682 research outputs found
Osservazioni sul progetto di paratie secondo gli Eurocodici e le Norme Tecniche per le Costruzioni (NTC08)
No full textIn questo articolo si prende in esame la progettazione geotecnica di opere di sostegno flessibili – paratie a sbalzo e ancorate – secondo le prescrizioni degli Eurocodici EC7, EC8 e della recente normativa italiana (NTC08). Per tali opere, la normativa italiana prescrive al progettista di eseguire verifiche SLU, in condizioni statiche e sismiche, secondo l’Approccio 1 dell’Eurocodice (DA1). Considerando i diversi valori dei coefficienti di sicurezza parziali per le azioni e le loro combinazioni, il progettista deve generalmente svolgere le verifiche di sicurezza in tre distinte condizioni (DA1-C1 e DA1-C2 in condizioni statiche; DA1-C2 in condizioni sismiche), al fine di valutare quella più severa nei confronti del dimensionamento geotecnico della paratia.
Nell’articolo, le equazioni che soddisfano il requisito fondamentale Ed Rd sono sviluppate in forma adimensionale per le tre condizioni su citate; ciò consente di individuare i gruppi adimensionali delle grandezze che governano l’equilibrio alla rotazione del sistema. Nello studio sono esaminate due semplici tipologie di strutture di sostegno - paratia a sbalzo e paratia ancorata in testa - in terreni incoerenti; per queste, è condotto uno studio parametrico considerando un ampio intervallo di valori dell’angolo di attrito del terreno, del coefficiente sismico orizzontale e dei sovraccarichi permanenti e variabili. I risultati ottenuti dallo studio, sintetizzati in grafici adimensionali, mostrano che spesso non è necessario analizzare le tre differenti condizioni di verifica e consentono di individuare immediatamente la condizione più gravosa per molte situazioni reali, in condizioni sia statiche sia sismiche; ciò conduce a una notevole utilità e semplificazione nella prassi progettuale corrente
Geotechnical properties of an unsaturated pyroclastic soil from Roma
No full textThe paper presents the results of an experimental investigation on the mechanical behaviour of an unsaturated pyroclastic soil typical of the subsoil of Roma (Italy). In its natural state, the material is a bonded coarsegrained weak rock. The deposits of pozzolana are unsaturated in situ; this has an important practical relevance in the evaluation of the stability conditions of natural slopes and cuts. The experimental investigation consisted mainly of pressure plate tests, oedometer tests and special isotropic and triaxial compression tests at increasing values of mean net pressures in the range 50–400 kPa and at different constant levels of suction (20–75 kPa). The compressibility and shear strength properties of the material are presented in some detail. Special attention is given to defining the failure envelope at relatively low confining stresses and assessing the influence of the degree of saturation on the failure conditions
Direct Displacement-Based Design of Embedded Retaining Structures
No full textThe paper presents the displacement seismic design method known as ???Direct Displacement ???
philosophy behind DDBD is that structures ??? including geotechnical structures ??? should be designed to achieve a specified performance level under a specified seismic intensity. The calculation steps of the method are described in detail with considerable discussion on their applicability to cantilever and anchored retaining structures. As a final result, the DDBD procedure provides a rational design approach which relies on a convenient reduction of seismic thrusts based on the system capacity of dissipating energy (ductility capacity)
On the design of embedded retaining structures following Eurocodes and the italian national code
No full textThe paper focuses on the design process of cantilever and anchored embedded retaining structures, following the prescriptions of Eurocodes EC7, EC8 and their implementation in the recent italian Code for Constructions (NTC08). For such structures, the Italian Code prescribes to the designer to perform ULS analyses in static and seismic conditions following the Eurocode Design Approach 1 (DA1). Considering the distinct values of partial factors relevant to the different actions and combinations, the designer generally has to face and to verify the stability of the structure in three distinct cases (i.e.:DA1-C1 and DA1-C2 in static condition; DA1-C2 in seismic condition) in order to assess the most critical one. In the paper, the equations satisfying the fundamental requirement Ed <= Rd for the three cases above are developed in a nondimensional form; this allows to detect the non-dimensional groups (geometrical, mechanical, loading) affecting the rotational equilibrium. Two simple kinds of retaining structure are considered, namely, cantilever and singly-propped embedded walls in cohesionless soil. A parametric study is then performed by considering wide ranges of values for soil friction angle, seismic horizontal coefficient, and unfavourable permanent and variable surcharges. The results obtained from the study, which are summarised into non-dimensional plots, show that often it is not necessary to analyse the three different conditions and immediately provide the most critical case for a wide range of practical situations, in both static and seismic conditions. This leads to a significant usefulness and simplification in current design practice
