ETDs: Doctoral Theses

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Browsing ETDs: Doctoral Theses by Author "Bastola, Subash"

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    Study of mechanical properties of jointed rock mass using lattice-spring-based synthetic rock mass (LS-SRM) modeling approach 
    (2019-12-16) Bastola, Subash
    With the recent development of high-end computation technology, it is feasible to use complex numerical modeling technique such as synthetic rock mass (SRM) modeling for the characterization of mechanical properties of rock mass. However, the SRM modeling approaches that have been used to date such as the ones based on bonded particle and bonded blocks cannot properly incorporate realistic discontinuity surface geometry (waviness and roughness) into the numerical model and discontinuities are often simplified as having planar surfaces. Models with simplified planar discontinuity surfaces do not represent the true geometry and physics of the natural discontinuities which raises the question on the reliability of the geotechnical parameters resulting from these models. It is widely known that the inherent surface roughness significantly influences the shear strength and stiffness of a non-planar discontinuity. The goal of this thesis is to develop numerical models that can incorporate these natural undulating discontinuities for the determination of reliable estimates of strength and deformation properties of jointed rock masses. Three-dimensional lattice-spring-based synthetic rock mass (LS-SRM) models are generated by incorporating both planar and non-planar discontinuities to simulate the mechanical behaviors of both laboratory-scale jointed rock and mine-scale jointed rock masses. A calibration methodology is established by means of extensive sensitivity analysis of lattice model parameters. Studies are also conducted to understand the crack evolution mechanism (initiation and propagation) in precracked marbles with both planar and non-planar cracks. Influences of joint properties (orientation, intensity, persistence, and roughness) on the strength and deformability of jointed rock under compression are also investigated. Influence of rock mass scale on the strength and deformation modulus is investigated to determine the representative elementary volume (REV) of the rock mass. Using the REV sized rock mass, the influence of discontinuity intensity and confining pressure on the mechanical properties (strength & deformability) of jointed rock masses are also investigated. In addition, the influence of the pre-existing natural discontinuity of different configurations (waviness, intensity, size) and in-situ stress on slope stability and deformability of an open pit mine are investigated. Complex crack propagation mechanism is observed in the laboratory-scale pre-cracked rocks with non-planar cracks under compression. There is an increase in the strength and deformation modulus for the laboratory-scale jointed rock models with non-planar discontinuities, lower discontinuity intensity, and lower discontinuity persistence. Peak strength and deformation modulus of the rock mass decreases with the increase of discontinuity intensity. Peak strength of the rock mass increases with the increase of confining pressure. Slopes excavated in the rock mass with non-planar discontinuities are found to be more stable than the slopes excavated in the rock mass with planar discontinuities. Similarly, slopes excavated in the rock mass with larger discontinuity size and higher discontinuity intensity are less stable than the ones excavated in the rock mass with smaller discontinuity size and lower discontinuity intensity. It is also found that the slopes exhibited localized instabilities under the influence of high in-situ stress. The findings of this research aid in better characterization of the mechanical behavior The findings of this research aid in better characterization of the mechanical behavior of jointed rock mass and provide more reliable estimates of geotechnical design parameters.