Risk-based bridge scour management:a survey

Scour is one of the major causes of bridge failure worldwide and results in significant economic losses through disruption to operation. This phenomenon naturally affects bridges with underwater foundations and is exacerbated during high river and/or turbulent flows (e.g. due to extreme events). When scour reaches the bottom or undermines shallow foundations it is likely to trigger various damage mechanisms that may in-fluence the safety of the structure and force asset managers to reduce traffic capacity. Currently, assessing risk of scour is a heuristic process, heavily reliant on qualitative approaches and expert opinion (e.g. visual inspections). These types of assessments typically suffer from insufficient knowledge of influencing factors (e.g. hydraulic parameters) and the requirement to rely on several assumptions (e.g. foundation depth). As a result, current scour assessment and bridge management practices do not provide reliable solutions for ad-dressing the potential risk of bridge failures. In this paper, cross-cutting needs and challenges related to the development of decision support tools for scour-risk management are highlighted and some preliminary re-sults of a literature survey are reported. The review has been performed with several objectives: (i) identify-ing scour-risk indicators describing hydrodynamic actions and the asset condition; (ii) defining indirect and direct consequences needed to assess the risks associated to different decision alternatives related to scour management; and (iii) identifying existing approaches to scour inspections and monitoring as support tools for informed decisions. The results of this survey will serve as a base for future research aimed to develop an informed decision support tool to manage scour risk at both the bridge and at the network level

Validation of the applicability of the PS logger borehole probe for diverse geotechnical scenarios

The PS logger is a low frequency dipole-based sonic logging probe which is used widely to measure P- and S- wave velocities of earth materials. It is of particular interest to offshore environments where the latter can be used to derive the small-strain stiffness Gmax, an important measurement in offshore construction. The method relies on the indirect excitation of the borehole via a dipole pressure wave excited in the borehole fluid, allowing shear wave velocity (Vs) to be measured in both fast and slow formations. In this study, the theoretical basis for the PS logger is presented, alongside the results of recent field projects which provide answers to key questions regarding the viability of the tool for a range of situations, and to the interpretation of results for widely ranging ground conditions. These include a comparison of results from both uncased (open) and cased boreholes, and from a wide range of ground velocities (Vs ≈ 220m/s to 3760m/s), and for varying borehole sizes. Full waveform analysis of time-series data is undertaken and underlines the need for consideration of theoretical principles in data interpretation. Ultimately, the results demonstrate the wide applicability of the tool beyond the geotechnical limits of traditional logging tools, which is attributed largely to the low frequency nature of the PS logger