Field monitoring sites
Field monitoring has helped to quantify typical magnitudes and spatial heterogeneity of moisture change and deformation at the appropriate scale. However, the detail of many mechanisms causing changes to the climate-vegetation-soil system in slopes remains uncertain, in particular:
- the development of near-surface instability, creep and deeper progressive failure — and how these are driven by cyclic changes in pore water pressure
- re-wetting processes, including wetting front progression via profile
- climate controlled infiltration and flow through tension cracks
- unsaturated soil behaviour and its influence on mechanisms of fluid flow, shrinkage, and accumulation of strain
Monitoring and experimentation at this scale at a range of sites are needed to determine the selection of suitable numerical models and parameters (e.g. permeability) for analysis and design for stability, serviceability and remediation.
These sites also provide a platform for the technical evaluation of emerging techniques for monitoring, including at real-time for both strategic and tactical level assessment, and to provide the inputs for data capture and visualisation.
Monitoring data are generated from both point sensors (e.g. tensiometers, TDR) and geophysical imaging sensor arrays (e.g. electrical resistivity tomography) to capture property variations at a range of scales. This approach facilitates fully volumetric (3D) subsurface characterisation and monitoring.
The field monitoring sites from which data are collected are:
- Newbury, Berkshire: an 8 m high cut slope in London Clay, built 1999, with rough grass and shrub cover. We have eight years continuous data from instruments measuring pore water pressure, water content and climate.
- Hawkwell, Southend: an 8 m high London Clay embankment, built around 1880. Mature trees on the slope were felled in March 2007 to give the present rough grass and shrub cover. We have five years of monitoring data of vertical and lateral displacement, water content, pore water pressure and rainfall.
- BIONICS, Newcastle: a purpose built embankment research facility, comprising a 6 m high, 90 m long glacial till embankment built in 2006 with extensive instrumentation measuring vertical and lateral displacement, pore water pressure/suction and water content. Uniquely, the facility allows climate control over parts of the slope.
- Loughbrickland, Northern Ireland: a 10 year old, 24 m high road cutting in glacial till overlying permeable shale, built and instrumented in 2003 to measure pore water pressure/suction and near surface water content changes.
- Craigmore, Northern Ireland: a 22 m high, 150 year old steep railway cutting in glacial till over low permeability granite rock. This site has a weather station, nested deep piezometers, two Enviroscan systems for measurement of water content, and a significant dataset on near-surface permeabilities using the Guelph permeameter.
These five sites provide a range of embankments or cuttings, age, soil types, vegetation and climatic environments representative of the UK. They are supplemented by monitoring data from other sites monitored by the iSMART team, e.g. Pound Green (London Clay embankment built about 1880, with three years of data), Tullyhappy (modern road cutting in glacial till), Charing (old Gault Clay railway embankment), Great Central Railway (end-tipped Mercia Mudstone; six years of data).