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Fluidised landslides are one of the most dangerous types of mass movements as they can run over long distances at high velocity. A flow-like landslide can occur in both artificially designed and natural slopes, resulting in extensive property damage and significant loss of life. Although various studies have examined the initiation mechanism of this type of landslide, the understanding of the phenomenon of instability which can occur in loose granular slopes deserves further attention. Specific influential factors, such as the changes in the soil microstructure due to water infiltration and seepage forces, still need to be further examined. In this study, the initiation of a fluidised landslide is investigated through flume tests. The tested material was collected from a coseismic landslide deposit in the 2008 Wenchuan earthquake area. These loose, granular deposits can fail due to intense rainfall and exhibit flow-like movement, potentially evolving into destructive debris flows. Two flume apparatuses have been used, which were equipped with multiple sensors to evaluate the pore pressures and the internal displacements. A high-sensitivity seismic accelerometer was installed at the bottom of the flume to record the vibrations produced by the movement of the soil particles during the tests. The soil mass was progressively wetted either by a uniform inflow from the ground surface at the top of the slope, to simulate the infiltration of run-off water arriving from upslope, or by a gradual rise of the water level at the upper boundary of the slope, to simulate a gradual rise of the groundwater table. Internal erosion of the finer soil fraction driven by the seepage forces is thought to have played a significant role in the slope collapse. Possible changes in the particle arrangement were recorded by the accelerometers in the form of an increasing high-frequency vibration signal before any significant rise of pore pressure and any significant displacement of the slope could be observed. Although further parametric investigation is still necessary, and tests at real scale should be devised, the observed behaviour suggests that seismic monitoring of loose, granular deposits could be a promising method for detecting an incipient slope collapse. [ABSTRACT FROM AUTHOR]

For a quantitative assessment of debris flow risk, it is essential to consider not only the hazardous process itself but also to perform an analysis of its consequences. This should include the estimation of the expected monetary losses as the product of the hazard with a given magnitude and the vulnerability of the elements exposed. A quantifi- able integrated approach of both hazard and vulnerability is becoming a required practice in risk reduction management. This study aims at developing physical vulnerability curves for debris flows through the use of a dynamic run-out model. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results can then be applied to consequence analyses and risk calculations. On 13 July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of the Valtellina Valley (Lombardy Region, Northern Italy). One of the largest debris flows events occurred in a village called Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. The Selvetta event was modelled with the FLO-2D program, an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The behaviour and run-out of the flow was reconstructed. The significance of calculated values of the flow depth, velocity, and pressure were investigated in terms of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which was calculated as the ratio between the monetary loss and the reconstruction value. Three different empirical vulnerability curves were obtained, which are functions of debris flow depth, impact pressure, and kinematic viscosity, respectively. A quantitative approach to estimate the vulnerability of an exposed element to a debris flow which can be independent of the temporal occurrence of the hazard event is presented. [ABSTRACT FROM AUTHOR]

Forecasting the possibility of flow-type failures within a slow-moving landslide mass is rarely taken into account in quantitative hazard assessments. Therefore, this paper focuses on the potential transition of sliding blocks (slumps) into flow-like processes due to the generation of excess pore water pressure in undrained conditions. The generation of excess pore water pressure may be the consequence of deformation of the landslide body during motion. Two model concepts are proposed and discussed. The first concept is the so called strain concept model where emphasis is laid on strain changes due to differential movement within the moving mass. This may create zones of compression and dilation and consequently excess pore water pressures. The second concept is the so called topographical concept model which focuses on changes in the stress field of the landslide caused by geometric changes in topography of the moving body. Both models were tested on two slumps which developed in secondary scarps of the Super-Sauze mudslide in the Barcelonnette Basin (South French Alps). The slump which developed in 1999 showed complete fluidization; all the material was removed from the source area and transformed into a mudflow. The second slump, dated from 2006, did not show fluidization; it has a relative short displacement and all the material remained in the source area. It appeared that the strain concept model predicted flow-type failure for both slumps, after relative short displacements, while the topographical concept model predicted only flow-type failure for the 1999 slump and not for the 2006 slump. The strain concept model seems too conservative in forecasting the fluidization potential of slumping blocks. [ABSTRACT FROM AUTHOR]

On the basis of measurements of hydrological parameters and field monitoring of a landslide in the Terres Noires in the basin of Barcelonnette (France), a hydrological model was developed, describing groundwater fluctuations in relation to precipitation. These groundwater fluctuations can be used as input to a stability model in order to assess the temporal frequency of instability of the landslide. The calculated groundwater fluctuations, which can forecast years with landslide incidents, were roughly calibrated against dated movements obtainedby dendrochronological research. The hydrological system of the landslide can be understood through a three-layer sequence: a rather permeable colluvial top layer underlain by a less permeable colluvial second layer, both overlying the nearly impermeable in situ nonweatheredblack marls (Terres Noires). The mean Ksat value for the matrix flowin the top layer is 15.7 cm/day and in the underlying layer 0.7 cm/day. However, water fluxes in these layers occur by two types of groundwater flow: matrix flow obeying Darcy's law, and more rapid gravitational flow through preferential flow paths, increasing the conductivity by a factor of 10 to 100, as cube method Ksat measurements revealed. The model shows long-term yearly fluctuations of the phreatic surface, with peaks at the end of winter, as well as at the beginning of spring, and minimum values during the dry summer period. These long-term fluctuations are explained by the high drainage capacity of the top colluvial layer and the relatively low vertical water fluxes within the underlying colluvial layer. The model shows that maximum critical peak height conditions of the groundwater, causing instability, occur in wet seasons, with at least six consecutive months with high amounts (more than 60 mm) of precipitation. [ABSTRACT FROM AUTHOR]