1,720,977 research outputs found
Local scour downstream of stilling basins
No full textIn this study some results on local scour downstream of stilling basins for low-head structures are presented. A number of laboratory experiments were conducted in a 1 m wide and 20 m long rectangular straight channel in which an ogee-crest spillway followed by a stilling basin type USBR IV (without chute blocks) was positioned. Two nearly uniform bed sediments were tested. The runs were of long durations, typically 3 days, to achieve conditions of quasi-equilibrium scour hole. Based on the data collected, a new relationship was conjectured relating the quasi-equilibrium scour depth to the tail water densimetric Froude number
Erosioni d'alveo in prossimita' degli attraversamenti fluviali: analisi di situazioni critiche osservate sui corsi d'acqua lucani
No full textVengono analizzate alcune criticita' osservate sui corsi d’acqua lucani la cui natura comporta che le situazioni di maggiore rischio di erosione siano spesso associabili a quegli attraversamenti realizzati in alvei alluvionati larghi. Almeno cio' e' quanto sembrerebbe emergere dagli oltre 200 sopralluoghi ad oggi effettuati. Sulla base poi dell’applicazione di un modello bidimensionale viene riportato un esempio di stima della vulnerabilita' delle strutture di appoggio di uno stesso attraversamento, dimostrando come essa possa assumere valori significativamente diversi
Riverbed scour induced by a long constriction
No full textThis study is a part of a more comprehensive research and is focused on the bed scour that would occur when rivers are forced by manmade or natural contractions. To this purpose, some experiments, typically lasted for days, were carried out at University of Basilicata in a straight rectangular channel and under clear water scour regime. The bed material was uniform sand and three contraction models, with opening ratio (i.e. ratio between the widths of the contracted and uncontracted reaches) of 0.9, 0.8, and 0.7, were used. Starting from the monomial form of sediment transport formulas, a new relationship for the quasi-equilibrium scour depth is conjectured based on Froude’s similarity and by relating the scour depth to the difference between the actual and the entrainment densimetric Froude numbers in the contracted zone. The proposed approach is validated by the data of the present study, and verified by available literature data
Fenomeni di erosione localizzata nell'interazione tra correnti fluviali e pile fondate su pali
No full textNella memoria vengono presentati i risultati ottenuti da un’indagine sperimentale sull’evoluzione temporale dei fenomeni erosivi locali nell’intorno di pile fondate su pali. Le prove sono state eseguite utilizzando due diverse installazioni e considerando la condizione, frequentemente riscontrata nella pratica, di plinto a raso rispetto al fondo alveo all’inizio dell’evento di piena. Sebbene non si proponga un’equazione di tipo generale, la cui definizione richiede ovviamente indagini aggiuntive dato il notevole numero di variabili in gioco, i risultati conseguiti forniscono significative indicazioni in tal senso, ma soprattutto evidenziano alcuni limiti degli attuali criteri proposti nella letteratura di settore
WebGIS per la ricostruzione storica dei paesaggi urbani
No full textIl saggio, dopo aver sviluppato il tema inerente la cartografia storica su Roma, espone i risultati di una lunga ricerca, coordinata da Paolo Micalizzi, finalizzata alla realizzazione e messa in rete di un sofisticato sistema informativo geografico sul centro storico di Roma, denominato Descriptio Romae WebGIS.The essay, having developed the theme concerning the historical maps of Rome, expounds the results of an extensive research, coordinated by Paolo Micalizzi, aimed at the creation and networking of a sophisticated geographic information system on the historic center of Rome, called Descriptio Romae WebGIS
Effects of pile caps on local scour at bridge piers
Full text linkThe most existing pier-scour equations mainly apply to uniformly shaped piers. However, pier footings may often project above the streambed because of scour. This may be caused by either long-term bed degradation or local scour. In such cases, the computation of the local bridge scour depth becomes complicated because of the difficulty in choosing an appropriate pier dimension. Referring to piers founded on piles, in previous papers some outcomes were achieved, mainly on the quasi-equilibrium scour depth. Based on additional experiments, this paper would like to come up with a deepening of the previous findings and provide new insights on the temporal evolution of the river-bed morphology around the complex pier-plinth-piles
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