Amodel of electrical conduction through clay-coated, silt-sized quartz-grains inter-connected by clay-bridges (e.g. brickearth) is developed. Underpinned by SEM studies of brickearth, the model predicts resistivity to be proportional to the size of the quartz-grains, where the resistance afforded by clay grain-coatings and clay-bridges is comparable. The model accommodates resistivity that increases through bridge breakage and decreases through bridge compression. The resistivity of in-situ undisturbed brickearth was found to be in the range 15 to 35 ohm-m. At such low values we demonstrate that electrical flow is dominated by conduction within clay-coatings and their interconnecting clay-bridges, rather than in mobile pore-water. A small electrode array, buried at shallow depth beneath the load plate (1.0 m by 1.0 m) of a field collapse experiment, monitored resistivity to a depth of 1.5 m over a 260 hour period. While the water level beneath the load plate remained below 1.0 m depth, the resulting 3D inverted resistivity models detected water injected immediately beneath the plate; recording rapid increases, in stages over 90 minutes, in the depth interval 0.45 to 0.75 m directly under the plate, during what appears to be collapse. These increases are attributed to breaking of clay-bridges weakened by injected water.
A landslide complex in the Whitby Mudstone Formation at Hollin Hill, North Yorkshire, UK is periodically re-activated in response to rainfall-induced pore-water pressure fluctuations. This paper compares long-term measurements (i.e., 2009–2014) obtained from a combination of monitoring techniques that have been employed together for the first time on an active landslide. The results highlight the relative performance of the different techniques, and can provide guidance for researchers and practitioners for selecting and installing appropriate monitoring techniques to assess unstable slopes. Particular attention is given to the spatial and temporal resolutions offered by the different approaches that include: Real Time Kinematic-GPS (RTK-GPS) monitoring of a ground surface marker array, conventional inclinometers, Shape Acceleration Arrays (SAA), tilt meters, active waveguides with Acoustic Emission (AE) monitoring, and piezometers. High spatial resolution information has allowed locating areas of stability and instability across a large slope. This has enabled identification of areas where further monitoring efforts should be focused. High temporal resolution information allowed the capture of ‘S’-shaped slope displacement-time behaviour (i.e. phases of slope acceleration, deceleration and stability) in response to elevations in pore-water pressures. This study shows that a well-balanced suite of monitoring techniques that provides high temporal and spatial resolutions on both measurement and slope scale is necessary to fully understand failure and movement mechanisms of slopes. In the case of the Hollin Hill landslide it enabled detailed interpretation of the geomorphological processes governing landslide activity. It highlights the benefit of regularly surveying a network of GPS markers to determine areas for installation of movement monitoring techniques that offer higher resolution both temporally and spatially. The small sensitivity of tilt meter measurements to translational movements limited the ability to record characteristic ‘S’-shaped landslide movements at Hollin Hill, which were identified using SAA and AE measurements. This high sensitivity to landslide movements indicates the applicability of SAA and AE monitoring to be used in early warning systems, through detecting and quantifying accelerations of slope movement.
The stability and integrity of a landfill barrier, in both the short and the long term, are vital to performance as a containment system for leachate and landfill gas, and are a requirement of the UK permitting process. The structural performance of steep, non-self-supporting barrier systems depends in part on the adjacent waste body for lateral support. This paper presents the results of an investigation into structural performance during construction of a typical UK mineral steep slope landfill lining system. Instrument installation, monitoring and results are presented. Measurements and observations have shown shear and overturning modes of clay barrier failure, leading to loss of integrity. Normal stresses measured at the waste/barrier interface demonstrate that waste adjacent to the barrier provides low and variable lateral support. It is concluded that this has led to the observed failure mechanisms. Temporary conditions during phased construction are shown to be critical. This investigation has demonstrated that current UK municipal solid waste, placed using standard practices, cannot by itself provide sufficient support to ensure the integrity of a clay barrier in a steep slope lining system. Waste/barrier interaction must be considered as part of the design process.
