In temperate European climates, the season of peak water demand by vegetation (summer) is out of phase with the season of greatest rainfall (winter). This results in seasonal fluctuations in soil water content and, in clay soils, associated problems of shrinking and swelling that can in turn contribute to strain-softening and progressive slope failure. This paper presents field measurements of seasonal moisture content and pore water pressure changes within the surface drying zone of a cut slope in the London Clay at Newbury, Berkshire, UK. A climate station was installed at the site to measure the parameters needed to determine specific plant evapotranspiration. This information was used to carry out a water balance calculation to estimate the year-round soil moisture deficit caused by the vegetation. The calculated soil moisture deficit matches reasonably closely the field measurements of soil drying. The field measurements of seasonal changes in pore water pressure and suction are linked quantitatively to the measured changes in water content using the soil water characteristic curve for the London Clay. The suctions generated by the light vegetation cover at Newbury were found not to persist into the winter and early spring.KEYWORDS: clays; field instrumentation; monitoring; pore pressures; slopes; suction Dans les zones européennes de climat tempéré, la période de demande d'approvisionnement en eau la plus importante pour la végétation ne correspond pas à la saison de pluviosité la plus forte (hiver). Il en résulte des fluctuations du taux d'humidité dans le sol, et, pour les terrains argileux, des problèmes associés de gonflement et rétré-cissement qui peuvent, à leur tour, contribuer à un écrouissage négatif et une fracture progressive du versant. Cet article présente des expérimentations réalisées in situ pour mesurer le taux d'humidité et les variations de pression hydrique interstitielle saisonniers à l'intérieur de la zone d'assèchement de la surface d'un versant découpé dans le London Clay à Newbury, dans le Berkshire, au Royaume-Uni. Une station climatologique a été installée sur le site afin de relever les paramètres néces-saires pour déterminer l'évapotranspiration végétale spé-cifique. Ces informations ont été utilisées pour calculer le bilan hydrique et estimer ainsi, sur une année, le déficit hydrique que la végétation provoque au niveau du sol. Les résultats de ces calculs en matière de déficit hydrique montrent une corrélation raisonnablement étroite avec les mesures de l'assèchement du sol in situ. Pour la succion et la pression interstitielle de l'eau, les mesures des variations saisonnières, relevées in situ, sont qualitativement liées aux variations de teneur en eau obtenues à l'aide de la courbe caractéristique d'humidité du sol pour le London Clay. Nous avons pu observer que les succions produites par la légère couverture végétale à Newbury ne persistent pas en hiver et au début du printemps.

Seasonal cycles of soil water content cause shrinking and swelling in clay soils, which can in turn contribute to strain-softening and progressive slope failure. This paper presents and analyses six years of field measurements of soil water content and pore water pressures in the upper layers of a lightly vegetated London Clay slope near Newbury, UK, and shows how they can be related quantitatively to the climate using a water balance model. The field observations are set in the context of a 40-year run of rainfall data for the site. Moderately extreme rainfall and drought events were experienced over the period [2003][2004][2005][2006][2007][2008], allowing almost the full variation in likely pore water pressures to be characterised. Pore water pressures were found to return to near hydrostatic during most winters. Variations in summer rainfall, particularly during June-August, are shown to have a large influence on the magnitude of the cycles of pore water pressure and effective stress. The 40-year rainfall dataset is used to calculate approximate return periods for the observed soil conditions, and provides a benchmark for calculating the impacts of expected climate change on similar sites.

Terrestrial laser scanning (TLS) has been used widely for various applications, such as measurement of movement caused by natural hazards and Earth surface processes. In TLS surveying, registration and georeferencing are two essential steps, and their accuracy often determines the usefulness of TLS surveys. So far, evaluation of registration and georeferencing errors has been based on statistics obtained from the data processing software provided by scanner manufacturers. This paper demonstrates that these statistics are incompetent measures of the actual registration and georeferencing errors in TLS data and, thus, should no longer be used in practice. To seek a suitable replacement, an investigation of the spatial pattern and the magnitude of the actual registration and georeferencing errors in TLS data points was undertaken. This led to the development of a quantitative means of estimating the registrationor georeferencing-induced positional error in point clouds. The solutions proposed can aid in the planning of TLS surveys where a minimum accuracy requirement is known, and are of use for subsequent analysis of the uncertainty in TLS datasets.

Discrete piles are used to stabilise infrastructure slopes, especially where there is insufficient additional land to allow construction of large toe berms or regrading of the slope. Compared with more conventional structures such as retaining walls, there are few field data on how discrete piles typically bend and displace under slope loading. This paper presents the results from monitoring a number of discrete piles used to stabilise a railway embankment at Hildenborough, Kent, UK. Bending deflections deduced from strain gauges are compared with the displacements and rotations measured by inclinometer tubes cast into the piles. Four years after pile installation, the piles were bending downslope over their lower halves, with little bending measured in the upper sections. Regrading of the rockfill piling platform shortly after pile construction caused some of the pile loading, with further loading caused by the continued tendency for slope movement. Analysis of the piles using a simple elastic analysis gives bending moments and displacements close to those measured.

Instrumentation is often used to monitor the performance of engineered infrastructure slopes. This paper looks at the current role of instrumentation and monitoring, including the reasons for monitoring infrastructure slopes, the instrumentation typically installed and parameters measured. The paper then investigates recent developments in technology and considers how these may change the way that monitoring is used in the future, and tries to summarize the barriers and challenges to greater use of instrumentation in slope engineering. The challenges relate to economics of instrumentation within a wider risk management system, a better understanding of the way in which slopes perform and/or lose performance, and the complexities of managing and making decisions from greater quantities of data.