Patent Publication Number: US-6664509-B2

Title: Method for securing sheet piles

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for securing two sheet piles interlocked by means of sheet pile interlocks. 
     BACKGROUND OF THE INVENTION 
     The use of sheet piles for constructing retaining walls is well known. The sheet piles used in such walls have sheet pile interlocks along their longitudinal edges, which can be interlocked so as to maintain the longitudinal edges of adjacent sheet piles interconnected with each other. Current sheet pile interlocks of the double-hook interlock type (type 1 according to EN10248 norm), as e.g. LARSSEN type sheet pile interlocks, are hook shaped elements with an internal interlock chamber. A sheet pile wall is formed by driving a first sheet pile into the ground, introducing the bottom end of the trailing sheet pile interlock of a second sheet pile with the top end of the leading sheet pile interlock of the first sheet pile, driving the second sheet pile into the ground, and then repeating the process to insert third, fourth etc sheet piles into the wall. 
     It is often necessary to secure two interconnected sheet piles against longitudinal shifting relative to one another for example at a harbour, canal, or building-excavation construction site. This is particularly the case for sheet pile walls constructed with U-shaped sheet piles having the sheet pile interlocks aligned along the neutral plane of the sheet pile wall. 
     It is known to secure two interconnected sheet piles by bonding the interlocked sheet pile interlocks with a curing mass, e.g. an adhesive or cement. However, the shearing strength of an adhesive bond is limited. Furthermore, this bond is often not reliable because of ground material and/or water penetrating the interlock chamber. 
     According to EP-0 898 021, two interconnected sheet piles can be secured by pressing impressions on the outer connection joint between the two interlocked sheet pile interlocks. The pressing of these impressions are effected by means of a punch adapted to be operated by a hydraulic percussion hammer. The securing of interconnected sheet piles by pressing impressions is e.g. used for combining sheet piles into double or triple sheets, also known as driving units, prior to driving them into the ground. Of course, such an impression can only be made on the sheet pile interlocks which are accessible from at least one side. It follows that driving sheets cannot be secured in this way once they are driven into the ground. After excavation on one side of the sheet pile wall the sheet pile interlocks are again accessible. It is however during excavation that the unsecured sheet pile interlocks tend to shift and the sheet pile wall is deformed. The securing of sheet piles after excavation is hence of little importance. It follows that there is a need for a method for securing sheet piles after they have been driven into the ground, but before excavation takes place. Furthermore, in order to render the interlocked sheet pile interlocks waterproof, a welding seam can be made on the outer connection joint between two interlocked sheet pile interlocks. This welding seam can of course only be made on the interlocks of two adjacent sheet piles which are accessible, i.e. before they are driven into the ground or after excavation. The interlocked sheet pile interlocks between two driving units cannot be rendered waterproof in this way. Even if the welding seam is made after excavation, the welding seam can only be made on the top half, often only the top third of the sheet pile interlocks, as the remaining part of the sheet pile wall is still not accessible. The remaining part of the sheet pile wall can hence not be rendered waterproof. 
     SUMMARY OF THE INVENTION 
     The technical problem underlying the present invention is to provide a reliable method for firmly securing sheet pile interlocks against longitudinal shifting relative to one another, even if the sheet pile interlocks are not accessible. This problem is solved by a method as claimed. 
     GENERAL DESCRIPTION OF THE INVENTION 
     In accordance with the method of the present invention a welding electrode is axially inserted into an axial groove between the sheet pile interlocks, which are then welded together in the groove. The sheet pile interlocks need not be accessible from the outside in order to make a welding. It follows that sheet piles or driving units can now also be secured after having been driven into the ground. This is of particular advantage in case excavation is to take place as the sheet piles or driving units can be secured beforehand. The sheet pile interlocks can hence not shift and the sheet pile wall cannot deform during the excavation process. 
     It will be appreciated that a method in accordance with the invention is particularly advantageous if the interlocked sheet pile interlocks are at least partially located below ground level. The welding electrode can then be axially introduced through the axial groove below ground level and the sheet pile interlocks can be welded together below ground level. The method hence allows firmly securing two sheet piles or driving units, after they are driven into the ground. It will be appreciated that the welding operation allows to provide a bond with a higher shearing strength than a bond achieved by injecting a curing mass, and that the welding operation is far less affected by ground material and/or water penetrating the interlock chamber than a curing operation. Furthermore, a continuous welding seam can be made along the whole length of the axial groove, whereby the sheet pile wall can be rendered waterproof along the whole of its height. 
