New geophysical approaches for the geotechnical assessment of safety critical infrastructure slope stability

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. Early identification of deteriorating condition allows for low cost preventative remediation (post failure interventions are typically ten times more expensive) and reduces the risk of catastrophic failures. 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 generally initiates). Consequently, they are inadequate for providing early warning of failure.

This project addresses these challenges 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 via lab-scale slope failures simulations and field-scale datasets from world-class UK-based and international slope monitoring sites. This will be achieved 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) Site scale investigations: The project will have access to several slope monitoring sites. The site investigation and monitoring data provided by these sites will be used by the student to develop, test and validate the slope stability modelling and early warning approach (see below (4) “Linked geophysical-geomechanical modelling”). Key UK sites available to the project include the BIONICS research embankment, near Hexham (Newcastle University), Warden Flood Embankment, near Hexham (Environment Agency) and 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 3 month placements with one or more of the partner organisation linked to these sites.

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

(3) 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 (4) “Linked geophysical-geomechanical modelling”). The student will make use of state-of-the-art geophysical and geotechnical laboratories at BGS and NU to investigate material properties and petrophysical relationships of samples from project test sites (see (1) “Site scale investigations”). This work will involve training in laboratory methods and a three month placement at Newcastle University.

(4) Linked geophysical-geomechanical modelling: Novel modelling methodologies will be developed based on site scale data from (1) and data in highly controlled conditions from (2). The student will need to familiarise themselves with the state-of-the-art in geophysical and geomechanical modelling. 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. The student will become familiar with key geophysical and slope stability modelling codes – and will receive appropriate training in these methods. A key aspect of the work will be to assess and quantify the uncertainty associated with the resulting models of slope stability.

Project Timeline

Year 1

Activities:
– Literature review
– Introduction to geophysical methods
– Training in experimental design, instrumentation and slope stability modelling
– Design of field, laboratory and modelling programme
Key milestones:
– Detailed project scope agreed
– Student progress review

Year 2

Activities:
– Main programme of laboratory testing initiated
– Sample collection for laboratory testing at identified field sites
– Tank-scale experiment running
– Linked geotechnical-geophysical modelling initiated
Key milestones:
– Annual review
– Conference paper given

Year 3

Activities:
– Complete lab activities and supporting field activities
– Complete data analysis and modelling
– Presentations in scientific/technical meetings
– Development of good practice guidance
Key milestones:
– Annual review
– Laboratory experiments complete
– Conference presentation
– Journal paper submitted

Year 3.5

Activities:
– Thesis completion
Key milestones:
– Journal paper submitted
– Thesis submitted

Training
& Skills

Formal training by the partner organisations:
The student will participate fully in the IAEPETUS training programme and events during their studentship. In addition, the student will benefit from technical training courses in the areas of programming (e.g. Matlab, Python), geospatial data manipulation and visualisation (e.g. ArcGIS, GOCAD), machine-learning approaches (Scikit-Learn), and geophysics, engineering geology, geotechnics, slope stability modelling and hydrogeology. The student will also have the opportunity to attend any module on the MSc courses Engineering Geology or Geotechnical Engineering delivered by Newcastle University. 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. 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. On-the-job training will also be undertaken through a placement (up to 3 months over the course of the PhD) at TerraDat Uk Ltd (CASE Partner) during which the student will gain experience in the use of geophysical methods applied to a series of ground hazard and geotechnical problems.

References & further reading

Chambers, JE, Gunn, DA, Wilkinson, PB, Meldrum, PI, Haslam, E, Holyoake, S, Kirkham, M, Kuras, O, Merritt, A, Wragg, J., 2014. 4D Electrical Resistivity Tomography monitoring of soil moisture dynamics in an operational railway embankment. Near Surface Geophysics, 12, 61-72.
Crawford, M. M. and Bryson, L. S., 2018. Assessment of active landslides using field electrical measurements. Engineering Geology 233, 146-159.
Glendinning, S., Hughes, P., Helm, P., Chambers, J., Mendes, J., Gunn, D., Wilkinson, P. and Uhlemann, S., 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.
Hen-Jones R.M., Hughes P.N., Stirling R.A., Glendinning S., Chambers J.E., Gunn D.A., Cui Y-J., 2017. Seasonal effects on geophysical-geotechnical relationships and their implications for electrical resistivity tomography monitoring of slopes. Acta Geotechnica, 12(5), 1159-1173.
Uhlemann, S., Chambers, J., Wilkinson, P., Maurer, H., Merritt, A., Meldrum, P., Kuras, O., Gunn, D., Smith, A. and Dijkstra, T., 2017. Four-dimensional imaging of moisture dynamics during landslide reactivation. Journal of Geophysical Research: Earth Surface 122(1), 398- 418.
Whiteley, J.S., Chambers, J.E., Uhlemann, S., Wilkinson, P.B. and Kendall, J.M., 2019. Geophysical monitoring of moisture-induced landslides: a review. Reviews of Geophysics, 57(1), pp.106-145.

Further Information

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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