1,720,972 research outputs found
Importance of full scale tests for the design of levees
Full text linkThis paper illustrates a case history, based on full-scale tests (trial embankment). More specifically, the settlements of a full-scale trial embankment on a very compressible soil (organic clay) for a period of 5 years are reported. The observed settlements are compared with those obtained from an A type prediction, as well as a B type prediction. The analysis results suggest the importance of an appropriate modelling of secondary settlements of organic soils. The difficulties in obtaining good quality undisturbed samples of organic clay and the peculiar creep behaviour point out the importance of full-scale tests
A case history on levee external erosion
No full textClimatic changes are expected to increase both the frequency and severity of flooding across the world. It is not possible to plan a continuous increase of levee height and its geometry. Therefore levees should resist to overtopping.
This Technical Note gives an updated review of the surface erosion phenomena that can occur during floods and mainly deals with a case history on the effect of overtopping on a trial embankment in stabilized soil. The possible use of recycled soil is also discussed
METODO INNOVATIVO PER LA VALUTAZIONE DELLO STATO DI COMPATTAZIONE DEI RILEVATI ARGINALI MEDIANTE PROVE CPT E DMT
Full text linkAnalysis of existing levee systems
No full textThe floodplain embankments of the Serchio River (Tuscany, Italy) have experienced several failures during their life. After the
event of December 2009 a detailed geotechnical investigation has been carried out. This paper discusses the necessary criteria for a
cost-effective investigation taking into account the total length of the embankments (30 km), the requested level of detail and analyses
and the capability of indirect methods (CPTu, 2D geo-electric tomography) to infer the soil stratigraphy. In this respect, it has been
confirmed that CPTu test is an expeditious, economical and effective indirect method for soil profiling, if the results are correctly
calibrated against borehole-logs. On the other hand, geo-electric investigations can be very useful to highlight anomalies and heterogeneities
in the embankment cross section.
Following the geotechnical characterization of the Serchio River a number of analyses have been carried out for various purposes:
to clarify the causes of the December 2009 failures, to design appropriate repair of the failures and retrofit of the embankments in
proximity of the failures and to identify the risk areas considering the whole extension of the embankments. The following Ultimate
Limit States have been considered:
Slope failure and hydraulic heave (under steady state flow conditions) by the Limit Equilibrium Method. The stability analyses
have been carried out using the Bishop simplified method with circular sliding surfaces and using three different commercial codes.
Safety factor against hydraulic heave has been computed according to NTC 2008.
Slope failure under transient flow conditions by means of FEM analysis (PLAXIS Flow), in order to assess the time to approach
the steady state flow conditions. FEM analysis also considered the stability in the case of partial saturation since the water table is
usually few meters below the embankment base.
Susceptibility of the embankment and foundation soil to internal erosion phenomena. The paper also tries to clarify the redundant
terminology that is used to describe the same phenomenon and, at the same time, points out the need to use appropriate terminology
to describe different phenomena related to internal erosion.
Appropriate design of both repair of the failures and retrofitting of the surrounding areas has been achieved on the basis of the
above analyses. Assessment of the riskiest areas, considering the whole extension of the embankments, has been carried out by means
of expeditious criteria, which were based on the embankment geometry and the mechanical soil characteristics.
