1,720,976 research outputs found
Discrete passive piles for infrastructure slope stabilization
No full textDiscrete piles are increasingly being used to stabilise infrastructure earthwork slopes such as road and railway embankments and cuttings. Historically, there have been a number of uncertainties relating to how such piles behave. These include the maximum spacing at which such piles can be installed and still be effective, appropriate methods of analysis especially when there no obvious pre-existing failure surface, and the limiting lateral pile soil pressure especially in an effective stress analysis. This paper discusses these issues, with reference to geotechnical centrifuge tests, three dimensional finite element analyses, and field measurements over a period of years at a number of sites that reveal a variety of different pile-soil interaction behavioural modes
Monitoring and analysis of the bending behaviour of discrete piles used to stabilise a railway embankment
Full text linkDiscrete 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 little 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. 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
Projections of climate change on the behaviour of clays in the UK
No full textThe impact of expected climate change on clay cuttings and embankments used for roads and railways is not well understood. Volume sensitive clays respond to seasonal variations in climate through vertical and horizontal displacements. These cause a variety of impacts at differing temporal and spatial scales, for example short term changes such as seasonal displacement of railway tracks or long term progressive failure of the slope. Daily changes in soil moisture content in the surface layers of a clay slope are simulated using a water balance model and expressed as soil moisture deficit and potential for surface runoff. Model results are validated against a 10 year run of field data in the UK. The impacts of anticipated climate change on soil water contents and equivalent pore water pressures are evaluated using stochastic climatic data over the 21st century based on the UK Climate Impacts Programme. Results indicate that recent summers considered to be exceptionally dry are likely to become the average condition later in the 21st century. Although winter rainfall is predicted to increase, average winter runoff will remain the same, although extreme wet events are still likely to occur. The implications for the design and maintenance of clay slopes and embankments are dis-cussed
Limiting pressure on a laterally loaded pile in a frictional soil
No full textThis Letter investigates by means of finite difference analyses the ultimate lateral pressure developed on a pile moving through a soil whose strength is characterised by an effective angle of shearing resistance (phi'). Analyses were carried out to determine the distribution of ultimate pressure with depth, with particular attention paid to nearsurface effects, for a value of (phi') representative of a clay soil. The model results are compared with popular empirical distributions of ultimate lateral pressure, obtained generally from full scale and model tests in sand. It was found that the depth to which the unconfined ground surface affects the ultimate lateral pressure developed is consistently about 5 m. Below the zone influenced by the surface effects, limiting lateral pressures were found to increase linearly with depth. The empirical distributions for the limiting pressure were found to bracket the numerical results for a frictionless pile-soil interface, and underestimate the numerical results for a full strength pile-soil interface
Factors controlling the seasonal variation in soil water content and pore water pressures within a lightly vegetated clay slope
Full text linkSeasonal cycles of soil water content cause shrinking and swelling in clay soils that can in turn contribute to strain-softening and progressive 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. 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 2003-2008, 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
Seasonal changes in pore water pressure in a grass covered cut slope in London clay
No full textIn 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
Seasonal slope surface deformation measured with terrestrial laser scanning
No full textIn temperate European climates, soil water removal due to vegetation transpiration peaks in summer and soil rewetting from higher levels of precipitation occurs in winter. In clays of high plasticity, the seasonal cycles of drying and wetting cause the soil to experience a volumetric change, resulting in seasonal shrinking and swelling. For a clay slope exhibiting volume change, such behaviour can lead to excessive deformation and could contribute to strain-softening and progressive slope failure. This can in turn cause traffic disruption and loss of life if roads and railways are founded on or surrounded by such slopes. This paper discusses the driving forces of seasonal surface movement, in particular the role of vegetation, and presents the use of Terrestrial Laser Scanning (TLS) to measure the surface movement of a lightly vegetated London Clay slope near Newbury, UK. Two TLS scans were carried out in early and late summer respectively, representing relative wet and dry conditions of the slope. Continuous field measurements of soil water content in upper layers of the slope were obtained from TDR ThetaProbes already installed at the site. The water content data are used to support the results obtained from TLS by indicating the likely volumetric change in the soil due to loss of water
Three dimensional numerical modelling of discrete piles used to stabilise landslides
No full textThree dimensional finite difference analyses have been carried out to investigate the behaviour of a single pile used to stabilise a slipping mass of soil, by embedment into a stable stratum. Analyses were initially carried out to determine the reduction in the limiting pile-soil lateral pressure, pu, close to the unconfined ground surface. The analyses then explore the failure mechanisms for landslide stabilising piles categorised by Viggiani. The effects of varying the strength of the slip plane interface between the sliding and stable strata, and of a sloping ground surface on the behaviour of the pile are then investigated. The results from numerical models with a rigid pile, a distinct plane of sliding and a horizontal ground surface, as assumed by Viggiani, agree closely with his theoretical solutions. Lower values of pu close to the ground surface and adjacent to the sliding plane are found to reduce the maximum shear resistance that piles can provide to the slipping mass, when compared with Viggiani’s theoretical solutions. The further analyses show that the strength of the slip plane interface has a considerable influence on pile behaviour, and that the slope of the ground surface is only significant above a certain angle
Error in target-based georeferencing and registration in terrestrial laser scanning
Full text linkTerrestrial 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 registration- or 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
Mechanical and hydrological impacts of tree removal on a clay fill railway embankment
Full text linkSeasonal shrinkage and swelling of clay fill railway embankments can disturb the track geometry, resulting in train speed restrictions that disrupt normal operations. Such movements are exacerbated by vegetation, but reliable analytical descriptions of the effects of trees on embankment behaviour are not yet established. This paper presents and analyses the results of a field experiment, carried out on a heavily vegetated clay railway embankment to investigate quantitatively the influence of trees. After the first year of monitoring, the mature trees initially present on the upper two-thirds of the embankment slopes were removed. The field monitoring data are used to assess and understand the mechanisms of soil water content and pore water pressure changes before and after tree removal, and their influence on the vertical and lateral displacements of the embankment slopes. Removal of the vegetation stopped seasonal volume changes in the clay fill at the crest of the earthwork, but also resulted in the loss of the deep-seated suctions generally beneficial to embankment stability. The wider implications for the management of vegetation on embankment slopes are discusse
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