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Ming Cai - One of the best experts on this subject based on the ideXlab platform.

  • a shear strength model for Anisotropic blocky Rock masses with persistent joints
    International Journal of Rock Mechanics and Mining Sciences, 2020
    Co-Authors: Jiayi Shen, Zheng Shu, Ming Cai
    Abstract:

    Abstract The Mohr-Coulomb (MC) shear strength parameters, cohesion c and angle of friction φ, are required in numerical models. Currently, the geological strength index (GSI) system has been widely used for estimating shear strength of blocky Rock masses in Rock engineering. However, the GSI system does not include the effect of joint orientation β on the mechanical properties of a Rock mass, which means that the shear strength model cannot reflect Anisotropic Rock mass strength behavior caused by joint orientation. In this research, UDEC-based synthetic Rock mass models, which are calibrated by experimental data, are adopted to study the effect of joint orientation on the shear strength of blocky Rock masses with two perpendicular joint sets. The values of cohesion c and angle of friction φ estimated from the numerical simulation are compared with those calculated from the empirical shear strength models based on the GSI system. Comparison of the results shows that the existing empirical model overestimates the shear strength of Rock mass when 10°

  • an empirical ucs model for Anisotropic blocky Rock masses
    Rock Mechanics and Rock Engineering, 2019
    Co-Authors: Fan Huang, Jiayi Shen, Ming Cai
    Abstract:

    The Hoek–Brown (HB) failure criterion is one of the most widely used failure criteria in Rock engineering. Based on the Geological Strength Index (GSI) system, a number of empirical models have been proposed in parallel with this criterion to estimate the strength and deformation properties of Rock masses such as uniaxial compressive strength (UCS) and deformation modulus. However, the GSI system does not incorporate the effects of joint orientation β on the quality of a Rock mass. This means that these empirical models cannot capture Anisotropic Rock mass strength caused by joint orientations. In this research, UDEC Rock mass models, which are calibrated by laboratory data, are used to investigate the effects of joint orientation on Rock mass strength in an unconfined state. The values of UCS obtained from the numerical simulation are then compared with those calculated from traditional empirical UCS models based on the GSI system. The comparison study shows that the value of UCS is significantly overestimated by the traditional empirical model when 10° < β < 45°, which will have serious safety implications for engineering designs. To rectify the problem, based on the analysis of numerical simulation results, an Anisotropic weighting factor fβ is proposed to be used to refine the empirical UCS model. The modified UCS model is demonstrated to be capable of giving conservative but more accurate prediction of the Rock mass strength for various joint orientations, which will result in more optimal and safer engineering designs.

Jiayi Shen - One of the best experts on this subject based on the ideXlab platform.

  • a shear strength model for Anisotropic blocky Rock masses with persistent joints
    International Journal of Rock Mechanics and Mining Sciences, 2020
    Co-Authors: Jiayi Shen, Zheng Shu, Ming Cai
    Abstract:

    Abstract The Mohr-Coulomb (MC) shear strength parameters, cohesion c and angle of friction φ, are required in numerical models. Currently, the geological strength index (GSI) system has been widely used for estimating shear strength of blocky Rock masses in Rock engineering. However, the GSI system does not include the effect of joint orientation β on the mechanical properties of a Rock mass, which means that the shear strength model cannot reflect Anisotropic Rock mass strength behavior caused by joint orientation. In this research, UDEC-based synthetic Rock mass models, which are calibrated by experimental data, are adopted to study the effect of joint orientation on the shear strength of blocky Rock masses with two perpendicular joint sets. The values of cohesion c and angle of friction φ estimated from the numerical simulation are compared with those calculated from the empirical shear strength models based on the GSI system. Comparison of the results shows that the existing empirical model overestimates the shear strength of Rock mass when 10°

  • a new damage model accounting the effect of joint orientation for the jointed Rock mass
    Arabian Journal of Geosciences, 2020
    Co-Authors: Changtai Zhou, Murat Karakus, Jiayi Shen
    Abstract:

    Damage accumulation in the Rock mass leading to failure is influenced by the properties of pre-existing discontinuities. In order to simulate Rock mass behaviour realistically, many damage models have been proposed. Amongst them, limited damage models consider joint orientation, one of the significant properties of discontinuities impacting the Rock mass failure, in the strongly Anisotropic Rock masses. In this study, we propose a statistical damage model using the Weibull distribution which takes into account joint orientation by incorporating the Jaeger’s and modified Hoek-Brown failure criteria for jointed Rock masses. The proposed statistical damage model is validated using experimental results. Furthermore, verification of the proposed model is conducted by distinct element method using Particle Flow Code (PFC). To investigate the influence of the shape parameter (m) and scale parameter (F0) of the Weibull distribution on the statistical damage model predictions, a sensitivity analysis is carried out. It is found that the parameter m only depends on strain parameter k. On the other hand, the parameter F0 is indirectly related to the failure strength of the jointed Rock mass in the proposed damage model. Considerable influence of joint stiffness on the damage variable D, damage evolution rate Dr and Rock mass responses are also identified.

