Water Film Mechanism In Seismically Induced Land And Submarine Slide

Kokusho, Takeji (Chuo University) | Kojima, Tetsuro (Chuo University)


ABSTRACT: Site investigation in sandy soil sites demonstrates extensive soil layering in actual sand deposits. One-dimensional liquefaction tests are carried out for several types of layered sand models, which indicates that water films develops beneath impermeable sublayers in layered sand. The mechanism for the water film generation is clarified. Thus the significant effect of water film on land and submarine slides due to seismic liquefaction is demonstrated. INTRODUCTION In past earthquakes, landslides in alluvial sand deposits or lateral flow took place in coastal or river-side areas as in Alaska and Niigata. Submarine slides have also been triggered seismically worldwide. Nom1ally the slope of the sliding surface in those slides is not steep, being much gentler than the intemal friction angle ofthe soil. In land areas, liquefied sand deposits often experienced lateral spread or flow not only during but also after earthquake shaking. The magnitude of flow distance sometimes reached more than several meters even in a very gentle slope ofless than a few percent. In Niigata city, a famous lateral flow occurred in the Meikun High School along the Shinano River where a rather large area of250m by 150m moved towards the river a maximum of 7 meters (Kawakami and Asada 1966). Pictures taken by a high-school student demonstrated that mud water started to come out violently and fissures gradually expanded after the end of shaking. Soil profiles in this area consisted not only of sand but also of sublayers ofsilts or clays (Kishida 1966). In Greece, on the occasion of the 1995 Aegion earthquake, a similar post-earthquake submarine slide involving coastal land with the slope of 12% occurred. The soil profile at the failure site was characterized by a continuous interchange between silty sand and clay layers (Bouckovalas et al. 1999).

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