Chalk-steel Interface testing for marine energy foundations

The Energy Technology Partnership (ETP) and Lloyd’s Register EMEA are gratefully acknowledged for the funding of this project. The authors would also like to acknowledge the support of the European Regional Development Fund (ERDF) SMART Centre at the University of Dundee that allowed purchase of the equipment used during this study. The views expressed are those of the authors alone, and do not necessarily represent the views of their respective companies or employing organizations.Peer reviewedPostprin

Influence of packing density and stress on the dynamic response of granular materials

Laboratory geophysics tests including bender elements and acoustic emission measure the speed of propagation of stress or sound waves in granular materials to derive elastic stiffness parameters. This contribution builds on earlier studies to assess whether the received signal characteristics can provide additional information about either the material’s behaviour or the nature of the material itself. Specifically it considers the maximum frequency that the material can transmit; it also assesses whether there is a simple link between the spectrum of the received signal and the natural frequencies of the sample. Discrete element method (DEM) simulations of planar compression wave propagation were performed to generate the data for the study. Restricting consideration to uniform (monodisperse) spheres, the material fabric was varied by considering face-centred cubic lattice packings as well as random configurations with different packing densities. Supplemental analyses, in addition to the DEM simulations, were used to develop a more comprehensive understanding of the system dynamics. The assembly stiffness and mass matrices were extracted from the DEM model and these data were used in an eigenmode analysis that provided significant insight into the observed overall dynamic response. The close agreement of the wave velocities estimated using eigenmode analysis with the DEM results confirms that DEM wave propagation simulations can reliably be used to extract material stiffness data. The data show that increasing either stress or density allows higher frequencies to propagate through the media, but the low-pass wavelength is a function of packing density rather than stress level. Prior research which had hypothesised that there is a simple link between the spectrum of the received signal and the natural sample frequencies was not substantiated

There is no such thing as ‘undisturbed’ soil and sediment sampling: sampler-induced deformation of salt marsh sediments revealed by 3D X-ray computed tomography

Purpose: Within most environmental contexts, the collection of 'undisturbed' samples is widely relied-upon in studies of soil and sediment properties and structure. However, the impact of sampler-induced disturbance is rarely acknowledged, despite the potential significance of modification to sediment structure for the robustness of data interpretation. In this study, 3D-computed X-ray microtomography (μCT) is used to evaluate and compare the disturbance imparted by four commonly-used sediment sampling methods within a coastal salt-marsh. Materials and methods: Paired sediment core samples from a restored salt-marsh at Orplands Farm, Essex, UK were collected using four common sampling methods (push, cut, hammer and gouge methods). Sampling using two different area-ratio cores resulted in a total of 16 cores that were scanned using 3D X-Ray computed tomography, to identify and evaluate sediment structural properties of samples that can be attributed to sampling method. Results and discussion: 3D qualitative analysis identifies a suite of sampling-disturbance structures including gross-scale changes to sediment integrity and substantial modification of pore-space, structure and distribution, independent of sediment strength and stiffness. Quantitative assessment of changes to pore-space and sediment density arising from the four sampling methods offer a means of direct comparison between the impact of depth-sampling methods. Considerable disturbance to samples result from use of push, hammer and auguring samplers, whilst least disturbance is found in samples recovered by cutting and advanced trimming approaches. Conclusions: It is evident that with the small-bore tubes and samplers commonly used in environmental studies, all techniques result in disturbance to sediment structure to a far greater extent than previously reported, revealed by μCT. This work identifies and evaluates for the first time the full nature, extent and significance of internal sediment disturbance arising from common sampling methods

Deformation, diagenesis and the mechanical behaviour of chalk

The chalk of England is a highly variable material resulting from numerous deformation processes of which the most important are diagenetic or tectonic in nature. The engineering behaviour of the chalk is influenced greatly by these processes thus giving rise to the necessity of carrying out studies of physical properties to aid the prediction of engineering performance. The results of these studies are of value when examining deformation mechanisms associated with diagenesis and tectonism. In this paper use is made of results obtained from engineering laboratory index tests to study deformation mechanisms associated with early diagenesis and the influence of overburden and tectonism. © 1987 The Geological Society

Deformation, diagenesis and the mechanical behaviour of chalk.

The chalk of England is a highly variable material resulting from numerous deformation processes of which the most important are diagenetic or tectonic in nature. The engineering behaviour of the chalk is influenced greatly by these processes thus giving rise to the necessity of carrying out studies of physical properties to aid the prediction of engineering performance. -from Author

The use of oblique aerial photography to investigate the extent and sequence of landslipping at Stag Hill, Guildford, Surrey

The University of Surrey is situated on the northern slopes of Stag Hill, below Guildford Cathedral, which occupies the summit. During the investigation for the design of the University, it became apparent that the site was underlain by a large landslip, 500 m wide from east to west and extending 160 m from rear scarp to toe. Considerable effort was made to establish its geometry and extent (Skempton & Petley (1967), and Morgenstern & Tchalenko (1967)). In recent years it was realised that because the construction of the Cathedral extended over a long period of time, the likelihood of Stag Hill being covered by oblique aerial photography would be high. Some forty oblique aerial photographs, spanning the period 1949 to 1982, were collected and analysed together with vertical aerial photographs and topographic maps. Although the landslip is visible on vertical aerial photographs, individual elements are not easily identified. Using oblique photography, in particular that in which recognition of subdued topography has been enhanced by low sun angles, up to six phases of landslipping were identified. This paper uses this example to demonstrate the usefulness of aerial photography in site investigation and in particular the value of oblique photography, a topic which receives little attention in BS5930:1981 considering how cost effective this tool can be