DAMAGE TO SEWER PIPES DURING THE 1993 KUSHIR0-0KI AND THE 1994 HOKKAIDO-TOH0-0KI EARTHQUAKES

JUNICHI KOSEKl, OSAMU MATSUO, TETSUYA SASAKl, KAZUO SAITO and MASAYOSHI YAMASHITA

ABSTRACT Damage to sewer pipes in Kushiro City caused by the January 15, 1993 Kushiro-Oki and the October 4, 19! Hokkaido-Toho-Oki earthquakes is reported and analyzed. Based on the results of a damage survey for restoration work of the pipes and on those of a boring survey conducted near both the damaged and undamaged sites, analyses are performed on the condition of the backfill and the original soil layers surrounding the pipes. In the wetland ar flood-plain region, liquefaction of the backfill soil was considered to be the major cause of the damage, while exitence of a peat layer with low permeability and/or a sandy layer that is liquefiable in the original soil was consider, to affect the extent of the damage. In the terrace region, instability of the original slope was also considered to ha' caused the damage.

Key words: earthquake damage, (Hokkaido-Toho-Oki earthquake), (Kushiro-Oki earthquake), liquefaction, (peal (sewer pipe) (IGC: E8/H8)