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Rob L Gawthorpe - One of the best experts on this subject based on the ideXlab platform.

  • submarine channels controlled by salt tectonics examples from 3d seismic data offshore angola
    Marine and Petroleum Geology, 2006
    Co-Authors: M J R Gee, Rob L Gawthorpe
    Abstract:

    The interaction between salt tectonics and sedimentation, offshore Angola has created a complex Slope Geometry of submarine channels, intra-Slope basins and diapiric salt structures. There are a wide range of Slope channel styles in close stratigraphic and geographic proximity, although the controls on these changes are not fully understood. Channels often follow complicated routes downSlope, and have developed highly variable channel geometries, with narrow, erosional confined systems, and aggradational, broader systems as end members. Many channels are organised into stacked channel complexes. Rapid transitions in channel Geometry are observed where channel systems pass through constrictions in salt wall structures or encounter decreases in Slope gradients, for example within intra-Slope depressions. Decreases in gradient and the exit points of incised channels mark the transition from narrow, well-defined linear or sinuous channels to broad, weakly confined channels. Important seismic facies changes are also observed where channels approach salt structures that created positive features on the seafloor. Results presented here show that linear, high gradient channels exhibit distinctive Geometry changes around salt structures, often forming discreet depositional forms in planview. Lateral changes in sedimentary architecture within depositional lows record salt movement, as facies migrate relative to growing salt structures.

Andrew J. Hill - One of the best experts on this subject based on the ideXlab platform.

  • Significance of the actual nonlinear Slope Geometry for catastrophic failure in submarine landslides.
    Proceedings. Mathematical physical and engineering sciences, 2015
    Co-Authors: Alexander M. Puzrin, Thomas Gray, Andrew J. Hill
    Abstract:

    A simple approach to Slope stability analysis of naturally occurring, mild nonlinear Slopes is proposed through extension of shear band propagation (SBP) theory. An initial weak zone appears in the steepest part of the Slope where the combined action of gravity and seismic loads overcomes the degraded peak shear resistance of the soil. If the length of this steepest part is larger than the critical length, the shear band will propagate into the quasi-stable parts of the Slope, where the gravitational and seismically induced shear stresses are smaller than the peak but larger than the residual shear strength of the soil. Growth of a shear band is strongly dependent on the shape of the Slope, seismic parameters and the strength of soil and less dependent on the Slope inclination and the sensitivity of clay. For the Slope surface with faster changing inclination, the criterion is more sensitive to the changes of the parameters. Accounting for the actual nonlinear Slope Geometry eliminates the main challenge of the SBP approach-determination of the length of the initial weak zone, because the Slope Geometry can be readily obtained from submarine site investigations. It also helps to identify conditions for the early arrest of the shear band, before failure in the sliding layer or a change in loading or excess pore water pressures occurs. The difference in the size of a landslide predicted by limiting equilibrium and SBP approaches can reach orders of magnitude, potentially providing an explanation for the immense dimensions of many observed submarine landslides that may be caused by local factors acting over a limited portion of the Slope.

Doug Stead - One of the best experts on this subject based on the ideXlab platform.

  • A Combined Remote Sensing–Numerical Modelling Approach to the Stability Analysis of Delabole Slate Quarry, Cornwall, UK
    Rock Mechanics and Rock Engineering, 2015
    Co-Authors: Mohsen Havaej, Doug Stead, John Coggan, Davide Elmo
    Abstract:

    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.

  • The possible role of brittle rock fracture in the 1963 Vajont Slide, Italy
    International Journal of Rock Mechanics and Mining Sciences, 2015
    Co-Authors: Mohsen Havaej, Andrea Wolter, Doug Stead
    Abstract:

    Abstract We use a state-of-the-art numerical simulation approach to investigate the Vajont Slope failure, a large catastrophic landslide that resulted in the loss of 1910 lives. This study represents the first three-dimensional (3D) brittle fracture simulation of the Vajont Slide that includes the effect of groundwater on the failure process. A realistic representation of the Vajont Slope Geometry, failure surface and discontinuities in a 3D lattice spring code allowed us to study the kinematics of the landslide. Using a lattice-spring block model approach, the relations among the number of blocks, Slope damage, and stability are investigated. The influence of an elevated groundwater table on displacements and cracking within the model is evaluated. The results show a good agreement with the reported microseismic events prior to the failure. Two new techniques, “damage intensity”, D 32 , and the “ellipsoid of damage”, are introduced and used to quantify brittle damage within the numerical simulations.