The analysis results show that, for the selected cross sections, the safety factors are rather small and approaching to unit if the
seepage forces are not considered. In the case of steady state flow, safety factor drastically reduces to values lower than one. The results
of the FEM analyses suggest that the partial saturation of the embankment-material mainly contributes to its stability in the absence
of filtration, leading to acceptable safety margins. A good characterization of the material under conditions of partial saturation would
allow applying the most appropriate hydraulic condition
GEOTECHNICAL CHARACTERIZATION OF THE FLOOD PLAIN EMBANKMENTS OF THE SERCHIO RIVER (TUSCANY, ITALY)
Full text linkThe flood plain embankments of the Serchio river have been constructed since the XVIII century and construction details are not known. These embankments have experienced failures several times during their life (last in December 2009). After the last event a detailed geotechnical investigation has been carried out. This paper discusses the necessary criteria for a cost – effective campaign considering the total length of the embankments (30 km) and the requested level of detail. In fact levee failure, although it is of limited extension, causes the achievement of the ultimate limit state of the entire embankment system. The campaign, in addition to laboratory tests, included boreholes, CPTu, permeability tests, 2D geo-electric tomography and 15 tests performed by the use of the continuous core drilling system. This last has proved to be a very useful tool for obtaining the more accurate evaluation of the in situ soil density (as confirmed by CPTu results). CPTu test, economical and expeditious, has proved to be an indispensable tool for delineating soil stratigraphy. In fact, their results combined with the borehole logs and laboratory testing provide extensive information. Geo-electric investigations can be very useful to highlight anomalies and heterogeneities in the cross section. Eventually, it is worthwhile to stress that embankments have generally a height of less than 4 m and a width between 1.2 and 3 m. This has restricted the investigation tools that could be used in this peculiar case
Adeguamento degli argini del Fiumer Serchio: Aspetti Geotecnici
Full text linkall’epoca, dei quali non si hanno sufficienti conoscenze. Essi sono stati oggetto di numerose rotte, di cui l’ultima
avvenuta in più sezioni nel dicembre del 2009. Dopo quest’ultimo evento le Autorità competenti hanno realizzato una
campagna di indagini geotecniche allo scopo di incrementare il livello di conoscenza sulle strutture arginali.
L’articolo si propone di discutere i criteri per la progettazione di una campagna di indagine che sia efficiente sotto il
profilo economico, considerato che la lunghezza complessiva degli argini è superiore ai 30 km ed il livello di dettaglio
richiesto deve garantire un livello di conoscenza alla scala della singola sezione. Il cedimento dell’arginatura in un
breve tratto, infatti, provoca l’allagamento di aree molto ampie e aumenta la fragilità del sistema di protezione. La
campagna di indagini effettuata comprende sondaggi geotecnici, CPTu, prove di permeabilità, tomografie elettriche
bidimensionali e l’uso di un campionatore stratigrafico autoinguainante, oltre a prove di laboratorio sui campioni
prelevati.
La disponibilità di dati ha consentito di verificare l’efficacia dei metodi indiretti (CPTu, tomografie elettriche) per la
definizione del profilo stratigrafico. Sotto questo aspetto si è potuto confermare che le prove CPTu sono uno strumento
molto efficace ed efficiente se l’interpretazione è opportunamente guidata e calibrata attraverso i sondaggi geognostici.
D’altra parte le tomografie geoelettriche consentono di individuare la presenza di anomalie o eterogeneità nelle sezioni
arginali. Si sottolinea che nel caso specifico non è stato possibile estendere il campo delle tecniche utilizzabili a causa
delle ridotte dimensioni degli argini.