  • an empirical ucs model for Anisotropic blocky Rock masses
    Rock Mechanics and Rock Engineering, 2019
    Co-Authors: Fan Huang, Jiayi Shen, Ming Cai
    Abstract:

    The Hoek–Brown (HB) failure criterion is one of the most widely used failure criteria in Rock engineering. Based on the Geological Strength Index (GSI) system, a number of empirical models have been proposed in parallel with this criterion to estimate the strength and deformation properties of Rock masses such as uniaxial compressive strength (UCS) and deformation modulus. However, the GSI system does not incorporate the effects of joint orientation β on the quality of a Rock mass. This means that these empirical models cannot capture Anisotropic Rock mass strength caused by joint orientations. In this research, UDEC Rock mass models, which are calibrated by laboratory data, are used to investigate the effects of joint orientation on Rock mass strength in an unconfined state. The values of UCS obtained from the numerical simulation are then compared with those calculated from traditional empirical UCS models based on the GSI system. The comparison study shows that the value of UCS is significantly overestimated by the traditional empirical model when 10° < β < 45°, which will have serious safety implications for engineering designs. To rectify the problem, based on the analysis of numerical simulation results, an Anisotropic weighting factor fβ is proposed to be used to refine the empirical UCS model. The modified UCS model is demonstrated to be capable of giving conservative but more accurate prediction of the Rock mass strength for various joint orientations, which will result in more optimal and safer engineering designs.

Antonio Bobet - One of the best experts on this subject based on the ideXlab platform.

  • deep tunnel in transversely Anisotropic Rock with groundwater flow
    Rock Mechanics and Rock Engineering, 2016
    Co-Authors: Antonio Bobet
    Abstract:

    Closed-form solutions for the stresses and deformations induced in the ground and tunnel liner are provided for a deep tunnel in a transversely Anisotropic elastic Rock, with Anisotropic permeability, when subjected to groundwater seepage. Complex variable theory and conformal mapping are used to obtain the solutions; additional complex functions, necessary to prevent multiple solutions of the displacements, are included. The analytical solutions are verified by comparing their results from those of a finite element method. Simplified formulations are presented for tunnels with a perfectly flexible and completely incompressible liner. A spreadsheet is included that can be used to obtain stresses and displacements of the liner due to groundwater flow and far-field geostatic stresses.

  • full stress and displacement fields for steel lined deep pressure tunnels in transversely Anisotropic Rock
    Tunnelling and Underground Space Technology, 2016
    Co-Authors: Antonio Bobet
    Abstract:

    Abstract An analytical solution is derived that provides closed-form formulations for stresses and displacements for a deep pressure tunnel in a transversely Anisotropic Rock, with a steel liner, and subjected to a uniform internal pressure. For the derivation, it is assumed that the tunnel support includes a thin steel liner, concrete backfill and that there is an annulus of damaged Rock around the concrete. It is also assumed that all materials remain elastic and that the concrete and the damaged Rock cannot transmit shear or tangential stresses. The solution is verified by providing comparisons between its results and those from the Finite Element program ABAQUS. For thin steel liners, it can be assumed that the contact pressure between the different materials is uniform, and thus the bending moments in the liner are negligible. This is due to the low bending stiffness of the steel liner. The paper is inspired by and expands the work by Pachoud and Schleiss (2015) who conducted an extensive numerical parametric analysis to obtain correction factors that, when used with an analytical solution for isotropic materials, approximate the maximum principal stress in the liner and intact Rock.

  • a stress and displacement discontinuity element method for elastic transversely Anisotropic Rock
    International Journal for Numerical and Analytical Methods in Geomechanics, 2014
    Co-Authors: Antonio Bobet, Garcia V Marin
    Abstract:

    SUMMARY The paper presents closed-form solutions for stress and displacement influence functions for stress discontinuity (SD) and displacement discontinuity (DD) elements, for a two-dimensional plane-strain elastic, transversely Anisotropic medium. The solutions for SD elements are based on Kelvin's problem and for DD elements on the concept of dipoles. Stress and displacement influence functions are derived for the following elements: constant SD, linear SD, constant DD, linear DD, square root DD, parabolic DD, constant DD surface, and linear DD surface elements. The formulations are incorporated into FRock, a hybridized boundary element method code, and are validated by providing comparisons between the results from FRock and the finite element code ABAQUS. A limited parametric analysis shows the effects of slight anisotropy on the stress field around the tip of a crack and of the orientation of the crack with respect to the axes of elastic symmetry. Copyright © 2014 John Wiley & Sons, Ltd.