Deformation of soil bodies and soil-structure systems generates acoustic emission (AE), which are high-frequency stress waves. Listening to this AE by coupling sensors to structural elements can provide information on asset condition and early warning of accelerating deformation behaviour. There is a need for experimentation to model the propagation of AE in buried pipe systems to enhance understanding of real behaviour. Analytical solutions are often based on many assumptions (e.g. homogeneity, isotropy, boundary conditions and material properties) and cannot exactly represent the behaviour of the in situ system. This paper details a series of experiments conducted on buried pipes to investigate AE attenuation in pipes due to couplings and soil surround. The attenuation coefficients reported provide guidance to engineers for designing sensor spacing along buried pipes for monitoring ground deformations, and active waveguide installation depths for slope deformation monitoring. Attenuation coefficients have been quantified for both air–pipe–air and air–pipe–soil trilayer systems for the frequency range of 20–30 kHz.
Abstract Reliable tomographic inversion of geoelectrical monitoring data from unstable slopes relies critically on knowing the electrode positions, which may move over time. We develop and present an innovative inverse method to recover movements in both surface directions from geoelectrical measurements made on a grid of monitoring electrodes. For the first time, we demonstrate this method using field data from an active landslide to recover sequences of movement over timescales of days to years. Comparison with GPS measurements demonstrated an accuracy of within 10% of the electrode spacing, sufficient to correct the majority of artifacts that would occur in subsequent image reconstructions if incorrect positions are used. Over short timescales where the corresponding subsurface resistivity changes were smaller, the constraints could be relaxed and an order‐of‐magnitude better accuracy was achievable. This enabled the onset and acceleration of landslide activity to be detected with a temporal resolution of a few days.
ABSTRACT: Changing climate and the damaging effects of carbon dioxide (CO 2 ) on the environment, has led to awareness throughout the construction industry of the need to deliver more sustainable solutions. Robust and rigorous carbon footprinting procedures for assessing solutions and projects can help to identify where action can be taken to reduce CO 2 emissions. It also promotes the marketing of those solutions and methods that produce lower CO 2 emissions. Geosynthetics often provide a cost-efficient alternative to more ‘traditional’ construction techniques. Recently, work by the Waste and Resources Action Programme in the UK has shown that geosynthetic solutions can also produce much lower CO 2 emissions. However, there are still questions as to the reliability of such calculations. Although the methodologies employed are relatively consistent worldwide, the accuracy of the embodied carbon data available for use in calculations remains uncertain. Geosynthetic products are not specifically included in the embodied carbon construction materials databases most commonly employed in Europe, and often generic values for polypropylene and polyethylene are used. This paper presents a study in which the embodied carbon data for geosynthetic products was calculated using first-hand manufacturing process data. The values calculated for two categories of geosynthetics were considerably lower than commonly employed database values. Nonwoven geotextiles had an average embodied carbon value of 2.35 tCO 2 e/t, with values for example geogrids of 2.97 tCO 2 e/t for extruded and 2.36 tCO 2 e/t woven.
The paper details the use of acoustic emission generated by active waveguide subsurface instrumentation to monitor the stability of a rail soil cutting slope failure. Operation of the active waveguide, unitary battery-operated acoustic emission sensor and warning communication system are described. Previous field trials reported by the authors demonstrate that acoustic emission rates generated by active waveguides are proportional to the velocity of slope movement, and can therefore be used to detect changes in rates of movement in response to destabilising and stabilising effects, such as rainfall and remediation, respectively. The paper presents a field trial of the acoustic emission monitoring system at a reactivated rail-cutting slope failure at Players Crescent, Totton, Southampton, UK. The results of the monitoring are compared with both periodic and continuous deformation measurements. The study demonstrated that acoustic emission monitoring can provide continuous information on displacement rates, with high temporal resolution. The ability of the monitoring system to detect slope movements and disseminate warnings by way of text messages is presented. The monitoring approach is shown to provide real-time information that could be used by operators to make decisions on traffic safety.
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