Steel sheet piles are used in general and marine engineering as permanent structures inter alia for retaining walls, basements, underground car parks, pumping stations, bridge abutments and marine structures. These are only examples of such structures.

The side edges of many steel sheet piles are shaped to define longitudinal links for connection to neighbouring piles. These piles include those known as Larssen or"U"piles with Larssen interlocks (Larssen is a Registered Trade Mark of British Steel PLC). For the sake of simplicity, such piles will hereinafter be referred to as U-shaped interlocking piles. The present invention relates particularly to structures produced from U-shaped interlocking piles and connectors for use with these interlocking piles.

A U-shaped interlocking pile comprises a pan defined by a central flange flanked by inclined side walls and each longitudinal link is formed with a longitudinally extending clutch having a locking toe of generally triangular cross-section which stands proud of a lip which extends along each side edge of the pile, the lip lying generally normal to the adjoining pile surface. The space between the toe and the lip defines a recess for receiving a locking toe of an adjoining pile. The lip defines the bottom wall of this recess.

Conventional sheet piling structures are generally connected together by their own interlocks. Such structures have limited strength and efficiency. Where enhanced strength is required, high modulus sheet piling structures are required. High modulus sheet piling structures include those known as"king"or"combined"sheet pile walls. Such sheet pile walls are fabricated from primary elements normally comprising steel tubular piles or "I"-sections, and secondary elements comprising steel sheet piles installed in the spacing between the primary elements and connected thereto by interlocks. An example of a combined sheet pile watt is shown in FR-A- 1557902. In these walls, strength is provided essentially by the primary elements.

Examples of double-walled sheet pile structures are disclosed in GB- PS-1343203. The sheet pile walls of such structures are cold-formed and interconnected by elongate members each of which comprises a web whose ends terminate in flanges which are shaped to define parallel-sided hooks which interlock with longitudinal links of opposed sheet piles. The hooks are formed in the flanges by bending each longitudinal edge of each flange back on itself towards the respective web with the returned flange edge lying generally parallel to the longitudinal axis of the flange itself. The longitudinal edges of each sheet pile are similarly bent back on themselves towards the centre line of the sheet pile body with each returned edge lying generally parallel to this centre line. On assembly, the links formed along each longitudinal edge of each sheet pile are retained within the hooks of the elongate locking members.

Connecting devices for individual Larssen piles and wall-like structures produced by linking individual Larssen piles using connectors are disclosed in GB-PS-1295359 and FR-PS-2671500. These connecting devices are not structural members and have no function other than to link adjoining piles where directional changes and continuity is required. Generally, they include locking toes of triangular of other cross-section which define with wall portions of the connecting devices recesses which receive and engage adjoining locking toes of Larssen piles to be joined.

In one aspect, this invention sets out to provide steel sheet piling structures which exhibit increased strength and stiffness characteristics when compared with conventional structures whilst attaining a saving in material in terms of weight per elevation area.

According to the present invention in one aspect there is provided a sheet pile wall structure having a generally corrugated profile which comprises first and second spaced rows of interlocking steel sheet piles with a plurality of elongate connectors linking interlocks of the piles of one row to interlocks of the piles of the other row to define a substantially corrugated profile, each connector defining a load bearing structural member of the wall structure and is of a length sufficient to span a distance at least equal to the pan depth of each pile with the neutral axis of the wall structure passing through each connector.

By"neutral axis"is meant the axis which passes through the centroid of the wall structure, its orientation being governed by the plane of bending.

The significance of the neutral axis is that during plane bending, the material on one side of the neutral axis is in compression whilst on the other side it is in tension.

Each connecting member may include a web at least one of whose edges is formed with a lip having a wall portion which lies in a plane which subtends an angle of between 70° and 1 10° to the longitudinal axis of the web and a toe which is of generally triangular cross-section and is upstanding from the wall portion and defines with the lip and the web a recess for receiving a locking toe of an interlocking sheet pile.

According to the present invention in a further aspect there is provided a wall structure of generally corrugated profile which comprises a plurality of interlocking steel sheet piles connected by a plurality of load bearing structural elongate connecting members to define the required generally corrugated profile of the wall structure, each connecting member having a central web formed at each of its end with a flange having a wall portion which lies in a plane which subtends an angle of between 70° and 110° to the longitudinal axis of the web and an end portion upstanding from the wall portion of generally triangular cross-section which defines with the flange wall portion and the web a shaped recess, each connecting member being of a length sufficient to span a distance at least equal to the pan depth of each pile with the neutral axis of the wall structure passing through each connecting member.

