Journal of Natural Disaster Science

A STUDY OF THE MECHANISM OF LOESS LANDSLIDES INDUCED BY EARTHQUAKES

Dexuan ZHANG
Researcher, Kyushu Laboratory, Geo-Research Institute Osaka (formerly at the Disaster Prevention Research Institute, Kyoto University)

(Received 2 July, 1996 and in revised from 17 December, 1996)

Abstract

Many large-scale landslides induced by earthquakes have been reported in loess soils. They often cause catastrophes because they travel long distances at high velocity. It is necessary to clarify the mechanism of these landslides in order to establish hazard mitigation measures. The initiation mechanism and mobility of loess soil collected from a landslide induced by the Haiyuan Earthquake (China, 1920) were examined with a ring shear apparatus.

Cyclic ring shear tests were made on saturated specimens in the undrained condition. When cyclic shear stress was applied to a loose loess specimen, negative dilatancy and the gradual built-up of pore pressure were observed, after which failure of the soil structure occurred and large pore pressure was generated.

To investigate the mechanism that produces the high mobility of loess landslides, ring shear tests were conducted on loess specimens with large shear displacement of up to several meters under the undrained condition. The specimens reached the steady state, the shear resistance, pore pressure, and volume remaining constant, with only shear displacement being increased. The apparent friction angle in the steady state was independent of the initial overconsolidation ratio of the specimen but greatly affected by the degree of saturation.

Key words

loess, earthquakes, landslides, ring shear tests, apparent friction angle