An experimental study on a partially saturated pyroclastic soil: the Pozzolana Nera from Roma
No full textThe paper presents the results of an experimental investigation on the mechanical behaviour of partially saturated Pozzolana Nera (Roma, Italy). Such natural deposits, which have been extensively studied in saturated conditions, are characterised by a marked heterogeneity in terms of grading, nature of grains, and inter-particle bonds. In situ, deposits of pozzolana are generally found in unsaturated conditions; this has an important practical relevance in the evaluation of the stability conditions of natural slopes and cuts. The experimental investigation consisted mainly of isotropic and triaxial compression tests on reconstituted samples, at increasing values of mean net pressures in the range 50 – 400 kPa, at different constant levels of suction (20 – 75 kPa). Volume pressure plate extractor tests were also conducted to obtain the water retention curve. In addition some wetting tests were carried out by means of conventional oedometer cells. The testing programme made it possible to examine the hydraulic and mechanical properties of unsaturated Pozzolana Nera at different values of the degree of saturation and to compare the mechanical behaviour of the same material in saturated conditions. Special attention was focused on defining the failure envelope at relatively low confining stress and assessing the influence of the degree of saturation on the failure conditions of the material
Soil dilatancy and suction: some remarks on their mutual effects on the shear strength of granular soils
No full textThe results of suction controlled triaxial compression tests on an unsaturated coarsegrained
soil are examined in detail. The tested material is a silty sand obtained by reconstituting a
pyroclastic weak rock from Roma. The stress-dilatancy data from triaxial tests on the reconstituted
and unsaturated material are compared to the experimental results obtained for the same
saturated material in reconstituted and natural state. The whole set of data shows clearly the
influence of suction on soil-dilatancy and shear strength; a significant difference can be noted in
the dilatant behaviour between the reconstituted unsaturated soil and the intact natural material
Review of: The Language of Defendants in the 17th-Century English Courtroom by Elisabetta Cecconi (Peter Lang, Bern, 2012)
No full textThis volume analyses the defence system in the 17th-century English courtroom and sees how defendants attempted to construct their discourse identity and articulate their defence in the arraignment section and in the evidence phase of the trial
Effects of grain size properties on the shear strength of a pyroclastic crushable soil
No full textThe paper presents some experimental results of a standard laboratory investigation carried out on reconstituted samples of a pyroclastic weak rock of the area of Roma, Italy. In its natural state the material may be assimilated to a bonded coarse-grained material; interparticle bonds are made of the same chemical and physical constituents of grains. Therefore bond degradation and grain crushing, which occur at relatively low stress levels, of the order of 50 kPa, can be regarded as indistinguishable features of the mechanical behaviour. The analysis of data obtained from conventional direct shear tests carried out on samples with different initial grain size distributions reveals that D50 is the main factor controlling the peak strength and the rate of dilation of the material; on the other hand the "ultimate" shear strength, evaluated at the end of test, is found to be mainly affected by both grading and grain crushing
Deep roots planting for surface slope protection
No full textSlope vegetation is currently finding wide applications all over the world to mitigate erosive phenomena and improve slope stability. An innovative natural technology for slope protection has been recently developed in Italy; this uses only natural perennial grass plants with deep roots and allows operating in areas where climatic conditions were, until a few years ago, considered prohibitive for the development of vegetation. Such technology appears promising with regard to shallow slope instability; the plant roots induce mechanical and hydraulic effects on slope equilibrium, which typically increase the soil shear strength. The mechanical effects of vegetation result from the root/soil interaction processes, while the hydraulic effects derive from the significant reduction of water content enhanced by plant transpiration. The quantitative evaluation of the mechanical effect has been modelled and implemented in a computing algorith
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