The wall structure may define a generally curved or straight wall structure with changes in direction or corners as required. The longitudinal links defined by the inwardly turned side edges of the piles may include an inclined face which, on assembly of the sheet piles to the connecting members, lies in contact with a complementary inclined face of the links of the connecting member.

The web of the or each connecting member may be straight or may be shaped to define sections which are inclined away from and towards the longitudinal axis of the member; the inclined wall sections may be joined by a central section which lies generally parallel to the longitudinal axis of the connector.

Sheet pile wall structures in accordance with this invention are similar to conventional sheet pile structures to the extent that the material of the structure follows a waveform or corrugated line caused by the interlocking of the piles and the connecting members, but which because of the increased spacing between the piles has the enhanced strength and efficiency characteristics of high modulus sheet pile structures. The increase spacing is achieved by the elongate connector members.

In the present invention, no interlock is employed along the neutral axis of the sheet piling wall structure, each connector member causing the interlocks to be positioned at a distance from the neutral axis.

Conventionally, the interlocks of a U-shaped sheet pile wall are centred on the neutral axis of the wall.

Structures in accordance with the invention have more efficient spread of weight of material per developed elevation of pile wall compared with conventional systems. Such structures are unique in that they conform with the definition of a high modulus sheet piled wall and are of wave corrugated profile form type with similarity to conventional sheet pile structures.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which:- Figure 1 is a plan view from above of a conventional steel sheet pile structure not in accordance with the invention comprising two linked U- shaped steel piles; Figures 2 and 3 are respectively a plan view from above and a perspective view of a sheet pile structure in accordance with the invention; Figure 4 is a plan view from above to an increased scale of a connector which forms parts of the structure illustrated in Figures 2 and 3; Figures 5 to 8 are graphical illustrations of characteristics of steel sheet pile structures in accordance with the invention; and Figure 9 is a side view of an alternative connector in accordance with the invention.

Linked steel sheet piles of a conventional wall structure having a corrugated profile are illustrated in Figure 1. As will be seen, rows of individual U-shaped piles 1,2 are connected through interlocks 3 which extend along each longitudinal edge of each pile 1,2. Each pile has a pan 4 defined by flanges 5 and inclined side walls 6. The thickness of the side walls 6 is less than the thickness of the flanges 5. Each interlock comprises a lip 7 which lies generally normal to the neighbouring side wall surface 8 of the pile and is formed with a locking toe 9. Each toe 9 is of generally triangular cross-section and is upstanding from the respective lip 7. Each locking toe 9 defines with the respective lip 7 and the adjoining wall surface 8 a recess 11. The modulus of the structure may be enhanced by the use of strengthening plates welded to the pile flanges 5.

The clutches or interlocks of a conventional steel sheet pile wall as illustrated in Figure 1 are close to the neutral axis"N"of the wall which is the axis along which the applied longitudinal shear stresses are at a maximum. These shear stresses can lead to longitudinal displacement of components of sheet pile walls. This phenomenon is known as clutch slippage.

In sheet pile wall structures in accordance with the invention, the individual steel sheet piles are moved away from the neutral axis of the wall structure thus increasing the lever arm and substantially reducing the effect of clutch slippage.

As will be seen from Figures 2 and 3 (in which integers common to Figure 1 have been given the same reference numerals), the individual piles 1,2 are linked by elongate connector members 12. A connector 12 is shown in greater detail in Figure 4. The letters"b"and"d"represent the connector width and depth respectively.

Each member 12 has a web 14 formed at each of its ends with lips 15. Each lip 15 subtends a right angle to the longitudinal axis of the web 14. This angle may be between 70° and 1 10°. Each lip is formed with an toe 16 of generally triangular cross-section. The space defined between the to 16, the lip surface 15 and the web 14 defines a recess 17. The lip surface 15 defines the bottom wall of this recess 17. Each recess of each pile receives a toe 16 of one connecting member; similarly, each recess 17 of each member 12 receives one toe 9 of a pile. The pile walls 1,2 are, thereby, linked together to form the illustrated structure.

