Author(s): Ricardo A. Gonzalez Flores; Luigiabrandimarte; Giuliano Di Baldassarre; Arthur Mynett
Linked Author(s): Arthur Mynett
Keywords: Contraction scour; Bridge scour; Monte Carlo; Cohesive soils; Probabilistic approach
Abstract: Abrupt contractions are frequently encountered along watercourses as a result of either natural catastrophic events (e. g., tree fall, landslides, river bank failures, etc. ) or of the construction of bridges and control sections. In the case of gentle slope channels, the velocity increases through the contraction. Depending on the shear strength of the bed sediments, the larger flow velocity may scour the river bed with a consequent increase in water depth at the contraction until the shear stress exerted by water flow is reduced below the shear strength of the bed material. Thus, after the stream width is locally reduced, the riverbed undergoes a local adjustment, leading to the development of a scour hole. In the case of cohesionless bed material, this transient can be relatively short. Conversely, in the case of cohesive bed, because of the physiochemical interactions between colloidal particles in fine-grain soils the scour progresses at a slower pace. This implies that a realistic scour depth assessment should be based on the analysis of a long sequence of river flows. Because of the limited length of the historical records, stochastic techniques can be used to generate longer series of stream discharges. This research work aims at understanding the behavior of contraction scour in cohesive soils along the lifetime of the structure, by analyzing the sensitivity of the variables playing a role in the scour process. A Monte Carlo approach is used to establish the probability density function and exceedance probability of the estimated scour depth values for different expected lifetime of the structure.