Geophysical assessments of river levee strength

The levee’s of many UK rivers provide not only important flood defenses, but also a platform for equipment used in dredging and weed control. Many levees were established centuries ago using poorly understood methods, and as such their geotechnical properties are also poorly understood. In 2010, the death of a crane operator dredging in Cambridgeshire led to a review of health and safety guidlines and the geotechnical properties of levees. Conventional geotechnical surveys assess soil and rock strength using borehole methods and laboratory testing of cored samples. Whilst these approaches are accurate along the borehole trajectory, they are time consuming and lack areal coverage. An attractive alternative is to use geophysical methods to assess ground strength. This requires a good understanding of the connections between geophysical properties, such as seismic velocity and electrical conductivity, and geotechnical parameters, such as shear strength and unconfined compressive strength.

Project Aims and Methods
The aim of this project is a systematic assessment of the geotechnical strength of river levees using a range of geophysical methods. Seismic methods will be used to determine the link between shear-velocity and shear-strength in UK river levees. Furthermore, the role of water in levee strength and how it affects seismic velocity and electrical conductivity will be evaluated. An objective is to develop a code of best practice for geophysical surveys of levee strength in the UK.

The project will start with fieldwork on rivers of the Somerset levels (e.g., the River Brue). Seismic P-wave and S-wave surveys will be conducted to assess seismic velocities. These will be complimented with the application of the MASW (Multi-channel Analysis of Surface-waves) method. Resistivity and electromagnetic surveying will be used to assess the conductivity structure of the levees. Geotechnical measurements will be obtained through standard tests (e.g., shear-vane resistance and penetration tests). These will be complimented by a systematic survey of existing geotechnical surveys of levees in the UK. The result should be region-specific guidelines for geophysical surveys to assess levee strength.

Candidate
This project would suit a candidate with a background in quantitative geosciences, geophysics, physics or engineering. A good numerical background, including programming skills are an asset. The project will involve field work in often harsh and challenging conditions. A clean driver’s licence would be advantageous.

Case Award
This project will be collaborative between Bristol, the British Geological Survey (BGS), the Environment Agency (EA) and RSK Geophysics. Bristol has extensive expertise in using seismic methods to study the near-surface, whilst the BGS are world-leaders in using electrical methods to monitor ground stability. The student will learn about river-levee management and collect geotechnical information during internships at the EA offices in Bridgwater. Training and exposure to current equipment will be provided by RSK, a consultancy that specialises in surveys of the built and natural environment.

Training
In addition to standard Bristol DTP training, the student will receive training in state-of-the-art geophysical surveying, such as those that employ seismic and electrical methods, and the accompanying data processing, reduction and interpretation. Additionally, the student will receive instruction in geotechnical methods such as soil and rock strength assessment, shear-vane surveys and land surveying. Skills in technical report writing will also be developed as the student will be required to present regular updates to the CASE partners. The resulting training will equip the student for a career in geotechnical or engineering geophysics on a range of length scales.

More information on the application process can be found here: http://nercgw4plus.ac.uk/research-themes/prospective-students/