Aldo Evangelista

Thermal expansion of Neapolitan Yellow Tuff

SummaryIn saturated rocks and soils it is possible to define different coefficients of thermal expansion depending on the drainage conditions. This topic is first examined from the theoretical point of view with regard to an ideal isotropic thermo-elastic porous medium. Some special features of the behaviour of natural soils and rocks during thermal expansion tests are subsequently discussed. An experimental evaluation of some of these coefficients is presented in the second part of the paper. The material investigated is a pyroclastic rock, the so-called Neapolitan Yellow Tuff. Thermal expansion coefficient in drairend conditions has been evaluated, when this material is saturated with water. The e pressure increase induced by heating has been measured in undrained tes temperatures investigated range between room temperature up to 225°C.Different types of apparatus have been used and, when possible, a comparison between the results has been proposed. The results obtained in undrained thermal expansion tests are in agreement with theoretical predictions. This research is part of an on-going study of the complex phenomena known as Bradyseism, which is occurring in a volcanic area a few kilometers from Naples (Italy). Some considerations on this phenomenon are drawn in the last paragraph of the paper.

Experimental Investigation of Dynamic Behavior of Cantilever Retaining Walls

The dynamic behaviour of cantilever retaining walls under earthquake action is explored by means of 1-g shaking table testing, carried out on scaled models at the Bristol Laboratory for Advanced Dynamics Engineering (BLADE), University of Bristol, UK. The experimental program encompasses different combinations of retaining wall geometries, soil configurations and input ground motions. The response analysis of the systems at hand aimed at shedding light onto the salient features of the problem, such as: (1) the magnitude of the soil thrust and its point of application; (2) the relative sliding as opposed to rocking of the wall base and the corresponding failure mode; (3) the importance/interplay between soil stiffness, wall dimensions, and excitation characteristics, as affecting the above. The results of the experimental investigations were in good agreement with the theoretical models used for the analysis and are expected to be useful for the better understanding and the optimization of earthquake design of this particular type of retaining structure.

Rheological behaviour of pyroclastic debris flow

The pyroclastic soils that cover the mountains of the Campania region in Italy are usually unsaturated and collapse due to rainfall infiltration triggering landslides. The evolution of these soils after collapse is not well understood. Indeed, their post-failure behaviour may be “solid-like” or “fluid-like”, depending on causes that are not well known. The objective of this paper is the study carried out on the rheological behaviour of the “fluid-like” pyroclastic material with fluid mechanics tools: a vane rotor rheometer and an inclined plane. Two natural pyroclastic deposits have been sampled and different soils-water mixtures have been analysed. The main results have been explained and discussed

Experimental Study On The RheologicalBehaviour Of Debris Flow Material In TheCampania Region

The rheological behaviour of the natural material collected in the source area of three debris flows occurring in the mountainsides of the North-western Campania region (southern Italy) has been investigated. The tests have been carried out at different solid volumetric concentration Cv with a standard rheometer equipped with two geometric configurations to avoid disturbing effects. All materials behave like a Non-Newtonian fluid with a threshold shear stress τy (yield stress) that increases with solid volumetric concentration. The experimental data have been fitted with standard model generally used for fluids. A simple relation between Cv and τy has been obtained.

Analysis of the Stability of a Rock Cavern: The Fontanelle Cemetery

The paper reports the study conducted to evaluate the stability condition of one the most suggestive rock cavity located in the city of Naples (Italy), the Fontanelle (little fountains) Cemetery. It is a chamber and pillar cavity, with a rectangular and elongated plan, consisting of three naves. The cavern was excavated in the Neapolitan Yellow Tuff, a soft rocks widespread used as construction material in the city and its origin goes back to the 16th century while its expansion to the 17th century, when the city was quickly battered by popular uprising, famines, earthquakes, eruptions of the Vesuvius and epidemics. The cavity was addresses to different uses; destined to become an ossuary in the 18th century, progressively turned into a Christian worship place, suffering many events during 400 years of life, until it finds, in the modern age, its stability as a place of worship. The paper reports the numerical analyses by means of a 3D finite difference code, carried out to evaluate the stability condition of the cavity and the hill on which was excavated, taking into account the various stages of life. The results obtained show that there are some stability problem for the roof of the cavity; further investigations on the shape of the pillars, partially hidden by the fill, and on the mechanical properties of the tuff are needed for a more satisfactory evaluation.

EXPERIMENTAL INVESTIGATION OF DYNAMIC BEHAVIOUR OF CANTILEVER RETAINING WALLS

The dynamic behaviour of cantilever retaining walls under earthquake action is explored by means of 1-g shaking table testing, carried out on scaled models at the Bristol Laboratory for Advanced Dynamics Engineering (BLADE), University of Bristol, UK. The experimental program encompasses different combinations of retaining wall geometries, soil configurations and input ground motions. The response analysis of the systems at hand aimed at shedding light onto the salient features of the problem, such as: (1) the magnitude of the soil thrust and its point of application; (2) the relative sliding as opposed to rocking of the wal land the corresponding failure mode; (3) the importance/interplay between soil stiffness, wall dimensions, and excitation characteristics, as affecting the above. The results of the experimental investigations are in good agreement with the theoretical models used for the analysis and are expected to be useful for the better understanding and the optimization of earthquake design of this type of retaining structure.

Influence of Suction on the Behaviour of Retaining Walls in the City of Naples, Italy

The general principles of EUROCODE 2008 prescribe that new constructions are designed, tested and subjected to maintenance during their lifetime. Safety and performance under service conditions are evaluated through the limit states that may occur during the nominal life of the construction. As it is well known, limit states are the conditions beyond which the construction no longer meets the requirements for which the design has been made. In general, during its lifetime, a construction can experience a variation of the external loading. A clear example is the occurrence of a seismic event. Yet, when the soil is in a partially saturated condition, its hydro-mechanical properties can vary with time as a consequence, for example, of rainfall events and subsequent infiltration. A more complex approach is in this case required as a variation of both soil hydro-mechanical properties and external loading can occur. The present work deals with the above issue. In particular, it refers to the city of Naples where unsaturated pyroclastic soils are widespread. Gravity walls, made of tuff masonry, and retaining unsaturated pyroclastic backfills have been analyzed in terms of general behavior and potential damage induced by rainfall events. A Two-Phase Flow module - FLAC2D (Itasca, 2000) has been employed for the numerical analysis.