1,721,015 research outputs found
The permeable concrete: A low energy consumption solution for deep draining trenches
No full textThe reduction of pore water pressures is one of the very effective measures to improve the stability conditions of marginally stable water-bearing slopes or to stabilise landslides. For this purpose the trench drains have been used long since. Like filling material of deep trenches the permeable concrete can be effectively employed. It presents relatively high hydraulic conductivity, filtering capacity in order to prevent the internal erosion of the soil in which the trench drain is installed, enough residual hydraulic conductivity after possible clogging, sufficient shear strength after a short curing time to avoid the instabilisation of adjacent previously built panels or piles. Results of a laboratory experimental research on the mix-design, hydraulic conductivity and strength of pervious concrete are reported in the paper, proving that proper mix-design can be devised meeting the above requirements. Permeable concrete is a very poor material and a low energy consumption solution for slope stabilisation
Microstructure and shear strength evolution of a lime-treated clay for use in road construction
Full text linkThe results of a comprehensive experimental programme are presented for assessing the long-term microstructural modifications and evaluating the effects of microstructural rearrangement on the stress–strain behaviour of a lime-treated high-plasticity clay for road embankments. The stress–strain behaviour at different lime content and curing time was investigated by means of direct shear tests; microstructural analyses were carried out combining Scanning Electron Microscope observations and Mercury Intrusion Porosimetry tests. The results show that the stress–strain behaviour of treated clay is strongly dilatant with a high peak of strength, which increases with time and lime content. Furthermore, a hyperbolic function may be used for predicting the increase in strength at the end of the stabilisation process. Microstructural analysis shows that the treatment induces a redistribution of the porosity between macro- and micropores and an increase in matric suction, associated to a low reduction of water content and to aggregates shrinkage. This behaviour is affected by lime content and curing time since it results from the formation of the pozzolanic compounds on the surface of clay aggregates that induces both a bonding between hardened clay aggregates and an increase of their interlocking degree, with a consequent increase in the shear strength
Water retention behaviour of compacted and reconstituted scaly clays
Full text linkThe paper presents the results of an experimental research devoted to investigate the response to
suction variations of a scaly clay in compacted and reconstituted conditions. Different experimental
techniques (axis translation, vapour equilibrium, dew point psychrometer suction measurements) were
combined in order to explore the water retention properties in a wide suction range (0 ÷ 110 MPa).
Experimental results allowed to define the water retention domains for a constant reference void ratio,
highlighting the significant role of the microstructure on the response of the investigated clays. In particular,
the collected results showed that in the low-medium suction range, the peculiar microstructural features give
to the reconstituted clay a better retention capability than the compacted clay. However, the increasing
suction induces a significative volumetric shrinkage on the saturated reconstituted clay, especially when the
latter is initially normally consolidated. On the other hand, quite similar retention properties were
recognized in the high suction range
ANALISI DEI MECCANISMI DI RIATTIVAZIONE DI UN’AREA IN FRANA NEL BACINO DEL FIUME IMERA SETTENTRIONALE
No full textAl fine di valutare le condizioni limite per la stabilità di un pendio in frana, sono state svolte delle analisi di stabilità all’equilibrio limite 2D e 3D in un’area ubicata nel bacino del fiume Imera Settentrionale (Sicilia). Tali analisi hanno permesso di ricostruire un modello geologico e geotecnico ottimale, di individuare il livello piezometrico che ha determinato le condizioni di instabilità e di definire i parametri operativi di resistenza a taglio dei terreni. Le recenti riattivazioni dei meccanismi di frana hanno fornito elementi che hanno permesso di validare in particolare i risultati delle analisi numeriche 3D. I risultati ottenuti hanno anche evidenziato che il metodo di analisi tridimensionale costituisce un valido strumento di analisi, capace di prevedere l’estensione areale dei dissesti e di fornire una migliore stima della resistenza a taglio operativa dei terreni, soprattutto nei casi in cui la morfologia del pendio è complessa e la direzione degli spostamenti non è omogenea
Microstructural characterization of a 3D-printed soil
Full text linkTransversal applications of 3D-printing (or Additive Manufacturing) have been recently implemented in the field of Geomechanics. In a 3D-printing process, the printed volume is obtained from successive layering of adjacent soil filaments. In this work, the fabric of an as-printed soil has been carried out by combining Mercury Intrusion Porosimetry (MIP) tests and Scanning Electron Microscope (SEM) observations, with the aim to highlight how the particle arrangements and the orientation and shape of pores are linked to the printing operation. The microstructural analyses showed that macropores are the result of the relative position of the filaments and their initial distortion in quasi-undrained conditions. Particle arrangement within the soil filament is strongly anisotropic, due to the rotative movement of the soil in the extruder
Evoluzione del comportamento idro-meccanico di una sabbia di quarzo dallo stato saturo allo stato asciutto