A valle della caratterizzazione geotecnica sono state eseguite alcune analisi allo scopo di chiarire le cause delle rotte del
2009, indirizzare la progettazione delle misure di rinforzo dei tratti coinvolti dalle rotte e individuare i tratti
maggiormente a rischio di cedimento in modo da fornire all’Amministrazione uno strumento per indirizzare e dare
priorità agli interventi
STABILITY ANALYSIS OF THE SERCHIO RIVER FLOOD PLAIN EMBANKMENTS (TUSCANY, ITALY)
Full text linkFollowing the geotechnical characterization of 30 km long flood - plain embankments of the Serchio River (Tuscany – Italy), a number of numerical analyses have been carried out. The embankments have been constructed since the XVIII century and have experienced several failures in the years (the last in December 2009). The geotechnical characterization of the river embankments and the 2009 flood are described in a companion paper in this Conference. This paper shows the results of numerical analyses that have been carried out for various purposes. More specifically, the numerical analyses were carried out a) to clarify the causes of the December 2009 failures, b) to design appropriate repair of the failures and retrofit of the embankments in proximity of the failures (about 6 km) and c) to identify the most risk areas considering the whole extension of the embankments (30 km). The limit equilibrium method was used to assess the stability of the embankments under steady state flow conditions (areas close to the failures). For this analysis three different types of commercial software were used. The stability analyses were carried out using the Bishop simplified method with circular sliding surfaces. The different codes indicated very similar failure surfaces corresponding to the minimum (meaningful) values of the global safety factor. Some differences on the values of the global safety factor were observed by comparing the results obtained from the three codes. More specifically, the analyses results show that, for the selected cross sections, the safety factors are rather small and approaching to unity, if the seepage forces are not considered. In the case of steady state flow, safety factor drastically reduces becoming lower than one. This result apparently contradicts the fact that the considered embankments are standing up since centuries and failures occurred only in the occasion of floods. The FEM analysis (PLAXIS Flow) shows that the safety margins of the considered sections, in absence of filtration, are assigned to the partial saturation of the embankment. Unfortunately, an appropriate characterization of the material under conditions of partial saturation was not available. Therefore, the FEM analyses were also aimed at determining the necessary time to approach the steady state flow conditions. For the case under consideration it was estimated that 10 days are necessary to approach the steady state flow conditions. This time is apparently much longer than the duration of the longest flood event (few hours). From the above it is possible to conclude that the hypothesis of permanent flow is generally too cautious. Anyway for the failures under consideration, that have occurred with the concurrence of various adverse factors like the melting of the snow because of a sudden temperature increase and the contemporary long raining period (two consecutive floods), it is reasonable to assume that the permanent flow conditions were probably reached. In addition to the numerical analyses, evidences of the considered event and the susceptibility of the analyzed soil to piping phenomena have also been considered to find out all the possible causes and to design in an appropriate way both repair of the failures and retrofitting of the surrounding areas. Assessment of the most risky areas, considering the whole extension of the embankments (30 km), has been carried out following expeditious criteria which were based on the embankment geometry and the mechanical soil characteristics
Chromium phytoextraction using Phyllostachys pubescens (Moso Bamboo)
Full text linkNOVELTY STATEMENT Moso Bamboo has shown a great adaptability of growing in Mediterranean semi-arid conditions Moso Bamboo tolerance to contaminated water has been registered up to 125 g/cm(3) of chromium. Cr Phytoextraction from soil was found to be significant -43%-and Cr is accumulated mostly in the rootsIn this study, a bamboo species, the Phyllostachys pubescens - Moso Bamboo (MB) -, was selected for its heavy metals accumulation and translocation potential to restore Chromium (Cr)-contaminated soil. In order to evaluate the MB Chromium growth, tolerance and the potential for phytoremediation using MB to restore Cr-contaminated soil, pot experiments were carried out in simulated Mediterranean conditions in a laboratory, in a controlled environment, at a temperature of 20 degrees C. The results showed that MB growth rate was 4.28 cm/week on average, with an irrigation flow of 1.644 mm/d. MB tolerance was tested over a 12-week irrigation period with the addition of Cr-contaminated water. Cr removal from soil was 43% starting from a Cr content of approx. 200 mg/kg dry weight (dw) and the quantity of Cr per gram of root and rhizome was equal to 1.31 mg/g dw, while the quantity of Cr per gram of stem and leaves was equal to 0.86 mg/g dw, after 12 weeks. Pot experiments confirm that phytoremediation using plants such as MB provides an alternative approach for handling Cr-contaminated soil
Interpretation of CPTu in “unusual” soils
Full text linkThe paper deals with the interpretation of CPTu in unusual soils, such as shallow clayey layers above the water table and loose,
intermediate - permeability soils (loose silt mixtures).
