Abstract
Earthquakes constantly hit Japan and liquefaction always lead serious damage to structures. Therefore, countermeasures against the liquefaction are urgently needed to prevent the small structures such as personal houses and underground structures from the damage. Unfortunately, however, countermeasures for small structures are not so intensively studied compared with the massive structures in civil engineering, especially there are few countermeasures for existing structure. In this paper, particular attention is paid to the enhancement effect of the dissipation of excess pore water pressure using drainage diaphragm wall with high permeability and large restraining effect of soft soil. The drainage diaphragm wall is made of the soil materials having high internal frictional angle and permeability, whose countermeasure against liquefaction is investigated by 1g shaking table test and finite element analyses. The results obtained in this research can be summarized as follows: (1) by using the drainage diaphragm wall around structure, it is possible to suppress the subsidence and inclination of the structure; (2) Due to the drainage diaphragm wall, the defamations of the wall and the soil near the wall are suppressed significantly due to the quick dissipation of the excess pore water pressure and the restraining effect of the diaphragm wall; (3) improvement effect by the drainage diaphragm wall is higher than those by column-shaped improvement wall, and so does the deformation; (4) improvement effect of the diaphragm wall depends not only on the wall depth, the rigidity of the wall but also on the permeability of the wall ; (5) the wall made of drainage material does not collapse even in the completely liquefied ground due to the strong recovery ability of the effective stress near the wall and the resistance against the horizontal osmotic pressure toward the wall.