  • A case study integrating remote sensing and distinct element analysis to quarry Slope stability assessment in the Monte Altissimo area, Italy
    Engineering Geology, 2014
    Co-Authors: Mirko Francioni, Riccardo Salvini, Doug Stead, S. Litrico
    Abstract:

    Abstract Over last decade geomatic techniques have been increasingly used for the geometrical characterization of rock Slopes. Terrestrial laser scanning and digital terrestrial photogrammetry in particular are now frequently used in the characterization of joint surfaces and Slope Geometry. Although the use of these techniques for the structural characterization of Slopes is widely documented, limited research has been undertaken to improve our understanding of the importance of the derived data quality in the construction of Slope Geometry imported into 3D numerical models. One of the most common problems encountered in the use of these techniques, especially in case of Slopes with complex Geometry, is the presence of occlusions. In this context, the aims of this paper are to describe how the integrated use of terrestrial laser scanning, digital terrestrial photogrammetry and topographic surveys can mitigate the influence of occlusions and how the Slope Geometry gained from these surveys can be important in Slope stability analyses. For this purpose a case study in the Monte Altissimo area (Apuan Alps, Italy) will be presented. Several geomatic techniques were used for studying a Slope overhanging the Granolesa quarry. Special emphasis will be given to the importance of using Total Station and Differential GPS surveys as tools for data fusion. Moreover, in order to validate this procedure, the accuracy and precision of the output were determined through comparison of 3D models derived from laser scanning and digital terrestrial photogrammetry. Furthermore, two different analyses with the three-dimensional distinct element code, 3DEC, were carried out in order to highlight the advantages and limitations of using data obtained from terrestrial remote sensing techniques as opposed to models based on topographic maps.

Gregory Ivey - One of the best experts on this subject based on the ideXlab platform.

Nazri Ali - One of the best experts on this subject based on the ideXlab platform.

  • Verification of tree induced suction with numerical model
    Physics and Chemistry of the Earth Parts A B C, 2021
    Co-Authors: M. F. Ishak, M. F. Zolkepli, Mohd Yusri Bin Mohd Yunus, Nazri Ali, Azman Kassim, M. S. I. Zaini
    Abstract:

    Abstract This study discusses the validation between explorations of transpiration on the unsaturated soil zone with unsaturated flow equation of tree water uptake model. Numerical simulation was performed to the model of the Slope in relation to moisture migration patterns in the unsaturated zone within the vicinity of mature tree. The results of numerical simulation conducted on typical Slope Geometry model with tree at the toe of the Slope of induced transpiration were later presented in this study. The results of numerical simulation and field monitoring of suction against depth are in acceptable condition. It is important to note that, several of the differences between simulated numerical and field measurement are related to inconsistence effect of root density.

  • Preliminary analysis of tree-induced suctions on Slope stability
    2008
    Co-Authors: Nazri Ali, Stephen William Rees
    Abstract:

    This paper explores the development and application of a numerical model of water uptake in the vicinity of established trees. A preliminary assessment of the significance of water content (and therefore suction) changes on the stability of soil Slopes is provided. This is a problem that is exacerbated by climate change and increasingly intense rainfall events. Design, repair, maintenance and operation of railway and road earthworks are particular areas where this issue is important. For a typical Slope Geometry the research indicates that tree-induced suction variations can cause the factor of safety against failure to vary by between 5% and 7%. This result is independent of other associated contributions that may arise from root reinforcement, windthrow, weight of vegetation etc. Therefore, further work is needed to consider the overall effect of vegetation and to reduce parametric uncertainty.