GEOLAB-FIM Flowslide Impact Modelling testing

The “Flowslide Impact Modelling” project (FIM) deals with the interaction mechanisms which develop when a flow-like mass movement hits an obstacle, such as a structure or a protection barrier.The focus of the project is mainly on understanding the behaviour of flowslides, which are landslides triggered by saturation of the ground and groundwater seepage along a slope. These events occur during intense rainfall events where the saturated soil has little strength. Fluid-like behaviour is predominant during the propagation and impact against structures, however solid-fluid interaction inside the flow plays a role and soil mechanics is fundamental for assessing the problem.Due to Climate Change heavy rainstorms are expected to become more frequent, with significant amount of mixture of water and debris potentially mobilized along the slopes. The increased role of water runoff during the intense rainstorms favour that different types of flows may be originated; however, they will always propagate at velocity of tens of metres per seconds. Such topic is clearly related to extreme geohazards.The impact of such destructive flows on urban settlements (such as public buildings and resident housing) and transport facilities (roads and rail infrastructures) has been caused severe damage to the structures and infrastructure all over the Europe and often victims are recorded.The Geo-Centrifuge hosted in Deltares (Delft) has been chosen to conduct a series of propagation-impact experiments. Such centrifuge offers the chance to explore a range of impact pressure values and time trends of total stresses and pore water pressure generated during the impact.The centrifuge tests were set at 40 g-level and involved the releasing from a height a saturated soil mass, that propagates downslope and finally impacts against a rigid instrumented barrier.A range of landslide scenarios (featured by different Froude number), protection structures (structure’s height relative to flow depth) and types of landslide-structure interaction (dead zone formation, run-up, overtopping) were inspected, also referring to Faug’s diagram for the interpretation of the results.A natural Vesuvian volcanic soil was used since it is prone to static liquefaction upon shearing and then susceptible to fast runout.The expected results from the FIM project are: time trend of total and pore water pressure for different impact mechanisms, insights about the role of fine content for different impact scenarios, enhancement of the Faug’s diagram, insights on the role of fine content and suggestions for updating the design criteria of the protection barriers. The latter can be achieved thanks to the collaboration of the industrial partner Geosintex s.r.l.The novelty relates to the use of natural soil instead of uniform particle size material as done before. The particle size regulates the flow dynamics.The simple modification of the model geometry (i.e., falling height of the soil from the storage container to the slope, and distance of the barrier) result in different impact mechanisms.The centrifuge model can accurately reproduce the fast movement of the sliding mass with realis-tic total stresses, pore water pressures, and inter-action between the constituents (drag forces) at prototype scale. Contrary to other devices (such as flume tests) used to model the same problem, these dominant factors are not scaled down in the centrifuge. Moreover, the centrifuge is the opti-mal experimental device to reproduce the field conditions of a dynamic impact loading problem experienced by a protection structure impacted by a flowslide.