Illuminating the internal condition of safety-critical infrastructure slopes: new geophysical approaches for landslide hazard assessment

Overview

Assessment of the condition of geotechnical infrastructure assets (e.g. cuttings, embankments, dams) and associated natural slopes is essential for cost effective maintenance and prevention of hazardous failure events. Infrastructure slopes in transportation, utilities and flood defences are experiencing increasingly high levels of failure and require considerable resources to maintain (hundreds of millions of pounds per year in the UK alone). This situation is being exacerbated by the greater prevalence of extreme rainfall events and flooding. However, slope stability monitoring is still dominated by surface observations, which provide infrequent information (walkover surveys are generally carried out only a few time per year) and deliver very little to no information on the internal condition of slopes (which is where failure processes generally occur). Consequently, they are inadequate for providing early warning of failure.

This project addresses this challenge by developing non-invasive geophysical approaches to improve our ability to model and monitor slope stability. The novelty in our approach is that we will shift slope monitoring from a sporadic ‘skin-deep’ approach to being able to continuously ‘see-inside’ the subsurface at high spatial and temporal resolutions. We aim to validate an integrated characterisation and slope stability modelling approach using two strongly complementary classes of geophysical techniques – geoelectrics and seismics. Geoelectrical measurements are sensitive to compositional variations and groundwater saturation/quality changes, whereas seismic measurements can provide information on geomechanical property variations (elastic stiffness and density) of the subsurface. The project will seek to harness 4D geophysical information streams to better inform geomechanical models of slope stability. The outcome of the project will be new tools to deliver enhanced condition assessment and early warning of infrastructure slope failure.

Methodology

(1) Geophysical – geotechnical property relationships: Property relationships between geophysical and geotechnical data will be investigated with the aim of providing geophysically derived geotechnical parameters for input into geomechanical models of slopes stability (see below (2) ‘Linked geophysical-geomechanical modelling’). The student will make use of state-of-the-art laboratories at BGS and NU to investigate material properties and petrophysical relationships of samples from project test sites (see below (4) ‘Site scale validation’). This work will involve training in laboratory methods and a three month placement at Newcastle University.

(2) Linked geophysical-geomechanical modelling: The student will become familiar with relevant geophysical and geomechanical modelling code, and will receive appropriate training in these methods. The aim of the project is not to develop new modelling code – instead the novelty will lie in developing interfaces between the geophysical and geomechanical models. The outcome of this component of the research will be an integrated slope modelling tool. A key aspect of the work will be to assess and quantify the uncertainty associated with the resulting models of slope stability.

(3) Controlled tank-scale testing: The methodologies developed in (1) and (2) will be tested using laboratory-scale simulations. Slopes will be constructed and monitored using geophysical and conventional sensors, and tested to failure in large laboratory tanks (BGS, Geophysical Hazards Laboratory). The resulting data will be used to assess the linked modelling approach, and given the highly controlled conditions, to investigate model uncertainty and resolution.

(4) Site scale validation: The project will have access to several slope monitoring sites that will be used by the student to test and validate the slope stability modelling and early warning approach. Key UK sites will include the BIONICS embankment, near Hexham (Newcastle University), Warden flood embankment, near Hexham (Environment Agency), Leys Bend highways slope, near Monmouth (Highways England). The student will also have the opportunity to work internationally at the Ripley Landslide Research Site in Canada (Canadian Geological Survey and CN and CP Rail) and the Munnar Landslide Research Site in India (Amrita University). The student will have the opportunity to undertake placements with one or more of the partner organisation linked to these sites.

Project Timeline

Year 1

• Literature review
• Design and set-up of laboratory programme to establish geophysical-geotechnical property relationships and tank-scale simulation studies.
• Familiarisation with geophysical and geomechanical modelling approaches.
• Selection of test sites – data review and initial analysis of existing data; initial data collection; refinement of monitoring/measurement infrastructure if required, and sample collection for laboratory testing.
• Training courses (dependent on background/skills/experience of student).

Year 2

• Laboratory investigation of petrophysical relationships for materials recovered from key test sites – particularly linking resistivity, shear wave velocity, soil suctions and soil moisture.
• Tank-scale experiments performed – with monitoring data generated for various slope and material types.
• Linked modelling approach tested initially against laboratory tank-scale data and calibrated using petrophysical relationship testing results. Initial assessments of model uncertainty.
• Ongoing collection of data at field test sites.
• LARAM training course (see ‘Training and Skills’) and other relevant training.
• Conference paper presented.

Year 3

• Detailed assessment of model uncertainty using synthetic and tank-scale data.
• Detailed assessment of linked modelling approach validated using field data.
• Case histories produced for key test sites.
• Journal paper submitted.
• Thesis preparation.

Year 3.5

• Thesis completion.
• International conference paper given.
• Journal paper submitted.

Training
& Skills

Formal training by the partner organisations:
The student will participate fully in the IAEPETUS training programme. In addition, the student will benefit from technical training in the areas of programming (e.g. Matlab, Python), geospatial data manipulation and visualisation (e.g. ArcGIS, GOCAD), and geophysics, engineering geology, geotechnics, slope stability modelling and hydrogeology. The appropriateness of specific courses will naturally depend on the background of the student. Likewise, personal effectiveness, engagement and communications training will be identified as appropriate.

External training courses:
The student will be encouraged to apply to attend the LARAM training course. LARAM is an International School on “LAndslide Risk Assessment and Mitigation” of the University of Salerno, Italy. The School is held annually and is aimed at PhD students selected every year from those working in the field of Civil Engineering, Environmental Engineering, and Engineering Geology or with a similar Engineering background. The School is residential.
‘Geophysics for environmental scientists’ is a NERC Advanced Training course designed for PhD students, with places allocated preferentially to NERC-funded students. The course runs periodically, and the student will be encouraged to attend if the opportunity arises.
Depending on the groundwater and slope stability modelling approaches identified by the student, additional external training for proprietary modelling packages will be arranged as necessary.

Informal training and supervisory arrangements:
The student will be embedded in the BGS Geophysical Tomography team, in which the BGS supervisors will operate an open-door policy. Formal supervisory arrangements will include 3-monthly supervision meetings including both BGS and Newcastle University supervisors. The student will also spend blocks of time (up to 6 months over the course of the PhD) at Newcastle University, where the focus will be particularly on geomechanical modelling and geotechnical testing.

References & further reading

Chambers, JE, et al., 2014. 4D Electrical Resistivity Tomography monitoring of soil moisture dynamics in an operational railway embankment. Near Surface Geophysics, 12, 61-72.

Crawford, MM, and Bryson, LS. [2018] Assessment of active landslides using field electrical measurements. Engineering Geology 233, 146-159.

Glendinning, S, et al., 2014. Construction, management and maintenance of embankments used for road and rail infrastructure: implications of weather induced pore water pressures. Acta Geotechnica, 9, 799-816.

Uhlemann, S, et al., 2014. Four-dimensional imaging of moisture dynamics during landslide reactivation. Journal of Geophysical Research: Earth Surface 122, 398- 418.

Further Information

For further information please contact:
Prof Jonathan Chambers, email: jecha@bgs.ac.uk, telephone: 01159363428
Prof Stephanie Glendinning, email: stephanie.glendinning@ncl.ac.uk, telephone: 01912086612

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