1,720,974 research outputs found
On the Effect of Grading and Degree of Saturation on Rockfill Volumetric Deformation
No full textThe use of rockfill in civil engineering works such as earth and rockfill dams, road and railway embankments, increased along the last century especially for sustainability reasons. In order to ensure the stability of these structures under a set of conditions expected to occur during their life (grain crushing, changes in degree of saturation), the prediction of mechanical behavior of rockfill is fundamental for land management and protection. The mechanical behavior of rockfill mainly depends on stress level and relative density, as usual for granular soils. However, because of the large size of the particles, their mineralogical characteristics play a relevant role too, influencing grain crushing and therefore the overall behavior. Furthermore, it has been demonstrated in literature that for a given state (defined as the combination of stress state, void ratio and average number of grain to grain contacts) the effect of grains mineralogy on grain crushing (or microcrushing) largely depends on relative humidity (RH). The paper presents the results of triaxial tests performed on gravel specimens in which different levels of relative humidity are explored in order to analyze the “driest” and “fully saturated” conditions, and the transition from one to the other. Grain size distributions of the specimens, both after compaction and after the triaxial tests, are also compared in the paper
Magnetic measurement system of sandy gravel specimens shape during tests in a large triaxial apparatus
No full textAs well known, rockfill behaviour is strongly influenced by both intrinsic (mineralogy and size of particles, grain shapes, soil grading etc.) and state parameters (relative density, stress state, relative humidity). To investigate their mechanical response to stresses and relative humidity (RH) loadings, a large size triaxial device (H = 410 mm, D = 200 mm) has been developed at the University of Naples Federico II (Italy), including modifications required to impose partially saturated conditions in the specimen by means of the vapour equilibrium technique. In order to evaluate local axial and radial strains and global volumetric strains in partially saturated conditions, a magnetic shape detector device has been designed and installed. The accuracy of this system has been evaluated in some isotropic compression triaxial tests on compacted sandy-gravel specimens. The experimental data clearly show the effectiveness of the magnetic system in the measurement of axial displacements while the measurement in radial direction appear to be strongly affected by the non-linearity of the complex magnetic field generated during the test and requires further checking tests
Effetto della suzione e tensione di confinamento sulla resistenza a taglio di una miscela sabbio-limosa costipata
Full text linkLa presente nota illustra sinteticamente le fasi di esecuzione e le modalità interpretative di prove triassiali consolidate drenate (TXCD) condotte su una miscela di sabbia e limo argilloso costipata in condizioni di parziale saturazione. I test a controllo di suzione sono stati eseguiti mediante un’apparecchiatura triassiale a doppia parete, il cui piedistallo è stato equipaggiato con una pietra porosa a elevato valore di ingresso d’aria, al
fine di prevenire il fenomeno di cavitazione all’interno delle linee di drenaggio. Nel corso delle prove la suzione target è stata imposta attraverso la tecnica della traslazione degli assi e la variazione di volume dei provini stimata mediante un dispositivo cilindrico a doppia camera, in grado di correlare tali modificazioni alle letture di un sensore di spostamento induttivo (LVDT). I risultati della campagna di indagine, comparati ai corrispettivi ottenuti da prove effettuate in condizioni sature, evidenziano che la suzione contribuisca in maniera significativa alla resistenza a taglio dei terreni e che il suo effetto vari in maniera non lineare in funzione del grado di saturazione e della tensione di confinamento
Experimental and numerical investigations of a river embankment model under transient seepage conditions
Full text linkThe evaluation of riverbank stability often represents an underrated problem in engineering practice, but is also a topical geotechnical research issue. In fact, it is certainly true that soil water content and pore water pressure distributions in the riverbank materials vary with time, due to the changeable effects of hydrometric and climatic boundary conditions, strongly influencing the bank stability conditions. Nonetheless, the assessment of hydraulic and mechanical behavior of embankments are currently performed under the simplified hypothesis of steady‐state seepage, generally neglecting the unsaturated soil related issues. In this paper, a comprehensive procedure for properly defining the key aspects of the problem is presented and, in particular, the soil characterization in partially saturated conditions of a suitably compacted mixture of sand and finer material, typical of flood embankments of the main river Po tributaries (Italy), is reported. The laboratory results have then been considered for modelling the embankment performance under transient seepage and following a set of possible hydrometric peaks. The outcome of the present contribution may provide meaningful geotechnical insights, for practitioners and researchers, in the flood risk assessment of river embankments
An experimental study of the behaviour of two rockfills accounting for the effects of degree of saturation
