Rational Analysis of Impervious Steel Sheet Pile Walls

Until recently no consistent methodology has been available for the assessment of the seepage resistance of steel sheet pile (SSP) walls. The lack of such a methodology can conceivably lead to uneconomic design, especially in cases where the seepage resiatance is substantially greater than specific design requires.

ProfilARBED, the world’s leading producer of sheet piles, has carried out an exhaustive research projects in collaboration with Delft Geotechnics. The aim of the project was to determine the rate of seepage through SSP walls for various joint filler materials, as well as for empty and welded joints.

Two key areas of research were addressed:

  • Setting up a consistent theoty to describe the leakage behaviour through individual joints.
  • In situ experimentation on SSP walls.

In this paper the research results are deployed to enable the practical designer to make a rational assessment of the rate of seepage for a specific case. A range of possibilities is discussed: highly permeability and completely impervious welded joints.

The cost involved in each case can be balanced against the seepage resistance requirements and the most appropriate solution will present itself on the basis of the analysis.

(This article comes from J Steel Australasia editor released)

The imperviousness of steel sheet pile walls

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:

  1. 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.
  2. 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.
  3. 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)

Repair and corrosion protection of steel sheet pile walls

In sea-water, especially in the variable waterline zone, sheet piles are exposed to major corrosive damages. Precedents are known, when over the years of operations, sheet pile walls were found with multiple holes through the whole section of the element, caused by corrosion.

Repair works in the zone of variable water level are performed in air-dry environment, using patented special underwater equipment – hermetic chamber. Works are performed keeping the structures in operational conditions. The repair technology depends on the degree of damages.

If the corrosive wear is less than 30% of the initial metal thickness, it will be sufficient to apply an anticorrosive coating on the steel surface. From the hermetic chamber the steel surface is blast cleaned and then a primer and a protective coatings are applied. Used materials are thoroughly selected, have the required certificates and have passed through long-term testing.

In presence of significant sheet piles damages and depending on the environmental conditions and Client request, a thin reinforced concrete wall could be built directly on the sheet piling surface or additional metallic elements could be added to the structure to increase the section. In underwater zone cathodic protection is applied.

(This article comes from GT Corporation editor released)