13.Sheet pile reinforcement work on pile foundations during ground liquefaction

  • A reinforcement technique has been developed using the addition of steel sheet piles with closed sections at the bottom to existing pile foundations during ground liquefaction.
  • Confirmation was obtained that this new technique can reduce the working load on existing pile foundations by 30%, and a guide to use of the technique was compiled.
  • This reinforcement technique costs approximately 20% less to apply than existing methods.

When liquefaction occurs during earthquakes, the ground suddenly loses its rigidity and hardness, leading to extensive pile foundation damage (Fig. 1).
Existing countermeasures to protect pile foundations from ground liquefaction, such as additional pile systems and soil improvement methods involve a major increase in the basic dimensions of the structure, which is difficult to apply when limited space is available.
Work was therefore undertaken to find a new method which would not require a great amount of space, and which was practical and economical to implement. As such a sheet pile reinforcement method was developed using steel sheet reinforcement which improves both the supporting force and rigidity of the structure (Fig. 2).
After clarifying the reinforcement mechanisms of steel sheet piles during shaking table tests on models using the new technique, confirmation was obtained that the developed method reduced shearing forces on the pile head by approximately 30% and axial force by approximately 20% (Fig. 3).
A manual for the technique was then compiled using insights gained from tests. Test designs produced following the manual showed that the cost of reinforcement work could be reduced by about 20% compared to existing methods.

Fig. 1 Damage to pile foundations from ground liquefaction
Fig. 2 Sheet pile reinforcement method
Fig. 3 Large shaking table tests confirmed the effectiveness of reinforcement work during ground liquefaction