  • Lined Circular Tunnels in Elastic Transversely Anisotropic Rock at Depth
    Rock Mechanics and Rock Engineering, 2011
    Co-Authors: Antonio Bobet
    Abstract:

    Closed-form solutions for displacements and stresses of both the liner and the Rock are presented for a deep circular tunnel excavated in transversely Anisotropic Rock above or below the water table subjected to static or seismic loading. The solutions are obtained with the assumption of elastic response of Rock and liner, tied contact between Rock and liner, impermeable liner, plane strain conditions along the tunnel axis and simultaneous excavation, and liner installation. The liner of a tunnel placed below the water table must support, in addition to the Rock stresses, the full water pressure, while a tunnel located above the water table must support only the Rock pressures. The solutions presented for static loading show, however, that displacements and stresses of the liner and Rock are the same when the tunnel is placed above or below the water table as long as the total far-field stresses are the same. With rapid loading, e.g. seismic loading, excess pore pressures may be generated in saturated Rock, which induce a different response than that of a tunnel excavated in dry Rock. The analyses indicate that stresses and displacements are more uniform when excess pore pressures are produced, which seems to indicate that pore pressure generation tends to reduce non-uniform response in Anisotropic Rock.

Anton J. Schleiss - One of the best experts on this subject based on the ideXlab platform.

  • Stresses and Displacements in Steel-Lined Pressure Tunnels and Shafts in Anisotropic Rock Under Quasi-Static Internal Water Pressure
    Rock Mechanics and Rock Engineering, 2016
    Co-Authors: Alexandre J. Pachoud, Anton J. Schleiss
    Abstract:

    Steel-lined pressure tunnels and shafts are constructed to convey water from reservoirs to hydroelectric power plants. They are multilayer structures made of a steel liner, a cracked backfill concrete layer, a cracked or loosened near-field Rock zone and a sound far-field Rock zone. Designers often assume isotropic behavior of the far-field Rock, considering the most unfavorable Rock mass elastic modulus measured in situ, and a quasi-static internal water pressure. Such a conventional model is thus axisymmetrical and has an analytical solution for stresses and displacements. However, Rock masses often have an Anisotropic behavior and such isotropic assumption is usually conservative in terms of quasi-static maximum stresses in the steel liner. In this work, the stresses and displacements in steel-lined pressure tunnels and shafts in Anisotropic Rock mass are studied by means of the finite element method. A quasi-static internal water pressure is considered. The materials are considered linear elastic, and tied contact is assumed between the layers. The constitutive models used for the Rock mass and the cracked layers are presented and the practical ranges of variation of the parameters are discussed. An extensive systematic parametric study is performed and stresses and displacements in the steel liner and in the far-field Rock mass are presented. Finally, correction factors are derived to be included in the axisymmetrical solution which allow a rapid estimate of the maximum stresses in the steel liners of pressure tunnels and shafts in Anisotropic Rock.

Baotang Shen - One of the best experts on this subject based on the ideXlab platform.

  • modelling fracture propagation in Anisotropic Rock mass
    Rock Mechanics and Rock Engineering, 2015
    Co-Authors: Baotang Shen, Topias Siren, Mikael Rinne
    Abstract:

    Anisotropic Rock mass is often encountered in Rock engineering, and cannot be simplified as an isotropic problem in numerical models. A good understanding of Rock fracturing processes and the ability to predict fracture initiation and propagation in Anisotropic Rock masses are required for many Rock engineering problems. This paper describes the development of the Anisotropic function in FRACOD—a specialized fracture propagation modelling software—and its recent applications to Rock engineering issues. Rock anisotropy includes strength anisotropy and modulus anisotropy. The level of complexity in developing the Anisotropic function for strength anisotropy and modulus anisotropy in FRACOD is significantly different. The strength anisotropy function alone does not require any alteration in the way that FRACOD calculates Rock stress and displacement, and therefore is relatively straightforward. The modulus anisotropy function, on the other hand, requires modification of the fundamental equations of stress and displacement in FRACOD, a boundary element code, and hence is more complex and difficult. In actual Rock engineering, the strength anisotropy is often considered to be more pronounced and important than the modulus anisotropy, and dominates the stability and failure pattern of the Rock mass. The modulus anisotropy will not be considered in this study. This paper discusses work related to the development of the strength anisotropy in FRACOD. The anisotropy function has been tested using numerical examples. The predicted failure surfaces are mostly along the weakest planes. Predictive modelling of the Posiva’s Olkiluoto Spalling Experiment was made. The model suggests that spalling is very sensitive to the direction of anisotropy. Recent observations from the in situ experiment showed that shear fractures rather than tensile fractures occur in the holes. According to the simulation, the maximum tensile stress is well below the tensile strength, but the maximum shear stress is probably enough to displace mica contact.

  • modelling Rock fracturing processes a fracture mechanics approach using fracod
    2013
    Co-Authors: Baotang Shen, Ove Stephansson, Mikael Rinne
    Abstract:

    Foreword Preface Acknowledgements 1. Introduction 2. Introduction to Rock Fracture Mechanics 3. Numerical Method 4. Iteration Process in FRACOD 5. Modelling Time Dependency 6. Simulation of Multiple Region System 7. Solving Gravitational Problems 8. Sequential Excavation Function 9. Thermo-Mechanical Coupling 10. Hydro-Mechanical Coupling 11. Anisotropic Rock Strength Function 12. Rock Properties for FRACOD Modelling 13. FRACOD Verification Tests 14. Application Case Studies Index