A STUDY ON INFLUENCE OF PHYSICAL AND MECHANICAL PROPERTIES ON CHANGE OF SEDIMENTARY STRUCTURE IN SAND LAYER CAUSED BY LIQUEFACTION

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Change in sedimentary structure and/or disturbance caused by liquefaction was investigated in the test pits of liquefied sand or gravel layrs, occured during the 1993 Hokkaido-Nansei-Oki (Southwest off Hokkaido) earthquake and 1995 Hyogo-Ken-Nanbu (South Hyogo prefecture) earthquake.(1) Liquefied sand dikes caused by Hokkaido-Nansei-Oki earthquake found in sandy silt layr of 1.5-2.0 m in thickness, were intruded from the underlying sand and gravel layr, including about 50% gravel-fraction.Lower part of the sand dikes is composed mainly of gravel, and flat ones tend to be turned nearly vertically. In the mid part of sand dikes, the amount of gravel decreasing, and in the upper part sand-sized fraction dominated. The liquefied layr is fluvial sand and gravel in the latest Holocene.(2) The liquefaction site distribution map was drew up after the Hyogo-Ken-Nanbu earthquake from Osaka bay area to Awaji Island and Naruto city.In the reclaimed land, liquefied layrs are the filled materials of weathered granite soil in Kobe. Matrix part among coarse granite blocks in the liquefied layr might be liquefied during the earthquake. Grain-size of liquefied materials in the sand dikes changes from coarse-grained and not well-sorted in the lower part, and fine-grained and well-sorted in the upper.(3) Result of cyclic triaxial compression tests, the change of strength ratio with excess pore water pressure during the cyclic loading was caused very little by the difference of initial structure of specimens taken from sand sample, but the volume change after liquefaction had influence on their specimens.