Scour at Bridge Foundations in Supercritical Flows: An Analysis of Knowledge Gaps

The scour at bridge foundations caused by supercritical flows is reviewed and knowledge gaps are analyzed focusing on the flow and scour patterns, on available measuring techniques for laboratory and field, and on physical and advanced numerical modeling techniques. Evidence suggest that scour depth caused by supercritical flows is much smaller than expected, in the order of magnitude of that found in subcritical flows, although the reasons explaining this behavior remain still unclear. Important questions on the interaction of the horseshoe vortex with the detached hydraulic-jump and the wall-jet flow observed in supercritical flows arise, e.g. does the interaction between the flow structures enhance or debilitate the bed shear stresses caused by the horseshoe vortex? What is the effect of the Froude number of the incoming flow on the flow structures around the foundation and on the scour process? Recommendations are provided to develop and adapt research methods used in the subcritical flow regime for the study of the more challenging supercritical flow case.

Figure 1. Instantaneous bed surface and streamlines around a cylindrical pier.

How to cite: Link, O., E. Mignot; S. Roux; B. Camenen; C. Escauriaza; J. Chauchat; W. Brevis; S. Manfreda, Scour at Bridge Foundations in Supercritical Flows: An Analysis of Knowledge Gaps, Water (MDPI), 11(8), 1656; https://doi.org/10.3390/w11081656, 2019. [pdf]

PROGETTI COMPETITIVI

[2020-23] Coordinatore locale del progetto intitolato “La mitigazione del rischio idraulico in bacini costieri con casse di espansione in linea: approccio di dimensionamento integrato” finanziato dal Ministero dell’Ambiente e della Tutela del Territorio e del Mare sul tema progetti di ricerca finalizzati alla previsione e alla prevenzione dei rischi geologici. Coordinatore Nazionale Prof. Francesco De Paola (Budget totale 260.000,00 €).

[2019-22] Coordinatore italiano del progetto WATER JPI 2018 intitolato “An integrative information aqueduct to close the gaps between global satellite observation of water cycle and local sustainable management of water resources – iAqueduct”. Coordinatore Europeo Prof. Bob Su (Budget totale 1.247.018,00 €).

[2019-22] Coordinatore di unità di ricerca del progetto “SPRINt – Strategie integrate per la PRevenzione e il monitoraggio del rischio INcendi e la sensibilizzazione delle comunità”, Fondazione SUD (Budget totale 361.536,00 €).

[2017-18] Coordinatore del Progetto “Pietro della Valle” sul tema “Monitoraggio dello stato di imbibizione dei suoli in ambienti semiaridi” finanziato dal MIUR (Budget totale 9.422,00 €).

[2018] Componente del progetto REDES sul tema: Bridge scour in supercritical flows, Chilean Research Council (Budget totale 10.000,00 $).

[2017-21] Coordinatore europeo dell’Azione COST intitolata “Harmonization of UAS
techniques for agricultural and natural ecosystems monitoring
” (Budget 780.000,00 €).

[2014-19] Componente del progetto “Technologies to stabilize soil organic carbon and farm productivity, promote waste value and climate change mitigation – CarbOnFarm” LIFE12 ENV/IT/00719 (Budget totale 3.051.265,00 €).

The Theoretically Derived Probability Distribution of Scour

Based on recent contributions regarding the treatment of unsteady hydraulic conditions in the state-of-the-art scour literature, theoretically derived probability distribution of bridge scour is introduced. The model has been derived assuming a rectangular hydrograph shape with a given duration, and a random flood peak, following a Gumbel distribution. A model extension for a more complex flood event has also been presented, assuming a synthetic exponential hydrograph shape. The mathematical formulation can be extended to any flood-peak probability distribution. The aim of the paper is to move forward the current approaches adopted for the bridge design, by coupling hydrological, hydraulic, and erosional models, in a mathematical closed form. An example of the application of the proposed distribution has been included with the aim to provide a guidance for the parameters estimation.