     The welding electrode is connected to a conductor, which is preferably a semi-rigid conductor, e.g. an electrically insulated copper conductor, so that it can be used to push the welding electrode far down into the axial groove. 
     According to a first embodiment, the welding electrode is axially introduced into the axial groove up to a first depth, where a first welding is made. The welding electrode is then drawn back to a second depth; where a second welding is made. This discontinuous welding allows for time saving securing operation. 
     According to a second embodiment, the welding electrode is axially introduced into the axial groove up to a first depth, where the welding electrode is consumed by making a welding. The conductor is then withdrawn from the groove and connected to a new welding electrode, which is then axially introduced into the axial groove up to a second depth, where it is consumed by making another welding. The second depth can for example correspond to the end of the first welding, so that a continuous welding seam is obtained. This continuous welding provides a sealed connection between two sheet piles. 
     It is advantageous to use a fluxed electrode, as such an electrode facilitates arc ignition and stability during welding. It also allows welding to take place under water and it can be easily used on site with conventional welding generators. The fluxed electrode also has the particular advantage that it allows for a discontinuous welding, i.e. local weldings can be made at different depths in the axial groove. 
     A straightener can be used for introducing the semi-rigid conductor with the welding electrode into the groove. It straightens the semi-rigid conductor and pushes it down the axial groove. It can further be used to pull the conductor back out of the axial groove. 
     When constructing a sheet pile wall, the first sheet pile is first driven into the ground. The leading sheet pile interlock of the first sheet pile has an interlock chamber protected from ground material. An interlock head of a trailing sheet pile interlock of a second sheet pile is engaged in the interlock chamber when the second sheet pile is driven into the ground. The interlock head preferably has an axial groove facing a wall of the interlock chamber for receiving the welding electrode. 
     The interlock chamber can have a substantially right angle corner. The interlock head engaging the interlock chamber preferably has a cross-section that is complementary to the cross-section of the interlock chamber, and the axial groove is located at the thickest part of the interlock head and facing the right angle corner of the interlock chamber. By providing the axial groove at the thickest part of the interlock head, the stability of the sheet pile interlock is maintained, as the sheet pile maintains a minimum thickness over the whole of its section. It will however be appreciated that the axial groove can also be located at any other part of the interlock head. It will also be appreciated that instead of being associated to the trailing sheet pile interlock, the axial groove can alternatively be associated to the leading sheet pile interlock. It is also possible to have two axial grooves between the sheet pile interlocks, one associated to the trailing sheet pile interlock, and the other associated to the leading sheet pile interlock. It is even conceivable to have two smaller axial grooves, one associated to each sheet pile interlock, located such that, when the sheet pile interlocks are interlocked, an axial groove, which is big enough to receive the electrode, is formed. 
     The interlock chamber can further comprise a sealant arranged at least along part of its walls for sealing, and hence rendering water proof the connection joint between two sheet piles. 
     In accordance with an embodiment of the present invention an obturating device comprising an inflatable tube is inserted into the interlock chamber of the sheet pile interlock to be protected. Once the obturating device is in place within the interlock chamber, its inflatable tube is inflated, so that the obturating device effectively closes the opening to the interlock chamber. It follows that no ground material can enter the interlock chamber while the sheet pile is being driven into the ground. Once the sheet pile is in place, the inflatable tube is again deflated, and the obturating device can be easily withdrawn from the interlock chamber. In short, while the inflatable tube is inflated, the obturating device ensures excellent protection for the interlock chamber against ground material, and while the inflatable tube is deflated, the obturating device can be easily inserted into or retracted from the interlock chamber. 
     The obturating device can further comprise a flexible tube with an open front end alongside the inflatable tube which has a closed front end. This flexible tube can then be used for filling the interlock chamber with sand or synthetic foam (as e.g. a PU foam) while the obturating device is withdrawn from the interlock chamber. Especially in case the sheet piles are driven into light or muddy ground material, it is advantageous to fill the interlock chamber with sand or synthetic foam material in order to prevent light or muddy ground material to enter the interlock chamber once the obturating device has been withdrawn. It is not excluded to conceive the flexible tube as a separate piece, but it is preferred to firmly attach it to the inflatable tube and, in particular, to form it in one piece with the inflatable tube. 
