1,721,016 research outputs found
The Navier–Stokes Cauchy Problem in a Class of Weighted Function Spaces
No full textWe consider the Navier-Stokes Cauchy problem with an initial datum in a weighted Lebesgue space. The weight is a radial function increasing at infinity. Our study partially follows the ideas of the paper by Galdi and Maremonti (J Math Fluid Mech 25:7, 2023). The authors of the quoted paper consider a special study of stability of steady fluid motions. The results hold in 3D and for small data. Here, relatively to the perturbations of the rest state, we generalize the result. We study the nD Navier-Stokes Cauchy problem, n >= 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\end{document}. We prove the existence (local) of a unique regular solution. Moreover, the solution enjoys a spatial asymptotic decay whose order of decay is connected to the weight
Confronto fra l'azione di trincee e pali drenanti
No full textL’obiettivo del presente lavoro è investigare l’efficienza dei sistemi di drenaggio per la stabilizzazione di frane profonde. In particolare sono state confrontate l’ efficienza di trincee profonde disposte lungo la direzione di massima pendenza, tecnologia attualmente in uso per la stabilizzazione delle frane, con quella relativa a trincee e pali drenanti disposte nella direzione delle curve di livello e ne è stata valutata l’efficienza al variare dell’interasse fra i pali. L’effetto dei differenti sistemi di drenaggio è stato analizzato in condizioni stazionarie mediante un codice numerico agli elementi finiti (FEM) adottando uno schema geometrico tridimensionale. Il software utilizzato per le analisi è SVFlux del paccheto Soil Vision 200
Modelling stress-strain-time behaviour of natural soils - part 1: monotonic loading
No full textGeneral Report Session
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)
Isteresi idraulica di piroclastiti non sature. confronto fra misure in sito e di laboratorio
No full textOn 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
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