How to cite: Manfreda S., O. Link, A. Pizarro, The Theoretically Derived Probability Distribution of Scour, Water, 10, 1520, 2018. [pdf]

BRISENT: An Entropy-Based Model for Bridge-Pier Scour Estimation under Complex Hydraulic Scenarios

The goal of this paper is to introduce the first clear-water scour model based on both the
informational entropy concept and the principle of maximum entropy, showing that a variational
approach is ideal for describing erosional processes under complex situations. The proposed
bridge–pier scour entropic (BRISENT) model is capable of reproducing the main dynamics of scour
depth evolution under steady hydraulic conditions, step-wise hydrographs, and flood waves. For the
calibration process, 266 clear-water scour experiments from 20 precedent studies were considered,
where the dimensionless parameters varied widely. Simple formulations are proposed to estimate
BRISENT’s fitting coefficients, in which the ratio between pier-diameter and sediment-size was the
most critical physical characteristic controlling scour model parametrization. A validation process
considering highly unsteady and multi-peaked hydrographs was carried out, showing that the
proposed BRISENT model reproduces scour evolution with high accuracy.

How to cite: Pizarro, A., C. Samela, M. Fiorentino, O. Link, and S. Manfreda, BRISENT: An entropy-based model for bridge-pier scour estimation under complex hydraulic scenariosWater, 9(11), 889 (doi:10.3390/w9110889), 2017. [pdf]

Effective Flow Work for Estimation of Pier Scour under Flood Waves

The pier scour caused by flood waves is analyzed, introducing the dimensionless effective work by the flow on the sediment bed around the pier, W*. The three-parameter exponential function is adopted to relate the normalized scour depth Z* with W*. A novel experimental installation able to reproduce any hydrograph with high precision in the laboratory flume is described and used to carry out four series of scour experiments in order to calibrate and validate the proposed relation. The first series consists of experiments with constant discharge until advanced stages of scour. The second and third series of experiments use single flood waves of different shapes and durations, respectively. The fourth series consists of scour experiments caused by more realistic flow hydrographs with multiple peaks. Results show that the relation between W* and Z* is unique and thus W* represents a reliable concept for the prediction of the flood wave scour because it appropriately integrates the effects of the hydrograph properties, duration, peak discharge, and shape, on scour. The proposed relation allows a straightforward prediction of maximum scour depth after a flood wave with high precision. A good agreement between measured and computed scour was observed in all cases.

How to cite: Pizarro, A., B. Ettmer, S. Manfreda, A. Rojas, and O. Link, Effective Flow Work for Estimation of Pier Scour under Flood WavesJournal of Hydraulic Engineering, 06017006-1-7, (doi: 10.1061/(ASCE)HY.1943-7900.0001295), 2017.  [pdf]

A Model for Local scour during Flood Waves

The time-dependent bridge pier scour during flood waves is analysed. Scour experiments were conducted in a novel installation able to produce complex hydrographs with high precision. Experimental data were used to test scour formulas including a new mathematical model. Results confirm the reliability and superior performance of the proposed dimensionless, effective flow work based model under steady and unsteady hydraulic conditions. Analyses highlight the impact of different hydrographs on scour, demonstrating the strong control by the hydrograph shape of the temporal evolution of scour depth and scour rate, although final scour after a flood only depends on the total effective flow work exerted by the hydrograph on the sediment bed. Hysteresis between flow discharge and scour rate is reported and explained. Flow acceleration is shown to play a minor role in scouring. The proposed model is a promising alternative for computation of local scour under highly unsteady hydraulic conditions.

How to cite: Link, O., C. Castillo, A. Pizarro, A. Rojas, C. Escauriaza, B. Ettmer, S. Manfreda, A Model for Local scour during Flood Waves, Journal of Hydraulic Research, 55(3), 310-323, (doi: 10.1080/00221686.2016.1252802), 2016.  [pdf]