The paper shows an approach that could be used for the first type of soil to infer the effective vertical stress from CPTu measurements
and in particular from the Ic index. The approach has been checked on a very limited amount of experimental evidence.
Moreover, an empirical correction of the Ic index is provided in order to obtain a more realistic soil profiling of loose silt mixtures.
The foundation soils of the Serchio River levee system and some dredged sediments, which had been stored in the Port of Livorno,
have been considered for the second type of soil
Manuale di Ingegneria Geotecnica volume II
No full textLa Geotecnica è una branca dell’Ingegneria Civile che rende possibile lo studio delle opere che interagiscono con il sottosuolo. Più precisamente ci si riferisce alla analisi di strutture di fondazione (superficiali o profonde), di opere di sostegno, di costruzioni in materiali sciolti (rilevati, argini, dighe in terra, etc.), di pendii naturali o artificiali (fronti di scavo, discariche, etc.), di costruzioni in sotterraneo (costruzioni interrate, gallerie, coltivazioni minerarie, etc.). Tali opere sono elementi importanti delle costruzioni e delle infrastrutture civili, il che fa della Geotecnica una disciplina trasversale.
L’analisi delle opere sopra menzionate ha l’obiettivo di verificarne la sicurezza e la fruibilità. Più semplicemente si tratta di verificare che la costruzione di una nuova opera non provochi fenomeni di collasso o spostamenti del terreno o della roccia tali da compromettere la sicurezza e l’uso dell’opera erigenda e di quelle limitrofe preesistenti.
Si comprende pertanto che la Geotecnica, come tutta l’Ingegneria, non ha finalità puramente scientifiche ma si pone il conseguimento di obiettivi pratici, il che fa della Geotecnica una disciplina Tecnico–Scientifica.
I terreni (o terreni sciolti) sono un mezzo poroso costituito da un insieme di particelle (scheletro solido) e da un fluido interstiziale (acqua e/o aria) che satura i vuoti o pori esistenti tra le particelle solide. Nonostante la natura particellare e multifase del mezzo e la grande variabilità delle dimensioni che tali particelle possono assumere, i terreni possono essere assimilati ad un mezzo continuo. Pertanto l’analisi dell’interazione opera – terreno può essere condotta facendo ricorso ai metodi tipici della Meccanica del Continuo. Al contrario l’ammasso roccioso (AR) è costituito da blocchi di roccia intatta (RI) separati da discontinuità. In questo caso, a seconda della scala del problema (dimensione dell’opera in rapporto alla distanza tra due discontinuità) è possibile continuare ad usare i metodi della Meccanica del Continuo oppure è necessario trattare l’AR come un mezzo discontinuo.
Premesso che l’Ingegneria Geotecnica, come per altro l’Ingegneria Civile tutta, fa spesso ricorso, in pratica, all’impiego di metodi empirici o semplificati, si comprende facilmente come la Meccanica dei Terreni e delle Rocce rappresenti lo strumento di analisi più avanzato disponibile. Per queste ragioni l’uso del presente manuale e lo studio della Geotecnica non può essere agevole senza un’adeguata conoscenza della Meccanica del Continuo (Scienza delle Costruzioni) e dell’Idraulica (si rammenti che l’acqua è presente anche nell’AR).
Il presente manuale è organizzato secondo le seguenti sezioni: a) genesi e classificazione di terreni e rocce, b) idraulica dei terreni, c) metodi di analisi e modelli di comportamento, d) metodi di indagine per la caratterizzazione meccanica dei terreni, e) la sicurezza e la Normativa Italiana, f) opere di sostegno, g) fondazioni superficiali, h) fondazioni profonde.
Il manuale è corredato da una serie di esercizi esemplificativi e da alcune esercitazioni progettuali di opere di sostegno e fondazioni.
Le esercitazioni progettuali e le sezioni indicate con f), g), h) sono contenute nel secondo tomo
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