction.

Presently sectional panel tanks are made usually in steel using flanged joints with a sealant and requiring many bolts. They are expensive to manufacture and install and suffer from several disadvantages namely, they are prone to leakage at the joint, they suffer from corrosion even when coated with glass, epoxy, etc. due to damage and wear, and have a limited life span.

Some attempts have been made to overcome these problems by making the panels in glassfibre reinforced polyester

(GRP) but the jointing system used has generally been a direct copy of the steel panel system, i.e. bolted joints.

This again is expensive and unsatisfactory and does not use the GRP material to best advantage. According to the present invention there is provided a connecting structure of two sections of a wall of a member wherein integral portions at the ends of each of the two sections are positioned adjacent one another and together define the wedge portion of a dovetail joint, and a locking rib which defines the groove portion of the dovetail joint is positioned over that wedge portion to lock the two sections together, the end portions of the sections and the

wedge portion being located in a recess or within the curve of the inner wall of the structure so as to define a relatively smooth continuation of the walls of the sections across the connecting structure. The dovetail joint, when the parts are connected together, creates a very secure connection and provides the possibility that the jointed areas between the parts of the joint can be filled with a sealing material. Ideally this sealing material will be situated in the region between the facing end portions of the sections. A compression member can readily be provided in that region. Additionally or alternatively sealing material may be situated in the space between the abutting walls of the wedge portion and the locking rib of the dovetail joint. It is also possible for sealing material to be formed over the joint areas of the dovetail joint.

Such an arrangement provides a quick, efficient and relatively inexpensive method of joining GRP panels whilst using the material to optimum design efficiency, but it could of course be used with any type of material from which wall sections are to be formed.

A single piece locking rib can be slid or snapped over the wedge portion of the dovetail joint. Alternatively the locking rib might be formed in two halves with temporary or permanent securing means holding them together. A further preferred possibility is for the end portions to be held in tight relationship within the locking rib by a locking wedge driven between the two portions after the locking rib is

located over the end portions.

The invention may be performed in various ways and preferred embodiments thereof will now be described with reference to the accompanying drawings, in which: Figures 1 to 5 are sections through five types of connecting structures of this invention, and

Figures 6 and 7 are sections through a further type of connecting structure of the invention as shown in two stages of construction. The basic form of connecting structure shown in Figure 1 is used to interconnect two sections 1 and 2 of a wall. Respective enlargements 3 and 4 are created which between them define a wedge portion 5 of a dovetail joint. Comple¬ mentary nesting formations 6 help to locate the two parts 3 and 4 together. A locking rib 7 is slid over the wedge portion 5 so as to hold the two parts 3 and 4 together. This locking rib fits closely against the adjacent wall surfaces of the parts 3 and 4 of the wall sections 1 and 2 and in turn helps to define a smooth wall surface 8 which is contiguous with the walls 1 and 2, the connecting structure effectively being situated within a recessed portion of the inner wall. A sealant material will be introduced into the spaces of the connecting structure, such as in the regions 9. The sealant can be a mastic or resin introduced into the joint during assembly or injected after assembly.

Once a structure has been connected together greater security and further protection against leakage can be acheived by coating the outer surface of the connecting

structure with a sealing layer 10 (as shown in Figure 2) . This could be a GRP overlay, particularly if the wall sections 1 and 2 ( and the locking rib 7) are themselves constructed from GRP. In the modified arrangement shown in Figure 3 the joint between the abutting portions 3 and 4 defines a recess for receipt of an compression sealing strip 11 of circular cross-section of solid or foamed rubber. Otherwise the structure is the same. Figure 4 shows how the locking rib 7 may be formed in two halves 7A and 7B which each incorporate a projecting flange 12. The flanges 12 are fixed together by securing bolts 13. This enables the locking rib to be located in position on to the wedge portion 5 relatively easily and indeed allows the connecting structure to be disassembled if required by removing the bolts 13.

In the modified design of Figure 5 the wall sections 1 and 2 are curved and the connecting structure comprising the enlargements 3 and 4 and the wedge portion 5 are located within the inner curve of the wall of the member so that a relatively smooth inner surface is achieved. The curvature of the outer face of the member is maintained in this design so that a smooth wound sealing overlay can be applied to the outer wall surface. The structure illustrated in Figures 6 and 7 is so formed that the ends of the enlargements 3 and 4 can be butted together to define a wedge portion of a width which enables the locking rib 7 to be placed over the wedge from

the side as shown in Figure 6. The enlargements 3 and 4 are then forced apart so that they enter the grooves in the rib 7 to form a tight joint, and are locked in place by a locking piece 14 which can be held there by a suitable mastic.

The advantage of this method is that the joint can be made in restricted spaces since the rib 7 is entered horizontally instead of being "slid ¹ from either end, which will also facilitate the easy dismantling of the joint should this be necessary.

This form of connecting system enables the construction of large tanks or the like from smaller or more compact initial components. Thus large tanks can be formed from circumferential sections which are linked together at vertical joints. The sections could be ready-shaped (for example curved) or flexible so that they can be bent into the required shape. Indeed a flexible cylindrical section could be closed into a tight spiral (held by strapping) for transportation, then opened out on site to full size for fixing in position. Such tanks can also be built up vertically in sections with horizontal joints.