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

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

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

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]

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

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

Severe loss of mechanical efficiency in COVID‐19 patients

Background: There is limited information about the impact of coronavirus disease (COVID-19) on the muscular dysfunction, despite the generalized weakness and fatigue that patients report after overcoming the acute phase of the infection. This study aimed to detect impaired muscle efficiency by evaluating delta efficiency (DE) in patients with COVID-19 compared with subjects with chronic obstructive pulmonary disease (COPD), ischaemic heart disease (IHD), and control group (CG). Methods: A total of 60 participants were assigned to four experimental groups: COVID-19, COPD, IHD, and CG (n = 15 each group). Incremental exercise tests in a cycle ergometer were performed to obtain peak oxygen uptake (VO2 peak). DE was obtained from the end of the first workload to the power output where the respiratory exchange ratio was 1. Results: A lower DE was detected in patients with COVID-19 and COPD compared with those in CG (P ≤ 0.033). However, no significant differences were observed among the experimental groups with diseases (P > 0.05). Lower VO2 peak, peak ventilation, peak power output, and total exercise time were observed in the groups with diseases than in the CG (P < 0.05). A higher VO2 , ventilation, and power output were detected in the CG compared with those in the groups with diseases at the first and second ventilatory threshold (P < 0.05). A higher power output was detected in the IHD group compared with those in the COVID-19 and COPD groups (P < 0.05) at the first and second ventilatory thresholds and when the respiratory exchange ratio was 1. A significant correlation (P < 0.001) was found between the VO2 peak and DE and between the peak power output and DE (P < 0.001). Conclusions: Patients with COVID-19 showed marked mechanical inefficiency similar to that observed in COPD and IHD patients. Patients with COVID-19 and COPD showed a significant decrease in power output compared to IHD during pedalling despite having similar response in VO2 at each intensity. Resistance training should be considered during the early phase of rehabilitation