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Title: Mechanical properties of rock joints under tension and application to tensile stress wave propagation
Authors: Han, Dongya
Degree: Ph.D.
Issue Date: 2020
Abstract: The presence of large-scale discontinuities such as joints can significantly affect the physical, mechanical and seismic properties of rock masses. Some rock joints, e.g., incipient and healed rock joints, have significant tensile strength. While rock joints are often subject to static or dynamic tensile loading and tensile failure is one of the main failure mechanisms of jointed rock masses, few attentions have been paid to study the strength and deformation and fracturing characteristics of rock joint under static tension, and no efforts have been devoted to investigating behavior of rock joints under dynamic tension. In this thesis, to study the tensile behaviors of jointed rocks, a series of tension tests were conducted, including Brazilian disc tests and direct static and dynamic tension tests on jointed rocks. Many efforts were made to select proper pulse shapers and improve the connection between specimens and tension bars. Experimental and theoretical studies were performed to study stress wave propagation across rock joints under tension. The two-parameter Weibull distribution was found to well capture the statistical characteristics of indirect and direct tensile strength and fracture toughness of intact rock and rock with joints at different load-joint angles. The single plane of weakness theory was found to best correlate between the anisotropy of indirect tensile strength induced by the load-joint angles. It was found that the joint dynamic tensile strength, the critical joint opening, the specific tensile stiffness and the specific fracture energy of rock joints were strain rate dependent. A non-linear empirical formula was proposed to describe the rate dependence of joint dynamic tensile strength. In addition, the deformation behaviors of rock joints were correlated with characteristic length and ductility. When subjected to tensile loading, rock joints deformed non-linearly, irrespective of the rock and joint type. An inverse hyperbolic function was proposed to best approximate the experimental data from direct tension tests on rock joints. The normal deformability of rock joint under tension was governed by the initial tensile stiffness and the joint tensile strength. Based on the proposed inverse hyperbolic function, a nonlinear displacement discontinuity formulation was developed to study the transmission of tensile stress wave across rock joints. The transmitted wave and transmission coefficients derived from this formulation showed good consistency with the experimental results of the modified split Hopkinson tension bar tests. The transmission of tensile stress wave significantly depended on the nonlinear deformation parameters (i.e., the initial tensile stiffness and the joint tensile strength) and on the incident waveforms (e.g., amplitude and frequency). The findings in this thesis can provide a more complete database of the distribution of tensile strength and fracture toughness of jointed rock. The proposed inverse hyperbolic model may offer a realistic expression of the joint deformation under tensile loading and a practical method to study the transmission of tensile stress wave across rock joints.
Subjects: Rocks -- Fracture
Rock mechanics
Rocks -- Testing
Rock pressure -- Measurement
Hong Kong Polytechnic University -- Dissertations
Pages: xxvii, 218 pages : color illustrations
Appears in Collections:Thesis

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