Characterization of Rock Fracturing for Vertical Boreability

This is the final version of the article. Available from Elsevier via the DOI in this record.Boreability can be defined as the ability of a bore to penetrate a rock mass. Understanding the factors influencing boreability is critical for enhanced project planning and reduce geotechnical risk in an offshore shaft boring environment. Large diameter drills are used for offshore shaft boring, which can be up to 7 m in diameter, and therefore more akin to tunnel boring machines due to the scale of the excavation and extent of ground interaction. With increases in bore diameter, there is a need to properly define and evaluate the effect of the degree of rock mass fracturing on machine performance for improved estimates of boreability. Discrete Fracture Network (DFN) simulation has been used as an innovative approach for stochastic realisation of rock mass fracturing by determination of the P32 volumetric fracture intensity in the context of boreability. P32 shows positive trend to specific penetration (SP), with maximum SP being achieved at moderate to high fracturing levels (20 - 25m-1). However, in this case, P32 shows a similar positive trend to P10, but with peak SP appearing at higher intensity levels. Increased RQD values result in reduced SP, with peak SP reached at moderate fracturing levels, similar to P10.This research is part of a wider study into excavatability, funded by the Engineering and Physical Sciences Research Council (ESPRC) of the UK

Negotiation of poor ground in an undersea tunnel

The 2.65 km Gwithian outfall tunnel formed part of the tunnelling operations under the 'Clean Sweep' sewage/sewerage distribution system upgrade within the South West Region during the 1990's. The 3.0 m high by 2.8 m wide rectangular, tracked-tunnel was constructed by Trafalgar House Construction using drill and blast techniques to intercept a series of pre-drilled diffuser units 25 m below the sea-bed in St Ives Bay. In view of the close proximity to the sea-bed, and the risk of water ingress, systematic probe drilling was performed at regular intervals during construction. Where necessary, in order to reduce the water-make to within pre-defined limits, cementitious grouting of the ground ahead of the advancing face was undertaken. One major fault zone required extensive grouting, as initial probe holes were making in the order of 200 gallons per minute. Tunnel advance through exceptionally poor ground required modification to the excavation methodology and implementation of additional support measures. Evaluation of geotechnical data from the undersea tunnel suggests that the Q-system provided a sound basis for assessment of rock quality and for guidance on associated support requirements. Good correlation was obtained between mapped Qvalues and tunnel advance rates. Importantly, engineering judgement informed final support recommendations

Application of discrete fracture networks (DFN) in the stability analysis of Delabole Slate Quarry, Cornwall, UK

This is the author accepted manuscript. The final version is available from ARMA.50th US Rock Mechanics/Geomechanics Symposium, Houston, USA, 26-29 June 2016The failure mechanism of rock slopes is mainly controlled by the strength and orientation of discontinuities within the rock mass. A realistic representation of the joint network within the rock mass is therefore an essential component of stability analysis of rock structures (e.g. rock slopes, tunnels etc.). Discontinuity persistence and connectivity are significant parameters which control the stability of rock slopes. A small percentage of rock bridges on the discontinuity surface can significantly increase its strength and prevent slope failure. Discontinuities within the rock mass are rarely fully connected. In practice, however, discontinuities are often assumed fully persistent due to the difficulties both in mapping and simulation of non-persistence. Discrete fracture networks (DFN) provide a rigorous and convenient tool for the simulation of joint systems within a rock mass. Utilizing statistical methods, DFNs consider the stochastic nature of some key parameters (e.g. persistence and orientation) within numerical models. Discrete fracture network engineering is increasingly used due to recent developments in discontinuity data acquisition techniques (e.g. ground-based digital photogrammetry and laser scanning). Recent development in geomechanical modelling codes and increased computing power have also allowed to either import DFN’s into models or to generate DFN’s within the numerical modelling code itself (e.g. 3DEC). This paper describes the use of photogrammetry at the Delabole slate quarry in Cornwall, UK for remotely acquiring key discontinuity parameter data (orientation, intensity and length) and its subsequent use in developing statistically validated discrete fracture network parameters. The 3D distinct element code, 3DEC, is used for the DFN generation and subsequent stability analysis. Several realizations of the 3DEC-DFN models are run to investigate the stochastic nature of discontinuities within the quarry and their potential influence on the stability of the pit. Finally the simulation results are used to determine the slope instability mechanisms and determine the most likely areas of potential instability

Investigation and modeling of direct toppling using a three-dimensional distinct element approach with incorporation of point cloud geometry