     In accordance with a preferred embodiment, inflation of the inflatable tube pushes an obturating block into the longitudinal opening of the interlock chamber. This obturating block closes the longitudinal opening of the interlock chamber. It will be appreciated that the obturating block can be made stronger than the inflatable tube and is hence less likely to be damaged during the driving process. It is preferably a semi-rigid body, because such a semi-rigid body may be more easily introduced in and withdrawn from the interlock chamber. Furthermore, it is preferably a wedge shaped body engaging the longitudinal opening of the interlock chamber. The wedge shape ensures that, when the inflatable tube is inflated, the obturating block centres itself in the longitudinal opening of the interlock chamber so as to effectively obturate this opening from the inside of the interlock chamber. It is not excluded to conceive the obturating block as a separate piece, but it is preferred to firmly attach it to the inflatable tube and, in particular, to form it in one piece with the inflatable tube. The fact that the inflatable tube and obturating block are firmly attached together allows for easy manipulation on the building site. 
     In particular, when constructing a sheet pile wall, the obturating device is inserted into the interlock chamber of the leading sheet pile interlock of a first sheet pile. The inflatable tube is inflated, e.g. by means of compressed air, and this first sheet pile is driven into the ground. Once this first sheet pile is in place, the inflatable tube is deflated and the obturating device is withdrawn from the interlock chamber. It will be appreciated that the withdrawn obturating device leaves an interlock chamber in the leading sheet pile interlock that is perfectly clean, i.e. free from any ground material. The obturating device is then inserted into the interlock chamber of the leading sheet pile interlock of a second sheet pile and the inflatable tube is inflated. The bottom end of the trailing sheet pile interlock of the second sheet pile is now interconnected with the top end of the leading sheet pile interlock of the first sheet pile. As the second sheet pile is driven into the ground, its trailing sheet pile interlock slides down through the clean interlock chamber of the leading sheet pile interlock of the first sheet pile. Once the sheet pile is in place, the inflatable tube is again deflated and the obturating device withdrawn. This process is repeated for the third, fourth, etc sheet piles. Consequently, the trailing sheet pile interlock of a sheet pile is always interconnected with a clean leading sheet pile interlock of the preceding sheet pile. 
     Before driving a sheet pile into the ground, it is recommended to insert a front end obturator in the bottom end of the interlock chamber of a leading sheet pile interlock. The front end obturator displaces ground material from under the axial opening of the interlock chamber and prevents ground material from axially entering the interlock chamber. It will be appreciated that the front end obturator can e.g. be a simple bolt. However, in order to be most effective, the front end obturator advantageously has a conical head. The front end obturator is preferably just inserted into the interlock chamber, rather than fixed to the sheet pile, so that the front end obturator can simply be pushed out of the interlock chamber of the leading sheet pile interlock by the trailing sheet pile interlock of the subsequent sheet pile. This is of particular interest in case a sheet pile needs to be driven deeper into the ground than the preceding one. 
     A short cleaning piece is preferably engaged with the leading sheet pile interlock of a first sheet pile before interconnecting this interlock with the trailing sheet pile interlock of a second sheet pile. When the second sheet pile is driven into the ground, its trailing sheet pile interlock pushes the cleaning piece along the leading sheet pile interlock of the first sheet pile. It will be appreciated that the cleaning piece can e.g. be a piece of an interlocking sheet pile interlock, which removes any ground material from the inner walls of the leading sheet pile interlock and preferably wraps the outer walls of the leading sheet pile interlock, so that it also effectively removes any ground material from the outer walls of the leading sheet pile interlock. It follows that all exterior and interior contact surfaces of the leading sheet pile interlock are free of ground material when coming into contact with the corresponding contact surfaces of the trailing sheet pile interlock of the subsequent sheet pile. Usage of the cleaning piece is particularly of advantage if the interlock chamber of the leading sheet pile interlock of the first sheet pile has been filled with sand as the obturating device was withdrawn from the interlock chamber. 
     It will be appreciated that alternative protection means for protecting the interlock chamber from ground material can be considered. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG.  1 : is a perspective view of a sheet pile wall; 
     FIG.  2 : is a section through a trailing sheet pile interlock; 
     FIG. 3 is a section through a trailing sheet pile interlock interlocked with a leading sheet pile interlock; 
     FIG. 4 is a perspective view of three sheet piles horizontally placed on the ground; 
     FIG. 5 is a section through a deflated obturating device inside a sheet pile interlock; 
     FIG. 6 is a section through an inflated obturating device inside a sheet pile interlock; 
     FIG. 7 is a section through an inflated obturating device with flexible tube inside a sheet pile interlock; 
     FIG. 8 is a perspective view of a front end obturator; and 
     FIG. 9 is a schematic underneath view of the front end obturator of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 shows a sheet pile wall  10  in place in the ground. The sheet pile wall  10  is constructed with interlocked sheet piles  12 , which each have a trailing  14  and a leading sheet pile interlock  16 . 
