Sections and interlocks
The following figure shows a Steel sheet pile wall made from LARSSEN U-sections and a wall made from Z-sections with off-centre interlocks.
Steel sheet pile walls made from U-sections (left) and Z-sections (right) plus details of their interlocks
Straight-websections have a high interlock strength for a ccommodating tensile forces. Applications include, for example, cellular cofferdams.
Steel sheet pile wall made from straight-web sections plus detail of interlock
The driving work calls for a certain amount of play in the interlocks and so these joints be- tween the sheet piles are not watertight. Owing to their convoluted form, however, water seep- ing through the joint does have to negotiate a relatively long path. Ultra-fine particles in the soil accumulate in the interlocks over time, which results in a “self-sealing” effect, which is augmented by corrosion. According to EAU 2004 section 126.96.36.199 (R 117), in walls standing in water this natural sealing process can be assisted by installing environmentally compatible synthetic seals. If a sheet pile wall is required to be especially watertight, the interlocks can be filled with a permanently plastic compound or fitted with a preformed polyurethane interlock seal. The materials used exhibit high ageing and weathering resistance plus good resistance to water, seawater and, if necessary, acids and alkalis. Polyurethane interlock seals are factoryfitted to the interlocks of multiple piles and the joints threaded on site are sealed with further preformed polyurethane seals.
Interlocks can be sealed with bituminous materials to achieve a watertight joint. Such mater ials can be applied in the works or on site. The watertightness is achieved according to the displacement principle: excess sealant is forced out of the interlock when threading the next pile.
Driving the sheet piles with an impact hammer places less load on the seals because the move ment takes place in one direction only. The load on polyurethane seals in piles driven by vibra tion is greater because of the friction and the associated temperature rise. The permeability of a sheet pile wall joint can be estimated using DIN EN 12063 appendix E.
Welding the interlocks achieves a completely watertight sheet pile wall. In the case of mul tiple piles, the interlocks are factorywelded, which means that only the remaining interlocks between groups of sheet piles have to be welded on site. Such joints must be cleaned and dried before welding.
Sheet pile walls can also be sealed by hammering in wooden wedges, which then swell when in water. Rubber or plastic cords together with a caulking compound with swelling and setting properties can also be used.
When a sheet pile no longer interlocks properly with its neighbour, this is known as declutching. Interlock damage cannot be ruled out completely even with careful driving. EAU 2004 section 188.8.131.52 (R 105) recommends checking for declutching to increase the reliability of sheet pile walls. Visual inspections can be carried out for the part of the sheet pile wall still visible after driving, but signal transmitters must be used for those parts of the wall that are buried or below the waterline, and especially in those cases where a high watertightness is critical, e.g. enclo sures to landfill or contaminated land.
The following figure shows various combination sheet steel pile walls made from single or double PSp pile sections with intermediate panels.
In such structures the sheet pile walls transfer the loads due to earth and water pressure to the piles, and this enables heavily loaded retaining walls, e.g. quay walls, to be built.
Examples of combination steel sheet pile walls