John Coggan

Numerical analysis of initiation and progressive failure in natural rock slopes—the 1991 Randa rockslide

The 1991 Randa rockslide in the Swiss Alps involved several complex mechanisms relating to geological, mechanical and hydrological processes for which no clear trigger can be asserted. This paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the Randa rockslide as a working example. Results from continuum (i.e. finite-element) modelling are presented to illustrate a hypothesis, suggesting that initiation of a progressive rock mass degradation process, ultimately leading to failure, began following deglaciation of the valley below. Discontinuum (distinct-element) modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide. Finally, the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure.

Characterization of harbor sediments from the English Channel: assessment of heavy metal enrichment, biological effect and mobility.

For a full assessment of the environmental risk posed by dredged sediments not only the anthropogenic enrichment of contaminants, but also their mobility and biological impact should be considered. This study reports on the enrichment factor (EF), mobility, and Adverse Effect Index (AEI) of metals and metalloids in nine dredged sediments. Significant enrichment of As, Cd, Pb and Zn with respect to background values is detected, and calculated AEI values for these elements suggest that it is possible that a corresponding biological effect may be observed. Correlation coefficients also reveal a link between mobility in HCl and enrichment for Cd, Cr, Ni, Pb and Zn, however As and Cu do not display such a link, possibly suggesting that the source of contamination for these elements is less recent. Mobility and enrichment are two parameters which are often studied separately; however this paper shows that in some cases strong correlations occur.

A Combined Remote Sensing–Numerical Modelling Approach to the Stability Analysis of Delabole Slate Quarry, Cornwall, UK

Rock slope geometry and discontinuity properties are among the most important factors in realistic rock slope analysis yet they are often oversimplified in numerical simulations. This is primarily due to the difficulties in obtaining accurate structural and geometrical data as well as the stochastic representation of discontinuities. Recent improvements in both digital data acquisition and incorporation of discrete fracture network data into numerical modelling software have provided better tools to capture rock mass characteristics, slope geometries and digital terrain models allowing more effective modelling of rock slopes. Advantages of using improved data acquisition technology include safer and faster data collection, greater areal coverage, and accurate data geo-referencing far exceed limitations due to orientation bias and occlusion. A key benefit of a detailed point cloud dataset is the ability to measure and evaluate discontinuity characteristics such as orientation, spacing/intensity and persistence. This data can be used to develop a discrete fracture network which can be imported into the numerical simulations to study the influence of the stochastic nature of the discontinuities on the failure mechanism. We demonstrate the application of digital terrestrial photogrammetry in discontinuity characterization and distinct element simulations within a slate quarry. An accurately geo-referenced photogrammetry model is used to derive the slope geometry and to characterize geological structures. We first show how a discontinuity dataset, obtained from a photogrammetry model can be used to characterize discontinuities and to develop discrete fracture networks. A deterministic three-dimensional distinct element model is then used to investigate the effect of some key input parameters (friction angle, spacing and persistence) on the stability of the quarry slope model. Finally, adopting a stochastic approach, discrete fracture networks are used as input for 3D distinct element simulations to better understand the stochastic nature of the geological structure and its effect on the quarry slope failure mechanism. The numerical modelling results highlight the influence of discontinuity characteristics and kinematics on the slope failure mechanism and the variability in the size and shape of the failed blocks.

Numerical modelling of slope behaviour of Delabole slate quarry (Cornwall, UK)

ABSTRACT Slope stability investigation of the north-east slope at Delabole slate quarry has been carried out using distinct-element modelling to provide further insight into potential mechanisms controlling deformation and instability. The case study emphasises the need for user awareness of potential effects of input parameter variation on model behaviour, and highlights the need for rigorous validation. Distinct-element modelling has confirmed the significance of both input value sensitivity and scale effects on modelled behaviour. The importance of development of representative rock mass geometry is also highlighted by changes in modelled slope behaviour resulting from both changes in scale, or representation of spacing of discontinuities, and variation of discontinuity input parameters. Field measurements of slope deformation have been used to validate and ensure confidence in the development of realistic models.

Trace element mobility in a polluted marine sediment after stabilisation with hydraulic binders.

Abstract The management of dredged marine sediment is an issue for many harbours, particularly when contaminant concentrations prevent disposal at sea. The stabilisation/solidification of the sediments with hydraulic binders for a use in road subgrade layer is a potential alternative solution. However, the environmental acceptability is not yet fully established. This paper presents the results of a case study to comprehensively determine the stabilisation of As, Cd, Cr, Cu, Ni, Pb and Zn. After demonstrating that stabilisation/solidification affects the microstructure of the sediment, a mobility study is realised (single, sequential and kinetic extractions). According to the regulatory/technical guidelines the studied elements do not pose a risk to the environment. However, results from more complex mobility studies reveal that stabilisation in the short term is only effective for Ni while other elements are mobilised after treatment by at least one type of extraction. Stabilisation in the long term is not universally effective.

