Permanent Displacement and Deformation of Liquefied Subsoil

Abstract

In 1984 a permanent lateral displacement was detected in a gentle slope in Noshiro City where a substantial liquefaction developed at the time of the 1983 Nihonkai Chubu earthquake (Hamada et al. 1986). Since the displacement was significant, exceeding 4 m at maximum, gas pipelines embedded in the area were broken in such manners as separation at connection and bending at curved portions. Figure 24.1 demonstrates an air photo of Noshiro City where liquefaction and lateral displacement occurred. Higher places in this photograph are sand dunes, including Maeyama. Liquefaction occurred in low places which used to be swamps. Dune sand fell into water and formed liquefaction-prone young loose water-saturated deposits. Liquefaction and lateral displacement occurred in dune hill slopes as well where the gradient was only a few percent and had never been a target of slope instability.