For practical design purposes it is advisable to assess the degress of the required seepage resistance in order that a cost effective solution may be selected. Depending on the requirements, there are basically three possible solutions:
- In applications such as temporary retaining walls a moderate rate of seepage is often tolerable. An SSP wall made of piles with the famous Larssen interlock provides sufficient seepage resistance.
- In applications where a medium to high seepage resistance is required – such as cut-off walls for contaminated sites, retaining structures for bridge abutments and tunnels – double piles with a workshop welded intermediate joint should be used. The workshop weld is as impervious as the steel itself. The free interlock of the double pile needs to be threaded on site with a filler material. The lower end of the resistance range is adequately served by the various bituminous fillers, but it is noted that their use is limited to water pressures less than 100 kPa.For high resistance requirements, as well as water pressures up to 200 kPa, a waterswelling product should be used as a filler material. A wall designed in this way is between 100 to 1000 times more impervious than the simple sheet pile wall with Larssen interlocks.
- A 100% watertightness may be obtained by welding every joint.
Double piles with a workshop weld are used for the construction of the wall. The interlock that needs to be threaded on the job has to be welded on site after excavation.
If a comparison needs to be made between the rate of seepage of an SSP walls and a slurry wall, the table below may be used. For a given SSP walls, the hydraulic conductivity which a slurry wall of thickness D has to provide in order to obtain the same upper limit on the discharge – at the same water pressure – as the SSP wall, can be determined.
(This article comes from J Steel Australasia editor released)