Assessment of Dynamic Soil Properties Effects on the Triggering of Slope Instabilities

Abstract eng:
Landslide effects have been numerous on infrastructures and on human lives, and their consequences during an earthquake might be a disaster. The pan Arab highway is a project comprising a network of roads binding the Middle East countries together. In the Lebanese mountains, in the Dahr el Baidar area and over the past twenty years, many slope instabilities and failures caused great damages in the highway projected area and other surrounding roads. This region is much known for its tectonic activity due to the fact that it is limited in the east by the major fault of Yammouneh, extension of the Dead Sea fault that crosses the Middle East, and by many minor faults in the west. Hundreds of boreholes have been executed and many geotechnical studies show that rain as well as presence of poor soil are two main causes of these landslides in the area. The purpose of this research work is to evaluate how a slope will behave under seismic loading, and how the factor of safety and the slip circle will vary during an earthquake, with a special attention given to the role of dynamic soil properties in understanding slope instabilities. First, it has been proven that the amplification period and the amplification value itself at surface depend on the dynamic properties of the soil profile. Indeed, the amplification varies differently with a change in the maximum shear modulus, shear modulus reduction curve and damping curve. In addition, increasing the shear modulus and reducing the damping would lower the amplification values at surface. Furthermore, this study showed that, while increasing the parameters of a single soil layer at surface, the slip circle will move to a different layer with weaker properties. Moreover, while increasing the parameters of soil layers in depth – in other words while increasing the stiffness contrast between surface and deep layers – the displacement of slip circle will not be observed, but the factor of safety will be reduced by 55% in some cases. It is interesting to see how amplification of acceleration in time domain will depend on mechanical and dynamic proprieties of the soil, whereas amplification of RRS in frequency domain will only depend on the layer height above rock and the rock’s acceleration response spectrum.

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