Improvements in the integration of remote sensing and rock slope modelling

Over the last two decades, the approach to the investigation of landslides has changed dramatically. The advent of new technologies for engineering geological surveys and slope analyses has led to step-change increases in the quality of data available for landslide studies. However, the use of such technologies in the survey and analysis of slopes is often complex and may not always be either desirable or feasible. In this context, this paper aims to improve the understanding of the use of remote sensing techniques for rock mass characterization and provide guidance and on how and when the data obtained from these techniques can be used as input for stability analyses. Advantages and limitations of available digital photogrammetry and laser scanning techniques will also be discussed in relation to their cost and the quality of data that can be obtained. A critique of recent research data obtained from remote sensing techniques is presented together with a discussion on use of the data for slope stability analysis. This highlights how data use may be optimized to reduce both parameter and model uncertainty in future slope analyses.

Geotechnical and mineralogical characterisations of marine-dredged sediments before and after stabilisation to optimise their use as a road material

ABSTRACT Dredging activities to extend, deepen and maintain access to harbours generate significant volumes of waste dredged material. Some ways are investigated to add value to these sediments. One solution described here is their use in road construction following treatment with hydraulic binders. This paper presents the characterisation of four sediments, in their raw state and after 90 days of curing following stabilisation treatment with lime and cement, using a combination of novel and established analytical techniques to investigate subsequent changes in mineralogy. These sediments are classified as fine, moderately to highly organic and highly plastic and their behaviour is linked to the presence of smectite clays. The main minerals found in the sediments using X-ray diffraction (XRD) and automated mineralogy are quartz, calcite, feldspars, aluminium silicates, pyrite and halite. Stabilisation was found to improve the mechanical performances of all the sediments. The formation of cementitious hydrates was not specifically detected using automated mineralogy or XRD. However, a decrease in the percentage volume of aluminium silicates and aluminium-iron silicates and an increase of the percentage volume of feldspars and carbonates was observed.

Evaluation of automated underground mapping solutions for mining and civil engineering applications

Abstract. The extractive and construction industries rely heavily on accurate geospatial data to control position, location, alignment, and orientation of planned excavations. Recent advancements in the survey industry, through the use of terrestrial laser scanning, can now provide engineering teams with three-dimensional (3-D) data in unprecedented detail via georeferenced point clouds. Furthermore, equipment is now available that provides fully mobile automated mapping solutions, independent of satellite positioning, utilizing simultaneous localization and mapping. This paper evaluates the surveying capability of three fully mobile automated mapping solutions against a benchmark laser scanning survey undertaken at the underground Camborne School of Mines Test Mine facility. The study highlights that handheld automated mapping solutions, in which closed-loops can be formed, have the potential to provide quicker data collection and processing time, as well as the required accuracy for underground surveying applications. However, the automated solution was unable to produce the necessary point cloud density to identify low-angled discontinuities that may have a major safety implication, leading to potential rockfall.

Investigation into Factors Affecting Roadway Deformation in the Selby Coalfield

The introduction of roofbolting in the UK coal mining industry has been well documented and is an example of reinforcement design utilizing a ‘design by measurement’ or ‘observational approach’. This has involved detailed monitoring of rock strata movements and rockbolt loads at a large number of sites. Analysis of roadway deformation monitoring information from across the Selby coalfield provided an ideal opportunity of assessing how geological and stress variations affect the stability of reinforced coal mine roadways. Statistical analysis of this data has confirmed the detrimental effects of maximum horizontal stress direction and relatively weak roof geology on the magnitude of roof deformation. Further analysis has led to the development of a roof lithology index for assessing the quality of the immediate roof geology and the use of geological hazard analysis for providing useful information for the development of a stability index for assessing support requirements of existing and future roadways. This investigation has also verified previous observations regarding mechanisms controlling roadway deformational behaviour and highlights the importance of the ‘site-specific’ nature of reinforcement design.

Integration of Laser Scanning and Three-dimensional Models in the Legal Process Following an Industrial Accident

Background In order to obtain a deeper understanding of an incident, it needs to be investigated to “peel back the layers” and examine both immediate and underlying failures that contributed to the event itself. One of the key elements of an effective accident investigation is recording the scene for future reference. In recent years, however, there have been major advances in survey technology, which have provided the ability to capture scenes in three dimension to an unprecedented level of detail, using laser scanners. Methods A case study involving a fatal incident was surveyed using three-dimensional laser scanning, and subsequently recreated through virtual and physical models. The created models were then utilized in both accident investigation and legal process, to explore the technologies used in this setting. Results Benefits include explanation of the event and environment, incident reconstruction, preservation of evidence, reducing the need for site visits, and testing of theories. Drawbacks include limited technology within courtrooms, confusion caused by models, cost, and personal interpretation and acceptance in the data. Conclusion Laser scanning surveys can be of considerable use in jury trials, for example, in case the location supports the use of a high-definition survey, or an object has to be altered after the accident and it has a specific influence on the case and needs to be recorded. However, consideration has to be made in its application and to ensure a fair trial, with emphasis being placed on the facts of the case and personal interpretation controlled.