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordBlock toppling instability can be a common problem in natural rock masses, especially in mining environments where excavation activity may trigger discontinuity-controlled instability by modifying the natural slope geometry. Traditional investigations of block toppling failure consider classic kinematic analyses and simplified two-dimensional limit equilibrium methods. This approach is still the most commonly adopted, but the simple two-dimensional conceptual model may often oversimplify the instability mechanisms, ignoring potential critical factors specifically related to the three-dimensional geometry. This paper uses a three-dimensional distinct element method approach applied to an example case study, identifying the critical parameters that influence direct toppling instability in an open pit environment. Terrestrial laser scanning was used to obtain detailed three-dimensional geometrical information of the slope face geometry for subsequent stability analyses. A series of sensitivity analyses on critical parameters such as friction angle, discontinuity shear and normal stiffness, discontinuity spacing, and orientation was performed, using simple conceptual three-dimensional numerical modeling. Results of the analyses revealed the importance of undertaking three-dimensional analyses for direct toppling investigations that allow identification of critical parameters. A three-dimensional distinct element analysis was then performed using a more realistic complex volumetric mesh model of the case study slope which confirmed the previous modeling results but also identified unstable blocks in high slope angle areas, providing useful information for life of mine design. The paper highlights the importance of slope geometry and fracture network orientation on potential slope instability mechanisms.European CommissionEuropean Commissio

Investigation of landslide failure mechanisms adjacent to lignite mining operations in North Bohemia (Czech Republic) through a limit equilibrium/finite element modelling approach

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Understanding the impact of data uncertainty is a fundamental part of ensuring safe design of manmade excavations. Although good levels of knowledge are achievable from field investigations and experience, a natural geological environment is subject to intrinsic variability that may compromise the correct prediction of the system response to the perturbations caused by mining, with direct consequences for the stability and safety of the operations. Different types of geoscientific evidence, including geological, geomorphic, geotechnical, geomatics, and geophysical data have been used to develop and perform two-dimensional Limit Equilibrium and Finite Element Method stability analyses of a lignite open-pit mine in North Bohemia (Czech Republic) affected by recent landslides. A deterministic-probabilistic approach was adopted to investigate the effect of uncertainty of the input parameters on model response. The key factors affecting the system response were identified by specific Limit Equilibrium sensitivity analyses and studied in further detail by Finite Element probabilistic analyses and the results were compared. The work highlights that complementary use of both approaches can be recommended for routine checks of model response and interpretation of the associated results. Such an approach allows a reduction of system uncertainty and provides an improved understanding of the landslides under study. Importantly, two separate failure mechanisms have been identified from the analyses performed and verified through comparisons with inclinometer data and field observations. The results confirm that the water table level and material input parameters have the greatest influence on the stability of the slope.This work was supported by the Research Fund for Coal and Steel of the European Union [grant number 752504]

Application of Remote Sensing Data for Evaluation of Rockfall Potential within a Quarry Slope

This is the final version. Available on open access from MDPI via the DOI in this recordIn recent years data acquisition from remote sensing has become readily available to the quarry sector. This study demonstrates how such data may be used to evaluate and back analyse rockfall potential of a legacy slope in a blocky rock mass. Use of data obtained from several aerial LiDAR (Light Detection and Ranging) and photogrammetric campaigns taken over a number of years (2011 to date) provides evidence for potential rockfall evolution from a slope within an active quarry operation in Cornwall, UK. Further investigation, through analysis of point cloud data obtained from terrestrial laser scanning, was undertaken to characterise the orientation of discontinuities present within the rock slope. Aerial and terrestrial LiDAR data were subsequently used for kinematic analysis, production of surface topography models and rockfall trajectory analyses using both 2D and 3D numerical simulations. The results of an Unmanned Aerial Vehicle (UAV)-based 3D photogrammetric analysis enabled the reconstruction of high resolution topography, allowing one to not only determine geometrical properties of the slope surface and geomechanical characterisation but provide data for validation of numerical simulations. The analysis undertaken shows the effectiveness of the existing rockfall barrier, while demonstrating how photogrammetric data can be used to inform back analyses of the underlying failure mechanism and investigate potential runout

Application of RQD-Number and RQD-Volume multifractal modelling to delineate rock mass characterisation in Kahang Cu-Mo porphyry deposit, central Iran.

