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2.3. DRIVING SHEET PILE WALLS 13
corrosion by more than 20 years. One way of virtually eliminating corrosion below the waterline
is to employ an electrolytic method in the form of a sacrificial anode. Another way of achieving
protection against corrosion is to overdesign the sections, but in this case an economic analysis
must be carried out first.
2.3 Driving sheet pile walls
Sheet pile walls can be threaded into precut trenches, or pressed, impact-driven or vibrated into
position. Threading and pressing do not involve any knocks or shocks, which is a complete
contrast to impact driving and vibration methods. In difficult soils, the driving can be eased by
pre-drilling, water-jetting, pre-blasting or even by replacing the soil.
When driving sheet pile walls, it is possible for the sheet piles to start leaning forwards or
backwards with respect to the direction of driving (Fig. 2.7). Forward lean is caused by friction
in the interlocks and by compaction of the soil while driving the previous sheet pile. The driving
force is transferred to the pile concentrically, but the reaction forces are distributed unevenly
across the sheet pile. Backward lean can occur in dense soils if the previous sheet pile has
loosened the soil. To prevent leaning of sheet piles, they should be held in a guide frame or
trestle. Vertical alignment during driving can be impaired by obstacles in the soil or hard strata
at unfavourable angles.
Backward lean Forward lean
Figure 2.7: Sheet pile sections exhibiting backward lean (left) and forward lean (right)
2.3.1 Threading piles into precut trenches
This method can be used in almost any soil. To do this, a trench must be excavated or holes
drilled in the ground first, which are then filled with a suspension. If necessary, the sheet piles
can be subsequently driven to their full depth.