Paolo Tommasi

Simple shear testing of sensitive, very soft offshore clay for wide strain range

Stiffness and damping properties of sensitive, very soft clay sediments of the Italian Adriatic continental shelf are determined by means of two series of cyclic simple shear tests (one with 12 stages and one with two stages). The apparatus used in this research is capable of investigating the stress–strain behaviour of the soil in a wide range of shear strains from about 0.0004% to 1%. Test results were expressed in terms of small-strain shear modulus (G0), normalized equivalent shear modulus (Geq/G0), and damping ratio (D) versus cyclic shear-strain amplitude (γc). These parameters were analyzed in the framework of existing literature by comparison with empirical correlations developed for onshore materials of different plasticity and, limited to G0, also for soft soils. The dependence of G0, Geq/G0–γc, and D–γc on factors such as void ratio, stress history, and loading cycles is analyzed and discussed.

Slope Failures Induced by the December 2002 Eruption at Stromboli Volcano

We reconstruct the sequence of landslides that occurred soon after the beginning of the December 2002 eruption on the NW flank of Stromboli volcano. Landslides involved the northeastern part of the Sciara del Fuoco (SdF) slope, an old collapse scar filled by products of volcanic activity, producing tsunami waves that severely damaged the coast of the island of Stromboli. Volumes of the mass detached from the subaerial and submarine slope were quantified by comparing preslide and postslide slope surfaces obtained by aerophotogrammetric and bathymetric data, which also allowed, in conjunction with field observations and helicopter surveys, the reconstruction of geometry and kinematics of landslides. According to the reconstructed sequence, 2 days after the beginning of the eruption, the upper part of the NE sector of the SdF slope experienced major displacements (few tens of meters). Movements propagated downslope and affected the nearshore portion of the submerged slope without a rapid sliding of the displaced mass into the sea. The following hours were characterized by a progressive increase of deformations, localized along shear zones extending over two thirds of the subaerial slope. This phase proceeded until a submarine slide about 6 x 10 6 m 3 in volume occurred, causing a first tsunami wave. The subaerial mass delimited by the shear zones and unbuttressed at its foot, then slipped into the sea producing a second tsunami wave. The main landslide event (and the minor slumps which followed) removed a volume of about 10 x 10 6 m 3 of the infilling deposit, to a thickness of at least 65 m. Hypotheses were formulated on the mechanisms that controlled the different phases of the instability sequence. Since hydraulic and stress/strain conditions progressively changed during the slope evolution, the formulated mechanisms are also based on geotechnical analyses and considerations on the mechanical behavior of volcaniclastic materials. The process that led to the landslide events.

Introduction: Monitoring, Prediction and Warning of Landslides

The WLF3 B5.Session Monitoring, prediction and warning of landslides, as a part of WLF3 session Group B. Sessions for Methods of Landslide Studies, gathers the main elements in the landslides risk reduction and landslides sustainable disaster management: monitoring, prediction and warning of landslides. Sixteen contributions from eleven countries around the world have been submitted and, after review process, accepted for publishing. The best practice techniques and experiences on monitoring, prediction and warning of landslides caused by different triggering factors are presented in this Session. In this introduction to the WLF3 B5 Session Monitoring, prediction and warning of landslides, a short summary of each of the accepted papers is presented divided regarding to their general topics.

Stability Conditions and Evaluation of the Runout of a Potential Landslide at the Northern Flank of La Fossa Active Volcano, Italy

This paper focuses on the quantitative investigations carried out to evaluate stability conditions of the northern flank of the La Fossa cone (Vulcano Island) and the consequent runout of the debris avalanche that would be generated by a possible failure. The contribution describes first the geological setting and the typical instability phenomena of the area. Then it illustrates how the global morphology of the flank was reconstructed by combining aerial photogrammetry and high resolution 3D surveying techniques such as terrestrial laser scanner. The resulting digital elevation model (DEM) permitted us to extract and measure structural and morphological elements that drive and influence past and potential instabilities. These elements were used to constrain limit equilibrium analyses (LE) that were used to estimate the volume of soil mass susceptible of failure. Strength parameters at large scale were obtained from laboratory tests, described in previous studies, and back analyses of a past failure whose geometry was reconstructed from the DEM. Finally, results of runout analyses of the debris avalanche are presented and discussed. Analyses were conducted by using DAN-W and DAN-3D codes which allowed an estimate of the maximum runout distance and extension of the accumulation zone with respect to the inhabited area.

The Impact of Climatic Changes on the Behaviour of Active Landslides in Clay

Forecasting the effects of forthcoming climate changes on natural hazards is a new frontier of the research. The problem is crucial for landslide hazard but available data are still doubtful, thus only some hypotheses can be drawn. The paper examines the potential effects of climate during next 50 years on two active landslides in clay. Considerations are based on data regarding local rainfall history, available climatic scenarios, monitoring and results of simple geotechnical analyses.

Geotechnical properties of soft clayey sediments from the submerged Tiber River delta, Italy

The geotechnical properties of the fine‐grained sediments of the Tiber River prodelta slope are described. Laboratory investigations depict the overall physical and mechanical behavior of the sediments and give information regarding their in‐situ conditions due to gravitational campaction. In spite of relative homogeneity in terms of the basic geotechnical properties, noticeable differences between materials sampled at different water depths and at different depths below the seafloor can be detected. This variation is observed when in‐situ material properties are taken into account and can be explained if the different depositional and burial conditions of the sediments are considered. In particular, differences in compressibility and undrained behavior have been found between sediments sampled immediately underneath the seafloor and the underlying materials as well as between the entire present‐day prodelta clays and the “aged”; sediments of the delta front, which were originally deposited in a prodelta ...