Literatura académica sobre el tema "SRICOS-EFA"

The scour rate found by the cohesive soil-erosion function apparatus (SRICOS-EFA) method provides more accurate and realistic scour predictions than the Richardson and Davis equation, which tends to overpredict scour, especially in cohesive soils. Scour of cohesive soil occurs more slowly than scour of cohesionless soils. The time-dependent nature of scour of cohesive soils can be understood by considering both the variation of flood intensity over time and the scour characteristics of the soil, with an erosion rate curve obtained with an erosion function apparatus (EFA). One drawback of the SRICOS-EFA method is that the EFA requires a significant cost outlay. A model for the erosion rate curve is proposed on the basis of EFA tests conducted on 31 undisturbed fine-grained soils from five water channels on the island of Oahu, Hawaii. A hyperbolic regression model was developed with four explanatory variables: water content, liquid limit, plasticity index, and activity, which are easily measured in the laboratory. Parameter estimates for the model were then obtained using nonlinear ordinary least squares. A key element of the model is that the parameter estimates logically affect the sign and magnitude of critical shear stress, in accord with observed soil behavior—that is, it was found that the model captured the effects of water content and plasticity index on the critical shear stress quite effectively. Also, the model provided reasonable estimates of the 31 erosion rate curves. Use of this model in the SRICOS-EFA method to estimate scour depth can result in less scour and can result in significant bridge cost savings.

A method called SRICOS-EFA is presented in this dissertation for scour prediction. The method is based on the calculation of two basic parameters: the maximum depth of scour and the initial rate of scour. The maximum depth of scour is based on an equation obtained from flume tests and the initial rate is based on an equation giving the initial shear stress obtained from numerical simulations. The initial scour rate is then read on the Erosion Function Apparatus (EFA) erosion function curve at the corresponding value of the calculated shear stress. A hyperbola is used to connect the initial scour rate to the maximum scour depth and describes the complete scour depth vs. time curve. The erodibility function curve can be measured in the EFA. As the results show, the SRICOS-EFA method can handle the multi-flood hydrograph and multilayer soil system. It can be used to solve the complex pier and contraction scour alone; it can also handle the superposition of complex pier scour and contraction scour. A simplified SRICOS-EFA method was developed based on the case histories for contraction scour. EFA tests were performed to investigate the influence of different pH values and different levels of salinity on the soil erodibility. An attempt was made to find the correlation between the critical shear stress, and the initial slope of the erodibility function on the one hand and some geotechnical parameters on the other. A solution for future hydrograph prediction was developed in this dissertation. The prediction consists of using a past hydrograph, preparing the frequency distribution plot for the daily stream flows, sampling the distribution randomly and preparing a future hydrograph, which has the same mean and standard deviation as the measured hydrograph. A frequency distribution plot of scour depths can be used to quote a scour depth with a corresponding probability of occurrence and risk level based on future hydrographs. In the verification process, 10 bridge case histories and 3 scour databases were used to check whether the method is good enough to provide sound results in real cases.

Thesis (M.S.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Dept. of Civil and Environmental Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

L’affouillement local autour des piles est considéré comme un des principaux risques de rupture et d’effondrement des ponts. Les expériences en laboratoire sont un élément crucial de l’étude du processus d’affouillement. Pourtant, il n’existe pas d’instrument robuste et standard pour suivre l’évolution de ce phénomène physique dans les études de laboratoire. Les études expérimentales en canal sur l’affouillement autour d’une pile circulaire dans un sol non cohésif sont nombreuses. Cependant, le lit des canaux alluviaux naturels contient souvent des sédiments cohésifs. Comparativement, il existe peu de recherches sur l’affouillement local autour des piles circulaires fondés dans des lits cohésifs. Dans le cadre de cette recherche doctorale, un scanner laser 3D est utilisé pour suivre l’affouillement local autour d’une pile circulaire. Les résultats obtenus avec cette technique, en accord avec les recherches précédentes, notamment celles effectuées sur un lit de sable, démontrent son efficacité. Elle offre des avantages tels qu’une résolution spatio-temporelle continue, mais aussi de nombreuses limitations. Dans une seconde étape, l’étude a porté sur l’effet du type et de la proportion des fines sur la profondeur et la forme de la fosse d’affouillement et sur la propagation temporelle du processus d’affouillement autour du pile circulaire. Les résultats montrent que l’augmentation de l’argile dans la fraction fine réduit significativement l’affouillement. Le mélange avec une gamme d’environ 7.5-10 % de teneur en argile fournit la composition seuil pour un comportement cohérent du sol dans le processus d’affouillement. En outre, la prédiction de la profondeur d’affouillement dans les sols cohésifs dans la conception des fondations de ponts n’est pas encore complètement développée. Dans la pratique, les méthodes d’estimation de la profondeur d’affouillement actuellement utilisées sont celles proposées pour des sols non cohérents. De nombreux chercheurs ont mis au point des méthodes pour optimiser la conception des piles de pont dans le cas d’un sol cohésif. Parmi elles, celle basée sur l’utilisation de l’érodimètre EFA (Erosion Function Apparatus) et appelée SRICOS (Scour Rate In COhesive Soil) a été examinée dans le cadre de ce travail afin de prédire la profondeur d’affouillement maximal dans un lit cohésif
Local scour is considered to be one of the main causes of bridge failure and collapse. Laboratory experiments are a crucial and important approach for the scour process investigation. Yet, there is no robust and standard instrumentation for tracking the evolution of this physical phenomenon in laboratory studies. There are several flume-based studies of scour around a circular bridge pier on cohesionless soil. However, the bed of natural alluvial channels often contains cohesive sediments. Comparatively, there is a limited research on local scour around circular pier founded in cohesive beds that has been documented. In this PhD research, a 3D Laser Scanner is used to monitor scour around a circular pier. The results obtained with this technique, in line with previous research, in particular that carried out on a sandy bed, demonstrate its effectiveness. The technique offers advantages such as continuous spatiotemporal monitoring, but also many limitations. In a next step, the study focused on the effect of the type and proportion of fines in the sediment mixture on the depth and the shape of the scour hole and the temporal propagation of scour process around a circular pier. Results show that increasing the clay in the fine fraction reduce significantly the scour. The mixture with a range around 7.5-10 % of clay fines content provides the threshold composition for coherent soil behavior in scouring process. In addition, scour depth prediction for bridge piers in cohesive soil is not yet fully developed. In engineering practice, scour depth estimation methods currently used are those proposed for sand bed. Many researches aimed to adress a method to optimize the design of bridge piers in the case of cohesive soil. Among the different methods, the one based on the use of the EFA (Erosion Function Apparatus) erodimeter and called SRICOS (Scour Rate In COhesive Soil) was examined as part of this work in order to predict the deepest scour in cohesive bed