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2.2. PROPERTIES OF STEEL 11
The reason for this is the exclusion of oxygen. The same corrosion rate can be expected on
sheet pile walls backfilled with sand. However, in this case it must be ensured that the troughs
of the sections are filled completely with sand. A coating with a high protective effect forms in
calcareous water and soils with a calcium carbonate content. Aggressive soils, e.g. humus, or
aggressive groundwater should not be allowed to come into contact with the surface of a sheet
pile wall. Furthermore, corrosion of the sheet piling can be promoted by bacteria in the soil.
Considerably more severe corrosion can be expected in hydraulic structures, which is, however,
not evenly distributed over the full height of the structure. Fig. 2.5, in accordance with EAU
2004 section 8.1.8 (R 35), illustrates the corrosion zones using the North Sea and Baltic Sea
as examples. The greatest weakening of the wall thickness and hence the resistance of the
component takes place in the low water zone. When designing a sheet pile wall, care should be
taken to ensure that the maximum bending moments do not occur at the same level as the main
corrosion zones.
Figure 2.5: Qualitative diagram of the corrosion zones for steel sheet piling using the North
Sea and Baltic Sea as examples (EAU 2004)
EAU 2004 includes diagrams in section 8.1.8.3 (R 35) with which the weakening of the wall
thickness due to corrosion can be calculated (Fig. 2.6). Using these diagrams, sheet pile walls
can be designed for the mean and maximum losses in wall thickness if no wall thickness measurements
are available from neighbouring structures. The areas shaded grey in the diagrams
represent the scatter for structures investigated hitherto. To avoid uneconomic forms of construction,
EAU 2004 recommends using the measurements above the regression curves only
when local experience renders this necessary. For structures located in briny water, i.e. in areas
in which freshwater mixes with seawater, the reduction in wall thickness can be interpolated
from the diagrams for seawater and freshwater.
According to current knowledge, adding a coating to the sheet piles can delay the onset of