Slope instability and landslides are frequently triggered during heavy rainfalls in mountainous areas. Geomaterials that are subject to this type of failure normally include coarse grains, which are made by weathering of mother rocks. These materials are called sandy gravel or gravelly sand in soil mechanics, depending upon the amount of gravelly components. This situation suggests a need for laboratory investigations that aim to understand the shear behavior of sand with gravel toward failure. Another feature of this type of failure is a quick rate of slope failure that is reasonably considered as an undrained process of shear distortion. Hence, the present study investigated by means of experiments the undrained shear behavior of sand with gravel. The torsion shear tests on hollow cylindrical specimens concerned the effects of gravel content on the undrained shear behavior. The tests revealed that the effect of gravel content is twofold. When the gravel content is relatively small, the effects of the sandy component are more important. Hence, the relative density of the sandy matrix among gravels has a predominant influence. In this situation, therefore, the overall relative density is a less important index to account for the shear behavior. In contrast, when the gravel content exceeds a threshold value, the amount of gravel comes to have a more predominant influence than the sandy matrix. This is probably because gravel particles start to have contact with each other to form a structural matrix of gravel grains that governs the overall stress-strain behavior. These results were summarized in three-dimensional diagrams that related the strength properties of gravelly sand varying with the density of sand matrix or the density of sand-gravel mixtures as well as the gravel content. IntroductionLandslides and debris flows have been the major cause of disasters resulting in significant loss of human lives and property damages. This is especially true in the Himalayan region, where the geomorphology consists of mountains and hills made up of mixtures of sand, gravels and boulders. Rainfall, earthquakes, changes in vegetation patterns and anthropogenic activities are the main triggering mechanisms of failure of the slopes. The stability of the slopes along the highways and in the residential areas in the mountainous terrains is extremely important, as human lives are directly threatened. This research aims to develop a thorough understanding of the undrained deformation of gravelly sand during static monotonic loading condition, as in the case of rainfall, with emphasis on liquefaction and residual strength at large strain. The findings can be used for better evaluation of flow-deformation potential of different mixtures of gravel and sand.

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Tsunami can cause severe damage to properties and loss of many human lives. Tsunami is often related to earthquakes. Within a close proximity and with similar magnitude, some earthquakes produce very severe tsunamis, e.g. the December 2004 Sumatra earthquake, and others produce very minor or insignificant wave height increase, e.g. the March 2005 Sumatra earthquake. Thus, the study of tsunamigenesis of earthquakes, i.e., whether an earthquake will generate significant tsunami, is critical to the prevention or minimization of damage due to tsunami. In this study, the seismic signals from earthquakes were analyzed in order to determine tsunamigenesis more accurately. Fast Fourier Transform (FFT) of the seismic signals of the earthquakes was performed for a number of historical earthquake records of both tsunamigenic and non-tsunamigenic earthquakes of similar magnitude and epicenter distance. The results showed that tsunamigenic earthquakes have lower amplitude in the high frequency range (0.15-0.3 Hz) as compared to non-tsunamigenic earthquakes. Preliminary wavelet analysis of these earthquakes also revealed that the intensity pattern of tsunamigenic and non-tsunamigenic earthquake was similar to the findings from FFT. Both techniques lead to the conclusion that the long period signal and the depletion of high frequency energy revealed in the seismic signal may well indicate the tsunamigenic potential of the earthquakes. Thus the techniques that analyze the frequency content of the seismic signals have a great potential to complement the existing Pacific Tsunami Warning System, which only takes the magnitude of earthquake as the determining factor in predicting the generation of tsunami. 171 J. Earthquake and Tsunami 2007.01:171-191. Downloaded from www.worldscientific.com by MCMASTER UNIVERSITY on 02/19/15. For personal use only. J. Earthquake and Tsunami 2007.01:171-191. Downloaded from www.worldscientific.com by MCMASTER UNIVERSITY on 02/19/15. For personal use only.

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