No full textLa nota presenta i risultati di un lavoro sperimentale condotto con lo scopo di analizzare il comportamento idro-meccanico di una sabbia quarzosa per un ampio intervallo del grado di saturazione. Per analizzare le caratteristiche di ritenzione del materiale e per investigare la relazione tra la tensione di snervamento e la suzione di matrice sono state eseguite prove edometriche a suzione controllata e a contenuto d'acqua costante. I risultati ottenuti mostrano che la tensione di snervamento della sabbia non aumenta monotonamente con la suzione. Tale andamento è caratterizzato da un punto di massimo e da valori della tensione di snervamento sostanzialmente coincidenti per la condizioni satura e asciutta. Questo aspetto, non considerato finora dai modelli elasto-plastici per i terreni non saturi, conferma una delle principali ipotesi della classica Meccanica dei Terreni, secondo cui il comportamento meccanico di mezzi granulari saturi e asciutti è lo stesso se descritto in termini di tensioni efficaci
Yielding of a quartz sand from saturated to dry state
Full text linkThe paper presents the results of an experimental work where we analyse the behaviour of an unsaturated quartz sand in a wide range of degree of saturation (from saturated to dry state). The possibility of anticipating the hydro-mechanical behaviour of the soils when they approach the dry state is fundamental in many areas. An extensive experimental program, including controlled-suction and constant water content oedometric tests, was carried out to deeply analyse the water retention behaviour and the relationship between the yield stress and suction (Loading-Collapse curve). All elasto-plastic models provide a monotonically increase of the yield stress with suction. This assumption implies that the yield stress in the dry state is larger than the one relative to the saturated state, in contrast with the classical geotechnical points of view, which suggest that the yield stress of dry granular material must be approximately the same as that of the saturated one. The obtained results show that the yield stress of the sand does not increase monotonically with the suction, as predicted by commons models. In fact, the Loading - Collapse curve showed in this work presents a maximum point, and the yield stress for saturated condition is almost the same of the dried one
On the hydro-mechanical behaviour of a lime-treated embankment during wetting and drying cycles
No full textThe paper presents some experimental results obtained on samples extracted from a full-scale embankment obtained by compacting a lime-treated clayey soil. A comprehensive test programme was carried out in order to highlight the improvement of mechanical behaviour induced by lime treatment as well as to assess the durability of the improved material, which may be affected by severe seasonal wetting and drying cycles. Direct shear tests, triaxial compression tests, swelling potential measurement and oedometric tests were performed on samples cured in controlled environmental conditions for at least 18 months. Wetting and drying cycles were applied in a very wide range of suction values with different experimental techniques. Test results show that the cyclic variations in total suction in the range 2-110 MPa give rise to significant irreversible deformations of shrinkage, since the material, during the wetting stages, proves to be unable to recover most of the deformations developed in the previous drying stages. However, this volumetric behaviour shows an almost reversible pattern after a few suction cycles. In contrast, saturation after drying implies a strong variation in the mechanical response due to the irreversible pattern of the observed volumetric behaviour. Accumulation of swelling deformation, reduction of the yielding stress, increase of compressibility and loss of shear strength due to softening of bonding, induced by the pozzolanic reaction products, were measured with the increase of the number of wetting and drying cycles. Mercury intrusion porosimetry (MIP) tests, carried out before and after the wetting and drying cycles, highlighted that cyclic suction paths result in a collapse of the structure since the pore size distribution of microstructure changes, its peculiar double-porosity network becoming almost unimodal in type
The residual shear strength of the shaly and sandy facies of the opalinus clay
No full textThe paper presents a comprehensive laboratory campaign carried out with the aim to asses the residual strength of the Opalinus Clay. Ring shear tests with vertical effective stress up to 1 MPa were performed on remoulded samples of two different facies of the Opalinus Clay. Test results show that the «Shaly» facies is characterized by a low range of variation of residual strength while the strength of the «Sandy» facies is very sensitive to the variation of grain size distribution. Microstructural analyses (SEM) suggest that the difference in the observed mechanical behavior of the two facies can be related to different particles arrangements along the shear surfaces
Finite Element Analyses of Piled Foundations: Interaction Domains Under Undrained Conditions
No full textMost of the bridges in Europe countries are now approaching their design life. Therefore, at present crucial is the choice of the most suitable retrofitting solution taking the current design standards into account. From an economic point of view the costs related to the foundations adaptation are not negligible at all, even because design approaches are in general over-conservative. For instance, in case of piled foundations, the presence of the raft is conventionally disregarded in the calculation of the pile group bearing capacity under general loading. In this work a pile group foundation embedded in a silty-clay soil stratum is studied to emphasise how the use of a non-standard approach may allow to make more sustainable the interventions. An extensive 3D pseudo-static finite element numerical analyses campaign, under general loading, accounting for the non-linear soil mechanical behaviour, was performed. The results were interpreted in terms of interaction domains for the piled foundation system (raft + piles).Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Geo-engineerin
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