A distributed optical fibre sensing system is used to measure landslide-induced strains on an optical fibre buried in a large scale physical model of a slope. The fibre sensing cable is deployed at the predefined failure surface and interrogated by means of optical frequency domain reflectometry. The strain evolution is measured with centimetre spatial resolution until the occurrence of the slope failure. Standard legacy sensors measuring soil moisture and pore water pressure are installed at different depths and positions along the slope for comparison and validation. The evolution of the strain field is related to landslide dynamics with unprecedented resolution and insight. In fact, the results of the experiment clearly identify several phases within the evolution of the landslide and show that optical fibres can detect precursory signs of failure well before the collapse, paving the way for the development of more effective early warning systems.

Small quantities of water in a granular slope increase the overall stability and justify the large slope angle which is sometime observable in nature. However, the evaporation usually changes the water content of soil, especially in very shallow layers, leading to a soil strength reduction and the trigger of erosion processes. This work presents some numerical tests simulating a small slope physical model constituted of monosized glass ballotini in a pendular state. After a brief review of the different theories describing the capillary bridge which forms between two spheres and its effects on inter-particle forces, this paper deals with the implementation of the minimum energy approach within a discrete element model (DEM).\ud Some numerical triaxial tests with different water contents and confinement stresses were performed: the analyses permitted to emphasize the shear strength increase occurring at low water content. Moreover, moving from the observations performed in the physical model, a law relating the evaporation rate with depth and air–water interface was also included in the DEM. Finally, the improved DEM was successfully adopted in the simulation of the erosion process occurring in the physical model: it very well captures the formation of a talus slope profile, typical of the long-term evolution of granular slopes. The monitoring of soil displacements and suction distribution during the numerical test also allows for the evaluation of erosion mechanisms: for instance, both in experimental and numerical tests, it was observed a rigid displacement at the slope toe after the initial phase of shallow erosion

The main feature of the shallowest quaternary basin of the well-renowned historic city of Venice, Italy and its surrounding lagoon, is the presence, apparently without any regular trend in depth and site, of a predominant silt fraction. This is always combined with clay and (or) sand, forming a chaotic and erratic interbedding of different sediments whose mineralogy is however variable in a relatively narrow range due to a unique geological origin and a common depositional environment. After a brief description of the basic soil indexes of the Venice lagoon soil, the present study, based on a comprehensive geotechnical laboratory investigation, describes the range of variation of the most relevant time-independent geotechnical properties. Moreover, a new grain size index, combining the geometrical characteristics of the particle distribution, is introduced. It is shown that the soil response at large and very small strains can be related to this grain size index, which appears to be able to include the influence of the soil grading on the description of the overall mechanical behavior.Key words: silt, mechanical behavior, Venice soil, grain-size index, laboratory investigation, critical state parameters.

This paper presents experimental research concerning the shear behavior of two types of Italian peat, one normally, the other over consolidated. Organic soils are characterized by very high compressibility and high fiber content; two features that give rise to several problems during laboratory tests. Under consideration here are the effects of fibers and over consolidation on friction angle and stress-strain behavior. These are evaluated by means of undrained compression triaxial tests, with isotropic and anisotropic (K o ) consolidation being performed on natural and remolded samples. The experimental results are also analyzed by means of a bilinear failure criterion based on soil-reinforcement interaction mechanisms.

[1] A fully coupled thermohydromechanical (THM) finite element approach is used here to model the groundwater and saturation response of a typical salt marsh of the Venice lagoon (Italy) subjected to both tide fluctuation and flooding. The soil forming the marsh, whose relevant material parameters have been measured experimentally in the laboratory, is assumed to be an homogeneous multiphase porous medium, in a thermodynamic equilibrium state both in fully saturated and partially saturated conditions. More particularly, the study is aimed at analyzing separately the various couplings of several factors such as soil stiffness, water conductivity, capillary suction, and humidity exchange with atmosphere including also the occurrence of marsh flooding on the overall mechanical response of the marsh subjected to tidal oscillations of very narrow amplitude. From the analysis carried out so far, the numerical approach adopted here seems capable of describing most of the relevant features of marsh behavior, thus showing the importance of THM couplings to explain the groundwater pressure evolution induced by lagoon tide cycles. In addition, the model seems to provide some interesting explanations concerning the evolving instability of marsh scarps, which is one of the main causes of the rapid overall deterioration of the typical Venice lagoon landscape.

This paper deals with the experimental characterization of the collapse of wet granular columns in the pendular state, with the purpose of collecting data on triggering and jamming phenomena in wet granular media. The final deposit shape and the runout dynamics were studied for samples of glass beads, varying particle diameter, liquid surface tension and liquid amount. We show how the runout distance decreases with increasing water amount (reaching a plateaux for w > 1%) and increases with increasing Bond number, while the top and toe angles, and the final deposit height increase with increasing water amount and decrease with decreasing Bond number. Dimensional analysis allowed to discuss possible scalings for the runout length and the top and toe angles: a satisfying scaling was found, based on the combination of Bond number and liquid amount.

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Small quantities of liquid in a granular material control the flow dynamics as well as the triggering and jamming phases. In order to study this problem, some experimental collapse tests conducted in a rectangular box were reproduced with a 1:1 scale numerical model using the Discrete Element Method. In simulations the effect of the capillary bridges has been investigated implementing a mid-range attractive force between particles based on the minimum energy approach. Also a bonding-debonding mechanism was incorporated in the algorithm and the volume of each sessile drop on the particle surface was considered during its motion. The influence of some variables was investigated with respect to the final slope profiles and the runout lengths: the initial liquid content, the particle size, the solid density, the liquid surface tension, and the liquid-solid contact angle. Also the crucial effect of the confinement walls on the collapse phenomenon was investigated: wet particles adhere to the lateral walls providing a higher flow resistance in comparison to the same material in dry conditions. It was observed that particles with largest path-lengths are localized near the movable wall at a middle-height of the initial column sample. Other particles at the surface moves in a rigid way especially if they were wet and with a low solid density. The “fidelity” of each particle with respect to the nearest neighbours was evaluated allowing to recognize the emergence of clusters of particles and rigid parts, to extract the failure surface and to localize where debonding mechanisms concentrate in the wet case