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Dissolution subsidence affords some of the most difficult ground conditions with which engineering geologists have to deal. Within the UK, areas underlain by gypsiferous Permo-Triassic strata, most notably around Ripon in Yorkshire, are prone to dissolution structures and resultant building failures are well documented. Conventional drilling of such unstable sites is often a 'hit and miss' affair and most geophysical techniques do not provide sufficient resolution to offer adequate confidence in the results. Proposals for the redevelopment of a site within the urban area at Ripon could not rely on such frequently inconclusive methods and it was necessary to implement a phased approach to site investigation. Following a desk study, high-resolution microgravity geophysics was carried out both inside and outside the existing building. This indicated a major negative anomaly of peak amplitude-74 µGal. Subsequent static core probing, rotary drilling and trial trenching confirmed the existence of a potentially unstable breccia pipe which could therefore be taken into account in the engineering design.

This paper presents an approach for considering the performance of infrastructure assets within a robust riskbased framework such that investment choices can be determined in a more transparent manner. Asset performance is defined in terms of the service delivered by the asset, not the asset condition alone. Risks associated with the future performance of infrastructure assets (roads, bridges, earthworks etc.) should be defined using cross-asset terminology and use the corporate risk scoring structure of the infrastructure owner/operator to ensure consistent investment decisions are made.A case study is presented for highway geotechnical assets, i.e. the embankments, cuttings and underlying ground that support the highway components. Important issues such as the inherent variability of geological materials, the low probability but high consequence of earthworks failures, and the complex interaction between earthworks and other highway assets are discussed. The benefits of making asset investment decisions with due consideration of the associated risks to service are illustrated.

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As part of a coordinated programme of knowledge improvement tasks, Highways England commissioned Mott MacDonald to research, develop and implement a series of maps to communicate clearly the threat posed by ground-related hazards to the Strategic Road Network (SRN) of England. Events associated with a number of hazards have occurred in the recent past. Understanding the presence, and relative likelihood of occurrence, of these hazards over the 7000 km of the SRN is an essential risk management activity. The maps draw on readily available data sources held on the Geotechnical Data Management System of Highways England (HAGDMS) and have been deliberately created to be open and simple, to convey the hazards to users who may not be specialists in engineering geology. This paper presents the development, validation and application of the hazard maps.Thematic collection: This article is part of the Ground-related risk to transportation infrastructure collection available at: https://www.lyellcollection.org/cc/Ground-related-risk-to-transportation-infrastructure

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