Landslides in hard soils and weak rocks

n/

Introduction to the Special Issue Containing the Papers Presented at the 4th IWL (November, 23-26, 2015)

Established in 2009, the Italian Workshop on Landslides is becoming a traditional meeting for scientists from different countries who want to discuss the most recent findings about landslide research. Every time, the workshop involves experts from different disciplines, such as geotechnical engineering, hydrology, geology, structural engineering, hydraulics, and is organized in such a way to leave ample space for open and lively discussions. In this respect, the Fourth Workshop was not an exception. Indeed, to favor focused discussions and interactions, it was structured in three topical sessions: Interaction between Slope Movements and Man-Made Works; Precipitation-Induced Landslides: Long-Term Predisposing Factors and Short-Term Triggers; Landslide Research: Modern Topics and Procedures (this session was reserved to young scientists). The great number of participants, giving presentations of high scientific level, covered three entire days. This book of proceedings collects a great number of the presented results, providing an overview of the various aspects of landslide research that were discussed in the workshop

Performance of Ground Anchors Built in a Flysch Deposit

AbstractThe ultimate pull-out tensile load of ground anchors is strongly dependent onsoil nature,grout injection and effective stress state around the bulb. In this paper, the comparison between the results of conventional pull-out testson instrumented anchors built in a flysch formation and those of small scale pull-out tests performed in the laboratory,on undisturbed soil samples recovered at the depth of the anchor bulb,allowed to closely examine the skin friction that can be mobilizedin undrained conditionsat the soil-structure interface. The experiments highlight a strong scale effect, probably depending on the real size androughness ofthe lateral surface of the bulb. In fact, theirregular bulb profiledue to flysch features strongly contributes to the pull-outstrength

The hysteretic response of a shallow pyroclastic deposit

In the last decades, in Campania (southern Italy), steep slopes mantled by loose air-fall pyroclastic soils have been the seat of shallow, fast, rainfall-induced landslides. The occurrence of such events has been the result of the combination of critical rainstorms and of unfavourable initial conditions determined by antecedent infiltration, evaporation, and drainage processes. In order to understand the nature of the phenomena at hand and to clarify the role of all influencing factors, an automatic monitoring station has been installed in an area already subject to a recent killer flowslide (December, 1999). The paper reports data collected in 2011 about volumetric water content and suction (used to investigate the soil water retention features) and rainfall depth and temperature (providing the boundary conditions). In particular, the installation at the same depths of tensiometers and time domain reflectometry (TDR) sensors allowed us to recognise the hysteretic nature of the wetting and drying soil response to weather forcing and its influence on the slope stability conditions. The data reported in the paper are freely available at https://doi.org/10.5281/zenodo.4281166 (Comegna et al., 2020)

Conceptual hydrological modeling of the soil-bedrock interface at the bottom of the pyroclastic cover of Cervinara (Italy)

On the basis of the data collected by a monitoring station, a simplified mathematical model of the hydrological behavior of the layered pyroclastic cover of the slope of Cervinara (southern Apennines) has been developed. The model considers a single homogeneous soil layer, for which effective hydraulic characteristic curves have been defined. The top boundary condition accounts for the effects of evapotranspiration. The bottom boundary condition conceptually simulates, by means of a linear reservoir model, the hypothesized effects, on the soil water potential at the soil-bedrock interface, of the fluctuations of the water table of an ephemeral aquifer stored in the underlying fractured limestone. Despite its simplifying assumptions, the model satisfactorily reproduces the observed soil water potential at all the monitored depths. The obtained results indicate that even the highest rainfall intensity can pass through the highly conductive unsaturated soil cover, and leak through the fractured bedrock. Only when the water level in the underlying aquifer is high, as it happens after long lasting periods of rainfall, the establishment of the vertical water potential gradients, needed for the leakage of high infiltration peaks, leads to soil saturation at the bottom of the cover. Such a picture provides a possible interpretation of the triggering mechanism of the landside occurred in 1999 along the slope

An Experimental Investigation on the Progressive Failure of Unsaturated Granular Slopes

Slope failure is a complex process which depends on several factors concerning nature and properties of soil, slope morphology and structure, past stress history, groundwater regime, boundary conditions, and their changes. As a consequence, the mechanism of slope failure is typically characterized by the development of a highly non-uniform strain field, which does not allow an easy prediction of the failure conditions. Usually, the process which will bring the slope to final collapse starts with local soil failure, which then leads to formation and propagation of a shear zone, and finally to general slope failure. This mechanical process is called progressive failure. However, in spite of the progresses in the knowledge of the slope behavior, a complete framework about the progressive failure is still missing; in particular, information about the response of granular unsaturated sloping soils is very poor. This paper reports the results of a couple of small-scale experiments on slopes reconstituted with unsaturated pyroclastic soils and subjected to continuous rainfall. The use of miniaturized sensors and optical fibers provided useful data to read some aspects of the mechanics of failure

Riflessioni sulla cinematica di una grande colata attiva della valle del Basento

La nota riporta alcune considerazioni sul meccanismo di spostamento di una grande e lenta colata attiva della valle del fiume Basento, in Basilicata. Le principali caratteristiche cinematiche sono: uniformità di spostamento nelle sezioni trasversali del canale, velocità sensibilmente decrescente da monte verso valle, modeste variazioni stagionali di velocità. Tra le potenziali cause di spostamento, qui si esamina il possibile ruolo dell’erosione al piede esercitata dal corso d’acqua con l’ausilio di analisi numeriche 2D basate su metodi dell’equilibrio limite e agli elementi finiti