Field investigation and model tests on differential settlement of houses due to liquefaction in the Niigata-ken Chuetsu-Oki earthquake of 2007

摘要

A massive earthquake struck the Niigata Chuetsu-Oki region of Japan on July 16th, 2007, claiming 11 lives and damaging about 6000 houses. The earthquake had a magnitude of 6.8, with data from an accelerograph managed by a nationwide strong-motion observation network known as Kyoshin Net (K-net) showing a maximum value of 668 gal (NS). In the Matsunami district of Kashiwazaki city (located on land filled and developed as a residential area from around 1970 onward) about 3 km northeast of Kashiwazaki Railway Station, many houses were damaged due to liquefaction. A field investigation, including a boring survey, surface wave exploration and measurement of differential settlement of houses knocked aslant by soil liquefaction, was conducted to determine the relationship between the extent of damage to houses and the area's geological structure. It was found that most houses severely damaged due to liquefaction were located around the boundary between sand dunes and the local river delta. Additionally, the relationships linking sloping geological structure, the thickness of the liquefaction layer and total/ differential settlement of houses were clarified from the results of shaking table model tests conducted in this study. Test results showed that it is important to consider multidimensional influences caused by sloping geological structure in the estimation method of liquefaction potential in order to predict and assess degree of damage to houses due to liquefaction.