     FIGS. 2 and 3 show a section through the trailing sheet pile interlock  14  on its own, and interlocked with a leading sheet pile interlock  16  of an adjacent sheet pile respectively. Each hook-shaped sheet pile interlock  14 ,  16  comprises an interlock chamber  18  and an interlock head  20 . The interlock head  20  of one sheet pile engages the interlock chamber  18  of the other sheet pile, the interlock chamber  18  and the interlock head  20  having complementary cross-sections. The thickest corner of the interlock head  20  of the trailing sheet pile interlock  14  comprises an axial groove  22 . Furthermore, the interlock chamber  18  of the trailing sheet pile interlock  14  comprises a sealant  24  arranged at least along part of its walls. The axial groove  22  preferably has a diameter between 5 and 15 mm, ideally 8 mm, so as to receive a welding electrode. 
     Referring back to FIG. 1, reference number  26  designates two interlocked sheet pile interlocks  14 ,  16 . A straightener  31  is used to introduce a semi-rigid copper conductor  28 , having a fluxed welding electrode  30  at its end, into the axial groove  22  arranged in the trailing sheet pile interlock  14 . Conventional welding apparatus  32  can be used for operating the welding electrode  30 . The welding electrode  30  is introduced into the axial groove  22  up to a first depth, where a first welding  33  is made. Once this first welding  33  is made, the welding electrode  30  is drawn back to a second depth, where a second welding  34  is then made. It will be appreciated that third, fourth, etc weldings can be made in the axial groove in the same way. Once an electrode  30  is consumed, the conductor  28  can be withdrawn from the axial groove  22  by means of the straightener  31 . A new electrode  30  is attached to the conductor  28 , which is then reintroduced into the axial groove  22  for making a further welding. If these weldings are created so close to each other that they touch, a continuous welding seam can be created in the axial groove  22 . 
     FIG. 4 shows some sheet piles  12  horizontally placed on the ground at the work site. An obturating device  36  is inserted in the leading sheet pile interlock  16  and inflated by compressed air means  38 . 
     The obturating device  36  is described in more detail by referring to FIGS. 5 and 6, in which the obturating device  36  is arranged. The obturating device  36  comprises an inflatable tube  38  and a wedge shaped obturating block  40 . FIGS. 5 and 6 show the inflatable tube  38  in its deflated and inflated state respectively. When the inflatable tube  38  is inflated, the obturating block  40  is firmly pressed in the longitudinal opening, which gives access to the interlock chamber  18 . In other words, it blocks off this longitudinal opening of the interlock chamber  18 , thereby preventing ground material from entering into the interlock chamber  18  through this opening. 
     FIG. 7 shows an obturating device  36  having a flexible tube  41  running alongside the inflatable tube  38 . The flexible tube  41  has an open front end and is used to insert sand into the interlock chamber  18  when the obturating device  36  is being removed from the interlock chamber  18 . The longitudinal opening of the interlock chamber  18  is thereby blocked off, whence preventing ground material from entering into the interlock chamber  18  through this opening. 
     It will be noted that the preferred obturating device  36  shown in FIGS. 5 and 6 and in FIG. 7 is a semi-rigid rubber piece. It may include synthetic or metallic reinforcement fibres or fabrics, which increase its tensile strength. Its surfaces coming into contact with the walls of the sheet pile interlock may receive a friction reducing coating. 
     In order to protect the interlock chamber  18  from soil being pushed in axially from below as the sheet pile  12  is being driven, a front end obturator  42  is inserted in the bottom end of the interlock chamber  18 . This front end obturator  42 , which is shown in FIGS. 8 and 9, has a cylindrical body  44  and a conical head  46 . 
     Before the second sheet pile is interlocked with the first sheet pile and driven into the ground, a short cleaning piece  48  is engaged in the leading sheet pile interlock  16  of the first sheet pile for removing any ground material from the inner walls of the leading sheet pile interlock  16 . The short cleaning piece  48  shown in FIG. 1 wraps the outer walls of the leading sheet pile interlock  16  and has an acute front end. Consequently, when it is pushed down along the leading sheet pile interlock  16  by the trailing sheet pile interlock  14  of the second sheet pile, it effectively removes any ground material from the outer walls of the leading sheet pile interlock  16 .