Identification of rock mass properties in terms of Rock Quality Designation (RQD) plays a significant role in mine planning and design. This study aims to separate the rock mass characterisation based on RQD data analysed from 48 boreholes in Kahang Cu-Mo porphyry deposit situated in the central Iran utilising RQD-Volume (RQD-V) and RQD-Number (RQD-N) fractal models. The log-log plots for RQD-V and RQD-N models show four rock mass populations defined by RQD thresholds of 3.55, 25.12 and 89.12% and 10.47, 41.68 and 83.17% respectively which represent very poor, poor, good and excellent rocks based on Deere and Miller rock classification. The RQD-V and RQD-N models indicate that the excellent rocks are situated in the NW and central parts of this deposit however, the good rocks are located in the most parts of the deposit. The results of validation of the fractal models with the RQD block model show that the RQD-N fractal model of excellent rock quality is better than the RQD-V fractal model of the same rock quality. Correlation between results of the fractal and the geological models illustrates that the excellent rocks are associated with porphyric quartz diorite (PQD) units. The results reveal that there is a multifractal nature in rock characterisation with respect to RQD for the Kahang deposit. The proposed fractal model can be intended for the better understanding of the rock quality for purpose of determination of the final pit slope.The authors are grateful to the National Iranian Copper Industries Co. (NICICO) for their permission to have access to the Kahang deposit dataset. Additionally, the authors would like to thank Mr. Reza Esfahanipour the head of Exploration and Development Department of the NICICO for his support. The authors also are hugely thankful to the Institute of Materials, Minerals and Mining (IOM3) for its financial support in order to conduct this research

Evaluation of the Use of UAV Photogrammetry for Rock Discontinuity Roughness Characterization

This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this recordThis paper describes the results of a field investigation with the objective of evaluating the possibility to produce drone-derived 3D digital point clouds sufficiently dense and accurate to determine discontinuity surface roughness characteristics. A discontinuous rock mass in Italy was chosen as the investigation site and Structure from Motion and Multi-View Stereo techniques adopted for producing three-dimensional point clouds from the two-dimensional image sequences. Since the roughness of discontinuities depends on direction, scale and resolution of the sampling, data were always collected along the maximum slope gradient. The scale effect was evaluated by analysing discontinuity profiles of different lengths (10 cm, 30 cm, 60 cm and 100 cm), with measurements taken from drone flights flown at different distances from the rocky slopes (10 m, 20 m and 30 m). The accuracy of the derived joint roughness coefficients was evaluated by direct comparison with discontinuity profiles measured during fieldwork using conventional techniques and from contemporaneous terrestrial laser scanning. Results from this research show that 3D digital point clouds, derived from the processing of drone-flight images, were successfully used for reliable representation of discontinuity roughness for profiles longer than 60 cm, whereas less reliable results were achieved for shorter profile lengths. This, even if strictly related to this case study since several factors can affect the minimum profile length, represents a significant contribution to improve the knowledge on the use of remotely captured data for characterising the discontinuities in natural or man-made rock outcrops, particularly where access difficulties do not allow conventional engineering-geological surveys to be undertaken

A Multi-Disciplinary Approach to the Study of Large Rock Avalanches Combining Remote Sensing, GIS and Field Surveys: The Case of the Scanno Landslide, Italy

This is the final version. Available from MDPI via the DOI in this record.This research aims to highlight the importance of adopting a multi-disciplinary approach to understanding the factors controlling large rock avalanches using the Scanno landslide, Italy, as a case study. The study area is the Mount Genzana, Abruzzi Central Apennines, characterized by the regional Difesa-Mount Genzana-Vallone delle Masserie fault zone. The Scanno landslide is famous for its role in the formation of the Scanno Lake. The landslide is characterized by a wide exposed scar, which was interpreted in previous studies as the intersection of high-angle joints and an outcropping bedding plane on which the landslide failed sometime between the Upper Pleistocene and the Holocene. In this study, the Scanno landslide was investigated through the integration of geological, geomechanical and geomorphological surveys. Remote sensing techniques were used to enrich the conventionally gathered datasets, while Geographic Information Systems (GIS) were used to integrate, manage and investigate the data. The results of the authors investigation show that the outcropping landslide scar can be interpreted as a low-angle fault, associated with the Difesa-Mount Genzana-Vallone delle Masserie fault zone, which di ers from previous investigations and interpretations of the area. The low-angle fault provides the basal failure surface of the landslide, with two systematic high-angle joint sets acting as lateral release and back scarp surfaces, respectively. In light of these new findings, pre- and post-failure models of the area have been created. The models were generated in GIS by combining LiDAR (Light Detection and Ranging) and geophysics data acquired on the landslide body and through bathymetric survey data of the Scanno Lake. Using the pre- and post-failure models it was possible to estimate the approximate volume of the landslide. Finally, back-analyses using static and dynamic limit equilibrium methods is also used to show the possible influence of medium-to-high magnitude seismic events in triggering the Scanno landslide

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

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.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