The connector members 12 have the effect of increasing the spacing between the rows of piles 1,2 whilst retaining the desired generally corrugated profile of the completed wall structure. One effect of the connectors 12 is to cause the neutral axis to pass through the webs 14 (preferably at or close to their mid-points) rather than the interlocks as for conventional structures as shown in Figure 1. This has the advantage of increasing the lever arm effect and, as described above, achieving a dramatic increase in structural performance and significantly reducing the possibility of clutch slippage. A further effect of the connectors 12 is to provide a significant efficiency gain which approximates to 100% of the strength to weight ratio of the wall structure. Thus, wall structures in accordance with the invention provide a more efficient spread of weight of material per developed elevation of piled wall when compared with conventional wall structures as shown in Figure 1.

As will be seen more clearly from Figure 4, the connector 12 has folds 18 to define a crank-like profile having end-sections 19 which lie generally normal to the lip 7 of each connector and a mid-section 20 which lies generally parallel to the lateral axis of the connector. These folds provide enhanced strength against local web buckling and overall buckling of the connectors, thus enhancing the robustness of the connectors. The enhanced strength is advantageous to resist high impact forces which may be necessary during pile driving, extraction and handling operations. The crank-like profiles of the connectors therefore provide local reinforcement of the connectors to prevent premature failure in local buckling and to limit the overall system section strength to resist bending and other loads imposed on the wall structure.

The piles 1,2 are shown as Larssen-type piles. These will typically be of LX32 or L6 specification. Other U-shaped piles may however be employed.

The connectors will typically have a depth"d"of between 200mm and 1 000mm. Preferred depths are between 400mm and 800mm.

Typically, the width"b"of the connectors will be between 100mm and 500mm, preferred depths being between 150mm and 300mm.

Enhancement of the strength of the individual piles 1,2 and therefore the structure can be achieved by welding plates 21 (see Figure 3) to the outside surfaces of the pile fanges. The plates have the effect of moving the increased extremity of material further away from the neutral axis"N".

A comparison of the modulae, weights and efficiency ratios of a conventional wall structure and a wall structure in accordance with the invention where the rows of piles 1 and 2 are spaced apart by 400mm is shown in the following Table A:- Table A lus Weight Efficiency Ratio"e" (cm3/m) (kg/m2) (cm3kg) Conventional Larssen sheet pile wall 5066 330.2 15.3 (Figure1) 1 1 Sheet pile wall in accordance with 5172 211.9 24.4 this invention (Figures 2 and 3) It will be seen from Table A that the modulus of a wall structure in accordance with the invention is higher than that of a conventional wall structure, that the weight of a wall structure in accordance with the invention is substantially less than that of a conventional structure, and that the efficiency ratio of a structure in accordance with the invention is significantly greater than that for a comparable conventional structure.

The effect of varying the spacing between the piles 1,2 by varying distances"d"and"b" (see Figure 4) between the interconnectors of the connector members 12 is shown in Figures 5 to 8.

Figure 5 shows the way in which the presence of the connector members 12 provides gains in efficiency"e". Figure 5 shows a range of distances"d"between 200mm and 800mm. It will be seen that with no connector 12 (i. e. a conventional structure) an elastic modulus of approximately 3000cm3/m is achieved. With a connector member 12 which spaces the piles 1, 2 apart by 200mm, an elastic modulus above 4000cm3/m is achieved. When this distance is increased to 600mm, an elastic modulus in excess of 7000cm3/m is achieved.

Figure 6 illustrates the effect which connector depth (d) has on structural efficiency as measured by the elastic modulus per unit weight of steel. From this Figure it will be seen that with a conventional structure as shown in Figure 1 (d=o), an efficiency approximating to 15cm3/kg is achieved. This efficiency increases to 20cm3/kg with a connector depth of 200mm and approaches 35cm3/kg with a connector depth of 600mm.

Figure 7 illustrates the effect which varying connector width (dimension"b"in Figure 4) has on the weight of steel per unit width of wall.

It will be seen from this Figure that a connector width of 200mm equates to a weight of around 230kg/m2 and a width"b"of 400mm equates to a weight of around 190kg/m2.

Figure 8 illustrates the effect which varying the connector width (dimension"b") has on bonding strength as measured by the elastic modulus per unit length of wall. Here it will be seen that a connector width"b"of 200mm produces an elastic modulus of 7000cm3/m and a width"b"of 400mm produces an elastic modulus of around 5600cm3/m. Increases in width do, therefore, reduce the elastic modulus of the wall structure. Such reductions may however be acceptable for particular structures and represent potential savings.

Figure 9 illustrates an alternative connector member 12.

It will be appreciated that the foregoing is merely exemplary of pile structures in accordance with the invention and that modifications can readily be made thereto without departing from the scope of the invention as set out in the appended claims.