“Rainfall-induced Landslides: Investigation of Structure & Hydraulic Processes”

1 2 1 1Andrew Merritt , Jonathan Chambers , William Murphy & Jared West 1School of Earth & Environment, Earth Surface Science Institute, University of Leeds; 2Geophysical Tomography & Transportation Geotechnics, British Geological Survey

Introduction

Conventional Landslide Monitoring

The need to develop geophysical imaging techniques which are capable of not [1], [2]only characterising subsurface geological structure but also of informing

about processes taking place in the subsurface are an essential step towards understanding the trigger mechanisms responsible for landslide activation and subsequent movement.The main aim of this presentation is to present the results of a conventional landslide monitoring investigation, plus, preliminary results of a landslide geophysical monitoring campaign using Electrical Resistivity Tomography.

Electrical resistivity tomography (ERT) is a geoelectrical geophysical method which is sensitive to subsurface lithology changes and structure, as well as

[4] [5]subsurface moisture saturation . Due to the sensitivity of ERT it is particularly appropriate for monitoring rainfall-induced landsliding as it has the potential to

[6]monitor subsurface hydraulic changes associated with slope failure .

Fig.3. Plot of Peg Movement by RTK-GPS , showing movement along geophysical survey lines (See fig.1 & 2).

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Fig.2. Peg Number(x-direction perpendicular to survey line, y-direction parallel to survey line

The Landslide at Hollin Hill is investigated by several means, including:

Fig.4. Effective Rainfall & Piezometry Plot at Hollin Hill

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32

Abstract

Fig.1. Aerial Image of Hollin Hill Research Site.

Geoelectrical Monitoring of Landslides

Fig.5. Tiltmeter Results from 2009 Fig.6.Interpreted Stratigraphy of Hollin Hill Landslide System

Borehole 1 Borehole 5 Borehole 7

References

The study area is located at Low Mowthorpe, 12 miles west of the North Yorkshire town of Malton. Geographically, the study area is located within a south-facing Lias Group escarpment and is bound to the south by a broad topographic embayment (Fig.1).

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Results of ERT Survey

Fig.9. (left) Interpreted profile of an ERT survey o f t h e H o l l i n H i l l Landslide System.

FlowSlumping

Fig.8. (below) Two volumetric images of resistivity distribution from Hollin Hill.

Fig.10. Photograph of an active flow deposit from Hollin Hill Landslide System.

North South

Peg Movement by GPS

Rainfall & Piezometric Level

Borehole Tiltmeter Intrusive Investigation - Drilling Campaign

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This poster presents the results to date of a landslide monitoring campaign featuring both geophysical and conventional monitoring methods. The landslide system is within Lias group formations of the Lower Jurassic. The landslide is monitored using a three-dimensional geophysical method, affording the ability to observe a three-dimensional subsurface geological structure in its entirety. This is as opposed to discrete sampling or two-dimensional geophysical methods, which do not permit volumetric observations.

Geological Model

Research Site

[2] FRIEDEL, S., THIELEN, A. & SPRINGMAN, S. M. 2006. Investigation of a slope endangered by rainfall-induced landslides using 3D resistivity tomography and geotechnical testing. Journal of Applied Geophysics 100-114.

[3] JONGMANS, D. & GARAMBOIS, S. 2007. Geophysical investigation of landslides : a review. Bull. Soc. géol. Fr. , 178, 101-112.

[1] PERRONE, A., IANNUZZI, A., LAPENNA, V., LORENZO, P., PISCITELLI, S., RIZZO, E. & SDAO, F. 2004. High-resolution electrical imaging of the Varco d'Izzo earthflow (southern Italy). Journal of Applied Geophysics, 17-29.

[4] CHAMBERS, J. E., GUNN, D. A., MELDRUM, P. I., WILKINSON, P. B., OGILVY, R. D., HASLAM, E., HOLYOAKE, S. & WRAGG, J. 2011a. Volumetric imaging of earth embankment internal structure and moisture movement as a tool for condition monitoring. Railway Engineering 2009, 11th International Conference and Exhibition, University of Westminster, London, UK, 29th-30th June.

[5] CHAMBERS, J. E., MELDRUM, P. I., GUNN, D. A., WILKINSON, P. B., MERRITT, A., MURPHY, W., WEST, L. J., KURAS, O., HASLAM, E., HOBBS, P., PENNINGTON, C. & MUNRO, C. Year. Geophysical-geotechnical sensor networks for landslide monitoring. In: The Second World Landslide Forum, 3-7 October 2011b Rome.

Staithes Sandstone Formation

Whitby Mudstone Formation

DoggerFormation

Redcar MudstoneFormation

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Mainscarp

Minorscarp

Ancient Flow Deposits

Recent Flow Deposits

Failure Surface

BH7 BH5Topsoil0.0

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Fig.7.Geological Model of Hollin Hill research site.