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Large-scale landslides, occurring when a large mass of soil is detached and slides down a slope, are a serious threat to human life and property. A wellknown example of such a landslide is the one that occurred in Vaiont, Italy, in 1963: part of the slope of a mountain slid down and fell into an adjacent reservoir. The velocity of the soil mass was so high that it caused water to overflow the dam, flooding a downstream village and killing 2,600 people. Such landslides also occur under sea, and they have been blamed for creating very large waves, known as tsunamis, that can travel long distances in the oceans and flood coastal areas.Engineers are familiar with the problem of slope stability and, in general, they can predict when a slope is stable or not. However, there is still major uncertainty about why, or under what circumstances, a destabilised slope can form a landslide of high velocity, becoming a catastrophic event and affecting a large area.A mechanism that has been proposed to explain the development of some slope instabilities into catastrophic slides, is frictional heating of the soil. Soils consist of solid particles that are in contact with each other, but which, no matter how well they are packed, always leave empty space between them. This pore space is usually full of groundwater. During a landslide, the soil at the base of the moving mass is in contact with the soil underneath. It has been suggested that friction due to sliding can heat the soil at the base of the slide, in the same manner that our hands warm up when we rub them together. As the temperature of the soil increases, the water in the pores expands, pushing the sliding soil mass upwards. On top of that, some soils become softer with heating, and easier to distort. The overall result is that, as heating continues, the soil at the base of the slide progressively loses its resistance and allows the landslide on top of it to move ever more freely.Although the existence of this mechanism was proposed long ago, it has not yet been investigated in detail and its possible impact is not fully understood. The aim of our research is to investigate the role of frictional heating in the development of catastrophic landslides, and determine the conditions that make a slope prone to catastrophic failure. To carry out this investigation, we will develop and use a mathematical landslide model , i.e. we will write a set of equations that describe the motion of a landslide, the generation and diffusion of heat in the soil, the changes in the pressure of pore water, and the temperature-dependent changes in the behaviour of soil. For any given set of slope inclination, soil properties and groundwater conditions, the solution of the equations will give us a prediction of whether a landslide develops or not and, if yes, what its characteristics are (e.g. what velocity will the sliding soil reach).We will use the model to simulate landslides for a wide range of slope inclinations, soil properties and groundwater conditions. From the results of these simulations we will be able to appreciate, for each particular case, the contribution of frictional heating to the development of a landslide. Following that, we will determine from our results the critical combinations of slope inclinations, soil properties and groundwater conditions that would make a slope prone to catastrophic failure.The results will provide useful guidance to engineers, as they will give an indication of the risk that different slopes pose. They are also expected to stimulate further research, that will eventually lead to the development of a general tool for modelling the initiation and evolution of landslides.
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