A Study on the Micromechanical Model of Jointed Rock Masses
Date Issued
2016
Date
2016
Author(s)
Chiu, Chia-Chi
Abstract
The mechanical behaviors of jointed rock masses are affected by rock material failure and joint surface sliding, showing nonlinear and anisotropic characteristics. Among the influencing factors of rock mass mechanical behaviors, the micro-cracks in rock materials and asperity ruptures under joint shearing are two major factors. Therefore, it is important to investigate the mechanical behaviors of jointed rock masses from microscopic perspective using discontinuum analysis – distinct element method. However, in the widely-used software distinct element method –Particle Flow Code (PFC), the “parallel bond model” designed to describe grain cementation and the “smooth-joint model” to handle joint surface sliding are too simplified and unreliable to represent the mechanical behaviors of rock mass appropriately. Thus, this study used PFC as the main subject to simulate jointed rock masses, to improve the simulation of mechanical behavior of rock material and joint surface in microscopic behavior. Finally, this study proposed a more reliable numerical model of jointed rock mass. To improve mechanical behavior of joint plane, this study considered the characteristics of joint roughness and used Barton’s shear strength model as the basis of mechanism in, thus it can reflect the influence of roughness and asperities. On the other hand, the limits of distinct element method has been ameliorated, and following modification has been adopted: (1)The modification of shear stiffness based on joint contact area; (2)The modification of shear stiffness based on joint sliding state; (3)The compensation of shear force increment and (4)The redistribution of normal force. Based on above modifications, this study proposed a joint model in PFC – rough-joint model – which can reflect Barton’s shear strength criterion precisely. To improve mechanical behavior of rock material, this study assumes a rock material is composed of particles with different sizes based on the observation of rock thin section, and the shape of cement between particles can be treated as biconcave shape. Based on this assumption, from the elastic solution of Dvorkin theory and three modifications proposed by this study: (1)Motion decomposition (2)Stress redistribution and (3)Algorithm improvement, the mechanical behavior of biconcave shape bond can be described by a series of particle-cementation analysis with different geometries under compression, tension, shearing and bending situations, agree well with the proposed “biconcave bond model”. Finally, this study combined the “rough-joint model” and the “biconcave bond model” to propose a “jointed rock masses microscopic mechanical model” that is able to well describe the macroscopic mechanical behaviors of jointed rock masses based on the micro parameters of joint surface and rock material, and to observe the microscopic evolutions such as local cracks in rock material and asperity ruptures in joint surface during loading.
Subjects
Joint surface
Rock material
Jointed rock masses
Distinct element method - Particle flow code (PFC)
Discrete element method (DEM)
Type
thesis
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