Advancing UK seismic safety: exploring the 2020 hazard maps, piezometer challenges, and soil dispersion insights

Overview

The lecture will take place following the British Dam Society (BDS) Annual General Meeting (AGM).

The BDS Annual General Meeting will be followed by a series of presentations covering papers submitted to the BDS conference in 2024, including the 2020 national seismic hazard maps (UK), the use of vibrating wire piezometers to measure pore water pressures, and the effect of pretreatment of organics in dispersion tests.

The 2020 national seismic hazard maps for the United Kingdom

The 2020 seismic hazard maps for the United Kingdom update the previous national maps published in 2007 and are used to revise the UK National Annex for the second-generation Eurocode 8. 

The 2020 national seismic hazard model uses an up-to-date earthquake catalogue for the British Isles, for which the completeness periods have been reassessed. It also uses a modified version of the 2007 source model and incorporates some advances in ground motion modelling since 2007.

For the first time, the national maps for the UK are provided for not only peak ground acceleration but also spectral acceleration at 0.2 s and 1.0 s for 5% damping on rock and the four return periods (i.e. 95, 475, 1100, and 2475 years).

The maps confirm that seismic hazard is generally low in the UK and is slightly higher in North Wales, the England-Wales border region, and western Scotland. We have disseminated the 2020 national seismic hazard maps for the UK via a dedicated webpage, downloadable data, models and outputs, interactive mapping tools, linkages with professional bodies and industry, as well as public seminars, webcasts, and attendance in scientific conferences.

This talk will present an overview of the 2020 national seismic hazard model and accompanying seismic hazard maps for the UK and will explain the general use and importance of a national hazard map to provide guidelines about designing earthquake-resistant structures.

The use of vibrating wire piezometers to measure pore water pressures in dams

A knowledge of pore water pressures in embankment dams and in mining dams is essential to monitor performance.

In many instances, this knowledge forms part of a critical risk control to prevent a high consequence event, such as global instability and release of containment.

Yet, the field measurement of pore water pressures can be challenging, particularly if these are below atmospheric pressure.

Vibrating wire piezometers are used in many instances to monitor pore water pressures in dams, both in the foundation and in the fill; yet, these instruments have not been designed to measure sub-atmospheric pressures. 

The presentation will touch on the challenges of interpreting data from vibrating wire piezometers installed in an unsaturated soil.

The Effect of Pretreatment of Organics in Dispersion Tests 

Internal erosion in clayey soils is associated to the identification of dispersion, as this can be a major contributing factor in piping failure of earth embankment dams. For dams constructed without filters and of poor construction, it is critical to understand the nature of dispersive soils so they can be treated or appropriate remedial measures applied.

This paper describes tests carried out using the Double Hydrometer Test, a type of physical dispersion test, on a representative core sample from a Pennine-type dam in Yorkshire. The determined potential for dispersion is compared for the soil tested with pretreatment using hydrogen peroxide to remove organic matter and without pretreatment.

As well as highlighting the importance of pretreatment in determining the potential for dispersion, the results demonstrate that the amount of soil used in the hydrometer test should be carefully considered to avoid both hindered settling (using too much soil) at one extreme and poor
hydrometer response (using too little soil) at the other end.

Programme