Study On The Generalized Hierarchical Model Of Rock

Rock is a combination of mineral grains, porosity and composition of cement mixed body. After millions of years of geological evolution and a complex multi-stage tectonic movements, the rock contains a random distribution at different levels of sub-micro-pores and cracks. At the macro-scale natural rock is cut by a variety of geological structures (joints, faults and weak-side).The rock is a very complex and very special material, it is not a discrete medium, nor is it a continuous medium, but under the continuous and discrete (or local discrete) coupling medium. Rock failure can also be seen as a process of their internal structure surface formation and reconstruction, the micro-crack initiate, macro-crack formate, structure surface slide along the contact surface in this process. As the failure process involing in cross-disciplinary, multi-level nature and the equation of state is unclear, the study of rock destruction issue has been hot and difficult. This paper define the spatial distribution of structure of rock, scale structure and fractal as the generalized hierarchical, put forward the hierarchical models of brittle rock, rock joints and non-persistent jointed rock mass respectively. The numerical model are implemented by ABAQUS subroutine UMAT and UEL. Details including:(1) Describes the user material subroutine (UMAT) and the user element subroutine (UEL). Including: elastic-plastic scale factor calculation, changing the amendment to sub-incremental-step explicit Euler stress integration method, the stress correction method, stiffness matrix AMATRX and residual load matrix RHS calculation method. In order to verify the validity of UMAT, comparing the results calculated by Drucke-Prager model embedded into the UMAT and the results calculated by the ABAQUS library Drcuke-Prager model. The elastic-plastic constitutive of Cosserate media is embedded into UEL and the behaviors of the Cosserate media is analyzed.(2) Describes the asymptotic expansion method, tangent modulus calculation method and calculation procedures. The two-scale computational model of brittle rock is proposed based on the combination of the micro-statistical model and the asymptotic expansion. Rankine-based criteria for brittle elastic constitutive is adopted in micro-scale , taking into account the statistical nature of materials, using the zero-value of material tangent modulus as the softening criterion, the blunt crack model is used in the softening process. Using two-scale method the effective properties of non-homogeneous material can be gotten easily, more importantly, there is no need to introduce virtual damage parameters, and the macroscopic mechanical behavior of material corresponds to the real physical processes.(3) Based on the fractal characteristics, the joint roughness is decomposed into different levels of structural surface, hierarchical model of rock joints is proposed combined with Plesha joints model. Using single-layer structure, the hierarchical model degenerates to Plesha joints model. the failure of joint is conceived as process of damage and destruction for the different levels of surfacess gradually, this model consider the mechanisms of interfacial slipping, shearing, crushing and separating. After the joint roughness is defined as the equivalent inclination angle, the model can simulate the behaviors of joints under cyclic loading. The model is applicable to analyze the interaction between structures and rock under low pressure.(4) Based on failure mechanism of coplanar non-persistent jointed rock mass, the hierarchical model of non-persistent jointed rock mass is proposed. the model degenerates to Zienkiewicz jointed material model when the joints become persistent. This model includie joints slip model and joints crack model. Joints slip model considers the joint micro-configuration. In the joint crack model, the shear strength constitute the shear strength of joints and rock bridges strength, joint shear strength reflected in the basic friction angle and rough angle, rock bridge stregth reflected in the equivalent cohesion, the continuous weakening process of the equivalent cohesion is the process of the transformation from discontinuous to continuous of joint. This model assumes the coplanar shear failure mechanism of the rock bridge, so it can be used under the circumstance that the length of rock bridges is far less than of the length of the joint.