Full text linkRockfill dams have become more and more recognized for their safety, economy and adaptability to widely varying site conditions. As a contribution to the understanding of the main factors affecting the rockfill behaviour, the paper reports and discusses experimental data on several aspects relevant to the interpretation and analysis of their in-situ response. The experimental programme involved three series of oedometric tests on specimens of two different gravels having the same grading, reconstituted at the same initial relative density. Experimental observations on rockfills compressibility are presented and discussed: attention is paid to the role of degree of saturation (Sr) through the analysis of "driest", "fully saturated"conditions, and the transition from one to the other. Grain crushing tests on dry and saturated soil particles are also reported. Grain size distributions of the specimens, both after compaction and after the oedometer tests, are compared in the paper. The results show that the effect of Sr cannot be overlooked in the mechanical characterization of the material, especially in rockfill/stress conditions prone to crushin
Sistema magnetico di rilevamento forma/volume in cella triassiche di grandi dimensioni
No full textIl comportamento dei materiali granulari è fortemente influenzato sia da parametri intrinseci (mineralogia e dimensione delle particelle, forma dei grani, assortimento granulometrico, ...) che da parametri di stato (densità relativa, stato tensionale, umidità relativa, ...). Presso l’Università degli Studi di Napoli Federico II un’apparecchiatura triassiale di grandi dimensioni (D = 200 mm, H = 410 mm) è stata upgradata con l’obiettivo di studiare la risposta meccanica di terreni a grana grossa. Nell’ambito delle operazioni di potenziamento è stato progettato ed installato un dispositivo magnetico di rilevamento forma/volume, concepito per la misura delle deformazioni assiali e radiali locali nonché delle deformazioni volumetriche globali. L'accuratezza di questo sistema è stata valutata in alcune prove triassiali su campioni di ghiaia debolmente sabbiosa compattati. I dati sperimentali mostrano chiaramente l'efficacia del sistema magnetico nella misurazione degli spostamenti assiali mentre la misurazione in direzione radiale sembra essere fortemente influenzata dalla non linearità del campo magnetico generato durante il test e richiede ulteriori verifiche
Soil water retention curves of a silty clayey sand compacted at different dry density
Full text linkThe study of the hydraulic behaviour of compacted soils in partially saturated conditions is essential for understanding the engineering performance of geotechnical structures such as river embankments. The paper presents the results of an experimental study focusing on the effects of the initial water content and dry density on soil water retention curve (SWRC) and volume change of a compacted soil mixture under hydraulic loading. For this purpose, soil specimens compacted at different water contents(dry, wet and optimum water content), chosen on the basis of standard Proctor compaction test, were used. Specimens of a mixture composed of 70% Ticino sand (TS) and 30% Pontida silt (PON) have been tested. This is a heterogeneous mixture of sand and silt, that usually constitute the embankments of tributaries of river Po (Italy). The SWRCs along drying paths were performed by means of evaporation tests starting from the saturated conditions gained in permeameter tests. For the investigation of the change in the void index during the evaporation test, the volume variation of the tested specimens was estimated by means of a calliper and photographic comparison. Changes in the SWRCs are consistent with changes in specimen initial condition while the soil volume change exhibited at the end of evaporation test is always negligible
A new frontier of BIM process: Geotechnical BIM. Atti del XVII European Conference on Soil Mechanics and Geotechnical Engineering
No full textInsights into the Hydromechanical Behavior of a River Embankment through Physical and Numerical Modeling
Full text linkIn the framework of a climate change scenario and growing land urbanization, a reliable assessment of river embankment safety conditions represents a key aspect to enhance the resilience of these critical infrastructures and support the development of design guidelines and flood risk reduction strategies. This paper aims at contributing to a deeper understanding of the effect of hydraulic loadings on the hydromechanical behavior of unsaturated river embankments through physical and numerical modeling. To fulfill this scope, two centrifuge tests were conducted on a small-scale physical model, representative for the tributary bank systems of the main river in Italy, the Po River. The model embankment featured a trapezoidal-shaped cross section and was made of a compacted silty sand mixture, overlying a homogeneous clayey silt foundation layer. A comprehensive laboratory investigation was carried out to estimate the geotechnical properties of both materials and the main outcomes are herein presented. To monitor the model response to the imposed hydraulic boundary conditions, the middle section of the embankment was extensively instrumented with miniaturized tensiometers, pore pressure transducers, and displacement sensors. Subsequently, a coupled flow-deformation finite-element (FE) model was set up to replicate the two centrifuge tests. Once validated, the numerical model was adopted to study the performance of an embankment under realistic flood scenarios as its hydraulic characteristics varied. The development of this numerical model made it possible to create a predictive tool for the assessment of the hydromechanical behavior of existing river embankments
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